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 static long ntp_tick_adj
;
81 * Update (tick_length, tick_length_base, tick_nsec), based
82 * on (tick_usec, ntp_tick_adj, time_freq):
84 static void ntp_update_frequency(void)
89 second_length
= (u64
)(tick_usec
* NSEC_PER_USEC
* USER_HZ
)
92 second_length
+= (s64
)ntp_tick_adj
<< NTP_SCALE_SHIFT
;
93 second_length
+= time_freq
;
95 tick_nsec
= div_u64(second_length
, HZ
) >> NTP_SCALE_SHIFT
;
96 new_base
= div_u64(second_length
, NTP_INTERVAL_FREQ
);
99 * Don't wait for the next second_overflow, apply
100 * the change to the tick length immediately:
102 tick_length
+= new_base
- tick_length_base
;
103 tick_length_base
= new_base
;
106 static inline s64
ntp_update_offset_fll(s64 offset64
, long secs
)
108 time_status
&= ~STA_MODE
;
113 if (!(time_status
& STA_FLL
) && (secs
<= MAXSEC
))
116 time_status
|= STA_MODE
;
118 return div_s64(offset64
<< (NTP_SCALE_SHIFT
- SHIFT_FLL
), secs
);
121 static void ntp_update_offset(long offset
)
127 if (!(time_status
& STA_PLL
))
130 if (!(time_status
& STA_NANO
))
131 offset
*= NSEC_PER_USEC
;
134 * Scale the phase adjustment and
135 * clamp to the operating range.
137 offset
= min(offset
, MAXPHASE
);
138 offset
= max(offset
, -MAXPHASE
);
141 * Select how the frequency is to be controlled
142 * and in which mode (PLL or FLL).
144 if (time_status
& STA_FREQHOLD
|| time_reftime
== 0)
145 time_reftime
= xtime
.tv_sec
;
147 secs
= xtime
.tv_sec
- time_reftime
;
148 time_reftime
= xtime
.tv_sec
;
151 freq_adj
= (offset64
* secs
) <<
152 (NTP_SCALE_SHIFT
- 2 * (SHIFT_PLL
+ 2 + time_constant
));
154 freq_adj
+= ntp_update_offset_fll(offset64
, secs
);
156 freq_adj
= min(freq_adj
+ time_freq
, MAXFREQ_SCALED
);
158 time_freq
= max(freq_adj
, -MAXFREQ_SCALED
);
160 time_offset
= div_s64(offset64
<< NTP_SCALE_SHIFT
, NTP_INTERVAL_FREQ
);
164 * ntp_clear - Clears the NTP state variables
166 * Must be called while holding a write on the xtime_lock
170 time_adjust
= 0; /* stop active adjtime() */
171 time_status
|= STA_UNSYNC
;
172 time_maxerror
= NTP_PHASE_LIMIT
;
173 time_esterror
= NTP_PHASE_LIMIT
;
175 ntp_update_frequency();
177 tick_length
= tick_length_base
;
182 * Leap second processing. If in leap-insert state at the end of the
183 * day, the system clock is set back one second; if in leap-delete
184 * state, the system clock is set ahead one second.
186 static enum hrtimer_restart
ntp_leap_second(struct hrtimer
*timer
)
188 enum hrtimer_restart res
= HRTIMER_NORESTART
;
190 write_seqlock(&xtime_lock
);
192 switch (time_state
) {
197 wall_to_monotonic
.tv_sec
++;
198 time_state
= TIME_OOP
;
200 "Clock: inserting leap second 23:59:60 UTC\n");
201 hrtimer_add_expires_ns(&leap_timer
, NSEC_PER_SEC
);
202 res
= HRTIMER_RESTART
;
207 wall_to_monotonic
.tv_sec
--;
208 time_state
= TIME_WAIT
;
210 "Clock: deleting leap second 23:59:59 UTC\n");
214 time_state
= TIME_WAIT
;
217 if (!(time_status
& (STA_INS
| STA_DEL
)))
218 time_state
= TIME_OK
;
221 update_vsyscall(&xtime
, clock
);
223 write_sequnlock(&xtime_lock
);
229 * this routine handles the overflow of the microsecond field
231 * The tricky bits of code to handle the accurate clock support
232 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
233 * They were originally developed for SUN and DEC kernels.
234 * All the kudos should go to Dave for this stuff.
