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"
23 * NTP timekeeping variables:
25 * Note: All of the NTP state is protected by the timekeeping locks.
29 /* USER_HZ period (usecs): */
30 unsigned long tick_usec
= TICK_USEC
;
32 /* SHIFTED_HZ period (nsecs): */
33 unsigned long tick_nsec
;
35 static u64 tick_length
;
36 static u64 tick_length_base
;
38 #define SECS_PER_DAY 86400
39 #define MAX_TICKADJ 500LL /* usecs */
40 #define MAX_TICKADJ_SCALED \
41 (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
44 * phase-lock loop variables
48 * clock synchronization status
50 * (TIME_ERROR prevents overwriting the CMOS clock)
52 static int time_state
= TIME_OK
;
54 /* clock status bits: */
55 static int time_status
= STA_UNSYNC
;
57 /* time adjustment (nsecs): */
58 static s64 time_offset
;
60 /* pll time constant: */
61 static long time_constant
= 2;
63 /* maximum error (usecs): */
64 static long time_maxerror
= NTP_PHASE_LIMIT
;
66 /* estimated error (usecs): */
67 static long time_esterror
= NTP_PHASE_LIMIT
;
69 /* frequency offset (scaled nsecs/secs): */
72 /* time at last adjustment (secs): */
73 static long time_reftime
;
75 static long time_adjust
;
77 /* constant (boot-param configurable) NTP tick adjustment (upscaled) */
78 static s64 ntp_tick_adj
;
80 /* second value of the next pending leapsecond, or TIME64_MAX if no leap */
81 static time64_t ntp_next_leap_sec
= TIME64_MAX
;
86 * The following variables are used when a pulse-per-second (PPS) signal
87 * is available. They establish the engineering parameters of the clock
88 * discipline loop when controlled by the PPS signal.
90 #define PPS_VALID 10 /* PPS signal watchdog max (s) */
91 #define PPS_POPCORN 4 /* popcorn spike threshold (shift) */
92 #define PPS_INTMIN 2 /* min freq interval (s) (shift) */
93 #define PPS_INTMAX 8 /* max freq interval (s) (shift) */
94 #define PPS_INTCOUNT 4 /* number of consecutive good intervals to
95 increase pps_shift or consecutive bad
96 intervals to decrease it */
97 #define PPS_MAXWANDER 100000 /* max PPS freq wander (ns/s) */
99 static int pps_valid
; /* signal watchdog counter */
100 static long pps_tf
[3]; /* phase median filter */
101 static long pps_jitter
; /* current jitter (ns) */
102 static struct timespec64 pps_fbase
; /* beginning of the last freq interval */
103 static int pps_shift
; /* current interval duration (s) (shift) */
104 static int pps_intcnt
; /* interval counter */
105 static s64 pps_freq
; /* frequency offset (scaled ns/s) */
106 static long pps_stabil
; /* current stability (scaled ns/s) */
109 * PPS signal quality monitors
111 static long pps_calcnt
; /* calibration intervals */
112 static long pps_jitcnt
; /* jitter limit exceeded */
113 static long pps_stbcnt
; /* stability limit exceeded */
114 static long pps_errcnt
; /* calibration errors */
117 /* PPS kernel consumer compensates the whole phase error immediately.
118 * Otherwise, reduce the offset by a fixed factor times the time constant.
