+++ /dev/null
-<?xml version="1.0" encoding="UTF-8"?>
-<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
- "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
-
-<!-- ****************************************************** -->
-<!-- Header -->
-<!-- ****************************************************** -->
-<book id="Writing-an-ALSA-Driver">
- <bookinfo>
- <title>Writing an ALSA Driver</title>
- <author>
- <firstname>Takashi</firstname>
- <surname>Iwai</surname>
- <affiliation>
- <address>
- <email>tiwai@suse.de</email>
- </address>
- </affiliation>
- </author>
-
- <date>Oct 15, 2007</date>
- <edition>0.3.7</edition>
-
- <abstract>
- <para>
- This document describes how to write an ALSA (Advanced Linux
- Sound Architecture) driver.
- </para>
- </abstract>
-
- <legalnotice>
- <para>
- Copyright (c) 2002-2005 Takashi Iwai <email>tiwai@suse.de</email>
- </para>
-
- <para>
- This document is free; you can redistribute it and/or modify it
- under the terms of the GNU General Public License as published by
- the Free Software Foundation; either version 2 of the License, or
- (at your option) any later version.
- </para>
-
- <para>
- This document is distributed in the hope that it will be useful,
- but <emphasis>WITHOUT ANY WARRANTY</emphasis>; without even the
- implied warranty of <emphasis>MERCHANTABILITY or FITNESS FOR A
- PARTICULAR PURPOSE</emphasis>. See the GNU General Public License
- for more details.
- </para>
-
- <para>
- You should have received a copy of the GNU General Public
- License along with this program; if not, write to the Free
- Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
- MA 02111-1307 USA
- </para>
- </legalnotice>
-
- </bookinfo>
-
-<!-- ****************************************************** -->
-<!-- Preface -->
-<!-- ****************************************************** -->
- <preface id="preface">
- <title>Preface</title>
- <para>
- This document describes how to write an
- <ulink url="http://www.alsa-project.org/"><citetitle>
- ALSA (Advanced Linux Sound Architecture)</citetitle></ulink>
- driver. The document focuses mainly on PCI soundcards.
- In the case of other device types, the API might
- be different, too. However, at least the ALSA kernel API is
- consistent, and therefore it would be still a bit help for
- writing them.
- </para>
-
- <para>
- This document targets people who already have enough
- C language skills and have basic linux kernel programming
- knowledge. This document doesn't explain the general
- topic of linux kernel coding and doesn't cover low-level
- driver implementation details. It only describes
- the standard way to write a PCI sound driver on ALSA.
- </para>
-
- <para>
- If you are already familiar with the older ALSA ver.0.5.x API, you
- can check the drivers such as <filename>sound/pci/es1938.c</filename> or
- <filename>sound/pci/maestro3.c</filename> which have also almost the same
- code-base in the ALSA 0.5.x tree, so you can compare the differences.
- </para>
-
- <para>
- This document is still a draft version. Any feedback and
- corrections, please!!
- </para>
- </preface>
-
-
-<!-- ****************************************************** -->
-<!-- File Tree Structure -->
-<!-- ****************************************************** -->
- <chapter id="file-tree">
- <title>File Tree Structure</title>
-
- <section id="file-tree-general">
- <title>General</title>
- <para>
- The ALSA drivers are provided in two ways.
- </para>
-
- <para>
- One is the trees provided as a tarball or via cvs from the
- ALSA's ftp site, and another is the 2.6 (or later) Linux kernel
- tree. To synchronize both, the ALSA driver tree is split into
- two different trees: alsa-kernel and alsa-driver. The former
- contains purely the source code for the Linux 2.6 (or later)
- tree. This tree is designed only for compilation on 2.6 or
- later environment. The latter, alsa-driver, contains many subtle
- files for compiling ALSA drivers outside of the Linux kernel tree,
- wrapper functions for older 2.2 and 2.4 kernels, to adapt the latest kernel API,
- and additional drivers which are still in development or in
- tests. The drivers in alsa-driver tree will be moved to
- alsa-kernel (and eventually to the 2.6 kernel tree) when they are
- finished and confirmed to work fine.
- </para>
-
- <para>
- The file tree structure of ALSA driver is depicted below. Both
- alsa-kernel and alsa-driver have almost the same file
- structure, except for <quote>core</quote> directory. It's
- named as <quote>acore</quote> in alsa-driver tree.
-
- <example>
- <title>ALSA File Tree Structure</title>
- <literallayout>
- sound
- /core
- /oss
- /seq
- /oss
- /instr
- /ioctl32
- /include
- /drivers
- /mpu401
- /opl3
- /i2c
- /l3
- /synth
- /emux
- /pci
- /(cards)
- /isa
- /(cards)
- /arm
- /ppc
- /sparc
- /usb
- /pcmcia /(cards)
- /oss
- </literallayout>
- </example>
- </para>
- </section>
-
- <section id="file-tree-core-directory">
- <title>core directory</title>
- <para>
- This directory contains the middle layer which is the heart
- of ALSA drivers. In this directory, the native ALSA modules are
- stored. The sub-directories contain different modules and are
- dependent upon the kernel config.
- </para>
-
- <section id="file-tree-core-directory-oss">
- <title>core/oss</title>
-
- <para>
- The codes for PCM and mixer OSS emulation modules are stored
- in this directory. The rawmidi OSS emulation is included in
- the ALSA rawmidi code since it's quite small. The sequencer
- code is stored in <filename>core/seq/oss</filename> directory (see
- <link linkend="file-tree-core-directory-seq-oss"><citetitle>
- below</citetitle></link>).
- </para>
- </section>
-
- <section id="file-tree-core-directory-ioctl32">
- <title>core/ioctl32</title>
-
- <para>
- This directory contains the 32bit-ioctl wrappers for 64bit
- architectures such like x86-64, ppc64 and sparc64. For 32bit
- and alpha architectures, these are not compiled.
- </para>
- </section>
-
- <section id="file-tree-core-directory-seq">
- <title>core/seq</title>
- <para>
- This directory and its sub-directories are for the ALSA
- sequencer. This directory contains the sequencer core and
- primary sequencer modules such like snd-seq-midi,
- snd-seq-virmidi, etc. They are compiled only when
- <constant>CONFIG_SND_SEQUENCER</constant> is set in the kernel
- config.
- </para>
- </section>
-
- <section id="file-tree-core-directory-seq-oss">
- <title>core/seq/oss</title>
- <para>
- This contains the OSS sequencer emulation codes.
- </para>
- </section>
-
- <section id="file-tree-core-directory-deq-instr">
- <title>core/seq/instr</title>
- <para>
- This directory contains the modules for the sequencer
- instrument layer.
- </para>
- </section>
- </section>
-
- <section id="file-tree-include-directory">
- <title>include directory</title>
- <para>
- This is the place for the public header files of ALSA drivers,
- which are to be exported to user-space, or included by
- several files at different directories. Basically, the private
- header files should not be placed in this directory, but you may
- still find files there, due to historical reasons :)
- </para>
- </section>
-
- <section id="file-tree-drivers-directory">
- <title>drivers directory</title>
- <para>
- This directory contains code shared among different drivers
- on different architectures. They are hence supposed not to be
- architecture-specific.
- For example, the dummy pcm driver and the serial MIDI
- driver are found in this directory. In the sub-directories,
- there is code for components which are independent from
- bus and cpu architectures.
- </para>
-
- <section id="file-tree-drivers-directory-mpu401">
- <title>drivers/mpu401</title>
- <para>
- The MPU401 and MPU401-UART modules are stored here.
- </para>
- </section>
-
- <section id="file-tree-drivers-directory-opl3">
- <title>drivers/opl3 and opl4</title>
- <para>
- The OPL3 and OPL4 FM-synth stuff is found here.
- </para>
- </section>
- </section>
-
- <section id="file-tree-i2c-directory">
- <title>i2c directory</title>
- <para>
- This contains the ALSA i2c components.
- </para>
-
- <para>
- Although there is a standard i2c layer on Linux, ALSA has its
- own i2c code for some cards, because the soundcard needs only a
- simple operation and the standard i2c API is too complicated for
- such a purpose.
- </para>
-
- <section id="file-tree-i2c-directory-l3">
- <title>i2c/l3</title>
- <para>
- This is a sub-directory for ARM L3 i2c.
- </para>
- </section>
- </section>
-
- <section id="file-tree-synth-directory">
- <title>synth directory</title>
- <para>
- This contains the synth middle-level modules.
- </para>
-
- <para>
- So far, there is only Emu8000/Emu10k1 synth driver under
- the <filename>synth/emux</filename> sub-directory.
- </para>
- </section>
-
- <section id="file-tree-pci-directory">
- <title>pci directory</title>
- <para>
- This directory and its sub-directories hold the top-level card modules
- for PCI soundcards and the code specific to the PCI BUS.
- </para>
-
- <para>
- The drivers compiled from a single file are stored directly
- in the pci directory, while the drivers with several source files are
- stored on their own sub-directory (e.g. emu10k1, ice1712).
- </para>
- </section>
-
- <section id="file-tree-isa-directory">
- <title>isa directory</title>
- <para>
- This directory and its sub-directories hold the top-level card modules
- for ISA soundcards.
- </para>
- </section>
-
- <section id="file-tree-arm-ppc-sparc-directories">
- <title>arm, ppc, and sparc directories</title>
- <para>
- They are used for top-level card modules which are
- specific to one of these architectures.
- </para>
- </section>
-
- <section id="file-tree-usb-directory">
- <title>usb directory</title>
- <para>
- This directory contains the USB-audio driver. In the latest version, the
- USB MIDI driver is integrated in the usb-audio driver.
- </para>
- </section>
-
- <section id="file-tree-pcmcia-directory">
- <title>pcmcia directory</title>
- <para>
- The PCMCIA, especially PCCard drivers will go here. CardBus
- drivers will be in the pci directory, because their API is identical
- to that of standard PCI cards.
- </para>
- </section>
-
- <section id="file-tree-oss-directory">
- <title>oss directory</title>
- <para>
- The OSS/Lite source files are stored here in Linux 2.6 (or
- later) tree. In the ALSA driver tarball, this directory is empty,
- of course :)
- </para>
- </section>
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Basic Flow for PCI Drivers -->
-<!-- ****************************************************** -->
- <chapter id="basic-flow">
- <title>Basic Flow for PCI Drivers</title>
-
- <section id="basic-flow-outline">
- <title>Outline</title>
- <para>
- The minimum flow for PCI soundcards is as follows:
-
- <itemizedlist>
- <listitem><para>define the PCI ID table (see the section
- <link linkend="pci-resource-entries"><citetitle>PCI Entries
- </citetitle></link>).</para></listitem>
- <listitem><para>create <function>probe()</function> callback.</para></listitem>
- <listitem><para>create <function>remove()</function> callback.</para></listitem>
- <listitem><para>create a <structname>pci_driver</structname> structure
- containing the three pointers above.</para></listitem>
- <listitem><para>create an <function>init()</function> function just calling
- the <function>pci_register_driver()</function> to register the pci_driver table
- defined above.</para></listitem>
- <listitem><para>create an <function>exit()</function> function to call
- the <function>pci_unregister_driver()</function> function.</para></listitem>
- </itemizedlist>
- </para>
- </section>
-
- <section id="basic-flow-example">
- <title>Full Code Example</title>
- <para>
- The code example is shown below. Some parts are kept
- unimplemented at this moment but will be filled in the
- next sections. The numbers in the comment lines of the
- <function>snd_mychip_probe()</function> function
- refer to details explained in the following section.
-
- <example>
- <title>Basic Flow for PCI Drivers - Example</title>
- <programlisting>
-<![CDATA[
- #include <linux/init.h>
- #include <linux/pci.h>
- #include <linux/slab.h>
- #include <sound/core.h>
- #include <sound/initval.h>
-
- /* module parameters (see "Module Parameters") */
- /* SNDRV_CARDS: maximum number of cards supported by this module */
- static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
- static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
- static bool enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP;
-
- /* definition of the chip-specific record */
- struct mychip {
- struct snd_card *card;
- /* the rest of the implementation will be in section
- * "PCI Resource Management"
- */
- };
-
- /* chip-specific destructor
- * (see "PCI Resource Management")
- */
- static int snd_mychip_free(struct mychip *chip)
- {
- .... /* will be implemented later... */
- }
-
- /* component-destructor
- * (see "Management of Cards and Components")
- */
- static int snd_mychip_dev_free(struct snd_device *device)
- {
- return snd_mychip_free(device->device_data);
- }
-
- /* chip-specific constructor
- * (see "Management of Cards and Components")
- */
- static int snd_mychip_create(struct snd_card *card,
- struct pci_dev *pci,
- struct mychip **rchip)
- {
- struct mychip *chip;
- int err;
- static struct snd_device_ops ops = {
- .dev_free = snd_mychip_dev_free,
- };
-
- *rchip = NULL;
-
- /* check PCI availability here
- * (see "PCI Resource Management")
- */
- ....
-
- /* allocate a chip-specific data with zero filled */
- chip = kzalloc(sizeof(*chip), GFP_KERNEL);
- if (chip == NULL)
- return -ENOMEM;
-
- chip->card = card;
-
- /* rest of initialization here; will be implemented
- * later, see "PCI Resource Management"
- */
- ....
-
- err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
- if (err < 0) {
- snd_mychip_free(chip);
- return err;
- }
-
- *rchip = chip;
- return 0;
- }
-
- /* constructor -- see "Constructor" sub-section */
- static int snd_mychip_probe(struct pci_dev *pci,
- const struct pci_device_id *pci_id)
- {
- static int dev;
- struct snd_card *card;
- struct mychip *chip;
- int err;
-
- /* (1) */
- if (dev >= SNDRV_CARDS)
- return -ENODEV;
- if (!enable[dev]) {
- dev++;
- return -ENOENT;
- }
-
- /* (2) */
- err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
- 0, &card);
- if (err < 0)
- return err;
-
- /* (3) */
- err = snd_mychip_create(card, pci, &chip);
- if (err < 0) {
- snd_card_free(card);
- return err;
- }
-
- /* (4) */
- strcpy(card->driver, "My Chip");
- strcpy(card->shortname, "My Own Chip 123");
- sprintf(card->longname, "%s at 0x%lx irq %i",
- card->shortname, chip->ioport, chip->irq);
-
- /* (5) */
- .... /* implemented later */
-
- /* (6) */
- err = snd_card_register(card);
- if (err < 0) {
- snd_card_free(card);
- return err;
- }
-
- /* (7) */
- pci_set_drvdata(pci, card);
- dev++;
- return 0;
- }
-
- /* destructor -- see the "Destructor" sub-section */
- static void snd_mychip_remove(struct pci_dev *pci)
- {
- snd_card_free(pci_get_drvdata(pci));
- pci_set_drvdata(pci, NULL);
- }
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="basic-flow-constructor">
- <title>Constructor</title>
- <para>
- The real constructor of PCI drivers is the <function>probe</function> callback.
- The <function>probe</function> callback and other component-constructors which are called
- from the <function>probe</function> callback cannot be used with
- the <parameter>__init</parameter> prefix
- because any PCI device could be a hotplug device.
- </para>
-
- <para>
- In the <function>probe</function> callback, the following scheme is often used.
- </para>
-
- <section id="basic-flow-constructor-device-index">
- <title>1) Check and increment the device index.</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int dev;
- ....
- if (dev >= SNDRV_CARDS)
- return -ENODEV;
- if (!enable[dev]) {
- dev++;
- return -ENOENT;
- }
-]]>
- </programlisting>
- </informalexample>
-
- where enable[dev] is the module option.
- </para>
-
- <para>
- Each time the <function>probe</function> callback is called, check the
- availability of the device. If not available, simply increment
- the device index and returns. dev will be incremented also
- later (<link
- linkend="basic-flow-constructor-set-pci"><citetitle>step
- 7</citetitle></link>).
- </para>
- </section>
-
- <section id="basic-flow-constructor-create-card">
- <title>2) Create a card instance</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_card *card;
- int err;
- ....
- err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
- 0, &card);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The details will be explained in the section
- <link linkend="card-management-card-instance"><citetitle>
- Management of Cards and Components</citetitle></link>.
- </para>
- </section>
-
- <section id="basic-flow-constructor-create-main">
- <title>3) Create a main component</title>
- <para>
- In this part, the PCI resources are allocated.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mychip *chip;
- ....
- err = snd_mychip_create(card, pci, &chip);
- if (err < 0) {
- snd_card_free(card);
- return err;
- }
-]]>
- </programlisting>
- </informalexample>
-
- The details will be explained in the section <link
- linkend="pci-resource"><citetitle>PCI Resource
- Management</citetitle></link>.
- </para>
- </section>
-
- <section id="basic-flow-constructor-main-component">
- <title>4) Set the driver ID and name strings.</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- strcpy(card->driver, "My Chip");
- strcpy(card->shortname, "My Own Chip 123");
- sprintf(card->longname, "%s at 0x%lx irq %i",
- card->shortname, chip->ioport, chip->irq);
-]]>
- </programlisting>
- </informalexample>
-
- The driver field holds the minimal ID string of the
- chip. This is used by alsa-lib's configurator, so keep it
- simple but unique.
- Even the same driver can have different driver IDs to
- distinguish the functionality of each chip type.
- </para>
-
- <para>
- The shortname field is a string shown as more verbose
- name. The longname field contains the information
- shown in <filename>/proc/asound/cards</filename>.
- </para>
- </section>
-
- <section id="basic-flow-constructor-create-other">
- <title>5) Create other components, such as mixer, MIDI, etc.</title>
- <para>
- Here you define the basic components such as
- <link linkend="pcm-interface"><citetitle>PCM</citetitle></link>,
- mixer (e.g. <link linkend="api-ac97"><citetitle>AC97</citetitle></link>),
- MIDI (e.g. <link linkend="midi-interface"><citetitle>MPU-401</citetitle></link>),
- and other interfaces.
- Also, if you want a <link linkend="proc-interface"><citetitle>proc
- file</citetitle></link>, define it here, too.
- </para>
- </section>
-
- <section id="basic-flow-constructor-register-card">
- <title>6) Register the card instance.</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- err = snd_card_register(card);
- if (err < 0) {
- snd_card_free(card);
- return err;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Will be explained in the section <link
- linkend="card-management-registration"><citetitle>Management
- of Cards and Components</citetitle></link>, too.
- </para>
- </section>
-
- <section id="basic-flow-constructor-set-pci">
- <title>7) Set the PCI driver data and return zero.</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- pci_set_drvdata(pci, card);
- dev++;
- return 0;
-]]>
- </programlisting>
- </informalexample>
-
- In the above, the card record is stored. This pointer is
- used in the remove callback and power-management
- callbacks, too.
- </para>
- </section>
- </section>
-
- <section id="basic-flow-destructor">
- <title>Destructor</title>
- <para>
- The destructor, remove callback, simply releases the card
- instance. Then the ALSA middle layer will release all the
- attached components automatically.
- </para>
-
- <para>
- It would be typically like the following:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void snd_mychip_remove(struct pci_dev *pci)
- {
- snd_card_free(pci_get_drvdata(pci));
- pci_set_drvdata(pci, NULL);
- }
-]]>
- </programlisting>
- </informalexample>
-
- The above code assumes that the card pointer is set to the PCI
- driver data.
- </para>
- </section>
-
- <section id="basic-flow-header-files">
- <title>Header Files</title>
- <para>
- For the above example, at least the following include files
- are necessary.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- #include <linux/init.h>
- #include <linux/pci.h>
- #include <linux/slab.h>
- #include <sound/core.h>
- #include <sound/initval.h>
-]]>
- </programlisting>
- </informalexample>
-
- where the last one is necessary only when module options are
- defined in the source file. If the code is split into several
- files, the files without module options don't need them.
- </para>
-
- <para>
- In addition to these headers, you'll need
- <filename><linux/interrupt.h></filename> for interrupt
- handling, and <filename><asm/io.h></filename> for I/O
- access. If you use the <function>mdelay()</function> or
- <function>udelay()</function> functions, you'll need to include
- <filename><linux/delay.h></filename> too.
- </para>
-
- <para>
- The ALSA interfaces like the PCM and control APIs are defined in other
- <filename><sound/xxx.h></filename> header files.
- They have to be included after
- <filename><sound/core.h></filename>.
- </para>
-
- </section>
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Management of Cards and Components -->
-<!-- ****************************************************** -->
- <chapter id="card-management">
- <title>Management of Cards and Components</title>
-
- <section id="card-management-card-instance">
- <title>Card Instance</title>
- <para>
- For each soundcard, a <quote>card</quote> record must be allocated.
- </para>
-
- <para>
- A card record is the headquarters of the soundcard. It manages
- the whole list of devices (components) on the soundcard, such as
- PCM, mixers, MIDI, synthesizer, and so on. Also, the card
- record holds the ID and the name strings of the card, manages
- the root of proc files, and controls the power-management states
- and hotplug disconnections. The component list on the card
- record is used to manage the correct release of resources at
- destruction.
- </para>
-
- <para>
- As mentioned above, to create a card instance, call
- <function>snd_card_new()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_card *card;
- int err;
- err = snd_card_new(&pci->dev, index, id, module, extra_size, &card);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The function takes six arguments: the parent device pointer,
- the card-index number, the id string, the module pointer (usually
- <constant>THIS_MODULE</constant>),
- the size of extra-data space, and the pointer to return the
- card instance. The extra_size argument is used to
- allocate card->private_data for the
- chip-specific data. Note that these data
- are allocated by <function>snd_card_new()</function>.
- </para>
-
- <para>
- The first argument, the pointer of struct
- <structname>device</structname>, specifies the parent device.
- For PCI devices, typically &pci-> is passed there.
- </para>
- </section>
-
- <section id="card-management-component">
- <title>Components</title>
- <para>
- After the card is created, you can attach the components
- (devices) to the card instance. In an ALSA driver, a component is
- represented as a struct <structname>snd_device</structname> object.
- A component can be a PCM instance, a control interface, a raw
- MIDI interface, etc. Each such instance has one component
- entry.
- </para>
-
- <para>
- A component can be created via
- <function>snd_device_new()</function> function.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_device_new(card, SNDRV_DEV_XXX, chip, &ops);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- This takes the card pointer, the device-level
- (<constant>SNDRV_DEV_XXX</constant>), the data pointer, and the
- callback pointers (<parameter>&ops</parameter>). The
- device-level defines the type of components and the order of
- registration and de-registration. For most components, the
- device-level is already defined. For a user-defined component,
- you can use <constant>SNDRV_DEV_LOWLEVEL</constant>.
- </para>
-
- <para>
- This function itself doesn't allocate the data space. The data
- must be allocated manually beforehand, and its pointer is passed
- as the argument. This pointer (<parameter>chip</parameter> in the
- above example) is used as the identifier for the instance.
- </para>
-
- <para>
- Each pre-defined ALSA component such as ac97 and pcm calls
- <function>snd_device_new()</function> inside its
- constructor. The destructor for each component is defined in the
- callback pointers. Hence, you don't need to take care of
- calling a destructor for such a component.
- </para>
-
- <para>
- If you wish to create your own component, you need to
- set the destructor function to the dev_free callback in
- the <parameter>ops</parameter>, so that it can be released
- automatically via <function>snd_card_free()</function>.
- The next example will show an implementation of chip-specific
- data.
- </para>
- </section>
-
- <section id="card-management-chip-specific">
- <title>Chip-Specific Data</title>
- <para>
- Chip-specific information, e.g. the I/O port address, its
- resource pointer, or the irq number, is stored in the
- chip-specific record.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mychip {
- ....
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- In general, there are two ways of allocating the chip record.
- </para>
-
- <section id="card-management-chip-specific-snd-card-new">
- <title>1. Allocating via <function>snd_card_new()</function>.</title>
- <para>
- As mentioned above, you can pass the extra-data-length
- to the 5th argument of <function>snd_card_new()</function>, i.e.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
- sizeof(struct mychip), &card);
-]]>
- </programlisting>
- </informalexample>
-
- struct <structname>mychip</structname> is the type of the chip record.
- </para>
-
- <para>
- In return, the allocated record can be accessed as
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mychip *chip = card->private_data;
-]]>
- </programlisting>
- </informalexample>
-
- With this method, you don't have to allocate twice.
- The record is released together with the card instance.
- </para>
- </section>
-
- <section id="card-management-chip-specific-allocate-extra">
- <title>2. Allocating an extra device.</title>
-
- <para>
- After allocating a card instance via
- <function>snd_card_new()</function> (with
- <constant>0</constant> on the 4th arg), call
- <function>kzalloc()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_card *card;
- struct mychip *chip;
- err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
- 0, &card);
- .....
- chip = kzalloc(sizeof(*chip), GFP_KERNEL);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The chip record should have the field to hold the card
- pointer at least,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mychip {
- struct snd_card *card;
- ....
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Then, set the card pointer in the returned chip instance.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- chip->card = card;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Next, initialize the fields, and register this chip
- record as a low-level device with a specified
- <parameter>ops</parameter>,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct snd_device_ops ops = {
- .dev_free = snd_mychip_dev_free,
- };
- ....
- snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
-]]>
- </programlisting>
- </informalexample>
-
- <function>snd_mychip_dev_free()</function> is the
- device-destructor function, which will call the real
- destructor.
- </para>
-
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_mychip_dev_free(struct snd_device *device)
- {
- return snd_mychip_free(device->device_data);
- }
-]]>
- </programlisting>
- </informalexample>
-
- where <function>snd_mychip_free()</function> is the real destructor.
- </para>
- </section>
- </section>
-
- <section id="card-management-registration">
- <title>Registration and Release</title>
- <para>
- After all components are assigned, register the card instance
- by calling <function>snd_card_register()</function>. Access
- to the device files is enabled at this point. That is, before
- <function>snd_card_register()</function> is called, the
- components are safely inaccessible from external side. If this
- call fails, exit the probe function after releasing the card via
- <function>snd_card_free()</function>.
- </para>
-
- <para>
- For releasing the card instance, you can call simply
- <function>snd_card_free()</function>. As mentioned earlier, all
- components are released automatically by this call.
- </para>
-
- <para>
- For a device which allows hotplugging, you can use
- <function>snd_card_free_when_closed</function>. This one will
- postpone the destruction until all devices are closed.
- </para>
-
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- PCI Resource Management -->
-<!-- ****************************************************** -->
- <chapter id="pci-resource">
- <title>PCI Resource Management</title>
-
- <section id="pci-resource-example">
- <title>Full Code Example</title>
- <para>
- In this section, we'll complete the chip-specific constructor,
- destructor and PCI entries. Example code is shown first,
- below.
-
- <example>
- <title>PCI Resource Management Example</title>
- <programlisting>
-<![CDATA[
- struct mychip {
- struct snd_card *card;
- struct pci_dev *pci;
-
- unsigned long port;
- int irq;
- };
-
- static int snd_mychip_free(struct mychip *chip)
- {
- /* disable hardware here if any */
- .... /* (not implemented in this document) */
-
- /* release the irq */
- if (chip->irq >= 0)
- free_irq(chip->irq, chip);
- /* release the I/O ports & memory */
- pci_release_regions(chip->pci);
- /* disable the PCI entry */
- pci_disable_device(chip->pci);
- /* release the data */
- kfree(chip);
- return 0;
- }
-
- /* chip-specific constructor */
- static int snd_mychip_create(struct snd_card *card,
- struct pci_dev *pci,
- struct mychip **rchip)
- {
- struct mychip *chip;
- int err;
- static struct snd_device_ops ops = {
- .dev_free = snd_mychip_dev_free,
- };
-
- *rchip = NULL;
-
- /* initialize the PCI entry */
- err = pci_enable_device(pci);
- if (err < 0)
- return err;
- /* check PCI availability (28bit DMA) */
- if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 ||
- pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) {
- printk(KERN_ERR "error to set 28bit mask DMA\n");
- pci_disable_device(pci);
- return -ENXIO;
- }
-
- chip = kzalloc(sizeof(*chip), GFP_KERNEL);
- if (chip == NULL) {
- pci_disable_device(pci);
- return -ENOMEM;
- }
-
- /* initialize the stuff */
- chip->card = card;
- chip->pci = pci;
- chip->irq = -1;
-
- /* (1) PCI resource allocation */
- err = pci_request_regions(pci, "My Chip");
- if (err < 0) {
- kfree(chip);
- pci_disable_device(pci);
- return err;
- }
- chip->port = pci_resource_start(pci, 0);
- if (request_irq(pci->irq, snd_mychip_interrupt,
- IRQF_SHARED, KBUILD_MODNAME, chip)) {
- printk(KERN_ERR "cannot grab irq %d\n", pci->irq);
- snd_mychip_free(chip);
- return -EBUSY;
- }
- chip->irq = pci->irq;
-
- /* (2) initialization of the chip hardware */
- .... /* (not implemented in this document) */
-
- err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
- if (err < 0) {
- snd_mychip_free(chip);
- return err;
- }
-
- *rchip = chip;
- return 0;
- }
-
- /* PCI IDs */
- static struct pci_device_id snd_mychip_ids[] = {
- { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR,
- PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, },
- ....
- { 0, }
- };
- MODULE_DEVICE_TABLE(pci, snd_mychip_ids);
-
- /* pci_driver definition */
- static struct pci_driver driver = {
- .name = KBUILD_MODNAME,
- .id_table = snd_mychip_ids,
- .probe = snd_mychip_probe,
- .remove = snd_mychip_remove,
- };
-
- /* module initialization */
- static int __init alsa_card_mychip_init(void)
- {
- return pci_register_driver(&driver);
- }
-
- /* module clean up */
- static void __exit alsa_card_mychip_exit(void)
- {
- pci_unregister_driver(&driver);
- }
-
- module_init(alsa_card_mychip_init)
- module_exit(alsa_card_mychip_exit)
-
- EXPORT_NO_SYMBOLS; /* for old kernels only */
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="pci-resource-some-haftas">
- <title>Some Hafta's</title>
- <para>
- The allocation of PCI resources is done in the
- <function>probe()</function> function, and usually an extra
- <function>xxx_create()</function> function is written for this
- purpose.
- </para>
-
- <para>
- In the case of PCI devices, you first have to call
- the <function>pci_enable_device()</function> function before
- allocating resources. Also, you need to set the proper PCI DMA
- mask to limit the accessed I/O range. In some cases, you might
- need to call <function>pci_set_master()</function> function,
- too.
- </para>
-
- <para>
- Suppose the 28bit mask, and the code to be added would be like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- err = pci_enable_device(pci);
- if (err < 0)
- return err;
- if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 ||
- pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) {
- printk(KERN_ERR "error to set 28bit mask DMA\n");
- pci_disable_device(pci);
- return -ENXIO;
- }
-
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- <section id="pci-resource-resource-allocation">
- <title>Resource Allocation</title>
- <para>
- The allocation of I/O ports and irqs is done via standard kernel
- functions. Unlike ALSA ver.0.5.x., there are no helpers for
- that. And these resources must be released in the destructor
- function (see below). Also, on ALSA 0.9.x, you don't need to
- allocate (pseudo-)DMA for PCI like in ALSA 0.5.x.
- </para>
-
- <para>
- Now assume that the PCI device has an I/O port with 8 bytes
- and an interrupt. Then struct <structname>mychip</structname> will have the
- following fields:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mychip {
- struct snd_card *card;
-
- unsigned long port;
- int irq;
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- For an I/O port (and also a memory region), you need to have
- the resource pointer for the standard resource management. For
- an irq, you have to keep only the irq number (integer). But you
- need to initialize this number as -1 before actual allocation,
- since irq 0 is valid. The port address and its resource pointer
- can be initialized as null by
- <function>kzalloc()</function> automatically, so you
- don't have to take care of resetting them.
- </para>
-
- <para>
- The allocation of an I/O port is done like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- err = pci_request_regions(pci, "My Chip");
- if (err < 0) {
- kfree(chip);
- pci_disable_device(pci);
- return err;
- }
- chip->port = pci_resource_start(pci, 0);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- <!-- obsolete -->
- It will reserve the I/O port region of 8 bytes of the given
- PCI device. The returned value, chip->res_port, is allocated
- via <function>kmalloc()</function> by
- <function>request_region()</function>. The pointer must be
- released via <function>kfree()</function>, but there is a
- problem with this. This issue will be explained later.
- </para>
-
- <para>
- The allocation of an interrupt source is done like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- if (request_irq(pci->irq, snd_mychip_interrupt,
- IRQF_SHARED, KBUILD_MODNAME, chip)) {
- printk(KERN_ERR "cannot grab irq %d\n", pci->irq);
- snd_mychip_free(chip);
- return -EBUSY;
- }
- chip->irq = pci->irq;
-]]>
- </programlisting>
- </informalexample>
-
- where <function>snd_mychip_interrupt()</function> is the
- interrupt handler defined <link
- linkend="pcm-interface-interrupt-handler"><citetitle>later</citetitle></link>.
- Note that chip->irq should be defined
- only when <function>request_irq()</function> succeeded.
- </para>
-
- <para>
- On the PCI bus, interrupts can be shared. Thus,
- <constant>IRQF_SHARED</constant> is used as the interrupt flag of
- <function>request_irq()</function>.
- </para>
-
- <para>
- The last argument of <function>request_irq()</function> is the
- data pointer passed to the interrupt handler. Usually, the
- chip-specific record is used for that, but you can use what you
- like, too.
- </para>
-
- <para>
- I won't give details about the interrupt handler at this
- point, but at least its appearance can be explained now. The
- interrupt handler looks usually like the following:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
- {
- struct mychip *chip = dev_id;
- ....
- return IRQ_HANDLED;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Now let's write the corresponding destructor for the resources
- above. The role of destructor is simple: disable the hardware
- (if already activated) and release the resources. So far, we
- have no hardware part, so the disabling code is not written here.
- </para>
-
- <para>
- To release the resources, the <quote>check-and-release</quote>
- method is a safer way. For the interrupt, do like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- if (chip->irq >= 0)
- free_irq(chip->irq, chip);
-]]>
- </programlisting>
- </informalexample>
-
- Since the irq number can start from 0, you should initialize
- chip->irq with a negative value (e.g. -1), so that you can
- check the validity of the irq number as above.
- </para>
-
- <para>
- When you requested I/O ports or memory regions via
- <function>pci_request_region()</function> or
- <function>pci_request_regions()</function> like in this example,
- release the resource(s) using the corresponding function,
- <function>pci_release_region()</function> or
- <function>pci_release_regions()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- pci_release_regions(chip->pci);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- When you requested manually via <function>request_region()</function>
- or <function>request_mem_region</function>, you can release it via
- <function>release_resource()</function>. Suppose that you keep
- the resource pointer returned from <function>request_region()</function>
- in chip->res_port, the release procedure looks like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- release_and_free_resource(chip->res_port);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Don't forget to call <function>pci_disable_device()</function>
- before the end.
- </para>
-
- <para>
- And finally, release the chip-specific record.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- kfree(chip);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- We didn't implement the hardware disabling part in the above.
- If you need to do this, please note that the destructor may be
- called even before the initialization of the chip is completed.
- It would be better to have a flag to skip hardware disabling
- if the hardware was not initialized yet.
- </para>
-
- <para>
- When the chip-data is assigned to the card using
- <function>snd_device_new()</function> with
- <constant>SNDRV_DEV_LOWLELVEL</constant> , its destructor is
- called at the last. That is, it is assured that all other
- components like PCMs and controls have already been released.
- You don't have to stop PCMs, etc. explicitly, but just
- call low-level hardware stopping.
- </para>
-
- <para>
- The management of a memory-mapped region is almost as same as
- the management of an I/O port. You'll need three fields like
- the following:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mychip {
- ....
- unsigned long iobase_phys;
- void __iomem *iobase_virt;
- };
-]]>
- </programlisting>
- </informalexample>
-
- and the allocation would be like below:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- if ((err = pci_request_regions(pci, "My Chip")) < 0) {
- kfree(chip);
- return err;
- }
- chip->iobase_phys = pci_resource_start(pci, 0);
- chip->iobase_virt = ioremap_nocache(chip->iobase_phys,
- pci_resource_len(pci, 0));
-]]>
- </programlisting>
- </informalexample>
-
- and the corresponding destructor would be:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_mychip_free(struct mychip *chip)
- {
- ....
- if (chip->iobase_virt)
- iounmap(chip->iobase_virt);
- ....
- pci_release_regions(chip->pci);
- ....
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- </section>
-
- <section id="pci-resource-entries">
- <title>PCI Entries</title>
- <para>
- So far, so good. Let's finish the missing PCI
- stuff. At first, we need a
- <structname>pci_device_id</structname> table for this
- chipset. It's a table of PCI vendor/device ID number, and some
- masks.
- </para>
-
- <para>
- For example,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct pci_device_id snd_mychip_ids[] = {
- { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR,
- PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, },
- ....
- { 0, }
- };
- MODULE_DEVICE_TABLE(pci, snd_mychip_ids);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The first and second fields of
- the <structname>pci_device_id</structname> structure are the vendor and
- device IDs. If you have no reason to filter the matching
- devices, you can leave the remaining fields as above. The last
- field of the <structname>pci_device_id</structname> struct contains
- private data for this entry. You can specify any value here, for
- example, to define specific operations for supported device IDs.
- Such an example is found in the intel8x0 driver.
- </para>
-
- <para>
- The last entry of this list is the terminator. You must
- specify this all-zero entry.
