1 /*
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>
9 #include <linux/irq.h>
10 #include <linux/io.h>
11 
12 #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 
23 static 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 
64 static irqreturn_t
65 isa_timer_interrupt(int irq, void *dev_id)
66 {
67 	timer_tick();
68 	return IRQ_HANDLED;
69 }
70 
71 static struct irqaction isa_timer_irq = {
72 	.name		= "ISA timer tick",
73 	.handler	= isa_timer_interrupt,
74 	.flags		= IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
75 };
76 
77 static 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 
90 struct sys_timer isa_timer = {
91 	.init		= isa_timer_init,
92 	.offset		= isa_gettimeoffset,
93 };
94