1 // SPDX-License-Identifier: GPL-2.0
3 * NTP state machine interfaces and logic.
5 * This code was mainly moved from kernel/timer.c and kernel/time.c
6 * Please see those files for relevant copyright info and historical
9 #include <linux/capability.h>
10 #include <linux/clocksource.h>
11 #include <linux/workqueue.h>
12 #include <linux/hrtimer.h>
13 #include <linux/jiffies.h>
14 #include <linux/math64.h>
15 #include <linux/timex.h>
16 #include <linux/time.h>
18 #include <linux/module.h>
19 #include <linux/rtc.h>
20 #include <linux/math64.h>
22 #include "ntp_internal.h"
23 #include "timekeeping_internal.h"
27 * NTP timekeeping variables:
29 * Note: All of the NTP state is protected by the timekeeping locks.
33 /* USER_HZ period (usecs): */
34 unsigned long tick_usec
= USER_TICK_USEC
;
36 /* SHIFTED_HZ period (nsecs): */
37 unsigned long tick_nsec
;
39 static u64 tick_length
;
40 static u64 tick_length_base
;
42 #define SECS_PER_DAY 86400
43 #define MAX_TICKADJ 500LL /* usecs */
44 #define MAX_TICKADJ_SCALED \
45 (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
48 * phase-lock loop variables
52 * clock synchronization status
54 * (TIME_ERROR prevents overwriting the CMOS clock)
56 static int time_state
= TIME_OK
;
58 /* clock status bits: */
59 static int time_status
= STA_UNSYNC
;
61 /* time adjustment (nsecs): */
62 static s64 time_offset
;
64 /* pll time constant: */
65 static long time_constant
= 2;
67 /* maximum error (usecs): */
68 static long time_maxerror
= NTP_PHASE_LIMIT
;
70 /* estimated error (usecs): */
71 static long time_esterror
= NTP_PHASE_LIMIT
;
73 /* frequency offset (scaled nsecs/secs): */
76 /* time at last adjustment (secs): */
77 static time64_t time_reftime
;
79 static long time_adjust
;
81 /* constant (boot-param configurable) NTP tick adjustment (upscaled) */
82 static s64 ntp_tick_adj
;
84 /* second value of the next pending leapsecond, or TIME64_MAX if no leap */
85 static time64_t ntp_next_leap_sec
= TIME64_MAX
;
90 * The following variables are used when a pulse-per-second (PPS) signal
91 * is available. They establish the engineering parameters of the clock
92 * discipline loop when controlled by the PPS signal.
94 #define PPS_VALID 10 /* PPS signal watchdog max (s) */
95 #define PPS_POPCORN 4 /* popcorn spike threshold (shift) */
96 #define PPS_INTMIN 2 /* min freq interval (s) (shift) */
97 #define PPS_INTMAX 8 /* max freq interval (s) (shift) */
98 #define PPS_INTCOUNT 4 /* number of consecutive good intervals to
99 increase pps_shift or consecutive bad
100 intervals to decrease it */
101 #define PPS_MAXWANDER 100000 /* max PPS freq wander (ns/s) */
103 static int pps_valid
; /* signal watchdog counter */
104 static long pps_tf
[3]; /* phase median filter */
105 static long pps_jitter
; /* current jitter (ns) */
106 static struct timespec64 pps_fbase
; /* beginning of the last freq interval */
107 static int pps_shift
; /* current interval duration (s) (shift) */
108 static int pps_intcnt
; /* interval counter */
109 static s64 pps_freq
; /* frequency offset (scaled ns/s) */
110 static long pps_stabil
; /* current stability (scaled ns/s) */
113 * PPS signal quality monitors
115 static long pps_calcnt
; /* calibration intervals */
116 static long pps_jitcnt
; /* jitter limit exceeded */
117 static long pps_stbcnt
; /* stability limit exceeded */
118 static long pps_errcnt
; /* calibration errors */
121 /* PPS kernel consumer compensates the whole phase error immediately.
