source: rtems-libbsd/freebsd/kern/kern_tc.c @ 562783d

#include <freebsd/machine/rtems-bsd-config.h>

/*-
 * ----------------------------------------------------------------------------
 * "THE BEER-WARE LICENSE" (Revision 42):
 * <phk@FreeBSD.ORG> wrote this file.  As long as you retain this notice you
 * can do whatever you want with this stuff. If we meet some day, and you think
 * this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
 * ----------------------------------------------------------------------------
 */

#include <freebsd/sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <freebsd/local/opt_ntp.h>

#include <freebsd/sys/param.h>
#include <freebsd/sys/kernel.h>
#include <freebsd/sys/sysctl.h>
#include <freebsd/sys/syslog.h>
#include <freebsd/sys/systm.h>
#include <freebsd/sys/timepps.h>
#include <freebsd/sys/timetc.h>
#include <freebsd/sys/timex.h>

/*
 * A large step happens on boot.  This constant detects such steps.
 * It is relatively small so that ntp_update_second gets called enough
 * in the typical 'missed a couple of seconds' case, but doesn't loop
 * forever when the time step is large.
 */
#define LARGE_STEP      200

/*
 * Implement a dummy timecounter which we can use until we get a real one
 * in the air.  This allows the console and other early stuff to use
 * time services.
 */

static u_int
dummy_get_timecount(struct timecounter *tc)
{
        static u_int now;

        return (++now);
}

static struct timecounter dummy_timecounter = {
        dummy_get_timecount, 0, ~0u, 1000000, "dummy", -1000000
};

struct timehands {
        /* These fields must be initialized by the driver. */
        struct timecounter      *th_counter;
        int64_t                 th_adjustment;
        u_int64_t               th_scale;
        u_int                   th_offset_count;
        struct bintime          th_offset;
        struct timeval          th_microtime;
        struct timespec         th_nanotime;
        /* Fields not to be copied in tc_windup start with th_generation. */
        volatile u_int          th_generation;
        struct timehands        *th_next;
};

static struct timehands th0;
static struct timehands th9 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th0};
static struct timehands th8 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th9};
static struct timehands th7 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th8};
static struct timehands th6 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th7};
static struct timehands th5 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th6};
static struct timehands th4 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th5};
static struct timehands th3 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th4};
static struct timehands th2 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th3};
static struct timehands th1 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th2};
static struct timehands th0 = {
        &dummy_timecounter,
        0,
        (uint64_t)-1 / 1000000,
        0,
        {1, 0},
        {0, 0},
        {0, 0},
        1,
        &th1
};

static struct timehands *volatile timehands = &th0;
struct timecounter *timecounter = &dummy_timecounter;
static struct timecounter *timecounters = &dummy_timecounter;

time_t time_second = 1;
time_t time_uptime = 1;

static struct bintime boottimebin;
struct timeval boottime;
static int sysctl_kern_boottime(SYSCTL_HANDLER_ARGS);
SYSCTL_PROC(_kern, KERN_BOOTTIME, boottime, CTLTYPE_STRUCT|CTLFLAG_RD,
    NULL, 0, sysctl_kern_boottime, "S,timeval", "System boottime");

SYSCTL_NODE(_kern, OID_AUTO, timecounter, CTLFLAG_RW, 0, "");
SYSCTL_NODE(_kern_timecounter, OID_AUTO, tc, CTLFLAG_RW, 0, "");

static int timestepwarnings;
SYSCTL_INT(_kern_timecounter, OID_AUTO, stepwarnings, CTLFLAG_RW,
    &timestepwarnings, 0, "Log time steps");

static void tc_windup(void);
static void cpu_tick_calibrate(int);

static int
sysctl_kern_boottime(SYSCTL_HANDLER_ARGS)
{
#ifdef SCTL_MASK32
        int tv[2];

