2 * linux/kernel/time/ntp.c
4 * NTP state machine interfaces and logic.
6 * This code was mainly moved from kernel/timer.c and kernel/time.c
7 * Please see those files for relevant copyright info and historical
12 #include <linux/time.h>
13 #include <linux/timer.h>
14 #include <linux/timex.h>
15 #include <linux/jiffies.h>
16 #include <linux/hrtimer.h>
17 #include <linux/capability.h>
18 #include <linux/math64.h>
19 #include <asm/timex.h>
22 * Timekeeping variables
24 unsigned long tick_usec = TICK_USEC; /* USER_HZ period (usec) */
25 unsigned long tick_nsec; /* ACTHZ period (nsec) */
27 static u64 tick_length_base;
29 #define MAX_TICKADJ 500 /* microsecs */
30 #define MAX_TICKADJ_SCALED (((u64)(MAX_TICKADJ * NSEC_PER_USEC) << \
31 NTP_SCALE_SHIFT) / NTP_INTERVAL_FREQ)
34 * phase-lock loop variables
36 /* TIME_ERROR prevents overwriting the CMOS clock */
37 static int time_state = TIME_OK; /* clock synchronization status */
38 int time_status = STA_UNSYNC; /* clock status bits */
39 static long time_tai; /* TAI offset (s) */
40 static s64 time_offset; /* time adjustment (ns) */
41 static long time_constant = 2; /* pll time constant */
42 long time_maxerror = NTP_PHASE_LIMIT; /* maximum error (us) */
43 long time_esterror = NTP_PHASE_LIMIT; /* estimated error (us) */
44 static s64 time_freq; /* frequency offset (scaled ns/s)*/
45 static long time_reftime; /* time at last adjustment (s) */
47 static long ntp_tick_adj;
49 static void ntp_update_frequency(void)
51 u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
53 second_length += (s64)ntp_tick_adj << NTP_SCALE_SHIFT;
54 second_length += time_freq;
56 tick_length_base = second_length;
58 tick_nsec = div_u64(second_length, HZ) >> NTP_SCALE_SHIFT;
59 tick_length_base = div_u64(tick_length_base, NTP_INTERVAL_FREQ);
62 static void ntp_update_offset(long offset)
67 if (!(time_status & STA_PLL))
70 if (!(time_status & STA_NANO))
71 offset *= NSEC_PER_USEC;
74 * Scale the phase adjustment and
75 * clamp to the operating range.
77 offset = min(offset, MAXPHASE);
78 offset = max(offset, -MAXPHASE);
81 * Select how the frequency is to be controlled
82 * and in which mode (PLL or FLL).
84 if (time_status & STA_FREQHOLD || time_reftime == 0)
85 time_reftime = xtime.tv_sec;
86 mtemp = xtime.tv_sec - time_reftime;
87 time_reftime = xtime.tv_sec;
89 freq_adj = (s64)offset * mtemp;
90 freq_adj <<= NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant);
91 time_status &= ~STA_MODE;
92 if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
93 freq_adj += div_s64((s64)offset << (NTP_SCALE_SHIFT - SHIFT_FLL),
95 time_status |= STA_MODE;
97 freq_adj += time_freq;
98 freq_adj = min(freq_adj, MAXFREQ_SCALED);
99 time_freq = max(freq_adj, -MAXFREQ_SCALED);
101 time_offset = div_s64((s64)offset << NTP_SCALE_SHIFT, NTP_INTERVAL_FREQ);
105 * ntp_clear - Clears the NTP state variables
107 * Must be called while holding a write on the xtime_lock
111 time_adjust = 0; /* stop active adjtime() */
112 time_status |= STA_UNSYNC;
113 time_maxerror = NTP_PHASE_LIMIT;
114 time_esterror = NTP_PHASE_LIMIT;
116 ntp_update_frequency();
118 tick_length = tick_length_base;
123 * this routine handles the overflow of the microsecond field
125 * The tricky bits of code to handle the accurate clock support
126 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
127 * They were originally developed for SUN and DEC kernels.
