systimer/cputimer: Add {systimer,cputimer}_intr_enable()

[dragonfly.git] / sys / platform / pc32 / isa / clock.c

/*-
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * William Jolitz and Don Ahn.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      from: @(#)clock.c       7.2 (Berkeley) 5/12/91
 * $FreeBSD: src/sys/i386/isa/clock.c,v 1.149.2.6 2002/11/02 04:41:50 iwasaki Exp $
 * $DragonFly: src/sys/platform/pc32/isa/clock.c,v 1.55 2008/08/02 01:14:43 dillon Exp $
 */

/*
 * Routines to handle clock hardware.
 */

/*
 * inittodr, settodr and support routines written
 * by Christoph Robitschko <chmr@edvz.tu-graz.ac.at>
 *
 * reintroduced and updated by Chris Stenton <chris@gnome.co.uk> 8/10/94
 */

#include "use_apm.h"
#include "opt_clock.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/eventhandler.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/bus.h>
#ifndef SMP
#include <sys/lock.h>
#endif
#include <sys/sysctl.h>
#include <sys/cons.h>
#include <sys/systimer.h>
#include <sys/globaldata.h>
#include <sys/thread2.h>
#include <sys/systimer.h>
#include <sys/machintr.h>

#include <machine/clock.h>
#ifdef CLK_CALIBRATION_LOOP
#endif
#include <machine/cputypes.h>
#include <machine/frame.h>
#include <machine/ipl.h>
#include <machine/limits.h>
#include <machine/md_var.h>
#include <machine/psl.h>
#include <machine/segments.h>
#include <machine/smp.h>
#include <machine/specialreg.h>

#include <machine_base/icu/icu.h>
#include <bus/isa/isa.h>
#include <bus/isa/rtc.h>
#include <machine_base/isa/timerreg.h>

#include <machine_base/isa/intr_machdep.h>

#ifdef APIC_IO
/* The interrupt triggered by the 8254 (timer) chip */
int apic_8254_intr;
static void setup_8254_mixed_mode (void);
#endif
static void i8254_restore(void);
static void resettodr_on_shutdown(void *arg __unused);

/*
 * 32-bit time_t's can't reach leap years before 1904 or after 2036, so we
 * can use a simple formula for leap years.
 */
#define LEAPYEAR(y) ((u_int)(y) % 4 == 0)
#define DAYSPERYEAR   (31+28+31+30+31+30+31+31+30+31+30+31)

#ifndef TIMER_FREQ
#define TIMER_FREQ   1193182
#endif

static uint8_t i8254_walltimer_sel;
static uint16_t i8254_walltimer_cntr;

int     adjkerntz;              /* local offset from GMT in seconds */
int     disable_rtc_set;        /* disable resettodr() if != 0 */
int     statclock_disable = 1;  /* we don't use the statclock right now */
int     tsc_present;
int64_t tsc_frequency;
int     tsc_is_broken;
int     wall_cmos_clock;        /* wall CMOS clock assumed if != 0 */
int     timer0_running;
enum tstate { RELEASED, ACQUIRED };
enum tstate timer0_state;
enum tstate timer1_state;
enum tstate timer2_state;

static  int     beeping = 0;
static  const u_char daysinmonth[] = {31,28,31,30,31,30,31,31,30,31,30,31};
static  u_char  rtc_statusa = RTCSA_DIVIDER | RTCSA_NOPROF;
static  u_char  rtc_statusb = RTCSB_24HR | RTCSB_PINTR;
static  int     rtc_loaded;

static int i8254_cputimer_div;

static struct callout sysbeepstop_ch;

static sysclock_t i8254_cputimer_count(void);
static void i8254_cputimer_construct(struct cputimer *cputimer, sysclock_t last);
static void i8254_cputimer_destruct(struct cputimer *cputimer);

static struct cputimer  i8254_cputimer = {
    SLIST_ENTRY_INITIALIZER,
    "i8254",
    CPUTIMER_PRI_8254,
    0,
    i8254_cputimer_count,
    cputimer_default_fromhz,
    cputimer_default_fromus,
    i8254_cputimer_construct,
    i8254_cputimer_destruct,
    TIMER_FREQ,
    0, 0, 0
};

/*
 * timer0 clock interrupt.  Timer0 is in one-shot mode and has stopped
 * counting as of this interrupt.  We use timer1 in free-running mode (not
 * generating any interrupts) as our main counter.  Each cpu has timeouts
 * pending.
 *
 * This code is INTR_MPSAFE and may be called without the BGL held.
 */
static void
clkintr(void *dummy, void *frame_arg)
{
        static sysclock_t sysclock_count;       /* NOTE! Must be static */
        struct globaldata *gd = mycpu;
#ifdef SMP
        struct globaldata *gscan;
        int n;
#endif

        /*
         * SWSTROBE mode is a one-shot, the timer is no longer running
         */
        timer0_running = 0;