122 * Otherwise, reduce the offset by a fixed factor times the time constant.
124 static inline s64
ntp_offset_chunk(s64 offset
)
126 if (time_status
& STA_PPSTIME
&& time_status
& STA_PPSSIGNAL
)
129 return shift_right(offset
, SHIFT_PLL
+ time_constant
);
132 static inline void pps_reset_freq_interval(void)
134 /* the PPS calibration interval may end
135 surprisingly early */
136 pps_shift
= PPS_INTMIN
;
141 * pps_clear - Clears the PPS state variables
143 static inline void pps_clear(void)
145 pps_reset_freq_interval();
149 pps_fbase
.tv_sec
= pps_fbase
.tv_nsec
= 0;
153 /* Decrease pps_valid to indicate that another second has passed since
154 * the last PPS signal. When it reaches 0, indicate that PPS signal is
157 static inline void pps_dec_valid(void)
162 time_status
&= ~(STA_PPSSIGNAL
| STA_PPSJITTER
|
163 STA_PPSWANDER
| STA_PPSERROR
);
168 static inline void pps_set_freq(s64 freq
)
173 static inline int is_error_status(int status
)
175 return (status
& (STA_UNSYNC
|STA_CLOCKERR
))
176 /* PPS signal lost when either PPS time or
177 * PPS frequency synchronization requested
179 || ((status
& (STA_PPSFREQ
|STA_PPSTIME
))
180 && !(status
& STA_PPSSIGNAL
))
181 /* PPS jitter exceeded when
182 * PPS time synchronization requested */
183 || ((status
& (STA_PPSTIME
|STA_PPSJITTER
))
184 == (STA_PPSTIME
|STA_PPSJITTER
))
185 /* PPS wander exceeded or calibration error when
186 * PPS frequency synchronization requested
188 || ((status
& STA_PPSFREQ
)
189 && (status
& (STA_PPSWANDER
|STA_PPSERROR
)));
192 static inline void pps_fill_timex(struct timex
*txc
)
194 txc
->ppsfreq
= shift_right((pps_freq
>> PPM_SCALE_INV_SHIFT
) *
195 PPM_SCALE_INV
, NTP_SCALE_SHIFT
);
196 txc
->jitter
= pps_jitter
;
197 if (!(time_status
& STA_NANO
))
198 txc
->jitter
/= NSEC_PER_USEC
;
199 txc
->shift
= pps_shift
;
200 txc
->stabil
= pps_stabil
;
201 txc
->jitcnt
= pps_jitcnt
;
202 txc
->calcnt
= pps_calcnt
;
203 txc
->errcnt
= pps_errcnt
;
204 txc
->stbcnt
= pps_stbcnt
;
207 #else /* !CONFIG_NTP_PPS */
209 static inline s64
ntp_offset_chunk(s64 offset
)
211 return shift_right(offset
, SHIFT_PLL
+ time_constant
);
214 static inline void pps_reset_freq_interval(void) {}
215 static inline void pps_clear(void) {}
216 static inline void pps_dec_valid(void) {}
217 static inline void pps_set_freq(s64 freq
) {}
219 static inline int is_error_status(int status
)
221 return status
& (STA_UNSYNC
|STA_CLOCKERR
);
224 static inline void pps_fill_timex(struct timex
*txc
)
226 /* PPS is not implemented, so these are zero */
237 #endif /* CONFIG_NTP_PPS */
241 * ntp_synced - Returns 1 if the NTP status is not UNSYNC
244 static inline int ntp_synced(void)
246 return !(time_status
& STA_UNSYNC
);
255 * Update (tick_length, tick_length_base, tick_nsec), based
256 * on (tick_usec, ntp_tick_adj, time_freq):
258 static void ntp_update_frequency(void)
263 second_length
= (u64
)(tick_usec
* NSEC_PER_USEC
* USER_HZ
)
266 second_length
+= ntp_tick_adj
;
267 second_length
+= time_freq
;
269 tick_nsec
= div_u64(second_length
, HZ
) >> NTP_SCALE_SHIFT
;
270 new_base