- </para>
-
- <para>
- Then, prepare the <structname>pci_driver</structname> record:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct pci_driver driver = {
- .name = KBUILD_MODNAME,
- .id_table = snd_mychip_ids,
- .probe = snd_mychip_probe,
- .remove = snd_mychip_remove,
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The <structfield>probe</structfield> and
- <structfield>remove</structfield> functions have already
- been defined in the previous sections.
- The <structfield>name</structfield>
- field is the name string of this device. Note that you must not
- use a slash <quote>/</quote> in this string.
- </para>
-
- <para>
- And at last, the module entries:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int __init alsa_card_mychip_init(void)
- {
- return pci_register_driver(&driver);
- }
-
- static void __exit alsa_card_mychip_exit(void)
- {
- pci_unregister_driver(&driver);
- }
-
- module_init(alsa_card_mychip_init)
- module_exit(alsa_card_mychip_exit)
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Note that these module entries are tagged with
- <parameter>__init</parameter> and
- <parameter>__exit</parameter> prefixes.
- </para>
-
- <para>
- Oh, one thing was forgotten. If you have no exported symbols,
- you need to declare it in 2.2 or 2.4 kernels (it's not necessary in 2.6 kernels).
-
- <informalexample>
- <programlisting>
-<![CDATA[
- EXPORT_NO_SYMBOLS;
-]]>
- </programlisting>
- </informalexample>
-
- That's all!
- </para>
- </section>
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- PCM Interface -->
-<!-- ****************************************************** -->
- <chapter id="pcm-interface">
- <title>PCM Interface</title>
-
- <section id="pcm-interface-general">
- <title>General</title>
- <para>
- The PCM middle layer of ALSA is quite powerful and it is only
- necessary for each driver to implement the low-level functions
- to access its hardware.
- </para>
-
- <para>
- For accessing to the PCM layer, you need to include
- <filename><sound/pcm.h></filename> first. In addition,
- <filename><sound/pcm_params.h></filename> might be needed
- if you access to some functions related with hw_param.
- </para>
-
- <para>
- Each card device can have up to four pcm instances. A pcm
- instance corresponds to a pcm device file. The limitation of
- number of instances comes only from the available bit size of
- the Linux's device numbers. Once when 64bit device number is
- used, we'll have more pcm instances available.
- </para>
-
- <para>
- A pcm instance consists of pcm playback and capture streams,
- and each pcm stream consists of one or more pcm substreams. Some
- soundcards support multiple playback functions. For example,
- emu10k1 has a PCM playback of 32 stereo substreams. In this case, at
- each open, a free substream is (usually) automatically chosen
- and opened. Meanwhile, when only one substream exists and it was
- already opened, the successful open will either block
- or error with <constant>EAGAIN</constant> according to the
- file open mode. But you don't have to care about such details in your
- driver. The PCM middle layer will take care of such work.
- </para>
- </section>
-
- <section id="pcm-interface-example">
- <title>Full Code Example</title>
- <para>
- The example code below does not include any hardware access
- routines but shows only the skeleton, how to build up the PCM
- interfaces.
-
- <example>
- <title>PCM Example Code</title>
- <programlisting>
-<![CDATA[
- #include <sound/pcm.h>
- ....
-
- /* hardware definition */
- static struct snd_pcm_hardware snd_mychip_playback_hw = {
- .info = (SNDRV_PCM_INFO_MMAP |
- SNDRV_PCM_INFO_INTERLEAVED |
- SNDRV_PCM_INFO_BLOCK_TRANSFER |
- SNDRV_PCM_INFO_MMAP_VALID),
- .formats = SNDRV_PCM_FMTBIT_S16_LE,
- .rates = SNDRV_PCM_RATE_8000_48000,
- .rate_min = 8000,
- .rate_max = 48000,
- .channels_min = 2,
- .channels_max = 2,
- .buffer_bytes_max = 32768,
- .period_bytes_min = 4096,
- .period_bytes_max = 32768,
- .periods_min = 1,
- .periods_max = 1024,
- };
-
- /* hardware definition */
- static struct snd_pcm_hardware snd_mychip_capture_hw = {
- .info = (SNDRV_PCM_INFO_MMAP |
- SNDRV_PCM_INFO_INTERLEAVED |
- SNDRV_PCM_INFO_BLOCK_TRANSFER |
- SNDRV_PCM_INFO_MMAP_VALID),
- .formats = SNDRV_PCM_FMTBIT_S16_LE,
- .rates = SNDRV_PCM_RATE_8000_48000,
- .rate_min = 8000,
- .rate_max = 48000,
- .channels_min = 2,
- .channels_max = 2,
- .buffer_bytes_max = 32768,
- .period_bytes_min = 4096,
- .period_bytes_max = 32768,
- .periods_min = 1,
- .periods_max = 1024,
- };
-
- /* open callback */
- static int snd_mychip_playback_open(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- struct snd_pcm_runtime *runtime = substream->runtime;
-
- runtime->hw = snd_mychip_playback_hw;
- /* more hardware-initialization will be done here */
- ....
- return 0;
- }
-
- /* close callback */
- static int snd_mychip_playback_close(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- /* the hardware-specific codes will be here */
- ....
- return 0;
-
- }
-
- /* open callback */
- static int snd_mychip_capture_open(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- struct snd_pcm_runtime *runtime = substream->runtime;
-
- runtime->hw = snd_mychip_capture_hw;
- /* more hardware-initialization will be done here */
- ....
- return 0;
- }
-
- /* close callback */
- static int snd_mychip_capture_close(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- /* the hardware-specific codes will be here */
- ....
- return 0;
-
- }
-
- /* hw_params callback */
- static int snd_mychip_pcm_hw_params(struct snd_pcm_substream *substream,
- struct snd_pcm_hw_params *hw_params)
- {
- return snd_pcm_lib_malloc_pages(substream,
- params_buffer_bytes(hw_params));
- }
-
- /* hw_free callback */
- static int snd_mychip_pcm_hw_free(struct snd_pcm_substream *substream)
- {
- return snd_pcm_lib_free_pages(substream);
- }
-
- /* prepare callback */
- static int snd_mychip_pcm_prepare(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- struct snd_pcm_runtime *runtime = substream->runtime;
-
- /* set up the hardware with the current configuration
- * for example...
- */
- mychip_set_sample_format(chip, runtime->format);
- mychip_set_sample_rate(chip, runtime->rate);
- mychip_set_channels(chip, runtime->channels);
- mychip_set_dma_setup(chip, runtime->dma_addr,
- chip->buffer_size,
- chip->period_size);
- return 0;
- }
-
- /* trigger callback */
- static int snd_mychip_pcm_trigger(struct snd_pcm_substream *substream,
- int cmd)
- {
- switch (cmd) {
- case SNDRV_PCM_TRIGGER_START:
- /* do something to start the PCM engine */
- ....
- break;
- case SNDRV_PCM_TRIGGER_STOP:
- /* do something to stop the PCM engine */
- ....
- break;
- default:
- return -EINVAL;
- }
- }
-
- /* pointer callback */
- static snd_pcm_uframes_t
- snd_mychip_pcm_pointer(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- unsigned int current_ptr;
-
- /* get the current hardware pointer */
- current_ptr = mychip_get_hw_pointer(chip);
- return current_ptr;
- }
-
- /* operators */
- static struct snd_pcm_ops snd_mychip_playback_ops = {
- .open = snd_mychip_playback_open,
- .close = snd_mychip_playback_close,
- .ioctl = snd_pcm_lib_ioctl,
- .hw_params = snd_mychip_pcm_hw_params,
- .hw_free = snd_mychip_pcm_hw_free,
- .prepare = snd_mychip_pcm_prepare,
- .trigger = snd_mychip_pcm_trigger,
- .pointer = snd_mychip_pcm_pointer,
- };
-
- /* operators */
- static struct snd_pcm_ops snd_mychip_capture_ops = {
- .open = snd_mychip_capture_open,
- .close = snd_mychip_capture_close,
- .ioctl = snd_pcm_lib_ioctl,
- .hw_params = snd_mychip_pcm_hw_params,
- .hw_free = snd_mychip_pcm_hw_free,
- .prepare = snd_mychip_pcm_prepare,
- .trigger = snd_mychip_pcm_trigger,
- .pointer = snd_mychip_pcm_pointer,
- };
-
- /*
- * definitions of capture are omitted here...
- */
-
- /* create a pcm device */
- static int snd_mychip_new_pcm(struct mychip *chip)
- {
- struct snd_pcm *pcm;
- int err;
-
- err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
- if (err < 0)
- return err;
- pcm->private_data = chip;
- strcpy(pcm->name, "My Chip");
- chip->pcm = pcm;
- /* set operators */
- snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
- &snd_mychip_playback_ops);
- snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
- &snd_mychip_capture_ops);
- /* pre-allocation of buffers */
- /* NOTE: this may fail */
- snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
- snd_dma_pci_data(chip->pci),
- 64*1024, 64*1024);
- return 0;
- }
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="pcm-interface-constructor">
- <title>Constructor</title>
- <para>
- A pcm instance is allocated by the <function>snd_pcm_new()</function>
- function. It would be better to create a constructor for pcm,
- namely,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_mychip_new_pcm(struct mychip *chip)
- {
- struct snd_pcm *pcm;
- int err;
-
- err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
- if (err < 0)
- return err;
- pcm->private_data = chip;
- strcpy(pcm->name, "My Chip");
- chip->pcm = pcm;
- ....
- return 0;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The <function>snd_pcm_new()</function> function takes four
- arguments. The first argument is the card pointer to which this
- pcm is assigned, and the second is the ID string.
- </para>
-
- <para>
- The third argument (<parameter>index</parameter>, 0 in the
- above) is the index of this new pcm. It begins from zero. If
- you create more than one pcm instances, specify the
- different numbers in this argument. For example,
- <parameter>index</parameter> = 1 for the second PCM device.
- </para>
-
- <para>
- The fourth and fifth arguments are the number of substreams
- for playback and capture, respectively. Here 1 is used for
- both arguments. When no playback or capture substreams are available,
- pass 0 to the corresponding argument.
- </para>
-
- <para>
- If a chip supports multiple playbacks or captures, you can
- specify more numbers, but they must be handled properly in
- open/close, etc. callbacks. When you need to know which
- substream you are referring to, then it can be obtained from
- struct <structname>snd_pcm_substream</structname> data passed to each callback
- as follows:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_pcm_substream *substream;
- int index = substream->number;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- After the pcm is created, you need to set operators for each
- pcm stream.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
- &snd_mychip_playback_ops);
- snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
- &snd_mychip_capture_ops);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The operators are defined typically like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct snd_pcm_ops snd_mychip_playback_ops = {
- .open = snd_mychip_pcm_open,
- .close = snd_mychip_pcm_close,
- .ioctl = snd_pcm_lib_ioctl,
- .hw_params = snd_mychip_pcm_hw_params,
- .hw_free = snd_mychip_pcm_hw_free,
- .prepare = snd_mychip_pcm_prepare,
- .trigger = snd_mychip_pcm_trigger,
- .pointer = snd_mychip_pcm_pointer,
- };
-]]>
- </programlisting>
- </informalexample>
-
- All the callbacks are described in the
- <link linkend="pcm-interface-operators"><citetitle>
- Operators</citetitle></link> subsection.
- </para>
-
- <para>
- After setting the operators, you probably will want to
- pre-allocate the buffer. For the pre-allocation, simply call
- the following:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
- snd_dma_pci_data(chip->pci),
- 64*1024, 64*1024);
-]]>
- </programlisting>
- </informalexample>
-
- It will allocate a buffer up to 64kB as default.
- Buffer management details will be described in the later section <link
- linkend="buffer-and-memory"><citetitle>Buffer and Memory
- Management</citetitle></link>.
- </para>
-
- <para>
- Additionally, you can set some extra information for this pcm
- in pcm->info_flags.
- The available values are defined as
- <constant>SNDRV_PCM_INFO_XXX</constant> in
- <filename><sound/asound.h></filename>, which is used for
- the hardware definition (described later). When your soundchip
- supports only half-duplex, specify like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- pcm->info_flags = SNDRV_PCM_INFO_HALF_DUPLEX;
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- <section id="pcm-interface-destructor">
- <title>... And the Destructor?</title>
- <para>
- The destructor for a pcm instance is not always
- necessary. Since the pcm device will be released by the middle
- layer code automatically, you don't have to call the destructor
- explicitly.
- </para>
-
- <para>
- The destructor would be necessary if you created
- special records internally and needed to release them. In such a
- case, set the destructor function to
- pcm->private_free:
-
- <example>
- <title>PCM Instance with a Destructor</title>
- <programlisting>
-<![CDATA[
- static void mychip_pcm_free(struct snd_pcm *pcm)
- {
- struct mychip *chip = snd_pcm_chip(pcm);
- /* free your own data */
- kfree(chip->my_private_pcm_data);
- /* do what you like else */
- ....
- }
-
- static int snd_mychip_new_pcm(struct mychip *chip)
- {
- struct snd_pcm *pcm;
- ....
- /* allocate your own data */
- chip->my_private_pcm_data = kmalloc(...);
- /* set the destructor */
- pcm->private_data = chip;
- pcm->private_free = mychip_pcm_free;
- ....
- }
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="pcm-interface-runtime">
- <title>Runtime Pointer - The Chest of PCM Information</title>
- <para>
- When the PCM substream is opened, a PCM runtime instance is
- allocated and assigned to the substream. This pointer is
- accessible via <constant>substream->runtime</constant>.
- This runtime pointer holds most information you need
- to control the PCM: the copy of hw_params and sw_params configurations, the buffer
- pointers, mmap records, spinlocks, etc.
- </para>
-
- <para>
- The definition of runtime instance is found in
- <filename><sound/pcm.h></filename>. Here are
- the contents of this file:
- <informalexample>
- <programlisting>
-<![CDATA[
-struct _snd_pcm_runtime {
- /* -- Status -- */
- struct snd_pcm_substream *trigger_master;
- snd_timestamp_t trigger_tstamp; /* trigger timestamp */
- int overrange;
- snd_pcm_uframes_t avail_max;
- snd_pcm_uframes_t hw_ptr_base; /* Position at buffer restart */
- snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time*/
-
- /* -- HW params -- */
- snd_pcm_access_t access; /* access mode */
- snd_pcm_format_t format; /* SNDRV_PCM_FORMAT_* */
- snd_pcm_subformat_t subformat; /* subformat */
- unsigned int rate; /* rate in Hz */
- unsigned int channels; /* channels */
- snd_pcm_uframes_t period_size; /* period size */
- unsigned int periods; /* periods */
- snd_pcm_uframes_t buffer_size; /* buffer size */
- unsigned int tick_time; /* tick time */
- snd_pcm_uframes_t min_align; /* Min alignment for the format */
- size_t byte_align;
- unsigned int frame_bits;
- unsigned int sample_bits;
- unsigned int info;
- unsigned int rate_num;
- unsigned int rate_den;
-
- /* -- SW params -- */
- struct timespec tstamp_mode; /* mmap timestamp is updated */
- unsigned int period_step;
- unsigned int sleep_min; /* min ticks to sleep */
- snd_pcm_uframes_t start_threshold;
- snd_pcm_uframes_t stop_threshold;
- snd_pcm_uframes_t silence_threshold; /* Silence filling happens when
- noise is nearest than this */
- snd_pcm_uframes_t silence_size; /* Silence filling size */
- snd_pcm_uframes_t boundary; /* pointers wrap point */
-
- snd_pcm_uframes_t silenced_start;
- snd_pcm_uframes_t silenced_size;
-
- snd_pcm_sync_id_t sync; /* hardware synchronization ID */
-
- /* -- mmap -- */
- volatile struct snd_pcm_mmap_status *status;
- volatile struct snd_pcm_mmap_control *control;
- atomic_t mmap_count;
-
- /* -- locking / scheduling -- */
- spinlock_t lock;
- wait_queue_head_t sleep;
- struct timer_list tick_timer;
- struct fasync_struct *fasync;
-
- /* -- private section -- */
- void *private_data;
- void (*private_free)(struct snd_pcm_runtime *runtime);
-
- /* -- hardware description -- */
- struct snd_pcm_hardware hw;
- struct snd_pcm_hw_constraints hw_constraints;
-
- /* -- timer -- */
- unsigned int timer_resolution; /* timer resolution */
-
- /* -- DMA -- */
- unsigned char *dma_area; /* DMA area */
- dma_addr_t dma_addr; /* physical bus address (not accessible from main CPU) */
- size_t dma_bytes; /* size of DMA area */
-
- struct snd_dma_buffer *dma_buffer_p; /* allocated buffer */
-
-#if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE)
- /* -- OSS things -- */
- struct snd_pcm_oss_runtime oss;
-#endif
-};
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- For the operators (callbacks) of each sound driver, most of
- these records are supposed to be read-only. Only the PCM
- middle-layer changes / updates them. The exceptions are
- the hardware description (hw) DMA buffer information and the
- private data. Besides, if you use the standard buffer allocation
- method via <function>snd_pcm_lib_malloc_pages()</function>,
- you don't need to set the DMA buffer information by yourself.
- </para>
-
- <para>
- In the sections below, important records are explained.
- </para>
-
- <section id="pcm-interface-runtime-hw">
- <title>Hardware Description</title>
- <para>
- The hardware descriptor (struct <structname>snd_pcm_hardware</structname>)
- contains the definitions of the fundamental hardware
- configuration. Above all, you'll need to define this in
- <link linkend="pcm-interface-operators-open-callback"><citetitle>
- the open callback</citetitle></link>.
- Note that the runtime instance holds the copy of the
- descriptor, not the pointer to the existing descriptor. That
- is, in the open callback, you can modify the copied descriptor
- (<constant>runtime->hw</constant>) as you need. For example, if the maximum
- number of channels is 1 only on some chip models, you can
- still use the same hardware descriptor and change the
- channels_max later:
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_pcm_runtime *runtime = substream->runtime;
- ...
- runtime->hw = snd_mychip_playback_hw; /* common definition */
- if (chip->model == VERY_OLD_ONE)
- runtime->hw.channels_max = 1;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Typically, you'll have a hardware descriptor as below:
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct snd_pcm_hardware snd_mychip_playback_hw = {
- .info = (SNDRV_PCM_INFO_MMAP |
- SNDRV_PCM_INFO_INTERLEAVED |
- SNDRV_PCM_INFO_BLOCK_TRANSFER |
- SNDRV_PCM_INFO_MMAP_VALID),
- .formats = SNDRV_PCM_FMTBIT_S16_LE,
- .rates = SNDRV_PCM_RATE_8000_48000,
- .rate_min = 8000,
- .rate_max = 48000,
- .channels_min = 2,
- .channels_max = 2,
- .buffer_bytes_max = 32768,
- .period_bytes_min = 4096,
- .period_bytes_max = 32768,
- .periods_min = 1,
- .periods_max = 1024,
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- <itemizedlist>
- <listitem><para>
- The <structfield>info</structfield> field contains the type and
- capabilities of this pcm. The bit flags are defined in
- <filename><sound/asound.h></filename> as
- <constant>SNDRV_PCM_INFO_XXX</constant>. Here, at least, you
- have to specify whether the mmap is supported and which
- interleaved format is supported.
- When the hardware supports mmap, add the
- <constant>SNDRV_PCM_INFO_MMAP</constant> flag here. When the
- hardware supports the interleaved or the non-interleaved
- formats, <constant>SNDRV_PCM_INFO_INTERLEAVED</constant> or
- <constant>SNDRV_PCM_INFO_NONINTERLEAVED</constant> flag must
- be set, respectively. If both are supported, you can set both,
- too.
- </para>
-
- <para>
- In the above example, <constant>MMAP_VALID</constant> and
- <constant>BLOCK_TRANSFER</constant> are specified for the OSS mmap
- mode. Usually both are set. Of course,
- <constant>MMAP_VALID</constant> is set only if the mmap is
- really supported.
- </para>
-
- <para>
- The other possible flags are
- <constant>SNDRV_PCM_INFO_PAUSE</constant> and
- <constant>SNDRV_PCM_INFO_RESUME</constant>. The
- <constant>PAUSE</constant> bit means that the pcm supports the
- <quote>pause</quote> operation, while the
- <constant>RESUME</constant> bit means that the pcm supports
- the full <quote>suspend/resume</quote> operation.
- If the <constant>PAUSE</constant> flag is set,
- the <structfield>trigger</structfield> callback below
- must handle the corresponding (pause push/release) commands.
- The suspend/resume trigger commands can be defined even without
- the <constant>RESUME</constant> flag. See <link
- linkend="power-management"><citetitle>
- Power Management</citetitle></link> section for details.
- </para>
-
- <para>
- When the PCM substreams can be synchronized (typically,
- synchronized start/stop of a playback and a capture streams),
- you can give <constant>SNDRV_PCM_INFO_SYNC_START</constant>,
- too. In this case, you'll need to check the linked-list of
- PCM substreams in the trigger callback. This will be
- described in the later section.
- </para>
- </listitem>
-
- <listitem>
- <para>
- <structfield>formats</structfield> field contains the bit-flags
- of supported formats (<constant>SNDRV_PCM_FMTBIT_XXX</constant>).
- If the hardware supports more than one format, give all or'ed
- bits. In the example above, the signed 16bit little-endian
- format is specified.
- </para>
- </listitem>
-
- <listitem>
- <para>
- <structfield>rates</structfield> field contains the bit-flags of
- supported rates (<constant>SNDRV_PCM_RATE_XXX</constant>).
- When the chip supports continuous rates, pass
- <constant>CONTINUOUS</constant> bit additionally.
- The pre-defined rate bits are provided only for typical
- rates. If your chip supports unconventional rates, you need to add
- the <constant>KNOT</constant> bit and set up the hardware
- constraint manually (explained later).
- </para>
- </listitem>
-
- <listitem>
- <para>
- <structfield>rate_min</structfield> and
- <structfield>rate_max</structfield> define the minimum and
- maximum sample rate. This should correspond somehow to
- <structfield>rates</structfield> bits.
- </para>
- </listitem>
-
- <listitem>
- <para>
- <structfield>channel_min</structfield> and
- <structfield>channel_max</structfield>
- define, as you might already expected, the minimum and maximum
- number of channels.
- </para>
- </listitem>
-
- <listitem>
- <para>
- <structfield>buffer_bytes_max</structfield> defines the
- maximum buffer size in bytes. There is no
- <structfield>buffer_bytes_min</structfield> field, since
- it can be calculated from the minimum period size and the
- minimum number of periods.
- Meanwhile, <structfield>period_bytes_min</structfield> and
- define the minimum and maximum size of the period in bytes.
- <structfield>periods_max</structfield> and
- <structfield>periods_min</structfield> define the maximum and
- minimum number of periods in the buffer.
- </para>
-
- <para>
- The <quote>period</quote> is a term that corresponds to
- a fragment in the OSS world. The period defines the size at
- which a PCM interrupt is generated. This size strongly
- depends on the hardware.
- Generally, the smaller period size will give you more
- interrupts, that is, more controls.
- In the case of capture, this size defines the input latency.
- On the other hand, the whole buffer size defines the
- output latency for the playback direction.
- </para>
- </listitem>
-
- <listitem>
- <para>
- There is also a field <structfield>fifo_size</structfield>.
- This specifies the size of the hardware FIFO, but currently it
- is neither used in the driver nor in the alsa-lib. So, you
- can ignore this field.
- </para>
- </listitem>
- </itemizedlist>
- </para>
- </section>
-
- <section id="pcm-interface-runtime-config">
- <title>PCM Configurations</title>
- <para>
- Ok, let's go back again to the PCM runtime records.
- The most frequently referred records in the runtime instance are
- the PCM configurations.
- The PCM configurations are stored in the runtime instance
- after the application sends <type>hw_params</type> data via
- alsa-lib. There are many fields copied from hw_params and
- sw_params structs. For example,
- <structfield>format</structfield> holds the format type
- chosen by the application. This field contains the enum value
- <constant>SNDRV_PCM_FORMAT_XXX</constant>.
- </para>
-
- <para>
- One thing to be noted is that the configured buffer and period
- sizes are stored in <quote>frames</quote> in the runtime.
- In the ALSA world, 1 frame = channels * samples-size.
- For conversion between frames and bytes, you can use the
- <function>frames_to_bytes()</function> and
- <function>bytes_to_frames()</function> helper functions.
- <informalexample>
- <programlisting>
-<![CDATA[
- period_bytes = frames_to_bytes(runtime, runtime->period_size);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Also, many software parameters (sw_params) are
- stored in frames, too. Please check the type of the field.
- <type>snd_pcm_uframes_t</type> is for the frames as unsigned
- integer while <type>snd_pcm_sframes_t</type> is for the frames
- as signed integer.
- </para>
- </section>
-
- <section id="pcm-interface-runtime-dma">
- <title>DMA Buffer Information</title>
- <para>
- The DMA buffer is defined by the following four fields,
- <structfield>dma_area</structfield>,
- <structfield>dma_addr</structfield>,
- <structfield>dma_bytes</structfield> and
- <structfield>dma_private</structfield>.
- The <structfield>dma_area</structfield> holds the buffer
- pointer (the logical address). You can call
- <function>memcpy</function> from/to
- this pointer. Meanwhile, <structfield>dma_addr</structfield>
- holds the physical address of the buffer. This field is
- specified only when the buffer is a linear buffer.
- <structfield>dma_bytes</structfield> holds the size of buffer
- in bytes. <structfield>dma_private</structfield> is used for
- the ALSA DMA allocator.
- </para>
-
- <para>
- If you use a standard ALSA function,
- <function>snd_pcm_lib_malloc_pages()</function>, for
- allocating the buffer, these fields are set by the ALSA middle
- layer, and you should <emphasis>not</emphasis> change them by
- yourself. You can read them but not write them.
- On the other hand, if you want to allocate the buffer by
- yourself, you'll need to manage it in hw_params callback.
- At least, <structfield>dma_bytes</structfield> is mandatory.
- <structfield>dma_area</structfield> is necessary when the
- buffer is mmapped. If your driver doesn't support mmap, this
- field is not necessary. <structfield>dma_addr</structfield>
- is also optional. You can use
- <structfield>dma_private</structfield> as you like, too.
- </para>
- </section>
-
- <section id="pcm-interface-runtime-status">
- <title>Running Status</title>
- <para>
- The running status can be referred via <constant>runtime->status</constant>.
- This is the pointer to the struct <structname>snd_pcm_mmap_status</structname>
- record. For example, you can get the current DMA hardware
- pointer via <constant>runtime->status->hw_ptr</constant>.
- </para>
-
- <para>
- The DMA application pointer can be referred via
- <constant>runtime->control</constant>, which points to the
- struct <structname>snd_pcm_mmap_control</structname> record.
- However, accessing directly to this value is not recommended.
- </para>
- </section>
-
- <section id="pcm-interface-runtime-private">
- <title>Private Data</title>
- <para>
- You can allocate a record for the substream and store it in
- <constant>runtime->private_data</constant>. Usually, this
- is done in
- <link linkend="pcm-interface-operators-open-callback"><citetitle>
- the open callback</citetitle></link>.
- Don't mix this with <constant>pcm->private_data</constant>.
- The <constant>pcm->private_data</constant> usually points to the
- chip instance assigned statically at the creation of PCM, while the
- <constant>runtime->private_data</constant> points to a dynamic
- data structure created at the PCM open callback.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_open(struct snd_pcm_substream *substream)
- {
- struct my_pcm_data *data;
- ....
- data = kmalloc(sizeof(*data), GFP_KERNEL);
- substream->runtime->private_data = data;
- ....
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The allocated object must be released in
- <link linkend="pcm-interface-operators-open-callback"><citetitle>
- the close callback</citetitle></link>.
- </para>
- </section>
-
- </section>
-
- <section id="pcm-interface-operators">
- <title>Operators</title>
- <para>
- OK, now let me give details about each pcm callback
- (<parameter>ops</parameter>). In general, every callback must
- return 0 if successful, or a negative error number
- such as <constant>-EINVAL</constant>. To choose an appropriate
- error number, it is advised to check what value other parts of
- the kernel return when the same kind of request fails.
- </para>
-
- <para>
- The callback function takes at least the argument with
- <structname>snd_pcm_substream</structname> pointer. To retrieve
- the chip record from the given substream instance, you can use the
- following macro.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- int xxx() {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- ....
- }
-]]>
- </programlisting>
- </informalexample>
-
- The macro reads <constant>substream->private_data</constant>,
- which is a copy of <constant>pcm->private_data</constant>.
- You can override the former if you need to assign different data
- records per PCM substream. For example, the cmi8330 driver assigns
- different private_data for playback and capture directions,
- because it uses two different codecs (SB- and AD-compatible) for
- different directions.
- </para>
-
- <section id="pcm-interface-operators-open-callback">
- <title>open callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_open(struct snd_pcm_substream *substream);
-]]>
- </programlisting>
- </informalexample>
-
- This is called when a pcm substream is opened.
- </para>
-
- <para>
- At least, here you have to initialize the runtime->hw
- record. Typically, this is done by like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_open(struct snd_pcm_substream *substream)
- {
- struct mychip *chip = snd_pcm_substream_chip(substream);
- struct snd_pcm_runtime *runtime = substream->runtime;
-
- runtime->hw = snd_mychip_playback_hw;
- return 0;
- }
-]]>
- </programlisting>
- </informalexample>
-
- where <parameter>snd_mychip_playback_hw</parameter> is the
- pre-defined hardware description.
- </para>
-
- <para>
- You can allocate a private data in this callback, as described
- in <link linkend="pcm-interface-runtime-private"><citetitle>
- Private Data</citetitle></link> section.
- </para>
-
- <para>
- If the hardware configuration needs more constraints, set the
- hardware constraints here, too.
- See <link linkend="pcm-interface-constraints"><citetitle>
- Constraints</citetitle></link> for more details.
- </para>
- </section>
-
- <section id="pcm-interface-operators-close-callback">
- <title>close callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_close(struct snd_pcm_substream *substream);
-]]>
- </programlisting>
- </informalexample>
-
- Obviously, this is called when a pcm substream is closed.
- </para>
-
- <para>
- Any private instance for a pcm substream allocated in the
- open callback will be released here.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_close(struct snd_pcm_substream *substream)
- {
- ....
- kfree(substream->runtime->private_data);
- ....
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- <section id="pcm-interface-operators-ioctl-callback">
- <title>ioctl callback</title>
- <para>
- This is used for any special call to pcm ioctls. But
- usually you can pass a generic ioctl callback,
- <function>snd_pcm_lib_ioctl</function>.
- </para>
- </section>
-
- <section id="pcm-interface-operators-hw-params-callback">
- <title>hw_params callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_hw_params(struct snd_pcm_substream *substream,
- struct snd_pcm_hw_params *hw_params);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- This is called when the hardware parameter
- (<structfield>hw_params</structfield>) is set
- up by the application,
- that is, once when the buffer size, the period size, the
- format, etc. are defined for the pcm substream.
- </para>
-
- <para>
- Many hardware setups should be done in this callback,
- including the allocation of buffers.
- </para>
-
- <para>
- Parameters to be initialized are retrieved by
- <function>params_xxx()</function> macros. To allocate
- buffer, you can call a helper function,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(hw_params));
-]]>
- </programlisting>
- </informalexample>
-
- <function>snd_pcm_lib_malloc_pages()</function> is available
- only when the DMA buffers have been pre-allocated.
- See the section <link
- linkend="buffer-and-memory-buffer-types"><citetitle>
- Buffer Types</citetitle></link> for more details.
- </para>
-
- <para>
- Note that this and <structfield>prepare</structfield> callbacks
- may be called multiple times per initialization.
- For example, the OSS emulation may
- call these callbacks at each change via its ioctl.
- </para>
-
- <para>
- Thus, you need to be careful not to allocate the same buffers
- many times, which will lead to memory leaks! Calling the
- helper function above many times is OK. It will release the
- previous buffer automatically when it was already allocated.
- </para>
-
- <para>
- Another note is that this callback is non-atomic
- (schedulable) as default, i.e. when no
- <structfield>nonatomic</structfield> flag set.
- This is important, because the
- <structfield>trigger</structfield> callback
- is atomic (non-schedulable). That is, mutexes or any
- schedule-related functions are not available in
- <structfield>trigger</structfield> callback.
- Please see the subsection
- <link linkend="pcm-interface-atomicity"><citetitle>
- Atomicity</citetitle></link> for details.
- </para>
- </section>
-
- <section id="pcm-interface-operators-hw-free-callback">
- <title>hw_free callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_hw_free(struct snd_pcm_substream *substream);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- This is called to release the resources allocated via
- <structfield>hw_params</structfield>. For example, releasing the
- buffer via
- <function>snd_pcm_lib_malloc_pages()</function> is done by
- calling the following:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_lib_free_pages(substream);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- This function is always called before the close callback is called.
- Also, the callback may be called multiple times, too.
- Keep track whether the resource was already released.
- </para>
- </section>
-
- <section id="pcm-interface-operators-prepare-callback">
- <title>prepare callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_prepare(struct snd_pcm_substream *substream);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- This callback is called when the pcm is
- <quote>prepared</quote>. You can set the format type, sample
- rate, etc. here. The difference from
- <structfield>hw_params</structfield> is that the
- <structfield>prepare</structfield> callback will be called each
- time
- <function>snd_pcm_prepare()</function> is called, i.e. when
- recovering after underruns, etc.
- </para>
-
- <para>
- Note that this callback is now non-atomic.
- You can use schedule-related functions safely in this callback.
- </para>
-
- <para>
- In this and the following callbacks, you can refer to the
- values via the runtime record,
- substream->runtime.
- For example, to get the current
- rate, format or channels, access to
- runtime->rate,
- runtime->format or
- runtime->channels, respectively.
- The physical address of the allocated buffer is set to
- runtime->dma_area. The buffer and period sizes are
- in runtime->buffer_size and runtime->period_size,
- respectively.
- </para>
-
- <para>
- Be careful that this callback will be called many times at
- each setup, too.
- </para>
- </section>
-
- <section id="pcm-interface-operators-trigger-callback">
- <title>trigger callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_trigger(struct snd_pcm_substream *substream, int cmd);
-]]>
- </programlisting>
- </informalexample>
-
- This is called when the pcm is started, stopped or paused.
- </para>
-
- <para>
- Which action is specified in the second argument,
- <constant>SNDRV_PCM_TRIGGER_XXX</constant> in
- <filename><sound/pcm.h></filename>. At least,
- the <constant>START</constant> and <constant>STOP</constant>
- commands must be defined in this callback.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- switch (cmd) {
- case SNDRV_PCM_TRIGGER_START:
- /* do something to start the PCM engine */
- break;
- case SNDRV_PCM_TRIGGER_STOP:
- /* do something to stop the PCM engine */
- break;
- default:
- return -EINVAL;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- When the pcm supports the pause operation (given in the info
- field of the hardware table), the <constant>PAUSE_PUSH</constant>
- and <constant>PAUSE_RELEASE</constant> commands must be
- handled here, too. The former is the command to pause the pcm,
- and the latter to restart the pcm again.
- </para>
-
- <para>
- When the pcm supports the suspend/resume operation,
- regardless of full or partial suspend/resume support,
- the <constant>SUSPEND</constant> and <constant>RESUME</constant>
- commands must be handled, too.
- These commands are issued when the power-management status is
- changed. Obviously, the <constant>SUSPEND</constant> and
- <constant>RESUME</constant> commands
- suspend and resume the pcm substream, and usually, they
- are identical to the <constant>STOP</constant> and
- <constant>START</constant> commands, respectively.
- See the <link linkend="power-management"><citetitle>
- Power Management</citetitle></link> section for details.
- </para>
-
- <para>
- As mentioned, this callback is atomic as default unless
- <structfield>nonatomic</structfield> flag set, and
- you cannot call functions which may sleep.
- The trigger callback should be as minimal as possible,
- just really triggering the DMA. The other stuff should be
- initialized hw_params and prepare callbacks properly
- beforehand.
- </para>
- </section>
-
- <section id="pcm-interface-operators-pointer-callback">
- <title>pointer callback</title>
- <para>
- <informalexample>
- <programlisting>
-<![CDATA[
- static snd_pcm_uframes_t snd_xxx_pointer(struct snd_pcm_substream *substream)
-]]>
- </programlisting>
- </informalexample>
-
- This callback is called when the PCM middle layer inquires
- the current hardware position on the buffer. The position must
- be returned in frames,
- ranging from 0 to buffer_size - 1.
- </para>
-
- <para>
- This is called usually from the buffer-update routine in the
- pcm middle layer, which is invoked when
- <function>snd_pcm_period_elapsed()</function> is called in the
- interrupt routine. Then the pcm middle layer updates the
- position and calculates the available space, and wakes up the
- sleeping poll threads, etc.
- </para>
-
- <para>
- This callback is also atomic as default.
- </para>
- </section>
-
- <section id="pcm-interface-operators-copy-silence">
- <title>copy and silence callbacks</title>
- <para>
- These callbacks are not mandatory, and can be omitted in
- most cases. These callbacks are used when the hardware buffer
- cannot be in the normal memory space. Some chips have their
- own buffer on the hardware which is not mappable. In such a
- case, you have to transfer the data manually from the memory
- buffer to the hardware buffer. Or, if the buffer is
- non-contiguous on both physical and virtual memory spaces,
- these callbacks must be defined, too.
