2.2.0-final

[davej-history.git] / arch / i386 / kernel / time.c

/*
 *  linux/arch/i386/kernel/time.c
 *
 *  Copyright (C) 1991, 1992, 1995  Linus Torvalds
 *
 * This file contains the PC-specific time handling details:
 * reading the RTC at bootup, etc..
 * 1994-07-02    Alan Modra
 *      fixed set_rtc_mmss, fixed time.year for >= 2000, new mktime
 * 1995-03-26    Markus Kuhn
 *      fixed 500 ms bug at call to set_rtc_mmss, fixed DS12887
 *      precision CMOS clock update
 * 1996-05-03    Ingo Molnar
 *      fixed time warps in do_[slow|fast]_gettimeoffset()
 * 1997-09-10   Updated NTP code according to technical memorandum Jan '96
 *              "A Kernel Model for Precision Timekeeping" by Dave Mills
 * 1998-09-05    (Various)
 *      More robust do_fast_gettimeoffset() algorithm implemented
 *      (works with APM, Cyrix 6x86MX and Centaur C6),
 *      monotonic gettimeofday() with fast_get_timeoffset(),
 *      drift-proof precision TSC calibration on boot
 *      (C. Scott Ananian <cananian@alumni.princeton.edu>, Andrew D.
 *      Balsa <andrebalsa@altern.org>, Philip Gladstone <philip@raptor.com>;
 *      ported from 2.0.35 Jumbo-9 by Michael Krause <m.krause@tu-harburg.de>).
 * 1998-12-16    Andrea Arcangeli
 *      Fixed Jumbo-9 code in 2.1.131: do_gettimeofday was missing 1 jiffy
 *      because was not accounting lost_ticks.
 * 1998-12-24 Copyright (C) 1998  Andrea Arcangeli
 *      Fixed a xtime SMP race (we need the xtime_lock rw spinlock to
 *      serialize accesses to xtime/lost_ticks).
 */

/* What about the "updated NTP code" stuff in 2.0 time.c? It's not in
 * 2.1, perhaps it should be ported, too.
 *
 * What about the BUGGY_NEPTUN_TIMER stuff in do_slow_gettimeoffset()?
 * Whatever it fixes, is it also fixed in the new code from the Jumbo
 * patch, so that that code can be used instead?
 *
 * The CPU Hz should probably be displayed in check_bugs() together
 * with the CPU vendor and type. Perhaps even only in MHz, though that
 * takes away some of the fun of the new code :)
 *
 * - Michael Krause */

#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/param.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/time.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/smp.h>

#include <asm/processor.h>
#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <asm/delay.h>

#include <linux/mc146818rtc.h>
#include <linux/timex.h>
#include <linux/config.h>

#include <asm/fixmap.h>
#include <asm/cobalt.h>

/*
 * for x86_do_profile()
 */
#include "irq.h"


unsigned long cpu_hz;   /* Detected as we calibrate the TSC */

/* Number of usecs that the last interrupt was delayed */
static int delay_at_last_interrupt;

static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */

/* Cached *multiplier* to convert TSC counts to microseconds.
 * (see the equation below).
 * Equal to 2^32 * (1 / (clocks per usec) ).
 * Initialized in time_init.
 */
static unsigned long fast_gettimeoffset_quotient=0;

extern rwlock_t xtime_lock;

static inline unsigned long do_fast_gettimeoffset(void)
{
        register unsigned long eax asm("ax");
        register unsigned long edx asm("dx");

        /* Read the Time Stamp Counter */
        __asm__("rdtsc"
                :"=a" (eax), "=d" (edx));

        /* .. relative to previous jiffy (32 bits is enough) */
        eax -= last_tsc_low;    /* tsc_low delta */

        /*
         * Time offset = (tsc_low delta) * fast_gettimeoffset_quotient
         *             = (tsc_low delta) * (usecs_per_clock)
         *             = (tsc_low delta) * (usecs_per_jiffy / clocks_per_jiffy)
         *
         * Using a mull instead of a divl saves up to 31 clock cycles
         * in the critical path.
         */