        if (req->flags & SCTL_MASK32) {
                tv[0] = boottime.tv_sec;
                tv[1] = boottime.tv_usec;
                return SYSCTL_OUT(req, tv, sizeof(tv));
        } else
#endif
                return SYSCTL_OUT(req, &boottime, sizeof(boottime));
}

static int
sysctl_kern_timecounter_get(SYSCTL_HANDLER_ARGS)
{
        u_int ncount;
        struct timecounter *tc = arg1;

        ncount = tc->tc_get_timecount(tc);
        return sysctl_handle_int(oidp, &ncount, 0, req);
}

static int
sysctl_kern_timecounter_freq(SYSCTL_HANDLER_ARGS)
{
        u_int64_t freq;
        struct timecounter *tc = arg1;

        freq = tc->tc_frequency;
        return sysctl_handle_quad(oidp, &freq, 0, req);
}

/*
 * Return the difference between the timehands' counter value now and what
 * was when we copied it to the timehands' offset_count.
 */
static __inline u_int
tc_delta(struct timehands *th)
{
        struct timecounter *tc;

        tc = th->th_counter;
        return ((tc->tc_get_timecount(tc) - th->th_offset_count) &
            tc->tc_counter_mask);
}

/*
 * Functions for reading the time.  We have to loop until we are sure that
 * the timehands that we operated on was not updated under our feet.  See
 * the comment in <sys/time.h> for a description of these 12 functions.
 */

void
binuptime(struct bintime *bt)
{
        struct timehands *th;
        u_int gen;

        do {
                th = timehands;
                gen = th->th_generation;
                *bt = th->th_offset;
                bintime_addx(bt, th->th_scale * tc_delta(th));
        } while (gen == 0 || gen != th->th_generation);
}

void
nanouptime(struct timespec *tsp)
{
        struct bintime bt;

        binuptime(&bt);
        bintime2timespec(&bt, tsp);
}

void
microuptime(struct timeval *tvp)
{
        struct bintime bt;

        binuptime(&bt);
        bintime2timeval(&bt, tvp);
}

void
bintime(struct bintime *bt)
{

        binuptime(bt);
        bintime_add(bt, &boottimebin);
}

void
nanotime(struct timespec *tsp)
{
        struct bintime bt;

        bintime(&bt);
        bintime2timespec(&bt, tsp);
}

void
microtime(struct timeval *tvp)
{
        struct bintime bt;

        bintime(&bt);
        bintime2timeval(&bt, tvp);
}

void
getbinuptime(struct bintime *bt)
{
        struct timehands *th;
        u_int gen;

        do {
                th = timehands;
                gen = th->th_generation;
                *bt = th->th_offset;
        } while (gen == 0 || gen != th->th_generation);
}

void
getnanouptime(struct timespec *tsp)
{
        struct timehands *th;
        u_int gen;

        do {
                th = timehands;
                gen = th->th_generation;
                bintime2timespec(&th->th_offset, tsp);
        } while (gen == 0 || gen != th->th_generation);
}

void
getmicrouptime(struct timeval *tvp)
{
        struct timehands *th;
        u_int gen;

        do {
                th = timehands;
                gen = th->th_generation;
                bintime2timeval(&th->th_offset, tvp);
        } while (gen == 0 || gen != th->th_generation);
}

void
getbintime(struct bintime *bt)
{
        struct timehands *th;
        u_int gen;

        do {
                th = timehands;
                gen = th->th_generation;
                *bt = th->th_offset;
        } while (gen == 0 || gen != th->th_generation);
        bintime_add(bt, &boottimebin);
}

void
getnanotime(struct timespec *tsp)
{
        struct timehands *th;
        u_int gen;

        do {
                th = timehands;
                gen = th->th_generation;
                *tsp = th->th_nanotime;
        } while (gen == 0 || gen != th->th_generation);
}

void
getmicrotime(struct timeval *tvp)
{
        struct timehands *th;
        u_int gen;

        do {
                th = timehands;
                gen = th->th_generation;
                *tvp = th->th_microtime;
        } while (gen == 0 || gen != th->th_generation);
}

