kernel - Fix excessive call stack depth on stuck interrupt

[dragonfly.git] / sys / kern / kern_ntptime.c

/***********************************************************************
 *                                                                     *
 * Copyright (c) David L. Mills 1993-2001                              *
 *                                                                     *
 * Permission to use, copy, modify, and distribute this software and   *
 * its documentation for any purpose and without fee is hereby         *
 * granted, provided that the above copyright notice appears in all    *
 * copies and that both the copyright notice and this permission       *
 * notice appear in supporting documentation, and that the name        *
 * University of Delaware not be used in advertising or publicity      *
 * pertaining to distribution of the software without specific,        *
 * written prior permission. The University of Delaware makes no       *
 * representations about the suitability this software for any         *
 * purpose. It is provided "as is" without express or implied          *
 * warranty.                                                           *
 *                                                                     *
 **********************************************************************/

/*
 * Adapted from the original sources for FreeBSD and timecounters by:
 * Poul-Henning Kamp <phk@FreeBSD.org>.
 *
 * The 32bit version of the "LP" macros seems a bit past its "sell by" 
 * date so I have retained only the 64bit version and included it directly
 * in this file.
 *
 * Only minor changes done to interface with the timecounters over in
 * sys/kern/kern_clock.c.   Some of the comments below may be (even more)
 * confusing and/or plain wrong in that context.
 *
 * $FreeBSD: src/sys/kern/kern_ntptime.c,v 1.32.2.2 2001/04/22 11:19:46 jhay Exp $
 */

#include "opt_ntp.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysproto.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/priv.h>
#include <sys/time.h>
#include <sys/timex.h>
#include <sys/timepps.h>
#include <sys/sysctl.h>

#include <sys/thread2.h>

/*
 * Single-precision macros for 64-bit machines
 */
typedef long long l_fp;
#define L_ADD(v, u)     ((v) += (u))
#define L_SUB(v, u)     ((v) -= (u))
#define L_ADDHI(v, a)   ((v) += (long long)(a) << 32)
#define L_NEG(v)        ((v) = -(v))
#define L_RSHIFT(v, n) \
        do { \
                if ((v) < 0) \
                        (v) = -(-(v) >> (n)); \
                else \
                        (v) = (v) >> (n); \
        } while (0)
#define L_MPY(v, a)     ((v) *= (a))
#define L_CLR(v)        ((v) = 0)
#define L_ISNEG(v)      ((v) < 0)
#define L_LINT(v, a)    ((v) = (long long)(a) << 32)
#define L_GINT(v)       ((v) < 0 ? -(-(v) >> 32) : (v) >> 32)

/*
 * Generic NTP kernel interface
 *
 * These routines constitute the Network Time Protocol (NTP) interfaces
 * for user and daemon application programs. The ntp_gettime() routine
 * provides the time, maximum error (synch distance) and estimated error
 * (dispersion) to client user application programs. The ntp_adjtime()
 * routine is used by the NTP daemon to adjust the system clock to an
 * externally derived time. The time offset and related variables set by
 * this routine are used by other routines in this module to adjust the
 * phase and frequency of the clock discipline loop which controls the
 * system clock.
 *
 * When the kernel time is reckoned directly in nanoseconds (NTP_NANO
 * defined), the time at each tick interrupt is derived directly from
 * the kernel time variable. When the kernel time is reckoned in
 * microseconds, (NTP_NANO undefined), the time is derived from the
 * kernel time variable together with a variable representing the
 * leftover nanoseconds at the last tick interrupt. In either case, the
 * current nanosecond time is reckoned from these values plus an
 * interpolated value derived by the clock routines in another
 * architecture-specific module. The interpolation can use either a
 * dedicated counter or a processor cycle counter (PCC) implemented in
 * some architectures.
 *
 * Note that all routines must run at priority splclock or higher.
 */
/*
 * Phase/frequency-lock loop (PLL/FLL) definitions
 *
 * The nanosecond clock discipline uses two variable types, time
 * variables and frequency variables. Both types are represented as 64-
 * bit fixed-point quantities with the decimal point between two 32-bit
 * halves. On a 32-bit machine, each half is represented as a single
 * word and mathematical operations are done using multiple-precision
 * arithmetic. On a 64-bit machine, ordinary computer arithmetic is
 * used.
 *
 * A time variable is a signed 64-bit fixed-point number in ns and
 * fraction. It represents the remaining time offset to be amortized
 * over succeeding tick interrupts. The maximum time offset is about
 * 0.5 s and the resolution is about 2.3e-10 ns.
 *
 *                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |s s s|                       ns                                |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                        fraction                               |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *
 * A frequency variable is a signed 64-bit fixed-point number in ns/s
 * and fraction. It represents the ns and fraction to be added to the
 * kernel time variable at each second. The maximum frequency offset is
 * about +-500000 ns/s and the resolution is about 2.3e-10 ns/s.
 *
 *                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |s s s s s s s s s s s s s|            ns/s                     |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |                        fraction                               |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 */
/*
 * The following variables establish the state of the PLL/FLL and the
 * residual time and frequency offset of the local clock.
 */
#define SHIFT_PLL       4               /* PLL loop gain (shift) */
#define SHIFT_FLL       2               /* FLL loop gain (shift) */

