2 * NTP state machine interfaces and logic.
4 * This code was mainly moved from kernel/timer.c and kernel/time.c
5 * Please see those files for relevant copyright info and historical
8 #include <linux/capability.h>
9 #include <linux/clocksource.h>
10 #include <linux/workqueue.h>
11 #include <linux/hrtimer.h>
12 #include <linux/jiffies.h>
13 #include <linux/math64.h>
14 #include <linux/timex.h>
15 #include <linux/time.h>
17 #include <linux/module.h>
18 #include <linux/rtc.h>
20 #include "ntp_internal.h"
21 #include "timekeeping_internal.h"
25 * NTP timekeeping variables:
27 * Note: All of the NTP state is protected by the timekeeping locks.
31 /* USER_HZ period (usecs): */
32 unsigned long tick_usec = TICK_USEC;
34 /* SHIFTED_HZ period (nsecs): */
35 unsigned long tick_nsec;
37 static u64 tick_length;
38 static u64 tick_length_base;
40 #define SECS_PER_DAY 86400
41 #define MAX_TICKADJ 500LL /* usecs */
42 #define MAX_TICKADJ_SCALED \
43 (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
46 * phase-lock loop variables
50 * clock synchronization status
52 * (TIME_ERROR prevents overwriting the CMOS clock)
54 static int time_state = TIME_OK;
56 /* clock status bits: */
57 static int time_status = STA_UNSYNC;
59 /* time adjustment (nsecs): */
60 static s64 time_offset;
62 /* pll time constant: */
63 static long time_constant = 2;
65 /* maximum error (usecs): */
66 static long time_maxerror = NTP_PHASE_LIMIT;
68 /* estimated error (usecs): */
69 static long time_esterror = NTP_PHASE_LIMIT;
71 /* frequency offset (scaled nsecs/secs): */
74 /* time at last adjustment (secs): */
75 static time64_t time_reftime;
77 static long time_adjust;
79 /* constant (boot-param configurable) NTP tick adjustment (upscaled) */
80 static s64 ntp_tick_adj;
82 /* second value of the next pending leapsecond, or TIME64_MAX if no leap */
83 static time64_t ntp_next_leap_sec = TIME64_MAX;
88 * The following variables are used when a pulse-per-second (PPS) signal
89 * is available. They establish the engineering parameters of the clock
90 * discipline loop when controlled by the PPS signal.
92 #define PPS_VALID 10 /* PPS signal watchdog max (s) */
93 #define PPS_POPCORN 4 /* popcorn spike threshold (shift) */
94 #define PPS_INTMIN 2 /* min freq interval (s) (shift) */
95 #define PPS_INTMAX 8 /* max freq interval (s) (shift) */
96 #define PPS_INTCOUNT 4 /* number of consecutive good intervals to
97 increase pps_shift or consecutive bad
98 intervals to decrease it */
99 #define PPS_MAXWANDER 100000 /* max PPS freq wander (ns/s) */
101 static int pps_valid; /* signal watchdog counter */
102 static long pps_tf[3]; /* phase median filter */
103 static long pps_jitter; /* current jitter (ns) */
104 static struct timespec64 pps_fbase; /* beginning of the last freq interval */
105 static int pps_shift; /* current interval duration (s) (shift) */
106 static int pps_intcnt; /* interval counter */
107 static s64 pps_freq; /* frequency offset (scaled ns/s) */
108 static long pps_stabil; /* current stability (scaled ns/s) */
111 * PPS signal quality monitors
113 static long pps_calcnt; /* calibration intervals */
114 static long pps_jitcnt; /* jitter limit exceeded */
115 static long pps_stbcnt; /* stability limit exceeded */
116 static long pps_errcnt; /* calibration errors */
119 /* PPS kernel consumer compensates the whole phase error immediately.
120 * Otherwise, reduce the offset by a fixed factor times the time constant.