= div_u64(second_length
, NTP_INTERVAL_FREQ
);
273 * Don't wait for the next second_overflow, apply
274 * the change to the tick length immediately:
276 tick_length
+= new_base
- tick_length_base
;
277 tick_length_base
= new_base
;
280 static inline s64
ntp_update_offset_fll(s64 offset64
, long secs
)
282 time_status
&= ~STA_MODE
;
287 if (!(time_status
& STA_FLL
) && (secs
<= MAXSEC
))
290 time_status
|= STA_MODE
;
292 return div64_long(offset64
<< (NTP_SCALE_SHIFT
- SHIFT_FLL
), secs
);
295 static void ntp_update_offset(long offset
)
301 if (!(time_status
& STA_PLL
))
304 if (!(time_status
& STA_NANO
)) {
305 /* Make sure the multiplication below won't overflow */
306 offset
= clamp(offset
, -USEC_PER_SEC
, USEC_PER_SEC
);
307 offset
*= NSEC_PER_USEC
;
311 * Scale the phase adjustment and
312 * clamp to the operating range.
314 offset
= clamp(offset
, -MAXPHASE
, MAXPHASE
);
317 * Select how the frequency is to be controlled
318 * and in which mode (PLL or FLL).
320 secs
= (long)(__ktime_get_real_seconds() - time_reftime
);
321 if (unlikely(time_status
& STA_FREQHOLD
))
324 time_reftime
= __ktime_get_real_seconds();
327 freq_adj
= ntp_update_offset_fll(offset64
, secs
);
330 * Clamp update interval to reduce PLL gain with low
331 * sampling rate (e.g. intermittent network connection)
332 * to avoid instability.
334 if (unlikely(secs
> 1 << (SHIFT_PLL
+ 1 + time_constant
)))
335 secs
= 1 << (SHIFT_PLL
+ 1 + time_constant
);
337 freq_adj
+= (offset64
* secs
) <<
338 (NTP_SCALE_SHIFT
- 2 * (SHIFT_PLL
+ 2 + time_constant
));
340 freq_adj
= min(freq_adj
+ time_freq
, MAXFREQ_SCALED
);
342 time_freq
= max(freq_adj
, -MAXFREQ_SCALED
);
344 time_offset
= div_s64(offset64
<< NTP_SCALE_SHIFT
, NTP_INTERVAL_FREQ
);
348 * ntp_clear - Clears the NTP state variables
352 time_adjust
= 0; /* stop active adjtime() */
353 time_status
|= STA_UNSYNC
;
354 time_maxerror
= NTP_PHASE_LIMIT
;
355 time_esterror
= NTP_PHASE_LIMIT
;
357 ntp_update_frequency();
359 tick_length
= tick_length_base
;
362 ntp_next_leap_sec
= TIME64_MAX
;
363 /* Clear PPS state variables */
368 u64
ntp_tick_length(void)
374 * ntp_get_next_leap - Returns the next leapsecond in CLOCK_REALTIME ktime_t
376 * Provides the time of the next leapsecond against CLOCK_REALTIME in
377 * a ktime_t format. Returns KTIME_MAX if no leapsecond is pending.
379 ktime_t
ntp_get_next_leap(void)
383 if ((time_state
== TIME_INS
) && (time_status
& STA_INS
))
384 return ktime_set(ntp_next_leap_sec
, 0);
390 * this routine handles the overflow of the microsecond field
392 * The tricky bits of code to handle the accurate clock support
393 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
394 * They were originally developed for SUN and DEC kernels.
395 * All the kudos should go to Dave for this stuff.
397 * Also handles leap second processing, and returns leap offset
399 int second_overflow(time64_t secs
)
406 * Leap second processing. If in leap-insert state at the end of the
407 * day, the system clock is set back one second; if in leap-delete
408 * state, the system clock is set ahead one second.