        __asm__("mull %2"
                :"=a" (eax), "=d" (edx)
                :"g" (fast_gettimeoffset_quotient),
                 "0" (eax));

        /* our adjusted time offset in microseconds */
        return delay_at_last_interrupt + edx;
}

#define TICK_SIZE tick

#ifndef CONFIG_X86_TSC

/* This function must be called with interrupts disabled 
 * It was inspired by Steve McCanne's microtime-i386 for BSD.  -- jrs
 * 
 * However, the pc-audio speaker driver changes the divisor so that
 * it gets interrupted rather more often - it loads 64 into the
 * counter rather than 11932! This has an adverse impact on
 * do_gettimeoffset() -- it stops working! What is also not
 * good is that the interval that our timer function gets called
 * is no longer 10.0002 ms, but 9.9767 ms. To get around this
 * would require using a different timing source. Maybe someone
 * could use the RTC - I know that this can interrupt at frequencies
 * ranging from 8192Hz to 2Hz. If I had the energy, I'd somehow fix
 * it so that at startup, the timer code in sched.c would select
 * using either the RTC or the 8253 timer. The decision would be
 * based on whether there was any other device around that needed
 * to trample on the 8253. I'd set up the RTC to interrupt at 1024 Hz,
 * and then do some jiggery to have a version of do_timer that 
 * advanced the clock by 1/1024 s. Every time that reached over 1/100
 * of a second, then do all the old code. If the time was kept correct
 * then do_gettimeoffset could just return 0 - there is no low order
 * divider that can be accessed.
 *
 * Ideally, you would be able to use the RTC for the speaker driver,
 * but it appears that the speaker driver really needs interrupt more
 * often than every 120 us or so.
 *
 * Anyway, this needs more thought....          pjsg (1993-08-28)
 * 
 * If you are really that interested, you should be reading
 * comp.protocols.time.ntp!
 */

static unsigned long do_slow_gettimeoffset(void)
{
        int count;

        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 */

        /*
         * 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.)
         */

/* you can safely undefine this if you don't have the Neptune chipset */

#define BUGGY_NEPTUN_TIMER

        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, that's why we call them lost, don't we? :)
                                 * [hmm, on the Pentium and Alpha we can ... sort of]
                                 */
                                count -= LATCH;
                        } else {
#ifdef BUGGY_NEPTUN_TIMER
                                /*
                                 * for the Neptun bug we know that the 'latch'
                                 * command doesnt latch the high and low value
                                 * of the counter atomically. Thus we have to 
                                 * substract 256 from the counter 
                                 * ... funny, isnt it? :)
                                 */

                                count -= 256;
#else
                                printk("do_slow_gettimeoffset(): hardware timer problem?\n");
#endif
                        }
                }
        } else
                jiffies_p = jiffies_t;

        count_p = count;

        count = ((LATCH-1) - count) * TICK_SIZE;
        count = (count + LATCH/2) / LATCH;

        return count;
}

static unsigned long (*do_gettimeoffset)(void) = do_slow_gettimeoffset;

#else

#define do_gettimeoffset()      do_fast_gettimeoffset()

#endif

/*
 * This version of gettimeofday has microsecond resolution
 * and better than microsecond precision on fast x86 machines with TSC.
 */
void do_gettimeofday(struct timeval *tv)
{
        extern volatile unsigned long lost_ticks;
        unsigned long flags;
        unsigned long usec, sec;

        read_lock_irqsave(&xtime_lock, flags);
        usec = do_gettimeoffset();
        {
                unsigned long lost = lost_ticks;
                if (lost)
                        usec += lost * (1000000 / HZ);
        }
        sec = xtime.tv_sec;
        usec += xtime.tv_usec;
        read_unlock_irqrestore(&xtime_lock, flags);

        while (usec >= 1000000) {
                usec -= 1000000;
                sec++;
        }