/*
 * Initialize a new timecounter and possibly use it.
 */
void
tc_init(struct timecounter *tc)
{
        u_int u;
        struct sysctl_oid *tc_root;

        u = tc->tc_frequency / tc->tc_counter_mask;
        /* XXX: We need some margin here, 10% is a guess */
        u *= 11;
        u /= 10;
        if (u > hz && tc->tc_quality >= 0) {
                tc->tc_quality = -2000;
                if (bootverbose) {
                        printf("Timecounter \"%s\" frequency %ju Hz",
                            tc->tc_name, (uintmax_t)tc->tc_frequency);
                        printf(" -- Insufficient hz, needs at least %u\n", u);
                }
        } else if (tc->tc_quality >= 0 || bootverbose) {
                printf("Timecounter \"%s\" frequency %ju Hz quality %d\n",
                    tc->tc_name, (uintmax_t)tc->tc_frequency,
                    tc->tc_quality);
        }

        tc->tc_next = timecounters;
        timecounters = tc;
        /*
         * Set up sysctl tree for this counter.
         */
        tc_root = SYSCTL_ADD_NODE(NULL,
            SYSCTL_STATIC_CHILDREN(_kern_timecounter_tc), OID_AUTO, tc->tc_name,
            CTLFLAG_RW, 0, "timecounter description");
        SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(tc_root), OID_AUTO,
            "mask", CTLFLAG_RD, &(tc->tc_counter_mask), 0,
            "mask for implemented bits");
        SYSCTL_ADD_PROC(NULL, SYSCTL_CHILDREN(tc_root), OID_AUTO,
            "counter", CTLTYPE_UINT | CTLFLAG_RD, tc, sizeof(*tc),
            sysctl_kern_timecounter_get, "IU", "current timecounter value");
        SYSCTL_ADD_PROC(NULL, SYSCTL_CHILDREN(tc_root), OID_AUTO,
            "frequency", CTLTYPE_QUAD | CTLFLAG_RD, tc, sizeof(*tc),
             sysctl_kern_timecounter_freq, "QU", "timecounter frequency");
        SYSCTL_ADD_INT(NULL, SYSCTL_CHILDREN(tc_root), OID_AUTO,
            "quality", CTLFLAG_RD, &(tc->tc_quality), 0,
            "goodness of time counter");
        /*
         * Never automatically use a timecounter with negative quality.
         * Even though we run on the dummy counter, switching here may be
         * worse since this timecounter may not be monotonous.
         */
        if (tc->tc_quality < 0)
                return;
        if (tc->tc_quality < timecounter->tc_quality)
                return;
        if (tc->tc_quality == timecounter->tc_quality &&
            tc->tc_frequency < timecounter->tc_frequency)
                return;
        (void)tc->tc_get_timecount(tc);
        (void)tc->tc_get_timecount(tc);
        timecounter = tc;
}

/* Report the frequency of the current timecounter. */
u_int64_t
tc_getfrequency(void)
{

        return (timehands->th_counter->tc_frequency);
}

/*
 * Step our concept of UTC.  This is done by modifying our estimate of
 * when we booted.
 * XXX: not locked.
 */
void
tc_setclock(struct timespec *ts)
{
        struct timespec tbef, taft;
        struct bintime bt, bt2;

        cpu_tick_calibrate(1);
        nanotime(&tbef);
        timespec2bintime(ts, &bt);
        binuptime(&bt2);
        bintime_sub(&bt, &bt2);
        bintime_add(&bt2, &boottimebin);
        boottimebin = bt;
        bintime2timeval(&bt, &boottime);