        /*
         * XXX the dispatcher needs work.  right now we call systimer_intr()
         * directly or via IPI for any cpu with systimers queued, which is
         * usually *ALL* of them.  We need to use the LAPIC timer for this.
         */
        sysclock_count = sys_cputimer->count();
#ifdef SMP
        for (n = 0; n < ncpus; ++n) {
            gscan = globaldata_find(n);
            if (TAILQ_FIRST(&gscan->gd_systimerq) == NULL)
                continue;
            if (gscan != gd) {
                lwkt_send_ipiq3(gscan, (ipifunc3_t)systimer_intr, 
                                &sysclock_count, 0);
            } else {
                systimer_intr(&sysclock_count, 0, frame_arg);
            }
        }
#else
        if (TAILQ_FIRST(&gd->gd_systimerq) != NULL)
            systimer_intr(&sysclock_count, 0, frame_arg);
#endif
}


/*
 * NOTE! not MP safe.
 */
int
acquire_timer2(int mode)
{
        if (timer2_state != RELEASED)
                return (-1);
        timer2_state = ACQUIRED;

        /*
         * This access to the timer registers is as atomic as possible
         * because it is a single instruction.  We could do better if we
         * knew the rate.
         */
        outb(TIMER_MODE, TIMER_SEL2 | (mode & 0x3f));
        return (0);
}

int
release_timer2(void)
{
        if (timer2_state != ACQUIRED)
                return (-1);
        outb(TIMER_MODE, TIMER_SEL2 | TIMER_SQWAVE | TIMER_16BIT);
        timer2_state = RELEASED;
        return (0);
}

/*
 * This routine receives statistical clock interrupts from the RTC.
 * As explained above, these occur at 128 interrupts per second.
 * When profiling, we receive interrupts at a rate of 1024 Hz.
 *
 * This does not actually add as much overhead as it sounds, because
 * when the statistical clock is active, the hardclock driver no longer
 * needs to keep (inaccurate) statistics on its own.  This decouples
 * statistics gathering from scheduling interrupts.
 *
 * The RTC chip requires that we read status register C (RTC_INTR)
 * to acknowledge an interrupt, before it will generate the next one.
 * Under high interrupt load, rtcintr() can be indefinitely delayed and
 * the clock can tick immediately after the read from RTC_INTR.  In this
 * case, the mc146818A interrupt signal will not drop for long enough
 * to register with the 8259 PIC.  If an interrupt is missed, the stat
 * clock will halt, considerably degrading system performance.  This is
 * why we use 'while' rather than a more straightforward 'if' below.
 * Stat clock ticks can still be lost, causing minor loss of accuracy
 * in the statistics, but the stat clock will no longer stop.
 */
static void
rtcintr(void *dummy, void *frame)
{
        while (rtcin(RTC_INTR) & RTCIR_PERIOD)
                ;
                /* statclock(frame); no longer used */
}

#include "opt_ddb.h"
#ifdef DDB
#include <ddb/ddb.h>

DB_SHOW_COMMAND(rtc, rtc)
{
        kprintf("%02x/%02x/%02x %02x:%02x:%02x, A = %02x, B = %02x, C = %02x\n",
               rtcin(RTC_YEAR), rtcin(RTC_MONTH), rtcin(RTC_DAY),
               rtcin(RTC_HRS), rtcin(RTC_MIN), rtcin(RTC_SEC),
               rtcin(RTC_STATUSA), rtcin(RTC_STATUSB), rtcin(RTC_INTR));
}
#endif /* DDB */

/*
 * Return the current cpu timer count as a 32 bit integer.
 */
static
sysclock_t
i8254_cputimer_count(void)
{
        static __uint16_t cputimer_last;
        __uint16_t count;
        sysclock_t ret;

        clock_lock();
        outb(TIMER_MODE, i8254_walltimer_sel | TIMER_LATCH);
        count = (__uint8_t)inb(i8254_walltimer_cntr);           /* get countdown */
        count |= ((__uint8_t)inb(i8254_walltimer_cntr) << 8);
        count = -count;                                 /* -> countup */
        if (count < cputimer_last)                      /* rollover */
                i8254_cputimer.base += 0x00010000;
        ret = i8254_cputimer.base | count;
        cputimer_last = count;
        clock_unlock();
        return(ret);
}

/*
 * This function is called whenever the system timebase changes, allowing
 * us to calculate what is needed to convert a system timebase tick 
 * into an 8254 tick for the interrupt timer.  If we can convert to a
 * simple shift, multiplication, or division, we do so.  Otherwise 64
 * bit arithmatic is required every time the interrupt timer is reloaded.
 */
void
cputimer_intr_config(struct cputimer *timer)
{
    int freq;
    int div;

    /*
     * Will a simple divide do the trick?
     */
    div = (timer->freq + (i8254_cputimer.freq / 2)) / i8254_cputimer.freq;
    freq = i8254_cputimer.freq * div;

    if (freq >= timer->freq - 1 && freq <= timer->freq + 1)
        i8254_cputimer_div = div;
    else
        i8254_cputimer_div = 0;
}

