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+>µITRON and eCos</TITLE
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+>eCos Reference Manual</TH
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+><A
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+>Prev</A
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+><TD
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+>Chapter 32. µITRON API</TD
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+><DIV
+CLASS="SECT1"
+><H1
+CLASS="SECT1"
+><A
+NAME="COMPAT-UITRON-OVER-ECOS">µITRON and <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>eCos</I
+></SPAN
+></H1
+><P
+>The <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>eCos</I
+></SPAN
+> kernel implements the functionality
+used by the µITRON compatibility subsystem.
+The configuration of the kernel influences the behavior of µITRON
+programs.</P
+><P
+>In particular, the default configuration has time slicing
+(also known as round-robin scheduling) switched on; this means that
+a task can be moved from <TT
+CLASS="VARNAME"
+>RUN</TT
+> state
+to <TT
+CLASS="VARNAME"
+>READY</TT
+> state at any time, in
+order that one of its peers may run. This is not strictly conformant
+to the µITRON specification, which
+states that timeslicing may be implemented by periodically issuing
+a <TT
+CLASS="LITERAL"
+>rot_rdq(0)</TT
+> call from
+within a periodic task or cyclic handler; otherwise it is expected
+that a task runs until it is pre-empted in consequence of synchronization
+or communication calls it makes, or the effects of an interrupt
+or other external event on a higher priority task cause that task
+to become <TT
+CLASS="VARNAME"
+>READY</TT
+>. To disable timeslicing
+functionality in the kernel and µITRON
+compatibility environment, please disable the
+<TT
+CLASS="LITERAL"
+>CYGSEM_KERNEL_SCHED_TIMESLICE</TT
+>
+configuration option in the kernel package. A description of kernel
+scheduling is in <A
+HREF="kernel-overview.html"
+>Kernel Overview</A
+>. </P
+><P
+>For another example, the semantics of task queueing when waiting
+on a synchronization object depend solely on the way the underlying
+kernel is configured. As discussed above, the multi-level queue
+scheduler is the only one which is µITRON
+compliant, and it queues waiting tasks in FIFO order. Future releases
+of that scheduler might be configurable to support priority ordering
+of task queues. Other schedulers might be different again: for example
+the bitmap scheduler can be used with the µITRON
+compatibility layer, even though it only allows one task at each
+priority and as such is not µITRON
+compliant, but it supports only priority ordering of task queues.
+So which queueing scheme is supported is not really a property of
+the µITRON compatibility layer; it
+depends on the kernel. </P
+><P
+>In this version of the µITRON
+compatibility layer, the calls to disable and enable scheduling
+and interrupts (<TT
+CLASS="FUNCTION"
+>dis_dsp()</TT
+>,
+<TT
+CLASS="FUNCTION"
+>ena_dsp()</TT
+>, <TT
+CLASS="FUNCTION"
+>loc_cpu()</TT
+>
+and <TT
+CLASS="FUNCTION"
+>unl_cpu()</TT
+>)
+call underlying kernel functions; in particular, the <TT
+CLASS="FUNCTION"
+>xxx_dsp()</TT
+> functions
+lock the scheduler entirely, which prevents dispatching of DSRs; functions
+implemented by DSRs include clock counters and alarm timers. Thus time “stops” while
+dispatching is disabled with <TT
+CLASS="FUNCTION"
+>dis_dsp()</TT
+>. </P
+><P
+>Like all parts of the <SPAN
+CLASS="emphasis"
+><I
+CLASS="EMPHASIS"
+>eCos</I
+></SPAN
+> system, the
+detailed semantics of the µITRON layer
+are dependent on its configuration and the configuration of other components
+that it uses. The µITRON configuration
+options are all defined in the file <TT
+CLASS="FILENAME"
+>pkgconf/uitron.h</TT
+>,
+and can be set using the configuration tool or editing the
+<TT
+CLASS="FILENAME"
+>.ecc</TT
+>
+file in your build directory by hand. </P
+><P
+>An important configuration option for the µITRON
+compatibility layer is “Option: Return Error Codes for Bad Params”
+(
+<TT
+CLASS="LITERAL"
+>CYGSEM_UITRON_BAD_PARAMS_RETURN_ERRORS</TT
+>
+), which allows a lot of the error
+checking code in the µITRON compatibility layer to
+be removed. Of course this leaves a program open to undetected errors,
+so it should only be used once an application is fully debugged and
+tested. Its benefits include reduced code size and faster execution.
+However, it affects the API significantly, in that with this option
+enabled, bad calls do not return errors, but cause an assert
+failure (if that is itself enabled) or malfunction internally. There
+is discussion in more detail about this in each section below.</P
+><P
+>We now give a brief description of the µITRON
+functions which are implemented in this release. Note that all C
+and C++ source files should have the following <TT
+CLASS="LITERAL"
+>#include</TT
+> statement: </P
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><PRE
+CLASS="PROGRAMLISTING"
+>#include <cyg/compat/uitron/uit_func.h></PRE
+></TD
+></TR
+></TABLE
+></DIV
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