410 switch (time_state
) {
412 if (time_status
& STA_INS
) {
413 time_state
= TIME_INS
;
414 div_s64_rem(secs
, SECS_PER_DAY
, &rem
);
415 ntp_next_leap_sec
= secs
+ SECS_PER_DAY
- rem
;
416 } else if (time_status
& STA_DEL
) {
417 time_state
= TIME_DEL
;
418 div_s64_rem(secs
+ 1, SECS_PER_DAY
, &rem
);
419 ntp_next_leap_sec
= secs
+ SECS_PER_DAY
- rem
;
423 if (!(time_status
& STA_INS
)) {
424 ntp_next_leap_sec
= TIME64_MAX
;
425 time_state
= TIME_OK
;
426 } else if (secs
== ntp_next_leap_sec
) {
428 time_state
= TIME_OOP
;
430 "Clock: inserting leap second 23:59:60 UTC\n");
434 if (!(time_status
& STA_DEL
)) {
435 ntp_next_leap_sec
= TIME64_MAX
;
436 time_state
= TIME_OK
;
437 } else if (secs
== ntp_next_leap_sec
) {
439 ntp_next_leap_sec
= TIME64_MAX
;
440 time_state
= TIME_WAIT
;
442 "Clock: deleting leap second 23:59:59 UTC\n");
446 ntp_next_leap_sec
= TIME64_MAX
;
447 time_state
= TIME_WAIT
;
450 if (!(time_status
& (STA_INS
| STA_DEL
)))
451 time_state
= TIME_OK
;
456 /* Bump the maxerror field */
457 time_maxerror
+= MAXFREQ
/ NSEC_PER_USEC
;
458 if (time_maxerror
> NTP_PHASE_LIMIT
) {
459 time_maxerror
= NTP_PHASE_LIMIT
;
460 time_status
|= STA_UNSYNC
;
463 /* Compute the phase adjustment for the next second */
464 tick_length
= tick_length_base
;
466 delta
= ntp_offset_chunk(time_offset
);
467 time_offset
-= delta
;
468 tick_length
+= delta
;
470 /* Check PPS signal */
476 if (time_adjust
> MAX_TICKADJ
) {
477 time_adjust
-= MAX_TICKADJ
;
478 tick_length
+= MAX_TICKADJ_SCALED
;
482 if (time_adjust
< -MAX_TICKADJ
) {
483 time_adjust
+= MAX_TICKADJ
;
484 tick_length
-= MAX_TICKADJ_SCALED
;
488 tick_length
+= (s64
)(time_adjust
* NSEC_PER_USEC
/ NTP_INTERVAL_FREQ
)
496 #ifdef CONFIG_GENERIC_CMOS_UPDATE
497 int __weak
update_persistent_clock(struct timespec now
)
502 int __weak
update_persistent_clock64(struct timespec64 now64
)
506 now
= timespec64_to_timespec(now64
);
507 return update_persistent_clock(now
);
511 #if defined(CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC)
512 static void sync_cmos_clock(struct work_struct
*work
);
514 static DECLARE_DELAYED_WORK(sync_cmos_work
, sync_cmos_clock
);
516 static void sync_cmos_clock(struct work_struct
*work
)
518 struct timespec64 now
;
519 struct timespec64 next
;
523 * If we have an externally synchronized Linux clock, then update
524 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
525 * called as close as possible to 500 ms before the new second starts.
526 * This code is run on a timer. If the clock is set, that timer
527 * may not expire at the correct time. Thus, we adjust...
528 * We want the clock to be within a couple of ticks from the target.
532 * Not synced, exit, do not restart a timer (if one is
533 * running, let it run out).