120 static inline s64
ntp_offset_chunk(s64 offset
)
122 if (time_status
& STA_PPSTIME
&& time_status
& STA_PPSSIGNAL
)
125 return shift_right(offset
, SHIFT_PLL
+ time_constant
);
128 static inline void pps_reset_freq_interval(void)
130 /* the PPS calibration interval may end
131 surprisingly early */
132 pps_shift
= PPS_INTMIN
;
137 * pps_clear - Clears the PPS state variables
139 static inline void pps_clear(void)
141 pps_reset_freq_interval();
145 pps_fbase
.tv_sec
= pps_fbase
.tv_nsec
= 0;
149 /* Decrease pps_valid to indicate that another second has passed since
150 * the last PPS signal. When it reaches 0, indicate that PPS signal is
153 static inline void pps_dec_valid(void)
158 time_status
&= ~(STA_PPSSIGNAL
| STA_PPSJITTER
|
159 STA_PPSWANDER
| STA_PPSERROR
);
164 static inline void pps_set_freq(s64 freq
)
169 static inline int is_error_status(int status
)
171 return (status
& (STA_UNSYNC
|STA_CLOCKERR
))
172 /* PPS signal lost when either PPS time or
173 * PPS frequency synchronization requested
175 || ((status
& (STA_PPSFREQ
|STA_PPSTIME
))
176 && !(status
& STA_PPSSIGNAL
))
177 /* PPS jitter exceeded when
178 * PPS time synchronization requested */
179 || ((status
& (STA_PPSTIME
|STA_PPSJITTER
))
180 == (STA_PPSTIME
|STA_PPSJITTER
))
181 /* PPS wander exceeded or calibration error when
182 * PPS frequency synchronization requested
184 || ((status
& STA_PPSFREQ
)
185 && (status
& (STA_PPSWANDER
|STA_PPSERROR
)));
188 static inline void pps_fill_timex(struct timex
*txc
)
190 txc
->ppsfreq
= shift_right((pps_freq
>> PPM_SCALE_INV_SHIFT
) *
191 PPM_SCALE_INV
, NTP_SCALE_SHIFT
);
192 txc
->jitter
= pps_jitter
;
193 if (!(time_status
& STA_NANO
))
194 txc
->jitter
/= NSEC_PER_USEC
;
195 txc
->shift
= pps_shift
;
196 txc
->stabil
= pps_stabil
;
197 txc
->jitcnt
= pps_jitcnt
;
198 txc
->calcnt
= pps_calcnt
;
199 txc
->errcnt
= pps_errcnt
;
200 txc
->stbcnt
= pps_stbcnt
;
203 #else /* !CONFIG_NTP_PPS */
205 static inline s64
ntp_offset_chunk(s64 offset
)
207 return shift_right(offset
, SHIFT_PLL
+ time_constant
);
210 static inline void pps_reset_freq_interval(void) {}
211 static inline void pps_clear(void) {}
212 static inline void pps_dec_valid(void) {}
213 static inline void pps_set_freq(s64 freq
) {}
215 static inline int is_error_status(int status
)
217 return status
& (STA_UNSYNC
|STA_CLOCKERR
);
220 static inline void pps_fill_timex(struct timex
*txc
)
222 /* PPS is not implemented, so these are zero */
233 #endif /* CONFIG_NTP_PPS */
237 * ntp_synced - Returns 1 if the NTP status is not UNSYNC
240 static inline int ntp_synced(void)
242 return !(time_status
& STA_UNSYNC
);
251 * Update (tick_length, tick_length_base, tick_nsec), based
252 * on (tick_usec, ntp_tick_adj, time_freq):
254 static void ntp_update_frequency(void)
259 second_length
= (u64
)(tick_usec
* NSEC_PER_USEC
* USER_HZ
)
262 second_length
+= ntp_tick_adj
;
263 second_length
+= time_freq
;
265 tick_nsec
= div_u64(second_length
, HZ
) >> NTP_SCALE_SHIFT
;
266 new_base
= div_u64(second_length
, NTP_INTERVAL_FREQ
);
269 * Don't wait for the next second_overflow, apply
270 * the change to the tick length immediately:
272 tick_length
+= new_base
- tick_length_base
;
273 tick_length_base
= new_base
;
276 static inline s64
ntp_update_offset_fll(s64 offset64
, long secs
)
278 time_status
&= ~STA_MODE
;
283 if (!(time_status
& STA_FLL
) && (secs
<= MAXSEC
))
286 time_status
|= STA_MODE
;
288 return div64_long(offset64
<< (NTP_SCALE_SHIFT
- SHIFT_FLL
), secs
);
291 static void ntp_update_offset(long offset
)
297 if (!(time_status
& STA_PLL
))
300 if (!(time_status
& STA_NANO
)) {
301 /* Make sure the multiplication below won't overflow */
302 offset
= clamp(offset
, -USEC_PER_SEC
, USEC_PER_SEC
);
303 offset
*= NSEC_PER_USEC
;
307 * Scale the phase adjustment and
308 * clamp to the operating range.
310 offset
= clamp(offset
, -MAXPHASE
, MAXPHASE
);
313 * Select how the frequency is to be controlled
314 * and in which mode (PLL or FLL).
