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isa-timer.c

/*
 *  linux/arch/arm/mach-footbridge/isa-timer.c
 *
 *  Copyright (C) 1998 Russell King.
 *  Copyright (C) 1998 Phil Blundell
 */
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/irq.h>

#include <asm/io.h>
#include <asm/irq.h>

#include <asm/mach/time.h>

#include "common.h"

/*
 * ISA timer tick support
 */
#define mSEC_10_from_14 ((14318180 + 100) / 200)

static unsigned long isa_gettimeoffset(void)
{
      int count;

      static int count_p = (mSEC_10_from_14/6);    /* for the first call after boot */
      static unsigned long jiffies_p = 0;

      /*
       * cache volatile jiffies temporarily; we have IRQs turned off. 
       */
      unsigned long jiffies_t;

      /* timer count may underflow right here */
      outb_p(0x00, 0x43);     /* latch the count ASAP */

      count = inb_p(0x40);    /* 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(0x40) << 8;

      /* Detect timer underflows.  If we haven't had a timer tick since 
         the last time we were called, and time is apparently going
         backwards, the counter must have wrapped during this routine. */
      if ((jiffies_t == jiffies_p) && (count > count_p))
            count -= (mSEC_10_from_14/6);
      else
            jiffies_p = jiffies_t;

      count_p = count;

      count = (((mSEC_10_from_14/6)-1) - count) * (tick_nsec / 1000);
      count = (count + (mSEC_10_from_14/6)/2) / (mSEC_10_from_14/6);

      return count;
}

static irqreturn_t
isa_timer_interrupt(int irq, void *dev_id)
{
      timer_tick();
      return IRQ_HANDLED;
}

static struct irqaction isa_timer_irq = {
      .name       = "ISA timer tick",
      .handler    = isa_timer_interrupt,
      .flags            = IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
};

static void __init isa_timer_init(void)
{
      isa_rtc_init();

      /* enable PIT timer */
      /* set for periodic (4) and LSB/MSB write (0x30) */
      outb(0x34, 0x43);
      outb((mSEC_10_from_14/6) & 0xFF, 0x40);
      outb((mSEC_10_from_14/6) >> 8, 0x40);

      setup_irq(IRQ_ISA_TIMER, &isa_timer_irq);
}

struct sys_timer isa_timer = {
      .init       = isa_timer_init,
      .offset           = isa_gettimeoffset,
};

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