        /* XXX fiddle all the little crinkly bits around the fiords... */
        tc_windup();
        nanotime(&taft);
        if (timestepwarnings) {
                log(LOG_INFO,
                    "Time stepped from %jd.%09ld to %jd.%09ld (%jd.%09ld)\n",
                    (intmax_t)tbef.tv_sec, tbef.tv_nsec,
                    (intmax_t)taft.tv_sec, taft.tv_nsec,
                    (intmax_t)ts->tv_sec, ts->tv_nsec);
        }
        cpu_tick_calibrate(1);
}

/*
 * Initialize the next struct timehands in the ring and make
 * it the active timehands.  Along the way we might switch to a different
 * timecounter and/or do seconds processing in NTP.  Slightly magic.
 */
static void
tc_windup(void)
{
        struct bintime bt;
        struct timehands *th, *tho;
        u_int64_t scale;
        u_int delta, ncount, ogen;
        int i;
        time_t t;

        /*
         * Make the next timehands a copy of the current one, but do not
         * overwrite the generation or next pointer.  While we update
         * the contents, the generation must be zero.
         */
        tho = timehands;
        th = tho->th_next;
        ogen = th->th_generation;
        th->th_generation = 0;
        bcopy(tho, th, offsetof(struct timehands, th_generation));

        /*
         * Capture a timecounter delta on the current timecounter and if
         * changing timecounters, a counter value from the new timecounter.
         * Update the offset fields accordingly.
         */
        delta = tc_delta(th);
        if (th->th_counter != timecounter)
                ncount = timecounter->tc_get_timecount(timecounter);
        else
                ncount = 0;
        th->th_offset_count += delta;
        th->th_offset_count &= th->th_counter->tc_counter_mask;
        while (delta > th->th_counter->tc_frequency) {
                /* Eat complete unadjusted seconds. */
                delta -= th->th_counter->tc_frequency;
                th->th_offset.sec++;
        }
        if ((delta > th->th_counter->tc_frequency / 2) &&
            (th->th_scale * delta < ((uint64_t)1 << 63))) {
                /* The product th_scale * delta just barely overflows. */
                th->th_offset.sec++;
        }
        bintime_addx(&th->th_offset, th->th_scale * delta);

        /*
         * Hardware latching timecounters may not generate interrupts on
         * PPS events, so instead we poll them.  There is a finite risk that
         * the hardware might capture a count which is later than the one we
         * got above, and therefore possibly in the next NTP second which might
         * have a different rate than the current NTP second.  It doesn't
         * matter in practice.
         */
        if (tho->th_counter->tc_poll_pps)
                tho->th_counter->tc_poll_pps(tho->th_counter);

        /*
         * Deal with NTP second processing.  The for loop normally
         * iterates at most once, but in extreme situations it might
         * keep NTP sane if timeouts are not run for several seconds.
         * At boot, the time step can be large when the TOD hardware
         * has been read, so on really large steps, we call
         * ntp_update_second only twice.  We need to call it twice in
         * case we missed a leap second.
         */
        bt = th->th_offset;
        bintime_add(&bt, &boottimebin);
        i = bt.sec - tho->th_microtime.tv_sec;
        if (i > LARGE_STEP)
                i = 2;
        for (; i > 0; i--) {
                t = bt.sec;
                ntp_update_second(&th->th_adjustment, &bt.sec);
                if (bt.sec != t)
                        boottimebin.sec += bt.sec - t;
        }
        /* Update the UTC timestamps used by the get*() functions. */
        /* XXX shouldn't do this here.  Should force non-`get' versions. */
        bintime2timeval(&bt, &th->th_microtime);
        bintime2timespec(&bt, &th->th_nanotime);

        /* Now is a good time to change timecounters. */
        if (th->th_counter != timecounter) {
                th->th_counter = timecounter;
                th->th_offset_count = ncount;
        }

