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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * linux/arch/arm/mach-footbridge/isa-timer.c
3 *
4 * Copyright (C) 1998 Russell King.
5 * Copyright (C) 1998 Phil Blundell
6 */
7#include <linux/init.h>
8#include <linux/interrupt.h>
Thomas Gleixner55e86982006-07-01 22:32:17 +01009#include <linux/irq.h>
Russell Kingfced80c2008-09-06 12:10:45 +010010#include <linux/io.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070011
Linus Torvalds1da177e2005-04-16 15:20:36 -070012#include <asm/irq.h>
13
14#include <asm/mach/time.h>
15
16#include "common.h"
17
18/*
19 * ISA timer tick support
20 */
21#define mSEC_10_from_14 ((14318180 + 100) / 200)
22
23static unsigned long isa_gettimeoffset(void)
24{
25 int count;
26
27 static int count_p = (mSEC_10_from_14/6); /* for the first call after boot */
28 static unsigned long jiffies_p = 0;
29
30 /*
31 * cache volatile jiffies temporarily; we have IRQs turned off.
32 */
33 unsigned long jiffies_t;
34
35 /* timer count may underflow right here */
36 outb_p(0x00, 0x43); /* latch the count ASAP */
37
38 count = inb_p(0x40); /* read the latched count */
39
40 /*
41 * We do this guaranteed double memory access instead of a _p
42 * postfix in the previous port access. Wheee, hackady hack
43 */
44 jiffies_t = jiffies;
45
46 count |= inb_p(0x40) << 8;
47
48 /* Detect timer underflows. If we haven't had a timer tick since
49 the last time we were called, and time is apparently going
50 backwards, the counter must have wrapped during this routine. */
51 if ((jiffies_t == jiffies_p) && (count > count_p))
52 count -= (mSEC_10_from_14/6);
53 else
54 jiffies_p = jiffies_t;
55
56 count_p = count;
57
58 count = (((mSEC_10_from_14/6)-1) - count) * (tick_nsec / 1000);
59 count = (count + (mSEC_10_from_14/6)/2) / (mSEC_10_from_14/6);
60
61 return count;
62}
63
64static irqreturn_t
Linus Torvalds0cd61b62006-10-06 10:53:39 -070065isa_timer_interrupt(int irq, void *dev_id)
Linus Torvalds1da177e2005-04-16 15:20:36 -070066{
Linus Torvalds0cd61b62006-10-06 10:53:39 -070067 timer_tick();
Linus Torvalds1da177e2005-04-16 15:20:36 -070068 return IRQ_HANDLED;
69}
70
71static struct irqaction isa_timer_irq = {
72 .name = "ISA timer tick",
73 .handler = isa_timer_interrupt,
Bernhard Walleb30faba2007-05-08 00:35:39 -070074 .flags = IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
Linus Torvalds1da177e2005-04-16 15:20:36 -070075};
76
77static void __init isa_timer_init(void)
78{
79 isa_rtc_init();
80
81 /* enable PIT timer */
82 /* set for periodic (4) and LSB/MSB write (0x30) */
83 outb(0x34, 0x43);
84 outb((mSEC_10_from_14/6) & 0xFF, 0x40);
85 outb((mSEC_10_from_14/6) >> 8, 0x40);
86
87 setup_irq(IRQ_ISA_TIMER, &isa_timer_irq);
88}
89
90struct sys_timer isa_timer = {
91 .init = isa_timer_init,
92 .offset = isa_gettimeoffset,
93};