- </para>
-
- <para>
- If these two callbacks are defined, copy and set-silence
- operations are done by them. The detailed will be described in
- the later section <link
- linkend="buffer-and-memory"><citetitle>Buffer and Memory
- Management</citetitle></link>.
- </para>
- </section>
-
- <section id="pcm-interface-operators-ack">
- <title>ack callback</title>
- <para>
- This callback is also not mandatory. This callback is called
- when the appl_ptr is updated in read or write operations.
- Some drivers like emu10k1-fx and cs46xx need to track the
- current appl_ptr for the internal buffer, and this callback
- is useful only for such a purpose.
- </para>
- <para>
- This callback is atomic as default.
- </para>
- </section>
-
- <section id="pcm-interface-operators-page-callback">
- <title>page callback</title>
-
- <para>
- This callback is optional too. This callback is used
- mainly for non-contiguous buffers. The mmap calls this
- callback to get the page address. Some examples will be
- explained in the later section <link
- linkend="buffer-and-memory"><citetitle>Buffer and Memory
- Management</citetitle></link>, too.
- </para>
- </section>
- </section>
-
- <section id="pcm-interface-interrupt-handler">
- <title>Interrupt Handler</title>
- <para>
- The rest of pcm stuff is the PCM interrupt handler. The
- role of PCM interrupt handler in the sound driver is to update
- the buffer position and to tell the PCM middle layer when the
- buffer position goes across the prescribed period size. To
- inform this, call the <function>snd_pcm_period_elapsed()</function>
- function.
- </para>
-
- <para>
- There are several types of sound chips to generate the interrupts.
- </para>
-
- <section id="pcm-interface-interrupt-handler-boundary">
- <title>Interrupts at the period (fragment) boundary</title>
- <para>
- This is the most frequently found type: the hardware
- generates an interrupt at each period boundary.
- In this case, you can call
- <function>snd_pcm_period_elapsed()</function> at each
- interrupt.
- </para>
-
- <para>
- <function>snd_pcm_period_elapsed()</function> takes the
- substream pointer as its argument. Thus, you need to keep the
- substream pointer accessible from the chip instance. For
- example, define substream field in the chip record to hold the
- current running substream pointer, and set the pointer value
- at open callback (and reset at close callback).
- </para>
-
- <para>
- If you acquire a spinlock in the interrupt handler, and the
- lock is used in other pcm callbacks, too, then you have to
- release the lock before calling
- <function>snd_pcm_period_elapsed()</function>, because
- <function>snd_pcm_period_elapsed()</function> calls other pcm
- callbacks inside.
- </para>
-
- <para>
- Typical code would be like:
-
- <example>
- <title>Interrupt Handler Case #1</title>
- <programlisting>
-<![CDATA[
- static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
- {
- struct mychip *chip = dev_id;
- spin_lock(&chip->lock);
- ....
- if (pcm_irq_invoked(chip)) {
- /* call updater, unlock before it */
- spin_unlock(&chip->lock);
- snd_pcm_period_elapsed(chip->substream);
- spin_lock(&chip->lock);
- /* acknowledge the interrupt if necessary */
- }
- ....
- spin_unlock(&chip->lock);
- return IRQ_HANDLED;
- }
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="pcm-interface-interrupt-handler-timer">
- <title>High frequency timer interrupts</title>
- <para>
- This happens when the hardware doesn't generate interrupts
- at the period boundary but issues timer interrupts at a fixed
- timer rate (e.g. es1968 or ymfpci drivers).
- In this case, you need to check the current hardware
- position and accumulate the processed sample length at each
- interrupt. When the accumulated size exceeds the period
- size, call
- <function>snd_pcm_period_elapsed()</function> and reset the
- accumulator.
- </para>
-
- <para>
- Typical code would be like the following.
-
- <example>
- <title>Interrupt Handler Case #2</title>
- <programlisting>
-<![CDATA[
- static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
- {
- struct mychip *chip = dev_id;
- spin_lock(&chip->lock);
- ....
- if (pcm_irq_invoked(chip)) {
- unsigned int last_ptr, size;
- /* get the current hardware pointer (in frames) */
- last_ptr = get_hw_ptr(chip);
- /* calculate the processed frames since the
- * last update
- */
- if (last_ptr < chip->last_ptr)
- size = runtime->buffer_size + last_ptr
- - chip->last_ptr;
- else
- size = last_ptr - chip->last_ptr;
- /* remember the last updated point */
- chip->last_ptr = last_ptr;
- /* accumulate the size */
- chip->size += size;
- /* over the period boundary? */
- if (chip->size >= runtime->period_size) {
- /* reset the accumulator */
- chip->size %= runtime->period_size;
- /* call updater */
- spin_unlock(&chip->lock);
- snd_pcm_period_elapsed(substream);
- spin_lock(&chip->lock);
- }
- /* acknowledge the interrupt if necessary */
- }
- ....
- spin_unlock(&chip->lock);
- return IRQ_HANDLED;
- }
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="pcm-interface-interrupt-handler-both">
- <title>On calling <function>snd_pcm_period_elapsed()</function></title>
- <para>
- In both cases, even if more than one period are elapsed, you
- don't have to call
- <function>snd_pcm_period_elapsed()</function> many times. Call
- only once. And the pcm layer will check the current hardware
- pointer and update to the latest status.
- </para>
- </section>
- </section>
-
- <section id="pcm-interface-atomicity">
- <title>Atomicity</title>
- <para>
- One of the most important (and thus difficult to debug) problems
- in kernel programming are race conditions.
- In the Linux kernel, they are usually avoided via spin-locks, mutexes
- or semaphores. In general, if a race condition can happen
- in an interrupt handler, it has to be managed atomically, and you
- have to use a spinlock to protect the critical session. If the
- critical section is not in interrupt handler code and
- if taking a relatively long time to execute is acceptable, you
- should use mutexes or semaphores instead.
- </para>
-
- <para>
- As already seen, some pcm callbacks are atomic and some are
- not. For example, the <parameter>hw_params</parameter> callback is
- non-atomic, while <parameter>trigger</parameter> callback is
- atomic. This means, the latter is called already in a spinlock
- held by the PCM middle layer. Please take this atomicity into
- account when you choose a locking scheme in the callbacks.
- </para>
-
- <para>
- In the atomic callbacks, you cannot use functions which may call
- <function>schedule</function> or go to
- <function>sleep</function>. Semaphores and mutexes can sleep,
- and hence they cannot be used inside the atomic callbacks
- (e.g. <parameter>trigger</parameter> callback).
- To implement some delay in such a callback, please use
- <function>udelay()</function> or <function>mdelay()</function>.
- </para>
-
- <para>
- All three atomic callbacks (trigger, pointer, and ack) are
- called with local interrupts disabled.
- </para>
-
- <para>
- The recent changes in PCM core code, however, allow all PCM
- operations to be non-atomic. This assumes that the all caller
- sides are in non-atomic contexts. For example, the function
- <function>snd_pcm_period_elapsed()</function> is called
- typically from the interrupt handler. But, if you set up the
- driver to use a threaded interrupt handler, this call can be in
- non-atomic context, too. In such a case, you can set
- <structfield>nonatomic</structfield> filed of
- <structname>snd_pcm</structname> object after creating it.
- When this flag is set, mutex and rwsem are used internally in
- the PCM core instead of spin and rwlocks, so that you can call
- all PCM functions safely in a non-atomic context.
- </para>
-
- </section>
- <section id="pcm-interface-constraints">
- <title>Constraints</title>
- <para>
- If your chip supports unconventional sample rates, or only the
- limited samples, you need to set a constraint for the
- condition.
- </para>
-
- <para>
- For example, in order to restrict the sample rates in the some
- supported values, use
- <function>snd_pcm_hw_constraint_list()</function>.
- You need to call this function in the open callback.
-
- <example>
- <title>Example of Hardware Constraints</title>
- <programlisting>
-<![CDATA[
- static unsigned int rates[] =
- {4000, 10000, 22050, 44100};
- static struct snd_pcm_hw_constraint_list constraints_rates = {
- .count = ARRAY_SIZE(rates),
- .list = rates,
- .mask = 0,
- };
-
- static int snd_mychip_pcm_open(struct snd_pcm_substream *substream)
- {
- int err;
- ....
- err = snd_pcm_hw_constraint_list(substream->runtime, 0,
- SNDRV_PCM_HW_PARAM_RATE,
- &constraints_rates);
- if (err < 0)
- return err;
- ....
- }
-]]>
- </programlisting>
- </example>
- </para>
-
- <para>
- There are many different constraints.
- Look at <filename>sound/pcm.h</filename> for a complete list.
- You can even define your own constraint rules.
- For example, let's suppose my_chip can manage a substream of 1 channel
- if and only if the format is S16_LE, otherwise it supports any format
- specified in the <structname>snd_pcm_hardware</structname> structure (or in any
- other constraint_list). You can build a rule like this:
-
- <example>
- <title>Example of Hardware Constraints for Channels</title>
- <programlisting>
-<![CDATA[
- static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params,
- struct snd_pcm_hw_rule *rule)
- {
- struct snd_interval *c = hw_param_interval(params,
- SNDRV_PCM_HW_PARAM_CHANNELS);
- struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
- struct snd_interval ch;
-
- snd_interval_any(&ch);
- if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) {
- ch.min = ch.max = 1;
- ch.integer = 1;
- return snd_interval_refine(c, &ch);
- }
- return 0;
- }
-]]>
- </programlisting>
- </example>
- </para>
-
- <para>
- Then you need to call this function to add your rule:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
- hw_rule_channels_by_format, NULL,
- SNDRV_PCM_HW_PARAM_FORMAT, -1);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The rule function is called when an application sets the PCM
- format, and it refines the number of channels accordingly.
- But an application may set the number of channels before
- setting the format. Thus you also need to define the inverse rule:
-
- <example>
- <title>Example of Hardware Constraints for Formats</title>
- <programlisting>
-<![CDATA[
- static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params,
- struct snd_pcm_hw_rule *rule)
- {
- struct snd_interval *c = hw_param_interval(params,
- SNDRV_PCM_HW_PARAM_CHANNELS);
- struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
- struct snd_mask fmt;
-
- snd_mask_any(&fmt); /* Init the struct */
- if (c->min < 2) {
- fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE;
- return snd_mask_refine(f, &fmt);
- }
- return 0;
- }
-]]>
- </programlisting>
- </example>
- </para>
-
- <para>
- ...and in the open callback:
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT,
- hw_rule_format_by_channels, NULL,
- SNDRV_PCM_HW_PARAM_CHANNELS, -1);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- I won't give more details here, rather I
- would like to say, <quote>Luke, use the source.</quote>
- </para>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Control Interface -->
-<!-- ****************************************************** -->
- <chapter id="control-interface">
- <title>Control Interface</title>
-
- <section id="control-interface-general">
- <title>General</title>
- <para>
- The control interface is used widely for many switches,
- sliders, etc. which are accessed from user-space. Its most
- important use is the mixer interface. In other words, since ALSA
- 0.9.x, all the mixer stuff is implemented on the control kernel API.
- </para>
-
- <para>
- ALSA has a well-defined AC97 control module. If your chip
- supports only the AC97 and nothing else, you can skip this
- section.
- </para>
-
- <para>
- The control API is defined in
- <filename><sound/control.h></filename>.
- Include this file if you want to add your own controls.
- </para>
- </section>
-
- <section id="control-interface-definition">
- <title>Definition of Controls</title>
- <para>
- To create a new control, you need to define the
- following three
- callbacks: <structfield>info</structfield>,
- <structfield>get</structfield> and
- <structfield>put</structfield>. Then, define a
- struct <structname>snd_kcontrol_new</structname> record, such as:
-
- <example>
- <title>Definition of a Control</title>
- <programlisting>
-<![CDATA[
- static struct snd_kcontrol_new my_control = {
- .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
- .name = "PCM Playback Switch",
- .index = 0,
- .access = SNDRV_CTL_ELEM_ACCESS_READWRITE,
- .private_value = 0xffff,
- .info = my_control_info,
- .get = my_control_get,
- .put = my_control_put
- };
-]]>
- </programlisting>
- </example>
- </para>
-
- <para>
- The <structfield>iface</structfield> field specifies the control
- type, <constant>SNDRV_CTL_ELEM_IFACE_XXX</constant>, which
- is usually <constant>MIXER</constant>.
- Use <constant>CARD</constant> for global controls that are not
- logically part of the mixer.
- If the control is closely associated with some specific device on
- the sound card, use <constant>HWDEP</constant>,
- <constant>PCM</constant>, <constant>RAWMIDI</constant>,
- <constant>TIMER</constant>, or <constant>SEQUENCER</constant>, and
- specify the device number with the
- <structfield>device</structfield> and
- <structfield>subdevice</structfield> fields.
- </para>
-
- <para>
- The <structfield>name</structfield> is the name identifier
- string. Since ALSA 0.9.x, the control name is very important,
- because its role is classified from its name. There are
- pre-defined standard control names. The details are described in
- the <link linkend="control-interface-control-names"><citetitle>
- Control Names</citetitle></link> subsection.
- </para>
-
- <para>
- The <structfield>index</structfield> field holds the index number
- of this control. If there are several different controls with
- the same name, they can be distinguished by the index
- number. This is the case when
- several codecs exist on the card. If the index is zero, you can
- omit the definition above.
- </para>
-
- <para>
- The <structfield>access</structfield> field contains the access
- type of this control. Give the combination of bit masks,
- <constant>SNDRV_CTL_ELEM_ACCESS_XXX</constant>, there.
- The details will be explained in
- the <link linkend="control-interface-access-flags"><citetitle>
- Access Flags</citetitle></link> subsection.
- </para>
-
- <para>
- The <structfield>private_value</structfield> field contains
- an arbitrary long integer value for this record. When using
- the generic <structfield>info</structfield>,
- <structfield>get</structfield> and
- <structfield>put</structfield> callbacks, you can pass a value
- through this field. If several small numbers are necessary, you can
- combine them in bitwise. Or, it's possible to give a pointer
- (casted to unsigned long) of some record to this field, too.
- </para>
-
- <para>
- The <structfield>tlv</structfield> field can be used to provide
- metadata about the control; see the
- <link linkend="control-interface-tlv">
- <citetitle>Metadata</citetitle></link> subsection.
- </para>
-
- <para>
- The other three are
- <link linkend="control-interface-callbacks"><citetitle>
- callback functions</citetitle></link>.
- </para>
- </section>
-
- <section id="control-interface-control-names">
- <title>Control Names</title>
- <para>
- There are some standards to define the control names. A
- control is usually defined from the three parts as
- <quote>SOURCE DIRECTION FUNCTION</quote>.
- </para>
-
- <para>
- The first, <constant>SOURCE</constant>, specifies the source
- of the control, and is a string such as <quote>Master</quote>,
- <quote>PCM</quote>, <quote>CD</quote> and
- <quote>Line</quote>. There are many pre-defined sources.
- </para>
-
- <para>
- The second, <constant>DIRECTION</constant>, is one of the
- following strings according to the direction of the control:
- <quote>Playback</quote>, <quote>Capture</quote>, <quote>Bypass
- Playback</quote> and <quote>Bypass Capture</quote>. Or, it can
- be omitted, meaning both playback and capture directions.
- </para>
-
- <para>
- The third, <constant>FUNCTION</constant>, is one of the
- following strings according to the function of the control:
- <quote>Switch</quote>, <quote>Volume</quote> and
- <quote>Route</quote>.
- </para>
-
- <para>
- The example of control names are, thus, <quote>Master Capture
- Switch</quote> or <quote>PCM Playback Volume</quote>.
- </para>
-
- <para>
- There are some exceptions:
- </para>
-
- <section id="control-interface-control-names-global">
- <title>Global capture and playback</title>
- <para>
- <quote>Capture Source</quote>, <quote>Capture Switch</quote>
- and <quote>Capture Volume</quote> are used for the global
- capture (input) source, switch and volume. Similarly,
- <quote>Playback Switch</quote> and <quote>Playback
- Volume</quote> are used for the global output gain switch and
- volume.
- </para>
- </section>
-
- <section id="control-interface-control-names-tone">
- <title>Tone-controls</title>
- <para>
- tone-control switch and volumes are specified like
- <quote>Tone Control - XXX</quote>, e.g. <quote>Tone Control -
- Switch</quote>, <quote>Tone Control - Bass</quote>,
- <quote>Tone Control - Center</quote>.
- </para>
- </section>
-
- <section id="control-interface-control-names-3d">
- <title>3D controls</title>
- <para>
- 3D-control switches and volumes are specified like <quote>3D
- Control - XXX</quote>, e.g. <quote>3D Control -
- Switch</quote>, <quote>3D Control - Center</quote>, <quote>3D
- Control - Space</quote>.
- </para>
- </section>
-
- <section id="control-interface-control-names-mic">
- <title>Mic boost</title>
- <para>
- Mic-boost switch is set as <quote>Mic Boost</quote> or
- <quote>Mic Boost (6dB)</quote>.
- </para>
-
- <para>
- More precise information can be found in
- <filename>Documentation/sound/alsa/ControlNames.txt</filename>.
- </para>
- </section>
- </section>
-
- <section id="control-interface-access-flags">
- <title>Access Flags</title>
-
- <para>
- The access flag is the bitmask which specifies the access type
- of the given control. The default access type is
- <constant>SNDRV_CTL_ELEM_ACCESS_READWRITE</constant>,
- which means both read and write are allowed to this control.
- When the access flag is omitted (i.e. = 0), it is
- considered as <constant>READWRITE</constant> access as default.
- </para>
-
- <para>
- When the control is read-only, pass
- <constant>SNDRV_CTL_ELEM_ACCESS_READ</constant> instead.
- In this case, you don't have to define
- the <structfield>put</structfield> callback.
- Similarly, when the control is write-only (although it's a rare
- case), you can use the <constant>WRITE</constant> flag instead, and
- you don't need the <structfield>get</structfield> callback.
- </para>
-
- <para>
- If the control value changes frequently (e.g. the VU meter),
- <constant>VOLATILE</constant> flag should be given. This means
- that the control may be changed without
- <link linkend="control-interface-change-notification"><citetitle>
- notification</citetitle></link>. Applications should poll such
- a control constantly.
- </para>
-
- <para>
- When the control is inactive, set
- the <constant>INACTIVE</constant> flag, too.
- There are <constant>LOCK</constant> and
- <constant>OWNER</constant> flags to change the write
- permissions.
- </para>
-
- </section>
-
- <section id="control-interface-callbacks">
- <title>Callbacks</title>
-
- <section id="control-interface-callbacks-info">
- <title>info callback</title>
- <para>
- The <structfield>info</structfield> callback is used to get
- detailed information on this control. This must store the
- values of the given struct <structname>snd_ctl_elem_info</structname>
- object. For example, for a boolean control with a single
- element:
-
- <example>
- <title>Example of info callback</title>
- <programlisting>
-<![CDATA[
- static int snd_myctl_mono_info(struct snd_kcontrol *kcontrol,
- struct snd_ctl_elem_info *uinfo)
- {
- uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN;
- uinfo->count = 1;
- uinfo->value.integer.min = 0;
- uinfo->value.integer.max = 1;
- return 0;
- }
-]]>
- </programlisting>
- </example>
- </para>
-
- <para>
- The <structfield>type</structfield> field specifies the type
- of the control. There are <constant>BOOLEAN</constant>,
- <constant>INTEGER</constant>, <constant>ENUMERATED</constant>,
- <constant>BYTES</constant>, <constant>IEC958</constant> and
- <constant>INTEGER64</constant>. The
- <structfield>count</structfield> field specifies the
- number of elements in this control. For example, a stereo
- volume would have count = 2. The
- <structfield>value</structfield> field is a union, and
- the values stored are depending on the type. The boolean and
- integer types are identical.
- </para>
-
- <para>
- The enumerated type is a bit different from others. You'll
- need to set the string for the currently given item index.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol,
- struct snd_ctl_elem_info *uinfo)
- {
- static char *texts[4] = {
- "First", "Second", "Third", "Fourth"
- };
- uinfo->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED;
- uinfo->count = 1;
- uinfo->value.enumerated.items = 4;
- if (uinfo->value.enumerated.item > 3)
- uinfo->value.enumerated.item = 3;
- strcpy(uinfo->value.enumerated.name,
- texts[uinfo->value.enumerated.item]);
- return 0;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The above callback can be simplified with a helper function,
- <function>snd_ctl_enum_info</function>. The final code
- looks like below.
- (You can pass ARRAY_SIZE(texts) instead of 4 in the third
- argument; it's a matter of taste.)
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol,
- struct snd_ctl_elem_info *uinfo)
- {
- static char *texts[4] = {
- "First", "Second", "Third", "Fourth"
- };
- return snd_ctl_enum_info(uinfo, 1, 4, texts);
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Some common info callbacks are available for your convenience:
- <function>snd_ctl_boolean_mono_info()</function> and
- <function>snd_ctl_boolean_stereo_info()</function>.
- Obviously, the former is an info callback for a mono channel
- boolean item, just like <function>snd_myctl_mono_info</function>
- above, and the latter is for a stereo channel boolean item.
- </para>
-
- </section>
-
- <section id="control-interface-callbacks-get">
- <title>get callback</title>
-
- <para>
- This callback is used to read the current value of the
- control and to return to user-space.
- </para>
-
- <para>
- For example,
-
- <example>
- <title>Example of get callback</title>
- <programlisting>
-<![CDATA[
- static int snd_myctl_get(struct snd_kcontrol *kcontrol,
- struct snd_ctl_elem_value *ucontrol)
- {
- struct mychip *chip = snd_kcontrol_chip(kcontrol);
- ucontrol->value.integer.value[0] = get_some_value(chip);
- return 0;
- }
-]]>
- </programlisting>
- </example>
- </para>
-
- <para>
- The <structfield>value</structfield> field depends on
- the type of control as well as on the info callback. For example,
- the sb driver uses this field to store the register offset,
- the bit-shift and the bit-mask. The
- <structfield>private_value</structfield> field is set as follows:
- <informalexample>
- <programlisting>
-<![CDATA[
- .private_value = reg | (shift << 16) | (mask << 24)
-]]>
- </programlisting>
- </informalexample>
- and is retrieved in callbacks like
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_sbmixer_get_single(struct snd_kcontrol *kcontrol,
- struct snd_ctl_elem_value *ucontrol)
- {
- int reg = kcontrol->private_value & 0xff;
- int shift = (kcontrol->private_value >> 16) & 0xff;
- int mask = (kcontrol->private_value >> 24) & 0xff;
- ....
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- In the <structfield>get</structfield> callback,
- you have to fill all the elements if the
- control has more than one elements,
- i.e. <structfield>count</structfield> > 1.
- In the example above, we filled only one element
- (<structfield>value.integer.value[0]</structfield>) since it's
- assumed as <structfield>count</structfield> = 1.
- </para>
- </section>
-
- <section id="control-interface-callbacks-put">
- <title>put callback</title>
-
- <para>
- This callback is used to write a value from user-space.
- </para>
-
- <para>
- For example,
-
- <example>
- <title>Example of put callback</title>
- <programlisting>
-<![CDATA[
- static int snd_myctl_put(struct snd_kcontrol *kcontrol,
- struct snd_ctl_elem_value *ucontrol)
- {
- struct mychip *chip = snd_kcontrol_chip(kcontrol);
- int changed = 0;
- if (chip->current_value !=
- ucontrol->value.integer.value[0]) {
- change_current_value(chip,
- ucontrol->value.integer.value[0]);
- changed = 1;
- }
- return changed;
- }
-]]>
- </programlisting>
- </example>
-
- As seen above, you have to return 1 if the value is
- changed. If the value is not changed, return 0 instead.
- If any fatal error happens, return a negative error code as
- usual.
- </para>
-
- <para>
- As in the <structfield>get</structfield> callback,
- when the control has more than one elements,
- all elements must be evaluated in this callback, too.
- </para>
- </section>
-
- <section id="control-interface-callbacks-all">
- <title>Callbacks are not atomic</title>
- <para>
- All these three callbacks are basically not atomic.
- </para>
- </section>
- </section>
-
- <section id="control-interface-constructor">
- <title>Constructor</title>
- <para>
- When everything is ready, finally we can create a new
- control. To create a control, there are two functions to be
- called, <function>snd_ctl_new1()</function> and
- <function>snd_ctl_add()</function>.
- </para>
-
- <para>
- In the simplest way, you can do like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- err = snd_ctl_add(card, snd_ctl_new1(&my_control, chip));
- if (err < 0)
- return err;
-]]>
- </programlisting>
- </informalexample>
-
- where <parameter>my_control</parameter> is the
- struct <structname>snd_kcontrol_new</structname> object defined above, and chip
- is the object pointer to be passed to
- kcontrol->private_data
- which can be referred to in callbacks.
- </para>
-
- <para>
- <function>snd_ctl_new1()</function> allocates a new
- <structname>snd_kcontrol</structname> instance,
- and <function>snd_ctl_add</function> assigns the given
- control component to the card.
- </para>
- </section>
-
- <section id="control-interface-change-notification">
- <title>Change Notification</title>
- <para>
- If you need to change and update a control in the interrupt
- routine, you can call <function>snd_ctl_notify()</function>. For
- example,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, id_pointer);
-]]>
- </programlisting>
- </informalexample>
-
- This function takes the card pointer, the event-mask, and the
- control id pointer for the notification. The event-mask
- specifies the types of notification, for example, in the above
- example, the change of control values is notified.
- The id pointer is the pointer of struct <structname>snd_ctl_elem_id</structname>
- to be notified.
- You can find some examples in <filename>es1938.c</filename> or
- <filename>es1968.c</filename> for hardware volume interrupts.
- </para>
- </section>
-
- <section id="control-interface-tlv">
- <title>Metadata</title>
- <para>
- To provide information about the dB values of a mixer control, use
- on of the <constant>DECLARE_TLV_xxx</constant> macros from
- <filename><sound/tlv.h></filename> to define a variable
- containing this information, set the<structfield>tlv.p
- </structfield> field to point to this variable, and include the
- <constant>SNDRV_CTL_ELEM_ACCESS_TLV_READ</constant> flag in the
- <structfield>access</structfield> field; like this:
- <informalexample>
- <programlisting>
-<![CDATA[
- static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0);
-
- static struct snd_kcontrol_new my_control = {
- ...
- .access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
- SNDRV_CTL_ELEM_ACCESS_TLV_READ,
- ...
- .tlv.p = db_scale_my_control,
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The <function>DECLARE_TLV_DB_SCALE</function> macro defines
- information about a mixer control where each step in the control's
- value changes the dB value by a constant dB amount.
- The first parameter is the name of the variable to be defined.
- The second parameter is the minimum value, in units of 0.01 dB.
- The third parameter is the step size, in units of 0.01 dB.
- Set the fourth parameter to 1 if the minimum value actually mutes
- the control.
- </para>
-
- <para>
- The <function>DECLARE_TLV_DB_LINEAR</function> macro defines
- information about a mixer control where the control's value affects
- the output linearly.
- The first parameter is the name of the variable to be defined.
- The second parameter is the minimum value, in units of 0.01 dB.
- The third parameter is the maximum value, in units of 0.01 dB.
- If the minimum value mutes the control, set the second parameter to
- <constant>TLV_DB_GAIN_MUTE</constant>.
- </para>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- API for AC97 Codec -->
-<!-- ****************************************************** -->
- <chapter id="api-ac97">
- <title>API for AC97 Codec</title>
-
- <section>
- <title>General</title>
- <para>
- The ALSA AC97 codec layer is a well-defined one, and you don't
- have to write much code to control it. Only low-level control
- routines are necessary. The AC97 codec API is defined in
- <filename><sound/ac97_codec.h></filename>.
- </para>
- </section>
-
- <section id="api-ac97-example">
- <title>Full Code Example</title>
- <para>
- <example>
- <title>Example of AC97 Interface</title>
- <programlisting>
-<![CDATA[
- struct mychip {
- ....
- struct snd_ac97 *ac97;
- ....
- };
-
- static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97,
- unsigned short reg)
- {
- struct mychip *chip = ac97->private_data;
- ....
- /* read a register value here from the codec */
- return the_register_value;
- }
-
- static void snd_mychip_ac97_write(struct snd_ac97 *ac97,
- unsigned short reg, unsigned short val)
- {
- struct mychip *chip = ac97->private_data;
- ....
- /* write the given register value to the codec */
- }
-
- static int snd_mychip_ac97(struct mychip *chip)
- {
- struct snd_ac97_bus *bus;
- struct snd_ac97_template ac97;
- int err;
- static struct snd_ac97_bus_ops ops = {
- .write = snd_mychip_ac97_write,
- .read = snd_mychip_ac97_read,
- };
-
- err = snd_ac97_bus(chip->card, 0, &ops, NULL, &bus);
- if (err < 0)
- return err;
- memset(&ac97, 0, sizeof(ac97));
- ac97.private_data = chip;
- return snd_ac97_mixer(bus, &ac97, &chip->ac97);
- }
-
-]]>
- </programlisting>
- </example>
- </para>
- </section>
-
- <section id="api-ac97-constructor">
- <title>Constructor</title>
- <para>
- To create an ac97 instance, first call <function>snd_ac97_bus</function>
- with an <type>ac97_bus_ops_t</type> record with callback functions.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_ac97_bus *bus;
- static struct snd_ac97_bus_ops ops = {
- .write = snd_mychip_ac97_write,
- .read = snd_mychip_ac97_read,
- };
-
- snd_ac97_bus(card, 0, &ops, NULL, &pbus);
-]]>
- </programlisting>
- </informalexample>
-
- The bus record is shared among all belonging ac97 instances.
- </para>
-
- <para>
- And then call <function>snd_ac97_mixer()</function> with an
- struct <structname>snd_ac97_template</structname>
- record together with the bus pointer created above.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_ac97_template ac97;
- int err;
-
- memset(&ac97, 0, sizeof(ac97));
- ac97.private_data = chip;
- snd_ac97_mixer(bus, &ac97, &chip->ac97);
-]]>
- </programlisting>
- </informalexample>
-
- where chip->ac97 is a pointer to a newly created
- <type>ac97_t</type> instance.
- In this case, the chip pointer is set as the private data, so that
- the read/write callback functions can refer to this chip instance.
- This instance is not necessarily stored in the chip
- record. If you need to change the register values from the
- driver, or need the suspend/resume of ac97 codecs, keep this
- pointer to pass to the corresponding functions.
- </para>
- </section>
-
- <section id="api-ac97-callbacks">
- <title>Callbacks</title>
- <para>
- The standard callbacks are <structfield>read</structfield> and
- <structfield>write</structfield>. Obviously they
- correspond to the functions for read and write accesses to the
- hardware low-level codes.
- </para>
-
- <para>
- The <structfield>read</structfield> callback returns the
- register value specified in the argument.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97,
- unsigned short reg)
- {
- struct mychip *chip = ac97->private_data;
- ....
- return the_register_value;
- }
-]]>
- </programlisting>
- </informalexample>
-
- Here, the chip can be cast from ac97->private_data.
- </para>
-
- <para>
- Meanwhile, the <structfield>write</structfield> callback is
- used to set the register value.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void snd_mychip_ac97_write(struct snd_ac97 *ac97,
- unsigned short reg, unsigned short val)
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- These callbacks are non-atomic like the control API callbacks.
- </para>
-
- <para>
- There are also other callbacks:
- <structfield>reset</structfield>,
- <structfield>wait</structfield> and
- <structfield>init</structfield>.
- </para>
-
- <para>
- The <structfield>reset</structfield> callback is used to reset
- the codec. If the chip requires a special kind of reset, you can
- define this callback.
- </para>
-
- <para>
- The <structfield>wait</structfield> callback is used to
- add some waiting time in the standard initialization of the codec. If the
- chip requires the extra waiting time, define this callback.
- </para>
-
- <para>
- The <structfield>init</structfield> callback is used for
- additional initialization of the codec.
- </para>
- </section>
-
- <section id="api-ac97-updating-registers">
- <title>Updating Registers in The Driver</title>
- <para>
- If you need to access to the codec from the driver, you can
- call the following functions:
- <function>snd_ac97_write()</function>,
- <function>snd_ac97_read()</function>,
- <function>snd_ac97_update()</function> and
- <function>snd_ac97_update_bits()</function>.
- </para>
-
- <para>
- Both <function>snd_ac97_write()</function> and
- <function>snd_ac97_update()</function> functions are used to
- set a value to the given register
- (<constant>AC97_XXX</constant>). The difference between them is
- that <function>snd_ac97_update()</function> doesn't write a
- value if the given value has been already set, while
- <function>snd_ac97_write()</function> always rewrites the
- value.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_ac97_write(ac97, AC97_MASTER, 0x8080);
- snd_ac97_update(ac97, AC97_MASTER, 0x8080);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- <function>snd_ac97_read()</function> is used to read the value
- of the given register. For example,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- value = snd_ac97_read(ac97, AC97_MASTER);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- <function>snd_ac97_update_bits()</function> is used to update
- some bits in the given register.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_ac97_update_bits(ac97, reg, mask, value);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Also, there is a function to change the sample rate (of a
- given register such as
- <constant>AC97_PCM_FRONT_DAC_RATE</constant>) when VRA or
- DRA is supported by the codec:
- <function>snd_ac97_set_rate()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_ac97_set_rate(ac97, AC97_PCM_FRONT_DAC_RATE, 44100);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The following registers are available to set the rate:
- <constant>AC97_PCM_MIC_ADC_RATE</constant>,
- <constant>AC97_PCM_FRONT_DAC_RATE</constant>,
- <constant>AC97_PCM_LR_ADC_RATE</constant>,
- <constant>AC97_SPDIF</constant>. When
- <constant>AC97_SPDIF</constant> is specified, the register is
- not really changed but the corresponding IEC958 status bits will
- be updated.
- </para>
- </section>
-
- <section id="api-ac97-clock-adjustment">
- <title>Clock Adjustment</title>
- <para>
- In some chips, the clock of the codec isn't 48000 but using a
- PCI clock (to save a quartz!). In this case, change the field
- bus->clock to the corresponding
- value. For example, intel8x0
- and es1968 drivers have their own function to read from the clock.
- </para>
- </section>
-
- <section id="api-ac97-proc-files">
- <title>Proc Files</title>
- <para>
- The ALSA AC97 interface will create a proc file such as
- <filename>/proc/asound/card0/codec97#0/ac97#0-0</filename> and
- <filename>ac97#0-0+regs</filename>. You can refer to these files to
- see the current status and registers of the codec.
- </para>
- </section>
-
- <section id="api-ac97-multiple-codecs">
- <title>Multiple Codecs</title>
- <para>
- When there are several codecs on the same card, you need to
- call <function>snd_ac97_mixer()</function> multiple times with
- ac97.num=1 or greater. The <structfield>num</structfield> field
- specifies the codec number.
- </para>
-
- <para>
- If you set up multiple codecs, you either need to write
- different callbacks for each codec or check
- ac97->num in the callback routines.
- </para>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- MIDI (MPU401-UART) Interface -->
-<!-- ****************************************************** -->
- <chapter id="midi-interface">
- <title>MIDI (MPU401-UART) Interface</title>
-
- <section id="midi-interface-general">
- <title>General</title>
- <para>
- Many soundcards have built-in MIDI (MPU401-UART)
- interfaces. When the soundcard supports the standard MPU401-UART
- interface, most likely you can use the ALSA MPU401-UART API. The
- MPU401-UART API is defined in
- <filename><sound/mpu401.h></filename>.
- </para>
-
- <para>
- Some soundchips have a similar but slightly different
- implementation of mpu401 stuff. For example, emu10k1 has its own
- mpu401 routines.
- </para>
- </section>
-
- <section id="midi-interface-constructor">
- <title>Constructor</title>
- <para>
- To create a rawmidi object, call
- <function>snd_mpu401_uart_new()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_rawmidi *rmidi;
- snd_mpu401_uart_new(card, 0, MPU401_HW_MPU401, port, info_flags,
- irq, &rmidi);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The first argument is the card pointer, and the second is the
- index of this component. You can create up to 8 rawmidi
- devices.
- </para>
-
- <para>
- The third argument is the type of the hardware,
- <constant>MPU401_HW_XXX</constant>. If it's not a special one,
- you can use <constant>MPU401_HW_MPU401</constant>.
- </para>
-
- <para>
- The 4th argument is the I/O port address. Many
- backward-compatible MPU401 have an I/O port such as 0x330. Or, it
- might be a part of its own PCI I/O region. It depends on the
- chip design.
- </para>
-
- <para>
- The 5th argument is a bitflag for additional information.
- When the I/O port address above is part of the PCI I/O
- region, the MPU401 I/O port might have been already allocated
- (reserved) by the driver itself. In such a case, pass a bit flag
- <constant>MPU401_INFO_INTEGRATED</constant>,
- and the mpu401-uart layer will allocate the I/O ports by itself.
- </para>
-
- <para>
- When the controller supports only the input or output MIDI stream,
- pass the <constant>MPU401_INFO_INPUT</constant> or
- <constant>MPU401_INFO_OUTPUT</constant> bitflag, respectively.
- Then the rawmidi instance is created as a single stream.
