kern_tc.c

/*-
 * ----------------------------------------------------------------------------
 * "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
 * ----------------------------------------------------------------------------
 *
 * Copyright (c) 2011, 2015, 2016 The FreeBSD Foundation
 * All rights reserved.
 *
 * Portions of this software were developed by Julien Ridoux at the University
 * of Melbourne under sponsorship from the FreeBSD Foundation.
 *
 * Portions of this software were developed by Konstantin Belousov
 * under sponsorship from the FreeBSD Foundation.
 */

#ifdef __rtems__
#include <sys/lock.h>
#define _KERNEL
#define binuptime(_bt) _Timecounter_Binuptime(_bt)
#define nanouptime(_tsp) _Timecounter_Nanouptime(_tsp)
#define microuptime(_tvp) _Timecounter_Microuptime(_tvp)
#define bintime(_bt) _Timecounter_Bintime(_bt)
#define nanotime(_tsp) _Timecounter_Nanotime(_tsp)
#define microtime(_tvp) _Timecounter_Microtime(_tvp)
#define getbinuptime(_bt) _Timecounter_Getbinuptime(_bt)
#define getnanouptime(_tsp) _Timecounter_Getnanouptime(_tsp)
#define getmicrouptime(_tvp) _Timecounter_Getmicrouptime(_tvp)
#define getbintime(_bt) _Timecounter_Getbintime(_bt)
#define getnanotime(_tsp) _Timecounter_Getnanotime(_tsp)
#define getmicrotime(_tvp) _Timecounter_Getmicrotime(_tvp)
#define getboottime(_tvp) _Timecounter_Getboottime(_tvp)
#define getboottimebin(_bt) _Timecounter_Getboottimebin(_bt)
#define tc_init _Timecounter_Install
#define timecounter _Timecounter
#define time_second _Timecounter_Time_second
#define time_uptime _Timecounter_Time_uptime
#include <rtems/score/timecounterimpl.h>
#include <rtems/score/atomic.h>
#include <rtems/score/smp.h>
#include <rtems/score/todimpl.h>
#include <rtems/score/watchdogimpl.h>
#endif /* __rtems__ */
#include <sys/cdefs.h>
__FBSDID("$FreeBSD: head/sys/kern/kern_tc.c 324528 2017-10-11 11:03:11Z kib $");

#include "opt_compat.h"
#include "opt_ntp.h"
#include "opt_ffclock.h"

#include <sys/param.h>
#ifndef __rtems__
#include <sys/kernel.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/sbuf.h>
#include <sys/sleepqueue.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/systm.h>
#endif /* __rtems__ */
#include <sys/timeffc.h>
#include <sys/timepps.h>
#include <sys/timetc.h>
#include <sys/timex.h>
#ifndef __rtems__
#include <sys/vdso.h>
#endif /* __rtems__ */
#ifdef __rtems__
#include <limits.h>
#include <string.h>
#include <rtems.h>
ISR_LOCK_DEFINE(, _Timecounter_Lock, "Timecounter")
#define _Timecounter_Release(lock_context) \
  _ISR_lock_Release_and_ISR_enable(&_Timecounter_Lock, lock_context)
#define hz rtems_clock_get_ticks_per_second()
#define printf(...)
#define bcopy(x, y, z) memcpy(y, x, z);
#define log(...)
static inline int
builtin_fls(int x)
{
        return x ? sizeof(x) * 8 - __builtin_clz(x) : 0;
}
#define fls(x) builtin_fls(x)
/* FIXME: https://devel.rtems.org/ticket/2348 */
#define ntp_update_second(a, b) do { (void) a; (void) b; } while (0)

static inline void
atomic_thread_fence_acq(void)
{

    _Atomic_Fence(ATOMIC_ORDER_ACQUIRE);
}

static inline void
atomic_thread_fence_rel(void)
{

    _Atomic_Fence(ATOMIC_ORDER_RELEASE);
}

static inline u_int
atomic_load_acq_int(Atomic_Uint *i)
{

    return (_Atomic_Load_uint(i, ATOMIC_ORDER_ACQUIRE));
}

static inline void
atomic_store_rel_int(Atomic_Uint *i, u_int val)
{

    _Atomic_Store_uint(i, val, ATOMIC_ORDER_RELEASE);
}
#endif /* __rtems__ */

/*
 * 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 uint32_t
dummy_get_timecount(struct timecounter *tc)
{
#ifndef __rtems__
    static uint32_t now;

    return (++now);
#else /* __rtems__ */
    return 0;
#endif /* __rtems__ */
}

static struct timecounter dummy_timecounter = {
#ifndef __rtems__
    dummy_get_timecount, 0, ~0u, 1000000, "dummy", -1000000
#else /* __rtems__ */
    dummy_get_timecount, ~(uint32_t)0, 1000000, "dummy", -1000000
#endif /* __rtems__ */
};

struct timehands {
    /* These fields must be initialized by the driver. */
    struct timecounter  *th_counter;
    int64_t         th_adjustment;
    uint64_t        th_scale;
    uint32_t        th_offset_count;
    struct bintime      th_offset;
    struct bintime      th_bintime;
    struct timeval      th_microtime;
    struct timespec     th_nanotime;
    struct bintime      th_boottime;
    /* Fields not to be copied in tc_windup start with th_generation. */
#ifndef __rtems__
    u_int           th_generation;
#else /* __rtems__ */
    Atomic_Uint     th_generation;
#endif /* __rtems__ */
    struct timehands    *th_next;
};

#if defined(RTEMS_SMP)
static struct timehands th0;
static struct timehands th1 = {
    .th_next = &th0
};
#endif
static struct timehands th0 = {
    .th_counter = &dummy_timecounter,
    .th_scale = (uint64_t)-1 / 1000000,
    .th_offset = { .sec = 1 },
    .th_generation = 1,
#ifdef __rtems__
    .th_bintime = { .sec = TOD_SECONDS_1970_THROUGH_1988 },
    .th_microtime = { TOD_SECONDS_1970_THROUGH_1988, 0 },
    .th_nanotime = { TOD_SECONDS_1970_THROUGH_1988, 0 },
    .th_boottime = { .sec = TOD_SECONDS_1970_THROUGH_1988 - 1 },
#endif /* __rtems__ */
#if defined(RTEMS_SMP)
    .th_next = &th1
#else
    .th_next = &th0
#endif
};

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

int tc_min_ticktock_freq = 1;
#endif /* __rtems__ */

#ifndef __rtems__
volatile time_t time_second = 1;
volatile time_t time_uptime = 1;
#else /* __rtems__ */
volatile time_t time_second = TOD_SECONDS_1970_THROUGH_1988;
volatile int32_t time_uptime = 1;
#endif /* __rtems__ */

#ifndef __rtems__
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, "");
static 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");

struct bintime bt_timethreshold;
struct bintime bt_tickthreshold;
sbintime_t sbt_timethreshold;
sbintime_t sbt_tickthreshold;
struct bintime tc_tick_bt;
sbintime_t tc_tick_sbt;
int tc_precexp;
int tc_timepercentage = TC_DEFAULTPERC;
static int sysctl_kern_timecounter_adjprecision(SYSCTL_HANDLER_ARGS);
SYSCTL_PROC(_kern_timecounter, OID_AUTO, alloweddeviation,
    CTLTYPE_INT | CTLFLAG_RWTUN | CTLFLAG_MPSAFE, 0, 0,
    sysctl_kern_timecounter_adjprecision, "I",
    "Allowed time interval deviation in percents");

volatile int rtc_generation = 1;

static int tc_chosen;   /* Non-zero if a specific tc was chosen via sysctl. */
#endif /* __rtems__ */

static void tc_windup(struct bintime *new_boottimebin);
#ifndef __rtems__
static void cpu_tick_calibrate(int);
#else /* __rtems__ */
static void _Timecounter_Windup(struct bintime *new_boottimebin,
    ISR_lock_Context *lock_context);
#endif /* __rtems__ */

void dtrace_getnanotime(struct timespec *tsp);