        tv->tv_sec = sec;
        tv->tv_usec = usec;
}

void do_settimeofday(struct timeval *tv)
{
        write_lock_irq(&xtime_lock);
        /* This is revolting. We need to set the xtime.tv_usec
         * correctly. However, the value in this location is
         * is value at the last tick.
         * Discover what correction gettimeofday
         * would have done, and then undo it!
         */
        tv->tv_usec -= do_gettimeoffset();

        while (tv->tv_usec < 0) {
                tv->tv_usec += 1000000;
                tv->tv_sec--;
        }

        xtime = *tv;
        time_adjust = 0;                /* stop active adjtime() */
        time_status |= STA_UNSYNC;
        time_state = TIME_ERROR;        /* p. 24, (a) */
        time_maxerror = NTP_PHASE_LIMIT;
        time_esterror = NTP_PHASE_LIMIT;
        write_unlock_irq(&xtime_lock);
}

/*
 * In order to set the CMOS clock precisely, set_rtc_mmss has to be
 * called 500 ms after the second nowtime has started, because when
 * nowtime is written into the registers of the CMOS clock, it will
 * jump to the next second precisely 500 ms later. Check the Motorola
 * MC146818A or Dallas DS12887 data sheet for details.
 *
 * BUG: This routine does not handle hour overflow properly; it just
 *      sets the minutes. Usually you'll only notice that after reboot!
 */
static int set_rtc_mmss(unsigned long nowtime)
{
        int retval = 0;
        int real_seconds, real_minutes, cmos_minutes;
        unsigned char save_control, save_freq_select;

        save_control = CMOS_READ(RTC_CONTROL); /* tell the clock it's being set */
        CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL);

        save_freq_select = CMOS_READ(RTC_FREQ_SELECT); /* stop and reset prescaler */
        CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);

        cmos_minutes = CMOS_READ(RTC_MINUTES);
        if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
                BCD_TO_BIN(cmos_minutes);

        /*
         * since we're only adjusting minutes and seconds,
         * don't interfere with hour overflow. This avoids
         * messing with unknown time zones but requires your
         * RTC not to be off by more than 15 minutes
         */
        real_seconds = nowtime % 60;
        real_minutes = nowtime / 60;
        if (((abs(real_minutes - cmos_minutes) + 15)/30) & 1)
                real_minutes += 30;             /* correct for half hour time zone */
        real_minutes %= 60;

        if (abs(real_minutes - cmos_minutes) < 30) {
                if (!(save_control & RTC_DM_BINARY) || RTC_ALWAYS_BCD) {
                        BIN_TO_BCD(real_seconds);
                        BIN_TO_BCD(real_minutes);
                }
                CMOS_WRITE(real_seconds,RTC_SECONDS);
                CMOS_WRITE(real_minutes,RTC_MINUTES);
        } else {
                printk(KERN_WARNING
                       "set_rtc_mmss: can't update from %d to %d\n",
                       cmos_minutes, real_minutes);
                retval = -1;
        }

        /* The following flags have to be released exactly in this order,
         * otherwise the DS12887 (popular MC146818A clone with integrated
         * 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
         */
        CMOS_WRITE(save_control, RTC_CONTROL);
        CMOS_WRITE(save_freq_select, RTC_FREQ_SELECT);

        return retval;
}

/* last time the cmos clock got updated */
static long last_rtc_update = 0;

/*
 * timer_interrupt() needs to keep up the real-time clock,
 * as well as call the "do_timer()" routine every clocktick
 */
static inline void do_timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
#ifdef CONFIG_VISWS
        /* Clear the interrupt */
        co_cpu_write(CO_CPU_STAT,co_cpu_read(CO_CPU_STAT) & ~CO_STAT_TIMEINTR);
#endif
        do_timer(regs);
/*
 * In the SMP case we use the local APIC timer interrupt to do the
 * profiling, except when we simulate SMP mode on a uniprocessor
 * system, in that case we have to call the local interrupt handler.
 */
#ifndef __SMP__
        if (!user_mode(regs))
                x86_do_profile(regs->eip);
#else
        if (!smp_found_config)
                smp_local_timer_interrupt(regs);
#endif