- </para>
-
- <para>
- <constant>MPU401_INFO_MMIO</constant> bitflag is used to change
- the access method to MMIO (via readb and writeb) instead of
- iob and outb. In this case, you have to pass the iomapped address
- to <function>snd_mpu401_uart_new()</function>.
- </para>
-
- <para>
- When <constant>MPU401_INFO_TX_IRQ</constant> is set, the output
- stream isn't checked in the default interrupt handler. The driver
- needs to call <function>snd_mpu401_uart_interrupt_tx()</function>
- by itself to start processing the output stream in the irq handler.
- </para>
-
- <para>
- If the MPU-401 interface shares its interrupt with the other logical
- devices on the card, set <constant>MPU401_INFO_IRQ_HOOK</constant>
- (see <link linkend="midi-interface-interrupt-handler"><citetitle>
- below</citetitle></link>).
- </para>
-
- <para>
- Usually, the port address corresponds to the command port and
- port + 1 corresponds to the data port. If not, you may change
- the <structfield>cport</structfield> field of
- struct <structname>snd_mpu401</structname> manually
- afterward. However, <structname>snd_mpu401</structname> pointer is not
- returned explicitly by
- <function>snd_mpu401_uart_new()</function>. You need to cast
- rmidi->private_data to
- <structname>snd_mpu401</structname> explicitly,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_mpu401 *mpu;
- mpu = rmidi->private_data;
-]]>
- </programlisting>
- </informalexample>
-
- and reset the cport as you like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- mpu->cport = my_own_control_port;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The 6th argument specifies the ISA irq number that will be
- allocated. If no interrupt is to be allocated (because your
- code is already allocating a shared interrupt, or because the
- device does not use interrupts), pass -1 instead.
- For a MPU-401 device without an interrupt, a polling timer
- will be used instead.
- </para>
- </section>
-
- <section id="midi-interface-interrupt-handler">
- <title>Interrupt Handler</title>
- <para>
- When the interrupt is allocated in
- <function>snd_mpu401_uart_new()</function>, an exclusive ISA
- interrupt handler is automatically used, hence you don't have
- anything else to do than creating the mpu401 stuff. Otherwise, you
- have to set <constant>MPU401_INFO_IRQ_HOOK</constant>, and call
- <function>snd_mpu401_uart_interrupt()</function> explicitly from your
- own interrupt handler when it has determined that a UART interrupt
- has occurred.
- </para>
-
- <para>
- In this case, you need to pass the private_data of the
- returned rawmidi object from
- <function>snd_mpu401_uart_new()</function> as the second
- argument of <function>snd_mpu401_uart_interrupt()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_mpu401_uart_interrupt(irq, rmidi->private_data, regs);
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- RawMIDI Interface -->
-<!-- ****************************************************** -->
- <chapter id="rawmidi-interface">
- <title>RawMIDI Interface</title>
-
- <section id="rawmidi-interface-overview">
- <title>Overview</title>
-
- <para>
- The raw MIDI interface is used for hardware MIDI ports that can
- be accessed as a byte stream. It is not used for synthesizer
- chips that do not directly understand MIDI.
- </para>
-
- <para>
- ALSA handles file and buffer management. All you have to do is
- to write some code to move data between the buffer and the
- hardware.
- </para>
-
- <para>
- The rawmidi API is defined in
- <filename><sound/rawmidi.h></filename>.
- </para>
- </section>
-
- <section id="rawmidi-interface-constructor">
- <title>Constructor</title>
-
- <para>
- To create a rawmidi device, call the
- <function>snd_rawmidi_new</function> function:
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_rawmidi *rmidi;
- err = snd_rawmidi_new(chip->card, "MyMIDI", 0, outs, ins, &rmidi);
- if (err < 0)
- return err;
- rmidi->private_data = chip;
- strcpy(rmidi->name, "My MIDI");
- rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT |
- SNDRV_RAWMIDI_INFO_INPUT |
- SNDRV_RAWMIDI_INFO_DUPLEX;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The first argument is the card pointer, the second argument is
- the ID string.
- </para>
-
- <para>
- The third argument is the index of this component. You can
- create up to 8 rawmidi devices.
- </para>
-
- <para>
- The fourth and fifth arguments are the number of output and
- input substreams, respectively, of this device (a substream is
- the equivalent of a MIDI port).
- </para>
-
- <para>
- Set the <structfield>info_flags</structfield> field to specify
- the capabilities of the device.
- Set <constant>SNDRV_RAWMIDI_INFO_OUTPUT</constant> if there is
- at least one output port,
- <constant>SNDRV_RAWMIDI_INFO_INPUT</constant> if there is at
- least one input port,
- and <constant>SNDRV_RAWMIDI_INFO_DUPLEX</constant> if the device
- can handle output and input at the same time.
- </para>
-
- <para>
- After the rawmidi device is created, you need to set the
- operators (callbacks) for each substream. There are helper
- functions to set the operators for all the substreams of a device:
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &snd_mymidi_output_ops);
- snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_INPUT, &snd_mymidi_input_ops);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The operators are usually defined like this:
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct snd_rawmidi_ops snd_mymidi_output_ops = {
- .open = snd_mymidi_output_open,
- .close = snd_mymidi_output_close,
- .trigger = snd_mymidi_output_trigger,
- };
-]]>
- </programlisting>
- </informalexample>
- These callbacks are explained in the <link
- linkend="rawmidi-interface-callbacks"><citetitle>Callbacks</citetitle></link>
- section.
- </para>
-
- <para>
- If there are more than one substream, you should give a
- unique name to each of them:
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_rawmidi_substream *substream;
- list_for_each_entry(substream,
- &rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams,
- list {
- sprintf(substream->name, "My MIDI Port %d", substream->number + 1);
- }
- /* same for SNDRV_RAWMIDI_STREAM_INPUT */
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- <section id="rawmidi-interface-callbacks">
- <title>Callbacks</title>
-
- <para>
- In all the callbacks, the private data that you've set for the
- rawmidi device can be accessed as
- substream->rmidi->private_data.
- <!-- <code> isn't available before DocBook 4.3 -->
- </para>
-
- <para>
- If there is more than one port, your callbacks can determine the
- port index from the struct snd_rawmidi_substream data passed to each
- callback:
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_rawmidi_substream *substream;
- int index = substream->number;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <section id="rawmidi-interface-op-open">
- <title><function>open</function> callback</title>
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_open(struct snd_rawmidi_substream *substream);
-]]>
- </programlisting>
- </informalexample>
-
- <para>
- This is called when a substream is opened.
- You can initialize the hardware here, but you shouldn't
- start transmitting/receiving data yet.
- </para>
- </section>
-
- <section id="rawmidi-interface-op-close">
- <title><function>close</function> callback</title>
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_xxx_close(struct snd_rawmidi_substream *substream);
-]]>
- </programlisting>
- </informalexample>
-
- <para>
- Guess what.
- </para>
-
- <para>
- The <function>open</function> and <function>close</function>
- callbacks of a rawmidi device are serialized with a mutex,
- and can sleep.
- </para>
- </section>
-
- <section id="rawmidi-interface-op-trigger-out">
- <title><function>trigger</function> callback for output
- substreams</title>
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void snd_xxx_output_trigger(struct snd_rawmidi_substream *substream, int up);
-]]>
- </programlisting>
- </informalexample>
-
- <para>
- This is called with a nonzero <parameter>up</parameter>
- parameter when there is some data in the substream buffer that
- must be transmitted.
- </para>
-
- <para>
- To read data from the buffer, call
- <function>snd_rawmidi_transmit_peek</function>. It will
- return the number of bytes that have been read; this will be
- less than the number of bytes requested when there are no more
- data in the buffer.
- After the data have been transmitted successfully, call
- <function>snd_rawmidi_transmit_ack</function> to remove the
- data from the substream buffer:
- <informalexample>
- <programlisting>
-<![CDATA[
- unsigned char data;
- while (snd_rawmidi_transmit_peek(substream, &data, 1) == 1) {
- if (snd_mychip_try_to_transmit(data))
- snd_rawmidi_transmit_ack(substream, 1);
- else
- break; /* hardware FIFO full */
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- If you know beforehand that the hardware will accept data, you
- can use the <function>snd_rawmidi_transmit</function> function
- which reads some data and removes them from the buffer at once:
- <informalexample>
- <programlisting>
-<![CDATA[
- while (snd_mychip_transmit_possible()) {
- unsigned char data;
- if (snd_rawmidi_transmit(substream, &data, 1) != 1)
- break; /* no more data */
- snd_mychip_transmit(data);
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- If you know beforehand how many bytes you can accept, you can
- use a buffer size greater than one with the
- <function>snd_rawmidi_transmit*</function> functions.
- </para>
-
- <para>
- The <function>trigger</function> callback must not sleep. If
- the hardware FIFO is full before the substream buffer has been
- emptied, you have to continue transmitting data later, either
- in an interrupt handler, or with a timer if the hardware
- doesn't have a MIDI transmit interrupt.
- </para>
-
- <para>
- The <function>trigger</function> callback is called with a
- zero <parameter>up</parameter> parameter when the transmission
- of data should be aborted.
- </para>
- </section>
-
- <section id="rawmidi-interface-op-trigger-in">
- <title><function>trigger</function> callback for input
- substreams</title>
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void snd_xxx_input_trigger(struct snd_rawmidi_substream *substream, int up);
-]]>
- </programlisting>
- </informalexample>
-
- <para>
- This is called with a nonzero <parameter>up</parameter>
- parameter to enable receiving data, or with a zero
- <parameter>up</parameter> parameter do disable receiving data.
- </para>
-
- <para>
- The <function>trigger</function> callback must not sleep; the
- actual reading of data from the device is usually done in an
- interrupt handler.
- </para>
-
- <para>
- When data reception is enabled, your interrupt handler should
- call <function>snd_rawmidi_receive</function> for all received
- data:
- <informalexample>
- <programlisting>
-<![CDATA[
- void snd_mychip_midi_interrupt(...)
- {
- while (mychip_midi_available()) {
- unsigned char data;
- data = mychip_midi_read();
- snd_rawmidi_receive(substream, &data, 1);
- }
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- <section id="rawmidi-interface-op-drain">
- <title><function>drain</function> callback</title>
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void snd_xxx_drain(struct snd_rawmidi_substream *substream);
-]]>
- </programlisting>
- </informalexample>
-
- <para>
- This is only used with output substreams. This function should wait
- until all data read from the substream buffer have been transmitted.
- This ensures that the device can be closed and the driver unloaded
- without losing data.
- </para>
-
- <para>
- This callback is optional. If you do not set
- <structfield>drain</structfield> in the struct snd_rawmidi_ops
- structure, ALSA will simply wait for 50 milliseconds
- instead.
- </para>
- </section>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Miscellaneous Devices -->
-<!-- ****************************************************** -->
- <chapter id="misc-devices">
- <title>Miscellaneous Devices</title>
-
- <section id="misc-devices-opl3">
- <title>FM OPL3</title>
- <para>
- The FM OPL3 is still used in many chips (mainly for backward
- compatibility). ALSA has a nice OPL3 FM control layer, too. The
- OPL3 API is defined in
- <filename><sound/opl3.h></filename>.
- </para>
-
- <para>
- FM registers can be directly accessed through the direct-FM API,
- defined in <filename><sound/asound_fm.h></filename>. In
- ALSA native mode, FM registers are accessed through
- the Hardware-Dependent Device direct-FM extension API, whereas in
- OSS compatible mode, FM registers can be accessed with the OSS
- direct-FM compatible API in <filename>/dev/dmfmX</filename> device.
- </para>
-
- <para>
- To create the OPL3 component, you have two functions to
- call. The first one is a constructor for the <type>opl3_t</type>
- instance.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_opl3 *opl3;
- snd_opl3_create(card, lport, rport, OPL3_HW_OPL3_XXX,
- integrated, &opl3);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The first argument is the card pointer, the second one is the
- left port address, and the third is the right port address. In
- most cases, the right port is placed at the left port + 2.
- </para>
-
- <para>
- The fourth argument is the hardware type.
- </para>
-
- <para>
- When the left and right ports have been already allocated by
- the card driver, pass non-zero to the fifth argument
- (<parameter>integrated</parameter>). Otherwise, the opl3 module will
- allocate the specified ports by itself.
- </para>
-
- <para>
- When the accessing the hardware requires special method
- instead of the standard I/O access, you can create opl3 instance
- separately with <function>snd_opl3_new()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_opl3 *opl3;
- snd_opl3_new(card, OPL3_HW_OPL3_XXX, &opl3);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Then set <structfield>command</structfield>,
- <structfield>private_data</structfield> and
- <structfield>private_free</structfield> for the private
- access function, the private data and the destructor.
- The l_port and r_port are not necessarily set. Only the
- command must be set properly. You can retrieve the data
- from the opl3->private_data field.
- </para>
-
- <para>
- After creating the opl3 instance via <function>snd_opl3_new()</function>,
- call <function>snd_opl3_init()</function> to initialize the chip to the
- proper state. Note that <function>snd_opl3_create()</function> always
- calls it internally.
- </para>
-
- <para>
- If the opl3 instance is created successfully, then create a
- hwdep device for this opl3.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_hwdep *opl3hwdep;
- snd_opl3_hwdep_new(opl3, 0, 1, &opl3hwdep);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The first argument is the <type>opl3_t</type> instance you
- created, and the second is the index number, usually 0.
- </para>
-
- <para>
- The third argument is the index-offset for the sequencer
- client assigned to the OPL3 port. When there is an MPU401-UART,
- give 1 for here (UART always takes 0).
- </para>
- </section>
-
- <section id="misc-devices-hardware-dependent">
- <title>Hardware-Dependent Devices</title>
- <para>
- Some chips need user-space access for special
- controls or for loading the micro code. In such a case, you can
- create a hwdep (hardware-dependent) device. The hwdep API is
- defined in <filename><sound/hwdep.h></filename>. You can
- find examples in opl3 driver or
- <filename>isa/sb/sb16_csp.c</filename>.
- </para>
-
- <para>
- The creation of the <type>hwdep</type> instance is done via
- <function>snd_hwdep_new()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_hwdep *hw;
- snd_hwdep_new(card, "My HWDEP", 0, &hw);
-]]>
- </programlisting>
- </informalexample>
-
- where the third argument is the index number.
- </para>
-
- <para>
- You can then pass any pointer value to the
- <parameter>private_data</parameter>.
- If you assign a private data, you should define the
- destructor, too. The destructor function is set in
- the <structfield>private_free</structfield> field.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct mydata *p = kmalloc(sizeof(*p), GFP_KERNEL);
- hw->private_data = p;
- hw->private_free = mydata_free;
-]]>
- </programlisting>
- </informalexample>
-
- and the implementation of the destructor would be:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void mydata_free(struct snd_hwdep *hw)
- {
- struct mydata *p = hw->private_data;
- kfree(p);
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The arbitrary file operations can be defined for this
- instance. The file operators are defined in
- the <parameter>ops</parameter> table. For example, assume that
- this chip needs an ioctl.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- hw->ops.open = mydata_open;
- hw->ops.ioctl = mydata_ioctl;
- hw->ops.release = mydata_release;
-]]>
- </programlisting>
- </informalexample>
-
- And implement the callback functions as you like.
- </para>
- </section>
-
- <section id="misc-devices-IEC958">
- <title>IEC958 (S/PDIF)</title>
- <para>
- Usually the controls for IEC958 devices are implemented via
- the control interface. There is a macro to compose a name string for
- IEC958 controls, <function>SNDRV_CTL_NAME_IEC958()</function>
- defined in <filename><include/asound.h></filename>.
- </para>
-
- <para>
- There are some standard controls for IEC958 status bits. These
- controls use the type <type>SNDRV_CTL_ELEM_TYPE_IEC958</type>,
- and the size of element is fixed as 4 bytes array
- (value.iec958.status[x]). For the <structfield>info</structfield>
- callback, you don't specify
- the value field for this type (the count field must be set,
- though).
- </para>
-
- <para>
- <quote>IEC958 Playback Con Mask</quote> is used to return the
- bit-mask for the IEC958 status bits of consumer mode. Similarly,
- <quote>IEC958 Playback Pro Mask</quote> returns the bitmask for
- professional mode. They are read-only controls, and are defined
- as MIXER controls (iface =
- <constant>SNDRV_CTL_ELEM_IFACE_MIXER</constant>).
- </para>
-
- <para>
- Meanwhile, <quote>IEC958 Playback Default</quote> control is
- defined for getting and setting the current default IEC958
- bits. Note that this one is usually defined as a PCM control
- (iface = <constant>SNDRV_CTL_ELEM_IFACE_PCM</constant>),
- although in some places it's defined as a MIXER control.
- </para>
-
- <para>
- In addition, you can define the control switches to
- enable/disable or to set the raw bit mode. The implementation
- will depend on the chip, but the control should be named as
- <quote>IEC958 xxx</quote>, preferably using
- the <function>SNDRV_CTL_NAME_IEC958()</function> macro.
- </para>
-
- <para>
- You can find several cases, for example,
- <filename>pci/emu10k1</filename>,
- <filename>pci/ice1712</filename>, or
- <filename>pci/cmipci.c</filename>.
- </para>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Buffer and Memory Management -->
-<!-- ****************************************************** -->
- <chapter id="buffer-and-memory">
- <title>Buffer and Memory Management</title>
-
- <section id="buffer-and-memory-buffer-types">
- <title>Buffer Types</title>
- <para>
- ALSA provides several different buffer allocation functions
- depending on the bus and the architecture. All these have a
- consistent API. The allocation of physically-contiguous pages is
- done via
- <function>snd_malloc_xxx_pages()</function> function, where xxx
- is the bus type.
- </para>
-
- <para>
- The allocation of pages with fallback is
- <function>snd_malloc_xxx_pages_fallback()</function>. This
- function tries to allocate the specified pages but if the pages
- are not available, it tries to reduce the page sizes until
- enough space is found.
- </para>
-
- <para>
- The release the pages, call
- <function>snd_free_xxx_pages()</function> function.
- </para>
-
- <para>
- Usually, ALSA drivers try to allocate and reserve
- a large contiguous physical space
- at the time the module is loaded for the later use.
- This is called <quote>pre-allocation</quote>.
- As already written, you can call the following function at
- pcm instance construction time (in the case of PCI bus).
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
- snd_dma_pci_data(pci), size, max);
-]]>
- </programlisting>
- </informalexample>
-
- where <parameter>size</parameter> is the byte size to be
- pre-allocated and the <parameter>max</parameter> is the maximum
- size to be changed via the <filename>prealloc</filename> proc file.
- The allocator will try to get an area as large as possible
- within the given size.
- </para>
-
- <para>
- The second argument (type) and the third argument (device pointer)
- are dependent on the bus.
- In the case of the ISA bus, pass <function>snd_dma_isa_data()</function>
- as the third argument with <constant>SNDRV_DMA_TYPE_DEV</constant> type.
- For the continuous buffer unrelated to the bus can be pre-allocated
- with <constant>SNDRV_DMA_TYPE_CONTINUOUS</constant> type and the
- <function>snd_dma_continuous_data(GFP_KERNEL)</function> device pointer,
- where <constant>GFP_KERNEL</constant> is the kernel allocation flag to
- use.
- For the PCI scatter-gather buffers, use
- <constant>SNDRV_DMA_TYPE_DEV_SG</constant> with
- <function>snd_dma_pci_data(pci)</function>
- (see the
- <link linkend="buffer-and-memory-non-contiguous"><citetitle>Non-Contiguous Buffers
- </citetitle></link> section).
- </para>
-
- <para>
- Once the buffer is pre-allocated, you can use the
- allocator in the <structfield>hw_params</structfield> callback:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_pcm_lib_malloc_pages(substream, size);
-]]>
- </programlisting>
- </informalexample>
-
- Note that you have to pre-allocate to use this function.
- </para>
- </section>
-
- <section id="buffer-and-memory-external-hardware">
- <title>External Hardware Buffers</title>
- <para>
- Some chips have their own hardware buffers and the DMA
- transfer from the host memory is not available. In such a case,
- you need to either 1) copy/set the audio data directly to the
- external hardware buffer, or 2) make an intermediate buffer and
- copy/set the data from it to the external hardware buffer in
- interrupts (or in tasklets, preferably).
- </para>
-
- <para>
- The first case works fine if the external hardware buffer is large
- enough. This method doesn't need any extra buffers and thus is
- more effective. You need to define the
- <structfield>copy</structfield> and
- <structfield>silence</structfield> callbacks for
- the data transfer. However, there is a drawback: it cannot
- be mmapped. The examples are GUS's GF1 PCM or emu8000's
- wavetable PCM.
- </para>
-
- <para>
- The second case allows for mmap on the buffer, although you have
- to handle an interrupt or a tasklet to transfer the data
- from the intermediate buffer to the hardware buffer. You can find an
- example in the vxpocket driver.
- </para>
-
- <para>
- Another case is when the chip uses a PCI memory-map
- region for the buffer instead of the host memory. In this case,
- mmap is available only on certain architectures like the Intel one.
- In non-mmap mode, the data cannot be transferred as in the normal
- way. Thus you need to define the <structfield>copy</structfield> and
- <structfield>silence</structfield> callbacks as well,
- as in the cases above. The examples are found in
- <filename>rme32.c</filename> and <filename>rme96.c</filename>.
- </para>
-
- <para>
- The implementation of the <structfield>copy</structfield> and
- <structfield>silence</structfield> callbacks depends upon
- whether the hardware supports interleaved or non-interleaved
- samples. The <structfield>copy</structfield> callback is
- defined like below, a bit
- differently depending whether the direction is playback or
- capture:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int playback_copy(struct snd_pcm_substream *substream, int channel,
- snd_pcm_uframes_t pos, void *src, snd_pcm_uframes_t count);
- static int capture_copy(struct snd_pcm_substream *substream, int channel,
- snd_pcm_uframes_t pos, void *dst, snd_pcm_uframes_t count);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- In the case of interleaved samples, the second argument
- (<parameter>channel</parameter>) is not used. The third argument
- (<parameter>pos</parameter>) points the
- current position offset in frames.
- </para>
-
- <para>
- The meaning of the fourth argument is different between
- playback and capture. For playback, it holds the source data
- pointer, and for capture, it's the destination data pointer.
- </para>
-
- <para>
- The last argument is the number of frames to be copied.
- </para>
-
- <para>
- What you have to do in this callback is again different
- between playback and capture directions. In the
- playback case, you copy the given amount of data
- (<parameter>count</parameter>) at the specified pointer
- (<parameter>src</parameter>) to the specified offset
- (<parameter>pos</parameter>) on the hardware buffer. When
- coded like memcpy-like way, the copy would be like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- my_memcpy(my_buffer + frames_to_bytes(runtime, pos), src,
- frames_to_bytes(runtime, count));
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- For the capture direction, you copy the given amount of
- data (<parameter>count</parameter>) at the specified offset
- (<parameter>pos</parameter>) on the hardware buffer to the
- specified pointer (<parameter>dst</parameter>).
-
- <informalexample>
- <programlisting>
-<![CDATA[
- my_memcpy(dst, my_buffer + frames_to_bytes(runtime, pos),
- frames_to_bytes(runtime, count));
-]]>
- </programlisting>
- </informalexample>
-
- Note that both the position and the amount of data are given
- in frames.
- </para>
-
- <para>
- In the case of non-interleaved samples, the implementation
- will be a bit more complicated.
- </para>
-
- <para>
- You need to check the channel argument, and if it's -1, copy
- the whole channels. Otherwise, you have to copy only the
- specified channel. Please check
- <filename>isa/gus/gus_pcm.c</filename> as an example.
- </para>
-
- <para>
- The <structfield>silence</structfield> callback is also
- implemented in a similar way.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int silence(struct snd_pcm_substream *substream, int channel,
- snd_pcm_uframes_t pos, snd_pcm_uframes_t count);
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The meanings of arguments are the same as in the
- <structfield>copy</structfield>
- callback, although there is no <parameter>src/dst</parameter>
- argument. In the case of interleaved samples, the channel
- argument has no meaning, as well as on
- <structfield>copy</structfield> callback.
- </para>
-
- <para>
- The role of <structfield>silence</structfield> callback is to
- set the given amount
- (<parameter>count</parameter>) of silence data at the
- specified offset (<parameter>pos</parameter>) on the hardware
- buffer. Suppose that the data format is signed (that is, the
- silent-data is 0), and the implementation using a memset-like
- function would be like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- my_memcpy(my_buffer + frames_to_bytes(runtime, pos), 0,
- frames_to_bytes(runtime, count));
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- In the case of non-interleaved samples, again, the
- implementation becomes a bit more complicated. See, for example,
- <filename>isa/gus/gus_pcm.c</filename>.
- </para>
- </section>
-
- <section id="buffer-and-memory-non-contiguous">
- <title>Non-Contiguous Buffers</title>
- <para>
- If your hardware supports the page table as in emu10k1 or the
- buffer descriptors as in via82xx, you can use the scatter-gather
- (SG) DMA. ALSA provides an interface for handling SG-buffers.
- The API is provided in <filename><sound/pcm.h></filename>.
- </para>
-
- <para>
- For creating the SG-buffer handler, call
- <function>snd_pcm_lib_preallocate_pages()</function> or
- <function>snd_pcm_lib_preallocate_pages_for_all()</function>
- with <constant>SNDRV_DMA_TYPE_DEV_SG</constant>
- in the PCM constructor like other PCI pre-allocator.
- You need to pass <function>snd_dma_pci_data(pci)</function>,
- where pci is the struct <structname>pci_dev</structname> pointer
- of the chip as well.
- The <type>struct snd_sg_buf</type> instance is created as
- substream->dma_private. You can cast
- the pointer like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_sg_buf *sgbuf = (struct snd_sg_buf *)substream->dma_private;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Then call <function>snd_pcm_lib_malloc_pages()</function>
- in the <structfield>hw_params</structfield> callback
- as well as in the case of normal PCI buffer.
- The SG-buffer handler will allocate the non-contiguous kernel
- pages of the given size and map them onto the virtually contiguous
- memory. The virtual pointer is addressed in runtime->dma_area.
- The physical address (runtime->dma_addr) is set to zero,
- because the buffer is physically non-contiguous.
- The physical address table is set up in sgbuf->table.
- You can get the physical address at a certain offset via
- <function>snd_pcm_sgbuf_get_addr()</function>.
- </para>
-
- <para>
- When a SG-handler is used, you need to set
- <function>snd_pcm_sgbuf_ops_page</function> as
- the <structfield>page</structfield> callback.
- (See <link linkend="pcm-interface-operators-page-callback">
- <citetitle>page callback section</citetitle></link>.)
- </para>
-
- <para>
- To release the data, call
- <function>snd_pcm_lib_free_pages()</function> in the
- <structfield>hw_free</structfield> callback as usual.
- </para>
- </section>
-
- <section id="buffer-and-memory-vmalloced">
- <title>Vmalloc'ed Buffers</title>
- <para>
- It's possible to use a buffer allocated via
- <function>vmalloc</function>, for example, for an intermediate
- buffer. Since the allocated pages are not contiguous, you need
- to set the <structfield>page</structfield> callback to obtain
- the physical address at every offset.
- </para>
-
- <para>
- The implementation of <structfield>page</structfield> callback
- would be like this:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- #include <linux/vmalloc.h>
-
- /* get the physical page pointer on the given offset */
- static struct page *mychip_page(struct snd_pcm_substream *substream,
- unsigned long offset)
- {
- void *pageptr = substream->runtime->dma_area + offset;
- return vmalloc_to_page(pageptr);
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Proc Interface -->
-<!-- ****************************************************** -->
- <chapter id="proc-interface">
- <title>Proc Interface</title>
- <para>
- ALSA provides an easy interface for procfs. The proc files are
- very useful for debugging. I recommend you set up proc files if
- you write a driver and want to get a running status or register
- dumps. The API is found in
- <filename><sound/info.h></filename>.
- </para>
-
- <para>
- To create a proc file, call
- <function>snd_card_proc_new()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- struct snd_info_entry *entry;
- int err = snd_card_proc_new(card, "my-file", &entry);
-]]>
- </programlisting>
- </informalexample>
-
- where the second argument specifies the name of the proc file to be
- created. The above example will create a file
- <filename>my-file</filename> under the card directory,
- e.g. <filename>/proc/asound/card0/my-file</filename>.
- </para>
-
- <para>
- Like other components, the proc entry created via
- <function>snd_card_proc_new()</function> will be registered and
- released automatically in the card registration and release
- functions.
- </para>
-
- <para>
- When the creation is successful, the function stores a new
- instance in the pointer given in the third argument.
- It is initialized as a text proc file for read only. To use
- this proc file as a read-only text file as it is, set the read
- callback with a private data via
- <function>snd_info_set_text_ops()</function>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_info_set_text_ops(entry, chip, my_proc_read);
-]]>
- </programlisting>
- </informalexample>
-
- where the second argument (<parameter>chip</parameter>) is the
- private data to be used in the callbacks. The third parameter
- specifies the read buffer size and the fourth
- (<parameter>my_proc_read</parameter>) is the callback function, which
- is defined like
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void my_proc_read(struct snd_info_entry *entry,
- struct snd_info_buffer *buffer);
-]]>
- </programlisting>
- </informalexample>
-
- </para>
-
- <para>
- In the read callback, use <function>snd_iprintf()</function> for
- output strings, which works just like normal
- <function>printf()</function>. For example,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static void my_proc_read(struct snd_info_entry *entry,
- struct snd_info_buffer *buffer)
- {
- struct my_chip *chip = entry->private_data;
-
- snd_iprintf(buffer, "This is my chip!\n");
- snd_iprintf(buffer, "Port = %ld\n", chip->port);
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The file permissions can be changed afterwards. As default, it's
- set as read only for all users. If you want to add write
- permission for the user (root as default), do as follows:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- entry->mode = S_IFREG | S_IRUGO | S_IWUSR;
-]]>
- </programlisting>
- </informalexample>
-
- and set the write buffer size and the callback
-
- <informalexample>
- <programlisting>
-<![CDATA[
- entry->c.text.write = my_proc_write;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- For the write callback, you can use
- <function>snd_info_get_line()</function> to get a text line, and
- <function>snd_info_get_str()</function> to retrieve a string from
- the line. Some examples are found in
- <filename>core/oss/mixer_oss.c</filename>, core/oss/and
- <filename>pcm_oss.c</filename>.
- </para>
-
- <para>
- For a raw-data proc-file, set the attributes as follows:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct snd_info_entry_ops my_file_io_ops = {
- .read = my_file_io_read,
- };
-
- entry->content = SNDRV_INFO_CONTENT_DATA;
- entry->private_data = chip;
- entry->c.ops = &my_file_io_ops;
- entry->size = 4096;
- entry->mode = S_IFREG | S_IRUGO;
-]]>
- </programlisting>
- </informalexample>
-
- For the raw data, <structfield>size</structfield> field must be
- set properly. This specifies the maximum size of the proc file access.
- </para>
-
- <para>
- The read/write callbacks of raw mode are more direct than the text mode.
- You need to use a low-level I/O functions such as
- <function>copy_from/to_user()</function> to transfer the
- data.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static ssize_t my_file_io_read(struct snd_info_entry *entry,
- void *file_private_data,
- struct file *file,
- char *buf,
- size_t count,
- loff_t pos)
- {
- if (copy_to_user(buf, local_data + pos, count))
- return -EFAULT;
- return count;
- }
-]]>
- </programlisting>
- </informalexample>
-
- If the size of the info entry has been set up properly,
- <structfield>count</structfield> and <structfield>pos</structfield> are
- guaranteed to fit within 0 and the given size.
- You don't have to check the range in the callbacks unless any
- other condition is required.
-
- </para>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Power Management -->
-<!-- ****************************************************** -->
- <chapter id="power-management">
- <title>Power Management</title>
- <para>
- If the chip is supposed to work with suspend/resume
- functions, you need to add power-management code to the
- driver. The additional code for power-management should be
- <function>ifdef</function>'ed with
- <constant>CONFIG_PM</constant>.
- </para>
-
- <para>
- If the driver <emphasis>fully</emphasis> supports suspend/resume
- that is, the device can be
- properly resumed to its state when suspend was called,
- you can set the <constant>SNDRV_PCM_INFO_RESUME</constant> flag
- in the pcm info field. Usually, this is possible when the
- registers of the chip can be safely saved and restored to
- RAM. If this is set, the trigger callback is called with
- <constant>SNDRV_PCM_TRIGGER_RESUME</constant> after the resume
- callback completes.
- </para>
-
- <para>
- Even if the driver doesn't support PM fully but
- partial suspend/resume is still possible, it's still worthy to
- implement suspend/resume callbacks. In such a case, applications
- would reset the status by calling
- <function>snd_pcm_prepare()</function> and restart the stream
- appropriately. Hence, you can define suspend/resume callbacks
- below but don't set <constant>SNDRV_PCM_INFO_RESUME</constant>
- info flag to the PCM.
- </para>
-
- <para>
- Note that the trigger with SUSPEND can always be called when
- <function>snd_pcm_suspend_all</function> is called,
- regardless of the <constant>SNDRV_PCM_INFO_RESUME</constant> flag.
- The <constant>RESUME</constant> flag affects only the behavior
- of <function>snd_pcm_resume()</function>.
- (Thus, in theory,
- <constant>SNDRV_PCM_TRIGGER_RESUME</constant> isn't needed
- to be handled in the trigger callback when no
- <constant>SNDRV_PCM_INFO_RESUME</constant> flag is set. But,
- it's better to keep it for compatibility reasons.)
- </para>
- <para>
- In the earlier version of ALSA drivers, a common
- power-management layer was provided, but it has been removed.
- The driver needs to define the suspend/resume hooks according to
- the bus the device is connected to. In the case of PCI drivers, the
- callbacks look like below:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- #ifdef CONFIG_PM
- static int snd_my_suspend(struct pci_dev *pci, pm_message_t state)
- {
- .... /* do things for suspend */
- return 0;
- }
- static int snd_my_resume(struct pci_dev *pci)
- {
- .... /* do things for suspend */
- return 0;
- }
- #endif
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The scheme of the real suspend job is as follows.
-
- <orderedlist>
- <listitem><para>Retrieve the card and the chip data.</para></listitem>
- <listitem><para>Call <function>snd_power_change_state()</function> with
- <constant>SNDRV_CTL_POWER_D3hot</constant> to change the
- power status.</para></listitem>
- <listitem><para>Call <function>snd_pcm_suspend_all()</function> to suspend the running PCM streams.</para></listitem>
- <listitem><para>If AC97 codecs are used, call
- <function>snd_ac97_suspend()</function> for each codec.</para></listitem>
- <listitem><para>Save the register values if necessary.</para></listitem>
- <listitem><para>Stop the hardware if necessary.</para></listitem>
- <listitem><para>Disable the PCI device by calling
- <function>pci_disable_device()</function>. Then, call
- <function>pci_save_state()</function> at last.</para></listitem>
- </orderedlist>
- </para>
-
- <para>
- A typical code would be like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int mychip_suspend(struct pci_dev *pci, pm_message_t state)
- {
- /* (1) */
- struct snd_card *card = pci_get_drvdata(pci);
- struct mychip *chip = card->private_data;
- /* (2) */
- snd_power_change_state(card, SNDRV_CTL_POWER_D3hot);
- /* (3) */
- snd_pcm_suspend_all(chip->pcm);
- /* (4) */
- snd_ac97_suspend(chip->ac97);
- /* (5) */
- snd_mychip_save_registers(chip);
- /* (6) */
- snd_mychip_stop_hardware(chip);
- /* (7) */
- pci_disable_device(pci);
- pci_save_state(pci);
- return 0;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- The scheme of the real resume job is as follows.
-
- <orderedlist>
- <listitem><para>Retrieve the card and the chip data.</para></listitem>
- <listitem><para>Set up PCI. First, call <function>pci_restore_state()</function>.
- Then enable the pci device again by calling <function>pci_enable_device()</function>.
- Call <function>pci_set_master()</function> if necessary, too.</para></listitem>
- <listitem><para>Re-initialize the chip.</para></listitem>
- <listitem><para>Restore the saved registers if necessary.</para></listitem>
- <listitem><para>Resume the mixer, e.g. calling
- <function>snd_ac97_resume()</function>.</para></listitem>
- <listitem><para>Restart the hardware (if any).</para></listitem>
- <listitem><para>Call <function>snd_power_change_state()</function> with
- <constant>SNDRV_CTL_POWER_D0</constant> to notify the processes.</para></listitem>
- </orderedlist>
- </para>
-
- <para>
- A typical code would be like:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int mychip_resume(struct pci_dev *pci)
- {
- /* (1) */
- struct snd_card *card = pci_get_drvdata(pci);
- struct mychip *chip = card->private_data;
- /* (2) */
- pci_restore_state(pci);
- pci_enable_device(pci);
- pci_set_master(pci);
- /* (3) */
- snd_mychip_reinit_chip(chip);
- /* (4) */
- snd_mychip_restore_registers(chip);
- /* (5) */
- snd_ac97_resume(chip->ac97);
- /* (6) */
- snd_mychip_restart_chip(chip);
- /* (7) */
- snd_power_change_state(card, SNDRV_CTL_POWER_D0);
- return 0;
- }
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- As shown in the above, it's better to save registers after
- suspending the PCM operations via
- <function>snd_pcm_suspend_all()</function> or
- <function>snd_pcm_suspend()</function>. It means that the PCM
- streams are already stopped when the register snapshot is
- taken. But, remember that you don't have to restart the PCM
- stream in the resume callback. It'll be restarted via
- trigger call with <constant>SNDRV_PCM_TRIGGER_RESUME</constant>
- when necessary.