122 static inline s64 ntp_offset_chunk(s64 offset)
124 if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)
127 return shift_right(offset, SHIFT_PLL + time_constant);
130 static inline void pps_reset_freq_interval(void)
132 /* the PPS calibration interval may end
133 surprisingly early */
134 pps_shift = PPS_INTMIN;
139 * pps_clear - Clears the PPS state variables
141 static inline void pps_clear(void)
143 pps_reset_freq_interval();
147 pps_fbase.tv_sec = pps_fbase.tv_nsec = 0;
151 /* Decrease pps_valid to indicate that another second has passed since
152 * the last PPS signal. When it reaches 0, indicate that PPS signal is
155 static inline void pps_dec_valid(void)
160 time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
161 STA_PPSWANDER | STA_PPSERROR);
166 static inline void pps_set_freq(s64 freq)
171 static inline int is_error_status(int status)
173 return (status & (STA_UNSYNC|STA_CLOCKERR))
174 /* PPS signal lost when either PPS time or
175 * PPS frequency synchronization requested
177 || ((status & (STA_PPSFREQ|STA_PPSTIME))
178 && !(status & STA_PPSSIGNAL))
179 /* PPS jitter exceeded when
180 * PPS time synchronization requested */
181 || ((status & (STA_PPSTIME|STA_PPSJITTER))
182 == (STA_PPSTIME|STA_PPSJITTER))
183 /* PPS wander exceeded or calibration error when
184 * PPS frequency synchronization requested
186 || ((status & STA_PPSFREQ)
187 && (status & (STA_PPSWANDER|STA_PPSERROR)));
190 static inline void pps_fill_timex(struct timex *txc)
192 txc->ppsfreq = shift_right((pps_freq >> PPM_SCALE_INV_SHIFT) *
193 PPM_SCALE_INV, NTP_SCALE_SHIFT);
194 txc->jitter = pps_jitter;
195 if (!(time_status & STA_NANO))
196 txc->jitter /= NSEC_PER_USEC;
197 txc->shift = pps_shift;
198 txc->stabil = pps_stabil;
199 txc->jitcnt = pps_jitcnt;
200 txc->calcnt = pps_calcnt;
201 txc->errcnt = pps_errcnt;
202 txc->stbcnt = pps_stbcnt;
205 #else /* !CONFIG_NTP_PPS */
207 static inline s64 ntp_offset_chunk(s64 offset)
209 return shift_right(offset, SHIFT_PLL + time_constant);
212 static inline void pps_reset_freq_interval(void) {}
213 static inline void pps_clear(void) {}
214 static inline void pps_dec_valid(void) {}
215 static inline void pps_set_freq(s64 freq) {}
217 static inline int is_error_status(int status)
219 return status & (STA_UNSYNC|STA_CLOCKERR);
222 static inline void pps_fill_timex(struct timex *txc)
224 /* PPS is not implemented, so these are zero */
235 #endif /* CONFIG_NTP_PPS */
239 * ntp_synced - Returns 1 if the NTP status is not UNSYNC
242 static inline int ntp_synced(void)
244 return !(time_status & STA_UNSYNC);
253 * Update (tick_length, tick_length_base, tick_nsec), based
254 * on (tick_usec, ntp_tick_adj, time_freq):
256 static void ntp_update_frequency(void)
261 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
264 second_length += ntp_tick_adj;
265 second_length += time_freq;
267 tick_nsec = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
268 new_base = div_u64(second_length, NTP_INTERVAL_FREQ);
271 * Don't wait for the next second_overflow, apply
272 * the change to the tick length immediately:
274 tick_length += new_base - tick_length_base;
275 tick_length_base = new_base;
278 static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
280 time_status &= ~STA_MODE;
285 if (!(time_status & STA_FLL) && (secs <= MAXSEC))
288 time_status |= STA_MODE;
290 return div64_long(offset64 << (NTP_SCALE_SHIFT - SHIFT_FLL), secs);
293 static void ntp_update_offset(long offset)
299 if (!(time_status & STA_PLL))
302 if (!(time_status & STA_NANO)) {
303 /* Make sure the multiplication below won't overflow */
304 offset = clamp(offset, -USEC_PER_SEC, USEC_PER_SEC);
305 offset *= NSEC_PER_USEC;
309 * Scale the phase adjustment and
310 * clamp to the operating range.