static int time_state = TIME_OK;        /* clock state */
static int time_status = STA_UNSYNC;    /* clock status bits */
static long time_tai;                   /* TAI offset (s) */
static long time_monitor;               /* last time offset scaled (ns) */
static long time_constant;              /* poll interval (shift) (s) */
static long time_precision = 1;         /* clock precision (ns) */
static long time_maxerror = MAXPHASE / 1000; /* maximum error (us) */
static long time_esterror = MAXPHASE / 1000; /* estimated error (us) */
static time_t time_reftime;             /* time at last adjustment (s) */
static long time_tick;                  /* nanoseconds per tick (ns) */
static l_fp time_offset;                /* time offset (ns) */
static l_fp time_freq;                  /* frequency offset (ns/s) */
static l_fp time_adj;                   /* tick adjust (ns/s) */

static struct lock ntp_lock = LOCK_INITIALIZER("ntplk", 0, 0);

#ifdef PPS_SYNC
/*
 * The following variables are used when a pulse-per-second (PPS) signal
 * is available and connected via a modem control lead. They establish
 * the engineering parameters of the clock discipline loop when
 * controlled by the PPS signal.
 */
#define PPS_FAVG        2               /* min freq avg interval (s) (shift) */
#define PPS_FAVGDEF     8               /* default freq avg int (s) (shift) */
#define PPS_FAVGMAX     15              /* max freq avg interval (s) (shift) */
#define PPS_PAVG        4               /* phase avg interval (s) (shift) */
#define PPS_VALID       120             /* PPS signal watchdog max (s) */
#define PPS_MAXWANDER   100000          /* max PPS wander (ns/s) */
#define PPS_POPCORN     2               /* popcorn spike threshold (shift) */

static struct timespec pps_tf[3];       /* phase median filter */
static l_fp pps_freq;                   /* scaled frequency offset (ns/s) */
static long pps_fcount;                 /* frequency accumulator */
static long pps_jitter;                 /* nominal jitter (ns) */
static long pps_stabil;                 /* nominal stability (scaled ns/s) */
static long pps_lastsec;                /* time at last calibration (s) */
static int pps_valid;                   /* signal watchdog counter */
static int pps_shift = PPS_FAVG;        /* interval duration (s) (shift) */
static int pps_shiftmax = PPS_FAVGDEF;  /* max interval duration (s) (shift) */
static int pps_intcnt;                  /* wander counter */

/*
 * PPS signal quality monitors
 */
static long pps_calcnt;                 /* calibration intervals */
static long pps_jitcnt;                 /* jitter limit exceeded */
static long pps_stbcnt;                 /* stability limit exceeded */
static long pps_errcnt;                 /* calibration errors */
#endif /* PPS_SYNC */
/*
 * End of phase/frequency-lock loop (PLL/FLL) definitions
 */

static void ntp_init(void);
static void hardupdate(long offset);

