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91 lines
2.1 KiB
91 lines
2.1 KiB
/*
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* linux/arch/arm/mach-footbridge/isa-timer.c
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*
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* Copyright (C) 1998 Russell King.
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* Copyright (C) 1998 Phil Blundell
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*/
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#include <linux/init.h>
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#include <linux/interrupt.h>
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#include <linux/irq.h>
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#include <linux/io.h>
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#include <asm/irq.h>
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#include <asm/mach/time.h>
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#include "common.h"
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/*
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* ISA timer tick support
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*/
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#define mSEC_10_from_14 ((14318180 + 100) / 200)
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static unsigned long isa_gettimeoffset(void)
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{
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int count;
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static int count_p = (mSEC_10_from_14/6); /* for the first call after boot */
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static unsigned long jiffies_p = 0;
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/*
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* cache volatile jiffies temporarily; we have IRQs turned off.
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*/
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unsigned long jiffies_t;
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/* timer count may underflow right here */
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outb_p(0x00, 0x43); /* latch the count ASAP */
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count = inb_p(0x40); /* 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(0x40) << 8;
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/* Detect timer underflows. If we haven't had a timer tick since
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the last time we were called, and time is apparently going
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backwards, the counter must have wrapped during this routine. */
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if ((jiffies_t == jiffies_p) && (count > count_p))
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count -= (mSEC_10_from_14/6);
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else
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jiffies_p = jiffies_t;
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count_p = count;
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count = (((mSEC_10_from_14/6)-1) - count) * (tick_nsec / 1000);
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count = (count + (mSEC_10_from_14/6)/2) / (mSEC_10_from_14/6);
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return count;
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}
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static irqreturn_t
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isa_timer_interrupt(int irq, void *dev_id)
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{
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timer_tick();
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return IRQ_HANDLED;
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}
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static struct irqaction isa_timer_irq = {
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.name = "ISA timer tick",
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.handler = isa_timer_interrupt,
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.flags = IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
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};
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static void __init isa_timer_init(void)
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{
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/* enable PIT timer */
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/* set for periodic (4) and LSB/MSB write (0x30) */
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outb(0x34, 0x43);
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outb((mSEC_10_from_14/6) & 0xFF, 0x40);
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outb((mSEC_10_from_14/6) >> 8, 0x40);
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setup_irq(IRQ_ISA_TIMER, &isa_timer_irq);
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}
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struct sys_timer isa_timer = {
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.init = isa_timer_init,
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.offset = isa_gettimeoffset,
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};
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