        /*-
         * Recalculate the scaling factor.  We want the number of 1/2^64
         * fractions of a second per period of the hardware counter, taking
         * into account the th_adjustment factor which the NTP PLL/adjtime(2)
         * processing provides us with.
         *
         * The th_adjustment is nanoseconds per second with 32 bit binary
         * fraction and we want 64 bit binary fraction of second:
         *
         *       x = a * 2^32 / 10^9 = a * 4.294967296
         *
         * The range of th_adjustment is +/- 5000PPM so inside a 64bit int
         * we can only multiply by about 850 without overflowing, that
         * leaves no suitably precise fractions for multiply before divide.
         *
         * Divide before multiply with a fraction of 2199/512 results in a
         * systematic undercompensation of 10PPM of th_adjustment.  On a
         * 5000PPM adjustment this is a 0.05PPM error.  This is acceptable.
         *
         * We happily sacrifice the lowest of the 64 bits of our result
         * to the goddess of code clarity.
         *
         */
        scale = (u_int64_t)1 << 63;
        scale += (th->th_adjustment / 1024) * 2199;
        scale /= th->th_counter->tc_frequency;
        th->th_scale = scale * 2;

        /*
         * Now that the struct timehands is again consistent, set the new
         * generation number, making sure to not make it zero.
         */
        if (++ogen == 0)
                ogen = 1;
        th->th_generation = ogen;

        /* Go live with the new struct timehands. */
        time_second = th->th_microtime.tv_sec;
        time_uptime = th->th_offset.sec;
        timehands = th;
}

/* Report or change the active timecounter hardware. */
static int
sysctl_kern_timecounter_hardware(SYSCTL_HANDLER_ARGS)
{
        char newname[32];
        struct timecounter *newtc, *tc;
        int error;

        tc = timecounter;
        strlcpy(newname, tc->tc_name, sizeof(newname));

        error = sysctl_handle_string(oidp, &newname[0], sizeof(newname), req);
        if (error != 0 || req->newptr == NULL ||
            strcmp(newname, tc->tc_name) == 0)
                return (error);
        for (newtc = timecounters; newtc != NULL; newtc = newtc->tc_next) {
                if (strcmp(newname, newtc->tc_name) != 0)
                        continue;

                /* Warm up new timecounter. */
                (void)newtc->tc_get_timecount(newtc);
                (void)newtc->tc_get_timecount(newtc);

                timecounter = newtc;
                return (0);
        }
        return (EINVAL);
}

SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING | CTLFLAG_RW,
    0, 0, sysctl_kern_timecounter_hardware, "A",
    "Timecounter hardware selected");


/* Report or change the active timecounter hardware. */
static int
sysctl_kern_timecounter_choice(SYSCTL_HANDLER_ARGS)
{
        char buf[32], *spc;
        struct timecounter *tc;
        int error;

        spc = "";
        error = 0;
        for (tc = timecounters; error == 0 && tc != NULL; tc = tc->tc_next) {
                sprintf(buf, "%s%s(%d)",
                    spc, tc->tc_name, tc->tc_quality);
                error = SYSCTL_OUT(req, buf, strlen(buf));
                spc = " ";
        }
        return (error);
}

SYSCTL_PROC(_kern_timecounter, OID_AUTO, choice, CTLTYPE_STRING | CTLFLAG_RD,
    0, 0, sysctl_kern_timecounter_choice, "A", "Timecounter hardware detected");

/*
 * RFC 2783 PPS-API implementation.
 */

int
pps_ioctl(u_long cmd, caddr_t data, struct pps_state *pps)
{
        pps_params_t *app;
        struct pps_fetch_args *fapi;
#ifdef PPS_SYNC
        struct pps_kcbind_args *kapi;
#endif