/*
 * ntp_gettime() - NTP user application interface
 *
 * See the timex.h header file for synopsis and API description. Note
 * that the TAI offset is returned in the ntvtimeval.tai structure
 * member.
 */
static int
ntp_sysctl(SYSCTL_HANDLER_ARGS)
{
        struct ntptimeval ntv;  /* temporary structure */
        struct timespec atv;    /* nanosecond time */
        int error;

        lockmgr(&ntp_lock, LK_EXCLUSIVE);

        nanotime(&atv);
        ntv.time.tv_sec = atv.tv_sec;
        ntv.time.tv_nsec = atv.tv_nsec;
        ntv.maxerror = time_maxerror;
        ntv.esterror = time_esterror;
        ntv.tai = time_tai;
        ntv.time_state = time_state;

        /*
         * Status word error decode. If any of these conditions occur,
         * an error is returned, instead of the status word. Most
         * applications will care only about the fact the system clock
         * may not be trusted, not about the details.
         *
         * Hardware or software error
         */
        if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||

        /*
         * PPS signal lost when either time or frequency synchronization
         * requested
         */
            (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
            !(time_status & STA_PPSSIGNAL)) ||

        /*
         * PPS jitter exceeded when time synchronization requested
         */
            (time_status & STA_PPSTIME &&
            time_status & STA_PPSJITTER) ||

        /*
         * PPS wander exceeded or calibration error when frequency
         * synchronization requested
         */
            (time_status & STA_PPSFREQ &&
            time_status & (STA_PPSWANDER | STA_PPSERROR))) {
                ntv.time_state = TIME_ERROR;
        }

        error = sysctl_handle_opaque(oidp, &ntv, sizeof ntv, req);
        lockmgr(&ntp_lock, LK_RELEASE);

        return error;
}

SYSCTL_NODE(_kern, OID_AUTO, ntp_pll, CTLFLAG_RW, 0, "");
SYSCTL_PROC(_kern_ntp_pll, OID_AUTO, gettime, CTLTYPE_OPAQUE|CTLFLAG_RD,
        0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", "");

#ifdef PPS_SYNC
SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shiftmax, CTLFLAG_RW, &pps_shiftmax, 0, "");
SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shift, CTLFLAG_RW, &pps_shift, 0, "");
SYSCTL_INT(_kern_ntp_pll, OID_AUTO, time_monitor, CTLFLAG_RD, &time_monitor, 0, "");

SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, &pps_freq, sizeof(pps_freq), "I", "");
SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, time_freq, CTLFLAG_RD, &time_freq, sizeof(time_freq), "I", "");
#endif
/*
 * ntp_adjtime() - NTP daemon application interface
 *
 * See the timex.h header file for synopsis and API description. Note
 * that the timex.constant structure member has a dual purpose to set
 * the time constant and to set the TAI offset.
 *
 * MPALMOSTSAFE
 */
int
sys_ntp_adjtime(struct ntp_adjtime_args *uap)
{
        struct thread *td = curthread;
        struct timex ntv;       /* temporary structure */
        long freq;              /* frequency ns/s) */
        int modes;              /* mode bits from structure */
        int error;

        error = copyin((caddr_t)uap->tp, (caddr_t)&ntv, sizeof(ntv));
        if (error)
                return(error);

        /*
         * Update selected clock variables - only the superuser can
         * change anything. Note that there is no error checking here on
         * the assumption the superuser should know what it is doing.
         * Note that either the time constant or TAI offset are loaded
         * from the ntv.constant member, depending on the mode bits. If
         * the STA_PLL bit in the status word is cleared, the state and
         * status words are reset to the initial values at boot.
         */
        modes = ntv.modes;
        if (modes)
                error = priv_check(td, PRIV_NTP_ADJTIME);
        if (error)
                return (error);