        /*
         * If we have an externally synchronized Linux clock, then update
         * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
         * called as close as possible to 500 ms before the new second starts.
         */
        if ((time_status & STA_UNSYNC) == 0 &&
            xtime.tv_sec > last_rtc_update + 660 &&
            xtime.tv_usec >= 500000 - ((unsigned) tick) / 2 &&
            xtime.tv_usec <= 500000 + ((unsigned) tick) / 2) {
                if (set_rtc_mmss(xtime.tv_sec) == 0)
                        last_rtc_update = xtime.tv_sec;
                else
                        last_rtc_update = xtime.tv_sec - 600; /* do it again in 60 s */
        }
            
#ifdef CONFIG_MCA
        if( MCA_bus ) {
                /* The PS/2 uses level-triggered interrupts.  You can't
                turn them off, nor would you want to (any attempt to
                enable edge-triggered interrupts usually gets intercepted by a
                special hardware circuit).  Hence we have to acknowledge
                the timer interrupt.  Through some incredibly stupid
                design idea, the reset for IRQ 0 is done by setting the
                high bit of the PPI port B (0x61).  Note that some PS/2s,
                notably the 55SX, work fine if this is removed.  */

                irq = inb_p( 0x61 );    /* read the current state */
                outb_p( irq|0x80, 0x61 );       /* reset the IRQ */
        }
#endif
}

static int use_tsc = 0;

/*
 * This is the same as the above, except we _also_ save the current
 * Time Stamp Counter value at the time of the timer interrupt, so that
 * we later on can estimate the time of day more exactly.
 */
static void timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
        int count;

        /*
         * Here we are in the timer irq handler. We just have irqs locally
         * disabled but we don't know if the timer_bh is running on the other
         * CPU. We need to avoid to SMP race with it. NOTE: we don' t need
         * the irq version of write_lock because as just said we have irq
         * locally disabled. -arca
         */
        write_lock(&xtime_lock);

        if (use_tsc)
        {
                /*
                 * It is important that these two operations happen almost at
                 * the same time. We do the RDTSC stuff first, since it's
                 * faster. To avoid any inconsistencies, we need interrupts
                 * disabled locally.
                 */

                /*
                 * Interrupts are just disabled locally since the timer irq
                 * has the SA_INTERRUPT flag set. -arca
                 */
        
                /* read Pentium cycle counter */
                __asm__("rdtsc" : "=a" (last_tsc_low) : : "edx");

                outb_p(0x00, 0x43);     /* latch the count ASAP */

                count = inb_p(0x40);    /* read the latched count */
                count |= inb(0x40) << 8;

                count = ((LATCH-1) - count) * TICK_SIZE;
                delay_at_last_interrupt = (count + LATCH/2) / LATCH;
        }
 
        do_timer_interrupt(irq, NULL, regs);

        write_unlock(&xtime_lock);

}

/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
 * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
 * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
 *
 * [For the Julian calendar (which was used in Russia before 1917,
 * Britain & colonies before 1752, anywhere else before 1582,
 * and is still in use by some communities) leave out the
 * -year/100+year/400 terms, and add 10.]
 *
 * This algorithm was first published by Gauss (I think).
 *
 * WARNING: this function will overflow on 2106-02-07 06:28:16 on
 * machines were long is 32-bit! (However, as time_t is signed, we
 * will already get problems at other places on 2038-01-19 03:14:08)
 */
static inline unsigned long mktime(unsigned int year, unsigned int mon,
        unsigned int day, unsigned int hour,
        unsigned int min, unsigned int sec)
{
        if (0 >= (int) (mon -= 2)) {    /* 1..12 -> 11,12,1..10 */
                mon += 12;      /* Puts Feb last since it has leap day */
                year -= 1;
        }
        return (((
            (unsigned long)(year/4 - year/100 + year/400 + 367*mon/12 + day) +
              year*365 - 719499
            )*24 + hour /* now have hours */
           )*60 + min /* now have minutes */
          )*60 + sec; /* finally seconds */
}

/* not static: needed by APM */
unsigned long get_cmos_time(void)
{
        unsigned int year, mon, day, hour, min, sec;
        int i;