/*
 * Reload for the next timeout.  It is possible for the reload value
 * to be 0 or negative, indicating that an immediate timer interrupt
 * is desired.  For now make the minimum 2 ticks.
 *
 * We may have to convert from the system timebase to the 8254 timebase.
 */
static void
i8254_intr_reload(sysclock_t reload)
{
    __uint16_t count;

    if (i8254_cputimer_div)
        reload /= i8254_cputimer_div;
    else
        reload = (int64_t)reload * i8254_cputimer.freq / sys_cputimer->freq;

    if ((int)reload < 2)
        reload = 2;

    clock_lock();
    if (timer0_running) {
        outb(TIMER_MODE, TIMER_SEL0 | TIMER_LATCH);     /* count-down timer */
        count = (__uint8_t)inb(TIMER_CNTR0);            /* lsb */
        count |= ((__uint8_t)inb(TIMER_CNTR0) << 8);    /* msb */
        if (reload < count) {
            outb(TIMER_MODE, TIMER_SEL0 | TIMER_SWSTROBE | TIMER_16BIT);
            outb(TIMER_CNTR0, (__uint8_t)reload);       /* lsb */
            outb(TIMER_CNTR0, (__uint8_t)(reload >> 8)); /* msb */
        }
    } else {
        timer0_running = 1;
        if (reload > 0xFFFF)
            reload = 0;         /* full count */
        outb(TIMER_MODE, TIMER_SEL0 | TIMER_SWSTROBE | TIMER_16BIT);
        outb(TIMER_CNTR0, (__uint8_t)reload);           /* lsb */
        outb(TIMER_CNTR0, (__uint8_t)(reload >> 8));    /* msb */
    }
    clock_unlock();
}

#ifdef SMP
extern void     lapic_timer_intr_reload(sysclock_t);
#endif

void
cputimer_intr_reload(sysclock_t reload)
{
        i8254_intr_reload(reload);
#ifdef SMP
        lapic_timer_intr_reload(reload);
#endif
}

void
cputimer_intr_enable(void)
{
}

/*
 * DELAY(usec)       - Spin for the specified number of microseconds.
 * DRIVERSLEEP(usec) - Spin for the specified number of microseconds,
 *                     but do a thread switch in the loop
 *
 * Relies on timer 1 counting down from (cputimer_freq / hz)
 * Note: timer had better have been programmed before this is first used!
 */
static void
DODELAY(int n, int doswitch)
{
        int delta, prev_tick, tick, ticks_left;

#ifdef DELAYDEBUG
        int getit_calls = 1;
        int n1;
        static int state = 0;

        if (state == 0) {
                state = 1;
                for (n1 = 1; n1 <= 10000000; n1 *= 10)
                        DELAY(n1);
                state = 2;
        }
        if (state == 1)
                kprintf("DELAY(%d)...", n);
#endif
        /*
         * Guard against the timer being uninitialized if we are called
         * early for console i/o.
         */
        if (timer0_state == RELEASED)
                i8254_restore();

        /*
         * Read the counter first, so that the rest of the setup overhead is
         * counted.  Then calculate the number of hardware timer ticks
         * required, rounding up to be sure we delay at least the requested
         * number of microseconds.
         */
        prev_tick = sys_cputimer->count();
        ticks_left = ((u_int)n * (int64_t)sys_cputimer->freq + 999999) /
                     1000000;

        /*
         * Loop until done.
         */
        while (ticks_left > 0) {
                tick = sys_cputimer->count();
#ifdef DELAYDEBUG
                ++getit_calls;
#endif
                delta = tick - prev_tick;
                prev_tick = tick;
                if (delta < 0)
                        delta = 0;
                ticks_left -= delta;
                if (doswitch && ticks_left > 0)
                        lwkt_switch();
        }
#ifdef DELAYDEBUG
        if (state == 1)
                kprintf(" %d calls to getit() at %d usec each\n",
                       getit_calls, (n + 5) / getit_calls);
#endif
}

void
DELAY(int n)
{
        DODELAY(n, 0);
}

void
DRIVERSLEEP(int usec)
{
        globaldata_t gd = mycpu;

        if (gd->gd_intr_nesting_level || 
            gd->gd_spinlock_rd ||
            gd->gd_spinlocks_wr) {
                DODELAY(usec, 0);
        } else {
                DODELAY(usec, 1);
        }
}

static void
sysbeepstop(void *chan)
{
        outb(IO_PPI, inb(IO_PPI)&0xFC); /* disable counter2 output to speaker */
        beeping = 0;
        release_timer2();
}

int
sysbeep(int pitch, int period)
{
        if (acquire_timer2(TIMER_SQWAVE|TIMER_16BIT))
                return(-1);
        /*
         * Nobody else is using timer2, we do not need the clock lock
         */
        outb(TIMER_CNTR2, pitch);
        outb(TIMER_CNTR2, (pitch>>8));
        if (!beeping) {
                /* enable counter2 output to speaker */
                outb(IO_PPI, inb(IO_PPI) | 3);
                beeping = period;
                callout_reset(&sysbeepstop_ch, period, sysbeepstop, NULL);
        }
        return (0);
}