312 offset = clamp(offset, -MAXPHASE, MAXPHASE);
315 * Select how the frequency is to be controlled
316 * and in which mode (PLL or FLL).
318 secs = (long)(__ktime_get_real_seconds() - time_reftime);
319 if (unlikely(time_status & STA_FREQHOLD))
322 time_reftime = __ktime_get_real_seconds();
325 freq_adj = ntp_update_offset_fll(offset64, secs);
328 * Clamp update interval to reduce PLL gain with low
329 * sampling rate (e.g. intermittent network connection)
330 * to avoid instability.
332 if (unlikely(secs > 1 << (SHIFT_PLL + 1 + time_constant)))
333 secs = 1 << (SHIFT_PLL + 1 + time_constant);
335 freq_adj += (offset64 * secs) <<
336 (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
338 freq_adj = min(freq_adj + time_freq, MAXFREQ_SCALED);
340 time_freq = max(freq_adj, -MAXFREQ_SCALED);
342 time_offset = div_s64(offset64 << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
346 * ntp_clear - Clears the NTP state variables
350 time_adjust = 0; /* stop active adjtime() */
351 time_status |= STA_UNSYNC;
352 time_maxerror = NTP_PHASE_LIMIT;
353 time_esterror = NTP_PHASE_LIMIT;
355 ntp_update_frequency();
357 tick_length = tick_length_base;
360 ntp_next_leap_sec = TIME64_MAX;
361 /* Clear PPS state variables */
366 u64 ntp_tick_length(void)
372 * ntp_get_next_leap - Returns the next leapsecond in CLOCK_REALTIME ktime_t
374 * Provides the time of the next leapsecond against CLOCK_REALTIME in
375 * a ktime_t format. Returns KTIME_MAX if no leapsecond is pending.
377 ktime_t ntp_get_next_leap(void)
381 if ((time_state == TIME_INS) && (time_status & STA_INS))
382 return ktime_set(ntp_next_leap_sec, 0);
383 ret.tv64 = KTIME_MAX;
388 * this routine handles the overflow of the microsecond field
390 * The tricky bits of code to handle the accurate clock support
391 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
392 * They were originally developed for SUN and DEC kernels.
393 * All the kudos should go to Dave for this stuff.
395 * Also handles leap second processing, and returns leap offset
397 int second_overflow(unsigned long secs)
403 * Leap second processing. If in leap-insert state at the end of the
404 * day, the system clock is set back one second; if in leap-delete
405 * state, the system clock is set ahead one second.