#ifndef __rtems__
static int
sysctl_kern_boottime(SYSCTL_HANDLER_ARGS)
{
    struct timeval boottime;

    getboottime(&boottime);

#ifndef __mips__
#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)));
    }
#endif
#endif
    return (SYSCTL_OUT(req, &boottime, sizeof(boottime)));
}

static int
sysctl_kern_timecounter_get(SYSCTL_HANDLER_ARGS)
{
    uint32_t 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)
{
    uint64_t freq;
    struct timecounter *tc = arg1;

    freq = tc->tc_frequency;
    return (sysctl_handle_64(oidp, &freq, 0, req));
}
#endif /* __rtems__ */

/*
 * Return the difference between the timehands' counter value now and what
 * was when we copied it to the timehands' offset_count.
 */
static __inline uint32_t
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.
 */

#ifdef FFCLOCK
void
fbclock_binuptime(struct bintime *bt)
{
    struct timehands *th;
    unsigned int gen;

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

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

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

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

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

void
fbclock_bintime(struct bintime *bt)
{
    struct timehands *th;
    unsigned int gen;

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

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

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

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

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

void
fbclock_getbinuptime(struct bintime *bt)
{
    struct timehands *th;
    unsigned int gen;

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

void
fbclock_getnanouptime(struct timespec *tsp)
{
    struct timehands *th;
    unsigned int gen;

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

void
fbclock_getmicrouptime(struct timeval *tvp)
{
    struct timehands *th;
    unsigned int gen;

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

void
fbclock_getbintime(struct bintime *bt)
{
    struct timehands *th;
    unsigned int gen;

    do {
        th = timehands;
        gen = atomic_load_acq_int(&th->th_generation);
        *bt = th->th_bintime;
        atomic_thread_fence_acq();
    } while (gen == 0 || gen != th->th_generation);
}

void
fbclock_getnanotime(struct timespec *tsp)
{
    struct timehands *th;
    unsigned int gen;

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

void
fbclock_getmicrotime(struct timeval *tvp)
{
    struct timehands *th;
    unsigned int gen;

    do {
        th = timehands;
        gen = atomic_load_acq_int(&th->th_generation);
        *tvp = th->th_microtime;
        atomic_thread_fence_acq();
    } while (gen == 0 || gen != th->th_generation);
}
#else /* !FFCLOCK */
void
binuptime(struct bintime *bt)
{
    struct timehands *th;
    uint32_t gen;

    do {
        th = timehands;
        gen = atomic_load_acq_int(&th->th_generation);
        *bt = th->th_offset;
        bintime_addx(bt, th->th_scale * tc_delta(th));
        atomic_thread_fence_acq();
    } while (gen == 0 || gen != th->th_generation);
}
#ifdef __rtems__
sbintime_t
_Timecounter_Sbinuptime(void)
{
    struct timehands *th;
    uint32_t gen;
    sbintime_t sbt;

    do {
        th = timehands;
        gen = atomic_load_acq_int(&th->th_generation);
        sbt = bttosbt(th->th_offset);
        sbt += (th->th_scale * tc_delta(th)) >> 32;
        atomic_thread_fence_acq();
    } while (gen == 0 || gen != th->th_generation);

    return (sbt);
}
#endif /* __rtems__ */

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)
{
    struct timehands *th;
    u_int gen;

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

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;
    uint32_t gen;

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

void
getnanouptime(struct timespec *tsp)
{
    struct timehands *th;
    uint32_t gen;

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

void
getmicrouptime(struct timeval *tvp)
{
    struct timehands *th;
    uint32_t gen;

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

void
getbintime(struct bintime *bt)
{
    struct timehands *th;
    uint32_t gen;

    do {
        th = timehands;
        gen = atomic_load_acq_int(&th->th_generation);
        *bt = th->th_bintime;
        atomic_thread_fence_acq();
    } while (gen == 0 || gen != th->th_generation);
}

void
getnanotime(struct timespec *tsp)
{
    struct timehands *th;
    uint32_t gen;

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

void
getmicrotime(struct timeval *tvp)
{
    struct timehands *th;
    uint32_t gen;

    do {
        th = timehands;
        gen = atomic_load_acq_int(&th->th_generation);
        *tvp = th->th_microtime;
        atomic_thread_fence_acq();
    } while (gen == 0 || gen != th->th_generation);
}
#endif /* FFCLOCK */

void
getboottime(struct timeval *boottime)
{
    struct bintime boottimebin;

    getboottimebin(&boottimebin);
    bintime2timeval(&boottimebin, boottime);
}

void
getboottimebin(struct bintime *boottimebin)
{
    struct timehands *th;
    u_int gen;

    do {
        th = timehands;
        gen = atomic_load_acq_int(&th->th_generation);
        *boottimebin = th->th_boottime;
        atomic_thread_fence_acq();
    } while (gen == 0 || gen != th->th_generation);
}

#ifdef FFCLOCK
/*
 * Support for feed-forward synchronization algorithms. This is heavily inspired
 * by the timehands mechanism but kept independent from it. *_windup() functions
 * have some connection to avoid accessing the timecounter hardware more than
 * necessary.
 */

/* Feed-forward clock estimates kept updated by the synchronization daemon. */
struct ffclock_estimate ffclock_estimate;
struct bintime ffclock_boottime;    /* Feed-forward boot time estimate. */
uint32_t ffclock_status;        /* Feed-forward clock status. */
int8_t ffclock_updated;         /* New estimates are available. */
struct mtx ffclock_mtx;         /* Mutex on ffclock_estimate. */

struct fftimehands {
    struct ffclock_estimate cest;
    struct bintime      tick_time;
    struct bintime      tick_time_lerp;
    ffcounter       tick_ffcount;
    uint64_t        period_lerp;
    volatile uint8_t    gen;
    struct fftimehands  *next;
};

#define NUM_ELEMENTS(x) (sizeof(x) / sizeof(*x))

static struct fftimehands ffth[10];
static struct fftimehands *volatile fftimehands = ffth;

static void
ffclock_init(void)
{
    struct fftimehands *cur;
    struct fftimehands *last;

    memset(ffth, 0, sizeof(ffth));

    last = ffth + NUM_ELEMENTS(ffth) - 1;
    for (cur = ffth; cur < last; cur++)
        cur->next = cur + 1;
    last->next = ffth;

    ffclock_updated = 0;
    ffclock_status = FFCLOCK_STA_UNSYNC;
    mtx_init(&ffclock_mtx, "ffclock lock", NULL, MTX_DEF);
}