/*
 * RTC support routines
 */

int
rtcin(int reg)
{
        u_char val;

        crit_enter();
        outb(IO_RTC, reg);
        inb(0x84);
        val = inb(IO_RTC + 1);
        inb(0x84);
        crit_exit();
        return (val);
}

static __inline void
writertc(u_char reg, u_char val)
{
        crit_enter();
        inb(0x84);
        outb(IO_RTC, reg);
        inb(0x84);
        outb(IO_RTC + 1, val);
        inb(0x84);              /* XXX work around wrong order in rtcin() */
        crit_exit();
}

static __inline int
readrtc(int port)
{
        return(bcd2bin(rtcin(port)));
}

static u_int
calibrate_clocks(void)
{
        u_int64_t old_tsc;
        u_int count, prev_count, tot_count;
        int sec, start_sec, timeout;

        if (bootverbose)
                kprintf("Calibrating clock(s) ... ");
        if (!(rtcin(RTC_STATUSD) & RTCSD_PWR))
                goto fail;
        timeout = 100000000;

        /* Read the mc146818A seconds counter. */
        for (;;) {
                if (!(rtcin(RTC_STATUSA) & RTCSA_TUP)) {
                        sec = rtcin(RTC_SEC);
                        break;
                }
                if (--timeout == 0)
                        goto fail;
        }

        /* Wait for the mC146818A seconds counter to change. */
        start_sec = sec;
        for (;;) {
                if (!(rtcin(RTC_STATUSA) & RTCSA_TUP)) {
                        sec = rtcin(RTC_SEC);
                        if (sec != start_sec)
                                break;
                }
                if (--timeout == 0)
                        goto fail;
        }

        /* Start keeping track of the i8254 counter. */
        prev_count = sys_cputimer->count();
        tot_count = 0;

        if (tsc_present) 
                old_tsc = rdtsc();
        else
                old_tsc = 0;            /* shut up gcc */

        /*
         * Wait for the mc146818A seconds counter to change.  Read the i8254
         * counter for each iteration since this is convenient and only
         * costs a few usec of inaccuracy. The timing of the final reads
         * of the counters almost matches the timing of the initial reads,
         * so the main cause of inaccuracy is the varying latency from 
         * inside getit() or rtcin(RTC_STATUSA) to the beginning of the
         * rtcin(RTC_SEC) that returns a changed seconds count.  The
         * maximum inaccuracy from this cause is < 10 usec on 486's.
         */
        start_sec = sec;
        for (;;) {
                if (!(rtcin(RTC_STATUSA) & RTCSA_TUP))
                        sec = rtcin(RTC_SEC);
                count = sys_cputimer->count();
                tot_count += (int)(count - prev_count);
                prev_count = count;
                if (sec != start_sec)
                        break;
                if (--timeout == 0)
                        goto fail;
        }

        /*
         * Read the cpu cycle counter.  The timing considerations are
         * similar to those for the i8254 clock.
         */
        if (tsc_present) {
                tsc_frequency = rdtsc() - old_tsc;
        }

        if (tsc_present)
                kprintf("TSC clock: %llu Hz, ", tsc_frequency);
        kprintf("i8254 clock: %u Hz\n", tot_count);
        return (tot_count);

fail:
        kprintf("failed, using default i8254 clock of %u Hz\n",
                i8254_cputimer.freq);
        return (i8254_cputimer.freq);
}

static void
i8254_restore(void)
{
        timer0_state = ACQUIRED;

        clock_lock();

        /*
         * Timer0 is our fine-grained variable clock interrupt
         */
        outb(TIMER_MODE, TIMER_SEL0 | TIMER_SWSTROBE | TIMER_16BIT);
        outb(TIMER_CNTR0, 2);   /* lsb */
        outb(TIMER_CNTR0, 0);   /* msb */
        clock_unlock();

        /*
         * Timer1 or timer2 is our free-running clock, but only if another
         * has not been selected.
         */
        cputimer_register(&i8254_cputimer);
        cputimer_select(&i8254_cputimer, 0);
}

static void
i8254_cputimer_construct(struct cputimer *timer, sysclock_t oldclock)
{
        int which;