538 getnstimeofday64(&now
);
539 if (abs(now
.tv_nsec
- (NSEC_PER_SEC
/ 2)) <= tick_nsec
* 5) {
540 struct timespec64 adjust
= now
;
543 if (persistent_clock_is_local
)
544 adjust
.tv_sec
-= (sys_tz
.tz_minuteswest
* 60);
545 #ifdef CONFIG_GENERIC_CMOS_UPDATE
546 fail
= update_persistent_clock64(adjust
);
549 #ifdef CONFIG_RTC_SYSTOHC
551 fail
= rtc_set_ntp_time(adjust
);
555 next
.tv_nsec
= (NSEC_PER_SEC
/ 2) - now
.tv_nsec
- (TICK_NSEC
/ 2);
556 if (next
.tv_nsec
<= 0)
557 next
.tv_nsec
+= NSEC_PER_SEC
;
559 if (!fail
|| fail
== -ENODEV
)
564 if (next
.tv_nsec
>= NSEC_PER_SEC
) {
566 next
.tv_nsec
-= NSEC_PER_SEC
;
568 queue_delayed_work(system_power_efficient_wq
,
569 &sync_cmos_work
, timespec64_to_jiffies(&next
));
572 void ntp_notify_cmos_timer(void)
574 queue_delayed_work(system_power_efficient_wq
, &sync_cmos_work
, 0);
578 void ntp_notify_cmos_timer(void) { }
583 * Propagate a new txc->status value into the NTP state:
585 static inline void process_adj_status(struct timex
*txc
, struct timespec64
*ts
)
587 if ((time_status
& STA_PLL
) && !(txc
->status
& STA_PLL
)) {
588 time_state
= TIME_OK
;
589 time_status
= STA_UNSYNC
;
590 ntp_next_leap_sec
= TIME64_MAX
;
591 /* restart PPS frequency calibration */
592 pps_reset_freq_interval();
596 * If we turn on PLL adjustments then reset the
597 * reference time to current time.
599 if (!(time_status
& STA_PLL
) && (txc
->status
& STA_PLL
))
600 time_reftime
= __ktime_get_real_seconds();
602 /* only set allowed bits */
603 time_status
&= STA_RONLY
;
604 time_status
|= txc
->status
& ~STA_RONLY
;
608 static inline void process_adjtimex_modes(struct timex
*txc
,
609 struct timespec64
*ts
,
612 if (txc
->modes
& ADJ_STATUS
)
613 process_adj_status(txc
, ts
);
615 if (txc
->modes
& ADJ_NANO
)
616 time_status
|= STA_NANO
;
618 if (txc
->modes
& ADJ_MICRO
)
619 time_status
&= ~STA_NANO
;
621 if (txc
->modes
& ADJ_FREQUENCY
) {
622 time_freq
= txc
->freq
* PPM_SCALE
;
623 time_freq
= min(time_freq
, MAXFREQ_SCALED
);
624 time_freq
= max(time_freq
, -MAXFREQ_SCALED
);
625 /* update pps_freq */
626 pps_set_freq(time_freq
);
629 if (txc
->modes
& ADJ_MAXERROR
)
630 time_maxerror
= txc
->maxerror
;
632 if (txc
->modes
& ADJ_ESTERROR
)
633 time_esterror
= txc
->esterror
;
635 if (txc
->modes
& ADJ_TIMECONST
) {
636 time_constant
= txc
->constant
;
637 if (!(time_status
& STA_NANO
))
639 time_constant
= min(time_constant
, (long)MAXTC
);
640 time_constant
= max(time_constant
, 0l);
643 if (txc
->modes
& ADJ_TAI
&& txc
->constant
> 0)
644 *time_tai
= txc
->constant
;
646 if (txc
->modes
& ADJ_OFFSET
)
647 ntp_update_offset(txc
->offset
);
649 if (txc
->modes
& ADJ_TICK
)
650 tick_usec
= txc
->tick
;
652 if (txc
->modes
& (ADJ_TICK
|ADJ_FREQUENCY
|ADJ_OFFSET
))
653 ntp_update_frequency();
659 * ntp_validate_timex - Ensures the timex is ok for use in do_adjtimex
661 int ntp_validate_timex(struct timex
*txc
)
663 if (txc
->modes
& ADJ_ADJTIME
) {
664 /* singleshot must not be used with any other mode bits */
665 if (!(txc
->modes
& ADJ_OFFSET_SINGLESHOT
))
667 if (!(txc
->modes
& ADJ_OFFSET_READONLY
) &&
668 !capable(CAP_SYS_TIME
))
671 /* In order to modify anything, you gotta be super-user! */
672 if (txc
->modes
&& !capable(CAP_SYS_TIME
))
675 * if the quartz is off by more than 10% then
676 * something is VERY wrong!