/*
 * Reset the feed-forward clock estimates. Called from inittodr() to get things
 * kick started and uses the timecounter nominal frequency as a first period
 * estimate. Note: this function may be called several time just after boot.
 * Note: this is the only function that sets the value of boot time for the
 * monotonic (i.e. uptime) version of the feed-forward clock.
 */
void
ffclock_reset_clock(struct timespec *ts)
{
    struct timecounter *tc;
    struct ffclock_estimate cest;

    tc = timehands->th_counter;
    memset(&cest, 0, sizeof(struct ffclock_estimate));

    timespec2bintime(ts, &ffclock_boottime);
    timespec2bintime(ts, &(cest.update_time));
    ffclock_read_counter(&cest.update_ffcount);
    cest.leapsec_next = 0;
    cest.period = ((1ULL << 63) / tc->tc_frequency) << 1;
    cest.errb_abs = 0;
    cest.errb_rate = 0;
    cest.status = FFCLOCK_STA_UNSYNC;
    cest.leapsec_total = 0;
    cest.leapsec = 0;

    mtx_lock(&ffclock_mtx);
    bcopy(&cest, &ffclock_estimate, sizeof(struct ffclock_estimate));
    ffclock_updated = INT8_MAX;
    mtx_unlock(&ffclock_mtx);

    printf("ffclock reset: %s (%llu Hz), time = %ld.%09lu\n", tc->tc_name,
        (unsigned long long)tc->tc_frequency, (long)ts->tv_sec,
        (unsigned long)ts->tv_nsec);
}

/*
 * Sub-routine to convert a time interval measured in RAW counter units to time
 * in seconds stored in bintime format.
 * NOTE: bintime_mul requires u_int, but the value of the ffcounter may be
 * larger than the max value of u_int (on 32 bit architecture). Loop to consume
 * extra cycles.
 */
static void
ffclock_convert_delta(ffcounter ffdelta, uint64_t period, struct bintime *bt)
{
    struct bintime bt2;
    ffcounter delta, delta_max;

    delta_max = (1ULL << (8 * sizeof(unsigned int))) - 1;
    bintime_clear(bt);
    do {
        if (ffdelta > delta_max)
            delta = delta_max;
        else
            delta = ffdelta;
        bt2.sec = 0;
        bt2.frac = period;
        bintime_mul(&bt2, (unsigned int)delta);
        bintime_add(bt, &bt2);
        ffdelta -= delta;
    } while (ffdelta > 0);
}

/*
 * Update the fftimehands.
 * Push the tick ffcount and time(s) forward based on current clock estimate.
 * The conversion from ffcounter to bintime relies on the difference clock
 * principle, whose accuracy relies on computing small time intervals. If a new
 * clock estimate has been passed by the synchronisation daemon, make it
 * current, and compute the linear interpolation for monotonic time if needed.
 */
static void
ffclock_windup(unsigned int delta)
{
    struct ffclock_estimate *cest;
    struct fftimehands *ffth;
    struct bintime bt, gap_lerp;
    ffcounter ffdelta;
    uint64_t frac;
    unsigned int polling;
    uint8_t forward_jump, ogen;

    /*
     * Pick the next timehand, copy current ffclock estimates and move tick
     * times and counter forward.
     */
    forward_jump = 0;
    ffth = fftimehands->next;
    ogen = ffth->gen;
    ffth->gen = 0;
    cest = &ffth->cest;
    bcopy(&fftimehands->cest, cest, sizeof(struct ffclock_estimate));
    ffdelta = (ffcounter)delta;
    ffth->period_lerp = fftimehands->period_lerp;

    ffth->tick_time = fftimehands->tick_time;
    ffclock_convert_delta(ffdelta, cest->period, &bt);
    bintime_add(&ffth->tick_time, &bt);

    ffth->tick_time_lerp = fftimehands->tick_time_lerp;
    ffclock_convert_delta(ffdelta, ffth->period_lerp, &bt);
    bintime_add(&ffth->tick_time_lerp, &bt);

    ffth->tick_ffcount = fftimehands->tick_ffcount + ffdelta;

    /*
     * Assess the status of the clock, if the last update is too old, it is
     * likely the synchronisation daemon is dead and the clock is free
     * running.
     */
    if (ffclock_updated == 0) {
        ffdelta = ffth->tick_ffcount - cest->update_ffcount;
        ffclock_convert_delta(ffdelta, cest->period, &bt);
        if (bt.sec > 2 * FFCLOCK_SKM_SCALE)
            ffclock_status |= FFCLOCK_STA_UNSYNC;
    }

    /*
     * If available, grab updated clock estimates and make them current.
     * Recompute time at this tick using the updated estimates. The clock
     * estimates passed the feed-forward synchronisation daemon may result
     * in time conversion that is not monotonically increasing (just after
     * the update). time_lerp is a particular linear interpolation over the
     * synchronisation algo polling period that ensures monotonicity for the
     * clock ids requesting it.
     */
    if (ffclock_updated > 0) {
        bcopy(&ffclock_estimate, cest, sizeof(struct ffclock_estimate));
        ffdelta = ffth->tick_ffcount - cest->update_ffcount;
        ffth->tick_time = cest->update_time;
        ffclock_convert_delta(ffdelta, cest->period, &bt);
        bintime_add(&ffth->tick_time, &bt);

        /* ffclock_reset sets ffclock_updated to INT8_MAX */
        if (ffclock_updated == INT8_MAX)
            ffth->tick_time_lerp = ffth->tick_time;

        if (bintime_cmp(&ffth->tick_time, &ffth->tick_time_lerp, >))
            forward_jump = 1;
        else
            forward_jump = 0;

        bintime_clear(&gap_lerp);
        if (forward_jump) {
            gap_lerp = ffth->tick_time;
            bintime_sub(&gap_lerp, &ffth->tick_time_lerp);
        } else {
            gap_lerp = ffth->tick_time_lerp;
            bintime_sub(&gap_lerp, &ffth->tick_time);
        }

        /*
         * The reset from the RTC clock may be far from accurate, and
         * reducing the gap between real time and interpolated time
         * could take a very long time if the interpolated clock insists
         * on strict monotonicity. The clock is reset under very strict
         * conditions (kernel time is known to be wrong and
         * synchronization daemon has been restarted recently.
         * ffclock_boottime absorbs the jump to ensure boot time is
         * correct and uptime functions stay consistent.
         */
        if (((ffclock_status & FFCLOCK_STA_UNSYNC) == FFCLOCK_STA_UNSYNC) &&
            ((cest->status & FFCLOCK_STA_UNSYNC) == 0) &&
            ((cest->status & FFCLOCK_STA_WARMUP) == FFCLOCK_STA_WARMUP)) {
            if (forward_jump)
                bintime_add(&ffclock_boottime, &gap_lerp);
            else
                bintime_sub(&ffclock_boottime, &gap_lerp);
            ffth->tick_time_lerp = ffth->tick_time;
            bintime_clear(&gap_lerp);
        }

        ffclock_status = cest->status;
        ffth->period_lerp = cest->period;

        /*
         * Compute corrected period used for the linear interpolation of
         * time. The rate of linear interpolation is capped to 5000PPM
         * (5ms/s).
         */
        if (bintime_isset(&gap_lerp)) {
            ffdelta = cest->update_ffcount;
            ffdelta -= fftimehands->cest.update_ffcount;
            ffclock_convert_delta(ffdelta, cest->period, &bt);
            polling = bt.sec;
            bt.sec = 0;
            bt.frac = 5000000 * (uint64_t)18446744073LL;
            bintime_mul(&bt, polling);
            if (bintime_cmp(&gap_lerp, &bt, >))
                gap_lerp = bt;

