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/timex.h>
15 #include <asm/div64.h>
16 #include <asm/timex.h>
19 * Timekeeping variables
21 unsigned long tick_usec = TICK_USEC; /* USER_HZ period (usec) */
22 unsigned long tick_nsec; /* ACTHZ period (nsec) */
23 static u64 tick_length, tick_length_base;
25 /* Don't completely fail for HZ > 500. */
26 int tickadj = 500/HZ ? : 1; /* microsecs */
29 * phase-lock loop variables
31 /* TIME_ERROR prevents overwriting the CMOS clock */
32 int time_state = TIME_OK; /* clock synchronization status */
33 int time_status = STA_UNSYNC; /* clock status bits */
34 long time_offset; /* time adjustment (us) */
35 long time_constant = 2; /* pll time constant */
36 long time_tolerance = MAXFREQ; /* frequency tolerance (ppm) */
37 long time_precision = 1; /* clock precision (us) */
38 long time_maxerror = NTP_PHASE_LIMIT; /* maximum error (us) */
39 long time_esterror = NTP_PHASE_LIMIT; /* estimated error (us) */
40 long time_freq = (((NSEC_PER_SEC + HZ/2) % HZ - HZ/2) << SHIFT_USEC) / NSEC_PER_USEC;
41 /* frequency offset (scaled ppm)*/
42 long time_reftime; /* time at last adjustment (s) */
44 long time_next_adjust;
47 * ntp_clear - Clears the NTP state variables
49 * Must be called while holding a write on the xtime_lock
53 time_adjust = 0; /* stop active adjtime() */
54 time_status |= STA_UNSYNC;
55 time_maxerror = NTP_PHASE_LIMIT;
56 time_esterror = NTP_PHASE_LIMIT;
58 ntp_update_frequency();
60 tick_length = tick_length_base;
63 #define CLOCK_TICK_OVERFLOW (LATCH * HZ - CLOCK_TICK_RATE)
64 #define CLOCK_TICK_ADJUST (((s64)CLOCK_TICK_OVERFLOW * NSEC_PER_SEC) / (s64)CLOCK_TICK_RATE)
66 void ntp_update_frequency(void)
68 tick_length_base = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ) << TICK_LENGTH_SHIFT;
69 tick_length_base += (s64)CLOCK_TICK_ADJUST << TICK_LENGTH_SHIFT;
71 do_div(tick_length_base, HZ);
73 tick_nsec = tick_length_base >> TICK_LENGTH_SHIFT;
77 * this routine handles the overflow of the microsecond field
79 * The tricky bits of code to handle the accurate clock support
80 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
81 * They were originally developed for SUN and DEC kernels.
82 * All the kudos should go to Dave for this stuff.
84 void second_overflow(void)
88 /* Bump the maxerror field */
89 time_maxerror += time_tolerance >> SHIFT_USEC;
90 if (time_maxerror > NTP_PHASE_LIMIT) {
91 time_maxerror = NTP_PHASE_LIMIT;
92 time_status |= STA_UNSYNC;
96 * Leap second processing. If in leap-insert state at the end of the
97 * day, the system clock is set back one second; if in leap-delete
98 * state, the system clock is set ahead one second. The microtime()
99 * routine or external clock driver will insure that reported time is
100 * always monotonic. The ugly divides should be replaced.
102 switch (time_state) {
104 if (time_status & STA_INS)
105 time_state = TIME_INS;
106 else if (time_status & STA_DEL)
107 time_state = TIME_DEL;
110 if (xtime.tv_sec % 86400 == 0) {
112 wall_to_monotonic.tv_sec++;
114 * The timer interpolator will make time change
115 * gradually instead of an immediate jump by one second
117 time_interpolator_update(-NSEC_PER_SEC);
118 time_state = TIME_OOP;
120 printk(KERN_NOTICE "Clock: inserting leap second "
125 if ((xtime.tv_sec + 1) % 86400 == 0) {
127 wall_to_monotonic.tv_sec--;
129 * Use of time interpolator for a gradual change of
132 time_interpolator_update(NSEC_PER_SEC);
133 time_state = TIME_WAIT;
135 printk(KERN_NOTICE "Clock: deleting leap second "
140 time_state = TIME_WAIT;
143 if (!(time_status & (STA_INS | STA_DEL)))
144 time_state = TIME_OK;
148 * Compute the phase adjustment for the next second. In PLL mode, the
149 * offset is reduced by a fixed factor times the time constant. In FLL
150 * mode the offset is used directly. In either mode, the maximum phase
151 * adjustment for each second is clamped so as to spread the adjustment
152 * over not more than the number of seconds between updates.
155 if (!(time_status & STA_FLL))
156 ltemp = shift_right(ltemp, SHIFT_KG + time_constant);
157 ltemp = min(ltemp, (MAXPHASE / MINSEC) << SHIFT_UPDATE);
158 ltemp = max(ltemp, -(MAXPHASE / MINSEC) << SHIFT_UPDATE);
159 time_offset -= ltemp;
160 time_adj = ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);
163 * Compute the frequency estimate and additional phase adjustment due
164 * to frequency error for the next second.