407 switch (time_state) {
409 if (time_status & STA_INS) {
410 time_state = TIME_INS;
411 ntp_next_leap_sec = secs + SECS_PER_DAY -
412 (secs % SECS_PER_DAY);
413 } else if (time_status & STA_DEL) {
414 time_state = TIME_DEL;
415 ntp_next_leap_sec = secs + SECS_PER_DAY -
416 ((secs+1) % SECS_PER_DAY);
420 if (!(time_status & STA_INS)) {
421 ntp_next_leap_sec = TIME64_MAX;
422 time_state = TIME_OK;
423 } else if (secs % SECS_PER_DAY == 0) {
425 time_state = TIME_OOP;
427 "Clock: inserting leap second 23:59:60 UTC\n");
431 if (!(time_status & STA_DEL)) {
432 ntp_next_leap_sec = TIME64_MAX;
433 time_state = TIME_OK;
434 } else if ((secs + 1) % SECS_PER_DAY == 0) {
436 ntp_next_leap_sec = TIME64_MAX;
437 time_state = TIME_WAIT;
439 "Clock: deleting leap second 23:59:59 UTC\n");
443 ntp_next_leap_sec = TIME64_MAX;
444 time_state = TIME_WAIT;
447 if (!(time_status & (STA_INS | STA_DEL)))
448 time_state = TIME_OK;
453 /* Bump the maxerror field */
454 time_maxerror += MAXFREQ / NSEC_PER_USEC;
455 if (time_maxerror > NTP_PHASE_LIMIT) {
456 time_maxerror = NTP_PHASE_LIMIT;
457 time_status |= STA_UNSYNC;
460 /* Compute the phase adjustment for the next second */
461 tick_length = tick_length_base;
463 delta = ntp_offset_chunk(time_offset);
464 time_offset -= delta;
465 tick_length += delta;
467 /* Check PPS signal */
473 if (time_adjust > MAX_TICKADJ) {
474 time_adjust -= MAX_TICKADJ;
475 tick_length += MAX_TICKADJ_SCALED;
479 if (time_adjust < -MAX_TICKADJ) {
480 time_adjust += MAX_TICKADJ;
481 tick_length -= MAX_TICKADJ_SCALED;
485 tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
493 #ifdef CONFIG_GENERIC_CMOS_UPDATE
494 int __weak update_persistent_clock(struct timespec now)
499 int __weak update_persistent_clock64(struct timespec64 now64)
503 now = timespec64_to_timespec(now64);
504 return update_persistent_clock(now);
508 #if defined(CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC)
509 static void sync_cmos_clock(struct work_struct *work);
511 static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);
513 static void sync_cmos_clock(struct work_struct *work)
515 struct timespec64 now;
516 struct timespec64 next;
520 * If we have an externally synchronized Linux clock, then update
521 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
522 * called as close as possible to 500 ms before the new second starts.
523 * This code is run on a timer. If the clock is set, that timer
524 * may not expire at the correct time. Thus, we adjust...
525 * We want the clock to be within a couple of ticks from the target.
529 * Not synced, exit, do not restart a timer (if one is
530 * running, let it run out).
535 getnstimeofday64(&now);
536 if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec * 5) {
537 struct timespec64 adjust = now;
540 if (persistent_clock_is_local)
541 adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);
542 #ifdef CONFIG_GENERIC_CMOS_UPDATE
543 fail = update_persistent_clock64(adjust);
546 #ifdef CONFIG_RTC_SYSTOHC
548 fail = rtc_set_ntp_time(adjust);
552 next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
553 if (next.tv_nsec <= 0)
554 next.tv_nsec += NSEC_PER_SEC;
556 if (!fail || fail == -ENODEV)
561 if (next.tv_nsec >= NSEC_PER_SEC) {
563 next.tv_nsec -= NSEC_PER_SEC;
565 queue_delayed_work(system_power_efficient_wq,
566 &sync_cmos_work, timespec64_to_jiffies(&next));
569 void ntp_notify_cmos_timer(void)
571 queue_delayed_work(system_power_efficient_wq, &sync_cmos_work, 0);
575 void ntp_notify_cmos_timer(void) { }
580 * Propagate a new txc->status value into the NTP state:
582 static inline void process_adj_status(struct timex *txc, struct timespec64 *ts)
584 if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
585 time_state = TIME_OK;
586 time_status = STA_UNSYNC;
587 ntp_next_leap_sec = TIME64_MAX;
588 /* restart PPS frequency calibration */
589 pps_reset_freq_interval();
593 * If we turn on PLL adjustments then reset the
594 * reference time to current time.