        KASSERT(pps != NULL, ("NULL pps pointer in pps_ioctl"));
        switch (cmd) {
        case PPS_IOC_CREATE:
                return (0);
        case PPS_IOC_DESTROY:
                return (0);
        case PPS_IOC_SETPARAMS:
                app = (pps_params_t *)data;
                if (app->mode & ~pps->ppscap)
                        return (EINVAL);
                pps->ppsparam = *app;
                return (0);
        case PPS_IOC_GETPARAMS:
                app = (pps_params_t *)data;
                *app = pps->ppsparam;
                app->api_version = PPS_API_VERS_1;
                return (0);
        case PPS_IOC_GETCAP:
                *(int*)data = pps->ppscap;
                return (0);
        case PPS_IOC_FETCH:
                fapi = (struct pps_fetch_args *)data;
                if (fapi->tsformat && fapi->tsformat != PPS_TSFMT_TSPEC)
                        return (EINVAL);
                if (fapi->timeout.tv_sec || fapi->timeout.tv_nsec)
                        return (EOPNOTSUPP);
                pps->ppsinfo.current_mode = pps->ppsparam.mode;
                fapi->pps_info_buf = pps->ppsinfo;
                return (0);
        case PPS_IOC_KCBIND:
#ifdef PPS_SYNC
                kapi = (struct pps_kcbind_args *)data;
                /* XXX Only root should be able to do this */
                if (kapi->tsformat && kapi->tsformat != PPS_TSFMT_TSPEC)
                        return (EINVAL);
                if (kapi->kernel_consumer != PPS_KC_HARDPPS)
                        return (EINVAL);
                if (kapi->edge & ~pps->ppscap)
                        return (EINVAL);
                pps->kcmode = kapi->edge;
                return (0);
#else
                return (EOPNOTSUPP);
#endif
        default:
                return (ENOIOCTL);
        }
}

void
pps_init(struct pps_state *pps)
{
        pps->ppscap |= PPS_TSFMT_TSPEC;
        if (pps->ppscap & PPS_CAPTUREASSERT)
                pps->ppscap |= PPS_OFFSETASSERT;
        if (pps->ppscap & PPS_CAPTURECLEAR)
                pps->ppscap |= PPS_OFFSETCLEAR;
}

void
pps_capture(struct pps_state *pps)
{
        struct timehands *th;

        KASSERT(pps != NULL, ("NULL pps pointer in pps_capture"));
        th = timehands;
        pps->capgen = th->th_generation;
        pps->capth = th;
        pps->capcount = th->th_counter->tc_get_timecount(th->th_counter);
        if (pps->capgen != th->th_generation)
                pps->capgen = 0;
}

void
pps_event(struct pps_state *pps, int event)
{
        struct bintime bt;
        struct timespec ts, *tsp, *osp;
        u_int tcount, *pcount;
        int foff, fhard;
        pps_seq_t *pseq;

        KASSERT(pps != NULL, ("NULL pps pointer in pps_event"));
        /* If the timecounter was wound up underneath us, bail out. */
        if (pps->capgen == 0 || pps->capgen != pps->capth->th_generation)
                return;

        /* Things would be easier with arrays. */
        if (event == PPS_CAPTUREASSERT) {
                tsp = &pps->ppsinfo.assert_timestamp;
                osp = &pps->ppsparam.assert_offset;
                foff = pps->ppsparam.mode & PPS_OFFSETASSERT;
                fhard = pps->kcmode & PPS_CAPTUREASSERT;
                pcount = &pps->ppscount[0];
                pseq = &pps->ppsinfo.assert_sequence;
        } else {
                tsp = &pps->ppsinfo.clear_timestamp;
                osp = &pps->ppsparam.clear_offset;
                foff = pps->ppsparam.mode & PPS_OFFSETCLEAR;
                fhard = pps->kcmode & PPS_CAPTURECLEAR;
                pcount = &pps->ppscount[1];
                pseq = &pps->ppsinfo.clear_sequence;
        }

        /*
         * If the timecounter changed, we cannot compare the count values, so
         * we have to drop the rest of the PPS-stuff until the next event.
         */
        if (pps->ppstc != pps->capth->th_counter) {
                pps->ppstc = pps->capth->th_counter;
                *pcount = pps->capcount;
                pps->ppscount[2] = pps->capcount;
                return;
        }