- </para>
-
- <para>
- OK, we have all callbacks now. Let's set them up. In the
- initialization of the card, make sure that you can get the chip
- data from the card instance, typically via
- <structfield>private_data</structfield> field, in case you
- created the chip data individually.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_mychip_probe(struct pci_dev *pci,
- const struct pci_device_id *pci_id)
- {
- ....
- struct snd_card *card;
- struct mychip *chip;
- int err;
- ....
- err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
- 0, &card);
- ....
- chip = kzalloc(sizeof(*chip), GFP_KERNEL);
- ....
- card->private_data = chip;
- ....
- }
-]]>
- </programlisting>
- </informalexample>
-
- When you created the chip data with
- <function>snd_card_new()</function>, it's anyway accessible
- via <structfield>private_data</structfield> field.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int snd_mychip_probe(struct pci_dev *pci,
- const struct pci_device_id *pci_id)
- {
- ....
- struct snd_card *card;
- struct mychip *chip;
- int err;
- ....
- err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
- sizeof(struct mychip), &card);
- ....
- chip = card->private_data;
- ....
- }
-]]>
- </programlisting>
- </informalexample>
-
- </para>
-
- <para>
- If you need a space to save the registers, allocate the
- buffer for it here, too, since it would be fatal
- if you cannot allocate a memory in the suspend phase.
- The allocated buffer should be released in the corresponding
- destructor.
- </para>
-
- <para>
- And next, set suspend/resume callbacks to the pci_driver.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static struct pci_driver driver = {
- .name = KBUILD_MODNAME,
- .id_table = snd_my_ids,
- .probe = snd_my_probe,
- .remove = snd_my_remove,
- #ifdef CONFIG_PM
- .suspend = snd_my_suspend,
- .resume = snd_my_resume,
- #endif
- };
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Module Parameters -->
-<!-- ****************************************************** -->
- <chapter id="module-parameters">
- <title>Module Parameters</title>
- <para>
- There are standard module options for ALSA. At least, each
- module should have the <parameter>index</parameter>,
- <parameter>id</parameter> and <parameter>enable</parameter>
- options.
- </para>
-
- <para>
- If the module supports multiple cards (usually up to
- 8 = <constant>SNDRV_CARDS</constant> cards), they should be
- arrays. The default initial values are defined already as
- constants for easier programming:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
- static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
- static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP;
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- If the module supports only a single card, they could be single
- variables, instead. <parameter>enable</parameter> option is not
- always necessary in this case, but it would be better to have a
- dummy option for compatibility.
- </para>
-
- <para>
- The module parameters must be declared with the standard
- <function>module_param()()</function>,
- <function>module_param_array()()</function> and
- <function>MODULE_PARM_DESC()</function> macros.
- </para>
-
- <para>
- The typical coding would be like below:
-
- <informalexample>
- <programlisting>
-<![CDATA[
- #define CARD_NAME "My Chip"
-
- module_param_array(index, int, NULL, 0444);
- MODULE_PARM_DESC(index, "Index value for " CARD_NAME " soundcard.");
- module_param_array(id, charp, NULL, 0444);
- MODULE_PARM_DESC(id, "ID string for " CARD_NAME " soundcard.");
- module_param_array(enable, bool, NULL, 0444);
- MODULE_PARM_DESC(enable, "Enable " CARD_NAME " soundcard.");
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- Also, don't forget to define the module description, classes,
- license and devices. Especially, the recent modprobe requires to
- define the module license as GPL, etc., otherwise the system is
- shown as <quote>tainted</quote>.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- MODULE_DESCRIPTION("My Chip");
- MODULE_LICENSE("GPL");
- MODULE_SUPPORTED_DEVICE("{{Vendor,My Chip Name}}");
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- How To Put Your Driver -->
-<!-- ****************************************************** -->
- <chapter id="how-to-put-your-driver">
- <title>How To Put Your Driver Into ALSA Tree</title>
- <section>
- <title>General</title>
- <para>
- So far, you've learned how to write the driver codes.
- And you might have a question now: how to put my own
- driver into the ALSA driver tree?
- Here (finally :) the standard procedure is described briefly.
- </para>
-
- <para>
- Suppose that you create a new PCI driver for the card
- <quote>xyz</quote>. The card module name would be
- snd-xyz. The new driver is usually put into the alsa-driver
- tree, <filename>alsa-driver/pci</filename> directory in
- the case of PCI cards.
- Then the driver is evaluated, audited and tested
- by developers and users. After a certain time, the driver
- will go to the alsa-kernel tree (to the corresponding directory,
- such as <filename>alsa-kernel/pci</filename>) and eventually
- will be integrated into the Linux 2.6 tree (the directory would be
- <filename>linux/sound/pci</filename>).
- </para>
-
- <para>
- In the following sections, the driver code is supposed
- to be put into alsa-driver tree. The two cases are covered:
- a driver consisting of a single source file and one consisting
- of several source files.
- </para>
- </section>
-
- <section>
- <title>Driver with A Single Source File</title>
- <para>
- <orderedlist>
- <listitem>
- <para>
- Modify alsa-driver/pci/Makefile
- </para>
-
- <para>
- Suppose you have a file xyz.c. Add the following
- two lines
- <informalexample>
- <programlisting>
-<![CDATA[
- snd-xyz-objs := xyz.o
- obj-$(CONFIG_SND_XYZ) += snd-xyz.o
-]]>
- </programlisting>
- </informalexample>
- </para>
- </listitem>
-
- <listitem>
- <para>
- Create the Kconfig entry
- </para>
-
- <para>
- Add the new entry of Kconfig for your xyz driver.
- <informalexample>
- <programlisting>
-<![CDATA[
- config SND_XYZ
- tristate "Foobar XYZ"
- depends on SND
- select SND_PCM
- help
- Say Y here to include support for Foobar XYZ soundcard.
-
- To compile this driver as a module, choose M here: the module
- will be called snd-xyz.
-]]>
- </programlisting>
- </informalexample>
-
- the line, select SND_PCM, specifies that the driver xyz supports
- PCM. In addition to SND_PCM, the following components are
- supported for select command:
- SND_RAWMIDI, SND_TIMER, SND_HWDEP, SND_MPU401_UART,
- SND_OPL3_LIB, SND_OPL4_LIB, SND_VX_LIB, SND_AC97_CODEC.
- Add the select command for each supported component.
- </para>
-
- <para>
- Note that some selections imply the lowlevel selections.
- For example, PCM includes TIMER, MPU401_UART includes RAWMIDI,
- AC97_CODEC includes PCM, and OPL3_LIB includes HWDEP.
- You don't need to give the lowlevel selections again.
- </para>
-
- <para>
- For the details of Kconfig script, refer to the kbuild
- documentation.
- </para>
-
- </listitem>
-
- <listitem>
- <para>
- Run cvscompile script to re-generate the configure script and
- build the whole stuff again.
- </para>
- </listitem>
- </orderedlist>
- </para>
- </section>
-
- <section>
- <title>Drivers with Several Source Files</title>
- <para>
- Suppose that the driver snd-xyz have several source files.
- They are located in the new subdirectory,
- pci/xyz.
-
- <orderedlist>
- <listitem>
- <para>
- Add a new directory (<filename>xyz</filename>) in
- <filename>alsa-driver/pci/Makefile</filename> as below
-
- <informalexample>
- <programlisting>
-<![CDATA[
- obj-$(CONFIG_SND) += xyz/
-]]>
- </programlisting>
- </informalexample>
- </para>
- </listitem>
-
- <listitem>
- <para>
- Under the directory <filename>xyz</filename>, create a Makefile
-
- <example>
- <title>Sample Makefile for a driver xyz</title>
- <programlisting>
-<![CDATA[
- ifndef SND_TOPDIR
- SND_TOPDIR=../..
- endif
-
- include $(SND_TOPDIR)/toplevel.config
- include $(SND_TOPDIR)/Makefile.conf
-
- snd-xyz-objs := xyz.o abc.o def.o
-
- obj-$(CONFIG_SND_XYZ) += snd-xyz.o
-
- include $(SND_TOPDIR)/Rules.make
-]]>
- </programlisting>
- </example>
- </para>
- </listitem>
-
- <listitem>
- <para>
- Create the Kconfig entry
- </para>
-
- <para>
- This procedure is as same as in the last section.
- </para>
- </listitem>
-
- <listitem>
- <para>
- Run cvscompile script to re-generate the configure script and
- build the whole stuff again.
- </para>
- </listitem>
- </orderedlist>
- </para>
- </section>
-
- </chapter>
-
-<!-- ****************************************************** -->
-<!-- Useful Functions -->
-<!-- ****************************************************** -->
- <chapter id="useful-functions">
- <title>Useful Functions</title>
-
- <section id="useful-functions-snd-printk">
- <title><function>snd_printk()</function> and friends</title>
- <para>
- ALSA provides a verbose version of the
- <function>printk()</function> function. If a kernel config
- <constant>CONFIG_SND_VERBOSE_PRINTK</constant> is set, this
- function prints the given message together with the file name
- and the line of the caller. The <constant>KERN_XXX</constant>
- prefix is processed as
- well as the original <function>printk()</function> does, so it's
- recommended to add this prefix, e.g.
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_printk(KERN_ERR "Oh my, sorry, it's extremely bad!\n");
-]]>
- </programlisting>
- </informalexample>
- </para>
-
- <para>
- There are also <function>printk()</function>'s for
- debugging. <function>snd_printd()</function> can be used for
- general debugging purposes. If
- <constant>CONFIG_SND_DEBUG</constant> is set, this function is
- compiled, and works just like
- <function>snd_printk()</function>. If the ALSA is compiled
- without the debugging flag, it's ignored.
- </para>
-
- <para>
- <function>snd_printdd()</function> is compiled in only when
- <constant>CONFIG_SND_DEBUG_VERBOSE</constant> is set. Please note
- that <constant>CONFIG_SND_DEBUG_VERBOSE</constant> is not set as default
- even if you configure the alsa-driver with
- <option>--with-debug=full</option> option. You need to give
- explicitly <option>--with-debug=detect</option> option instead.
- </para>
- </section>
-
- <section id="useful-functions-snd-bug">
- <title><function>snd_BUG()</function></title>
- <para>
- It shows the <computeroutput>BUG?</computeroutput> message and
- stack trace as well as <function>snd_BUG_ON</function> at the point.
- It's useful to show that a fatal error happens there.
- </para>
- <para>
- When no debug flag is set, this macro is ignored.
- </para>
- </section>
-
- <section id="useful-functions-snd-bug-on">
- <title><function>snd_BUG_ON()</function></title>
- <para>
- <function>snd_BUG_ON()</function> macro is similar with
- <function>WARN_ON()</function> macro. For example,
-
- <informalexample>
- <programlisting>
-<![CDATA[
- snd_BUG_ON(!pointer);
-]]>
- </programlisting>
- </informalexample>
-
- or it can be used as the condition,
- <informalexample>
- <programlisting>
-<![CDATA[
- if (snd_BUG_ON(non_zero_is_bug))
- return -EINVAL;
-]]>
- </programlisting>
- </informalexample>
-
- </para>
-
- <para>
- The macro takes an conditional expression to evaluate.
- When <constant>CONFIG_SND_DEBUG</constant>, is set, if the
- expression is non-zero, it shows the warning message such as
- <computeroutput>BUG? (xxx)</computeroutput>
- normally followed by stack trace.
-
- In both cases it returns the evaluated value.
- </para>
-
- </section>
-
- </chapter>
-
-
-<!-- ****************************************************** -->
-<!-- Acknowledgments -->
-<!-- ****************************************************** -->
- <chapter id="acknowledgments">
- <title>Acknowledgments</title>
- <para>
- I would like to thank Phil Kerr for his help for improvement and
- corrections of this document.
- </para>
- <para>
- Kevin Conder reformatted the original plain-text to the
- DocBook format.
- </para>
- <para>
- Giuliano Pochini corrected typos and contributed the example codes
- in the hardware constraints section.
- </para>
- </chapter>
-</book>
--- /dev/null
+======================
+Writing an ALSA Driver
+======================
+
+:Author: Takashi Iwai <tiwai@suse.de>
+:Date: Oct 15, 2007
+:Edition: 0.3.7
+
+Preface
+=======
+
+This document describes how to write an `ALSA (Advanced Linux Sound
+Architecture) <http://www.alsa-project.org/>`__ driver. The document
+focuses mainly on PCI soundcards. In the case of other device types, the
+API might be different, too. However, at least the ALSA kernel API is
+consistent, and therefore it would be still a bit help for writing them.
+
+This document targets people who already have enough C language skills
+and have basic linux kernel programming knowledge. This document doesn't
+explain the general topic of linux kernel coding and doesn't cover
+low-level driver implementation details. It only describes the standard
+way to write a PCI sound driver on ALSA.
+
+If you are already familiar with the older ALSA ver.0.5.x API, you can
+check the drivers such as ``sound/pci/es1938.c`` or
+``sound/pci/maestro3.c`` which have also almost the same code-base in
+the ALSA 0.5.x tree, so you can compare the differences.
+
+This document is still a draft version. Any feedback and corrections,
+please!!
+
+File Tree Structure
+===================
+
+General
+-------
+
+The ALSA drivers are provided in two ways.
+
+One is the trees provided as a tarball or via cvs from the ALSA's ftp
+site, and another is the 2.6 (or later) Linux kernel tree. To
+synchronize both, the ALSA driver tree is split into two different
+trees: alsa-kernel and alsa-driver. The former contains purely the
+source code for the Linux 2.6 (or later) tree. This tree is designed
+only for compilation on 2.6 or later environment. The latter,
+alsa-driver, contains many subtle files for compiling ALSA drivers
+outside of the Linux kernel tree, wrapper functions for older 2.2 and
+2.4 kernels, to adapt the latest kernel API, and additional drivers
+which are still in development or in tests. The drivers in alsa-driver
+tree will be moved to alsa-kernel (and eventually to the 2.6 kernel
+tree) when they are finished and confirmed to work fine.
+
+The file tree structure of ALSA driver is depicted below. Both
+alsa-kernel and alsa-driver have almost the same file structure, except
+for “core” directory. It's named as “acore” in alsa-driver tree.
+
+::
+
+ sound
+ /core
+ /oss
+ /seq
+ /oss
+ /instr
+ /ioctl32
+ /include
+ /drivers
+ /mpu401
+ /opl3
+ /i2c
+ /l3
+ /synth
+ /emux
+ /pci
+ /(cards)
+ /isa
+ /(cards)
+ /arm
+ /ppc
+ /sparc
+ /usb
+ /pcmcia /(cards)
+ /oss
+
+
+core directory
+--------------
+
+This directory contains the middle layer which is the heart of ALSA
+drivers. In this directory, the native ALSA modules are stored. The
+sub-directories contain different modules and are dependent upon the
+kernel config.
+
+core/oss
+~~~~~~~~
+
+The codes for PCM and mixer OSS emulation modules are stored in this
+directory. The rawmidi OSS emulation is included in the ALSA rawmidi
+code since it's quite small. The sequencer code is stored in
+``core/seq/oss`` directory (see `below <#core-seq-oss>`__).
+
+core/ioctl32
+~~~~~~~~~~~~
+
+This directory contains the 32bit-ioctl wrappers for 64bit architectures
+such like x86-64, ppc64 and sparc64. For 32bit and alpha architectures,
+these are not compiled.
+
+core/seq
+~~~~~~~~
+
+This directory and its sub-directories are for the ALSA sequencer. This
+directory contains the sequencer core and primary sequencer modules such
+like snd-seq-midi, snd-seq-virmidi, etc. They are compiled only when
+``CONFIG_SND_SEQUENCER`` is set in the kernel config.
+
+core/seq/oss
+~~~~~~~~~~~~
+
+This contains the OSS sequencer emulation codes.
+
+core/seq/instr
+~~~~~~~~~~~~~~
+
+This directory contains the modules for the sequencer instrument layer.
+
+include directory
+-----------------
+
+This is the place for the public header files of ALSA drivers, which are
+to be exported to user-space, or included by several files at different
+directories. Basically, the private header files should not be placed in
+this directory, but you may still find files there, due to historical
+reasons :)
+
+drivers directory
+-----------------
+
+This directory contains code shared among different drivers on different
+architectures. They are hence supposed not to be architecture-specific.
+For example, the dummy pcm driver and the serial MIDI driver are found
+in this directory. In the sub-directories, there is code for components
+which are independent from bus and cpu architectures.
+
+drivers/mpu401
+~~~~~~~~~~~~~~
+
+The MPU401 and MPU401-UART modules are stored here.
+
+drivers/opl3 and opl4
+~~~~~~~~~~~~~~~~~~~~~
+
+The OPL3 and OPL4 FM-synth stuff is found here.
+
+i2c directory
+-------------
+
+This contains the ALSA i2c components.
+
+Although there is a standard i2c layer on Linux, ALSA has its own i2c
+code for some cards, because the soundcard needs only a simple operation
+and the standard i2c API is too complicated for such a purpose.
+
+i2c/l3
+~~~~~~
+
+This is a sub-directory for ARM L3 i2c.
+
+synth directory
+---------------
+
+This contains the synth middle-level modules.
+
+So far, there is only Emu8000/Emu10k1 synth driver under the
+``synth/emux`` sub-directory.
+
+pci directory
+-------------
+
+This directory and its sub-directories hold the top-level card modules
+for PCI soundcards and the code specific to the PCI BUS.
+
+The drivers compiled from a single file are stored directly in the pci
+directory, while the drivers with several source files are stored on
+their own sub-directory (e.g. emu10k1, ice1712).
+
+isa directory
+-------------
+
+This directory and its sub-directories hold the top-level card modules
+for ISA soundcards.
+
+arm, ppc, and sparc directories
+-------------------------------
+
+They are used for top-level card modules which are specific to one of
+these architectures.
+
+usb directory
+-------------
+
+This directory contains the USB-audio driver. In the latest version, the
+USB MIDI driver is integrated in the usb-audio driver.
+
+pcmcia directory
+----------------
+
+The PCMCIA, especially PCCard drivers will go here. CardBus drivers will
+be in the pci directory, because their API is identical to that of
+standard PCI cards.
+
+oss directory
+-------------
+
+The OSS/Lite source files are stored here in Linux 2.6 (or later) tree.
+In the ALSA driver tarball, this directory is empty, of course :)
+
+Basic Flow for PCI Drivers
+==========================
+
+Outline
+-------
+
+The minimum flow for PCI soundcards is as follows:
+
+- define the PCI ID table (see the section `PCI Entries`_).
+
+- create ``probe`` callback.
+
+- create ``remove`` callback.
+
+- create a :c:type:`struct pci_driver <pci_driver>` structure
+ containing the three pointers above.
+
+- create an ``init`` function just calling the
+ :c:func:`pci_register_driver()` to register the pci_driver
+ table defined above.
+
+- create an ``exit`` function to call the
+ :c:func:`pci_unregister_driver()` function.
+
+Full Code Example
+-----------------
+
+The code example is shown below. Some parts are kept unimplemented at
+this moment but will be filled in the next sections. The numbers in the
+comment lines of the :c:func:`snd_mychip_probe()` function refer
+to details explained in the following section.
+
+::
+
+ #include <linux/init.h>
+ #include <linux/pci.h>
+ #include <linux/slab.h>
+ #include <sound/core.h>
+ #include <sound/initval.h>
+
+ /* module parameters (see "Module Parameters") */
+ /* SNDRV_CARDS: maximum number of cards supported by this module */
+ static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
+ static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
+ static bool enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP;
+
+ /* definition of the chip-specific record */
+ struct mychip {
+ struct snd_card *card;
+ /* the rest of the implementation will be in section
+ * "PCI Resource Management"
+ */
+ };
+
+ /* chip-specific destructor
+ * (see "PCI Resource Management")
+ */
+ static int snd_mychip_free(struct mychip *chip)
+ {
+ .... /* will be implemented later... */
+ }
+
+ /* component-destructor
+ * (see "Management of Cards and Components")
+ */
+ static int snd_mychip_dev_free(struct snd_device *device)
+ {
+ return snd_mychip_free(device->device_data);
+ }
+
+ /* chip-specific constructor
+ * (see "Management of Cards and Components")
+ */
+ static int snd_mychip_create(struct snd_card *card,
+ struct pci_dev *pci,
+ struct mychip **rchip)
+ {
+ struct mychip *chip;
+ int err;
+ static struct snd_device_ops ops = {
+ .dev_free = snd_mychip_dev_free,
+ };
+
+ *rchip = NULL;
+
+ /* check PCI availability here
+ * (see "PCI Resource Management")
+ */
+ ....
+
+ /* allocate a chip-specific data with zero filled */
+ chip = kzalloc(sizeof(*chip), GFP_KERNEL);
+ if (chip == NULL)
+ return -ENOMEM;
+
+ chip->card = card;
+
+ /* rest of initialization here; will be implemented
+ * later, see "PCI Resource Management"
+ */
+ ....
+
+ err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
+ if (err < 0) {
+ snd_mychip_free(chip);
+ return err;
+ }
+
+ *rchip = chip;
+ return 0;
+ }
+
+ /* constructor -- see "Driver Constructor" sub-section */
+ static int snd_mychip_probe(struct pci_dev *pci,
+ const struct pci_device_id *pci_id)
+ {
+ static int dev;
+ struct snd_card *card;
+ struct mychip *chip;
+ int err;
+
+ /* (1) */
+ if (dev >= SNDRV_CARDS)
+ return -ENODEV;
+ if (!enable[dev]) {
+ dev++;
+ return -ENOENT;
+ }
+
+ /* (2) */
+ err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
+ 0, &card);
+ if (err < 0)
+ return err;
+
+ /* (3) */
+ err = snd_mychip_create(card, pci, &chip);
+ if (err < 0) {
+ snd_card_free(card);
+ return err;
+ }
+
+ /* (4) */
+ strcpy(card->driver, "My Chip");
+ strcpy(card->shortname, "My Own Chip 123");
+ sprintf(card->longname, "%s at 0x%lx irq %i",
+ card->shortname, chip->ioport, chip->irq);
+
+ /* (5) */
+ .... /* implemented later */
+
+ /* (6) */
+ err = snd_card_register(card);
+ if (err < 0) {
+ snd_card_free(card);
+ return err;
+ }
+
+ /* (7) */
+ pci_set_drvdata(pci, card);
+ dev++;
+ return 0;
+ }
+
+ /* destructor -- see the "Destructor" sub-section */
+ static void snd_mychip_remove(struct pci_dev *pci)
+ {
+ snd_card_free(pci_get_drvdata(pci));
+ pci_set_drvdata(pci, NULL);
+ }
+
+
+
+Driver Constructor
+------------------
+
+The real constructor of PCI drivers is the ``probe`` callback. The
+``probe`` callback and other component-constructors which are called
+from the ``probe`` callback cannot be used with the ``__init`` prefix
+because any PCI device could be a hotplug device.
+
+In the ``probe`` callback, the following scheme is often used.
+
+1) Check and increment the device index.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ static int dev;
+ ....
+ if (dev >= SNDRV_CARDS)
+ return -ENODEV;
+ if (!enable[dev]) {
+ dev++;
+ return -ENOENT;
+ }
+
+
+where ``enable[dev]`` is the module option.
+
+Each time the ``probe`` callback is called, check the availability of
+the device. If not available, simply increment the device index and
+returns. dev will be incremented also later (`step 7
+<#set-the-pci-driver-data-and-return-zero>`__).
+
+2) Create a card instance
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ struct snd_card *card;
+ int err;
+ ....
+ err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
+ 0, &card);
+
+
+The details will be explained in the section `Management of Cards and
+Components`_.
+
+3) Create a main component
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In this part, the PCI resources are allocated.
+
+::
+
+ struct mychip *chip;
+ ....
+ err = snd_mychip_create(card, pci, &chip);
+ if (err < 0) {
+ snd_card_free(card);
+ return err;
+ }
+
+The details will be explained in the section `PCI Resource
+Management`_.
+
+4) Set the driver ID and name strings.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ strcpy(card->driver, "My Chip");
+ strcpy(card->shortname, "My Own Chip 123");
+ sprintf(card->longname, "%s at 0x%lx irq %i",
+ card->shortname, chip->ioport, chip->irq);
+
+The driver field holds the minimal ID string of the chip. This is used
+by alsa-lib's configurator, so keep it simple but unique. Even the
+same driver can have different driver IDs to distinguish the
+functionality of each chip type.
+
+The shortname field is a string shown as more verbose name. The longname
+field contains the information shown in ``/proc/asound/cards``.
+
+5) Create other components, such as mixer, MIDI, etc.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Here you define the basic components such as `PCM <#PCM-Interface>`__,
+mixer (e.g. `AC97 <#API-for-AC97-Codec>`__), MIDI (e.g.
+`MPU-401 <#MIDI-MPU401-UART-Interface>`__), and other interfaces.
+Also, if you want a `proc file <#Proc-Interface>`__, define it here,
+too.
+
+6) Register the card instance.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ err = snd_card_register(card);
+ if (err < 0) {
+ snd_card_free(card);
+ return err;
+ }
+
+Will be explained in the section `Management of Cards and
+Components`_, too.
+
+7) Set the PCI driver data and return zero.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ pci_set_drvdata(pci, card);
+ dev++;
+ return 0;
+
+In the above, the card record is stored. This pointer is used in the
+remove callback and power-management callbacks, too.
+
+Destructor
+----------
+
+The destructor, remove callback, simply releases the card instance. Then
+the ALSA middle layer will release all the attached components
+automatically.
+
+It would be typically like the following:
+
+::
+
+ static void snd_mychip_remove(struct pci_dev *pci)
+ {
+ snd_card_free(pci_get_drvdata(pci));
+ pci_set_drvdata(pci, NULL);
+ }
+
+
+The above code assumes that the card pointer is set to the PCI driver
+data.
+
+Header Files
+------------
+
+For the above example, at least the following include files are
+necessary.
+
+::
+
+ #include <linux/init.h>
+ #include <linux/pci.h>
+ #include <linux/slab.h>
+ #include <sound/core.h>
+ #include <sound/initval.h>
+
+where the last one is necessary only when module options are defined
+in the source file. If the code is split into several files, the files
+without module options don't need them.
+
+In addition to these headers, you'll need ``<linux/interrupt.h>`` for
+interrupt handling, and ``<asm/io.h>`` for I/O access. If you use the
+:c:func:`mdelay()` or :c:func:`udelay()` functions, you'll need
+to include ``<linux/delay.h>`` too.
+
+The ALSA interfaces like the PCM and control APIs are defined in other
+``<sound/xxx.h>`` header files. They have to be included after
+``<sound/core.h>``.
+
+Management of Cards and Components
+==================================
+
+Card Instance
+-------------
+
+For each soundcard, a “card” record must be allocated.
+
+A card record is the headquarters of the soundcard. It manages the whole
+list of devices (components) on the soundcard, such as PCM, mixers,
+MIDI, synthesizer, and so on. Also, the card record holds the ID and the
+name strings of the card, manages the root of proc files, and controls
+the power-management states and hotplug disconnections. The component
+list on the card record is used to manage the correct release of
+resources at destruction.
+
+As mentioned above, to create a card instance, call
+:c:func:`snd_card_new()`.
+
+::
+
+ struct snd_card *card;
+ int err;
+ err = snd_card_new(&pci->dev, index, id, module, extra_size, &card);
+
+
+The function takes six arguments: the parent device pointer, the
+card-index number, the id string, the module pointer (usually
+``THIS_MODULE``), the size of extra-data space, and the pointer to
+return the card instance. The extra_size argument is used to allocate
+card->private_data for the chip-specific data. Note that these data are
+allocated by :c:func:`snd_card_new()`.
+
+The first argument, the pointer of struct :c:type:`struct device
+<device>`, specifies the parent device. For PCI devices, typically
+``&pci->`` is passed there.
+
+Components
+----------
+
+After the card is created, you can attach the components (devices) to
+the card instance. In an ALSA driver, a component is represented as a
+:c:type:`struct snd_device <snd_device>` object. A component
+can be a PCM instance, a control interface, a raw MIDI interface, etc.
+Each such instance has one component entry.
+
+A component can be created via :c:func:`snd_device_new()`
+function.
+
+::
+
+ snd_device_new(card, SNDRV_DEV_XXX, chip, &ops);
+
+This takes the card pointer, the device-level (``SNDRV_DEV_XXX``), the
+data pointer, and the callback pointers (``&ops``). The device-level
+defines the type of components and the order of registration and
+de-registration. For most components, the device-level is already
+defined. For a user-defined component, you can use
+``SNDRV_DEV_LOWLEVEL``.
+
+This function itself doesn't allocate the data space. The data must be
+allocated manually beforehand, and its pointer is passed as the
+argument. This pointer (``chip`` in the above example) is used as the
+identifier for the instance.
+
+Each pre-defined ALSA component such as ac97 and pcm calls
+:c:func:`snd_device_new()` inside its constructor. The destructor
+for each component is defined in the callback pointers. Hence, you don't
+need to take care of calling a destructor for such a component.
+
+If you wish to create your own component, you need to set the destructor
+function to the dev_free callback in the ``ops``, so that it can be
+released automatically via :c:func:`snd_card_free()`. The next
+example will show an implementation of chip-specific data.
+
+Chip-Specific Data
+------------------
+
+Chip-specific information, e.g. the I/O port address, its resource
+pointer, or the irq number, is stored in the chip-specific record.
+
+::
+
+ struct mychip {
+ ....
+ };
+
+
+In general, there are two ways of allocating the chip record.
+
+1. Allocating via :c:func:`snd_card_new()`.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+As mentioned above, you can pass the extra-data-length to the 5th
+argument of :c:func:`snd_card_new()`, i.e.
+
+::
+
+ err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
+ sizeof(struct mychip), &card);
+
+:c:type:`struct mychip <mychip>` is the type of the chip record.
+
+In return, the allocated record can be accessed as
+
+::
+
+ struct mychip *chip = card->private_data;
+
+With this method, you don't have to allocate twice. The record is
+released together with the card instance.
+
+2. Allocating an extra device.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+After allocating a card instance via :c:func:`snd_card_new()`
+(with ``0`` on the 4th arg), call :c:func:`kzalloc()`.
+
+::
+
+ struct snd_card *card;
+ struct mychip *chip;
+ err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
+ 0, &card);
+ .....
+ chip = kzalloc(sizeof(*chip), GFP_KERNEL);
+
+The chip record should have the field to hold the card pointer at least,
+
+::
+
+ struct mychip {
+ struct snd_card *card;
+ ....
+ };
+
+
+Then, set the card pointer in the returned chip instance.
+
+::
+
+ chip->card = card;
+
+Next, initialize the fields, and register this chip record as a
+low-level device with a specified ``ops``,
+
+::
+
+ static struct snd_device_ops ops = {
+ .dev_free = snd_mychip_dev_free,
+ };
+ ....
+ snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
+
+:c:func:`snd_mychip_dev_free()` is the device-destructor
+function, which will call the real destructor.
+
+::
+
+ static int snd_mychip_dev_free(struct snd_device *device)
+ {
+ return snd_mychip_free(device->device_data);
+ }
+
+where :c:func:`snd_mychip_free()` is the real destructor.
+
+Registration and Release
+------------------------
+
+After all components are assigned, register the card instance by calling
+:c:func:`snd_card_register()`. Access to the device files is
+enabled at this point. That is, before
+:c:func:`snd_card_register()` is called, the components are safely
+inaccessible from external side. If this call fails, exit the probe
+function after releasing the card via :c:func:`snd_card_free()`.
+
+For releasing the card instance, you can call simply
+:c:func:`snd_card_free()`. As mentioned earlier, all components
+are released automatically by this call.
+
+For a device which allows hotplugging, you can use
+:c:func:`snd_card_free_when_closed()`. This one will postpone
+the destruction until all devices are closed.
+
+PCI Resource Management
+=======================
+
+Full Code Example
+-----------------
+
+In this section, we'll complete the chip-specific constructor,
+destructor and PCI entries. Example code is shown first, below.
+
+::
+
+ struct mychip {
+ struct snd_card *card;
+ struct pci_dev *pci;
+
+ unsigned long port;
+ int irq;
+ };
+
+ static int snd_mychip_free(struct mychip *chip)
+ {
+ /* disable hardware here if any */
+ .... /* (not implemented in this document) */
+
+ /* release the irq */
+ if (chip->irq >= 0)
+ free_irq(chip->irq, chip);
+ /* release the I/O ports & memory */
+ pci_release_regions(chip->pci);
+ /* disable the PCI entry */
+ pci_disable_device(chip->pci);
+ /* release the data */
+ kfree(chip);
+ return 0;
+ }
+
+ /* chip-specific constructor */
+ static int snd_mychip_create(struct snd_card *card,
+ struct pci_dev *pci,
+ struct mychip **rchip)
+ {
+ struct mychip *chip;
+ int err;
+ static struct snd_device_ops ops = {
+ .dev_free = snd_mychip_dev_free,
+ };
+
+ *rchip = NULL;
+
+ /* initialize the PCI entry */
+ err = pci_enable_device(pci);
+ if (err < 0)
+ return err;
+ /* check PCI availability (28bit DMA) */
+ if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 ||
+ pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) {
+ printk(KERN_ERR "error to set 28bit mask DMA\n");
+ pci_disable_device(pci);
+ return -ENXIO;
+ }
+
+ chip = kzalloc(sizeof(*chip), GFP_KERNEL);
+ if (chip == NULL) {
+ pci_disable_device(pci);
+ return -ENOMEM;
+ }
+
+ /* initialize the stuff */
+ chip->card = card;
+ chip->pci = pci;
+ chip->irq = -1;
+
+ /* (1) PCI resource allocation */
+ err = pci_request_regions(pci, "My Chip");
+ if (err < 0) {
+ kfree(chip);
+ pci_disable_device(pci);
+ return err;
+ }
+ chip->port = pci_resource_start(pci, 0);
+ if (request_irq(pci->irq, snd_mychip_interrupt,
+ IRQF_SHARED, KBUILD_MODNAME, chip)) {
+ printk(KERN_ERR "cannot grab irq %d\n", pci->irq);
+ snd_mychip_free(chip);
+ return -EBUSY;
+ }
+ chip->irq = pci->irq;
+
+ /* (2) initialization of the chip hardware */
+ .... /* (not implemented in this document) */
+
+ err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops);
+ if (err < 0) {
+ snd_mychip_free(chip);
+ return err;
+ }
+
+ *rchip = chip;
+ return 0;
+ }
+
+ /* PCI IDs */
+ static struct pci_device_id snd_mychip_ids[] = {
+ { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR,
+ PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, },
+ ....
+ { 0, }
+ };
+ MODULE_DEVICE_TABLE(pci, snd_mychip_ids);
+
+ /* pci_driver definition */
+ static struct pci_driver driver = {
+ .name = KBUILD_MODNAME,
+ .id_table = snd_mychip_ids,
+ .probe = snd_mychip_probe,
+ .remove = snd_mychip_remove,
+ };
+
+ /* module initialization */
+ static int __init alsa_card_mychip_init(void)
+ {
+ return pci_register_driver(&driver);
+ }
+
+ /* module clean up */
+ static void __exit alsa_card_mychip_exit(void)
+ {
+ pci_unregister_driver(&driver);
+ }
+
+ module_init(alsa_card_mychip_init)
+ module_exit(alsa_card_mychip_exit)
+
+ EXPORT_NO_SYMBOLS; /* for old kernels only */
+
+Some Hafta's
+------------
+
+The allocation of PCI resources is done in the ``probe`` function, and
+usually an extra :c:func:`xxx_create()` function is written for this
+purpose.
+
+In the case of PCI devices, you first have to call the
+:c:func:`pci_enable_device()` function before allocating
+resources. Also, you need to set the proper PCI DMA mask to limit the
+accessed I/O range. In some cases, you might need to call
+:c:func:`pci_set_master()` function, too.
+
+Suppose the 28bit mask, and the code to be added would be like:
+
+::
+
+ err = pci_enable_device(pci);
+ if (err < 0)
+ return err;
+ if (pci_set_dma_mask(pci, DMA_BIT_MASK(28)) < 0 ||
+ pci_set_consistent_dma_mask(pci, DMA_BIT_MASK(28)) < 0) {
+ printk(KERN_ERR "error to set 28bit mask DMA\n");
+ pci_disable_device(pci);
+ return -ENXIO;
+ }
+
+
+Resource Allocation
+-------------------
+
+The allocation of I/O ports and irqs is done via standard kernel
+functions. Unlike ALSA ver.0.5.x., there are no helpers for that. And
+these resources must be released in the destructor function (see below).
+Also, on ALSA 0.9.x, you don't need to allocate (pseudo-)DMA for PCI
+like in ALSA 0.5.x.