        lockmgr(&ntp_lock, LK_EXCLUSIVE);
        crit_enter();
        if (modes & MOD_MAXERROR)
                time_maxerror = ntv.maxerror;
        if (modes & MOD_ESTERROR)
                time_esterror = ntv.esterror;
        if (modes & MOD_STATUS) {
                if (time_status & STA_PLL && !(ntv.status & STA_PLL)) {
                        time_state = TIME_OK;
                        time_status = STA_UNSYNC;
#ifdef PPS_SYNC
                        pps_shift = PPS_FAVG;
#endif /* PPS_SYNC */
                }
                time_status &= STA_RONLY;
                time_status |= ntv.status & ~STA_RONLY;
        }
        if (modes & MOD_TIMECONST) {
                if (ntv.constant < 0)
                        time_constant = 0;
                else if (ntv.constant > MAXTC)
                        time_constant = MAXTC;
                else
                        time_constant = ntv.constant;
        }
        if (modes & MOD_TAI) {
                if (ntv.constant > 0) /* XXX zero & negative numbers ? */
                        time_tai = ntv.constant;
        }
#ifdef PPS_SYNC
        if (modes & MOD_PPSMAX) {
                if (ntv.shift < PPS_FAVG)
                        pps_shiftmax = PPS_FAVG;
                else if (ntv.shift > PPS_FAVGMAX)
                        pps_shiftmax = PPS_FAVGMAX;
                else
                        pps_shiftmax = ntv.shift;
        }
#endif /* PPS_SYNC */
        if (modes & MOD_NANO)
                time_status |= STA_NANO;
        if (modes & MOD_MICRO)
                time_status &= ~STA_NANO;
        if (modes & MOD_CLKB)
                time_status |= STA_CLK;
        if (modes & MOD_CLKA)
                time_status &= ~STA_CLK;
        if (modes & MOD_OFFSET) {
                if (time_status & STA_NANO)
                        hardupdate(ntv.offset);
                else
                        hardupdate(ntv.offset * 1000);
        }
        /*
         * Note: the userland specified frequency is in seconds per second
         * times 65536e+6.  Multiply by a thousand and divide by 65336 to
         * get nanoseconds.
         */
        if (modes & MOD_FREQUENCY) {
                freq = (ntv.freq * 1000LL) >> 16;
                if (freq > MAXFREQ)
                        L_LINT(time_freq, MAXFREQ);
                else if (freq < -MAXFREQ)
                        L_LINT(time_freq, -MAXFREQ);
                else
                        L_LINT(time_freq, freq);
#ifdef PPS_SYNC
                pps_freq = time_freq;
#endif /* PPS_SYNC */
        }

        /*
         * Retrieve all clock variables. Note that the TAI offset is
         * returned only by ntp_gettime();
         */
        if (time_status & STA_NANO)
                ntv.offset = time_monitor;
        else
                ntv.offset = time_monitor / 1000; /* XXX rounding ? */
        ntv.freq = L_GINT((time_freq / 1000LL) << 16);
        ntv.maxerror = time_maxerror;
        ntv.esterror = time_esterror;
        ntv.status = time_status;
        ntv.constant = time_constant;
        if (time_status & STA_NANO)
                ntv.precision = time_precision;
        else
                ntv.precision = time_precision / 1000;
        ntv.tolerance = MAXFREQ * SCALE_PPM;
#ifdef PPS_SYNC
        ntv.shift = pps_shift;
        ntv.ppsfreq = L_GINT((pps_freq / 1000LL) << 16);
        if (time_status & STA_NANO)
                ntv.jitter = pps_jitter;
        else
                ntv.jitter = pps_jitter / 1000;
        ntv.stabil = pps_stabil;
        ntv.calcnt = pps_calcnt;
        ntv.errcnt = pps_errcnt;
        ntv.jitcnt = pps_jitcnt;
        ntv.stbcnt = pps_stbcnt;
#endif /* PPS_SYNC */
        crit_exit();
        lockmgr(&ntp_lock, LK_RELEASE);

        error = copyout((caddr_t)&ntv, (caddr_t)uap->tp, sizeof(ntv));
        if (error)
                return (error);

        /*
         * Status word error decode. See comments in
         * ntp_gettime() routine.
         */
        if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||
            (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
            !(time_status & STA_PPSSIGNAL)) ||
            (time_status & STA_PPSTIME &&
            time_status & STA_PPSJITTER) ||
            (time_status & STA_PPSFREQ &&
            time_status & (STA_PPSWANDER | STA_PPSERROR))) {
                uap->sysmsg_result = TIME_ERROR;
        } else {
                uap->sysmsg_result = time_state;
        }
        return (error);
}