678 if (txc
->modes
& ADJ_TICK
&&
679 (txc
->tick
< 900000/USER_HZ
||
680 txc
->tick
> 1100000/USER_HZ
))
684 if (txc
->modes
& ADJ_SETOFFSET
) {
685 /* In order to inject time, you gotta be super-user! */
686 if (!capable(CAP_SYS_TIME
))
689 if (txc
->modes
& ADJ_NANO
) {
692 ts
.tv_sec
= txc
->time
.tv_sec
;
693 ts
.tv_nsec
= txc
->time
.tv_usec
;
694 if (!timespec_inject_offset_valid(&ts
))
698 if (!timeval_inject_offset_valid(&txc
->time
))
704 * Check for potential multiplication overflows that can
705 * only happen on 64-bit systems:
707 if ((txc
->modes
& ADJ_FREQUENCY
) && (BITS_PER_LONG
== 64)) {
708 if (LLONG_MIN
/ PPM_SCALE
> txc
->freq
)
710 if (LLONG_MAX
/ PPM_SCALE
< txc
->freq
)
719 * adjtimex mainly allows reading (and writing, if superuser) of
720 * kernel time-keeping variables. used by xntpd.
722 int __do_adjtimex(struct timex
*txc
, struct timespec64
*ts
, s32
*time_tai
)
726 if (txc
->modes
& ADJ_ADJTIME
) {
727 long save_adjust
= time_adjust
;
729 if (!(txc
->modes
& ADJ_OFFSET_READONLY
)) {
730 /* adjtime() is independent from ntp_adjtime() */
731 time_adjust
= txc
->offset
;
732 ntp_update_frequency();
734 txc
->offset
= save_adjust
;
737 /* If there are input parameters, then process them: */
739 process_adjtimex_modes(txc
, ts
, time_tai
);
741 txc
->offset
= shift_right(time_offset
* NTP_INTERVAL_FREQ
,
743 if (!(time_status
& STA_NANO
))
744 txc
->offset
/= NSEC_PER_USEC
;
747 result
= time_state
; /* mostly `TIME_OK' */
748 /* check for errors */
749 if (is_error_status(time_status
))
752 txc
->freq
= shift_right((time_freq
>> PPM_SCALE_INV_SHIFT
) *
753 PPM_SCALE_INV
, NTP_SCALE_SHIFT
);
754 txc
->maxerror
= time_maxerror
;
755 txc
->esterror
= time_esterror
;
756 txc
->status
= time_status
;
757 txc
->constant
= time_constant
;
759 txc
->tolerance
= MAXFREQ_SCALED
/ PPM_SCALE
;
760 txc
->tick
= tick_usec
;
761 txc
->tai
= *time_tai
;
763 /* fill PPS status fields */
766 txc
->time
.tv_sec
= (time_t)ts
->tv_sec
;
767 txc
->time
.tv_usec
= ts
->tv_nsec
;
768 if (!(time_status
& STA_NANO
))
769 txc
->time
.tv_usec
/= NSEC_PER_USEC
;
771 /* Handle leapsec adjustments */
772 if (unlikely(ts
->tv_sec
>= ntp_next_leap_sec
)) {
773 if ((time_state
== TIME_INS
) && (time_status
& STA_INS
)) {
778 if ((time_state
== TIME_DEL
) && (time_status
& STA_DEL
)) {
783 if ((time_state
== TIME_OOP
) &&
784 (ts
->tv_sec
== ntp_next_leap_sec
)) {
792 #ifdef CONFIG_NTP_PPS
794 /* actually struct pps_normtime is good old struct timespec, but it is
795 * semantically different (and it is the reason why it was invented):
796 * pps_normtime.nsec has a range of ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ]
797 * while timespec.tv_nsec has a range of [0, NSEC_PER_SEC) */
798 struct pps_normtime
{
799 s64 sec
; /* seconds */
800 long nsec
; /* nanoseconds */
803 /* normalize the timestamp so that nsec is in the
804 ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
805 static inline struct pps_normtime
pps_normalize_ts(struct timespec64 ts
)
807 struct pps_normtime norm
= {
812 if (norm
.nsec
> (NSEC_PER_SEC
>> 1)) {
813 norm
.nsec
-= NSEC_PER_SEC
;
