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) */
26 static u64 tick_length, tick_length_base;
28 #define MAX_TICKADJ 500 /* microsecs */
29 #define MAX_TICKADJ_SCALED (((u64)(MAX_TICKADJ * NSEC_PER_USEC) << \
30 TICK_LENGTH_SHIFT) / NTP_INTERVAL_FREQ)
33 * phase-lock loop variables
35 /* TIME_ERROR prevents overwriting the CMOS clock */
36 static int time_state = TIME_OK; /* clock synchronization status */
37 int time_status = STA_UNSYNC; /* clock status bits */
38 static s64 time_offset; /* time adjustment (ns) */
39 static long time_constant = 2; /* pll time constant */
40 long time_maxerror = NTP_PHASE_LIMIT; /* maximum error (us) */
41 long time_esterror = NTP_PHASE_LIMIT; /* estimated error (us) */
42 long time_freq; /* frequency offset (scaled ppm)*/
43 static long time_reftime; /* time at last adjustment (s) */
45 static long ntp_tick_adj;
47 static void ntp_update_frequency(void)
49 u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)
51 second_length += (s64)ntp_tick_adj << TICK_LENGTH_SHIFT;
52 second_length += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC);
54 tick_length_base = second_length;
56 tick_nsec = div_u64(second_length, HZ) >> TICK_LENGTH_SHIFT;
57 tick_length_base = div_u64(tick_length_base, NTP_INTERVAL_FREQ);
60 static void ntp_update_offset(long offset)
65 if (!(time_status & STA_PLL))
68 time_offset = offset * NSEC_PER_USEC;
71 * Scale the phase adjustment and
72 * clamp to the operating range.
74 time_offset = min(time_offset, (s64)MAXPHASE * NSEC_PER_USEC);
75 time_offset = max(time_offset, (s64)-MAXPHASE * NSEC_PER_USEC);
78 * Select how the frequency is to be controlled
79 * and in which mode (PLL or FLL).
81 if (time_status & STA_FREQHOLD || time_reftime == 0)
82 time_reftime = xtime.tv_sec;
83 mtemp = xtime.tv_sec - time_reftime;
84 time_reftime = xtime.tv_sec;
86 freq_adj = time_offset * mtemp;
87 freq_adj = shift_right(freq_adj, time_constant * 2 +
88 (SHIFT_PLL + 2) * 2 - SHIFT_NSEC);
89 if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC))
90 freq_adj += div_s64(time_offset << (SHIFT_NSEC - SHIFT_FLL), mtemp);
91 freq_adj += time_freq;
92 freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);
93 time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);
94 time_offset = div_s64(time_offset, NTP_INTERVAL_FREQ);
95 time_offset <<= SHIFT_UPDATE;
99 * ntp_clear - Clears the NTP state variables
101 * Must be called while holding a write on the xtime_lock
105 time_adjust = 0; /* stop active adjtime() */
106 time_status |= STA_UNSYNC;
107 time_maxerror = NTP_PHASE_LIMIT;
108 time_esterror = NTP_PHASE_LIMIT;
110 ntp_update_frequency();
112 tick_length = tick_length_base;
117 * this routine handles the overflow of the microsecond field
119 * The tricky bits of code to handle the accurate clock support
120 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
121 * They were originally developed for SUN and DEC kernels.
122 * All the kudos should go to Dave for this stuff.
124 void second_overflow(void)
128 /* Bump the maxerror field */
129 time_maxerror += MAXFREQ >> SHIFT_USEC;
130 if (time_maxerror > NTP_PHASE_LIMIT) {
131 time_maxerror = NTP_PHASE_LIMIT;
132 time_status |= STA_UNSYNC;
136 * Leap second processing. If in leap-insert state at the end of the
137 * day, the system clock is set back one second; if in leap-delete
138 * state, the system clock is set ahead one second. The microtime()
139 * routine or external clock driver will insure that reported time is
140 * always monotonic. The ugly divides should be replaced.