+
+Now assume that the PCI device has an I/O port with 8 bytes and an
+interrupt. Then :c:type:`struct mychip <mychip>` will have the
+following fields:
+
+::
+
+ struct mychip {
+ struct snd_card *card;
+
+ unsigned long port;
+ int irq;
+ };
+
+
+For an I/O port (and also a memory region), you need to have the
+resource pointer for the standard resource management. For an irq, you
+have to keep only the irq number (integer). But you need to initialize
+this number as -1 before actual allocation, since irq 0 is valid. The
+port address and its resource pointer can be initialized as null by
+:c:func:`kzalloc()` automatically, so you don't have to take care of
+resetting them.
+
+The allocation of an I/O port is done like this:
+
+::
+
+ err = pci_request_regions(pci, "My Chip");
+ if (err < 0) {
+ kfree(chip);
+ pci_disable_device(pci);
+ return err;
+ }
+ chip->port = pci_resource_start(pci, 0);
+
+It will reserve the I/O port region of 8 bytes of the given PCI device.
+The returned value, ``chip->res_port``, is allocated via
+:c:func:`kmalloc()` by :c:func:`request_region()`. The pointer
+must be released via :c:func:`kfree()`, but there is a problem with
+this. This issue will be explained later.
+
+The allocation of an interrupt source is done like this:
+
+::
+
+ if (request_irq(pci->irq, snd_mychip_interrupt,
+ IRQF_SHARED, KBUILD_MODNAME, chip)) {
+ printk(KERN_ERR "cannot grab irq %d\n", pci->irq);
+ snd_mychip_free(chip);
+ return -EBUSY;
+ }
+ chip->irq = pci->irq;
+
+where :c:func:`snd_mychip_interrupt()` is the interrupt handler
+defined `later <#pcm-interface-interrupt-handler>`__. Note that
+``chip->irq`` should be defined only when :c:func:`request_irq()`
+succeeded.
+
+On the PCI bus, interrupts can be shared. Thus, ``IRQF_SHARED`` is used
+as the interrupt flag of :c:func:`request_irq()`.
+
+The last argument of :c:func:`request_irq()` is the data pointer
+passed to the interrupt handler. Usually, the chip-specific record is
+used for that, but you can use what you like, too.
+
+I won't give details about the interrupt handler at this point, but at
+least its appearance can be explained now. The interrupt handler looks
+usually like the following:
+
+::
+
+ static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
+ {
+ struct mychip *chip = dev_id;
+ ....
+ return IRQ_HANDLED;
+ }
+
+
+Now let's write the corresponding destructor for the resources above.
+The role of destructor is simple: disable the hardware (if already
+activated) and release the resources. So far, we have no hardware part,
+so the disabling code is not written here.
+
+To release the resources, the “check-and-release” method is a safer way.
+For the interrupt, do like this:
+
+::
+
+ if (chip->irq >= 0)
+ free_irq(chip->irq, chip);
+
+Since the irq number can start from 0, you should initialize
+``chip->irq`` with a negative value (e.g. -1), so that you can check
+the validity of the irq number as above.
+
+When you requested I/O ports or memory regions via
+:c:func:`pci_request_region()` or
+:c:func:`pci_request_regions()` like in this example, release the
+resource(s) using the corresponding function,
+:c:func:`pci_release_region()` or
+:c:func:`pci_release_regions()`.
+
+::
+
+ pci_release_regions(chip->pci);
+
+When you requested manually via :c:func:`request_region()` or
+:c:func:`request_mem_region()`, you can release it via
+:c:func:`release_resource()`. Suppose that you keep the resource
+pointer returned from :c:func:`request_region()` in
+chip->res_port, the release procedure looks like:
+
+::
+
+ release_and_free_resource(chip->res_port);
+
+Don't forget to call :c:func:`pci_disable_device()` before the
+end.
+
+And finally, release the chip-specific record.
+
+::
+
+ kfree(chip);
+
+We didn't implement the hardware disabling part in the above. If you
+need to do this, please note that the destructor may be called even
+before the initialization of the chip is completed. It would be better
+to have a flag to skip hardware disabling if the hardware was not
+initialized yet.
+
+When the chip-data is assigned to the card using
+:c:func:`snd_device_new()` with ``SNDRV_DEV_LOWLELVEL`` , its
+destructor is called at the last. That is, it is assured that all other
+components like PCMs and controls have already been released. You don't
+have to stop PCMs, etc. explicitly, but just call low-level hardware
+stopping.
+
+The management of a memory-mapped region is almost as same as the
+management of an I/O port. You'll need three fields like the
+following:
+
+::
+
+ struct mychip {
+ ....
+ unsigned long iobase_phys;
+ void __iomem *iobase_virt;
+ };
+
+and the allocation would be like below:
+
+::
+
+ if ((err = pci_request_regions(pci, "My Chip")) < 0) {
+ kfree(chip);
+ return err;
+ }
+ chip->iobase_phys = pci_resource_start(pci, 0);
+ chip->iobase_virt = ioremap_nocache(chip->iobase_phys,
+ pci_resource_len(pci, 0));
+
+and the corresponding destructor would be:
+
+::
+
+ static int snd_mychip_free(struct mychip *chip)
+ {
+ ....
+ if (chip->iobase_virt)
+ iounmap(chip->iobase_virt);
+ ....
+ pci_release_regions(chip->pci);
+ ....
+ }
+
+PCI Entries
+-----------
+
+So far, so good. Let's finish the missing PCI stuff. At first, we need a
+:c:type:`struct pci_device_id <pci_device_id>` table for
+this chipset. It's a table of PCI vendor/device ID number, and some
+masks.
+
+For example,
+
+::
+
+ static struct pci_device_id snd_mychip_ids[] = {
+ { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR,
+ PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, },
+ ....
+ { 0, }
+ };
+ MODULE_DEVICE_TABLE(pci, snd_mychip_ids);
+
+The first and second fields of the :c:type:`struct pci_device_id
+<pci_device_id>` structure are the vendor and device IDs. If you
+have no reason to filter the matching devices, you can leave the
+remaining fields as above. The last field of the :c:type:`struct
+pci_device_id <pci_device_id>` struct contains private data
+for this entry. You can specify any value here, for example, to define
+specific operations for supported device IDs. Such an example is found
+in the intel8x0 driver.
+
+The last entry of this list is the terminator. You must specify this
+all-zero entry.
+
+Then, prepare the :c:type:`struct pci_driver <pci_driver>`
+record:
+
+::
+
+ static struct pci_driver driver = {
+ .name = KBUILD_MODNAME,
+ .id_table = snd_mychip_ids,
+ .probe = snd_mychip_probe,
+ .remove = snd_mychip_remove,
+ };
+
+The ``probe`` and ``remove`` functions have already been defined in
+the previous sections. The ``name`` field is the name string of this
+device. Note that you must not use a slash “/” in this string.
+
+And at last, the module entries:
+
+::
+
+ static int __init alsa_card_mychip_init(void)
+ {
+ return pci_register_driver(&driver);
+ }
+
+ static void __exit alsa_card_mychip_exit(void)
+ {
+ pci_unregister_driver(&driver);
+ }
+
+ module_init(alsa_card_mychip_init)
+ module_exit(alsa_card_mychip_exit)
+
+Note that these module entries are tagged with ``__init`` and ``__exit``
+prefixes.
+
+Oh, one thing was forgotten. If you have no exported symbols, you need
+to declare it in 2.2 or 2.4 kernels (it's not necessary in 2.6 kernels).
+
+::
+
+ EXPORT_NO_SYMBOLS;
+
+That's all!
+
+PCM Interface
+=============
+
+General
+-------
+
+The PCM middle layer of ALSA is quite powerful and it is only necessary
+for each driver to implement the low-level functions to access its
+hardware.
+
+For accessing to the PCM layer, you need to include ``<sound/pcm.h>``
+first. In addition, ``<sound/pcm_params.h>`` might be needed if you
+access to some functions related with hw_param.
+
+Each card device can have up to four pcm instances. A pcm instance
+corresponds to a pcm device file. The limitation of number of instances
+comes only from the available bit size of the Linux's device numbers.
+Once when 64bit device number is used, we'll have more pcm instances
+available.
+
+A pcm instance consists of pcm playback and capture streams, and each
+pcm stream consists of one or more pcm substreams. Some soundcards
+support multiple playback functions. For example, emu10k1 has a PCM
+playback of 32 stereo substreams. In this case, at each open, a free
+substream is (usually) automatically chosen and opened. Meanwhile, when
+only one substream exists and it was already opened, the successful open
+will either block or error with ``EAGAIN`` according to the file open
+mode. But you don't have to care about such details in your driver. The
+PCM middle layer will take care of such work.
+
+Full Code Example
+-----------------
+
+The example code below does not include any hardware access routines but
+shows only the skeleton, how to build up the PCM interfaces.
+
+::
+
+ #include <sound/pcm.h>
+ ....
+
+ /* hardware definition */
+ static struct snd_pcm_hardware snd_mychip_playback_hw = {
+ .info = (SNDRV_PCM_INFO_MMAP |
+ SNDRV_PCM_INFO_INTERLEAVED |
+ SNDRV_PCM_INFO_BLOCK_TRANSFER |
+ SNDRV_PCM_INFO_MMAP_VALID),
+ .formats = SNDRV_PCM_FMTBIT_S16_LE,
+ .rates = SNDRV_PCM_RATE_8000_48000,
+ .rate_min = 8000,
+ .rate_max = 48000,
+ .channels_min = 2,
+ .channels_max = 2,
+ .buffer_bytes_max = 32768,
+ .period_bytes_min = 4096,
+ .period_bytes_max = 32768,
+ .periods_min = 1,
+ .periods_max = 1024,
+ };
+
+ /* hardware definition */
+ static struct snd_pcm_hardware snd_mychip_capture_hw = {
+ .info = (SNDRV_PCM_INFO_MMAP |
+ SNDRV_PCM_INFO_INTERLEAVED |
+ SNDRV_PCM_INFO_BLOCK_TRANSFER |
+ SNDRV_PCM_INFO_MMAP_VALID),
+ .formats = SNDRV_PCM_FMTBIT_S16_LE,
+ .rates = SNDRV_PCM_RATE_8000_48000,
+ .rate_min = 8000,
+ .rate_max = 48000,
+ .channels_min = 2,
+ .channels_max = 2,
+ .buffer_bytes_max = 32768,
+ .period_bytes_min = 4096,
+ .period_bytes_max = 32768,
+ .periods_min = 1,
+ .periods_max = 1024,
+ };
+
+ /* open callback */
+ static int snd_mychip_playback_open(struct snd_pcm_substream *substream)
+ {
+ struct mychip *chip = snd_pcm_substream_chip(substream);
+ struct snd_pcm_runtime *runtime = substream->runtime;
+
+ runtime->hw = snd_mychip_playback_hw;
+ /* more hardware-initialization will be done here */
+ ....
+ return 0;
+ }
+
+ /* close callback */
+ static int snd_mychip_playback_close(struct snd_pcm_substream *substream)
+ {
+ struct mychip *chip = snd_pcm_substream_chip(substream);
+ /* the hardware-specific codes will be here */
+ ....
+ return 0;
+
+ }
+
+ /* open callback */
+ static int snd_mychip_capture_open(struct snd_pcm_substream *substream)
+ {
+ struct mychip *chip = snd_pcm_substream_chip(substream);
+ struct snd_pcm_runtime *runtime = substream->runtime;
+
+ runtime->hw = snd_mychip_capture_hw;
+ /* more hardware-initialization will be done here */
+ ....
+ return 0;
+ }
+
+ /* close callback */
+ static int snd_mychip_capture_close(struct snd_pcm_substream *substream)
+ {
+ struct mychip *chip = snd_pcm_substream_chip(substream);
+ /* the hardware-specific codes will be here */
+ ....
+ return 0;
+
+ }
+
+ /* hw_params callback */
+ static int snd_mychip_pcm_hw_params(struct snd_pcm_substream *substream,
+ struct snd_pcm_hw_params *hw_params)
+ {
+ return snd_pcm_lib_malloc_pages(substream,
+ params_buffer_bytes(hw_params));
+ }
+
+ /* hw_free callback */
+ static int snd_mychip_pcm_hw_free(struct snd_pcm_substream *substream)
+ {
+ return snd_pcm_lib_free_pages(substream);
+ }
+
+ /* prepare callback */
+ static int snd_mychip_pcm_prepare(struct snd_pcm_substream *substream)
+ {
+ struct mychip *chip = snd_pcm_substream_chip(substream);
+ struct snd_pcm_runtime *runtime = substream->runtime;
+
+ /* set up the hardware with the current configuration
+ * for example...
+ */
+ mychip_set_sample_format(chip, runtime->format);
+ mychip_set_sample_rate(chip, runtime->rate);
+ mychip_set_channels(chip, runtime->channels);
+ mychip_set_dma_setup(chip, runtime->dma_addr,
+ chip->buffer_size,
+ chip->period_size);
+ return 0;
+ }
+
+ /* trigger callback */
+ static int snd_mychip_pcm_trigger(struct snd_pcm_substream *substream,
+ int cmd)
+ {
+ switch (cmd) {
+ case SNDRV_PCM_TRIGGER_START:
+ /* do something to start the PCM engine */
+ ....
+ break;
+ case SNDRV_PCM_TRIGGER_STOP:
+ /* do something to stop the PCM engine */
+ ....
+ break;
+ default:
+ return -EINVAL;
+ }
+ }
+
+ /* pointer callback */
+ static snd_pcm_uframes_t
+ snd_mychip_pcm_pointer(struct snd_pcm_substream *substream)
+ {
+ struct mychip *chip = snd_pcm_substream_chip(substream);
+ unsigned int current_ptr;
+
+ /* get the current hardware pointer */
+ current_ptr = mychip_get_hw_pointer(chip);
+ return current_ptr;
+ }
+
+ /* operators */
+ static struct snd_pcm_ops snd_mychip_playback_ops = {
+ .open = snd_mychip_playback_open,
+ .close = snd_mychip_playback_close,
+ .ioctl = snd_pcm_lib_ioctl,
+ .hw_params = snd_mychip_pcm_hw_params,
+ .hw_free = snd_mychip_pcm_hw_free,
+ .prepare = snd_mychip_pcm_prepare,
+ .trigger = snd_mychip_pcm_trigger,
+ .pointer = snd_mychip_pcm_pointer,
+ };
+
+ /* operators */
+ static struct snd_pcm_ops snd_mychip_capture_ops = {
+ .open = snd_mychip_capture_open,
+ .close = snd_mychip_capture_close,
+ .ioctl = snd_pcm_lib_ioctl,
+ .hw_params = snd_mychip_pcm_hw_params,
+ .hw_free = snd_mychip_pcm_hw_free,
+ .prepare = snd_mychip_pcm_prepare,
+ .trigger = snd_mychip_pcm_trigger,
+ .pointer = snd_mychip_pcm_pointer,
+ };
+
+ /*
+ * definitions of capture are omitted here...
+ */
+
+ /* create a pcm device */
+ static int snd_mychip_new_pcm(struct mychip *chip)
+ {
+ struct snd_pcm *pcm;
+ int err;
+
+ err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
+ if (err < 0)
+ return err;
+ pcm->private_data = chip;
+ strcpy(pcm->name, "My Chip");
+ chip->pcm = pcm;
+ /* set operators */
+ snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
+ &snd_mychip_playback_ops);
+ snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
+ &snd_mychip_capture_ops);
+ /* pre-allocation of buffers */
+ /* NOTE: this may fail */
+ snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
+ snd_dma_pci_data(chip->pci),
+ 64*1024, 64*1024);
+ return 0;
+ }
+
+
+PCM Constructor
+---------------
+
+A pcm instance is allocated by the :c:func:`snd_pcm_new()`
+function. It would be better to create a constructor for pcm, namely,
+
+::
+
+ static int snd_mychip_new_pcm(struct mychip *chip)
+ {
+ struct snd_pcm *pcm;
+ int err;
+
+ err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm);
+ if (err < 0)
+ return err;
+ pcm->private_data = chip;
+ strcpy(pcm->name, "My Chip");
+ chip->pcm = pcm;
+ ....
+ return 0;
+ }
+
+The :c:func:`snd_pcm_new()` function takes four arguments. The
+first argument is the card pointer to which this pcm is assigned, and
+the second is the ID string.
+
+The third argument (``index``, 0 in the above) is the index of this new
+pcm. It begins from zero. If you create more than one pcm instances,
+specify the different numbers in this argument. For example, ``index =
+1`` for the second PCM device.
+
+The fourth and fifth arguments are the number of substreams for playback
+and capture, respectively. Here 1 is used for both arguments. When no
+playback or capture substreams are available, pass 0 to the
+corresponding argument.
+
+If a chip supports multiple playbacks or captures, you can specify more
+numbers, but they must be handled properly in open/close, etc.
+callbacks. When you need to know which substream you are referring to,
+then it can be obtained from :c:type:`struct snd_pcm_substream
+<snd_pcm_substream>` data passed to each callback as follows:
+
+::
+
+ struct snd_pcm_substream *substream;
+ int index = substream->number;
+
+
+After the pcm is created, you need to set operators for each pcm stream.
+
+::
+
+ snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
+ &snd_mychip_playback_ops);
+ snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
+ &snd_mychip_capture_ops);
+
+The operators are defined typically like this:
+
+::
+
+ static struct snd_pcm_ops snd_mychip_playback_ops = {
+ .open = snd_mychip_pcm_open,
+ .close = snd_mychip_pcm_close,
+ .ioctl = snd_pcm_lib_ioctl,
+ .hw_params = snd_mychip_pcm_hw_params,
+ .hw_free = snd_mychip_pcm_hw_free,
+ .prepare = snd_mychip_pcm_prepare,
+ .trigger = snd_mychip_pcm_trigger,
+ .pointer = snd_mychip_pcm_pointer,
+ };
+
+All the callbacks are described in the Operators_ subsection.
+
+After setting the operators, you probably will want to pre-allocate the
+buffer. For the pre-allocation, simply call the following:
+
+::
+
+ snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
+ snd_dma_pci_data(chip->pci),
+ 64*1024, 64*1024);
+
+It will allocate a buffer up to 64kB as default. Buffer management
+details will be described in the later section `Buffer and Memory
+Management`_.
+
+Additionally, you can set some extra information for this pcm in
+``pcm->info_flags``. The available values are defined as
+``SNDRV_PCM_INFO_XXX`` in ``<sound/asound.h>``, which is used for the
+hardware definition (described later). When your soundchip supports only
+half-duplex, specify like this:
+
+::
+
+ pcm->info_flags = SNDRV_PCM_INFO_HALF_DUPLEX;
+
+
+... And the Destructor?
+-----------------------
+
+The destructor for a pcm instance is not always necessary. Since the pcm
+device will be released by the middle layer code automatically, you
+don't have to call the destructor explicitly.
+
+The destructor would be necessary if you created special records
+internally and needed to release them. In such a case, set the
+destructor function to ``pcm->private_free``:
+
+::
+
+ static void mychip_pcm_free(struct snd_pcm *pcm)
+ {
+ struct mychip *chip = snd_pcm_chip(pcm);
+ /* free your own data */
+ kfree(chip->my_private_pcm_data);
+ /* do what you like else */
+ ....
+ }
+
+ static int snd_mychip_new_pcm(struct mychip *chip)
+ {
+ struct snd_pcm *pcm;
+ ....
+ /* allocate your own data */
+ chip->my_private_pcm_data = kmalloc(...);
+ /* set the destructor */
+ pcm->private_data = chip;
+ pcm->private_free = mychip_pcm_free;
+ ....
+ }
+
+
+
+Runtime Pointer - The Chest of PCM Information
+----------------------------------------------
+
+When the PCM substream is opened, a PCM runtime instance is allocated
+and assigned to the substream. This pointer is accessible via
+``substream->runtime``. This runtime pointer holds most information you
+need to control the PCM: the copy of hw_params and sw_params
+configurations, the buffer pointers, mmap records, spinlocks, etc.
+
+The definition of runtime instance is found in ``<sound/pcm.h>``. Here
+are the contents of this file:
+
+::
+
+ struct _snd_pcm_runtime {
+ /* -- Status -- */
+ struct snd_pcm_substream *trigger_master;
+ snd_timestamp_t trigger_tstamp; /* trigger timestamp */
+ int overrange;
+ snd_pcm_uframes_t avail_max;
+ snd_pcm_uframes_t hw_ptr_base; /* Position at buffer restart */
+ snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time*/
+
+ /* -- HW params -- */
+ snd_pcm_access_t access; /* access mode */
+ snd_pcm_format_t format; /* SNDRV_PCM_FORMAT_* */
+ snd_pcm_subformat_t subformat; /* subformat */
+ unsigned int rate; /* rate in Hz */
+ unsigned int channels; /* channels */
+ snd_pcm_uframes_t period_size; /* period size */
+ unsigned int periods; /* periods */
+ snd_pcm_uframes_t buffer_size; /* buffer size */
+ unsigned int tick_time; /* tick time */
+ snd_pcm_uframes_t min_align; /* Min alignment for the format */
+ size_t byte_align;
+ unsigned int frame_bits;
+ unsigned int sample_bits;
+ unsigned int info;
+ unsigned int rate_num;
+ unsigned int rate_den;
+
+ /* -- SW params -- */
+ struct timespec tstamp_mode; /* mmap timestamp is updated */
+ unsigned int period_step;
+ unsigned int sleep_min; /* min ticks to sleep */
+ snd_pcm_uframes_t start_threshold;
+ snd_pcm_uframes_t stop_threshold;
+ snd_pcm_uframes_t silence_threshold; /* Silence filling happens when
+ noise is nearest than this */
+ snd_pcm_uframes_t silence_size; /* Silence filling size */
+ snd_pcm_uframes_t boundary; /* pointers wrap point */
+
+ snd_pcm_uframes_t silenced_start;
+ snd_pcm_uframes_t silenced_size;
+
+ snd_pcm_sync_id_t sync; /* hardware synchronization ID */
+
+ /* -- mmap -- */
+ volatile struct snd_pcm_mmap_status *status;
+ volatile struct snd_pcm_mmap_control *control;
+ atomic_t mmap_count;
+
+ /* -- locking / scheduling -- */
+ spinlock_t lock;
+ wait_queue_head_t sleep;
+ struct timer_list tick_timer;
+ struct fasync_struct *fasync;
+
+ /* -- private section -- */
+ void *private_data;
+ void (*private_free)(struct snd_pcm_runtime *runtime);
+
+ /* -- hardware description -- */
+ struct snd_pcm_hardware hw;
+ struct snd_pcm_hw_constraints hw_constraints;
+
+ /* -- timer -- */
+ unsigned int timer_resolution; /* timer resolution */
+
+ /* -- DMA -- */
+ unsigned char *dma_area; /* DMA area */
+ dma_addr_t dma_addr; /* physical bus address (not accessible from main CPU) */
+ size_t dma_bytes; /* size of DMA area */
+
+ struct snd_dma_buffer *dma_buffer_p; /* allocated buffer */
+
+ #if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE)
+ /* -- OSS things -- */
+ struct snd_pcm_oss_runtime oss;
+ #endif
+ };
+
+
+For the operators (callbacks) of each sound driver, most of these
+records are supposed to be read-only. Only the PCM middle-layer changes
+/ updates them. The exceptions are the hardware description (hw) DMA
+buffer information and the private data. Besides, if you use the
+standard buffer allocation method via
+:c:func:`snd_pcm_lib_malloc_pages()`, you don't need to set the
+DMA buffer information by yourself.
+
+In the sections below, important records are explained.
+
+Hardware Description
+~~~~~~~~~~~~~~~~~~~~
+
+The hardware descriptor (:c:type:`struct snd_pcm_hardware
+<snd_pcm_hardware>`) contains the definitions of the fundamental
+hardware configuration. Above all, you'll need to define this in the
+`PCM open callback`_. Note that the runtime instance holds the copy of
+the descriptor, not the pointer to the existing descriptor. That is,
+in the open callback, you can modify the copied descriptor
+(``runtime->hw``) as you need. For example, if the maximum number of
+channels is 1 only on some chip models, you can still use the same
+hardware descriptor and change the channels_max later:
+
+::
+
+ struct snd_pcm_runtime *runtime = substream->runtime;
+ ...
+ runtime->hw = snd_mychip_playback_hw; /* common definition */
+ if (chip->model == VERY_OLD_ONE)
+ runtime->hw.channels_max = 1;
+
+Typically, you'll have a hardware descriptor as below:
+
+::
+
+ static struct snd_pcm_hardware snd_mychip_playback_hw = {
+ .info = (SNDRV_PCM_INFO_MMAP |
+ SNDRV_PCM_INFO_INTERLEAVED |
+ SNDRV_PCM_INFO_BLOCK_TRANSFER |
+ SNDRV_PCM_INFO_MMAP_VALID),
+ .formats = SNDRV_PCM_FMTBIT_S16_LE,
+ .rates = SNDRV_PCM_RATE_8000_48000,
+ .rate_min = 8000,
+ .rate_max = 48000,
+ .channels_min = 2,
+ .channels_max = 2,
+ .buffer_bytes_max = 32768,
+ .period_bytes_min = 4096,
+ .period_bytes_max = 32768,
+ .periods_min = 1,
+ .periods_max = 1024,
+ };
+
+- The ``info`` field contains the type and capabilities of this
+ pcm. The bit flags are defined in ``<sound/asound.h>`` as
+ ``SNDRV_PCM_INFO_XXX``. Here, at least, you have to specify whether
+ the mmap is supported and which interleaved format is
+ supported. When the hardware supports mmap, add the
+ ``SNDRV_PCM_INFO_MMAP`` flag here. When the hardware supports the
+ interleaved or the non-interleaved formats,
+ ``SNDRV_PCM_INFO_INTERLEAVED`` or ``SNDRV_PCM_INFO_NONINTERLEAVED``
+ flag must be set, respectively. If both are supported, you can set
+ both, too.
+
+ In the above example, ``MMAP_VALID`` and ``BLOCK_TRANSFER`` are
+ specified for the OSS mmap mode. Usually both are set. Of course,
+ ``MMAP_VALID`` is set only if the mmap is really supported.
+
+ The other possible flags are ``SNDRV_PCM_INFO_PAUSE`` and
+ ``SNDRV_PCM_INFO_RESUME``. The ``PAUSE`` bit means that the pcm
+ supports the “pause” operation, while the ``RESUME`` bit means that
+ the pcm supports the full “suspend/resume” operation. If the
+ ``PAUSE`` flag is set, the ``trigger`` callback below must handle
+ the corresponding (pause push/release) commands. The suspend/resume
+ trigger commands can be defined even without the ``RESUME``
+ flag. See `Power Management`_ section for details.
+
+ When the PCM substreams can be synchronized (typically,
+ synchronized start/stop of a playback and a capture streams), you
+ can give ``SNDRV_PCM_INFO_SYNC_START``, too. In this case, you'll
+ need to check the linked-list of PCM substreams in the trigger
+ callback. This will be described in the later section.
+
+- ``formats`` field contains the bit-flags of supported formats
+ (``SNDRV_PCM_FMTBIT_XXX``). If the hardware supports more than one
+ format, give all or'ed bits. In the example above, the signed 16bit
+ little-endian format is specified.
+
+- ``rates`` field contains the bit-flags of supported rates
+ (``SNDRV_PCM_RATE_XXX``). When the chip supports continuous rates,
+ pass ``CONTINUOUS`` bit additionally. The pre-defined rate bits are
+ provided only for typical rates. If your chip supports
+ unconventional rates, you need to add the ``KNOT`` bit and set up
+ the hardware constraint manually (explained later).
+
+- ``rate_min`` and ``rate_max`` define the minimum and maximum sample
+ rate. This should correspond somehow to ``rates`` bits.
+
+- ``channel_min`` and ``channel_max`` define, as you might already
+ expected, the minimum and maximum number of channels.
+
+- ``buffer_bytes_max`` defines the maximum buffer size in
+ bytes. There is no ``buffer_bytes_min`` field, since it can be
+ calculated from the minimum period size and the minimum number of
+ periods. Meanwhile, ``period_bytes_min`` and define the minimum and
+ maximum size of the period in bytes. ``periods_max`` and
+ ``periods_min`` define the maximum and minimum number of periods in
+ the buffer.
+
+ The “period” is a term that corresponds to a fragment in the OSS
+ world. The period defines the size at which a PCM interrupt is
+ generated. This size strongly depends on the hardware. Generally,
+ the smaller period size will give you more interrupts, that is,
+ more controls. In the case of capture, this size defines the input
+ latency. On the other hand, the whole buffer size defines the
+ output latency for the playback direction.
+
+- There is also a field ``fifo_size``. This specifies the size of the
+ hardware FIFO, but currently it is neither used in the driver nor
+ in the alsa-lib. So, you can ignore this field.
+
+PCM Configurations
+~~~~~~~~~~~~~~~~~~
+
+Ok, let's go back again to the PCM runtime records. The most
+frequently referred records in the runtime instance are the PCM
+configurations. The PCM configurations are stored in the runtime
+instance after the application sends ``hw_params`` data via
+alsa-lib. There are many fields copied from hw_params and sw_params
+structs. For example, ``format`` holds the format type chosen by the
+application. This field contains the enum value
+``SNDRV_PCM_FORMAT_XXX``.
+
+One thing to be noted is that the configured buffer and period sizes
+are stored in “frames” in the runtime. In the ALSA world, ``1 frame =
+channels \* samples-size``. For conversion between frames and bytes,
+you can use the :c:func:`frames_to_bytes()` and
+:c:func:`bytes_to_frames()` helper functions.
+
+::
+
+ period_bytes = frames_to_bytes(runtime, runtime->period_size);
+
+Also, many software parameters (sw_params) are stored in frames, too.
+Please check the type of the field. ``snd_pcm_uframes_t`` is for the
+frames as unsigned integer while ``snd_pcm_sframes_t`` is for the
+frames as signed integer.
+
+DMA Buffer Information
+~~~~~~~~~~~~~~~~~~~~~~
+
+The DMA buffer is defined by the following four fields, ``dma_area``,
+``dma_addr``, ``dma_bytes`` and ``dma_private``. The ``dma_area``
+holds the buffer pointer (the logical address). You can call
+:c:func:`memcpy()` from/to this pointer. Meanwhile, ``dma_addr`` holds
+the physical address of the buffer. This field is specified only when
+the buffer is a linear buffer. ``dma_bytes`` holds the size of buffer
+in bytes. ``dma_private`` is used for the ALSA DMA allocator.
+
+If you use a standard ALSA function,
+:c:func:`snd_pcm_lib_malloc_pages()`, for allocating the buffer,
+these fields are set by the ALSA middle layer, and you should *not*
+change them by yourself. You can read them but not write them. On the
+other hand, if you want to allocate the buffer by yourself, you'll
+need to manage it in hw_params callback. At least, ``dma_bytes`` is
+mandatory. ``dma_area`` is necessary when the buffer is mmapped. If
+your driver doesn't support mmap, this field is not
+necessary. ``dma_addr`` is also optional. You can use dma_private as
+you like, too.
+
+Running Status
+~~~~~~~~~~~~~~
+
+The running status can be referred via ``runtime->status``. This is
+the pointer to the :c:type:`struct snd_pcm_mmap_status
+<snd_pcm_mmap_status>` record. For example, you can get the current
+DMA hardware pointer via ``runtime->status->hw_ptr``.
+
+The DMA application pointer can be referred via ``runtime->control``,
+which points to the :c:type:`struct snd_pcm_mmap_control
+<snd_pcm_mmap_control>` record. However, accessing directly to
+this value is not recommended.
+
+Private Data
+~~~~~~~~~~~~
+
+You can allocate a record for the substream and store it in
+``runtime->private_data``. Usually, this is done in the `PCM open
+callback`_. Don't mix this with ``pcm->private_data``. The
+``pcm->private_data`` usually points to the chip instance assigned
+statically at the creation of PCM, while the ``runtime->private_data``
+points to a dynamic data structure created at the PCM open
+callback.
+
+::
+
+ static int snd_xxx_open(struct snd_pcm_substream *substream)
+ {
+ struct my_pcm_data *data;
+ ....
+ data = kmalloc(sizeof(*data), GFP_KERNEL);
+ substream->runtime->private_data = data;
+ ....
+ }
+
+
+The allocated object must be released in the `close callback`_.
+
+Operators
+---------
+
+OK, now let me give details about each pcm callback (``ops``). In
+general, every callback must return 0 if successful, or a negative
+error number such as ``-EINVAL``. To choose an appropriate error
+number, it is advised to check what value other parts of the kernel
+return when the same kind of request fails.
+
+The callback function takes at least the argument with :c:type:`struct
+snd_pcm_substream <snd_pcm_substream>` pointer. To retrieve the chip
+record from the given substream instance, you can use the following
+macro.
+
+::
+
+ int xxx() {
+ struct mychip *chip = snd_pcm_substream_chip(substream);
+ ....
+ }
+
+The macro reads ``substream->private_data``, which is a copy of
+``pcm->private_data``. You can override the former if you need to
+assign different data records per PCM substream. For example, the
+cmi8330 driver assigns different ``private_data`` for playback and
+capture directions, because it uses two different codecs (SB- and
+AD-compatible) for different directions.
+
+PCM open callback
+~~~~~~~~~~~~~~~~~
+
+::
+
+ static int snd_xxx_open(struct snd_pcm_substream *substream);
+
+This is called when a pcm substream is opened.
+
+At least, here you have to initialize the ``runtime->hw``
+record. Typically, this is done by like this:
+
+::
+
+ static int snd_xxx_open(struct snd_pcm_substream *substream)
+ {
+ struct mychip *chip = snd_pcm_substream_chip(substream);
+ struct snd_pcm_runtime *runtime = substream->runtime;
+
+ runtime->hw = snd_mychip_playback_hw;
+ return 0;
+ }
+
+where ``snd_mychip_playback_hw`` is the pre-defined hardware
+description.
+
+You can allocate a private data in this callback, as described in
+`Private Data`_ section.
+
+If the hardware configuration needs more constraints, set the hardware
+constraints here, too. See Constraints_ for more details.
+
+close callback
+~~~~~~~~~~~~~~
+
+::
+
+ static int snd_xxx_close(struct snd_pcm_substream *substream);
+
+
+Obviously, this is called when a pcm substream is closed.
+
+Any private instance for a pcm substream allocated in the ``open``
+callback will be released here.
+
+::
+
+ static int snd_xxx_close(struct snd_pcm_substream *substream)
+ {
+ ....
+ kfree(substream->runtime->private_data);
+ ....
+ }
+
+ioctl callback
+~~~~~~~~~~~~~~
+
+This is used for any special call to pcm ioctls. But usually you can
+pass a generic ioctl callback, :c:func:`snd_pcm_lib_ioctl()`.
+
+hw_params callback
+~~~~~~~~~~~~~~~~~~~
+
+::
+
+ static int snd_xxx_hw_params(struct snd_pcm_substream *substream,
+ struct snd_pcm_hw_params *hw_params);
+
+This is called when the hardware parameter (``hw_params``) is set up
+by the application, that is, once when the buffer size, the period
+size, the format, etc. are defined for the pcm substream.
+
+Many hardware setups should be done in this callback, including the
+allocation of buffers.
+
+Parameters to be initialized are retrieved by
+:c:func:`params_xxx()` macros. To allocate buffer, you can call a
+helper function,
+
+::
+
+ snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(hw_params));
+
+:c:func:`snd_pcm_lib_malloc_pages()` is available only when the
+DMA buffers have been pre-allocated. See the section `Buffer Types`_
+for more details.
+
+Note that this and ``prepare`` callbacks may be called multiple times
+per initialization. For example, the OSS emulation may call these
+callbacks at each change via its ioctl.
+
+Thus, you need to be careful not to allocate the same buffers many
+times, which will lead to memory leaks! Calling the helper function
+above many times is OK. It will release the previous buffer
+automatically when it was already allocated.
+
+Another note is that this callback is non-atomic (schedulable) as
+default, i.e. when no ``nonatomic`` flag set. This is important,
+because the ``trigger`` callback is atomic (non-schedulable). That is,
+mutexes or any schedule-related functions are not available in
+``trigger`` callback. Please see the subsection Atomicity_ for
+details.
+
+hw_free callback
+~~~~~~~~~~~~~~~~~
+
+::
+
+ static int snd_xxx_hw_free(struct snd_pcm_substream *substream);
+
+This is called to release the resources allocated via
+``hw_params``. For example, releasing the buffer via
+:c:func:`snd_pcm_lib_malloc_pages()` is done by calling the
+following:
+
+::
+
+ snd_pcm_lib_free_pages(substream);
+
+This function is always called before the close callback is called.
+Also, the callback may be called multiple times, too. Keep track
+whether the resource was already released.
+
+prepare callback
+~~~~~~~~~~~~~~~~
+
+::
+
+ static int snd_xxx_prepare(struct snd_pcm_substream *substream);
+
+This callback is called when the pcm is “prepared”. You can set the
+format type, sample rate, etc. here. The difference from ``hw_params``
+is that the ``prepare`` callback will be called each time
+:c:func:`snd_pcm_prepare()` is called, i.e. when recovering after
+underruns, etc.
+
+Note that this callback is now non-atomic. You can use
+schedule-related functions safely in this callback.
+
+In this and the following callbacks, you can refer to the values via
+the runtime record, ``substream->runtime``. For example, to get the
+current rate, format or channels, access to ``runtime->rate``,
+``runtime->format`` or ``runtime->channels``, respectively. The
+physical address of the allocated buffer is set to
+``runtime->dma_area``. The buffer and period sizes are in
+``runtime->buffer_size`` and ``runtime->period_size``, respectively.
