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>
19 * NTP timekeeping variables:
22 /* USER_HZ period (usecs): */
23 unsigned long tick_usec = TICK_USEC;
25 /* ACTHZ period (nsecs): */
26 unsigned long tick_nsec;
29 static u64 tick_length_base;
31 static struct hrtimer leap_timer;
33 #define MAX_TICKADJ 500LL /* usecs */
34 #define MAX_TICKADJ_SCALED \
35 (((MAX_TICKADJ * NSEC_PER_USEC) << NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
38 * phase-lock loop variables
42 * clock synchronization status
44 * (TIME_ERROR prevents overwriting the CMOS clock)
46 static int time_state = TIME_OK;
48 /* clock status bits: */
49 int time_status = STA_UNSYNC;
51 /* TAI offset (secs): */
54 /* time adjustment (nsecs): */
55 static s64 time_offset;
57 /* pll time constant: */
58 static long time_constant = 2;
60 /* maximum error (usecs): */
61 long time_maxerror = NTP_PHASE_LIMIT;
63 /* estimated error (usecs): */
64 long time_esterror = NTP_PHASE_LIMIT;
66 /* frequency offset (scaled nsecs/secs): */
69 /* time at last adjustment (secs): */
70 static long time_reftime;
74 /* constant (boot-param configurable) NTP tick adjustment (upscaled) */
75 static s64 ntp_tick_adj;
82 * Update (tick_length, tick_length_base, tick_nsec), based
83 * on (tick_usec, ntp_tick_adj, time_freq):
85 static void ntp_update_frequency(void)
90 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
93 second_length += ntp_tick_adj;
94 second_length += time_freq;
96 tick_nsec = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
97 new_base = div_u64(second_length, NTP_INTERVAL_FREQ);
100 * Don't wait for the next second_overflow, apply
101 * the change to the tick length immediately:
103 tick_length += new_base - tick_length_base;
104 tick_length_base = new_base;
107 static inline s64 ntp_update_offset_fll(s64 offset64, long secs)
109 time_status &= ~STA_MODE;
114 if (!(time_status & STA_FLL) && (secs <= MAXSEC))
117 time_status |= STA_MODE;
119 return div_s64(offset64 << (NTP_SCALE_SHIFT - SHIFT_FLL), secs);
122 static void ntp_update_offset(long offset)
128 if (!(time_status & STA_PLL))
131 if (!(time_status & STA_NANO))
132 offset *= NSEC_PER_USEC;
135 * Scale the phase adjustment and
136 * clamp to the operating range.
138 offset = min(offset, MAXPHASE);
139 offset = max(offset, -MAXPHASE);
142 * Select how the frequency is to be controlled
143 * and in which mode (PLL or FLL).
145 secs = xtime.tv_sec - time_reftime;
146 if (unlikely(time_status & STA_FREQHOLD))
149 time_reftime = xtime.tv_sec;
152 freq_adj = (offset64 * secs) <<
153 (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
155 freq_adj += ntp_update_offset_fll(offset64, secs);
157 freq_adj = min(freq_adj + time_freq, MAXFREQ_SCALED);
159 time_freq = max(freq_adj, -MAXFREQ_SCALED);
161 time_offset = div_s64(offset64 << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
165 * ntp_clear - Clears the NTP state variables
167 * Must be called while holding a write on the xtime_lock
171 time_adjust = 0; /* stop active adjtime() */
172 time_status |= STA_UNSYNC;
173 time_maxerror = NTP_PHASE_LIMIT;
174 time_esterror = NTP_PHASE_LIMIT;
176 ntp_update_frequency();
178 tick_length = tick_length_base;
183 * Leap second processing. If in leap-insert state at the end of the
184 * day, the system clock is set back one second; if in leap-delete
185 * state, the system clock is set ahead one second.
187 static enum hrtimer_restart ntp_leap_second(struct hrtimer *timer)
189 enum hrtimer_restart res = HRTIMER_NORESTART;
191 write_seqlock(&xtime_lock);
193 switch (time_state) {
198 wall_to_monotonic.tv_sec++;
199 time_state = TIME_OOP;
201 "Clock: inserting leap second 23:59:60 UTC\n");
202 hrtimer_add_expires_ns(&leap_timer, NSEC_PER_SEC);
203 res = HRTIMER_RESTART;
208 wall_to_monotonic.tv_sec--;
209 time_state = TIME_WAIT;
211 "Clock: deleting leap second 23:59:59 UTC\n");
215 time_state = TIME_WAIT;
218 if (!(time_status & (STA_INS | STA_DEL)))
219 time_state = TIME_OK;
222 update_vsyscall(&xtime, clock);
224 write_sequnlock(&xtime_lock);
230 * this routine handles the overflow of the microsecond field
232 * The tricky bits of code to handle the accurate clock support
233 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
234 * They were originally developed for SUN and DEC kernels.