        /* Convert the count to a timespec. */
        tcount = pps->capcount - pps->capth->th_offset_count;
        tcount &= pps->capth->th_counter->tc_counter_mask;
        bt = pps->capth->th_offset;
        bintime_addx(&bt, pps->capth->th_scale * tcount);
        bintime_add(&bt, &boottimebin);
        bintime2timespec(&bt, &ts);

        /* If the timecounter was wound up underneath us, bail out. */
        if (pps->capgen != pps->capth->th_generation)
                return;

        *pcount = pps->capcount;
        (*pseq)++;
        *tsp = ts;

        if (foff) {
                timespecadd(tsp, osp);
                if (tsp->tv_nsec < 0) {
                        tsp->tv_nsec += 1000000000;
                        tsp->tv_sec -= 1;
                }
        }
#ifdef PPS_SYNC
        if (fhard) {
                u_int64_t scale;

                /*
                 * Feed the NTP PLL/FLL.
                 * The FLL wants to know how many (hardware) nanoseconds
                 * elapsed since the previous event.
                 */
                tcount = pps->capcount - pps->ppscount[2];
                pps->ppscount[2] = pps->capcount;
                tcount &= pps->capth->th_counter->tc_counter_mask;
                scale = (u_int64_t)1 << 63;
                scale /= pps->capth->th_counter->tc_frequency;
                scale *= 2;
                bt.sec = 0;
                bt.frac = 0;
                bintime_addx(&bt, scale * tcount);
                bintime2timespec(&bt, &ts);
                hardpps(tsp, ts.tv_nsec + 1000000000 * ts.tv_sec);
        }
#endif
}

/*
 * Timecounters need to be updated every so often to prevent the hardware
 * counter from overflowing.  Updating also recalculates the cached values
 * used by the get*() family of functions, so their precision depends on
 * the update frequency.
 */

static int tc_tick;
SYSCTL_INT(_kern_timecounter, OID_AUTO, tick, CTLFLAG_RD, &tc_tick, 0,
    "Approximate number of hardclock ticks in a millisecond");

void
tc_ticktock(void)
{
        static int count;
        static time_t last_calib;

        if (++count < tc_tick)
                return;
        count = 0;
        tc_windup();
        if (time_uptime != last_calib && !(time_uptime & 0xf)) {
                cpu_tick_calibrate(0);
                last_calib = time_uptime;
        }
}

static void
inittimecounter(void *dummy)
{
        u_int p;

        /*
         * Set the initial timeout to
         * max(1, <approx. number of hardclock ticks in a millisecond>).
         * People should probably not use the sysctl to set the timeout
         * to smaller than its inital value, since that value is the
         * smallest reasonable one.  If they want better timestamps they
         * should use the non-"get"* functions.
         */
        if (hz > 1000)
                tc_tick = (hz + 500) / 1000;
        else
                tc_tick = 1;
        p = (tc_tick * 1000000) / hz;
        printf("Timecounters tick every %d.%03u msec\n", p / 1000, p % 1000);

        /* warm up new timecounter (again) and get rolling. */
        (void)timecounter->tc_get_timecount(timecounter);
        (void)timecounter->tc_get_timecount(timecounter);
}

SYSINIT(timecounter, SI_SUB_CLOCKS, SI_ORDER_SECOND, inittimecounter, NULL);

/* Cpu tick handling -------------------------------------------------*/

static int cpu_tick_variable;
static uint64_t cpu_tick_frequency;

static uint64_t
tc_cpu_ticks(void)
{
        static uint64_t base;
        static unsigned last;
        unsigned u;
        struct timecounter *tc;

        tc = timehands->th_counter;
        u = tc->tc_get_timecount(tc) & tc->tc_counter_mask;
        if (u < last)
                base += (uint64_t)tc->tc_counter_mask + 1;
        last = u;
        return (u + base);
}