        /*
         * Should we use timer 1 or timer 2 ?
         */
        which = 0;
        TUNABLE_INT_FETCH("hw.i8254.walltimer", &which);
        if (which != 1 && which != 2)
                which = 2;

        switch(which) {
        case 1:
                timer->name = "i8254_timer1";
                timer->type = CPUTIMER_8254_SEL1;
                i8254_walltimer_sel = TIMER_SEL1;
                i8254_walltimer_cntr = TIMER_CNTR1;
                timer1_state = ACQUIRED;
                break;
        case 2:
                timer->name = "i8254_timer2";
                timer->type = CPUTIMER_8254_SEL2;
                i8254_walltimer_sel = TIMER_SEL2;
                i8254_walltimer_cntr = TIMER_CNTR2;
                timer2_state = ACQUIRED;
                break;
        }

        timer->base = (oldclock + 0xFFFF) & ~0xFFFF;

        clock_lock();
        outb(TIMER_MODE, i8254_walltimer_sel | TIMER_RATEGEN | TIMER_16BIT);
        outb(i8254_walltimer_cntr, 0);  /* lsb */
        outb(i8254_walltimer_cntr, 0);  /* msb */
        outb(IO_PPI, inb(IO_PPI) | 1);  /* bit 0: enable gate, bit 1: spkr */
        clock_unlock();
}

static void
i8254_cputimer_destruct(struct cputimer *timer)
{
        switch(timer->type) {
        case CPUTIMER_8254_SEL1:
            timer1_state = RELEASED;
            break;
        case CPUTIMER_8254_SEL2:
            timer2_state = RELEASED;
            break;
        default:
            break;
        }
        timer->type = 0;
}

static void
rtc_restore(void)
{
        /* Restore all of the RTC's "status" (actually, control) registers. */
        writertc(RTC_STATUSB, RTCSB_24HR);
        writertc(RTC_STATUSA, rtc_statusa);
        writertc(RTC_STATUSB, rtc_statusb);
}

/*
 * Restore all the timers.
 *
 * This function is called to resynchronize our core timekeeping after a
 * long halt, e.g. from apm_default_resume() and friends.  It is also 
 * called if after a BIOS call we have detected munging of the 8254.
 * It is necessary because cputimer_count() counter's delta may have grown
 * too large for nanouptime() and friends to handle, or (in the case of 8254
 * munging) might cause the SYSTIMER code to prematurely trigger.
 */
void
timer_restore(void)
{
        crit_enter();
        i8254_restore();                /* restore timer_freq and hz */
        rtc_restore();                  /* reenable RTC interrupts */
        crit_exit();
}

/*
 * Initialize 8254 timer 0 early so that it can be used in DELAY().
 */
void
startrtclock(void)
{
        u_int delta, freq;

        /* 
         * Can we use the TSC?
         */
        if (cpu_feature & CPUID_TSC)
                tsc_present = 1;
        else
                tsc_present = 0;

        /*
         * Initial RTC state, don't do anything unexpected
         */
        writertc(RTC_STATUSA, rtc_statusa);
        writertc(RTC_STATUSB, RTCSB_24HR);

        /*
         * Set the 8254 timer0 in TIMER_SWSTROBE mode and cause it to 
         * generate an interrupt, which we will ignore for now.
         *
         * Set the 8254 timer1 in TIMER_RATEGEN mode and load 0x0000
         * (so it counts a full 2^16 and repeats).  We will use this timer
         * for our counting.
         */
        i8254_restore();
        freq = calibrate_clocks();
#ifdef CLK_CALIBRATION_LOOP
        if (bootverbose) {
                kprintf(
                "Press a key on the console to abort clock calibration\n");
                while (cncheckc() == -1)
                        calibrate_clocks();
        }
#endif

        /*
         * Use the calibrated i8254 frequency if it seems reasonable.
         * Otherwise use the default, and don't use the calibrated i586
         * frequency.
         */
        delta = freq > i8254_cputimer.freq ? 
                        freq - i8254_cputimer.freq : i8254_cputimer.freq - freq;
        if (delta < i8254_cputimer.freq / 100) {
#ifndef CLK_USE_I8254_CALIBRATION
                if (bootverbose)
                        kprintf(
"CLK_USE_I8254_CALIBRATION not specified - using default frequency\n");
                freq = i8254_cputimer.freq;
#endif
                cputimer_set_frequency(&i8254_cputimer, freq);
        } else {
                if (bootverbose)
                        kprintf(
                    "%d Hz differs from default of %d Hz by more than 1%%\n",
                               freq, i8254_cputimer.freq);
                tsc_frequency = 0;
        }

#ifndef CLK_USE_TSC_CALIBRATION
        if (tsc_frequency != 0) {
                if (bootverbose)
                        kprintf(
"CLK_USE_TSC_CALIBRATION not specified - using old calibration method\n");
                tsc_frequency = 0;
        }
#endif
        if (tsc_present && tsc_frequency == 0) {
                /*
                 * Calibration of the i586 clock relative to the mc146818A
                 * clock failed.  Do a less accurate calibration relative
                 * to the i8254 clock.
                 */
                u_int64_t old_tsc = rdtsc();

                DELAY(1000000);
                tsc_frequency = rdtsc() - old_tsc;
#ifdef CLK_USE_TSC_CALIBRATION
                if (bootverbose) {
                        kprintf("TSC clock: %llu Hz (Method B)\n",
                                tsc_frequency);
                }
#endif
        }

        EVENTHANDLER_REGISTER(shutdown_post_sync, resettodr_on_shutdown, NULL, SHUTDOWN_PRI_LAST);

