2 * This code largely moved from arch/i386/kernel/time.c.
3 * See comments there for proper credits.
6 #include <linux/spinlock.h>
7 #include <linux/module.h>
8 #include <linux/device.h>
9 #include <linux/sysdev.h>
10 #include <linux/timex.h>
11 #include <asm/delay.h>
12 #include <asm/mpspec.h>
13 #include <asm/timer.h>
16 #include <asm/arch_hooks.h>
17 #include <asm/i8253.h>
22 static int count_p; /* counter in get_offset_pit() */
24 static int __init init_pit(char* override)
26 /* check clock override */
27 if (override[0] && strncmp(override,"pit",3))
28 printk(KERN_ERR "Warning: clock= override failed. Defaulting to PIT\n");
34 static void mark_offset_pit(void)
39 static unsigned long long monotonic_clock_pit(void)
44 static void delay_pit(unsigned long loops)
52 "2:\tdecl %0\n\tjns 2b"
58 /* This function must be called with xtime_lock held.
59 * It was inspired by Steve McCanne's microtime-i386 for BSD. -- jrs
61 * However, the pc-audio speaker driver changes the divisor so that
62 * it gets interrupted rather more often - it loads 64 into the
63 * counter rather than 11932! This has an adverse impact on
64 * do_gettimeoffset() -- it stops working! What is also not
65 * good is that the interval that our timer function gets called
66 * is no longer 10.0002 ms, but 9.9767 ms. To get around this
67 * would require using a different timing source. Maybe someone
68 * could use the RTC - I know that this can interrupt at frequencies
69 * ranging from 8192Hz to 2Hz. If I had the energy, I'd somehow fix
70 * it so that at startup, the timer code in sched.c would select
71 * using either the RTC or the 8253 timer. The decision would be
72 * based on whether there was any other device around that needed
73 * to trample on the 8253. I'd set up the RTC to interrupt at 1024 Hz,
74 * and then do some jiggery to have a version of do_timer that
75 * advanced the clock by 1/1024 s. Every time that reached over 1/100
76 * of a second, then do all the old code. If the time was kept correct
77 * then do_gettimeoffset could just return 0 - there is no low order
78 * divider that can be accessed.
80 * Ideally, you would be able to use the RTC for the speaker driver,
81 * but it appears that the speaker driver really needs interrupt more
82 * often than every 120 us or so.
84 * Anyway, this needs more thought.... pjsg (1993-08-28)
86 * If you are really that interested, you should be reading
87 * comp.protocols.time.ntp!
90 static unsigned long get_offset_pit(void)
94 static unsigned long jiffies_p = 0;
97 * cache volatile jiffies temporarily; we have xtime_lock.
99 unsigned long jiffies_t;
101 spin_lock_irqsave(&i8253_lock, flags);
102 /* timer count may underflow right here */
103 outb_p(0x00, PIT_MODE); /* latch the count ASAP */
105 count = inb_p(PIT_CH0); /* read the latched count */
108 * We do this guaranteed double memory access instead of a _p
109 * postfix in the previous port access. Wheee, hackady hack
113 count |= inb_p(PIT_CH0) << 8;
115 /* VIA686a test code... reset the latch if count > max + 1 */
117 outb_p(0x34, PIT_MODE);
118 outb_p(LATCH & 0xff, PIT_CH0);
119 outb(LATCH >> 8, PIT_CH0);
124 * avoiding timer inconsistencies (they are rare, but they happen)...
125 * there are two kinds of problems that must be avoided here:
126 * 1. the timer counter underflows
127 * 2. hardware problem with the timer, not giving us continuous time,
128 * the counter does small "jumps" upwards on some Pentium systems,
129 * (see c't 95/10 page 335 for Neptun bug.)
132 if( jiffies_t == jiffies_p ) {
133 if( count > count_p ) {
135 count = do_timer_overflow(count);
138 jiffies_p = jiffies_t;
142 spin_unlock_irqrestore(&i8253_lock, flags);
144 count = ((LATCH-1) - count) * TICK_SIZE;
145 count = (count + LATCH/2) / LATCH;
151 /* tsc timer_opts struct */
152 struct timer_opts timer_pit = {
154 .mark_offset = mark_offset_pit,
155 .get_offset = get_offset_pit,
156 .monotonic_clock = monotonic_clock_pit,
160 struct init_timer_opts __initdata timer_pit_init = {
165 void setup_pit_timer(void)
169 spin_lock_irqsave(&i8253_lock, flags);
170 outb_p(0x34,PIT_MODE); /* binary, mode 2, LSB/MSB, ch 0 */
172 outb_p(LATCH & 0xff , PIT_CH0); /* LSB */
174 outb(LATCH >> 8 , PIT_CH0); /* MSB */
175 spin_unlock_irqrestore(&i8253_lock, flags);