596 if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
597 time_reftime = __ktime_get_real_seconds();
599 /* only set allowed bits */
600 time_status &= STA_RONLY;
601 time_status |= txc->status & ~STA_RONLY;
605 static inline void process_adjtimex_modes(struct timex *txc,
606 struct timespec64 *ts,
609 if (txc->modes & ADJ_STATUS)
610 process_adj_status(txc, ts);
612 if (txc->modes & ADJ_NANO)
613 time_status |= STA_NANO;
615 if (txc->modes & ADJ_MICRO)
616 time_status &= ~STA_NANO;
618 if (txc->modes & ADJ_FREQUENCY) {
619 time_freq = txc->freq * PPM_SCALE;
620 time_freq = min(time_freq, MAXFREQ_SCALED);
621 time_freq = max(time_freq, -MAXFREQ_SCALED);
622 /* update pps_freq */
623 pps_set_freq(time_freq);
626 if (txc->modes & ADJ_MAXERROR)
627 time_maxerror = txc->maxerror;
629 if (txc->modes & ADJ_ESTERROR)
630 time_esterror = txc->esterror;
632 if (txc->modes & ADJ_TIMECONST) {
633 time_constant = txc->constant;
634 if (!(time_status & STA_NANO))
636 time_constant = min(time_constant, (long)MAXTC);
637 time_constant = max(time_constant, 0l);
640 if (txc->modes & ADJ_TAI && txc->constant > 0)
641 *time_tai = txc->constant;
643 if (txc->modes & ADJ_OFFSET)
644 ntp_update_offset(txc->offset);
646 if (txc->modes & ADJ_TICK)
647 tick_usec = txc->tick;
649 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
650 ntp_update_frequency();
656 * ntp_validate_timex - Ensures the timex is ok for use in do_adjtimex
658 int ntp_validate_timex(struct timex *txc)
660 if (txc->modes & ADJ_ADJTIME) {
661 /* singleshot must not be used with any other mode bits */
662 if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
664 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
665 !capable(CAP_SYS_TIME))
668 /* In order to modify anything, you gotta be super-user! */
669 if (txc->modes && !capable(CAP_SYS_TIME))
672 * if the quartz is off by more than 10% then
673 * something is VERY wrong!
675 if (txc->modes & ADJ_TICK &&
676 (txc->tick < 900000/USER_HZ ||
677 txc->tick > 1100000/USER_HZ))
681 if (txc->modes & ADJ_SETOFFSET) {
682 /* In order to inject time, you gotta be super-user! */
683 if (!capable(CAP_SYS_TIME))
686 if (!timeval_inject_offset_valid(&txc->time))
691 * Check for potential multiplication overflows that can
692 * only happen on 64-bit systems:
694 if ((txc->modes & ADJ_FREQUENCY) && (BITS_PER_LONG == 64)) {
695 if (LLONG_MIN / PPM_SCALE > txc->freq)
697 if (LLONG_MAX / PPM_SCALE < txc->freq)
706 * adjtimex mainly allows reading (and writing, if superuser) of
707 * kernel time-keeping variables. used by xntpd.
709 int __do_adjtimex(struct timex *txc, struct timespec64 *ts, s32 *time_tai)
713 if (txc->modes & ADJ_ADJTIME) {
714 long save_adjust = time_adjust;
716 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
717 /* adjtime() is independent from ntp_adjtime() */
718 time_adjust = txc->offset;
719 ntp_update_frequency();
721 txc->offset = save_adjust;
724 /* If there are input parameters, then process them: */
726 process_adjtimex_modes(txc, ts, time_tai);
728 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
730 if (!(time_status & STA_NANO))
731 txc->offset /= NSEC_PER_USEC;
734 result = time_state; /* mostly `TIME_OK' */
735 /* check for errors */
736 if (is_error_status(time_status))
739 txc->freq = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