820 /* get current phase correction and jitter */
821 static inline long pps_phase_filter_get(long *jitter
)
823 *jitter
= pps_tf
[0] - pps_tf
[1];
827 /* TODO: test various filters */
831 /* add the sample to the phase filter */
832 static inline void pps_phase_filter_add(long err
)
834 pps_tf
[2] = pps_tf
[1];
835 pps_tf
[1] = pps_tf
[0];
839 /* decrease frequency calibration interval length.
840 * It is halved after four consecutive unstable intervals.
842 static inline void pps_dec_freq_interval(void)
844 if (--pps_intcnt
<= -PPS_INTCOUNT
) {
845 pps_intcnt
= -PPS_INTCOUNT
;
846 if (pps_shift
> PPS_INTMIN
) {
853 /* increase frequency calibration interval length.
854 * It is doubled after four consecutive stable intervals.
856 static inline void pps_inc_freq_interval(void)
858 if (++pps_intcnt
>= PPS_INTCOUNT
) {
859 pps_intcnt
= PPS_INTCOUNT
;
860 if (pps_shift
< PPS_INTMAX
) {
867 /* update clock frequency based on MONOTONIC_RAW clock PPS signal
870 * At the end of the calibration interval the difference between the
871 * first and last MONOTONIC_RAW clock timestamps divided by the length
872 * of the interval becomes the frequency update. If the interval was
873 * too long, the data are discarded.
874 * Returns the difference between old and new frequency values.
876 static long hardpps_update_freq(struct pps_normtime freq_norm
)
878 long delta
, delta_mod
;
881 /* check if the frequency interval was too long */
882 if (freq_norm
.sec
> (2 << pps_shift
)) {
883 time_status
|= STA_PPSERROR
;
885 pps_dec_freq_interval();
886 printk_deferred(KERN_ERR
887 "hardpps: PPSERROR: interval too long - %lld s\n",
892 /* here the raw frequency offset and wander (stability) is
893 * calculated. If the wander is less than the wander threshold
894 * the interval is increased; otherwise it is decreased.
896 ftemp
= div_s64(((s64
)(-freq_norm
.nsec
)) << NTP_SCALE_SHIFT
,
898 delta
= shift_right(ftemp
- pps_freq
, NTP_SCALE_SHIFT
);
900 if (delta
> PPS_MAXWANDER
|| delta
< -PPS_MAXWANDER
) {
901 printk_deferred(KERN_WARNING
902 "hardpps: PPSWANDER: change=%ld\n", delta
);
903 time_status
|= STA_PPSWANDER
;
905 pps_dec_freq_interval();
906 } else { /* good sample */
907 pps_inc_freq_interval();
910 /* the stability metric is calculated as the average of recent
911 * frequency changes, but is used only for performance
916 delta_mod
= -delta_mod
;
917 pps_stabil
+= (div_s64(((s64
)delta_mod
) <<
918 (NTP_SCALE_SHIFT
- SHIFT_USEC
),
919 NSEC_PER_USEC
) - pps_stabil
) >> PPS_INTMIN
;
921 /* if enabled, the system clock frequency is updated */
922 if ((time_status
& STA_PPSFREQ
) != 0 &&
923 (time_status
& STA_FREQHOLD
) == 0) {
924 time_freq
= pps_freq
;
925 ntp_update_frequency();
931 /* correct REALTIME clock phase error against PPS signal */
932 static void hardpps_update_phase(long error
)
934 long correction
= -error
;
937 /* add the sample to the median filter */
938 pps_phase_filter_add(correction
);
939 correction
= pps_phase_filter_get(&jitter
);
941 /* Nominal jitter is due to PPS signal noise. If it exceeds the
942 * threshold, the sample is discarded; otherwise, if so enabled,
943 * the time offset is updated.