        /* The Linux interpretation of the CMOS clock register contents:
         * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
         * RTC registers show the second which has precisely just started.
         * Let's hope other operating systems interpret the RTC the same way.
         */
        /* read RTC exactly on falling edge of update flag */
        for (i = 0 ; i < 1000000 ; i++) /* may take up to 1 second... */
                if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
                        break;
        for (i = 0 ; i < 1000000 ; i++) /* must try at least 2.228 ms */
                if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
                        break;
        do { /* Isn't this overkill ? UIP above should guarantee consistency */
                sec = CMOS_READ(RTC_SECONDS);
                min = CMOS_READ(RTC_MINUTES);
                hour = CMOS_READ(RTC_HOURS);
                day = CMOS_READ(RTC_DAY_OF_MONTH);
                mon = CMOS_READ(RTC_MONTH);
                year = CMOS_READ(RTC_YEAR);
        } while (sec != CMOS_READ(RTC_SECONDS));
        if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
          {
            BCD_TO_BIN(sec);
            BCD_TO_BIN(min);
            BCD_TO_BIN(hour);
            BCD_TO_BIN(day);
            BCD_TO_BIN(mon);
            BCD_TO_BIN(year);
          }
        if ((year += 1900) < 1970)
                year += 100;
        return mktime(year, mon, day, hour, min, sec);
}

static struct irqaction irq0  = { timer_interrupt, SA_INTERRUPT, 0, "timer", NULL, NULL};

/* ------ Calibrate the TSC ------- 
 * Return 2^32 * (1 / (TSC clocks per usec)) for do_fast_gettimeoffset().
 * Too much 64-bit arithmetic here to do this cleanly in C, and for
 * accuracy's sake we want to keep the overhead on the CTC speaker (channel 2)
 * output busy loop as low as possible. We avoid reading the CTC registers
 * directly because of the awkward 8-bit access mechanism of the 82C54
 * device.
 */

__initfunc(static unsigned long calibrate_tsc(void))
{
       unsigned long retval;

       __asm__( /* set the Gate high, program CTC channel 2 for mode 0
                 * (interrupt on terminal count mode), binary count, 
                 * load 5 * LATCH count, (LSB and MSB)
                 * to begin countdown, read the TSC and busy wait.
                 * BTW LATCH is calculated in timex.h from the HZ value
                 */

               /* Set the Gate high, disable speaker */
               "inb  $0x61, %%al\n\t" /* Read port */
               "andb $0xfd, %%al\n\t" /* Turn off speaker Data */
               "orb  $0x01, %%al\n\t" /* Set Gate high */
               "outb %%al, $0x61\n\t" /* Write port */

               /* Now let's take care of CTC channel 2 */
               "movb $0xb0, %%al\n\t" /* binary, mode 0, LSB/MSB, ch 2*/
               "outb %%al, $0x43\n\t" /* Write to CTC command port */
               "movl %1, %%eax\n\t"
               "outb %%al, $0x42\n\t" /* LSB of count */
               "shrl $8, %%eax\n\t"
               "outb %%al, $0x42\n\t" /* MSB of count */

               /* Read the TSC; counting has just started */
               "rdtsc\n\t"
               /* Move the value for safe-keeping. */
               "movl %%eax, %%ebx\n\t"
               "movl %%edx, %%ecx\n\t"

               /* Busy wait. Only 50 ms wasted at boot time. */
               "0: inb $0x61, %%al\n\t" /* Read Speaker Output Port */
               "testb $0x20, %%al\n\t" /* Check CTC channel 2 output (bit 5) */
               "jz 0b\n\t"

               /* And read the TSC.  5 jiffies (50.00077ms) have elapsed. */
               "rdtsc\n\t"