142 switch (time_state) {
144 if (time_status & STA_INS)
145 time_state = TIME_INS;
146 else if (time_status & STA_DEL)
147 time_state = TIME_DEL;
150 if (xtime.tv_sec % 86400 == 0) {
152 wall_to_monotonic.tv_sec++;
153 time_state = TIME_OOP;
154 printk(KERN_NOTICE "Clock: inserting leap second "
159 if ((xtime.tv_sec + 1) % 86400 == 0) {
161 wall_to_monotonic.tv_sec--;
162 time_state = TIME_WAIT;
163 printk(KERN_NOTICE "Clock: deleting leap second "
168 time_state = TIME_WAIT;
171 if (!(time_status & (STA_INS | STA_DEL)))
172 time_state = TIME_OK;
176 * Compute the phase adjustment for the next second. The offset is
177 * reduced by a fixed factor times the time constant.
179 tick_length = tick_length_base;
180 time_adj = shift_right(time_offset, SHIFT_PLL + time_constant);
181 time_offset -= time_adj;
182 tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - SHIFT_UPDATE);
184 if (unlikely(time_adjust)) {
185 if (time_adjust > MAX_TICKADJ) {
186 time_adjust -= MAX_TICKADJ;
187 tick_length += MAX_TICKADJ_SCALED;
188 } else if (time_adjust < -MAX_TICKADJ) {
189 time_adjust += MAX_TICKADJ;
190 tick_length -= MAX_TICKADJ_SCALED;
192 tick_length += (s64)(time_adjust * NSEC_PER_USEC /
193 NTP_INTERVAL_FREQ) << TICK_LENGTH_SHIFT;
200 * Return how long ticks are at the moment, that is, how much time
201 * update_wall_time_one_tick will add to xtime next time we call it
202 * (assuming no calls to do_adjtimex in the meantime).
203 * The return value is in fixed-point nanoseconds shifted by the
204 * specified number of bits to the right of the binary point.
205 * This function has no side-effects.
207 u64 current_tick_length(void)
212 #ifdef CONFIG_GENERIC_CMOS_UPDATE
214 /* Disable the cmos update - used by virtualization and embedded */
215 int no_sync_cmos_clock __read_mostly;
217 static void sync_cmos_clock(unsigned long dummy);
219 static DEFINE_TIMER(sync_cmos_timer, sync_cmos_clock, 0, 0);
221 static void sync_cmos_clock(unsigned long dummy)
223 struct timespec now, next;
227 * If we have an externally synchronized Linux clock, then update
228 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
229 * called as close as possible to 500 ms before the new second starts.
230 * This code is run on a timer. If the clock is set, that timer
231 * may not expire at the correct time. Thus, we adjust...
235 * Not synced, exit, do not restart a timer (if one is
236 * running, let it run out).
240 getnstimeofday(&now);
241 if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2)
242 fail = update_persistent_clock(now);
244 next.tv_nsec = (NSEC_PER_SEC / 2) - now.tv_nsec;
245 if (next.tv_nsec <= 0)
246 next.tv_nsec += NSEC_PER_SEC;
253 if (next.tv_nsec >= NSEC_PER_SEC) {
255 next.tv_nsec -= NSEC_PER_SEC;
257 mod_timer(&sync_cmos_timer, jiffies + timespec_to_jiffies(&next));
260 static void notify_cmos_timer(void)
262 if (!no_sync_cmos_clock)
263 mod_timer(&sync_cmos_timer, jiffies + 1);
267 static inline void notify_cmos_timer(void) { }
270 /* adjtimex mainly allows reading (and writing, if superuser) of
271 * kernel time-keeping variables. used by xntpd.