            /* Approximate 1 sec by 1-(1/2^64) to ease arithmetic */
            frac = 0;
            if (gap_lerp.sec > 0) {
                frac -= 1;
                frac /= ffdelta / gap_lerp.sec;
            }
            frac += gap_lerp.frac / ffdelta;

            if (forward_jump)
                ffth->period_lerp += frac;
            else
                ffth->period_lerp -= frac;
        }

        ffclock_updated = 0;
    }
    if (++ogen == 0)
        ogen = 1;
    ffth->gen = ogen;
    fftimehands = ffth;
}

/*
 * Adjust the fftimehands when the timecounter is changed. Stating the obvious,
 * the old and new hardware counter cannot be read simultaneously. tc_windup()
 * does read the two counters 'back to back', but a few cycles are effectively
 * lost, and not accumulated in tick_ffcount. This is a fairly radical
 * operation for a feed-forward synchronization daemon, and it is its job to not
 * pushing irrelevant data to the kernel. Because there is no locking here,
 * simply force to ignore pending or next update to give daemon a chance to
 * realize the counter has changed.
 */
static void
ffclock_change_tc(struct timehands *th)
{
    struct fftimehands *ffth;
    struct ffclock_estimate *cest;
    struct timecounter *tc;
    uint8_t ogen;

    tc = th->th_counter;
    ffth = fftimehands->next;
    ogen = ffth->gen;
    ffth->gen = 0;

    cest = &ffth->cest;
    bcopy(&(fftimehands->cest), cest, sizeof(struct ffclock_estimate));
    cest->period = ((1ULL << 63) / tc->tc_frequency ) << 1;
    cest->errb_abs = 0;
    cest->errb_rate = 0;
    cest->status |= FFCLOCK_STA_UNSYNC;

    ffth->tick_ffcount = fftimehands->tick_ffcount;
    ffth->tick_time_lerp = fftimehands->tick_time_lerp;
    ffth->tick_time = fftimehands->tick_time;
    ffth->period_lerp = cest->period;

    /* Do not lock but ignore next update from synchronization daemon. */
    ffclock_updated--;

    if (++ogen == 0)
        ogen = 1;
    ffth->gen = ogen;
    fftimehands = ffth;
}

/*
 * Retrieve feed-forward counter and time of last kernel tick.
 */
void
ffclock_last_tick(ffcounter *ffcount, struct bintime *bt, uint32_t flags)
{
    struct fftimehands *ffth;
    uint8_t gen;

    /*
     * No locking but check generation has not changed. Also need to make
     * sure ffdelta is positive, i.e. ffcount > tick_ffcount.
     */
    do {
        ffth = fftimehands;
        gen = ffth->gen;
        if ((flags & FFCLOCK_LERP) == FFCLOCK_LERP)
            *bt = ffth->tick_time_lerp;
        else
            *bt = ffth->tick_time;
        *ffcount = ffth->tick_ffcount;
    } while (gen == 0 || gen != ffth->gen);
}

/*
 * Absolute clock conversion. Low level function to convert ffcounter to
 * bintime. The ffcounter is converted using the current ffclock period estimate
 * or the "interpolated period" to ensure monotonicity.
 * NOTE: this conversion may have been deferred, and the clock updated since the
 * hardware counter has been read.
 */
void
ffclock_convert_abs(ffcounter ffcount, struct bintime *bt, uint32_t flags)
{
    struct fftimehands *ffth;
    struct bintime bt2;
    ffcounter ffdelta;
    uint8_t gen;

    /*
     * No locking but check generation has not changed. Also need to make
     * sure ffdelta is positive, i.e. ffcount > tick_ffcount.
     */
    do {
        ffth = fftimehands;
        gen = ffth->gen;
        if (ffcount > ffth->tick_ffcount)
            ffdelta = ffcount - ffth->tick_ffcount;
        else
            ffdelta = ffth->tick_ffcount - ffcount;

        if ((flags & FFCLOCK_LERP) == FFCLOCK_LERP) {
            *bt = ffth->tick_time_lerp;
            ffclock_convert_delta(ffdelta, ffth->period_lerp, &bt2);
        } else {
            *bt = ffth->tick_time;
            ffclock_convert_delta(ffdelta, ffth->cest.period, &bt2);
        }

        if (ffcount > ffth->tick_ffcount)
            bintime_add(bt, &bt2);
        else
            bintime_sub(bt, &bt2);
    } while (gen == 0 || gen != ffth->gen);
}

/*
 * Difference clock conversion.
 * Low level function to Convert a time interval measured in RAW counter units
 * into bintime. The difference clock allows measuring small intervals much more
 * reliably than the absolute clock.
 */
void
ffclock_convert_diff(ffcounter ffdelta, struct bintime *bt)
{
    struct fftimehands *ffth;
    uint8_t gen;

    /* No locking but check generation has not changed. */
    do {
        ffth = fftimehands;
        gen = ffth->gen;
        ffclock_convert_delta(ffdelta, ffth->cest.period, bt);
    } while (gen == 0 || gen != ffth->gen);
}

/*
 * Access to current ffcounter value.
 */
void
ffclock_read_counter(ffcounter *ffcount)
{
    struct timehands *th;
    struct fftimehands *ffth;
    unsigned int gen, delta;

    /*
     * ffclock_windup() called from tc_windup(), safe to rely on
     * th->th_generation only, for correct delta and ffcounter.
     */
    do {
        th = timehands;
        gen = atomic_load_acq_int(&th->th_generation);
        ffth = fftimehands;
        delta = tc_delta(th);
        *ffcount = ffth->tick_ffcount;
        atomic_thread_fence_acq();
    } while (gen == 0 || gen != th->th_generation);

    *ffcount += delta;
}

void
binuptime(struct bintime *bt)
{

    binuptime_fromclock(bt, sysclock_active);
}

void
nanouptime(struct timespec *tsp)
{

    nanouptime_fromclock(tsp, sysclock_active);
}

void
microuptime(struct timeval *tvp)
{

    microuptime_fromclock(tvp, sysclock_active);
}

void
bintime(struct bintime *bt)
{

    bintime_fromclock(bt, sysclock_active);
}

void
nanotime(struct timespec *tsp)
{

    nanotime_fromclock(tsp, sysclock_active);
}

void
microtime(struct timeval *tvp)
{

    microtime_fromclock(tvp, sysclock_active);
}

void
getbinuptime(struct bintime *bt)
{

    getbinuptime_fromclock(bt, sysclock_active);
}

void
getnanouptime(struct timespec *tsp)
{

    getnanouptime_fromclock(tsp, sysclock_active);
}

void
getmicrouptime(struct timeval *tvp)
{

    getmicrouptime_fromclock(tvp, sysclock_active);
}

void
getbintime(struct bintime *bt)
{

    getbintime_fromclock(bt, sysclock_active);
}

void
getnanotime(struct timespec *tsp)
{

    getnanotime_fromclock(tsp, sysclock_active);
}

void
getmicrotime(struct timeval *tvp)
{

    getmicrouptime_fromclock(tvp, sysclock_active);
}

#endif /* FFCLOCK */

#ifndef __rtems__
/*
 * This is a clone of getnanotime and used for walltimestamps.
 * The dtrace_ prefix prevents fbt from creating probes for
 * it so walltimestamp can be safely used in all fbt probes.
 */
void
dtrace_getnanotime(struct timespec *tsp)
{
    struct timehands *th;
    uint32_t gen;

    do {
        th = timehands;
        gen = atomic_load_acq_int(&th->th_generation);
        *tsp = th->th_nanotime;
        atomic_thread_fence_acq();
    } while (gen == 0 || gen != th->th_generation);
}
#endif /* __rtems__ */