316 secs
= get_seconds() - time_reftime
;
317 if (unlikely(time_status
& STA_FREQHOLD
))
320 time_reftime
= get_seconds();
323 freq_adj
= ntp_update_offset_fll(offset64
, secs
);
326 * Clamp update interval to reduce PLL gain with low
327 * sampling rate (e.g. intermittent network connection)
328 * to avoid instability.
330 if (unlikely(secs
> 1 << (SHIFT_PLL
+ 1 + time_constant
)))
331 secs
= 1 << (SHIFT_PLL
+ 1 + time_constant
);
333 freq_adj
+= (offset64
* secs
) <<
334 (NTP_SCALE_SHIFT
- 2 * (SHIFT_PLL
+ 2 + time_constant
));
336 freq_adj
= min(freq_adj
+ time_freq
, MAXFREQ_SCALED
);
338 time_freq
= max(freq_adj
, -MAXFREQ_SCALED
);
340 time_offset
= div_s64(offset64
<< NTP_SCALE_SHIFT
, NTP_INTERVAL_FREQ
);
344 * ntp_clear - Clears the NTP state variables
348 time_adjust
= 0; /* stop active adjtime() */
349 time_status
|= STA_UNSYNC
;
350 time_maxerror
= NTP_PHASE_LIMIT
;
351 time_esterror
= NTP_PHASE_LIMIT
;
353 ntp_update_frequency();
355 tick_length
= tick_length_base
;
358 ntp_next_leap_sec
= TIME64_MAX
;
359 /* Clear PPS state variables */
364 u64
ntp_tick_length(void)
370 * ntp_get_next_leap - Returns the next leapsecond in CLOCK_REALTIME ktime_t
372 * Provides the time of the next leapsecond against CLOCK_REALTIME in
373 * a ktime_t format. Returns KTIME_MAX if no leapsecond is pending.
375 ktime_t
ntp_get_next_leap(void)
379 if ((time_state
== TIME_INS
) && (time_status
& STA_INS
))
380 return ktime_set(ntp_next_leap_sec
, 0);
381 ret
.tv64
= KTIME_MAX
;
386 * this routine handles the overflow of the microsecond field
388 * The tricky bits of code to handle the accurate clock support
389 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
390 * They were originally developed for SUN and DEC kernels.
391 * All the kudos should go to Dave for this stuff.
393 * Also handles leap second processing, and returns leap offset
395 int second_overflow(unsigned long secs
)
401 * Leap second processing. If in leap-insert state at the end of the
402 * day, the system clock is set back one second; if in leap-delete
403 * state, the system clock is set ahead one second.
405 switch (time_state
) {
407 if (time_status
& STA_INS
) {
408 time_state
= TIME_INS
;
409 ntp_next_leap_sec
= secs
+ SECS_PER_DAY
-
410 (secs
% SECS_PER_DAY
);
411 } else if (time_status
& STA_DEL
) {
412 time_state
= TIME_DEL
;
413 ntp_next_leap_sec
= secs
+ SECS_PER_DAY
-
414 ((secs
+1) % SECS_PER_DAY
);
418 if (!(time_status
& STA_INS
)) {
419 ntp_next_leap_sec
= TIME64_MAX
;
420 time_state
= TIME_OK
;
421 } else if (secs
% SECS_PER_DAY
== 0) {
423 time_state
= TIME_OOP
;
425 "Clock: inserting leap second 23:59:60 UTC\n");
429 if (!(time_status
& STA_DEL
)) {
430 ntp_next_leap_sec
= TIME64_MAX
;
431 time_state
= TIME_OK
;
432 } else if ((secs
+ 1) % SECS_PER_DAY
== 0) {
434 ntp_next_leap_sec
= TIME64_MAX
;
435 time_state
= TIME_WAIT
;
437 "Clock: deleting leap second 23:59:59 UTC\n");
441 ntp_next_leap_sec
= TIME64_MAX
;
442 time_state
= TIME_WAIT
;
445 if (!(time_status
& (STA_INS
| STA_DEL
)))
446 time_state
= TIME_OK
;
451 /* Bump the maxerror field */