128 * All the kudos should go to Dave for this stuff.
130 void second_overflow(void)
134 /* Bump the maxerror field */
135 time_maxerror += MAXFREQ / NSEC_PER_USEC;
136 if (time_maxerror > NTP_PHASE_LIMIT) {
137 time_maxerror = NTP_PHASE_LIMIT;
138 time_status |= STA_UNSYNC;
142 * Leap second processing. If in leap-insert state at the end of the
143 * day, the system clock is set back one second; if in leap-delete
144 * state, the system clock is set ahead one second. The microtime()
145 * routine or external clock driver will insure that reported time is
146 * always monotonic. The ugly divides should be replaced.
148 switch (time_state) {
150 if (time_status & STA_INS)
151 time_state = TIME_INS;
152 else if (time_status & STA_DEL)
153 time_state = TIME_DEL;
156 if (xtime.tv_sec % 86400 == 0) {
158 wall_to_monotonic.tv_sec++;
159 time_state = TIME_OOP;
160 printk(KERN_NOTICE "Clock: inserting leap second "
165 if ((xtime.tv_sec + 1) % 86400 == 0) {
168 wall_to_monotonic.tv_sec--;
169 time_state = TIME_WAIT;
170 printk(KERN_NOTICE "Clock: deleting leap second "
176 time_state = TIME_WAIT;
179 if (!(time_status & (STA_INS | STA_DEL)))
180 time_state = TIME_OK;
184 * Compute the phase adjustment for the next second. The offset is
185 * reduced by a fixed factor times the time constant.
187 tick_length = tick_length_base;
188 time_adj = shift_right(time_offset, SHIFT_PLL + time_constant);
189 time_offset -= time_adj;
190 tick_length += time_adj;
192 if (unlikely(time_adjust)) {
193 if (time_adjust > MAX_TICKADJ) {
194 time_adjust -= MAX_TICKADJ;
195 tick_length += MAX_TICKADJ_SCALED;
196 } else if (time_adjust < -MAX_TICKADJ) {
197 time_adjust += MAX_TICKADJ;
198 tick_length -= MAX_TICKADJ_SCALED;
200 tick_length += (s64)(time_adjust * NSEC_PER_USEC /
201 NTP_INTERVAL_FREQ) << NTP_SCALE_SHIFT;
207 #ifdef CONFIG_GENERIC_CMOS_UPDATE
209 /* Disable the cmos update - used by virtualization and embedded */
210 int no_sync_cmos_clock __read_mostly;
212 static void sync_cmos_clock(unsigned long dummy);
214 static DEFINE_TIMER(sync_cmos_timer, sync_cmos_clock, 0, 0);
216 static void sync_cmos_clock(unsigned long dummy)
218 struct timespec now, next;
222 * If we have an externally synchronized Linux clock, then update
223 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
224 * called as close as possible to 500 ms before the new second starts.
225 * This code is run on a timer. If the clock is set, that timer
226 * may not expire at the correct time. Thus, we adjust...
230 * Not synced, exit, do not restart a timer (if one is
231 * running, let it run out).
235 getnstimeofday(&now);
236 if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
237 fail = update_persistent_clock(now);
239 next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec;
240 if (next.tv_nsec <= 0)
241 next.tv_nsec += NSEC_PER_SEC;
248 if (next.tv_nsec >= NSEC_PER_SEC) {
250 next.tv_nsec -= NSEC_PER_SEC;
252 mod_timer(&sync_cmos_timer, jiffies + timespec_to_jiffies(&next));
255 static void notify_cmos_timer(void)
257 if (!no_sync_cmos_clock)
258 mod_timer(&sync_cmos_timer, jiffies + 1);
262 static inline void notify_cmos_timer(void) { }
265 /* adjtimex mainly allows reading (and writing, if superuser) of
266 * kernel time-keeping variables. used by xntpd.