/*
 * second_overflow() - called after ntp_tick_adjust()
 *
 * This routine is ordinarily called from hardclock() whenever the seconds
 * hand rolls over.  It returns leap seconds to add or drop, and sets nsec_adj
 * to the total adjustment to make over the next second in (ns << 32).
 *
 * This routine is only called by cpu #0.
 */
int
ntp_update_second(time_t newsec, int64_t *nsec_adj)
{
        l_fp ftemp;             /* 32/64-bit temporary */
        int  adjsec = 0;

        /*
         * On rollover of the second both the nanosecond and microsecond
         * clocks are updated and the state machine cranked as
         * necessary. The phase adjustment to be used for the next
         * second is calculated and the maximum error is increased by
         * the tolerance.
         */
        time_maxerror += MAXFREQ / 1000;

        /*
         * Leap second processing. If in leap-insert state at
         * the end of the day, the system clock is set back one
         * second; if in leap-delete state, the system clock is
         * set ahead one second. The nano_time() routine or
         * external clock driver will insure that reported time
         * is always monotonic.
         */
        switch (time_state) {

                /*
                 * No warning.
                 */
                case TIME_OK:
                if (time_status & STA_INS)
                        time_state = TIME_INS;
                else if (time_status & STA_DEL)
                        time_state = TIME_DEL;
                break;

                /*
                 * Insert second 23:59:60 following second
                 * 23:59:59.
                 */
                case TIME_INS:
                if (!(time_status & STA_INS))
                        time_state = TIME_OK;
                else if ((newsec) % 86400 == 0) {
                        --adjsec;
                        time_state = TIME_OOP;
                }
                break;

                /*
                 * Delete second 23:59:59.
                 */
                case TIME_DEL:
                if (!(time_status & STA_DEL))
                        time_state = TIME_OK;
                else if (((newsec) + 1) % 86400 == 0) {
                        ++adjsec;
                        time_tai--;
                        time_state = TIME_WAIT;
                }
                break;

                /*
                 * Insert second in progress.
                 */
                case TIME_OOP:
                        time_tai++;
                        time_state = TIME_WAIT;
                break;

                /*
                 * Wait for status bits to clear.
                 */
                case TIME_WAIT:
                if (!(time_status & (STA_INS | STA_DEL)))
                        time_state = TIME_OK;
        }

        /*
         * time_offset represents the total time adjustment we wish to
         * make (over no particular period of time).  time_freq represents
         * the frequency compensation we wish to apply.
         *
         * time_adj represents the total adjustment we wish to make over
         * one full second.  hardclock usually applies this adjustment in
         * time_adj / hz jumps, hz times a second.
         */
        ftemp = time_offset;
#ifdef PPS_SYNC
        /* XXX even if PPS signal dies we should finish adjustment ? */
        if ((time_status & STA_PPSTIME) && (time_status & STA_PPSSIGNAL))
                L_RSHIFT(ftemp, pps_shift);
        else
                L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
#else
                L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
#endif /* PPS_SYNC */
        time_adj = ftemp;               /* adjustment for part of the offset */
        L_SUB(time_offset, ftemp);
        L_ADD(time_adj, time_freq);     /* add frequency correction */
        *nsec_adj = time_adj;
#ifdef PPS_SYNC
        if (pps_valid > 0)
                pps_valid--;
        else
                time_status &= ~STA_PPSSIGNAL;
#endif /* PPS_SYNC */
        return(adjsec);
}

/*
 * ntp_init() - initialize variables and structures
 *
 * This routine must be called after the kernel variables hz and tick
 * are set or changed and before the next tick interrupt. In this
 * particular implementation, these values are assumed set elsewhere in
 * the kernel. The design allows the clock frequency and tick interval
 * to be changed while the system is running. So, this routine should
 * probably be integrated with the code that does that.
 */
static void
ntp_init(void)
{

        /*
         * The following variable must be initialized any time the
         * kernel variable hz is changed.
         */
        time_tick = NANOSECOND / hz;