452 time_maxerror
+= MAXFREQ
/ NSEC_PER_USEC
;
453 if (time_maxerror
> NTP_PHASE_LIMIT
) {
454 time_maxerror
= NTP_PHASE_LIMIT
;
455 time_status
|= STA_UNSYNC
;
458 /* Compute the phase adjustment for the next second */
459 tick_length
= tick_length_base
;
461 delta
= ntp_offset_chunk(time_offset
);
462 time_offset
-= delta
;
463 tick_length
+= delta
;
465 /* Check PPS signal */
471 if (time_adjust
> MAX_TICKADJ
) {
472 time_adjust
-= MAX_TICKADJ
;
473 tick_length
+= MAX_TICKADJ_SCALED
;
477 if (time_adjust
< -MAX_TICKADJ
) {
478 time_adjust
+= MAX_TICKADJ
;
479 tick_length
-= MAX_TICKADJ_SCALED
;
483 tick_length
+= (s64
)(time_adjust
* NSEC_PER_USEC
/ NTP_INTERVAL_FREQ
)
491 #ifdef CONFIG_GENERIC_CMOS_UPDATE
492 int __weak
update_persistent_clock(struct timespec now
)
497 int __weak
update_persistent_clock64(struct timespec64 now64
)
501 now
= timespec64_to_timespec(now64
);
502 return update_persistent_clock(now
);
506 #if defined(CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC)
507 static void sync_cmos_clock(struct work_struct
*work
);
509 static DECLARE_DELAYED_WORK(sync_cmos_work
, sync_cmos_clock
);
511 static void sync_cmos_clock(struct work_struct
*work
)
513 struct timespec64 now
;
514 struct timespec64 next
;
518 * If we have an externally synchronized Linux clock, then update
519 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
520 * called as close as possible to 500 ms before the new second starts.
521 * This code is run on a timer. If the clock is set, that timer
522 * may not expire at the correct time. Thus, we adjust...
523 * We want the clock to be within a couple of ticks from the target.
527 * Not synced, exit, do not restart a timer (if one is
528 * running, let it run out).
533 getnstimeofday64(&now
);
534 if (abs(now
.tv_nsec
- (NSEC_PER_SEC
/ 2)) <= tick_nsec
* 5) {
535 struct timespec64 adjust
= now
;
538 if (persistent_clock_is_local
)
539 adjust
.tv_sec
-= (sys_tz
.tz_minuteswest
* 60);
540 #ifdef CONFIG_GENERIC_CMOS_UPDATE
541 fail
= update_persistent_clock64(adjust
);
544 #ifdef CONFIG_RTC_SYSTOHC
546 fail
= rtc_set_ntp_time(adjust
);
550 next
.tv_nsec
= (NSEC_PER_SEC
/ 2) - now
.tv_nsec
- (TICK_NSEC
/ 2);
551 if (next
.tv_nsec
<= 0)
552 next
.tv_nsec
+= NSEC_PER_SEC
;
554 if (!fail
|| fail
== -ENODEV
)
559 if (next
.tv_nsec
>= NSEC_PER_SEC
) {
561 next
.tv_nsec
-= NSEC_PER_SEC
;
563 queue_delayed_work(system_power_efficient_wq
,
564 &sync_cmos_work
, timespec64_to_jiffies(&next
));
567 void ntp_notify_cmos_timer(void)
569 queue_delayed_work(system_power_efficient_wq
, &sync_cmos_work
, 0);
573 void ntp_notify_cmos_timer(void) { }
578 * Propagate a new txc->status value into the NTP state:
580 static inline void process_adj_status(struct timex
*txc
, struct timespec64
*ts
)
582 if ((time_status
& STA_PLL
) && !(txc
->status
& STA_PLL
)) {
583 time_state
= TIME_OK
;
584 time_status
= STA_UNSYNC
;
585 ntp_next_leap_sec
= TIME64_MAX
;
586 /* restart PPS frequency calibration */
587 pps_reset_freq_interval();
591 * If we turn on PLL adjustments then reset the
592 * reference time to current time.