268 int do_adjtimex(struct timex *txc)
274 /* In order to modify anything, you gotta be super-user! */
275 if (txc->modes && !capable(CAP_SYS_TIME))
278 /* Now we validate the data before disabling interrupts */
280 if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT) {
281 /* singleshot must not be used with any other mode bits */
282 if (txc->modes & ~ADJ_OFFSET_SS_READ)
286 /* if the quartz is off by more than 10% something is VERY wrong ! */
287 if (txc->modes & ADJ_TICK)
288 if (txc->tick < 900000/USER_HZ ||
289 txc->tick > 1100000/USER_HZ)
292 write_seqlock_irq(&xtime_lock);
294 /* Save for later - semantics of adjtime is to return old value */
295 save_adjust = time_adjust;
297 /* If there are input parameters, then process them */
299 if (txc->modes & ADJ_STATUS) {
300 if ((time_status & STA_PLL) &&
301 !(txc->status & STA_PLL)) {
302 time_state = TIME_OK;
303 time_status = STA_UNSYNC;
305 /* only set allowed bits */
306 time_status &= STA_RONLY;
307 time_status |= txc->status & ~STA_RONLY;
310 if (txc->modes & ADJ_NANO)
311 time_status |= STA_NANO;
312 if (txc->modes & ADJ_MICRO)
313 time_status &= ~STA_NANO;
315 if (txc->modes & ADJ_FREQUENCY) {
316 time_freq = (s64)txc->freq * PPM_SCALE;
317 time_freq = min(time_freq, MAXFREQ_SCALED);
318 time_freq = max(time_freq, -MAXFREQ_SCALED);
321 if (txc->modes & ADJ_MAXERROR)
322 time_maxerror = txc->maxerror;
323 if (txc->modes & ADJ_ESTERROR)
324 time_esterror = txc->esterror;
326 if (txc->modes & ADJ_TIMECONST) {
327 time_constant = txc->constant;
328 if (!(time_status & STA_NANO))
330 time_constant = min(time_constant, (long)MAXTC);
331 time_constant = max(time_constant, 0l);
334 if (txc->modes & ADJ_TAI && txc->constant > 0)
335 time_tai = txc->constant;
337 if (txc->modes & ADJ_OFFSET) {
338 if (txc->modes == ADJ_OFFSET_SINGLESHOT)
339 /* adjtime() is independent from ntp_adjtime() */
340 time_adjust = txc->offset;
342 ntp_update_offset(txc->offset);
344 if (txc->modes & ADJ_TICK)
345 tick_usec = txc->tick;
347 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
348 ntp_update_frequency();
351 result = time_state; /* mostly `TIME_OK' */
352 if (time_status & (STA_UNSYNC|STA_CLOCKERR))
355 if ((txc->modes == ADJ_OFFSET_SINGLESHOT) ||
356 (txc->modes == ADJ_OFFSET_SS_READ))
357 txc->offset = save_adjust;
359 txc->offset = shift_right(time_offset * NTP_INTERVAL_FREQ,
361 if (!(time_status & STA_NANO))
362 txc->offset /= NSEC_PER_USEC;
364 txc->freq = shift_right((s32)(time_freq >> PPM_SCALE_INV_SHIFT) *
367 txc->maxerror = time_maxerror;
368 txc->esterror = time_esterror;
369 txc->status = time_status;
370 txc->constant = time_constant;
372 txc->tolerance = MAXFREQ_SCALED / PPM_SCALE;
373 txc->tick = tick_usec;
376 /* PPS is not implemented, so these are zero */
385 write_sequnlock_irq(&xtime_lock);
388 txc->time.tv_sec = ts.tv_sec;
389 txc->time.tv_usec = ts.tv_nsec;
390 if (!(time_status & STA_NANO))
391 txc->time.tv_usec /= NSEC_PER_USEC;
398 static int __init ntp_tick_adj_setup(char *str)
400 ntp_tick_adj = simple_strtol(str, NULL, 0);
404 __setup("ntp_tick_adj=", ntp_tick_adj_setup);