#if !defined(SMP)
        /*
         * We can not use the TSC in SMP mode, until we figure out a
         * cheap (impossible), reliable and precise (yeah right!)  way
         * to synchronize the TSCs of all the CPUs.
         * Curse Intel for leaving the counter out of the I/O APIC.
         */

#if NAPM > 0
        /*
         * We can not use the TSC if we support APM. Precise timekeeping
         * on an APM'ed machine is at best a fools pursuit, since 
         * any and all of the time spent in various SMM code can't 
         * be reliably accounted for.  Reading the RTC is your only
         * source of reliable time info.  The i8254 looses too of course
         * but we need to have some kind of time...
         * We don't know at this point whether APM is going to be used
         * or not, nor when it might be activated.  Play it safe.
         */
        return;
#endif /* NAPM > 0 */

#endif /* !defined(SMP) */
}

/*
 * Sync the time of day back to the RTC on shutdown, but only if
 * we have already loaded it and have not crashed.
 */
static void
resettodr_on_shutdown(void *arg __unused)
{
        if (rtc_loaded && panicstr == NULL) {
                resettodr();
        }
}

/*
 * Initialize the time of day register, based on the time base which is, e.g.
 * from a filesystem.
 */
void
inittodr(time_t base)
{
        unsigned long   sec, days;
        int             yd;
        int             year, month;
        int             y, m;
        struct timespec ts;

        if (base) {
                ts.tv_sec = base;
                ts.tv_nsec = 0;
                set_timeofday(&ts);
        }

        /* Look if we have a RTC present and the time is valid */
        if (!(rtcin(RTC_STATUSD) & RTCSD_PWR))
                goto wrong_time;

        /* wait for time update to complete */
        /* If RTCSA_TUP is zero, we have at least 244us before next update */
        crit_enter();
        while (rtcin(RTC_STATUSA) & RTCSA_TUP) {
                crit_exit();
                crit_enter();
        }

        days = 0;
#ifdef USE_RTC_CENTURY
        year = readrtc(RTC_YEAR) + readrtc(RTC_CENTURY) * 100;
#else
        year = readrtc(RTC_YEAR) + 1900;
        if (year < 1970)
                year += 100;
#endif
        if (year < 1970) {
                crit_exit();
                goto wrong_time;
        }
        month = readrtc(RTC_MONTH);
        for (m = 1; m < month; m++)
                days += daysinmonth[m-1];
        if ((month > 2) && LEAPYEAR(year))
                days ++;
        days += readrtc(RTC_DAY) - 1;
        yd = days;
        for (y = 1970; y < year; y++)
                days += DAYSPERYEAR + LEAPYEAR(y);
        sec = ((( days * 24 +
                  readrtc(RTC_HRS)) * 60 +
                  readrtc(RTC_MIN)) * 60 +
                  readrtc(RTC_SEC));
        /* sec now contains the number of seconds, since Jan 1 1970,
           in the local time zone */

        sec += tz.tz_minuteswest * 60 + (wall_cmos_clock ? adjkerntz : 0);

        y = time_second - sec;
        if (y <= -2 || y >= 2) {
                /* badly off, adjust it */
                ts.tv_sec = sec;
                ts.tv_nsec = 0;
                set_timeofday(&ts);
        }
        rtc_loaded = 1;
        crit_exit();
        return;

wrong_time:
        kprintf("Invalid time in real time clock.\n");
        kprintf("Check and reset the date immediately!\n");
}

/*
 * Write system time back to RTC
 */
void
resettodr(void)
{
        struct timeval tv;
        unsigned long tm;
        int m;
        int y;

        if (disable_rtc_set)
                return;

        microtime(&tv);
        tm = tv.tv_sec;

        crit_enter();
        /* Disable RTC updates and interrupts. */
        writertc(RTC_STATUSB, RTCSB_HALT | RTCSB_24HR);

        /* Calculate local time to put in RTC */

        tm -= tz.tz_minuteswest * 60 + (wall_cmos_clock ? adjkerntz : 0);

        writertc(RTC_SEC, bin2bcd(tm%60)); tm /= 60;    /* Write back Seconds */
        writertc(RTC_MIN, bin2bcd(tm%60)); tm /= 60;    /* Write back Minutes */
        writertc(RTC_HRS, bin2bcd(tm%24)); tm /= 24;    /* Write back Hours   */

        /* We have now the days since 01-01-1970 in tm */
        writertc(RTC_WDAY, (tm+4)%7);                   /* Write back Weekday */
        for (y = 1970, m = DAYSPERYEAR + LEAPYEAR(y);
             tm >= m;
             y++,      m = DAYSPERYEAR + LEAPYEAR(y))
             tm -= m;