235 * All the kudos should go to Dave for this stuff.
237 void second_overflow(void)
241 /* Bump the maxerror field */
242 time_maxerror += MAXFREQ / NSEC_PER_USEC;
243 if (time_maxerror > NTP_PHASE_LIMIT) {
244 time_maxerror = NTP_PHASE_LIMIT;
245 time_status |= STA_UNSYNC;
249 * Compute the phase adjustment for the next second. The offset is
250 * reduced by a fixed factor times the time constant.
252 tick_length = tick_length_base;
254 delta = shift_right(time_offset, SHIFT_PLL + time_constant);
255 time_offset -= delta;
256 tick_length += delta;
261 if (time_adjust > MAX_TICKADJ) {
262 time_adjust -= MAX_TICKADJ;
263 tick_length += MAX_TICKADJ_SCALED;
267 if (time_adjust < -MAX_TICKADJ) {
268 time_adjust += MAX_TICKADJ;
269 tick_length -= MAX_TICKADJ_SCALED;
273 tick_length += (s64)(time_adjust * NSEC_PER_USEC / NTP_INTERVAL_FREQ)
278 #ifdef CONFIG_GENERIC_CMOS_UPDATE
280 /* Disable the cmos update - used by virtualization and embedded */
281 int no_sync_cmos_clock __read_mostly;
283 static void sync_cmos_clock(struct work_struct *work);
285 static DECLARE_DELAYED_WORK(sync_cmos_work, sync_cmos_clock);
287 static void sync_cmos_clock(struct work_struct *work)
289 struct timespec now, next;
293 * If we have an externally synchronized Linux clock, then update
294 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
295 * called as close as possible to 500 ms before the new second starts.
296 * This code is run on a timer. If the clock is set, that timer
297 * may not expire at the correct time. Thus, we adjust...
301 * Not synced, exit, do not restart a timer (if one is
302 * running, let it run out).
307 getnstimeofday(&now);
308 if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
309 fail = update_persistent_clock(now);
311 next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec - (TICK_NSEC / 2);
312 if (next.tv_nsec <= 0)
313 next.tv_nsec += NSEC_PER_SEC;
320 if (next.tv_nsec >= NSEC_PER_SEC) {
322 next.tv_nsec -= NSEC_PER_SEC;
324 schedule_delayed_work(&sync_cmos_work, timespec_to_jiffies(&next));
327 static void notify_cmos_timer(void)
329 if (!no_sync_cmos_clock)
330 schedule_delayed_work(&sync_cmos_work, 0);
334 static inline void notify_cmos_timer(void) { }
338 * Start the leap seconds timer:
340 static inline void ntp_start_leap_timer(struct timespec *ts)
342 long now = ts->tv_sec;
344 if (time_status & STA_INS) {
345 time_state = TIME_INS;
346 now += 86400 - now % 86400;
347 hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);
352 if (time_status & STA_DEL) {
353 time_state = TIME_DEL;
354 now += 86400 - (now + 1) % 86400;
355 hrtimer_start(&leap_timer, ktime_set(now, 0), HRTIMER_MODE_ABS);
360 * Propagate a new txc->status value into the NTP state:
362 static inline void process_adj_status(struct timex *txc, struct timespec *ts)
364 if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
365 time_state = TIME_OK;
366 time_status = STA_UNSYNC;
370 * If we turn on PLL adjustments then reset the
371 * reference time to current time.