740 PPM_SCALE_INV, NTP_SCALE_SHIFT);
741 txc->maxerror = time_maxerror;
742 txc->esterror = time_esterror;
743 txc->status = time_status;
744 txc->constant = time_constant;
746 txc->tolerance = MAXFREQ_SCALED / PPM_SCALE;
747 txc->tick = tick_usec;
748 txc->tai = *time_tai;
750 /* fill PPS status fields */
753 txc->time.tv_sec = (time_t)ts->tv_sec;
754 txc->time.tv_usec = ts->tv_nsec;
755 if (!(time_status & STA_NANO))
756 txc->time.tv_usec /= NSEC_PER_USEC;
758 /* Handle leapsec adjustments */
759 if (unlikely(ts->tv_sec >= ntp_next_leap_sec)) {
760 if ((time_state == TIME_INS) && (time_status & STA_INS)) {
765 if ((time_state == TIME_DEL) && (time_status & STA_DEL)) {
770 if ((time_state == TIME_OOP) &&
771 (ts->tv_sec == ntp_next_leap_sec)) {
779 #ifdef CONFIG_NTP_PPS
781 /* actually struct pps_normtime is good old struct timespec, but it is
782 * semantically different (and it is the reason why it was invented):
783 * pps_normtime.nsec has a range of ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ]
784 * while timespec.tv_nsec has a range of [0, NSEC_PER_SEC) */
785 struct pps_normtime {
786 s64 sec; /* seconds */
787 long nsec; /* nanoseconds */
790 /* normalize the timestamp so that nsec is in the
791 ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
792 static inline struct pps_normtime pps_normalize_ts(struct timespec64 ts)
794 struct pps_normtime norm = {
799 if (norm.nsec > (NSEC_PER_SEC >> 1)) {
800 norm.nsec -= NSEC_PER_SEC;
807 /* get current phase correction and jitter */
808 static inline long pps_phase_filter_get(long *jitter)
810 *jitter = pps_tf[0] - pps_tf[1];
814 /* TODO: test various filters */
818 /* add the sample to the phase filter */
819 static inline void pps_phase_filter_add(long err)
821 pps_tf[2] = pps_tf[1];
822 pps_tf[1] = pps_tf[0];
826 /* decrease frequency calibration interval length.
827 * It is halved after four consecutive unstable intervals.
829 static inline void pps_dec_freq_interval(void)
831 if (--pps_intcnt <= -PPS_INTCOUNT) {
832 pps_intcnt = -PPS_INTCOUNT;
833 if (pps_shift > PPS_INTMIN) {
840 /* increase frequency calibration interval length.
841 * It is doubled after four consecutive stable intervals.
843 static inline void pps_inc_freq_interval(void)
845 if (++pps_intcnt >= PPS_INTCOUNT) {
846 pps_intcnt = PPS_INTCOUNT;
847 if (pps_shift < PPS_INTMAX) {
854 /* update clock frequency based on MONOTONIC_RAW clock PPS signal
857 * At the end of the calibration interval the difference between the
858 * first and last MONOTONIC_RAW clock timestamps divided by the length
859 * of the interval becomes the frequency update. If the interval was
860 * too long, the data are discarded.
861 * Returns the difference between old and new frequency values.
863 static long hardpps_update_freq(struct pps_normtime freq_norm)
865 long delta, delta_mod;
868 /* check if the frequency interval was too long */
869 if (freq_norm.sec > (2 << pps_shift)) {
870 time_status |= STA_PPSERROR;
872 pps_dec_freq_interval();
873 printk_deferred(KERN_ERR
874 "hardpps: PPSERROR: interval too long - %lld s\n",
879 /* here the raw frequency offset and wander (stability) is
880 * calculated. If the wander is less than the wander threshold
881 * the interval is increased; otherwise it is decreased.