        /* Now we have the years in y and the day-of-the-year in tm */
        writertc(RTC_YEAR, bin2bcd(y%100));             /* Write back Year    */
#ifdef USE_RTC_CENTURY
        writertc(RTC_CENTURY, bin2bcd(y/100));          /* ... and Century    */
#endif
        for (m = 0; ; m++) {
                int ml;

                ml = daysinmonth[m];
                if (m == 1 && LEAPYEAR(y))
                        ml++;
                if (tm < ml)
                        break;
                tm -= ml;
        }

        writertc(RTC_MONTH, bin2bcd(m + 1));            /* Write back Month   */
        writertc(RTC_DAY, bin2bcd(tm + 1));             /* Write back Month Day */

        /* Reenable RTC updates and interrupts. */
        writertc(RTC_STATUSB, rtc_statusb);
        crit_exit();
}


/*
 * Start both clocks running.  DragonFly note: the stat clock is no longer
 * used.  Instead, 8254 based systimers are used for all major clock
 * interrupts.  statclock_disable is set by default.
 */
void
cpu_initclocks(void *arg __unused)
{
        int diag;
#ifdef APIC_IO
        int apic_8254_trial;
        void *clkdesc;
#endif /* APIC_IO */

        callout_init(&sysbeepstop_ch);

        if (statclock_disable) {
                /*
                 * The stat interrupt mask is different without the
                 * statistics clock.  Also, don't set the interrupt
                 * flag which would normally cause the RTC to generate
                 * interrupts.
                 */
                rtc_statusb = RTCSB_24HR;
        } else {
                /* Setting stathz to nonzero early helps avoid races. */
                stathz = RTC_NOPROFRATE;
                profhz = RTC_PROFRATE;
        }

        /* Finish initializing 8253 timer 0. */
#ifdef APIC_IO

        apic_8254_intr = isa_apic_irq(0);
        apic_8254_trial = 0;
        if (apic_8254_intr >= 0 ) {
                if (apic_int_type(0, 0) == 3)
                        apic_8254_trial = 1;
        } else {
                /* look for ExtInt on pin 0 */
                if (apic_int_type(0, 0) == 3) {
                        apic_8254_intr = apic_irq(0, 0);
                        setup_8254_mixed_mode();
                } else 
                        panic("APIC_IO: Cannot route 8254 interrupt to CPU");
        }

        clkdesc = register_int(apic_8254_intr, clkintr, NULL, "clk",
                               NULL,
                               INTR_EXCL | INTR_FAST | 
                               INTR_NOPOLL | INTR_MPSAFE | 
                               INTR_NOENTROPY);
        machintr_intren(apic_8254_intr);
        
#else /* APIC_IO */

        register_int(0, clkintr, NULL, "clk", NULL,
                     INTR_EXCL | INTR_FAST | 
                     INTR_NOPOLL | INTR_MPSAFE |
                     INTR_NOENTROPY);
        machintr_intren(ICU_IRQ0);

#endif /* APIC_IO */

        /* Initialize RTC. */
        writertc(RTC_STATUSA, rtc_statusa);
        writertc(RTC_STATUSB, RTCSB_24HR);

        if (statclock_disable == 0) {
                diag = rtcin(RTC_DIAG);
                if (diag != 0)
                        kprintf("RTC BIOS diagnostic error %b\n", diag, RTCDG_BITS);

#ifdef APIC_IO
                if (isa_apic_irq(8) != 8)
                        panic("APIC RTC != 8");
#endif /* APIC_IO */

                register_int(8, (inthand2_t *)rtcintr, NULL, "rtc", NULL,
                             INTR_EXCL | INTR_FAST | INTR_NOPOLL |
                             INTR_NOENTROPY);
                machintr_intren(8);

                writertc(RTC_STATUSB, rtc_statusb);
        }

#ifdef APIC_IO
        if (apic_8254_trial) {
                sysclock_t base;
                long lastcnt;

                /*
                 * Following code assumes the 8254 is the cpu timer,
                 * so make sure it is.
                 */
                KKASSERT(sys_cputimer == &i8254_cputimer);

                lastcnt = get_interrupt_counter(apic_8254_intr);

                /*
                 * Force an 8254 Timer0 interrupt and wait 1/100s for
                 * it to happen, then see if we got it.
                 */
                kprintf("APIC_IO: Testing 8254 interrupt delivery\n");
                i8254_intr_reload(2);
                base = sys_cputimer->count();
                while (sys_cputimer->count() - base < sys_cputimer->freq / 100)
                        ;       /* nothing */
                if (get_interrupt_counter(apic_8254_intr) - lastcnt == 0) {
                        /* 
                         * The MP table is broken.
                         * The 8254 was not connected to the specified pin
                         * on the IO APIC.
                         * Workaround: Limited variant of mixed mode.
                         */
                        machintr_intrdis(apic_8254_intr);
                        unregister_int(clkdesc);
                        kprintf("APIC_IO: Broken MP table detected: "
                               "8254 is not connected to "
                               "IOAPIC #%d intpin %d\n",
                               int_to_apicintpin[apic_8254_intr].ioapic,
                               int_to_apicintpin[apic_8254_intr].int_pin);
                        /* 
                         * Revoke current ISA IRQ 0 assignment and 
                         * configure a fallback interrupt routing from
                         * the 8254 Timer via the 8259 PIC to the
                         * an ExtInt interrupt line on IOAPIC #0 intpin 0.
                         * We reuse the low level interrupt handler number.
                         */
                        if (apic_irq(0, 0) < 0) {
                                revoke_apic_irq(apic_8254_intr);
                                assign_apic_irq(0, 0, apic_8254_intr);
                        }
                        apic_8254_intr = apic_irq(0, 0);
                        setup_8254_mixed_mode();
                        register_int(apic_8254_intr, clkintr, NULL, "clk",
                                     NULL,
                                     INTR_EXCL | INTR_FAST | 
                                     INTR_NOPOLL | INTR_MPSAFE |
                                     INTR_NOENTROPY);
                        machintr_intren(apic_8254_intr);
                }
                