#ifdef FFCLOCK
/*
 * System clock currently providing time to the system. Modifiable via sysctl
 * when the FFCLOCK option is defined.
 */
int sysclock_active = SYSCLOCK_FBCK;
#endif

/* Internal NTP status and error estimates. */
extern int time_status;
extern long time_esterror;

#ifndef __rtems__
/*
 * Take a snapshot of sysclock data which can be used to compare system clocks
 * and generate timestamps after the fact.
 */
void
sysclock_getsnapshot(struct sysclock_snap *clock_snap, int fast)
{
    struct fbclock_info *fbi;
    struct timehands *th;
    struct bintime bt;
    unsigned int delta, gen;
#ifdef FFCLOCK
    ffcounter ffcount;
    struct fftimehands *ffth;
    struct ffclock_info *ffi;
    struct ffclock_estimate cest;

    ffi = &clock_snap->ff_info;
#endif

    fbi = &clock_snap->fb_info;
    delta = 0;

    do {
        th = timehands;
        gen = atomic_load_acq_int(&th->th_generation);
        fbi->th_scale = th->th_scale;
        fbi->tick_time = th->th_offset;
#ifdef FFCLOCK
        ffth = fftimehands;
        ffi->tick_time = ffth->tick_time_lerp;
        ffi->tick_time_lerp = ffth->tick_time_lerp;
        ffi->period = ffth->cest.period;
        ffi->period_lerp = ffth->period_lerp;
        clock_snap->ffcount = ffth->tick_ffcount;
        cest = ffth->cest;
#endif
        if (!fast)
            delta = tc_delta(th);
        atomic_thread_fence_acq();
    } while (gen == 0 || gen != th->th_generation);

    clock_snap->delta = delta;
#ifdef FFCLOCK
    clock_snap->sysclock_active = sysclock_active;
#endif

    /* Record feedback clock status and error. */
    clock_snap->fb_info.status = time_status;
    /* XXX: Very crude estimate of feedback clock error. */
    bt.sec = time_esterror / 1000000;
    bt.frac = ((time_esterror - bt.sec) * 1000000) *
        (uint64_t)18446744073709ULL;
    clock_snap->fb_info.error = bt;

#ifdef FFCLOCK
    if (!fast)
        clock_snap->ffcount += delta;

    /* Record feed-forward clock leap second adjustment. */
    ffi->leapsec_adjustment = cest.leapsec_total;
    if (clock_snap->ffcount > cest.leapsec_next)
        ffi->leapsec_adjustment -= cest.leapsec;

    /* Record feed-forward clock status and error. */
    clock_snap->ff_info.status = cest.status;
    ffcount = clock_snap->ffcount - cest.update_ffcount;
    ffclock_convert_delta(ffcount, cest.period, &bt);
    /* 18446744073709 = int(2^64/1e12), err_bound_rate in [ps/s]. */
    bintime_mul(&bt, cest.errb_rate * (uint64_t)18446744073709ULL);
    /* 18446744073 = int(2^64 / 1e9), since err_abs in [ns]. */
    bintime_addx(&bt, cest.errb_abs * (uint64_t)18446744073ULL);
    clock_snap->ff_info.error = bt;
#endif
}

/*
 * Convert a sysclock snapshot into a struct bintime based on the specified
 * clock source and flags.
 */
int
sysclock_snap2bintime(struct sysclock_snap *cs, struct bintime *bt,
    int whichclock, uint32_t flags)
{
    struct bintime boottimebin;
#ifdef FFCLOCK
    struct bintime bt2;
    uint64_t period;
#endif

    switch (whichclock) {
    case SYSCLOCK_FBCK:
        *bt = cs->fb_info.tick_time;

        /* If snapshot was created with !fast, delta will be >0. */
        if (cs->delta > 0)
            bintime_addx(bt, cs->fb_info.th_scale * cs->delta);

        if ((flags & FBCLOCK_UPTIME) == 0) {
            getboottimebin(&boottimebin);
            bintime_add(bt, &boottimebin);
        }
        break;
#ifdef FFCLOCK
    case SYSCLOCK_FFWD:
        if (flags & FFCLOCK_LERP) {
            *bt = cs->ff_info.tick_time_lerp;
            period = cs->ff_info.period_lerp;
        } else {
            *bt = cs->ff_info.tick_time;
            period = cs->ff_info.period;
        }

        /* If snapshot was created with !fast, delta will be >0. */
        if (cs->delta > 0) {
            ffclock_convert_delta(cs->delta, period, &bt2);
            bintime_add(bt, &bt2);
        }

        /* Leap second adjustment. */
        if (flags & FFCLOCK_LEAPSEC)
            bt->sec -= cs->ff_info.leapsec_adjustment;

        /* Boot time adjustment, for uptime/monotonic clocks. */
        if (flags & FFCLOCK_UPTIME)
            bintime_sub(bt, &ffclock_boottime);
        break;
#endif
    default:
        return (EINVAL);
        break;
    }

    return (0);
}
#endif /* __rtems__ */

/*
 * Initialize a new timecounter and possibly use it.
 */
void
tc_init(struct timecounter *tc)
{
#ifndef __rtems__
    uint32_t 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_WITH_LABEL(NULL,
        SYSCTL_STATIC_CHILDREN(_kern_timecounter_tc), OID_AUTO, tc->tc_name,
        CTLFLAG_RW, 0, "timecounter description", "timecounter");
    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_U64 | 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");
    /*
     * Do not automatically switch if the current tc was specifically
     * chosen.  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 monotonic.
     */
    if (tc_chosen)
        return;
    if (tc->tc_quality < 0)
        return;
#endif /* __rtems__ */
    if (tc->tc_quality < timecounter->tc_quality)
        return;
    if (tc->tc_quality == timecounter->tc_quality &&
        tc->tc_frequency < timecounter->tc_frequency)
        return;
#ifndef __rtems__
    (void)tc->tc_get_timecount(tc);
    (void)tc->tc_get_timecount(tc);
#endif /* __rtems__ */
    timecounter = tc;
#ifdef __rtems__
    tc_windup(NULL);
#endif /* __rtems__ */
}

#ifndef __rtems__
/* Report the frequency of the current timecounter. */
uint64_t
tc_getfrequency(void)
{

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

static bool
sleeping_on_old_rtc(struct thread *td)
{

    /*
     * td_rtcgen is modified by curthread when it is running,
     * and by other threads in this function.  By finding the thread
     * on a sleepqueue and holding the lock on the sleepqueue
     * chain, we guarantee that the thread is not running and that
     * modifying td_rtcgen is safe.  Setting td_rtcgen to zero informs
     * the thread that it was woken due to a real-time clock adjustment.
     * (The declaration of td_rtcgen refers to this comment.)
     */
    if (td->td_rtcgen != 0 && td->td_rtcgen != rtc_generation) {
        td->td_rtcgen = 0;
        return (true);
    }
    return (false);
}

static struct mtx tc_setclock_mtx;
MTX_SYSINIT(tc_setclock_init, &tc_setclock_mtx, "tcsetc", MTX_SPIN);
#endif /* __rtems__ */

