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 /* enable PIT timer */ 80 /* set for periodic (4) and LSB/MSB write (0x30) */ 81 outb(0x34, 0x43); 82 outb((mSEC_10_from_14/6) & 0xFF, 0x40); 83 outb((mSEC_10_from_14/6) >> 8, 0x40); 84 85 setup_irq(IRQ_ISA_TIMER, &isa_timer_irq); 86 } 87 88 struct sys_timer isa_timer = { 89 .init = isa_timer_init, 90 .offset = isa_gettimeoffset, 91 }; 92