        }
        if (apic_int_type(0, 0) != 3 ||
            int_to_apicintpin[apic_8254_intr].ioapic != 0 ||
            int_to_apicintpin[apic_8254_intr].int_pin != 0) {
                kprintf("APIC_IO: routing 8254 via IOAPIC #%d intpin %d\n",
                       int_to_apicintpin[apic_8254_intr].ioapic,
                       int_to_apicintpin[apic_8254_intr].int_pin);
        } else {
                kprintf("APIC_IO: "
                       "routing 8254 via 8259 and IOAPIC #0 intpin 0\n");
        }
#endif
}
SYSINIT(clocks8254, SI_BOOT2_CLOCKREG, SI_ORDER_FIRST, cpu_initclocks, NULL)

#ifdef APIC_IO

static void 
setup_8254_mixed_mode(void)
{
        /*
         * Allow 8254 timer to INTerrupt 8259:
         *  re-initialize master 8259:
         *   reset; prog 4 bytes, single ICU, edge triggered
         */
        outb(IO_ICU1, 0x13);
        outb(IO_ICU1 + 1, IDT_OFFSET);  /* start vector (unused) */
        outb(IO_ICU1 + 1, 0x00);        /* ignore slave */
        outb(IO_ICU1 + 1, 0x03);        /* auto EOI, 8086 */
        outb(IO_ICU1 + 1, 0xfe);        /* unmask INT0 */
        
        /* program IO APIC for type 3 INT on INT0 */
        if (ext_int_setup(0, 0) < 0)
                panic("8254 redirect via APIC pin0 impossible!");
}
#endif

void
setstatclockrate(int newhz)
{
        if (newhz == RTC_PROFRATE)
                rtc_statusa = RTCSA_DIVIDER | RTCSA_PROF;
        else
                rtc_statusa = RTCSA_DIVIDER | RTCSA_NOPROF;
        writertc(RTC_STATUSA, rtc_statusa);
}

#if 0
static unsigned
tsc_get_timecount(struct timecounter *tc)
{
        return (rdtsc());
}
#endif

#ifdef KERN_TIMESTAMP
#define KERN_TIMESTAMP_SIZE 16384
static u_long tsc[KERN_TIMESTAMP_SIZE] ;
SYSCTL_OPAQUE(_debug, OID_AUTO, timestamp, CTLFLAG_RD, tsc,
        sizeof(tsc), "LU", "Kernel timestamps");
void  
_TSTMP(u_int32_t x)
{
        static int i;

        tsc[i] = (u_int32_t)rdtsc();
        tsc[i+1] = x;
        i = i + 2;
        if (i >= KERN_TIMESTAMP_SIZE)
                i = 0;
        tsc[i] = 0; /* mark last entry */
}
#endif /* KERN_TIMESTAMP */

/*
 *
 */

static int
hw_i8254_timestamp(SYSCTL_HANDLER_ARGS)
{
    sysclock_t count;
    __uint64_t tscval;
    char buf[32];

    crit_enter();
    if (sys_cputimer == &i8254_cputimer)
        count = sys_cputimer->count();
    else
        count = 0;
    if (tsc_present)
        tscval = rdtsc();
    else
        tscval = 0;
    crit_exit();
    ksnprintf(buf, sizeof(buf), "%08x %016llx", count, (long long)tscval);
    return(SYSCTL_OUT(req, buf, strlen(buf) + 1));
}

SYSCTL_NODE(_hw, OID_AUTO, i8254, CTLFLAG_RW, 0, "I8254");
SYSCTL_UINT(_hw_i8254, OID_AUTO, freq, CTLFLAG_RD, &i8254_cputimer.freq, 0,
            "frequency");
SYSCTL_PROC(_hw_i8254, OID_AUTO, timestamp, CTLTYPE_STRING|CTLFLAG_RD,
            0, 0, hw_i8254_timestamp, "A", "");

SYSCTL_INT(_hw, OID_AUTO, tsc_present, CTLFLAG_RD,
            &tsc_present, 0, "TSC Available");
SYSCTL_QUAD(_hw, OID_AUTO, tsc_frequency, CTLFLAG_RD,
            &tsc_frequency, 0, "TSC Frequency");