        /*
         * The following variables are initialized only at startup. Only
         * those structures not cleared by the compiler need to be
         * initialized, and these only in the simulator. In the actual
         * kernel, any nonzero values here will quickly evaporate.
         */
        L_CLR(time_offset);
        L_CLR(time_freq);
#ifdef PPS_SYNC
        pps_tf[0].tv_sec = pps_tf[0].tv_nsec = 0;
        pps_tf[1].tv_sec = pps_tf[1].tv_nsec = 0;
        pps_tf[2].tv_sec = pps_tf[2].tv_nsec = 0;
        pps_fcount = 0;
        L_CLR(pps_freq);
#endif /* PPS_SYNC */      
}

SYSINIT(ntpclocks, SI_BOOT2_CLOCKS, SI_ORDER_FIRST, ntp_init, NULL);

/*
 * hardupdate() - local clock update
 *
 * This routine is called by ntp_adjtime() to update the local clock
 * phase and frequency. The implementation is of an adaptive-parameter,
 * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
 * time and frequency offset estimates for each call. If the kernel PPS
 * discipline code is configured (PPS_SYNC), the PPS signal itself
 * determines the new time offset, instead of the calling argument.
 * Presumably, calls to ntp_adjtime() occur only when the caller
 * believes the local clock is valid within some bound (+-128 ms with
 * NTP). If the caller's time is far different than the PPS time, an
 * argument will ensue, and it's not clear who will lose.
 *
 * For uncompensated quartz crystal oscillators and nominal update
 * intervals less than 256 s, operation should be in phase-lock mode,
 * where the loop is disciplined to phase. For update intervals greater
 * than 1024 s, operation should be in frequency-lock mode, where the
 * loop is disciplined to frequency. Between 256 s and 1024 s, the mode
 * is selected by the STA_MODE status bit.
 */
static void
hardupdate(long offset)
{
        long mtemp;
        l_fp ftemp;

        /*
         * Select how the phase is to be controlled and from which
         * source. If the PPS signal is present and enabled to
         * discipline the time, the PPS offset is used; otherwise, the
         * argument offset is used.
         */
        if (!(time_status & STA_PLL))
                return;
        if (!((time_status & STA_PPSTIME) && (time_status & STA_PPSSIGNAL))) {
                if (offset > MAXPHASE)
                        time_monitor = MAXPHASE;
                else if (offset < -MAXPHASE)
                        time_monitor = -MAXPHASE;
                else
                        time_monitor = offset;
                L_LINT(time_offset, time_monitor);
        }

        /*
         * Select how the frequency is to be controlled and in which
         * mode (PLL or FLL). If the PPS signal is present and enabled
         * to discipline the frequency, the PPS frequency is used;
         * otherwise, the argument offset is used to compute it.
         */
        if ((time_status & STA_PPSFREQ) && time_status & STA_PPSSIGNAL) {
                time_reftime = time_uptime;
                return;
        }
        if ((time_status & STA_FREQHOLD) || time_reftime == 0)
                time_reftime = time_uptime;
        mtemp = time_uptime - time_reftime;
        L_LINT(ftemp, time_monitor);
        L_RSHIFT(ftemp, (SHIFT_PLL + 2 + time_constant) << 1);
        L_MPY(ftemp, mtemp);
        L_ADD(time_freq, ftemp);
        time_status &= ~STA_MODE;
        if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
                L_LINT(ftemp, (time_monitor << 4) / mtemp);
                L_RSHIFT(ftemp, SHIFT_FLL + 4);
                L_ADD(time_freq, ftemp);
                time_status |= STA_MODE;
        }
        time_reftime = time_uptime;
        if (L_GINT(time_freq) > MAXFREQ)
                L_LINT(time_freq, MAXFREQ);
        else if (L_GINT(time_freq) < -MAXFREQ)
                L_LINT(time_freq, -MAXFREQ);
}