+
+Be careful that this callback will be called many times at each setup,
+too.
+
+trigger callback
+~~~~~~~~~~~~~~~~
+
+::
+
+ static int snd_xxx_trigger(struct snd_pcm_substream *substream, int cmd);
+
+This is called when the pcm is started, stopped or paused.
+
+Which action is specified in the second argument,
+``SNDRV_PCM_TRIGGER_XXX`` in ``<sound/pcm.h>``. At least, the ``START``
+and ``STOP`` commands must be defined in this callback.
+
+::
+
+ switch (cmd) {
+ case SNDRV_PCM_TRIGGER_START:
+ /* do something to start the PCM engine */
+ break;
+ case SNDRV_PCM_TRIGGER_STOP:
+ /* do something to stop the PCM engine */
+ break;
+ default:
+ return -EINVAL;
+ }
+
+When the pcm supports the pause operation (given in the info field of
+the hardware table), the ``PAUSE_PUSH`` and ``PAUSE_RELEASE`` commands
+must be handled here, too. The former is the command to pause the pcm,
+and the latter to restart the pcm again.
+
+When the pcm supports the suspend/resume operation, regardless of full
+or partial suspend/resume support, the ``SUSPEND`` and ``RESUME``
+commands must be handled, too. These commands are issued when the
+power-management status is changed. Obviously, the ``SUSPEND`` and
+``RESUME`` commands suspend and resume the pcm substream, and usually,
+they are identical to the ``STOP`` and ``START`` commands, respectively.
+See the `Power Management`_ section for details.
+
+As mentioned, this callback is atomic as default unless ``nonatomic``
+flag set, and you cannot call functions which may sleep. The
+``trigger`` callback should be as minimal as possible, just really
+triggering the DMA. The other stuff should be initialized
+``hw_params`` and ``prepare`` callbacks properly beforehand.
+
+pointer callback
+~~~~~~~~~~~~~~~~
+
+::
+
+ static snd_pcm_uframes_t snd_xxx_pointer(struct snd_pcm_substream *substream)
+
+This callback is called when the PCM middle layer inquires the current
+hardware position on the buffer. The position must be returned in
+frames, ranging from 0 to ``buffer_size - 1``.
+
+This is called usually from the buffer-update routine in the pcm
+middle layer, which is invoked when :c:func:`snd_pcm_period_elapsed()`
+is called in the interrupt routine. Then the pcm middle layer updates
+the position and calculates the available space, and wakes up the
+sleeping poll threads, etc.
+
+This callback is also atomic as default.
+
+copy and silence callbacks
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+These callbacks are not mandatory, and can be omitted in most cases.
+These callbacks are used when the hardware buffer cannot be in the
+normal memory space. Some chips have their own buffer on the hardware
+which is not mappable. In such a case, you have to transfer the data
+manually from the memory buffer to the hardware buffer. Or, if the
+buffer is non-contiguous on both physical and virtual memory spaces,
+these callbacks must be defined, too.
+
+If these two callbacks are defined, copy and set-silence operations
+are done by them. The detailed will be described in the later section
+`Buffer and Memory Management`_.
+
+ack callback
+~~~~~~~~~~~~
+
+This callback is also not mandatory. This callback is called when the
+``appl_ptr`` is updated in read or write operations. Some drivers like
+emu10k1-fx and cs46xx need to track the current ``appl_ptr`` for the
+internal buffer, and this callback is useful only for such a purpose.
+
+This callback is atomic as default.
+
+page callback
+~~~~~~~~~~~~~
+
+This callback is optional too. This callback is used mainly for
+non-contiguous buffers. The mmap calls this callback to get the page
+address. Some examples will be explained in the later section `Buffer
+and Memory Management`_, too.
+
+PCM Interrupt Handler
+---------------------
+
+The rest of pcm stuff is the PCM interrupt handler. The role of PCM
+interrupt handler in the sound driver is to update the buffer position
+and to tell the PCM middle layer when the buffer position goes across
+the prescribed period size. To inform this, call the
+:c:func:`snd_pcm_period_elapsed()` function.
+
+There are several types of sound chips to generate the interrupts.
+
+Interrupts at the period (fragment) boundary
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This is the most frequently found type: the hardware generates an
+interrupt at each period boundary. In this case, you can call
+:c:func:`snd_pcm_period_elapsed()` at each interrupt.
+
+:c:func:`snd_pcm_period_elapsed()` takes the substream pointer as
+its argument. Thus, you need to keep the substream pointer accessible
+from the chip instance. For example, define ``substream`` field in the
+chip record to hold the current running substream pointer, and set the
+pointer value at ``open`` callback (and reset at ``close`` callback).
+
+If you acquire a spinlock in the interrupt handler, and the lock is used
+in other pcm callbacks, too, then you have to release the lock before
+calling :c:func:`snd_pcm_period_elapsed()`, because
+:c:func:`snd_pcm_period_elapsed()` calls other pcm callbacks
+inside.
+
+Typical code would be like:
+
+::
+
+
+ static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
+ {
+ struct mychip *chip = dev_id;
+ spin_lock(&chip->lock);
+ ....
+ if (pcm_irq_invoked(chip)) {
+ /* call updater, unlock before it */
+ spin_unlock(&chip->lock);
+ snd_pcm_period_elapsed(chip->substream);
+ spin_lock(&chip->lock);
+ /* acknowledge the interrupt if necessary */
+ }
+ ....
+ spin_unlock(&chip->lock);
+ return IRQ_HANDLED;
+ }
+
+
+
+High frequency timer interrupts
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This happens when the hardware doesn't generate interrupts at the period
+boundary but issues timer interrupts at a fixed timer rate (e.g. es1968
+or ymfpci drivers). In this case, you need to check the current hardware
+position and accumulate the processed sample length at each interrupt.
+When the accumulated size exceeds the period size, call
+:c:func:`snd_pcm_period_elapsed()` and reset the accumulator.
+
+Typical code would be like the following.
+
+::
+
+
+ static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id)
+ {
+ struct mychip *chip = dev_id;
+ spin_lock(&chip->lock);
+ ....
+ if (pcm_irq_invoked(chip)) {
+ unsigned int last_ptr, size;
+ /* get the current hardware pointer (in frames) */
+ last_ptr = get_hw_ptr(chip);
+ /* calculate the processed frames since the
+ * last update
+ */
+ if (last_ptr < chip->last_ptr)
+ size = runtime->buffer_size + last_ptr
+ - chip->last_ptr;
+ else
+ size = last_ptr - chip->last_ptr;
+ /* remember the last updated point */
+ chip->last_ptr = last_ptr;
+ /* accumulate the size */
+ chip->size += size;
+ /* over the period boundary? */
+ if (chip->size >= runtime->period_size) {
+ /* reset the accumulator */
+ chip->size %= runtime->period_size;
+ /* call updater */
+ spin_unlock(&chip->lock);
+ snd_pcm_period_elapsed(substream);
+ spin_lock(&chip->lock);
+ }
+ /* acknowledge the interrupt if necessary */
+ }
+ ....
+ spin_unlock(&chip->lock);
+ return IRQ_HANDLED;
+ }
+
+
+
+On calling :c:func:`snd_pcm_period_elapsed()`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+In both cases, even if more than one period are elapsed, you don't have
+to call :c:func:`snd_pcm_period_elapsed()` many times. Call only
+once. And the pcm layer will check the current hardware pointer and
+update to the latest status.
+
+Atomicity
+---------
+
+One of the most important (and thus difficult to debug) problems in
+kernel programming are race conditions. In the Linux kernel, they are
+usually avoided via spin-locks, mutexes or semaphores. In general, if a
+race condition can happen in an interrupt handler, it has to be managed
+atomically, and you have to use a spinlock to protect the critical
+session. If the critical section is not in interrupt handler code and if
+taking a relatively long time to execute is acceptable, you should use
+mutexes or semaphores instead.
+
+As already seen, some pcm callbacks are atomic and some are not. For
+example, the ``hw_params`` callback is non-atomic, while ``trigger``
+callback is atomic. This means, the latter is called already in a
+spinlock held by the PCM middle layer. Please take this atomicity into
+account when you choose a locking scheme in the callbacks.
+
+In the atomic callbacks, you cannot use functions which may call
+:c:func:`schedule()` or go to :c:func:`sleep()`. Semaphores and
+mutexes can sleep, and hence they cannot be used inside the atomic
+callbacks (e.g. ``trigger`` callback). To implement some delay in such a
+callback, please use :c:func:`udelay()` or :c:func:`mdelay()`.
+
+All three atomic callbacks (trigger, pointer, and ack) are called with
+local interrupts disabled.
+
+The recent changes in PCM core code, however, allow all PCM operations
+to be non-atomic. This assumes that the all caller sides are in
+non-atomic contexts. For example, the function
+:c:func:`snd_pcm_period_elapsed()` is called typically from the
+interrupt handler. But, if you set up the driver to use a threaded
+interrupt handler, this call can be in non-atomic context, too. In such
+a case, you can set ``nonatomic`` filed of :c:type:`struct snd_pcm
+<snd_pcm>` object after creating it. When this flag is set, mutex
+and rwsem are used internally in the PCM core instead of spin and
+rwlocks, so that you can call all PCM functions safely in a non-atomic
+context.
+
+Constraints
+-----------
+
+If your chip supports unconventional sample rates, or only the limited
+samples, you need to set a constraint for the condition.
+
+For example, in order to restrict the sample rates in the some supported
+values, use :c:func:`snd_pcm_hw_constraint_list()`. You need to
+call this function in the open callback.
+
+::
+
+ static unsigned int rates[] =
+ {4000, 10000, 22050, 44100};
+ static struct snd_pcm_hw_constraint_list constraints_rates = {
+ .count = ARRAY_SIZE(rates),
+ .list = rates,
+ .mask = 0,
+ };
+
+ static int snd_mychip_pcm_open(struct snd_pcm_substream *substream)
+ {
+ int err;
+ ....
+ err = snd_pcm_hw_constraint_list(substream->runtime, 0,
+ SNDRV_PCM_HW_PARAM_RATE,
+ &constraints_rates);
+ if (err < 0)
+ return err;
+ ....
+ }
+
+
+
+There are many different constraints. Look at ``sound/pcm.h`` for a
+complete list. You can even define your own constraint rules. For
+example, let's suppose my_chip can manage a substream of 1 channel if
+and only if the format is ``S16_LE``, otherwise it supports any format
+specified in the :c:type:`struct snd_pcm_hardware
+<snd_pcm_hardware>` structure (or in any other
+constraint_list). You can build a rule like this:
+
+::
+
+ static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params,
+ struct snd_pcm_hw_rule *rule)
+ {
+ struct snd_interval *c = hw_param_interval(params,
+ SNDRV_PCM_HW_PARAM_CHANNELS);
+ struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
+ struct snd_interval ch;
+
+ snd_interval_any(&ch);
+ if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) {
+ ch.min = ch.max = 1;
+ ch.integer = 1;
+ return snd_interval_refine(c, &ch);
+ }
+ return 0;
+ }
+
+
+Then you need to call this function to add your rule:
+
+::
+
+ snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
+ hw_rule_channels_by_format, NULL,
+ SNDRV_PCM_HW_PARAM_FORMAT, -1);
+
+The rule function is called when an application sets the PCM format, and
+it refines the number of channels accordingly. But an application may
+set the number of channels before setting the format. Thus you also need
+to define the inverse rule:
+
+::
+
+ static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params,
+ struct snd_pcm_hw_rule *rule)
+ {
+ struct snd_interval *c = hw_param_interval(params,
+ SNDRV_PCM_HW_PARAM_CHANNELS);
+ struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
+ struct snd_mask fmt;
+
+ snd_mask_any(&fmt); /* Init the struct */
+ if (c->min < 2) {
+ fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE;
+ return snd_mask_refine(f, &fmt);
+ }
+ return 0;
+ }
+
+
+... and in the open callback:
+
+::
+
+ snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT,
+ hw_rule_format_by_channels, NULL,
+ SNDRV_PCM_HW_PARAM_CHANNELS, -1);
+
+I won't give more details here, rather I would like to say, “Luke, use
+the source.”
+
+Control Interface
+=================
+
+General
+-------
+
+The control interface is used widely for many switches, sliders, etc.
+which are accessed from user-space. Its most important use is the mixer
+interface. In other words, since ALSA 0.9.x, all the mixer stuff is
+implemented on the control kernel API.
+
+ALSA has a well-defined AC97 control module. If your chip supports only
+the AC97 and nothing else, you can skip this section.
+
+The control API is defined in ``<sound/control.h>``. Include this file
+if you want to add your own controls.
+
+Definition of Controls
+----------------------
+
+To create a new control, you need to define the following three
+callbacks: ``info``, ``get`` and ``put``. Then, define a
+:c:type:`struct snd_kcontrol_new <snd_kcontrol_new>` record, such as:
+
+::
+
+
+ static struct snd_kcontrol_new my_control = {
+ .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+ .name = "PCM Playback Switch",
+ .index = 0,
+ .access = SNDRV_CTL_ELEM_ACCESS_READWRITE,
+ .private_value = 0xffff,
+ .info = my_control_info,
+ .get = my_control_get,
+ .put = my_control_put
+ };
+
+
+The ``iface`` field specifies the control type,
+``SNDRV_CTL_ELEM_IFACE_XXX``, which is usually ``MIXER``. Use ``CARD``
+for global controls that are not logically part of the mixer. If the
+control is closely associated with some specific device on the sound
+card, use ``HWDEP``, ``PCM``, ``RAWMIDI``, ``TIMER``, or ``SEQUENCER``,
+and specify the device number with the ``device`` and ``subdevice``
+fields.
+
+The ``name`` is the name identifier string. Since ALSA 0.9.x, the
+control name is very important, because its role is classified from
+its name. There are pre-defined standard control names. The details
+are described in the `Control Names`_ subsection.
+
+The ``index`` field holds the index number of this control. If there
+are several different controls with the same name, they can be
+distinguished by the index number. This is the case when several
+codecs exist on the card. If the index is zero, you can omit the
+definition above.
+
+The ``access`` field contains the access type of this control. Give
+the combination of bit masks, ``SNDRV_CTL_ELEM_ACCESS_XXX``,
+there. The details will be explained in the `Access Flags`_
+subsection.
+
+The ``private_value`` field contains an arbitrary long integer value
+for this record. When using the generic ``info``, ``get`` and ``put``
+callbacks, you can pass a value through this field. If several small
+numbers are necessary, you can combine them in bitwise. Or, it's
+possible to give a pointer (casted to unsigned long) of some record to
+this field, too.
+
+The ``tlv`` field can be used to provide metadata about the control;
+see the `Metadata`_ subsection.
+
+The other three are `Control Callbacks`_.
+
+Control Names
+-------------
+
+There are some standards to define the control names. A control is
+usually defined from the three parts as “SOURCE DIRECTION FUNCTION”.
+
+The first, ``SOURCE``, specifies the source of the control, and is a
+string such as “Master”, “PCM”, “CD” and “Line”. There are many
+pre-defined sources.
+
+The second, ``DIRECTION``, is one of the following strings according to
+the direction of the control: “Playback”, “Capture”, “Bypass Playback”
+and “Bypass Capture”. Or, it can be omitted, meaning both playback and
+capture directions.
+
+The third, ``FUNCTION``, is one of the following strings according to
+the function of the control: “Switch”, “Volume” and “Route”.
+
+The example of control names are, thus, “Master Capture Switch” or “PCM
+Playback Volume”.
+
+There are some exceptions:
+
+Global capture and playback
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+“Capture Source”, “Capture Switch” and “Capture Volume” are used for the
+global capture (input) source, switch and volume. Similarly, “Playback
+Switch” and “Playback Volume” are used for the global output gain switch
+and volume.
+
+Tone-controls
+~~~~~~~~~~~~~
+
+tone-control switch and volumes are specified like “Tone Control - XXX”,
+e.g. “Tone Control - Switch”, “Tone Control - Bass”, “Tone Control -
+Center”.
+
+3D controls
+~~~~~~~~~~~
+
+3D-control switches and volumes are specified like “3D Control - XXX”,
+e.g. “3D Control - Switch”, “3D Control - Center”, “3D Control - Space”.
+
+Mic boost
+~~~~~~~~~
+
+Mic-boost switch is set as “Mic Boost” or “Mic Boost (6dB)”.
+
+More precise information can be found in
+``Documentation/sound/alsa/ControlNames.txt``.
+
+Access Flags
+------------
+
+The access flag is the bitmask which specifies the access type of the
+given control. The default access type is
+``SNDRV_CTL_ELEM_ACCESS_READWRITE``, which means both read and write are
+allowed to this control. When the access flag is omitted (i.e. = 0), it
+is considered as ``READWRITE`` access as default.
+
+When the control is read-only, pass ``SNDRV_CTL_ELEM_ACCESS_READ``
+instead. In this case, you don't have to define the ``put`` callback.
+Similarly, when the control is write-only (although it's a rare case),
+you can use the ``WRITE`` flag instead, and you don't need the ``get``
+callback.
+
+If the control value changes frequently (e.g. the VU meter),
+``VOLATILE`` flag should be given. This means that the control may be
+changed without `Change notification`_. Applications should poll such
+a control constantly.
+
+When the control is inactive, set the ``INACTIVE`` flag, too. There are
+``LOCK`` and ``OWNER`` flags to change the write permissions.
+
+Control Callbacks
+-----------------
+
+info callback
+~~~~~~~~~~~~~
+
+The ``info`` callback is used to get detailed information on this
+control. This must store the values of the given :c:type:`struct
+snd_ctl_elem_info <snd_ctl_elem_info>` object. For example,
+for a boolean control with a single element:
+
+::
+
+
+ static int snd_myctl_mono_info(struct snd_kcontrol *kcontrol,
+ struct snd_ctl_elem_info *uinfo)
+ {
+ uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN;
+ uinfo->count = 1;
+ uinfo->value.integer.min = 0;
+ uinfo->value.integer.max = 1;
+ return 0;
+ }
+
+
+
+The ``type`` field specifies the type of the control. There are
+``BOOLEAN``, ``INTEGER``, ``ENUMERATED``, ``BYTES``, ``IEC958`` and
+``INTEGER64``. The ``count`` field specifies the number of elements in
+this control. For example, a stereo volume would have count = 2. The
+``value`` field is a union, and the values stored are depending on the
+type. The boolean and integer types are identical.
+
+The enumerated type is a bit different from others. You'll need to set
+the string for the currently given item index.
+
+::
+
+ static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol,
+ struct snd_ctl_elem_info *uinfo)
+ {
+ static char *texts[4] = {
+ "First", "Second", "Third", "Fourth"
+ };
+ uinfo->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED;
+ uinfo->count = 1;
+ uinfo->value.enumerated.items = 4;
+ if (uinfo->value.enumerated.item > 3)
+ uinfo->value.enumerated.item = 3;
+ strcpy(uinfo->value.enumerated.name,
+ texts[uinfo->value.enumerated.item]);
+ return 0;
+ }
+
+The above callback can be simplified with a helper function,
+:c:func:`snd_ctl_enum_info()`. The final code looks like below.
+(You can pass ``ARRAY_SIZE(texts)`` instead of 4 in the third argument;
+it's a matter of taste.)
+
+::
+
+ static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol,
+ struct snd_ctl_elem_info *uinfo)
+ {
+ static char *texts[4] = {
+ "First", "Second", "Third", "Fourth"
+ };
+ return snd_ctl_enum_info(uinfo, 1, 4, texts);
+ }
+
+
+Some common info callbacks are available for your convenience:
+:c:func:`snd_ctl_boolean_mono_info()` and
+:c:func:`snd_ctl_boolean_stereo_info()`. Obviously, the former
+is an info callback for a mono channel boolean item, just like
+:c:func:`snd_myctl_mono_info()` above, and the latter is for a
+stereo channel boolean item.
+
+get callback
+~~~~~~~~~~~~
+
+This callback is used to read the current value of the control and to
+return to user-space.
+
+For example,
+
+::
+
+
+ static int snd_myctl_get(struct snd_kcontrol *kcontrol,
+ struct snd_ctl_elem_value *ucontrol)
+ {
+ struct mychip *chip = snd_kcontrol_chip(kcontrol);
+ ucontrol->value.integer.value[0] = get_some_value(chip);
+ return 0;
+ }
+
+
+
+The ``value`` field depends on the type of control as well as on the
+info callback. For example, the sb driver uses this field to store the
+register offset, the bit-shift and the bit-mask. The ``private_value``
+field is set as follows:
+
+::
+
+ .private_value = reg | (shift << 16) | (mask << 24)
+
+and is retrieved in callbacks like
+
+::
+
+ static int snd_sbmixer_get_single(struct snd_kcontrol *kcontrol,
+ struct snd_ctl_elem_value *ucontrol)
+ {
+ int reg = kcontrol->private_value & 0xff;
+ int shift = (kcontrol->private_value >> 16) & 0xff;
+ int mask = (kcontrol->private_value >> 24) & 0xff;
+ ....
+ }
+
+In the ``get`` callback, you have to fill all the elements if the
+control has more than one elements, i.e. ``count > 1``. In the example
+above, we filled only one element (``value.integer.value[0]``) since
+it's assumed as ``count = 1``.
+
+put callback
+~~~~~~~~~~~~
+
+This callback is used to write a value from user-space.
+
+For example,
+
+::
+
+
+ static int snd_myctl_put(struct snd_kcontrol *kcontrol,
+ struct snd_ctl_elem_value *ucontrol)
+ {
+ struct mychip *chip = snd_kcontrol_chip(kcontrol);
+ int changed = 0;
+ if (chip->current_value !=
+ ucontrol->value.integer.value[0]) {
+ change_current_value(chip,
+ ucontrol->value.integer.value[0]);
+ changed = 1;
+ }
+ return changed;
+ }
+
+
+
+As seen above, you have to return 1 if the value is changed. If the
+value is not changed, return 0 instead. If any fatal error happens,
+return a negative error code as usual.
+
+As in the ``get`` callback, when the control has more than one
+elements, all elements must be evaluated in this callback, too.
+
+Callbacks are not atomic
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+All these three callbacks are basically not atomic.
+
+Control Constructor
+-------------------
+
+When everything is ready, finally we can create a new control. To create
+a control, there are two functions to be called,
+:c:func:`snd_ctl_new1()` and :c:func:`snd_ctl_add()`.
+
+In the simplest way, you can do like this:
+
+::
+
+ err = snd_ctl_add(card, snd_ctl_new1(&my_control, chip));
+ if (err < 0)
+ return err;
+
+where ``my_control`` is the :c:type:`struct snd_kcontrol_new
+<snd_kcontrol_new>` object defined above, and chip is the object
+pointer to be passed to kcontrol->private_data which can be referred
+to in callbacks.
+
+:c:func:`snd_ctl_new1()` allocates a new :c:type:`struct
+snd_kcontrol <snd_kcontrol>` instance, and
+:c:func:`snd_ctl_add()` assigns the given control component to the
+card.
+
+Change Notification
+-------------------
+
+If you need to change and update a control in the interrupt routine, you
+can call :c:func:`snd_ctl_notify()`. For example,
+
+::
+
+ snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, id_pointer);
+
+This function takes the card pointer, the event-mask, and the control id
+pointer for the notification. The event-mask specifies the types of
+notification, for example, in the above example, the change of control
+values is notified. The id pointer is the pointer of :c:type:`struct
+snd_ctl_elem_id <snd_ctl_elem_id>` to be notified. You can
+find some examples in ``es1938.c`` or ``es1968.c`` for hardware volume
+interrupts.
+
+Metadata
+--------
+
+To provide information about the dB values of a mixer control, use on of
+the ``DECLARE_TLV_xxx`` macros from ``<sound/tlv.h>`` to define a
+variable containing this information, set the ``tlv.p`` field to point to
+this variable, and include the ``SNDRV_CTL_ELEM_ACCESS_TLV_READ`` flag
+in the ``access`` field; like this:
+
+::
+
+ static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0);
+
+ static struct snd_kcontrol_new my_control = {
+ ...
+ .access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
+ SNDRV_CTL_ELEM_ACCESS_TLV_READ,
+ ...
+ .tlv.p = db_scale_my_control,
+ };
+
+
+The :c:func:`DECLARE_TLV_DB_SCALE()` macro defines information
+about a mixer control where each step in the control's value changes the
+dB value by a constant dB amount. The first parameter is the name of the
+variable to be defined. The second parameter is the minimum value, in
+units of 0.01 dB. The third parameter is the step size, in units of 0.01
+dB. Set the fourth parameter to 1 if the minimum value actually mutes
+the control.
+
+The :c:func:`DECLARE_TLV_DB_LINEAR()` macro defines information
+about a mixer control where the control's value affects the output
+linearly. The first parameter is the name of the variable to be defined.
+The second parameter is the minimum value, in units of 0.01 dB. The
+third parameter is the maximum value, in units of 0.01 dB. If the
+minimum value mutes the control, set the second parameter to
+``TLV_DB_GAIN_MUTE``.
+
+API for AC97 Codec
+==================
+
+General
+-------
+
+The ALSA AC97 codec layer is a well-defined one, and you don't have to
+write much code to control it. Only low-level control routines are
+necessary. The AC97 codec API is defined in ``<sound/ac97_codec.h>``.
+
+Full Code Example
+-----------------
+
+::
+
+ struct mychip {
+ ....
+ struct snd_ac97 *ac97;
+ ....
+ };
+
+ static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97,
+ unsigned short reg)
+ {
+ struct mychip *chip = ac97->private_data;
+ ....
+ /* read a register value here from the codec */
+ return the_register_value;
+ }
+
+ static void snd_mychip_ac97_write(struct snd_ac97 *ac97,
+ unsigned short reg, unsigned short val)
+ {
+ struct mychip *chip = ac97->private_data;
+ ....
+ /* write the given register value to the codec */
+ }
+
+ static int snd_mychip_ac97(struct mychip *chip)
+ {
+ struct snd_ac97_bus *bus;
+ struct snd_ac97_template ac97;
+ int err;
+ static struct snd_ac97_bus_ops ops = {
+ .write = snd_mychip_ac97_write,
+ .read = snd_mychip_ac97_read,
+ };
+
+ err = snd_ac97_bus(chip->card, 0, &ops, NULL, &bus);
+ if (err < 0)
+ return err;
+ memset(&ac97, 0, sizeof(ac97));
+ ac97.private_data = chip;
+ return snd_ac97_mixer(bus, &ac97, &chip->ac97);
+ }
+
+
+AC97 Constructor
+----------------
+
+To create an ac97 instance, first call :c:func:`snd_ac97_bus()`
+with an ``ac97_bus_ops_t`` record with callback functions.
+
+::
+
+ struct snd_ac97_bus *bus;
+ static struct snd_ac97_bus_ops ops = {
+ .write = snd_mychip_ac97_write,
+ .read = snd_mychip_ac97_read,
+ };
+
+ snd_ac97_bus(card, 0, &ops, NULL, &pbus);
+
+The bus record is shared among all belonging ac97 instances.
+
+And then call :c:func:`snd_ac97_mixer()` with an :c:type:`struct
+snd_ac97_template <snd_ac97_template>` record together with
+the bus pointer created above.
+
+::
+
+ struct snd_ac97_template ac97;
+ int err;
+
+ memset(&ac97, 0, sizeof(ac97));
+ ac97.private_data = chip;
+ snd_ac97_mixer(bus, &ac97, &chip->ac97);
+
+where chip->ac97 is a pointer to a newly created ``ac97_t``
+instance. In this case, the chip pointer is set as the private data,
+so that the read/write callback functions can refer to this chip
+instance. This instance is not necessarily stored in the chip
+record. If you need to change the register values from the driver, or
+need the suspend/resume of ac97 codecs, keep this pointer to pass to
+the corresponding functions.
+
+AC97 Callbacks
+--------------
+
+The standard callbacks are ``read`` and ``write``. Obviously they
+correspond to the functions for read and write accesses to the
+hardware low-level codes.
+
+The ``read`` callback returns the register value specified in the
+argument.
+
+::
+
+ static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97,
+ unsigned short reg)
+ {
+ struct mychip *chip = ac97->private_data;
+ ....
+ return the_register_value;
+ }
+
+Here, the chip can be cast from ``ac97->private_data``.
+
+Meanwhile, the ``write`` callback is used to set the register
+value
+
+::
+
+ static void snd_mychip_ac97_write(struct snd_ac97 *ac97,
+ unsigned short reg, unsigned short val)
+
+
+These callbacks are non-atomic like the control API callbacks.
+
+There are also other callbacks: ``reset``, ``wait`` and ``init``.
+
+The ``reset`` callback is used to reset the codec. If the chip
+requires a special kind of reset, you can define this callback.
+
+The ``wait`` callback is used to add some waiting time in the standard
+initialization of the codec. If the chip requires the extra waiting
+time, define this callback.
+
+The ``init`` callback is used for additional initialization of the
+codec.
+
+Updating Registers in The Driver
+--------------------------------
+
+If you need to access to the codec from the driver, you can call the
+following functions: :c:func:`snd_ac97_write()`,
+:c:func:`snd_ac97_read()`, :c:func:`snd_ac97_update()` and
+:c:func:`snd_ac97_update_bits()`.
+
+Both :c:func:`snd_ac97_write()` and
+:c:func:`snd_ac97_update()` functions are used to set a value to
+the given register (``AC97_XXX``). The difference between them is that
+:c:func:`snd_ac97_update()` doesn't write a value if the given
+value has been already set, while :c:func:`snd_ac97_write()`
+always rewrites the value.
+
+::
+
+ snd_ac97_write(ac97, AC97_MASTER, 0x8080);
+ snd_ac97_update(ac97, AC97_MASTER, 0x8080);
+
+:c:func:`snd_ac97_read()` is used to read the value of the given
+register. For example,
+
+::
+
+ value = snd_ac97_read(ac97, AC97_MASTER);
+
+:c:func:`snd_ac97_update_bits()` is used to update some bits in
+the given register.
+
+::
+
+ snd_ac97_update_bits(ac97, reg, mask, value);
+
+Also, there is a function to change the sample rate (of a given register
+such as ``AC97_PCM_FRONT_DAC_RATE``) when VRA or DRA is supported by the
+codec: :c:func:`snd_ac97_set_rate()`.
+
+::
+
+ snd_ac97_set_rate(ac97, AC97_PCM_FRONT_DAC_RATE, 44100);
+
+
+The following registers are available to set the rate:
+``AC97_PCM_MIC_ADC_RATE``, ``AC97_PCM_FRONT_DAC_RATE``,
+``AC97_PCM_LR_ADC_RATE``, ``AC97_SPDIF``. When ``AC97_SPDIF`` is
+specified, the register is not really changed but the corresponding
+IEC958 status bits will be updated.
+
+Clock Adjustment
+----------------
+
+In some chips, the clock of the codec isn't 48000 but using a PCI clock
+(to save a quartz!). In this case, change the field ``bus->clock`` to
+the corresponding value. For example, intel8x0 and es1968 drivers have
+their own function to read from the clock.
+
+Proc Files
+----------
+
+The ALSA AC97 interface will create a proc file such as
+``/proc/asound/card0/codec97#0/ac97#0-0`` and ``ac97#0-0+regs``. You
+can refer to these files to see the current status and registers of
+the codec.
+
+Multiple Codecs
+---------------
+
+When there are several codecs on the same card, you need to call
+:c:func:`snd_ac97_mixer()` multiple times with ``ac97.num=1`` or
+greater. The ``num`` field specifies the codec number.
+
+If you set up multiple codecs, you either need to write different
+callbacks for each codec or check ``ac97->num`` in the callback
+routines.
+
+MIDI (MPU401-UART) Interface
+============================
+
+General
+-------
+
+Many soundcards have built-in MIDI (MPU401-UART) interfaces. When the
+soundcard supports the standard MPU401-UART interface, most likely you
+can use the ALSA MPU401-UART API. The MPU401-UART API is defined in
+``<sound/mpu401.h>``.
+
+Some soundchips have a similar but slightly different implementation of
+mpu401 stuff. For example, emu10k1 has its own mpu401 routines.
+
+MIDI Constructor
+----------------
+
+To create a rawmidi object, call :c:func:`snd_mpu401_uart_new()`.
+
+::
+
+ struct snd_rawmidi *rmidi;
+ snd_mpu401_uart_new(card, 0, MPU401_HW_MPU401, port, info_flags,
+ irq, &rmidi);
+
+
+The first argument is the card pointer, and the second is the index of
+this component. You can create up to 8 rawmidi devices.
+
+The third argument is the type of the hardware, ``MPU401_HW_XXX``. If
+it's not a special one, you can use ``MPU401_HW_MPU401``.
+
+The 4th argument is the I/O port address. Many backward-compatible
+MPU401 have an I/O port such as 0x330. Or, it might be a part of its own
+PCI I/O region. It depends on the chip design.
+
+The 5th argument is a bitflag for additional information. When the I/O
+port address above is part of the PCI I/O region, the MPU401 I/O port
+might have been already allocated (reserved) by the driver itself. In
+such a case, pass a bit flag ``MPU401_INFO_INTEGRATED``, and the
+mpu401-uart layer will allocate the I/O ports by itself.
+
+When the controller supports only the input or output MIDI stream, pass
+the ``MPU401_INFO_INPUT`` or ``MPU401_INFO_OUTPUT`` bitflag,
+respectively. Then the rawmidi instance is created as a single stream.
+
+``MPU401_INFO_MMIO`` bitflag is used to change the access method to MMIO
+(via readb and writeb) instead of iob and outb. In this case, you have
+to pass the iomapped address to :c:func:`snd_mpu401_uart_new()`.
+
+When ``MPU401_INFO_TX_IRQ`` is set, the output stream isn't checked in
+the default interrupt handler. The driver needs to call
+:c:func:`snd_mpu401_uart_interrupt_tx()` by itself to start
+processing the output stream in the irq handler.
+
+If the MPU-401 interface shares its interrupt with the other logical
+devices on the card, set ``MPU401_INFO_IRQ_HOOK`` (see
+`below <#MIDI-Interrupt-Handler>`__).
+
+Usually, the port address corresponds to the command port and port + 1
+corresponds to the data port. If not, you may change the ``cport``
+field of :c:type:`struct snd_mpu401 <snd_mpu401>` manually afterward.
+However, :c:type:`struct snd_mpu401 <snd_mpu401>` pointer is
+not returned explicitly by :c:func:`snd_mpu401_uart_new()`. You
+need to cast ``rmidi->private_data`` to :c:type:`struct snd_mpu401
+<snd_mpu401>` explicitly,
+
+::
+
+ struct snd_mpu401 *mpu;
+ mpu = rmidi->private_data;
+
+and reset the ``cport`` as you like:
+
+::
+
+ mpu->cport = my_own_control_port;
+
+The 6th argument specifies the ISA irq number that will be allocated. If
+no interrupt is to be allocated (because your code is already allocating
+a shared interrupt, or because the device does not use interrupts), pass
+-1 instead. For a MPU-401 device without an interrupt, a polling timer
+will be used instead.
+
+MIDI Interrupt Handler
+----------------------
+
+When the interrupt is allocated in
+:c:func:`snd_mpu401_uart_new()`, an exclusive ISA interrupt
+handler is automatically used, hence you don't have anything else to do
+than creating the mpu401 stuff. Otherwise, you have to set
+``MPU401_INFO_IRQ_HOOK``, and call
+:c:func:`snd_mpu401_uart_interrupt()` explicitly from your own
+interrupt handler when it has determined that a UART interrupt has
+occurred.
+
+In this case, you need to pass the private_data of the returned rawmidi
+object from :c:func:`snd_mpu401_uart_new()` as the second
+argument of :c:func:`snd_mpu401_uart_interrupt()`.
+
+::
+
+ snd_mpu401_uart_interrupt(irq, rmidi->private_data, regs);
+
+
+RawMIDI Interface
+=================
+
+Overview
+--------
+
+The raw MIDI interface is used for hardware MIDI ports that can be
+accessed as a byte stream. It is not used for synthesizer chips that do
+not directly understand MIDI.
+
+ALSA handles file and buffer management. All you have to do is to write
+some code to move data between the buffer and the hardware.
+
+The rawmidi API is defined in ``<sound/rawmidi.h>``.
+
+RawMIDI Constructor
+-------------------
+
+To create a rawmidi device, call the :c:func:`snd_rawmidi_new()`
+function:
+
+::
+
+ struct snd_rawmidi *rmidi;
+ err = snd_rawmidi_new(chip->card, "MyMIDI", 0, outs, ins, &rmidi);
+ if (err < 0)
+ return err;
+ rmidi->private_data = chip;
+ strcpy(rmidi->name, "My MIDI");
+ rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT |
+ SNDRV_RAWMIDI_INFO_INPUT |
+ SNDRV_RAWMIDI_INFO_DUPLEX;
+
+The first argument is the card pointer, the second argument is the ID
+string.
+
+The third argument is the index of this component. You can create up to
+8 rawmidi devices.
+
+The fourth and fifth arguments are the number of output and input
+substreams, respectively, of this device (a substream is the equivalent
+of a MIDI port).