373 if (!(time_status & STA_PLL) && (txc->status & STA_PLL))
374 time_reftime = xtime.tv_sec;
376 /* only set allowed bits */
377 time_status &= STA_RONLY;
378 time_status |= txc->status & ~STA_RONLY;
380 switch (time_state) {
382 ntp_start_leap_timer(ts);
386 time_state = TIME_OK;
387 ntp_start_leap_timer(ts);
389 if (!(time_status & (STA_INS | STA_DEL)))
390 time_state = TIME_OK;
393 hrtimer_restart(&leap_timer);
398 * Called with the xtime lock held, so we can access and modify
399 * all the global NTP state:
401 static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts)
403 if (txc->modes & ADJ_STATUS)
404 process_adj_status(txc, ts);
406 if (txc->modes & ADJ_NANO)
407 time_status |= STA_NANO;
409 if (txc->modes & ADJ_MICRO)
410 time_status &= ~STA_NANO;
412 if (txc->modes & ADJ_FREQUENCY) {
413 time_freq = txc->freq * PPM_SCALE;
414 time_freq = min(time_freq, MAXFREQ_SCALED);
415 time_freq = max(time_freq, -MAXFREQ_SCALED);
418 if (txc->modes & ADJ_MAXERROR)
419 time_maxerror = txc->maxerror;
421 if (txc->modes & ADJ_ESTERROR)
422 time_esterror = txc->esterror;
424 if (txc->modes & ADJ_TIMECONST) {
425 time_constant = txc->constant;
426 if (!(time_status & STA_NANO))
428 time_constant = min(time_constant, (long)MAXTC);
429 time_constant = max(time_constant, 0l);
432 if (txc->modes & ADJ_TAI && txc->constant > 0)
433 time_tai = txc->constant;
435 if (txc->modes & ADJ_OFFSET)
436 ntp_update_offset(txc->offset);
438 if (txc->modes & ADJ_TICK)
439 tick_usec = txc->tick;
441 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
442 ntp_update_frequency();
446 * adjtimex mainly allows reading (and writing, if superuser) of
447 * kernel time-keeping variables. used by xntpd.
449 int do_adjtimex(struct timex *txc)
454 /* Validate the data before disabling interrupts */
455 if (txc->modes & ADJ_ADJTIME) {
456 /* singleshot must not be used with any other mode bits */
457 if (!(txc->modes & ADJ_OFFSET_SINGLESHOT))
459 if (!(txc->modes & ADJ_OFFSET_READONLY) &&
460 !capable(CAP_SYS_TIME))
463 /* In order to modify anything, you gotta be super-user! */
464 if (txc->modes && !capable(CAP_SYS_TIME))
468 * if the quartz is off by more than 10% then
469 * something is VERY wrong!
471 if (txc->modes & ADJ_TICK &&
472 (txc->tick < 900000/USER_HZ ||
473 txc->tick > 1100000/USER_HZ))
476 if (txc->modes & ADJ_STATUS && time_state != TIME_OK)
477 hrtimer_cancel(&leap_timer);
482 write_seqlock_irq(&xtime_lock);
484 if (txc->modes & ADJ_ADJTIME) {
485 long save_adjust = time_adjust;
487 if (!(txc->modes & ADJ_OFFSET_READONLY)) {
488 /* adjtime() is independent from ntp_adjtime() */
489 time_adjust = txc->offset;
490 ntp_update_frequency();
492 txc->offset = save_adjust;
495 /* If there are input parameters, then process them: */
497 process_adjtimex_modes(txc, &ts);
499 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
501 if (!(time_status & STA_NANO))
502 txc->offset /= NSEC_PER_USEC;
505 result = time_state; /* mostly `TIME_OK' */
506 if (time_status & (STA_UNSYNC|STA_CLOCKERR))
509 txc->freq = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
510 PPM_SCALE_INV, NTP_SCALE_SHIFT);
511 txc->maxerror = time_maxerror;
512 txc->esterror = time_esterror;
513 txc->status = time_status;
514 txc->constant = time_constant;
516 txc->tolerance = MAXFREQ_SCALED / PPM_SCALE;
517 txc->tick = tick_usec;
520 /* PPS is not implemented, so these are zero */
530 write_sequnlock_irq(&xtime_lock);
532 txc->time.tv_sec = ts.tv_sec;
533 txc->time.tv_usec = ts.tv_nsec;
534 if (!(time_status & STA_NANO))
535 txc->time.tv_usec /= NSEC_PER_USEC;
542 static int __init ntp_tick_adj_setup(char *str)
544 ntp_tick_adj = simple_strtol(str, NULL, 0);
545 ntp_tick_adj <<= NTP_SCALE_SHIFT;
550 __setup("ntp_tick_adj=", ntp_tick_adj_setup);
552 void __init ntp_init(void)
555 hrtimer_init(&leap_timer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
556 leap_timer.function = ntp_leap_second;