594 if (!(time_status
& STA_PLL
) && (txc
->status
& STA_PLL
))
595 time_reftime
= get_seconds();
597 /* only set allowed bits */
598 time_status
&= STA_RONLY
;
599 time_status
|= txc
->status
& ~STA_RONLY
;
603 static inline void process_adjtimex_modes(struct timex
*txc
,
604 struct timespec64
*ts
,
607 if (txc
->modes
& ADJ_STATUS
)
608 process_adj_status(txc
, ts
);
610 if (txc
->modes
& ADJ_NANO
)
611 time_status
|= STA_NANO
;
613 if (txc
->modes
& ADJ_MICRO
)
614 time_status
&= ~STA_NANO
;
616 if (txc
->modes
& ADJ_FREQUENCY
) {
617 time_freq
= txc
->freq
* PPM_SCALE
;
618 time_freq
= min(time_freq
, MAXFREQ_SCALED
);
619 time_freq
= max(time_freq
, -MAXFREQ_SCALED
);
620 /* update pps_freq */
621 pps_set_freq(time_freq
);
624 if (txc
->modes
& ADJ_MAXERROR
)
625 time_maxerror
= txc
->maxerror
;
627 if (txc
->modes
& ADJ_ESTERROR
)
628 time_esterror
= txc
->esterror
;
630 if (txc
->modes
& ADJ_TIMECONST
) {
631 time_constant
= txc
->constant
;
632 if (!(time_status
& STA_NANO
))
634 time_constant
= min(time_constant
, (long)MAXTC
);
635 time_constant
= max(time_constant
, 0l);
638 if (txc
->modes
& ADJ_TAI
&& txc
->constant
> 0)
639 *time_tai
= txc
->constant
;
641 if (txc
->modes
& ADJ_OFFSET
)
642 ntp_update_offset(txc
->offset
);
644 if (txc
->modes
& ADJ_TICK
)
645 tick_usec
= txc
->tick
;
647 if (txc
->modes
& (ADJ_TICK
|ADJ_FREQUENCY
|ADJ_OFFSET
))
648 ntp_update_frequency();
654 * ntp_validate_timex - Ensures the timex is ok for use in do_adjtimex
656 int ntp_validate_timex(struct timex
*txc
)
658 if (txc
->modes
& ADJ_ADJTIME
) {
659 /* singleshot must not be used with any other mode bits */
660 if (!(txc
->modes
& ADJ_OFFSET_SINGLESHOT
))
662 if (!(txc
->modes
& ADJ_OFFSET_READONLY
) &&
663 !capable(CAP_SYS_TIME
))
666 /* In order to modify anything, you gotta be super-user! */
667 if (txc
->modes
&& !capable(CAP_SYS_TIME
))
670 * if the quartz is off by more than 10% then
671 * something is VERY wrong!
673 if (txc
->modes
& ADJ_TICK
&&
674 (txc
->tick
< 900000/USER_HZ
||
675 txc
->tick
> 1100000/USER_HZ
))
679 if (txc
->modes
& ADJ_SETOFFSET
) {
680 /* In order to inject time, you gotta be super-user! */
681 if (!capable(CAP_SYS_TIME
))
684 if (!timeval_inject_offset_valid(&txc
->time
))
689 * Check for potential multiplication overflows that can
690 * only happen on 64-bit systems:
692 if ((txc
->modes
& ADJ_FREQUENCY
) && (BITS_PER_LONG
== 64)) {
693 if (LLONG_MIN
/ PPM_SCALE
> txc
->freq
)
695 if (LLONG_MAX
/ PPM_SCALE
< txc
->freq
)
704 * adjtimex mainly allows reading (and writing, if superuser) of
705 * kernel time-keeping variables. used by xntpd.
707 int __do_adjtimex(struct timex
*txc
, struct timespec64
*ts
, s32
*time_tai
)
711 if (txc
->modes
& ADJ_ADJTIME
) {
712 long save_adjust
= time_adjust
;
714 if (!(txc
->modes
& ADJ_OFFSET_READONLY
)) {
715 /* adjtime() is independent from ntp_adjtime() */
716 time_adjust
= txc
->offset
;
717 ntp_update_frequency();
719 txc
->offset
= save_adjust
;
722 /* If there are input parameters, then process them: */
724 process_adjtimex_modes(txc
, ts
, time_tai
);
726 txc
->offset
= shift_right(time_offset
* NTP_INTERVAL_FREQ
,
728 if (!(time_status
& STA_NANO
))
729 txc
->offset
/= NSEC_PER_USEC
;
732 result
= time_state
; /* mostly `TIME_OK' */
733 /* check for errors */
734 if (is_error_status(time_status
))
737 txc
->freq
= shift_right((time_freq
