178 lines
4.8 KiB
C
178 lines
4.8 KiB
C
/*
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* This code largely moved from arch/i386/kernel/time.c.
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* See comments there for proper credits.
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*/
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#include <linux/spinlock.h>
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#include <linux/module.h>
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#include <linux/device.h>
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#include <linux/sysdev.h>
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#include <linux/timex.h>
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#include <asm/delay.h>
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#include <asm/mpspec.h>
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#include <asm/timer.h>
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#include <asm/smp.h>
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#include <asm/io.h>
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#include <asm/arch_hooks.h>
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#include <asm/i8253.h>
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#include "do_timer.h"
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#include "io_ports.h"
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static int count_p; /* counter in get_offset_pit() */
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static int __init init_pit(char* override)
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{
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/* check clock override */
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if (override[0] && strncmp(override,"pit",3))
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printk(KERN_ERR "Warning: clock= override failed. Defaulting "
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"to PIT\n");
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init_cpu_khz();
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count_p = LATCH;
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return 0;
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}
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static void mark_offset_pit(void)
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{
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/* nothing needed */
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}
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static unsigned long long monotonic_clock_pit(void)
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{
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return 0;
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}
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static void delay_pit(unsigned long loops)
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{
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int d0;
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__asm__ __volatile__(
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"\tjmp 1f\n"
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".align 16\n"
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"1:\tjmp 2f\n"
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".align 16\n"
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"2:\tdecl %0\n\tjns 2b"
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:"=&a" (d0)
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:"0" (loops));
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}
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/* This function must be called with xtime_lock held.
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* It was inspired by Steve McCanne's microtime-i386 for BSD. -- jrs
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*
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* However, the pc-audio speaker driver changes the divisor so that
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* it gets interrupted rather more often - it loads 64 into the
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* counter rather than 11932! This has an adverse impact on
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* do_gettimeoffset() -- it stops working! What is also not
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* good is that the interval that our timer function gets called
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* is no longer 10.0002 ms, but 9.9767 ms. To get around this
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* would require using a different timing source. Maybe someone
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* could use the RTC - I know that this can interrupt at frequencies
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* ranging from 8192Hz to 2Hz. If I had the energy, I'd somehow fix
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* it so that at startup, the timer code in sched.c would select
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* using either the RTC or the 8253 timer. The decision would be
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* based on whether there was any other device around that needed
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* to trample on the 8253. I'd set up the RTC to interrupt at 1024 Hz,
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* and then do some jiggery to have a version of do_timer that
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* advanced the clock by 1/1024 s. Every time that reached over 1/100
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* of a second, then do all the old code. If the time was kept correct
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* then do_gettimeoffset could just return 0 - there is no low order
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* divider that can be accessed.
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*
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* Ideally, you would be able to use the RTC for the speaker driver,
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* but it appears that the speaker driver really needs interrupt more
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* often than every 120 us or so.
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*
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* Anyway, this needs more thought.... pjsg (1993-08-28)
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*
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* If you are really that interested, you should be reading
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* comp.protocols.time.ntp!
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*/
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static unsigned long get_offset_pit(void)
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{
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int count;
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unsigned long flags;
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static unsigned long jiffies_p = 0;
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/*
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* cache volatile jiffies temporarily; we have xtime_lock.
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*/
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unsigned long jiffies_t;
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spin_lock_irqsave(&i8253_lock, flags);
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/* timer count may underflow right here */
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outb_p(0x00, PIT_MODE); /* latch the count ASAP */
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count = inb_p(PIT_CH0); /* read the latched count */
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/*
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* We do this guaranteed double memory access instead of a _p
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* postfix in the previous port access. Wheee, hackady hack
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*/
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jiffies_t = jiffies;
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count |= inb_p(PIT_CH0) << 8;
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/* VIA686a test code... reset the latch if count > max + 1 */
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if (count > LATCH) {
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outb_p(0x34, PIT_MODE);
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outb_p(LATCH & 0xff, PIT_CH0);
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outb(LATCH >> 8, PIT_CH0);
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count = LATCH - 1;
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}
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/*
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* avoiding timer inconsistencies (they are rare, but they happen)...
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* there are two kinds of problems that must be avoided here:
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* 1. the timer counter underflows
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* 2. hardware problem with the timer, not giving us continuous time,
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* the counter does small "jumps" upwards on some Pentium systems,
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* (see c't 95/10 page 335 for Neptun bug.)
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*/
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if( jiffies_t == jiffies_p ) {
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if( count > count_p ) {
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/* the nutcase */
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count = do_timer_overflow(count);
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}
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} else
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jiffies_p = jiffies_t;
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count_p = count;
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spin_unlock_irqrestore(&i8253_lock, flags);
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count = ((LATCH-1) - count) * TICK_SIZE;
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count = (count + LATCH/2) / LATCH;
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return count;
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}
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/* tsc timer_opts struct */
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struct timer_opts timer_pit = {
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.name = "pit",
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.mark_offset = mark_offset_pit,
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.get_offset = get_offset_pit,
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.monotonic_clock = monotonic_clock_pit,
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.delay = delay_pit,
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};
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struct init_timer_opts __initdata timer_pit_init = {
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.init = init_pit,
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.opts = &timer_pit,
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};
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void setup_pit_timer(void)
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{
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unsigned long flags;
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spin_lock_irqsave(&i8253_lock, flags);
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outb_p(0x34,PIT_MODE); /* binary, mode 2, LSB/MSB, ch 0 */
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udelay(10);
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outb_p(LATCH & 0xff , PIT_CH0); /* LSB */
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udelay(10);
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outb(LATCH >> 8 , PIT_CH0); /* MSB */
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spin_unlock_irqrestore(&i8253_lock, flags);
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}
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