86 lines
1.8 KiB
C
86 lines
1.8 KiB
C
/*
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* i8253.c 8253/PIT functions
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*
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*/
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#include <linux/clocksource.h>
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#include <linux/spinlock.h>
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#include <linux/jiffies.h>
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#include <linux/sysdev.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <asm/smp.h>
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#include <asm/delay.h>
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#include <asm/i8253.h>
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#include <asm/io.h>
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#include "io_ports.h"
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DEFINE_SPINLOCK(i8253_lock);
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EXPORT_SYMBOL(i8253_lock);
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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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/*
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* Since the PIT overflows every tick, its not very useful
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* to just read by itself. So use jiffies to emulate a free
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* running counter:
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*/
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static cycle_t pit_read(void)
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{
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unsigned long flags;
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int count;
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u64 jifs;
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spin_lock_irqsave(&i8253_lock, flags);
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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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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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spin_unlock_irqrestore(&i8253_lock, flags);
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jifs = jiffies_64;
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jifs -= INITIAL_JIFFIES;
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count = (LATCH-1) - count;
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return (cycle_t)(jifs * LATCH) + count;
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}
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static struct clocksource clocksource_pit = {
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.name = "pit",
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.rating = 110,
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.read = pit_read,
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.mask = CLOCKSOURCE_MASK(64),
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.mult = 0,
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.shift = 20,
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};
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static int __init init_pit_clocksource(void)
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{
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if (num_possible_cpus() > 4) /* PIT does not scale! */
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return 0;
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clocksource_pit.mult = clocksource_hz2mult(CLOCK_TICK_RATE, 20);
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return clocksource_register(&clocksource_pit);
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}
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module_init(init_pit_clocksource);
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