               /* Great.  So far so good.  Store last TSC reading in
                * last_tsc_low (only 32 lsb bits needed) */
               "movl %%eax, last_tsc_low\n\t"
               /* And now calculate the difference between the readings. */
               "subl %%ebx, %%eax\n\t"
               "sbbl %%ecx, %%edx\n\t" /* 64-bit subtract */
               /* but probably edx = 0 at this point (see below). */
               /* Now we have 5 * (TSC counts per jiffy) in eax.  We want
                * to calculate TSC->microsecond conversion factor. */

               /* Note that edx (high 32-bits of difference) will now be 
                * zero iff CPU clock speed is less than 85 GHz.  Moore's
                * law says that this is likely to be true for the next
                * 12 years or so.  You will have to change this code to
                * do a real 64-by-64 divide before that time's up. */
               "movl %%eax, %%ecx\n\t"
               "xorl %%eax, %%eax\n\t"
               "movl %2, %%edx\n\t"
               "divl %%ecx\n\t" /* eax= 2^32 / (1 * TSC counts per microsecond) */
               /* Return eax for the use of fast_gettimeoffset */
               "movl %%eax, %0\n\t"
               : "=r" (retval)
               : "r" (5 * LATCH), "r" (5 * 1000020/HZ)
               : /* we clobber: */ "ax", "bx", "cx", "dx", "cc", "memory");
       return retval;
}

__initfunc(void time_init(void))
{
        xtime.tv_sec = get_cmos_time();
        xtime.tv_usec = 0;

/*
 * If we have APM enabled or the CPU clock speed is variable
 * (CPU stops clock on HLT or slows clock to save power)
 * then the TSC timestamps may diverge by up to 1 jiffy from
 * 'real time' but nothing will break.
 * The most frequent case is that the CPU is "woken" from a halt
 * state by the timer interrupt itself, so we get 0 error. In the
 * rare cases where a driver would "wake" the CPU and request a
 * timestamp, the maximum error is < 1 jiffy. But timestamps are
 * still perfectly ordered.
 * Note that the TSC counter will be reset if APM suspends
 * to disk; this won't break the kernel, though, 'cuz we're
 * smart.  See arch/i386/kernel/apm.c.
 */
        /*
         *      Firstly we have to do a CPU check for chips with
         *      a potentially buggy TSC. At this point we haven't run
         *      the ident/bugs checks so we must run this hook as it
         *      may turn off the TSC flag.
         *
         *      NOTE: this doesnt yet handle SMP 486 machines where only
         *      some CPU's have a TSC. Thats never worked and nobody has
         *      moaned if you have the only one in the world - you fix it!
         */
 
        dodgy_tsc();
        
        if (boot_cpu_data.x86_capability & X86_FEATURE_TSC) {
#ifndef do_gettimeoffset
                do_gettimeoffset = do_fast_gettimeoffset;
#endif
                do_get_fast_time = do_gettimeofday;
                use_tsc = 1;
                fast_gettimeoffset_quotient = calibrate_tsc();
                
                /* report CPU clock rate in Hz.
                 * The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
                 * clock/second. Our precision is about 100 ppm.
                 */
                {       unsigned long eax=0, edx=1000000;
                        __asm__("divl %2"
                        :"=a" (cpu_hz), "=d" (edx)
                        :"r" (fast_gettimeoffset_quotient),
                        "0" (eax), "1" (edx));
                        printk("Detected %ld Hz processor.\n", cpu_hz);
                }
        }

#ifdef CONFIG_VISWS
        printk("Starting Cobalt Timer system clock\n");

        /* Set the countdown value */
        co_cpu_write(CO_CPU_TIMEVAL, CO_TIME_HZ/HZ);

        /* Start the timer */
        co_cpu_write(CO_CPU_CTRL, co_cpu_read(CO_CPU_CTRL) | CO_CTRL_TIMERUN);

        /* Enable (unmask) the timer interrupt */
        co_cpu_write(CO_CPU_CTRL, co_cpu_read(CO_CPU_CTRL) & ~CO_CTRL_TIMEMASK);

        /* Wire cpu IDT entry to s/w handler (and Cobalt APIC to IDT) */
        setup_x86_irq(CO_IRQ_TIMER, &irq0);
#else
        setup_x86_irq(0, &irq0);
#endif
}