236 void second_overflow(void)
240 /* Bump the maxerror field */
241 time_maxerror
+= MAXFREQ
/ NSEC_PER_USEC
;
242 if (time_maxerror
> NTP_PHASE_LIMIT
) {
243 time_maxerror
= NTP_PHASE_LIMIT
;
244 time_status
|= STA_UNSYNC
;
248 * Compute the phase adjustment for the next second. The offset is
249 * reduced by a fixed factor times the time constant.
251 tick_length
= tick_length_base
;
252 time_adj
= shift_right(time_offset
, SHIFT_PLL
+ time_constant
);
253 time_offset
-= time_adj
;
254 tick_length
+= time_adj
;
259 if (time_adjust
> MAX_TICKADJ
) {
260 time_adjust
-= MAX_TICKADJ
;
261 tick_length
+= MAX_TICKADJ_SCALED
;
265 if (time_adjust
< -MAX_TICKADJ
) {
266 time_adjust
+= MAX_TICKADJ
;
267 tick_length
-= MAX_TICKADJ_SCALED
;
271 tick_length
+= (s64
)(time_adjust
* NSEC_PER_USEC
/ NTP_INTERVAL_FREQ
)
276 #ifdef CONFIG_GENERIC_CMOS_UPDATE
278 /* Disable the cmos update - used by virtualization and embedded */
279 int no_sync_cmos_clock __read_mostly
;
281 static void sync_cmos_clock(struct work_struct
*work
);
283 static DECLARE_DELAYED_WORK(sync_cmos_work
, sync_cmos_clock
);
285 static void sync_cmos_clock(struct work_struct
*work
)
287 struct timespec now
, next
;
291 * If we have an externally synchronized Linux clock, then update
292 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
293 * called as close as possible to 500 ms before the new second starts.
294 * This code is run on a timer. If the clock is set, that timer
295 * may not expire at the correct time. Thus, we adjust...
299 * Not synced, exit, do not restart a timer (if one is
300 * running, let it run out).
305 getnstimeofday(&now
);
306 if (abs(now
.tv_nsec
- (NSEC_PER_SEC
/ 2)) <= tick_nsec
/ 2)
307 fail
= update_persistent_clock(now
);
309 next
.tv_nsec
= (NSEC_PER_SEC
/ 2) - now
.tv_nsec
- (TICK_NSEC
/ 2);
310 if (next
.tv_nsec
<= 0)
311 next
.tv_nsec
+= NSEC_PER_SEC
;
318 if (next
.tv_nsec
>= NSEC_PER_SEC
) {
320 next
.tv_nsec
-= NSEC_PER_SEC
;
322 schedule_delayed_work(&sync_cmos_work
, timespec_to_jiffies(&next
));
325 static void notify_cmos_timer(void)
327 if (!no_sync_cmos_clock
)
328 schedule_delayed_work(&sync_cmos_work
, 0);
332 static inline void notify_cmos_timer(void) { }
336 * adjtimex mainly allows reading (and writing, if superuser) of
337 * kernel time-keeping variables. used by xntpd.
339 int do_adjtimex(struct timex
*txc
)
344 /* Validate the data before disabling interrupts */
345 if (txc
->modes
& ADJ_ADJTIME
) {
346 /* singleshot must not be used with any other mode bits */
347 if (!(txc
->modes
& ADJ_OFFSET_SINGLESHOT
))
349 if (!(txc
->modes
& ADJ_OFFSET_READONLY
) &&
350 !capable(CAP_SYS_TIME
))
353 /* In order to modify anything, you gotta be super-user! */
354 if (txc
->modes
&& !capable(CAP_SYS_TIME
))
358 * if the quartz is off by more than 10% then
359 * something is VERY wrong!