>> PPM_SCALE_INV_SHIFT
) *
738 PPM_SCALE_INV
, NTP_SCALE_SHIFT
);
739 txc
->maxerror
= time_maxerror
;
740 txc
->esterror
= time_esterror
;
741 txc
->status
= time_status
;
742 txc
->constant
= time_constant
;
744 txc
->tolerance
= MAXFREQ_SCALED
/ PPM_SCALE
;
745 txc
->tick
= tick_usec
;
746 txc
->tai
= *time_tai
;
748 /* fill PPS status fields */
751 txc
->time
.tv_sec
= (time_t)ts
->tv_sec
;
752 txc
->time
.tv_usec
= ts
->tv_nsec
;
753 if (!(time_status
& STA_NANO
))
754 txc
->time
.tv_usec
/= NSEC_PER_USEC
;
756 /* Handle leapsec adjustments */
757 if (unlikely(ts
->tv_sec
>= ntp_next_leap_sec
)) {
758 if ((time_state
== TIME_INS
) && (time_status
& STA_INS
)) {
763 if ((time_state
== TIME_DEL
) && (time_status
& STA_DEL
)) {
768 if ((time_state
== TIME_OOP
) &&
769 (ts
->tv_sec
== ntp_next_leap_sec
)) {
777 #ifdef CONFIG_NTP_PPS
779 /* actually struct pps_normtime is good old struct timespec, but it is
780 * semantically different (and it is the reason why it was invented):
781 * pps_normtime.nsec has a range of ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ]
782 * while timespec.tv_nsec has a range of [0, NSEC_PER_SEC) */
783 struct pps_normtime
{
784 s64 sec
; /* seconds */
785 long nsec
; /* nanoseconds */
788 /* normalize the timestamp so that nsec is in the
789 ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
790 static inline struct pps_normtime
pps_normalize_ts(struct timespec64 ts
)
792 struct pps_normtime norm
= {
797 if (norm
.nsec
> (NSEC_PER_SEC
>> 1)) {
798 norm
.nsec
-= NSEC_PER_SEC
;
805 /* get current phase correction and jitter */
806 static inline long pps_phase_filter_get(long *jitter
)
808 *jitter
= pps_tf
[0] - pps_tf
[1];
812 /* TODO: test various filters */
816 /* add the sample to the phase filter */
817 static inline void pps_phase_filter_add(long err
)
819 pps_tf
[2] = pps_tf
[1];
820 pps_tf
[1] = pps_tf
[0];
824 /* decrease frequency calibration interval length.
825 * It is halved after four consecutive unstable intervals.
827 static inline void pps_dec_freq_interval(void)
829 if (--pps_intcnt
<= -PPS_INTCOUNT
) {
830 pps_intcnt
= -PPS_INTCOUNT
;
831 if (pps_shift
> PPS_INTMIN
) {
838 /* increase frequency calibration interval length.
839 * It is doubled after four consecutive stable intervals.
841 static inline void pps_inc_freq_interval(void)
843 if (++pps_intcnt
>= PPS_INTCOUNT
) {
844 pps_intcnt
= PPS_INTCOUNT
;
845 if (pps_shift
< PPS_INTMAX
) {
852 /* update clock frequency based on MONOTONIC_RAW clock PPS signal
855 * At the end of the calibration interval the difference between the
856 * first and last MONOTONIC_RAW clock timestamps divided by the length
857 * of the interval becomes the frequency update. If the interval was
858 * too long, the data are discarded.
859 * Returns the difference between old and new frequency values.
861 static long hardpps_update_freq(struct pps_normtime freq_norm
)
863 long delta
, delta_mod
;
866 /* check if the frequency interval was too long */
867 if (freq_norm
.sec
> (2 << pps_shift
)) {
868 time_status
|= STA_PPSERROR
;
870 pps_dec_freq_interval();
871 printk_deferred(KERN_ERR
872 "hardpps: PPSERROR: interval too long - %lld s\n",
877 /* here the raw frequency offset and wander (stability) is
878 * calculated. If the wander is less than the wander threshold
879 * the interval is increased; otherwise it is decreased.