945 if (jitter
> (pps_jitter
<< PPS_POPCORN
)) {
946 printk_deferred(KERN_WARNING
947 "hardpps: PPSJITTER: jitter=%ld, limit=%ld\n",
948 jitter
, (pps_jitter
<< PPS_POPCORN
));
949 time_status
|= STA_PPSJITTER
;
951 } else if (time_status
& STA_PPSTIME
) {
952 /* correct the time using the phase offset */
953 time_offset
= div_s64(((s64
)correction
) << NTP_SCALE_SHIFT
,
955 /* cancel running adjtime() */
959 pps_jitter
+= (jitter
- pps_jitter
) >> PPS_INTMIN
;
963 * __hardpps() - discipline CPU clock oscillator to external PPS signal
965 * This routine is called at each PPS signal arrival in order to
966 * discipline the CPU clock oscillator to the PPS signal. It takes two
967 * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former
968 * is used to correct clock phase error and the latter is used to
969 * correct the frequency.
971 * This code is based on David Mills's reference nanokernel
972 * implementation. It was mostly rewritten but keeps the same idea.
974 void __hardpps(const struct timespec64
*phase_ts
, const struct timespec64
*raw_ts
)
976 struct pps_normtime pts_norm
, freq_norm
;
978 pts_norm
= pps_normalize_ts(*phase_ts
);
980 /* clear the error bits, they will be set again if needed */
981 time_status
&= ~(STA_PPSJITTER
| STA_PPSWANDER
| STA_PPSERROR
);
983 /* indicate signal presence */
984 time_status
|= STA_PPSSIGNAL
;
985 pps_valid
= PPS_VALID
;
987 /* when called for the first time,
988 * just start the frequency interval */
989 if (unlikely(pps_fbase
.tv_sec
== 0)) {
994 /* ok, now we have a base for frequency calculation */
995 freq_norm
= pps_normalize_ts(timespec64_sub(*raw_ts
, pps_fbase
));
997 /* check that the signal is in the range
998 * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */
999 if ((freq_norm
.sec
== 0) ||
1000 (freq_norm
.nsec
> MAXFREQ
* freq_norm
.sec
) ||
1001 (freq_norm
.nsec
< -MAXFREQ
* freq_norm
.sec
)) {
1002 time_status
|= STA_PPSJITTER
;
1003 /* restart the frequency calibration interval */
1004 pps_fbase
= *raw_ts
;
1005 printk_deferred(KERN_ERR
"hardpps: PPSJITTER: bad pulse\n");
1011 /* check if the current frequency interval is finished */
1012 if (freq_norm
.sec
>= (1 << pps_shift
)) {
1014 /* restart the frequency calibration interval */
1015 pps_fbase
= *raw_ts
;
1016 hardpps_update_freq(freq_norm
);
1019 hardpps_update_phase(pts_norm
.nsec
);
1022 #endif /* CONFIG_NTP_PPS */
1024 static int __init
ntp_tick_adj_setup(char *str
)
1026 int rc
= kstrtol(str
, 0, (long *)&ntp_tick_adj
);
1030 ntp_tick_adj
<<= NTP_SCALE_SHIFT
;
1035 __setup("ntp_tick_adj=", ntp_tick_adj_setup
);
1037 void __init
ntp_init(void)