/*
 * Step our concept of UTC.  This is done by modifying our estimate of
 * when we booted.
 */
void
#ifndef __rtems__
tc_setclock(struct timespec *ts)
#else /* __rtems__ */
_Timecounter_Set_clock(const struct bintime *_bt,
    ISR_lock_Context *lock_context)
#endif /* __rtems__ */
{
#ifndef __rtems__
    struct timespec tbef, taft;
#endif /* __rtems__ */
    struct bintime bt, bt2;

#ifndef __rtems__
    timespec2bintime(ts, &bt);
    nanotime(&tbef);
    mtx_lock_spin(&tc_setclock_mtx);
    cpu_tick_calibrate(1);
#else /* __rtems__ */
    bt = *_bt;
#endif /* __rtems__ */
    binuptime(&bt2);
    bintime_sub(&bt, &bt2);

    /* XXX fiddle all the little crinkly bits around the fiords... */
#ifndef __rtems__
    tc_windup(&bt);
    mtx_unlock_spin(&tc_setclock_mtx);

    /* Avoid rtc_generation == 0, since td_rtcgen == 0 is special. */
    atomic_add_rel_int(&rtc_generation, 2);
    sleepq_chains_remove_matching(sleeping_on_old_rtc);
    if (timestepwarnings) {
        nanotime(&taft);
        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);
    }
#else /* __rtems__ */
    _Timecounter_Windup(&bt, lock_context);
#endif /* __rtems__ */
}

/*
 * 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(struct bintime *new_boottimebin)
#ifdef __rtems__
{
        ISR_lock_Context lock_context;

        _Timecounter_Acquire(&lock_context);
        _Timecounter_Windup(new_boottimebin, &lock_context);
}

static void
_Timecounter_Windup(struct bintime *new_boottimebin,
    ISR_lock_Context *lock_context)
#endif /* __rtems__ */
{
    struct bintime bt;
    struct timehands *th, *tho;
    uint64_t scale;
    uint32_t 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.  We need
     * to ensure that the zero generation is visible before the
     * data updates become visible, which requires release fence.
     * For similar reasons, re-reading of the generation after the
     * data is read should use acquire fence.
     */
    tho = timehands;
#if defined(RTEMS_SMP)
    th = tho->th_next;
#else
    th = tho;
#endif
    ogen = th->th_generation;
    th->th_generation = 0;
    atomic_thread_fence_rel();
#if defined(RTEMS_SMP)
    bcopy(tho, th, offsetof(struct timehands, th_generation));
#endif
    if (new_boottimebin != NULL)
        th->th_boottime = *new_boottimebin;

    /*
     * 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;
#ifdef FFCLOCK
    ffclock_windup(delta);
#endif
    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);

#ifndef __rtems__
    /*
     * 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);
#endif /* __rtems__ */

    /*
     * 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, &th->th_boottime);
    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)
            th->th_boottime.sec += bt.sec - t;
    }
    /* Update the UTC timestamps used by the get*() functions. */
    th->th_bintime = bt;
    bintime2timeval(&bt, &th->th_microtime);
    bintime2timespec(&bt, &th->th_nanotime);

    /* Now is a good time to change timecounters. */
    if (th->th_counter != timecounter) {
#ifndef __rtems__
#ifndef __arm__
        if ((timecounter->tc_flags & TC_FLAGS_C2STOP) != 0)
            cpu_disable_c2_sleep++;
        if ((th->th_counter->tc_flags & TC_FLAGS_C2STOP) != 0)
            cpu_disable_c2_sleep--;
#endif
#endif /* __rtems__ */
        th->th_counter = timecounter;
        th->th_offset_count = ncount;
#ifndef __rtems__
        tc_min_ticktock_freq = max(1, timecounter->tc_frequency /
            (((uint64_t)timecounter->tc_counter_mask + 1) / 3));
#endif /* __rtems__ */
#ifdef FFCLOCK
        ffclock_change_tc(th);
#endif
    }

    /*-
     * 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 = (uint64_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;
    atomic_store_rel_int(&th->th_generation, ogen);

    /* Go live with the new struct timehands. */
#ifdef FFCLOCK
    switch (sysclock_active) {
    case SYSCLOCK_FBCK:
#endif
        time_second = th->th_microtime.tv_sec;
        time_uptime = th->th_offset.sec;
#ifdef FFCLOCK
        break;
    case SYSCLOCK_FFWD:
        time_second = fftimehands->tick_time_lerp.sec;
        time_uptime = fftimehands->tick_time_lerp.sec - ffclock_boottime.sec;
        break;
    }
#endif

#if defined(RTEMS_SMP)
    timehands = th;
#endif
#ifndef __rtems__
    timekeep_push_vdso();
#endif /* __rtems__ */
#ifdef __rtems__
    _Timecounter_Release(lock_context);
#endif /* __rtems__ */
}

#ifndef __rtems__
/* 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)
        return (error);
    /* Record that the tc in use now was specifically chosen. */
    tc_chosen = 1;
    if (strcmp(newname, tc->tc_name) == 0)
        return (0);
    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;

        /*
         * The vdso timehands update is deferred until the next
         * 'tc_windup()'.
         *
         * This is prudent given that 'timekeep_push_vdso()' does not
         * use any locking and that it can be called in hard interrupt
         * context via 'tc_windup()'.
         */
        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 the available timecounter hardware. */
static int
sysctl_kern_timecounter_choice(SYSCTL_HANDLER_ARGS)
{
    struct sbuf sb;
    struct timecounter *tc;
    int error;

    sbuf_new_for_sysctl(&sb, NULL, 0, req);
    for (tc = timecounters; tc != NULL; tc = tc->tc_next) {
        if (tc != timecounters)
            sbuf_putc(&sb, ' ');
        sbuf_printf(&sb, "%s(%d)", tc->tc_name, tc->tc_quality);
    }
    error = sbuf_finish(&sb);
    sbuf_delete(&sb);
    return (error);
}

SYSCTL_PROC(_kern_timecounter, OID_AUTO, choice, CTLTYPE_STRING | CTLFLAG_RD,
    0, 0, sysctl_kern_timecounter_choice, "A", "Timecounter hardware detected");
#endif /* __rtems__ */

#ifndef __rtems__
/*
 * RFC 2783 PPS-API implementation.
 */

/*
 *  Return true if the driver is aware of the abi version extensions in the
 *  pps_state structure, and it supports at least the given abi version number.
 */
static inline int
abi_aware(struct pps_state *pps, int vers)
{

    return ((pps->kcmode & KCMODE_ABIFLAG) && pps->driver_abi >= vers);
}

static int
pps_fetch(struct pps_fetch_args *fapi, struct pps_state *pps)
{
    int err, timo;
    pps_seq_t aseq, cseq;
    struct timeval tv;

    if (fapi->tsformat && fapi->tsformat != PPS_TSFMT_TSPEC)
        return (EINVAL);

