1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
|
/*
* 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 <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, struct pt_regs *regs)
{
write_seqlock(&xtime_lock);
timer_tick(regs);
write_sequnlock(&xtime_lock);
return IRQ_HANDLED;
}
static struct irqaction isa_timer_irq = {
.name = "ISA timer tick",
.handler = isa_timer_interrupt,
.flags = SA_INTERRUPT | SA_TIMER,
};
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,
};
|