+
+Set the ``info_flags`` field to specify the capabilities of the
+device. Set ``SNDRV_RAWMIDI_INFO_OUTPUT`` if there is at least one
+output port, ``SNDRV_RAWMIDI_INFO_INPUT`` if there is at least one
+input port, and ``SNDRV_RAWMIDI_INFO_DUPLEX`` if the device can handle
+output and input at the same time.
+
+After the rawmidi device is created, you need to set the operators
+(callbacks) for each substream. There are helper functions to set the
+operators for all the substreams of a device:
+
+::
+
+ snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &snd_mymidi_output_ops);
+ snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_INPUT, &snd_mymidi_input_ops);
+
+The operators are usually defined like this:
+
+::
+
+ static struct snd_rawmidi_ops snd_mymidi_output_ops = {
+ .open = snd_mymidi_output_open,
+ .close = snd_mymidi_output_close,
+ .trigger = snd_mymidi_output_trigger,
+ };
+
+These callbacks are explained in the `RawMIDI Callbacks`_ section.
+
+If there are more than one substream, you should give a unique name to
+each of them:
+
+::
+
+ struct snd_rawmidi_substream *substream;
+ list_for_each_entry(substream,
+ &rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams,
+ list {
+ sprintf(substream->name, "My MIDI Port %d", substream->number + 1);
+ }
+ /* same for SNDRV_RAWMIDI_STREAM_INPUT */
+
+RawMIDI Callbacks
+-----------------
+
+In all the callbacks, the private data that you've set for the rawmidi
+device can be accessed as ``substream->rmidi->private_data``.
+
+If there is more than one port, your callbacks can determine the port
+index from the struct snd_rawmidi_substream data passed to each
+callback:
+
+::
+
+ struct snd_rawmidi_substream *substream;
+ int index = substream->number;
+
+RawMIDI open callback
+~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ static int snd_xxx_open(struct snd_rawmidi_substream *substream);
+
+
+This is called when a substream is opened. You can initialize the
+hardware here, but you shouldn't start transmitting/receiving data yet.
+
+RawMIDI close callback
+~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ static int snd_xxx_close(struct snd_rawmidi_substream *substream);
+
+Guess what.
+
+The ``open`` and ``close`` callbacks of a rawmidi device are
+serialized with a mutex, and can sleep.
+
+Rawmidi trigger callback for output substreams
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ static void snd_xxx_output_trigger(struct snd_rawmidi_substream *substream, int up);
+
+
+This is called with a nonzero ``up`` parameter when there is some data
+in the substream buffer that must be transmitted.
+
+To read data from the buffer, call
+:c:func:`snd_rawmidi_transmit_peek()`. It will return the number
+of bytes that have been read; this will be less than the number of bytes
+requested when there are no more data in the buffer. After the data have
+been transmitted successfully, call
+:c:func:`snd_rawmidi_transmit_ack()` to remove the data from the
+substream buffer:
+
+::
+
+ unsigned char data;
+ while (snd_rawmidi_transmit_peek(substream, &data, 1) == 1) {
+ if (snd_mychip_try_to_transmit(data))
+ snd_rawmidi_transmit_ack(substream, 1);
+ else
+ break; /* hardware FIFO full */
+ }
+
+If you know beforehand that the hardware will accept data, you can use
+the :c:func:`snd_rawmidi_transmit()` function which reads some
+data and removes them from the buffer at once:
+
+::
+
+ while (snd_mychip_transmit_possible()) {
+ unsigned char data;
+ if (snd_rawmidi_transmit(substream, &data, 1) != 1)
+ break; /* no more data */
+ snd_mychip_transmit(data);
+ }
+
+If you know beforehand how many bytes you can accept, you can use a
+buffer size greater than one with the
+:c:func:`snd_rawmidi_transmit\*()` functions.
+
+The ``trigger`` callback must not sleep. If the hardware FIFO is full
+before the substream buffer has been emptied, you have to continue
+transmitting data later, either in an interrupt handler, or with a
+timer if the hardware doesn't have a MIDI transmit interrupt.
+
+The ``trigger`` callback is called with a zero ``up`` parameter when
+the transmission of data should be aborted.
+
+RawMIDI trigger callback for input substreams
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ static void snd_xxx_input_trigger(struct snd_rawmidi_substream *substream, int up);
+
+
+This is called with a nonzero ``up`` parameter to enable receiving data,
+or with a zero ``up`` parameter do disable receiving data.
+
+The ``trigger`` callback must not sleep; the actual reading of data
+from the device is usually done in an interrupt handler.
+
+When data reception is enabled, your interrupt handler should call
+:c:func:`snd_rawmidi_receive()` for all received data:
+
+::
+
+ void snd_mychip_midi_interrupt(...)
+ {
+ while (mychip_midi_available()) {
+ unsigned char data;
+ data = mychip_midi_read();
+ snd_rawmidi_receive(substream, &data, 1);
+ }
+ }
+
+
+drain callback
+~~~~~~~~~~~~~~
+
+::
+
+ static void snd_xxx_drain(struct snd_rawmidi_substream *substream);
+
+
+This is only used with output substreams. This function should wait
+until all data read from the substream buffer have been transmitted.
+This ensures that the device can be closed and the driver unloaded
+without losing data.
+
+This callback is optional. If you do not set ``drain`` in the struct
+snd_rawmidi_ops structure, ALSA will simply wait for 50 milliseconds
+instead.
+
+Miscellaneous Devices
+=====================
+
+FM OPL3
+-------
+
+The FM OPL3 is still used in many chips (mainly for backward
+compatibility). ALSA has a nice OPL3 FM control layer, too. The OPL3 API
+is defined in ``<sound/opl3.h>``.
+
+FM registers can be directly accessed through the direct-FM API, defined
+in ``<sound/asound_fm.h>``. In ALSA native mode, FM registers are
+accessed through the Hardware-Dependent Device direct-FM extension API,
+whereas in OSS compatible mode, FM registers can be accessed with the
+OSS direct-FM compatible API in ``/dev/dmfmX`` device.
+
+To create the OPL3 component, you have two functions to call. The first
+one is a constructor for the ``opl3_t`` instance.
+
+::
+
+ struct snd_opl3 *opl3;
+ snd_opl3_create(card, lport, rport, OPL3_HW_OPL3_XXX,
+ integrated, &opl3);
+
+The first argument is the card pointer, the second one is the left port
+address, and the third is the right port address. In most cases, the
+right port is placed at the left port + 2.
+
+The fourth argument is the hardware type.
+
+When the left and right ports have been already allocated by the card
+driver, pass non-zero to the fifth argument (``integrated``). Otherwise,
+the opl3 module will allocate the specified ports by itself.
+
+When the accessing the hardware requires special method instead of the
+standard I/O access, you can create opl3 instance separately with
+:c:func:`snd_opl3_new()`.
+
+::
+
+ struct snd_opl3 *opl3;
+ snd_opl3_new(card, OPL3_HW_OPL3_XXX, &opl3);
+
+Then set ``command``, ``private_data`` and ``private_free`` for the
+private access function, the private data and the destructor. The
+``l_port`` and ``r_port`` are not necessarily set. Only the command
+must be set properly. You can retrieve the data from the
+``opl3->private_data`` field.
+
+After creating the opl3 instance via :c:func:`snd_opl3_new()`,
+call :c:func:`snd_opl3_init()` to initialize the chip to the
+proper state. Note that :c:func:`snd_opl3_create()` always calls
+it internally.
+
+If the opl3 instance is created successfully, then create a hwdep device
+for this opl3.
+
+::
+
+ struct snd_hwdep *opl3hwdep;
+ snd_opl3_hwdep_new(opl3, 0, 1, &opl3hwdep);
+
+The first argument is the ``opl3_t`` instance you created, and the
+second is the index number, usually 0.
+
+The third argument is the index-offset for the sequencer client assigned
+to the OPL3 port. When there is an MPU401-UART, give 1 for here (UART
+always takes 0).
+
+Hardware-Dependent Devices
+--------------------------
+
+Some chips need user-space access for special controls or for loading
+the micro code. In such a case, you can create a hwdep
+(hardware-dependent) device. The hwdep API is defined in
+``<sound/hwdep.h>``. You can find examples in opl3 driver or
+``isa/sb/sb16_csp.c``.
+
+The creation of the ``hwdep`` instance is done via
+:c:func:`snd_hwdep_new()`.
+
+::
+
+ struct snd_hwdep *hw;
+ snd_hwdep_new(card, "My HWDEP", 0, &hw);
+
+where the third argument is the index number.
+
+You can then pass any pointer value to the ``private_data``. If you
+assign a private data, you should define the destructor, too. The
+destructor function is set in the ``private_free`` field.
+
+::
+
+ struct mydata *p = kmalloc(sizeof(*p), GFP_KERNEL);
+ hw->private_data = p;
+ hw->private_free = mydata_free;
+
+and the implementation of the destructor would be:
+
+::
+
+ static void mydata_free(struct snd_hwdep *hw)
+ {
+ struct mydata *p = hw->private_data;
+ kfree(p);
+ }
+
+The arbitrary file operations can be defined for this instance. The file
+operators are defined in the ``ops`` table. For example, assume that
+this chip needs an ioctl.
+
+::
+
+ hw->ops.open = mydata_open;
+ hw->ops.ioctl = mydata_ioctl;
+ hw->ops.release = mydata_release;
+
+And implement the callback functions as you like.
+
+IEC958 (S/PDIF)
+---------------
+
+Usually the controls for IEC958 devices are implemented via the control
+interface. There is a macro to compose a name string for IEC958
+controls, :c:func:`SNDRV_CTL_NAME_IEC958()` defined in
+``<include/asound.h>``.
+
+There are some standard controls for IEC958 status bits. These controls
+use the type ``SNDRV_CTL_ELEM_TYPE_IEC958``, and the size of element is
+fixed as 4 bytes array (value.iec958.status[x]). For the ``info``
+callback, you don't specify the value field for this type (the count
+field must be set, though).
+
+“IEC958 Playback Con Mask” is used to return the bit-mask for the IEC958
+status bits of consumer mode. Similarly, “IEC958 Playback Pro Mask”
+returns the bitmask for professional mode. They are read-only controls,
+and are defined as MIXER controls (iface =
+``SNDRV_CTL_ELEM_IFACE_MIXER``).
+
+Meanwhile, “IEC958 Playback Default” control is defined for getting and
+setting the current default IEC958 bits. Note that this one is usually
+defined as a PCM control (iface = ``SNDRV_CTL_ELEM_IFACE_PCM``),
+although in some places it's defined as a MIXER control.
+
+In addition, you can define the control switches to enable/disable or to
+set the raw bit mode. The implementation will depend on the chip, but
+the control should be named as “IEC958 xxx”, preferably using the
+:c:func:`SNDRV_CTL_NAME_IEC958()` macro.
+
+You can find several cases, for example, ``pci/emu10k1``,
+``pci/ice1712``, or ``pci/cmipci.c``.
+
+Buffer and Memory Management
+============================
+
+Buffer Types
+------------
+
+ALSA provides several different buffer allocation functions depending on
+the bus and the architecture. All these have a consistent API. The
+allocation of physically-contiguous pages is done via
+:c:func:`snd_malloc_xxx_pages()` function, where xxx is the bus
+type.
+
+The allocation of pages with fallback is
+:c:func:`snd_malloc_xxx_pages_fallback()`. This function tries
+to allocate the specified pages but if the pages are not available, it
+tries to reduce the page sizes until enough space is found.
+
+The release the pages, call :c:func:`snd_free_xxx_pages()`
+function.
+
+Usually, ALSA drivers try to allocate and reserve a large contiguous
+physical space at the time the module is loaded for the later use. This
+is called “pre-allocation”. As already written, you can call the
+following function at pcm instance construction time (in the case of PCI
+bus).
+
+::
+
+ snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
+ snd_dma_pci_data(pci), size, max);
+
+where ``size`` is the byte size to be pre-allocated and the ``max`` is
+the maximum size to be changed via the ``prealloc`` proc file. The
+allocator will try to get an area as large as possible within the
+given size.
+
+The second argument (type) and the third argument (device pointer) are
+dependent on the bus. In the case of the ISA bus, pass
+:c:func:`snd_dma_isa_data()` as the third argument with
+``SNDRV_DMA_TYPE_DEV`` type. For the continuous buffer unrelated to the
+bus can be pre-allocated with ``SNDRV_DMA_TYPE_CONTINUOUS`` type and the
+``snd_dma_continuous_data(GFP_KERNEL)`` device pointer, where
+``GFP_KERNEL`` is the kernel allocation flag to use. For the PCI
+scatter-gather buffers, use ``SNDRV_DMA_TYPE_DEV_SG`` with
+``snd_dma_pci_data(pci)`` (see the `Non-Contiguous Buffers`_
+section).
+
+Once the buffer is pre-allocated, you can use the allocator in the
+``hw_params`` callback:
+
+::
+
+ snd_pcm_lib_malloc_pages(substream, size);
+
+Note that you have to pre-allocate to use this function.
+
+External Hardware Buffers
+-------------------------
+
+Some chips have their own hardware buffers and the DMA transfer from the
+host memory is not available. In such a case, you need to either 1)
+copy/set the audio data directly to the external hardware buffer, or 2)
+make an intermediate buffer and copy/set the data from it to the
+external hardware buffer in interrupts (or in tasklets, preferably).
+
+The first case works fine if the external hardware buffer is large
+enough. This method doesn't need any extra buffers and thus is more
+effective. You need to define the ``copy`` and ``silence`` callbacks
+for the data transfer. However, there is a drawback: it cannot be
+mmapped. The examples are GUS's GF1 PCM or emu8000's wavetable PCM.
+
+The second case allows for mmap on the buffer, although you have to
+handle an interrupt or a tasklet to transfer the data from the
+intermediate buffer to the hardware buffer. You can find an example in
+the vxpocket driver.
+
+Another case is when the chip uses a PCI memory-map region for the
+buffer instead of the host memory. In this case, mmap is available only
+on certain architectures like the Intel one. In non-mmap mode, the data
+cannot be transferred as in the normal way. Thus you need to define the
+``copy`` and ``silence`` callbacks as well, as in the cases above. The
+examples are found in ``rme32.c`` and ``rme96.c``.
+
+The implementation of the ``copy`` and ``silence`` callbacks depends
+upon whether the hardware supports interleaved or non-interleaved
+samples. The ``copy`` callback is defined like below, a bit
+differently depending whether the direction is playback or capture:
+
+::
+
+ static int playback_copy(struct snd_pcm_substream *substream, int channel,
+ snd_pcm_uframes_t pos, void *src, snd_pcm_uframes_t count);
+ static int capture_copy(struct snd_pcm_substream *substream, int channel,
+ snd_pcm_uframes_t pos, void *dst, snd_pcm_uframes_t count);
+
+In the case of interleaved samples, the second argument (``channel``) is
+not used. The third argument (``pos``) points the current position
+offset in frames.
+
+The meaning of the fourth argument is different between playback and
+capture. For playback, it holds the source data pointer, and for
+capture, it's the destination data pointer.
+
+The last argument is the number of frames to be copied.
+
+What you have to do in this callback is again different between playback
+and capture directions. In the playback case, you copy the given amount
+of data (``count``) at the specified pointer (``src``) to the specified
+offset (``pos``) on the hardware buffer. When coded like memcpy-like
+way, the copy would be like:
+
+::
+
+ my_memcpy(my_buffer + frames_to_bytes(runtime, pos), src,
+ frames_to_bytes(runtime, count));
+
+For the capture direction, you copy the given amount of data (``count``)
+at the specified offset (``pos``) on the hardware buffer to the
+specified pointer (``dst``).
+
+::
+
+ my_memcpy(dst, my_buffer + frames_to_bytes(runtime, pos),
+ frames_to_bytes(runtime, count));
+
+Note that both the position and the amount of data are given in frames.
+
+In the case of non-interleaved samples, the implementation will be a bit
+more complicated.
+
+You need to check the channel argument, and if it's -1, copy the whole
+channels. Otherwise, you have to copy only the specified channel. Please
+check ``isa/gus/gus_pcm.c`` as an example.
+
+The ``silence`` callback is also implemented in a similar way
+
+::
+
+ static int silence(struct snd_pcm_substream *substream, int channel,
+ snd_pcm_uframes_t pos, snd_pcm_uframes_t count);
+
+The meanings of arguments are the same as in the ``copy`` callback,
+although there is no ``src/dst`` argument. In the case of interleaved
+samples, the channel argument has no meaning, as well as on ``copy``
+callback.
+
+The role of ``silence`` callback is to set the given amount
+(``count``) of silence data at the specified offset (``pos``) on the
+hardware buffer. Suppose that the data format is signed (that is, the
+silent-data is 0), and the implementation using a memset-like function
+would be like:
+
+::
+
+ my_memcpy(my_buffer + frames_to_bytes(runtime, pos), 0,
+ frames_to_bytes(runtime, count));
+
+In the case of non-interleaved samples, again, the implementation
+becomes a bit more complicated. See, for example, ``isa/gus/gus_pcm.c``.
+
+Non-Contiguous Buffers
+----------------------
+
+If your hardware supports the page table as in emu10k1 or the buffer
+descriptors as in via82xx, you can use the scatter-gather (SG) DMA. ALSA
+provides an interface for handling SG-buffers. The API is provided in
+``<sound/pcm.h>``.
+
+For creating the SG-buffer handler, call
+:c:func:`snd_pcm_lib_preallocate_pages()` or
+:c:func:`snd_pcm_lib_preallocate_pages_for_all()` with
+``SNDRV_DMA_TYPE_DEV_SG`` in the PCM constructor like other PCI
+pre-allocator. You need to pass ``snd_dma_pci_data(pci)``, where pci is
+the :c:type:`struct pci_dev <pci_dev>` pointer of the chip as
+well. The ``struct snd_sg_buf`` instance is created as
+``substream->dma_private``. You can cast the pointer like:
+
+::
+
+ struct snd_sg_buf *sgbuf = (struct snd_sg_buf *)substream->dma_private;
+
+Then call :c:func:`snd_pcm_lib_malloc_pages()` in the ``hw_params``
+callback as well as in the case of normal PCI buffer. The SG-buffer
+handler will allocate the non-contiguous kernel pages of the given size
+and map them onto the virtually contiguous memory. The virtual pointer
+is addressed in runtime->dma_area. The physical address
+(``runtime->dma_addr``) is set to zero, because the buffer is
+physically non-contiguous. The physical address table is set up in
+``sgbuf->table``. You can get the physical address at a certain offset
+via :c:func:`snd_pcm_sgbuf_get_addr()`.
+
+When a SG-handler is used, you need to set
+:c:func:`snd_pcm_sgbuf_ops_page()` as the ``page`` callback. (See
+`page callback`_ section.)
+
+To release the data, call :c:func:`snd_pcm_lib_free_pages()` in
+the ``hw_free`` callback as usual.
+
+Vmalloc'ed Buffers
+------------------
+
+It's possible to use a buffer allocated via :c:func:`vmalloc()`, for
+example, for an intermediate buffer. Since the allocated pages are not
+contiguous, you need to set the ``page`` callback to obtain the physical
+address at every offset.
+
+The implementation of ``page`` callback would be like this:
+
+::
+
+ #include <linux/vmalloc.h>
+
+ /* get the physical page pointer on the given offset */
+ static struct page *mychip_page(struct snd_pcm_substream *substream,
+ unsigned long offset)
+ {
+ void *pageptr = substream->runtime->dma_area + offset;
+ return vmalloc_to_page(pageptr);
+ }
+
+Proc Interface
+==============
+
+ALSA provides an easy interface for procfs. The proc files are very
+useful for debugging. I recommend you set up proc files if you write a
+driver and want to get a running status or register dumps. The API is
+found in ``<sound/info.h>``.
+
+To create a proc file, call :c:func:`snd_card_proc_new()`.
+
+::
+
+ struct snd_info_entry *entry;
+ int err = snd_card_proc_new(card, "my-file", &entry);
+
+where the second argument specifies the name of the proc file to be
+created. The above example will create a file ``my-file`` under the
+card directory, e.g. ``/proc/asound/card0/my-file``.
+
+Like other components, the proc entry created via
+:c:func:`snd_card_proc_new()` will be registered and released
+automatically in the card registration and release functions.
+
+When the creation is successful, the function stores a new instance in
+the pointer given in the third argument. It is initialized as a text
+proc file for read only. To use this proc file as a read-only text file
+as it is, set the read callback with a private data via
+:c:func:`snd_info_set_text_ops()`.
+
+::
+
+ snd_info_set_text_ops(entry, chip, my_proc_read);
+
+where the second argument (``chip``) is the private data to be used in
+the callbacks. The third parameter specifies the read buffer size and
+the fourth (``my_proc_read``) is the callback function, which is
+defined like
+
+::
+
+ static void my_proc_read(struct snd_info_entry *entry,
+ struct snd_info_buffer *buffer);
+
+In the read callback, use :c:func:`snd_iprintf()` for output
+strings, which works just like normal :c:func:`printf()`. For
+example,
+
+::
+
+ static void my_proc_read(struct snd_info_entry *entry,
+ struct snd_info_buffer *buffer)
+ {
+ struct my_chip *chip = entry->private_data;
+
+ snd_iprintf(buffer, "This is my chip!\n");
+ snd_iprintf(buffer, "Port = %ld\n", chip->port);
+ }
+
+The file permissions can be changed afterwards. As default, it's set as
+read only for all users. If you want to add write permission for the
+user (root as default), do as follows:
+
+::
+
+ entry->mode = S_IFREG | S_IRUGO | S_IWUSR;
+
+and set the write buffer size and the callback
+
+::
+
+ entry->c.text.write = my_proc_write;
+
+For the write callback, you can use :c:func:`snd_info_get_line()`
+to get a text line, and :c:func:`snd_info_get_str()` to retrieve
+a string from the line. Some examples are found in
+``core/oss/mixer_oss.c``, core/oss/and ``pcm_oss.c``.
+
+For a raw-data proc-file, set the attributes as follows:
+
+::
+
+ static struct snd_info_entry_ops my_file_io_ops = {
+ .read = my_file_io_read,
+ };
+
+ entry->content = SNDRV_INFO_CONTENT_DATA;
+ entry->private_data = chip;
+ entry->c.ops = &my_file_io_ops;
+ entry->size = 4096;
+ entry->mode = S_IFREG | S_IRUGO;
+
+For the raw data, ``size`` field must be set properly. This specifies
+the maximum size of the proc file access.
+
+The read/write callbacks of raw mode are more direct than the text mode.
+You need to use a low-level I/O functions such as
+:c:func:`copy_from/to_user()` to transfer the data.
+
+::
+
+ static ssize_t my_file_io_read(struct snd_info_entry *entry,
+ void *file_private_data,
+ struct file *file,
+ char *buf,
+ size_t count,
+ loff_t pos)
+ {
+ if (copy_to_user(buf, local_data + pos, count))
+ return -EFAULT;
+ return count;
+ }
+
+If the size of the info entry has been set up properly, ``count`` and
+``pos`` are guaranteed to fit within 0 and the given size. You don't
+have to check the range in the callbacks unless any other condition is
+required.
+
+Power Management
+================
+
+If the chip is supposed to work with suspend/resume functions, you need
+to add power-management code to the driver. The additional code for
+power-management should be ifdef-ed with ``CONFIG_PM``.
+
+If the driver *fully* supports suspend/resume that is, the device can be
+properly resumed to its state when suspend was called, you can set the
+``SNDRV_PCM_INFO_RESUME`` flag in the pcm info field. Usually, this is
+possible when the registers of the chip can be safely saved and restored
+to RAM. If this is set, the trigger callback is called with
+``SNDRV_PCM_TRIGGER_RESUME`` after the resume callback completes.
+
+Even if the driver doesn't support PM fully but partial suspend/resume
+is still possible, it's still worthy to implement suspend/resume
+callbacks. In such a case, applications would reset the status by
+calling :c:func:`snd_pcm_prepare()` and restart the stream
+appropriately. Hence, you can define suspend/resume callbacks below but
+don't set ``SNDRV_PCM_INFO_RESUME`` info flag to the PCM.
+
+Note that the trigger with SUSPEND can always be called when
+:c:func:`snd_pcm_suspend_all()` is called, regardless of the
+``SNDRV_PCM_INFO_RESUME`` flag. The ``RESUME`` flag affects only the
+behavior of :c:func:`snd_pcm_resume()`. (Thus, in theory,
+``SNDRV_PCM_TRIGGER_RESUME`` isn't needed to be handled in the trigger
+callback when no ``SNDRV_PCM_INFO_RESUME`` flag is set. But, it's better
+to keep it for compatibility reasons.)
+
+In the earlier version of ALSA drivers, a common power-management layer
+was provided, but it has been removed. The driver needs to define the
+suspend/resume hooks according to the bus the device is connected to. In
+the case of PCI drivers, the callbacks look like below:
+
+::
+
+ #ifdef CONFIG_PM
+ static int snd_my_suspend(struct pci_dev *pci, pm_message_t state)
+ {
+ .... /* do things for suspend */
+ return 0;
+ }
+ static int snd_my_resume(struct pci_dev *pci)
+ {
+ .... /* do things for suspend */
+ return 0;
+ }
+ #endif
+
+The scheme of the real suspend job is as follows.
+
+1. Retrieve the card and the chip data.
+
+2. Call :c:func:`snd_power_change_state()` with
+ ``SNDRV_CTL_POWER_D3hot`` to change the power status.
+
+3. Call :c:func:`snd_pcm_suspend_all()` to suspend the running
+ PCM streams.
+
+4. If AC97 codecs are used, call :c:func:`snd_ac97_suspend()` for
+ each codec.
+
+5. Save the register values if necessary.
+
+6. Stop the hardware if necessary.
+
+7. Disable the PCI device by calling
+ :c:func:`pci_disable_device()`. Then, call
+ :c:func:`pci_save_state()` at last.
+
+A typical code would be like:
+
+::
+
+ static int mychip_suspend(struct pci_dev *pci, pm_message_t state)
+ {
+ /* (1) */
+ struct snd_card *card = pci_get_drvdata(pci);
+ struct mychip *chip = card->private_data;
+ /* (2) */
+ snd_power_change_state(card, SNDRV_CTL_POWER_D3hot);
+ /* (3) */
+ snd_pcm_suspend_all(chip->pcm);
+ /* (4) */
+ snd_ac97_suspend(chip->ac97);
+ /* (5) */
+ snd_mychip_save_registers(chip);
+ /* (6) */
+ snd_mychip_stop_hardware(chip);
+ /* (7) */
+ pci_disable_device(pci);
+ pci_save_state(pci);
+ return 0;
+ }
+
+
+The scheme of the real resume job is as follows.
+
+1. Retrieve the card and the chip data.
+
+2. Set up PCI. First, call :c:func:`pci_restore_state()`. Then
+ enable the pci device again by calling
+ :c:func:`pci_enable_device()`. Call
+ :c:func:`pci_set_master()` if necessary, too.
+
+3. Re-initialize the chip.
+
+4. Restore the saved registers if necessary.
+
+5. Resume the mixer, e.g. calling :c:func:`snd_ac97_resume()`.
+
+6. Restart the hardware (if any).
+
+7. Call :c:func:`snd_power_change_state()` with
+ ``SNDRV_CTL_POWER_D0`` to notify the processes.
+
+A typical code would be like:
+
+::
+
+ static int mychip_resume(struct pci_dev *pci)
+ {
+ /* (1) */
+ struct snd_card *card = pci_get_drvdata(pci);
+ struct mychip *chip = card->private_data;
+ /* (2) */
+ pci_restore_state(pci);
+ pci_enable_device(pci);
+ pci_set_master(pci);
+ /* (3) */
+ snd_mychip_reinit_chip(chip);
+ /* (4) */
+ snd_mychip_restore_registers(chip);
+ /* (5) */
+ snd_ac97_resume(chip->ac97);
+ /* (6) */
+ snd_mychip_restart_chip(chip);
+ /* (7) */
+ snd_power_change_state(card, SNDRV_CTL_POWER_D0);
+ return 0;
+ }
+
+As shown in the above, it's better to save registers after suspending
+the PCM operations via :c:func:`snd_pcm_suspend_all()` or
+:c:func:`snd_pcm_suspend()`. It means that the PCM streams are
+already stopped when the register snapshot is taken. But, remember that
+you don't have to restart the PCM stream in the resume callback. It'll
+be restarted via trigger call with ``SNDRV_PCM_TRIGGER_RESUME`` when
+necessary.
+
+OK, we have all callbacks now. Let's set them up. In the initialization
+of the card, make sure that you can get the chip data from the card
+instance, typically via ``private_data`` field, in case you created the
+chip data individually.
+
+::
+
+ static int snd_mychip_probe(struct pci_dev *pci,
+ const struct pci_device_id *pci_id)
+ {
+ ....
+ struct snd_card *card;
+ struct mychip *chip;
+ int err;
+ ....
+ err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
+ 0, &card);
+ ....
+ chip = kzalloc(sizeof(*chip), GFP_KERNEL);
+ ....
+ card->private_data = chip;
+ ....
+ }
+
+When you created the chip data with :c:func:`snd_card_new()`, it's
+anyway accessible via ``private_data`` field.
+
+::
+
+ static int snd_mychip_probe(struct pci_dev *pci,
+ const struct pci_device_id *pci_id)
+ {
+ ....
+ struct snd_card *card;
+ struct mychip *chip;
+ int err;
+ ....
+ err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
+ sizeof(struct mychip), &card);
+ ....
+ chip = card->private_data;
+ ....
+ }
+
+If you need a space to save the registers, allocate the buffer for it
+here, too, since it would be fatal if you cannot allocate a memory in
+the suspend phase. The allocated buffer should be released in the
+corresponding destructor.
+
+And next, set suspend/resume callbacks to the pci_driver.
+
+::
+
+ static struct pci_driver driver = {
+ .name = KBUILD_MODNAME,
+ .id_table = snd_my_ids,
+ .probe = snd_my_probe,
+ .remove = snd_my_remove,
+ #ifdef CONFIG_PM
+ .suspend = snd_my_suspend,
+ .resume = snd_my_resume,
+ #endif
+ };
+
+Module Parameters
+=================
+
+There are standard module options for ALSA. At least, each module should
+have the ``index``, ``id`` and ``enable`` options.
+
+If the module supports multiple cards (usually up to 8 = ``SNDRV_CARDS``
+cards), they should be arrays. The default initial values are defined
+already as constants for easier programming:
+
+::
+
+ static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX;
+ static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR;
+ static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP;
+
+If the module supports only a single card, they could be single
+variables, instead. ``enable`` option is not always necessary in this
+case, but it would be better to have a dummy option for compatibility.
+
+The module parameters must be declared with the standard
+``module_param()()``, ``module_param_array()()`` and
+:c:func:`MODULE_PARM_DESC()` macros.
+
+The typical coding would be like below:
+
+::
+
+ #define CARD_NAME "My Chip"
+
+ module_param_array(index, int, NULL, 0444);
+ MODULE_PARM_DESC(index, "Index value for " CARD_NAME " soundcard.");
+ module_param_array(id, charp, NULL, 0444);
+ MODULE_PARM_DESC(id, "ID string for " CARD_NAME " soundcard.");
+ module_param_array(enable, bool, NULL, 0444);
+ MODULE_PARM_DESC(enable, "Enable " CARD_NAME " soundcard.");
+
+Also, don't forget to define the module description, classes, license
+and devices. Especially, the recent modprobe requires to define the
+module license as GPL, etc., otherwise the system is shown as “tainted”.
+
+::
+
+ MODULE_DESCRIPTION("My Chip");
+ MODULE_LICENSE("GPL");
+ MODULE_SUPPORTED_DEVICE("{{Vendor,My Chip Name}}");
+
+
+How To Put Your Driver Into ALSA Tree
+=====================================
+
+General
+-------
+
+So far, you've learned how to write the driver codes. And you might have
+a question now: how to put my own driver into the ALSA driver tree? Here
+(finally :) the standard procedure is described briefly.
+
+Suppose that you create a new PCI driver for the card “xyz”. The card
+module name would be snd-xyz. The new driver is usually put into the
+alsa-driver tree, ``alsa-driver/pci`` directory in the case of PCI
+cards. Then the driver is evaluated, audited and tested by developers
+and users. After a certain time, the driver will go to the alsa-kernel
+tree (to the corresponding directory, such as ``alsa-kernel/pci``) and
+eventually will be integrated into the Linux 2.6 tree (the directory
+would be ``linux/sound/pci``).
+
+In the following sections, the driver code is supposed to be put into
+alsa-driver tree. The two cases are covered: a driver consisting of a
+single source file and one consisting of several source files.
+
+Driver with A Single Source File
+--------------------------------
+
+1. Modify alsa-driver/pci/Makefile
+
+ Suppose you have a file xyz.c. Add the following two lines
+
+::
+
+ snd-xyz-objs := xyz.o
+ obj-$(CONFIG_SND_XYZ) += snd-xyz.o
+
+2. Create the Kconfig entry
+
+ Add the new entry of Kconfig for your xyz driver. config SND_XYZ
+ tristate "Foobar XYZ" depends on SND select SND_PCM help Say Y here
+ to include support for Foobar XYZ soundcard. To compile this driver
+ as a module, choose M here: the module will be called snd-xyz. the
+ line, select SND_PCM, specifies that the driver xyz supports PCM. In
+ addition to SND_PCM, the following components are supported for
+ select command: SND_RAWMIDI, SND_TIMER, SND_HWDEP,
+ SND_MPU401_UART, SND_OPL3_LIB, SND_OPL4_LIB, SND_VX_LIB,
+ SND_AC97_CODEC. Add the select command for each supported
+ component.
+
+ Note that some selections imply the lowlevel selections. For example,
+ PCM includes TIMER, MPU401_UART includes RAWMIDI, AC97_CODEC
+ includes PCM, and OPL3_LIB includes HWDEP. You don't need to give
+ the lowlevel selections again.
+
+ For the details of Kconfig script, refer to the kbuild documentation.
+
+3. Run cvscompile script to re-generate the configure script and build
+ the whole stuff again.
+
+Drivers with Several Source Files
+---------------------------------
+
+Suppose that the driver snd-xyz have several source files. They are
+located in the new subdirectory, pci/xyz.
+
+1. Add a new directory (``xyz``) in ``alsa-driver/pci/Makefile`` as
+ below
+
+::
+
+ obj-$(CONFIG_SND) += xyz/
+
+
+2. Under the directory ``xyz``, create a Makefile
+
+::
+
+ ifndef SND_TOPDIR
+ SND_TOPDIR=../..
+ endif
+
+ include $(SND_TOPDIR)/toplevel.config
+ include $(SND_TOPDIR)/Makefile.conf
+
+ snd-xyz-objs := xyz.o abc.o def.o
+
+ obj-$(CONFIG_SND_XYZ) += snd-xyz.o
+
+ include $(SND_TOPDIR)/Rules.make
+
+3. Create the Kconfig entry
+
+ This procedure is as same as in the last section.
+
+4. Run cvscompile script to re-generate the configure script and build
+ the whole stuff again.
+
+Useful Functions
+================
+
+:c:func:`snd_printk()` and friends
+---------------------------------------
+
+ALSA provides a verbose version of the :c:func:`printk()` function.
+If a kernel config ``CONFIG_SND_VERBOSE_PRINTK`` is set, this function
+prints the given message together with the file name and the line of the
+caller. The ``KERN_XXX`` prefix is processed as well as the original
+:c:func:`printk()` does, so it's recommended to add this prefix,
+e.g. snd_printk(KERN_ERR "Oh my, sorry, it's extremely bad!\\n");
+
+There are also :c:func:`printk()`'s for debugging.
+:c:func:`snd_printd()` can be used for general debugging purposes.
+If ``CONFIG_SND_DEBUG`` is set, this function is compiled, and works
+just like :c:func:`snd_printk()`. If the ALSA is compiled without
+the debugging flag, it's ignored.
+
+:c:func:`snd_printdd()` is compiled in only when
+``CONFIG_SND_DEBUG_VERBOSE`` is set. Please note that
+``CONFIG_SND_DEBUG_VERBOSE`` is not set as default even if you configure
+the alsa-driver with ``--with-debug=full`` option. You need to give
+explicitly ``--with-debug=detect`` option instead.
+
+:c:func:`snd_BUG()`
+------------------------
+
+It shows the ``BUG?`` message and stack trace as well as
+:c:func:`snd_BUG_ON()` at the point. It's useful to show that a
+fatal error happens there.
+
+When no debug flag is set, this macro is ignored.
+
+:c:func:`snd_BUG_ON()`
+----------------------------
+
+:c:func:`snd_BUG_ON()` macro is similar with
+:c:func:`WARN_ON()` macro. For example, snd_BUG_ON(!pointer); or
+it can be used as the condition, if (snd_BUG_ON(non_zero_is_bug))
+return -EINVAL;
+
+The macro takes an conditional expression to evaluate. When
+``CONFIG_SND_DEBUG``, is set, if the expression is non-zero, it shows
+the warning message such as ``BUG? (xxx)`` normally followed by stack
+trace. In both cases it returns the evaluated value.
+
+Acknowledgments
+===============
+
+I would like to thank Phil Kerr for his help for improvement and
+corrections of this document.
+
+Kevin Conder reformatted the original plain-text to the DocBook format.
+
+Giuliano Pochini corrected typos and contributed the example codes in
+the hardware constraints section.
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