    /*
     * If no timeout is requested, immediately return whatever values were
     * most recently captured.  If timeout seconds is -1, that's a request
     * to block without a timeout.  WITNESS won't let us sleep forever
     * without a lock (we really don't need a lock), so just repeatedly
     * sleep a long time.
     */
    if (fapi->timeout.tv_sec || fapi->timeout.tv_nsec) {
        if (fapi->timeout.tv_sec == -1)
            timo = 0x7fffffff;
        else {
            tv.tv_sec = fapi->timeout.tv_sec;
            tv.tv_usec = fapi->timeout.tv_nsec / 1000;
            timo = tvtohz(&tv);
        }
        aseq = pps->ppsinfo.assert_sequence;
        cseq = pps->ppsinfo.clear_sequence;
        while (aseq == pps->ppsinfo.assert_sequence &&
            cseq == pps->ppsinfo.clear_sequence) {
            if (abi_aware(pps, 1) && pps->driver_mtx != NULL) {
                if (pps->flags & PPSFLAG_MTX_SPIN) {
                    err = msleep_spin(pps, pps->driver_mtx,
                        "ppsfch", timo);
                } else {
                    err = msleep(pps, pps->driver_mtx, PCATCH,
                        "ppsfch", timo);
                }
            } else {
                err = tsleep(pps, PCATCH, "ppsfch", timo);
            }
            if (err == EWOULDBLOCK) {
                if (fapi->timeout.tv_sec == -1) {
                    continue;
                } else {
                    return (ETIMEDOUT);
                }
            } else if (err != 0) {
                return (err);
            }
        }
    }

    pps->ppsinfo.current_mode = pps->ppsparam.mode;
    fapi->pps_info_buf = pps->ppsinfo;

    return (0);
}

int
pps_ioctl(u_long cmd, caddr_t data, struct pps_state *pps)
{
    pps_params_t *app;
    struct pps_fetch_args *fapi;
#ifdef FFCLOCK
    struct pps_fetch_ffc_args *fapi_ffc;
#endif
#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);
#ifdef FFCLOCK
        /* Ensure only a single clock is selected for ffc timestamp. */
        if ((app->mode & PPS_TSCLK_MASK) == PPS_TSCLK_MASK)
            return (EINVAL);
#endif
        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;
        return (pps_fetch(fapi, pps));
#ifdef FFCLOCK
    case PPS_IOC_FETCH_FFCOUNTER:
        fapi_ffc = (struct pps_fetch_ffc_args *)data;
        if (fapi_ffc->tsformat && fapi_ffc->tsformat !=
            PPS_TSFMT_TSPEC)
            return (EINVAL);
        if (fapi_ffc->timeout.tv_sec || fapi_ffc->timeout.tv_nsec)
            return (EOPNOTSUPP);
        pps->ppsinfo_ffc.current_mode = pps->ppsparam.mode;
        fapi_ffc->pps_info_buf_ffc = pps->ppsinfo_ffc;
        /* Overwrite timestamps if feedback clock selected. */
        switch (pps->ppsparam.mode & PPS_TSCLK_MASK) {
        case PPS_TSCLK_FBCK:
            fapi_ffc->pps_info_buf_ffc.assert_timestamp =
                pps->ppsinfo.assert_timestamp;
            fapi_ffc->pps_info_buf_ffc.clear_timestamp =
                pps->ppsinfo.clear_timestamp;
            break;
        case PPS_TSCLK_FFWD:
            break;
        default:
            break;
        }
        return (0);
#endif /* FFCLOCK */
    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 & KCMODE_EDGEMASK) |
            (pps->kcmode & KCMODE_ABIFLAG);
        return (0);
#else
        return (EOPNOTSUPP);
#endif
    default:
        return (ENOIOCTL);
    }
}

void
pps_init(struct pps_state *pps)
{
    pps->ppscap |= PPS_TSFMT_TSPEC | PPS_CANWAIT;
    if (pps->ppscap & PPS_CAPTUREASSERT)
        pps->ppscap |= PPS_OFFSETASSERT;
    if (pps->ppscap & PPS_CAPTURECLEAR)
        pps->ppscap |= PPS_OFFSETCLEAR;
#ifdef FFCLOCK
    pps->ppscap |= PPS_TSCLK_MASK;
#endif
    pps->kcmode &= ~KCMODE_ABIFLAG;
}

void
pps_init_abi(struct pps_state *pps)
{

    pps_init(pps);
    if (pps->driver_abi > 0) {
        pps->kcmode |= KCMODE_ABIFLAG;
        pps->kernel_abi = PPS_ABI_VERSION;
    }
}

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

    KASSERT(pps != NULL, ("NULL pps pointer in pps_capture"));
    th = timehands;
    pps->capgen = atomic_load_acq_int(&th->th_generation);
    pps->capth = th;
#ifdef FFCLOCK
    pps->capffth = fftimehands;
#endif
    pps->capcount = th->th_counter->tc_get_timecount(th->th_counter);
    atomic_thread_fence_acq();
    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;
    uint32_t tcount, *pcount;
    int foff;
    pps_seq_t *pseq;
#ifdef FFCLOCK
    struct timespec *tsp_ffc;
    pps_seq_t *pseq_ffc;
    ffcounter *ffcount;
#endif
#ifdef PPS_SYNC
    int fhard;
#endif

    KASSERT(pps != NULL, ("NULL pps pointer in pps_event"));
    /* Nothing to do if not currently set to capture this event type. */
    if ((event & pps->ppsparam.mode) == 0)
        return;
    /* If the timecounter was wound up underneath us, bail out. */
    if (pps->capgen == 0 || pps->capgen !=
        atomic_load_acq_int(&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;
#ifdef PPS_SYNC
        fhard = pps->kcmode & PPS_CAPTUREASSERT;
#endif
        pcount = &pps->ppscount[0];
        pseq = &pps->ppsinfo.assert_sequence;
#ifdef FFCLOCK
        ffcount = &pps->ppsinfo_ffc.assert_ffcount;
        tsp_ffc = &pps->ppsinfo_ffc.assert_timestamp;
        pseq_ffc = &pps->ppsinfo_ffc.assert_sequence;
#endif
    } else {
        tsp = &pps->ppsinfo.clear_timestamp;
        osp = &pps->ppsparam.clear_offset;
        foff = pps->ppsparam.mode & PPS_OFFSETCLEAR;
#ifdef PPS_SYNC
        fhard = pps->kcmode & PPS_CAPTURECLEAR;
#endif
        pcount = &pps->ppscount[1];
        pseq = &pps->ppsinfo.clear_sequence;
#ifdef FFCLOCK
        ffcount = &pps->ppsinfo_ffc.clear_ffcount;
        tsp_ffc = &pps->ppsinfo_ffc.clear_timestamp;
        pseq_ffc = &pps->ppsinfo_ffc.clear_sequence;
#endif
    }

    /*
     * 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_bintime;
    bintime_addx(&bt, pps->capth->th_scale * tcount);
    bintime2timespec(&bt, &ts);

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

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

    if (foff) {
        timespecadd(tsp, osp, tsp);
        if (tsp->tv_nsec < 0) {
            tsp->tv_nsec += 1000000000;
            tsp->tv_sec -= 1;
        }
    }

#ifdef FFCLOCK
    *ffcount = pps->capffth->tick_ffcount + tcount;
    bt = pps->capffth->tick_time;
    ffclock_convert_delta(tcount, pps->capffth->cest.period, &bt);
    bintime_add(&bt, &pps->capffth->tick_time);
    bintime2timespec(&bt, &ts);
    (*pseq_ffc)++;
    *tsp_ffc = ts;
#endif

#ifdef PPS_SYNC
    if (fhard) {
        uint64_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 = (uint64_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

    /* Wakeup anyone sleeping in pps_fetch().  */
    wakeup(pps);
}
#else /* __rtems__ */
/* FIXME: https://devel.rtems.org/ticket/2349 */
#endif /* __rtems__ */