#ifdef PPS_SYNC
/*
 * hardpps() - discipline CPU clock oscillator to external PPS signal
 *
 * This routine is called at each PPS interrupt in order to discipline
 * the CPU clock oscillator to the PPS signal. There are two independent
 * first-order feedback loops, one for the phase, the other for the
 * frequency. The phase loop measures and grooms the PPS phase offset
 * and leaves it in a handy spot for the seconds overflow routine. The
 * frequency loop averages successive PPS phase differences and
 * calculates the PPS frequency offset, which is also processed by the
 * seconds overflow routine. The code requires the caller to capture the
 * time and architecture-dependent hardware counter values in
 * nanoseconds at the on-time PPS signal transition.
 *
 * Note that, on some Unix systems this routine runs at an interrupt
 * priority level higher than the timer interrupt routine hardclock().
 * Therefore, the variables used are distinct from the hardclock()
 * variables, except for the actual time and frequency variables, which
 * are determined by this routine and updated atomically.
 */
void
hardpps(struct timespec *tsp, long nsec)
{
        long u_sec, u_nsec, v_nsec; /* temps */
        l_fp ftemp;

        /*
         * The signal is first processed by a range gate and frequency
         * discriminator. The range gate rejects noise spikes outside
         * the range +-500 us. The frequency discriminator rejects input
         * signals with apparent frequency outside the range 1 +-500
         * PPM. If two hits occur in the same second, we ignore the
         * later hit; if not and a hit occurs outside the range gate,
         * keep the later hit for later comparison, but do not process
         * it.
         */
        time_status |= STA_PPSSIGNAL | STA_PPSJITTER;
        time_status &= ~(STA_PPSWANDER | STA_PPSERROR);
        pps_valid = PPS_VALID;
        u_sec = tsp->tv_sec;
        u_nsec = tsp->tv_nsec;
        if (u_nsec >= (NANOSECOND >> 1)) {
                u_nsec -= NANOSECOND;
                u_sec++;
        }
        v_nsec = u_nsec - pps_tf[0].tv_nsec;
        if (u_sec == pps_tf[0].tv_sec && v_nsec < NANOSECOND -
            MAXFREQ)
                return;
        pps_tf[2] = pps_tf[1];
        pps_tf[1] = pps_tf[0];
        pps_tf[0].tv_sec = u_sec;
        pps_tf[0].tv_nsec = u_nsec;

        /*
         * Compute the difference between the current and previous
         * counter values. If the difference exceeds 0.5 s, assume it
         * has wrapped around, so correct 1.0 s. If the result exceeds
         * the tick interval, the sample point has crossed a tick
         * boundary during the last second, so correct the tick. Very
         * intricate.
         */
        u_nsec = nsec;
        if (u_nsec > (NANOSECOND >> 1))
                u_nsec -= NANOSECOND;
        else if (u_nsec < -(NANOSECOND >> 1))
                u_nsec += NANOSECOND;
        pps_fcount += u_nsec;
        if (v_nsec > MAXFREQ || v_nsec < -MAXFREQ)
                return;
        time_status &= ~STA_PPSJITTER;

        /*
         * A three-stage median filter is used to help denoise the PPS
         * time. The median sample becomes the time offset estimate; the
         * difference between the other two samples becomes the time
         * dispersion (jitter) estimate.
         */
        if (pps_tf[0].tv_nsec > pps_tf[1].tv_nsec) {
                if (pps_tf[1].tv_nsec > pps_tf[2].tv_nsec) {
                        v_nsec = pps_tf[1].tv_nsec;     /* 0 1 2 */
                        u_nsec = pps_tf[0].tv_nsec - pps_tf[2].tv_nsec;
                } else if (pps_tf[2].tv_nsec > pps_tf[0].tv_nsec) {
                        v_nsec = pps_tf[0].tv_nsec;     /* 2 0 1 */
                        u_nsec = pps_tf[2].tv_nsec - pps_tf[1].tv_nsec;
                } else {
                        v_nsec = pps_tf[2].tv_nsec;     /* 0 2 1 */
                        u_nsec = pps_tf[0].tv_nsec - pps_tf[1].tv_nsec;
                }
        } else {
                if (pps_tf[1].tv_nsec < pps_tf[2].tv_nsec) {
                        v_nsec = pps_tf[1].tv_nsec;     /* 2 1 0 */
                        u_nsec = pps_tf[2].tv_nsec - pps_tf[0].tv_nsec;
                } else if (pps_tf[2].tv_nsec < pps_tf[0].tv_nsec) {
                        v_nsec = pps_tf[0].tv_nsec;     /* 1 0 2 */
                        u_nsec = pps_tf[1].tv_nsec - pps_tf[2].tv_nsec;
                } else {
                        v_nsec = pps_tf[2].tv_nsec;     /* 1 2 0 */
                        u_nsec = pps_tf[1].tv_nsec - pps_tf[0].tv_nsec;
                }
        }