883 ftemp = div_s64(((s64)(-freq_norm.nsec)) << NTP_SCALE_SHIFT,
885 delta = shift_right(ftemp - pps_freq, NTP_SCALE_SHIFT);
887 if (delta > PPS_MAXWANDER || delta < -PPS_MAXWANDER) {
888 printk_deferred(KERN_WARNING
889 "hardpps: PPSWANDER: change=%ld\n", delta);
890 time_status |= STA_PPSWANDER;
892 pps_dec_freq_interval();
893 } else { /* good sample */
894 pps_inc_freq_interval();
897 /* the stability metric is calculated as the average of recent
898 * frequency changes, but is used only for performance
903 delta_mod = -delta_mod;
904 pps_stabil += (div_s64(((s64)delta_mod) <<
905 (NTP_SCALE_SHIFT - SHIFT_USEC),
906 NSEC_PER_USEC) - pps_stabil) >> PPS_INTMIN;
908 /* if enabled, the system clock frequency is updated */
909 if ((time_status & STA_PPSFREQ) != 0 &&
910 (time_status & STA_FREQHOLD) == 0) {
911 time_freq = pps_freq;
912 ntp_update_frequency();
918 /* correct REALTIME clock phase error against PPS signal */
919 static void hardpps_update_phase(long error)
921 long correction = -error;
924 /* add the sample to the median filter */
925 pps_phase_filter_add(correction);
926 correction = pps_phase_filter_get(&jitter);
928 /* Nominal jitter is due to PPS signal noise. If it exceeds the
929 * threshold, the sample is discarded; otherwise, if so enabled,
930 * the time offset is updated.
932 if (jitter > (pps_jitter << PPS_POPCORN)) {
933 printk_deferred(KERN_WARNING
934 "hardpps: PPSJITTER: jitter=%ld, limit=%ld\n",
935 jitter, (pps_jitter << PPS_POPCORN));
936 time_status |= STA_PPSJITTER;
938 } else if (time_status & STA_PPSTIME) {
939 /* correct the time using the phase offset */
940 time_offset = div_s64(((s64)correction) << NTP_SCALE_SHIFT,
942 /* cancel running adjtime() */
946 pps_jitter += (jitter - pps_jitter) >> PPS_INTMIN;
950 * __hardpps() - discipline CPU clock oscillator to external PPS signal
952 * This routine is called at each PPS signal arrival in order to
953 * discipline the CPU clock oscillator to the PPS signal. It takes two
954 * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former
955 * is used to correct clock phase error and the latter is used to
956 * correct the frequency.
958 * This code is based on David Mills's reference nanokernel
959 * implementation. It was mostly rewritten but keeps the same idea.
961 void __hardpps(const struct timespec64 *phase_ts, const struct timespec64 *raw_ts)
963 struct pps_normtime pts_norm, freq_norm;
965 pts_norm = pps_normalize_ts(*phase_ts);
967 /* clear the error bits, they will be set again if needed */
968 time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
970 /* indicate signal presence */
971 time_status |= STA_PPSSIGNAL;
972 pps_valid = PPS_VALID;
974 /* when called for the first time,
975 * just start the frequency interval */
976 if (unlikely(pps_fbase.tv_sec == 0)) {
981 /* ok, now we have a base for frequency calculation */
982 freq_norm = pps_normalize_ts(timespec64_sub(*raw_ts, pps_fbase));
984 /* check that the signal is in the range
985 * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */
986 if ((freq_norm.sec == 0) ||
987 (freq_norm.nsec > MAXFREQ * freq_norm.sec) ||
988 (freq_norm.nsec < -MAXFREQ * freq_norm.sec)) {
989 time_status |= STA_PPSJITTER;
990 /* restart the frequency calibration interval */
992 printk_deferred(KERN_ERR "hardpps: PPSJITTER: bad pulse\n");
998 /* check if the current frequency interval is finished */
999 if (freq_norm.sec >= (1 << pps_shift)) {
1001 /* restart the frequency calibration interval */
1002 pps_fbase = *raw_ts;
1003 hardpps_update_freq(freq_norm);
1006 hardpps_update_phase(pts_norm.nsec);
1009 #endif /* CONFIG_NTP_PPS */
1011 static int __init ntp_tick_adj_setup(char *str)
1013 int rc = kstrtol(str, 0, (long *)&ntp_tick_adj);
1017 ntp_tick_adj <<= NTP_SCALE_SHIFT;
1022 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
1024 void __init ntp_init(void)