273 int do_adjtimex(struct timex *txc)
278 /* In order to modify anything, you gotta be super-user! */
279 if (txc->modes && !capable(CAP_SYS_TIME))
282 /* Now we validate the data before disabling interrupts */
284 if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT) {
285 /* singleshot must not be used with any other mode bits */
286 if (txc->modes != ADJ_OFFSET_SINGLESHOT &&
287 txc->modes != ADJ_OFFSET_SS_READ)
291 if (txc->modes != ADJ_OFFSET_SINGLESHOT && (txc->modes & ADJ_OFFSET))
292 /* adjustment Offset limited to +- .512 seconds */
293 if (txc->offset <= - MAXPHASE || txc->offset >= MAXPHASE )
296 /* if the quartz is off by more than 10% something is VERY wrong ! */
297 if (txc->modes & ADJ_TICK)
298 if (txc->tick < 900000/USER_HZ ||
299 txc->tick > 1100000/USER_HZ)
302 write_seqlock_irq(&xtime_lock);
303 result = time_state; /* mostly `TIME_OK' */
305 /* Save for later - semantics of adjtime is to return old value */
306 save_adjust = time_adjust;
308 #if 0 /* STA_CLOCKERR is never set yet */
309 time_status &= ~STA_CLOCKERR; /* reset STA_CLOCKERR */
311 /* If there are input parameters, then process them */
313 if (txc->modes & ADJ_STATUS) /* only set allowed bits */
314 time_status = (txc->status & ~STA_RONLY) |
315 (time_status & STA_RONLY);
317 if (txc->modes & ADJ_FREQUENCY) {
318 if (txc->freq > MAXFREQ || txc->freq < -MAXFREQ) {
322 time_freq = ((s64)txc->freq * NSEC_PER_USEC)
323 >> (SHIFT_USEC - SHIFT_NSEC);
326 if (txc->modes & ADJ_MAXERROR) {
327 if (txc->maxerror < 0 || txc->maxerror >= NTP_PHASE_LIMIT) {
331 time_maxerror = txc->maxerror;
334 if (txc->modes & ADJ_ESTERROR) {
335 if (txc->esterror < 0 || txc->esterror >= NTP_PHASE_LIMIT) {
339 time_esterror = txc->esterror;
342 if (txc->modes & ADJ_TIMECONST) {
343 if (txc->constant < 0) { /* NTP v4 uses values > 6 */
347 time_constant = min(txc->constant + 4, (long)MAXTC);
350 if (txc->modes & ADJ_OFFSET) {
351 if (txc->modes == ADJ_OFFSET_SINGLESHOT)
352 /* adjtime() is independent from ntp_adjtime() */
353 time_adjust = txc->offset;
355 ntp_update_offset(txc->offset);
357 if (txc->modes & ADJ_TICK)
358 tick_usec = txc->tick;
360 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
361 ntp_update_frequency();
364 if (time_status & (STA_UNSYNC|STA_CLOCKERR))
367 if ((txc->modes == ADJ_OFFSET_SINGLESHOT) ||
368 (txc->modes == ADJ_OFFSET_SS_READ))
369 txc->offset = save_adjust;
371 txc->offset = ((long)shift_right(time_offset, SHIFT_UPDATE)) *
372 NTP_INTERVAL_FREQ / 1000;
373 txc->freq = (time_freq / NSEC_PER_USEC) <<
374 (SHIFT_USEC - SHIFT_NSEC);
375 txc->maxerror = time_maxerror;
376 txc->esterror = time_esterror;
377 txc->status = time_status;
378 txc->constant = time_constant;
380 txc->tolerance = MAXFREQ;
381 txc->tick = tick_usec;
383 /* PPS is not implemented, so these are zero */
392 write_sequnlock_irq(&xtime_lock);
394 do_gettimeofday(&txc->time);
401 static int __init ntp_tick_adj_setup(char *str)
403 ntp_tick_adj = simple_strtol(str, NULL, 0);
407 __setup("ntp_tick_adj=", ntp_tick_adj_setup);