        /*
         * Nominal jitter is due to PPS signal noise and interrupt
         * latency. If it exceeds the popcorn threshold, the sample is
         * discarded. otherwise, if so enabled, the time offset is
         * updated. We can tolerate a modest loss of data here without
         * much degrading time accuracy.
         */
        if (u_nsec > (pps_jitter << PPS_POPCORN)) {
                time_status |= STA_PPSJITTER;
                pps_jitcnt++;
        } else if (time_status & STA_PPSTIME) {
                time_monitor = -v_nsec;
                L_LINT(time_offset, time_monitor);
        }
        pps_jitter += (u_nsec - pps_jitter) >> PPS_FAVG;
        u_sec = pps_tf[0].tv_sec - pps_lastsec;
        if (u_sec < (1 << pps_shift))
                return;

        /*
         * At the end of the calibration interval the difference between
         * the first and last counter values becomes the scaled
         * frequency. It will later be divided by the length of the
         * interval to determine the frequency update. If the frequency
         * exceeds a sanity threshold, or if the actual calibration
         * interval is not equal to the expected length, the data are
         * discarded. We can tolerate a modest loss of data here without
         * much degrading frequency accuracy.
         */
        pps_calcnt++;
        v_nsec = -pps_fcount;
        pps_lastsec = pps_tf[0].tv_sec;
        pps_fcount = 0;
        u_nsec = MAXFREQ << pps_shift;
        if (v_nsec > u_nsec || v_nsec < -u_nsec || u_sec != (1 <<
            pps_shift)) {
                time_status |= STA_PPSERROR;
                pps_errcnt++;
                return;
        }

        /*
         * Here the raw frequency offset and wander (stability) is
         * calculated. If the wander is less than the wander threshold
         * for four consecutive averaging intervals, the interval is
         * doubled; if it is greater than the threshold for four
         * consecutive intervals, the interval is halved. The scaled
         * frequency offset is converted to frequency offset. The
         * stability metric is calculated as the average of recent
         * frequency changes, but is used only for performance
         * monitoring.
         */
        L_LINT(ftemp, v_nsec);
        L_RSHIFT(ftemp, pps_shift);
        L_SUB(ftemp, pps_freq);
        u_nsec = L_GINT(ftemp);
        if (u_nsec > PPS_MAXWANDER) {
                L_LINT(ftemp, PPS_MAXWANDER);
                pps_intcnt--;
                time_status |= STA_PPSWANDER;
                pps_stbcnt++;
        } else if (u_nsec < -PPS_MAXWANDER) {
                L_LINT(ftemp, -PPS_MAXWANDER);
                pps_intcnt--;
                time_status |= STA_PPSWANDER;
                pps_stbcnt++;
        } else {
                pps_intcnt++;
        }
        if (pps_intcnt >= 4) {
                pps_intcnt = 4;
                if (pps_shift < pps_shiftmax) {
                        pps_shift++;
                        pps_intcnt = 0;
                }
        } else if (pps_intcnt <= -4 || pps_shift > pps_shiftmax) {
                pps_intcnt = -4;
                if (pps_shift > PPS_FAVG) {
                        pps_shift--;
                        pps_intcnt = 0;
                }
        }
        if (u_nsec < 0)
                u_nsec = -u_nsec;
        pps_stabil += (u_nsec * SCALE_PPM - pps_stabil) >> PPS_FAVG;

        /*
         * The PPS frequency is recalculated and clamped to the maximum
         * MAXFREQ. If enabled, the system clock frequency is updated as
         * well.
         */
        L_ADD(pps_freq, ftemp);
        u_nsec = L_GINT(pps_freq);
        if (u_nsec > MAXFREQ)
                L_LINT(pps_freq, MAXFREQ);
        else if (u_nsec < -MAXFREQ)
                L_LINT(pps_freq, -MAXFREQ);
        if (time_status & STA_PPSFREQ)
                time_freq = pps_freq;
}
#endif /* PPS_SYNC */