diff options
Diffstat (limited to 'arch/mips/kernel/time.c')
| -rw-r--r-- | arch/mips/kernel/time.c | 84 |
1 files changed, 70 insertions, 14 deletions
diff --git a/arch/mips/kernel/time.c b/arch/mips/kernel/time.c index 2dd1d54ee..aa4547456 100644 --- a/arch/mips/kernel/time.c +++ b/arch/mips/kernel/time.c @@ -22,6 +22,11 @@ #include <linux/mc146818rtc.h> #include <linux/timex.h> +extern volatile unsigned long lost_ticks; + +/* change this if you have some constant time drift */ +#define USECS_PER_JIFFY (1000020/HZ) + /* This function must be called with interrupts disabled * It was inspired by Steve McCanne's microtime-i386 for BSD. -- jrs * @@ -59,22 +64,64 @@ static unsigned long do_slow_gettimeoffset(void) { int count; - unsigned long offset = 0; + + static int count_p = LATCH; /* 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 */ - count |= inb(0x40) << 8; - /* we know probability of underflow is always MUCH less than 1% */ - if (count > (LATCH - LATCH/100)) { - /* check for pending timer interrupt */ - outb_p(0x0a, 0x20); - if (inb(0x20) & 1) - offset = TICK_SIZE; - } + + /* + * 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; + + /* + * avoiding timer inconsistencies (they are rare, but they happen)... + * there are two kinds of problems that must be avoided here: + * 1. the timer counter underflows + * 2. hardware problem with the timer, not giving us continuous time, + * the counter does small "jumps" upwards on some Pentium systems, + * (see c't 95/10 page 335 for Neptun bug.) + */ + + if( jiffies_t == jiffies_p ) { + if( count > count_p ) { + /* the nutcase */ + + outb_p(0x0A, 0x20); + + /* assumption about timer being IRQ1 */ + if( inb(0x20) & 0x01 ) { + /* + * We cannot detect lost timer interrupts ... + * well, thats why we call them lost, dont we? :) + * [hmm, on the Pentium and Alpha we can ... sort of] + */ + count -= LATCH; + } else { + printk("do_slow_gettimeoffset(): hardware timer problem?\n"); + } + } + } else + jiffies_p = jiffies_t; + + count_p = count; + count = ((LATCH-1) - count) * TICK_SIZE; count = (count + LATCH/2) / LATCH; - return offset + count; + + return count; } static unsigned long (*do_gettimeoffset)(void) = do_slow_gettimeoffset; @@ -90,11 +137,20 @@ void do_gettimeofday(struct timeval *tv) cli(); *tv = xtime; tv->tv_usec += do_gettimeoffset(); + + /* + * xtime is atomically updated in timer_bh. lost_ticks is + * nonzero if the timer bottom half hasnt executed yet. + */ + if (lost_ticks) + tv->tv_usec += USECS_PER_JIFFY; + + restore_flags(flags); + if (tv->tv_usec >= 1000000) { tv->tv_usec -= 1000000; tv->tv_sec++; } - restore_flags(flags); } void do_settimeofday(struct timeval *tv) @@ -167,7 +223,7 @@ static int set_rtc_mmss(unsigned long nowtime) /* The following flags have to be released exactly in this order, * otherwise the DS12887 (popular MC146818A clone with integrated - * battery and crystal) will not reset the oscillator and will not + * battery and quartz) will not reset the oscillator and will not * update precisely 500 ms later. You won't find this mentioned in * the Dallas Semiconductor data sheets, but who believes data * sheets anyway ... -- Markus Kuhn @@ -205,7 +261,7 @@ static void timer_interrupt(int irq, void *dev_id, struct pt_regs * regs) basically because we don't yet share IRQ's around. This message is rigged to be safe on the 386 - basically it's a hack, so don't look closely for now.. */ - smp_message_pass(MSG_ALL_BUT_SELF, MSG_RESCHEDULE, 0L, 0); + /*smp_message_pass(MSG_ALL_BUT_SELF, MSG_RESCHEDULE, 0L, 0); */ } /* Converts Gregorian date to seconds since 1970-01-01 00:00:00. @@ -281,7 +337,7 @@ void time_init(void) if ((year += 1900) < 1970) year += 100; #else - /* true for all MIPS machines? */ + /* Acer PICA clock starts from 1980. True for all MIPS machines? */ year += 1980; #endif xtime.tv_sec = mktime(year, mon, day, hour, min, sec); |