881 ftemp
= div_s64(((s64
)(-freq_norm
.nsec
)) << NTP_SCALE_SHIFT
,
883 delta
= shift_right(ftemp
- pps_freq
, NTP_SCALE_SHIFT
);
885 if (delta
> PPS_MAXWANDER
|| delta
< -PPS_MAXWANDER
) {
886 printk_deferred(KERN_WARNING
887 "hardpps: PPSWANDER: change=%ld\n", delta
);
888 time_status
|= STA_PPSWANDER
;
890 pps_dec_freq_interval();
891 } else { /* good sample */
892 pps_inc_freq_interval();
895 /* the stability metric is calculated as the average of recent
896 * frequency changes, but is used only for performance
901 delta_mod
= -delta_mod
;
902 pps_stabil
+= (div_s64(((s64
)delta_mod
) <<
903 (NTP_SCALE_SHIFT
- SHIFT_USEC
),
904 NSEC_PER_USEC
) - pps_stabil
) >> PPS_INTMIN
;
906 /* if enabled, the system clock frequency is updated */
907 if ((time_status
& STA_PPSFREQ
) != 0 &&
908 (time_status
& STA_FREQHOLD
) == 0) {
909 time_freq
= pps_freq
;
910 ntp_update_frequency();
916 /* correct REALTIME clock phase error against PPS signal */
917 static void hardpps_update_phase(long error
)
919 long correction
= -error
;
922 /* add the sample to the median filter */
923 pps_phase_filter_add(correction
);
924 correction
= pps_phase_filter_get(&jitter
);
926 /* Nominal jitter is due to PPS signal noise. If it exceeds the
927 * threshold, the sample is discarded; otherwise, if so enabled,
928 * the time offset is updated.
930 if (jitter
> (pps_jitter
<< PPS_POPCORN
)) {
931 printk_deferred(KERN_WARNING
932 "hardpps: PPSJITTER: jitter=%ld, limit=%ld\n",
933 jitter
, (pps_jitter
<< PPS_POPCORN
));
934 time_status
|= STA_PPSJITTER
;
936 } else if (time_status
& STA_PPSTIME
) {
937 /* correct the time using the phase offset */
938 time_offset
= div_s64(((s64
)correction
) << NTP_SCALE_SHIFT
,
940 /* cancel running adjtime() */
944 pps_jitter
+= (jitter
- pps_jitter
) >> PPS_INTMIN
;
948 * __hardpps() - discipline CPU clock oscillator to external PPS signal
950 * This routine is called at each PPS signal arrival in order to
951 * discipline the CPU clock oscillator to the PPS signal. It takes two
952 * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former
953 * is used to correct clock phase error and the latter is used to
954 * correct the frequency.
956 * This code is based on David Mills's reference nanokernel
957 * implementation. It was mostly rewritten but keeps the same idea.
959 void __hardpps(const struct timespec64
*phase_ts
, const struct timespec64
*raw_ts
)
961 struct pps_normtime pts_norm
, freq_norm
;
963 pts_norm
= pps_normalize_ts(*phase_ts
);
965 /* clear the error bits, they will be set again if needed */
966 time_status
&= ~(STA_PPSJITTER
| STA_PPSWANDER
| STA_PPSERROR
);
968 /* indicate signal presence */
969 time_status
|= STA_PPSSIGNAL
;
970 pps_valid
= PPS_VALID
;
972 /* when called for the first time,
973 * just start the frequency interval */
974 if (unlikely(pps_fbase
.tv_sec
== 0)) {
979 /* ok, now we have a base for frequency calculation */
980 freq_norm
= pps_normalize_ts(timespec64_sub(*raw_ts
, pps_fbase
));
982 /* check that the signal is in the range
983 * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */
984 if ((freq_norm
.sec
== 0) ||
985 (freq_norm
.nsec
> MAXFREQ
* freq_norm
.sec
) ||
986 (freq_norm
.nsec
< -MAXFREQ
* freq_norm
.sec
)) {
987 time_status
|= STA_PPSJITTER
;
988 /* restart the frequency calibration interval */
990 printk_deferred(KERN_ERR
"hardpps: PPSJITTER: bad pulse\n");
996 /* check if the current frequency interval is finished */
997 if (freq_norm
.sec
>= (1 << pps_shift
)) {
999 /* restart the frequency calibration interval */
1000 pps_fbase
= *raw_ts
;
1001 hardpps_update_freq(freq_norm
);
1004 hardpps_update_phase(pts_norm
.nsec
);
1007 #endif /* CONFIG_NTP_PPS */
1009 static int __init
ntp_tick_adj_setup(char *str
)
1011 int rc
= kstrtol(str
, 0, (long *)&ntp_tick_adj
);
1015 ntp_tick_adj
<<= NTP_SCALE_SHIFT
;
1020 __setup("ntp_tick_adj=", ntp_tick_adj_setup
);
1022 void __init
ntp_init(void)