/*
 * 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.
 */

#ifndef __rtems__
static int tc_tick;
SYSCTL_INT(_kern_timecounter, OID_AUTO, tick, CTLFLAG_RD, &tc_tick, 0,
    "Approximate number of hardclock ticks in a millisecond");
#endif /* __rtems__ */

#ifndef __rtems__
void
tc_ticktock(int cnt)
{
    static int count;

    if (mtx_trylock_spin(&tc_setclock_mtx)) {
        count += cnt;
        if (count >= tc_tick) {
            count = 0;
            tc_windup(NULL);
        }
        mtx_unlock_spin(&tc_setclock_mtx);
    }
}
#else /* __rtems__ */
void
_Timecounter_Tick(void)
{
    Per_CPU_Control *cpu_self = _Per_CPU_Get();

    if (_Per_CPU_Is_boot_processor(cpu_self)) {
                tc_windup(NULL);
    }

    _Watchdog_Tick(cpu_self);
}

void
_Timecounter_Tick_simple(uint32_t delta, uint32_t offset,
    ISR_lock_Context *lock_context)
{
    struct bintime bt;
    struct timehands *th;
    uint32_t ogen;

    th = timehands;
    ogen = th->th_generation;
    th->th_offset_count = offset;
    bintime_addx(&th->th_offset, th->th_scale * delta);

    bt = th->th_offset;
    bintime_add(&bt, &th->th_boottime);
    /* Update the UTC timestamps used by the get*() functions. */
    th->th_bintime = bt;
    bintime2timeval(&bt, &th->th_microtime);
    bintime2timespec(&bt, &th->th_nanotime);

    /*
     * 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;

    _Timecounter_Release(lock_context);

    _Watchdog_Tick(_Per_CPU_Get_snapshot());
}
#endif /* __rtems__ */

#ifndef __rtems__
static void __inline
tc_adjprecision(void)
{
    int t;

    if (tc_timepercentage > 0) {
        t = (99 + tc_timepercentage) / tc_timepercentage;
        tc_precexp = fls(t + (t >> 1)) - 1;
        FREQ2BT(hz / tc_tick, &bt_timethreshold);
        FREQ2BT(hz, &bt_tickthreshold);
        bintime_shift(&bt_timethreshold, tc_precexp);
        bintime_shift(&bt_tickthreshold, tc_precexp);
    } else {
        tc_precexp = 31;
        bt_timethreshold.sec = INT_MAX;
        bt_timethreshold.frac = ~(uint64_t)0;
        bt_tickthreshold = bt_timethreshold;
    }
    sbt_timethreshold = bttosbt(bt_timethreshold);
    sbt_tickthreshold = bttosbt(bt_tickthreshold);
}
#endif /* __rtems__ */

#ifndef __rtems__
static int
sysctl_kern_timecounter_adjprecision(SYSCTL_HANDLER_ARGS)
{
    int error, val;

    val = tc_timepercentage;
    error = sysctl_handle_int(oidp, &val, 0, req);
    if (error != 0 || req->newptr == NULL)
        return (error);
    tc_timepercentage = val;
    if (cold)
        goto done;
    tc_adjprecision();
done:
    return (0);
}

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

    /*
     * 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 initial 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;
    tc_adjprecision();
    FREQ2BT(hz, &tick_bt);
    tick_sbt = bttosbt(tick_bt);
    tick_rate = hz / tc_tick;
    FREQ2BT(tick_rate, &tc_tick_bt);
    tc_tick_sbt = bttosbt(tc_tick_bt);
    p = (tc_tick * 1000000) / hz;
    printf("Timecounters tick every %d.%03u msec\n", p / 1000, p % 1000);

#ifdef FFCLOCK
    ffclock_init();
#endif
    /* warm up new timecounter (again) and get rolling. */
    (void)timecounter->tc_get_timecount(timecounter);
    (void)timecounter->tc_get_timecount(timecounter);
    mtx_lock_spin(&tc_setclock_mtx);
    tc_windup(NULL);
    mtx_unlock_spin(&tc_setclock_mtx);
}

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 DPCPU_DEFINE(uint64_t, tc_cpu_ticks_base);
static DPCPU_DEFINE(unsigned, tc_cpu_ticks_last);

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

    critical_enter();
    base = DPCPU_PTR(tc_cpu_ticks_base);
    last = DPCPU_PTR(tc_cpu_ticks_last);
    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;
    res = u + *base;
    critical_exit();
    return (res);
}

void
cpu_tick_calibration(void)
{
    static time_t last_calib;

    if (time_uptime != last_calib && !(time_uptime & 0xf)) {
        cpu_tick_calibrate(0);
        last_calib = time_uptime;
    }
}

/*
 * This function gets called every 16 seconds on only one designated
 * CPU in the system from hardclock() via cpu_tick_calibration()().
 *
 * 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);
        /*
         * 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;
#endif /* __rtems__ */

#ifndef __rtems__
static int vdso_th_enable = 1;
static int
sysctl_fast_gettime(SYSCTL_HANDLER_ARGS)
{
    int old_vdso_th_enable, error;

    old_vdso_th_enable = vdso_th_enable;
    error = sysctl_handle_int(oidp, &old_vdso_th_enable, 0, req);
    if (error != 0)
        return (error);
    vdso_th_enable = old_vdso_th_enable;
    return (0);
}
SYSCTL_PROC(_kern_timecounter, OID_AUTO, fast_gettime,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE,
    NULL, 0, sysctl_fast_gettime, "I", "Enable fast time of day");

uint32_t
tc_fill_vdso_timehands(struct vdso_timehands *vdso_th)
{
    struct timehands *th;
    uint32_t enabled;

    th = timehands;
    vdso_th->th_scale = th->th_scale;
    vdso_th->th_offset_count = th->th_offset_count;
    vdso_th->th_counter_mask = th->th_counter->tc_counter_mask;
    vdso_th->th_offset = th->th_offset;
    vdso_th->th_boottime = th->th_boottime;
    if (th->th_counter->tc_fill_vdso_timehands != NULL) {
        enabled = th->th_counter->tc_fill_vdso_timehands(vdso_th,
            th->th_counter);
    } else
        enabled = 0;
    if (!vdso_th_enable)
        enabled = 0;
    return (enabled);
}
#endif /* __rtems__ */

#ifdef COMPAT_FREEBSD32
uint32_t
tc_fill_vdso_timehands32(struct vdso_timehands32 *vdso_th32)
{
    struct timehands *th;
    uint32_t enabled;

    th = timehands;
    *(uint64_t *)&vdso_th32->th_scale[0] = th->th_scale;
    vdso_th32->th_offset_count = th->th_offset_count;
    vdso_th32->th_counter_mask = th->th_counter->tc_counter_mask;
    vdso_th32->th_offset.sec = th->th_offset.sec;
    *(uint64_t *)&vdso_th32->th_offset.frac[0] = th->th_offset.frac;
    vdso_th32->th_boottime.sec = th->th_boottime.sec;
    *(uint64_t *)&vdso_th32->th_boottime.frac[0] = th->th_boottime.frac;
    if (th->th_counter->tc_fill_vdso_timehands32 != NULL) {
        enabled = th->th_counter->tc_fill_vdso_timehands32(vdso_th32,
            th->th_counter);
    } else
        enabled = 0;
    if (!vdso_th_enable)
        enabled = 0;
    return (enabled);
}
#endif