Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 | |
| 10 | #include <asm/io.h> |
| 11 | #include <asm/irq.h> |
| 12 | |
| 13 | #include <asm/mach/time.h> |
| 14 | |
| 15 | #include "common.h" |
| 16 | |
| 17 | /* |
| 18 | * ISA timer tick support |
| 19 | */ |
| 20 | #define mSEC_10_from_14 ((14318180 + 100) / 200) |
| 21 | |
| 22 | static unsigned long isa_gettimeoffset(void) |
| 23 | { |
| 24 | int count; |
| 25 | |
| 26 | static int count_p = (mSEC_10_from_14/6); /* for the first call after boot */ |
| 27 | static unsigned long jiffies_p = 0; |
| 28 | |
| 29 | /* |
| 30 | * cache volatile jiffies temporarily; we have IRQs turned off. |
| 31 | */ |
| 32 | unsigned long jiffies_t; |
| 33 | |
| 34 | /* timer count may underflow right here */ |
| 35 | outb_p(0x00, 0x43); /* latch the count ASAP */ |
| 36 | |
| 37 | count = inb_p(0x40); /* read the latched count */ |
| 38 | |
| 39 | /* |
| 40 | * We do this guaranteed double memory access instead of a _p |
| 41 | * postfix in the previous port access. Wheee, hackady hack |
| 42 | */ |
| 43 | jiffies_t = jiffies; |
| 44 | |
| 45 | count |= inb_p(0x40) << 8; |
| 46 | |
| 47 | /* Detect timer underflows. If we haven't had a timer tick since |
| 48 | the last time we were called, and time is apparently going |
| 49 | backwards, the counter must have wrapped during this routine. */ |
| 50 | if ((jiffies_t == jiffies_p) && (count > count_p)) |
| 51 | count -= (mSEC_10_from_14/6); |
| 52 | else |
| 53 | jiffies_p = jiffies_t; |
| 54 | |
| 55 | count_p = count; |
| 56 | |
| 57 | count = (((mSEC_10_from_14/6)-1) - count) * (tick_nsec / 1000); |
| 58 | count = (count + (mSEC_10_from_14/6)/2) / (mSEC_10_from_14/6); |
| 59 | |
| 60 | return count; |
| 61 | } |
| 62 | |
| 63 | static irqreturn_t |
| 64 | isa_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs) |
| 65 | { |
| 66 | write_seqlock(&xtime_lock); |
| 67 | timer_tick(regs); |
| 68 | write_sequnlock(&xtime_lock); |
| 69 | return IRQ_HANDLED; |
| 70 | } |
| 71 | |
| 72 | static struct irqaction isa_timer_irq = { |
| 73 | .name = "ISA timer tick", |
| 74 | .handler = isa_timer_interrupt, |
Russell King | 09b8b5f | 2005-06-26 17:06:36 +0100 | [diff] [blame] | 75 | .flags = SA_INTERRUPT | SA_TIMER, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 76 | }; |
| 77 | |
| 78 | static void __init isa_timer_init(void) |
| 79 | { |
| 80 | isa_rtc_init(); |
| 81 | |
| 82 | /* enable PIT timer */ |
| 83 | /* set for periodic (4) and LSB/MSB write (0x30) */ |
| 84 | outb(0x34, 0x43); |
| 85 | outb((mSEC_10_from_14/6) & 0xFF, 0x40); |
| 86 | outb((mSEC_10_from_14/6) >> 8, 0x40); |
| 87 | |
| 88 | setup_irq(IRQ_ISA_TIMER, &isa_timer_irq); |
| 89 | } |
| 90 | |
| 91 | struct sys_timer isa_timer = { |
| 92 | .init = isa_timer_init, |
| 93 | .offset = isa_gettimeoffset, |
| 94 | }; |