/*
 * This function gets called every 16 seconds on only one designated
 * CPU in the system from hardclock() via tc_ticktock().
 *
 * Whenever the real time clock is stepped we get called with reset=1
 * to make sure we handle suspend/resume and similar events correctly.
 */

static void
cpu_tick_calibrate(int reset)
{
        static uint64_t c_last;
        uint64_t c_this, c_delta;
        static struct bintime  t_last;
        struct bintime t_this, t_delta;
        uint32_t divi;

        if (reset) {
                /* The clock was stepped, abort & reset */
                t_last.sec = 0;
                return;
        }

        /* we don't calibrate fixed rate cputicks */
        if (!cpu_tick_variable)
                return;

        getbinuptime(&t_this);
        c_this = cpu_ticks();
        if (t_last.sec != 0) {
                c_delta = c_this - c_last;
                t_delta = t_this;
                bintime_sub(&t_delta, &t_last);
                /*
                 * Validate that 16 +/- 1/256 seconds passed. 
                 * After division by 16 this gives us a precision of
                 * roughly 250PPM which is sufficient
                 */
                if (t_delta.sec > 16 || (
                    t_delta.sec == 16 && t_delta.frac >= (0x01LL << 56))) {
                        /* too long */
                        if (bootverbose)
                                printf("t_delta %ju.%016jx too long\n",
                                    (uintmax_t)t_delta.sec,
                                    (uintmax_t)t_delta.frac);
                } else if (t_delta.sec < 15 ||
                    (t_delta.sec == 15 && t_delta.frac <= (0xffLL << 56))) {
                        /* too short */
                        if (bootverbose)
                                printf("t_delta %ju.%016jx too short\n",
                                    (uintmax_t)t_delta.sec,
                                    (uintmax_t)t_delta.frac);
                } else {
                        /* just right */
                        /*
                         * Headroom:
                         *      2^(64-20) / 16[s] =
                         *      2^(44) / 16[s] =
                         *      17.592.186.044.416 / 16 =
                         *      1.099.511.627.776 [Hz]
                         */
                        divi = t_delta.sec << 20;
                        divi |= t_delta.frac >> (64 - 20);
                        c_delta <<= 20;
                        c_delta /= divi;
                        if (c_delta  > cpu_tick_frequency) {
                                if (0 && bootverbose)
                                        printf("cpu_tick increased to %ju Hz\n",
                                            c_delta);
                                cpu_tick_frequency = c_delta;
                        }
                }
        }
        c_last = c_this;
        t_last = t_this;
}

void
set_cputicker(cpu_tick_f *func, uint64_t freq, unsigned var)
{

        if (func == NULL) {
                cpu_ticks = tc_cpu_ticks;
        } else {
                cpu_tick_frequency = freq;
                cpu_tick_variable = var;
                cpu_ticks = func;
        }
}

uint64_t
cpu_tickrate(void)
{

        if (cpu_ticks == tc_cpu_ticks) 
                return (tc_getfrequency());
        return (cpu_tick_frequency);
}

/*
 * We need to be slightly careful converting cputicks to microseconds.
 * There is plenty of margin in 64 bits of microseconds (half a million
 * years) and in 64 bits at 4 GHz (146 years), but if we do a multiply
 * before divide conversion (to retain precision) we find that the
 * margin shrinks to 1.5 hours (one millionth of 146y).
 * With a three prong approach we never lose significant bits, no
 * matter what the cputick rate and length of timeinterval is.
 */

uint64_t
cputick2usec(uint64_t tick)
{

        if (tick > 18446744073709551LL)         /* floor(2^64 / 1000) */
                return (tick / (cpu_tickrate() / 1000000LL));
        else if (tick > 18446744073709LL)       /* floor(2^64 / 1000000) */
                return ((tick * 1000LL) / (cpu_tickrate() / 1000LL));
        else
                return ((tick * 1000000LL) / cpu_tickrate());
}

cpu_tick_f      *cpu_ticks = tc_cpu_ticks;