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