361 if (txc
->modes
& ADJ_TICK
&&
362 (txc
->tick
< 900000/USER_HZ
||
363 txc
->tick
> 1100000/USER_HZ
))
366 if (txc
->modes
& ADJ_STATUS
&& time_state
!= TIME_OK
)
367 hrtimer_cancel(&leap_timer
);
372 write_seqlock_irq(&xtime_lock
);
374 /* If there are input parameters, then process them */
375 if (txc
->modes
& ADJ_ADJTIME
) {
376 long save_adjust
= time_adjust
;
378 if (!(txc
->modes
& ADJ_OFFSET_READONLY
)) {
379 /* adjtime() is independent from ntp_adjtime() */
380 time_adjust
= txc
->offset
;
381 ntp_update_frequency();
383 txc
->offset
= save_adjust
;
389 if (txc
->modes
& ADJ_STATUS
) {
390 if ((time_status
& STA_PLL
) &&
391 !(txc
->status
& STA_PLL
)) {
392 time_state
= TIME_OK
;
393 time_status
= STA_UNSYNC
;
395 /* only set allowed bits */
396 time_status
&= STA_RONLY
;
397 time_status
|= txc
->status
& ~STA_RONLY
;
399 switch (time_state
) {
403 if (time_status
& STA_INS
) {
404 time_state
= TIME_INS
;
405 sec
+= 86400 - sec
% 86400;
406 hrtimer_start(&leap_timer
, ktime_set(sec
, 0), HRTIMER_MODE_ABS
);
407 } else if (time_status
& STA_DEL
) {
408 time_state
= TIME_DEL
;
409 sec
+= 86400 - (sec
+ 1) % 86400;
410 hrtimer_start(&leap_timer
, ktime_set(sec
, 0), HRTIMER_MODE_ABS
);
415 time_state
= TIME_OK
;
419 if (!(time_status
& (STA_INS
| STA_DEL
)))
420 time_state
= TIME_OK
;
423 hrtimer_restart(&leap_timer
);
428 if (txc
->modes
& ADJ_NANO
)
429 time_status
|= STA_NANO
;
430 if (txc
->modes
& ADJ_MICRO
)
431 time_status
&= ~STA_NANO
;
433 if (txc
->modes
& ADJ_FREQUENCY
) {
434 time_freq
= (s64
)txc
->freq
* PPM_SCALE
;
435 time_freq
= min(time_freq
, MAXFREQ_SCALED
);
436 time_freq
= max(time_freq
, -MAXFREQ_SCALED
);
439 if (txc
->modes
& ADJ_MAXERROR
)
440 time_maxerror
= txc
->maxerror
;
441 if (txc
->modes
& ADJ_ESTERROR
)
442 time_esterror
= txc
->esterror
;
444 if (txc
->modes
& ADJ_TIMECONST
) {
445 time_constant
= txc
->constant
;
446 if (!(time_status
& STA_NANO
))
448 time_constant
= min(time_constant
, (long)MAXTC
);
449 time_constant
= max(time_constant
, 0l);
452 if (txc
->modes
& ADJ_TAI
&& txc
->constant
> 0)
453 time_tai
= txc
->constant
;
455 if (txc
->modes
& ADJ_OFFSET
)
456 ntp_update_offset(txc
->offset
);
457 if (txc
->modes
& ADJ_TICK
)
458 tick_usec
= txc
->tick
;
460 if (txc
->modes
& (ADJ_TICK
|ADJ_FREQUENCY
|ADJ_OFFSET
))
461 ntp_update_frequency();
464 txc
->offset
= shift_right(time_offset
* NTP_INTERVAL_FREQ
,
466 if (!(time_status
& STA_NANO
))
467 txc
->offset
/= NSEC_PER_USEC
;
470 result
= time_state
; /* mostly `TIME_OK' */
471 if (time_status
& (STA_UNSYNC
|STA_CLOCKERR
))
474 txc
->freq
= shift_right((time_freq
>> PPM_SCALE_INV_SHIFT
) *
475 (s64
)PPM_SCALE_INV
, NTP_SCALE_SHIFT
);
476 txc
->maxerror
= time_maxerror
;
477 txc
->esterror
= time_esterror
;
478 txc
->status
= time_status
;
479 txc
->constant
= time_constant
;
481 txc
->tolerance
= MAXFREQ_SCALED
/ PPM_SCALE
;
482 txc
->tick
= tick_usec
;
485 /* PPS is not implemented, so these are zero */
494 write_sequnlock_irq(&xtime_lock
);
496 txc
->time
.tv_sec
= ts
.tv_sec
;
497 txc
->time
.tv_usec
= ts
.tv_nsec
;
498 if (!(time_status
& STA_NANO
))
499 txc
->time
.tv_usec
/= NSEC_PER_USEC
;
506 static int __init
ntp_tick_adj_setup(char *str
)
508 ntp_tick_adj
= simple_strtol(str
, NULL
, 0);
512 __setup("ntp_tick_adj=", ntp_tick_adj_setup
);
514 void __init
ntp_init(void)
517 hrtimer_init(&leap_timer
, CLOCK_REALTIME
, HRTIMER_MODE_ABS
);
518 leap_timer
.function
= ntp_leap_second
;