167 time_adj += shift_right(ltemp,(SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE));
171 * Compensate for (HZ==100) != (1 << SHIFT_HZ). Add 25% and 3.125% to
172 * get 128.125; => only 0.125% error (p. 14)
174 time_adj += shift_right(time_adj, 2) + shift_right(time_adj, 5);
178 * Compensate for (HZ==250) != (1 << SHIFT_HZ). Add 1.5625% and
179 * 0.78125% to get 255.85938; => only 0.05% error (p. 14)
181 time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7);
185 * Compensate for (HZ==1000) != (1 << SHIFT_HZ). Add 1.5625% and
186 * 0.78125% to get 1023.4375; => only 0.05% error (p. 14)
188 time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7);
190 tick_length = tick_length_base;
191 tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - (SHIFT_SCALE - 10));
195 * Returns how many microseconds we need to add to xtime this tick
196 * in doing an adjustment requested with adjtime.
198 static long adjtime_adjustment(void)
200 long time_adjust_step;
202 time_adjust_step = time_adjust;
203 if (time_adjust_step) {
205 * We are doing an adjtime thing. Prepare time_adjust_step to
206 * be within bounds. Note that a positive time_adjust means we
207 * want the clock to run faster.
209 * Limit the amount of the step to be in the range
210 * -tickadj .. +tickadj
212 time_adjust_step = min(time_adjust_step, (long)tickadj);
213 time_adjust_step = max(time_adjust_step, (long)-tickadj);
215 return time_adjust_step;
218 /* in the NTP reference this is called "hardclock()" */
219 void update_ntp_one_tick(void)
221 long time_adjust_step;
223 time_adjust_step = adjtime_adjustment();
224 if (time_adjust_step)
225 /* Reduce by this step the amount of time left */
226 time_adjust -= time_adjust_step;
228 /* Changes by adjtime() do not take effect till next tick. */
229 if (time_next_adjust != 0) {
230 time_adjust = time_next_adjust;
231 time_next_adjust = 0;
236 * Return how long ticks are at the moment, that is, how much time
237 * update_wall_time_one_tick will add to xtime next time we call it
238 * (assuming no calls to do_adjtimex in the meantime).
239 * The return value is in fixed-point nanoseconds shifted by the
240 * specified number of bits to the right of the binary point.
241 * This function has no side-effects.
243 u64 current_tick_length(void)
247 /* calculate the finest interval NTP will allow.
250 ret += (u64)(adjtime_adjustment() * 1000) << TICK_LENGTH_SHIFT;
256 void __attribute__ ((weak)) notify_arch_cmos_timer(void)
261 /* adjtimex mainly allows reading (and writing, if superuser) of
262 * kernel time-keeping variables. used by xntpd.
264 int do_adjtimex(struct timex *txc)
266 long ltemp, mtemp, save_adjust;
269 /* In order to modify anything, you gotta be super-user! */
270 if (txc->modes && !capable(CAP_SYS_TIME))
273 /* Now we validate the data before disabling interrupts */
275 if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
276 /* singleshot must not be used with any other mode bits */
277 if (txc->modes != ADJ_OFFSET_SINGLESHOT)
280 if (txc->modes != ADJ_OFFSET_SINGLESHOT && (txc->modes & ADJ_OFFSET))
281 /* adjustment Offset limited to +- .512 seconds */
282 if (txc->offset <= - MAXPHASE || txc->offset >= MAXPHASE )
285 /* if the quartz is off by more than 10% something is VERY wrong ! */
286 if (txc->modes & ADJ_TICK)
287 if (txc->tick < 900000/USER_HZ ||
288 txc->tick > 1100000/USER_HZ)
291 write_seqlock_irq(&xtime_lock);
292 result = time_state; /* mostly `TIME_OK' */
294 /* Save for later - semantics of adjtime is to return old value */
295 save_adjust = time_next_adjust ? time_next_adjust : time_adjust;
297 #if 0 /* STA_CLOCKERR is never set yet */
298 time_status &= ~STA_CLOCKERR; /* reset STA_CLOCKERR */
300 /* If there are input parameters, then process them */
303 if (txc->modes & ADJ_STATUS) /* only set allowed bits */
304 time_status = (txc->status & ~STA_RONLY) |
305 (time_status & STA_RONLY);
307 if (txc->modes & ADJ_FREQUENCY) { /* p. 22 */
308 if (txc->freq > MAXFREQ || txc->freq < -MAXFREQ) {
312 time_freq = txc->freq;
315 if (txc->modes & ADJ_MAXERROR) {
316 if (txc->maxerror < 0 || txc->maxerror >= NTP_PHASE_LIMIT) {
320 time_maxerror = txc->maxerror;
323 if (txc->modes & ADJ_ESTERROR) {
324 if (txc->esterror < 0 || txc->esterror >= NTP_PHASE_LIMIT) {
328 time_esterror = txc->esterror;
331 if (txc->modes & ADJ_TIMECONST) { /* p. 24 */
332 if (txc->constant < 0) { /* NTP v4 uses values > 6 */
336 time_constant = txc->constant;
339 if (txc->modes & ADJ_OFFSET) { /* values checked earlier */
340 if (txc->modes == ADJ_OFFSET_SINGLESHOT) {
341 /* adjtime() is independent from ntp_adjtime() */
342 if ((time_next_adjust = txc->offset) == 0)
345 else if (time_status & STA_PLL) {
349 * Scale the phase adjustment and
350 * clamp to the operating range.
352 if (ltemp > MAXPHASE)
353 time_offset = MAXPHASE << SHIFT_UPDATE;
354 else if (ltemp < -MAXPHASE)
355 time_offset = -(MAXPHASE << SHIFT_UPDATE);
357 time_offset = ltemp << SHIFT_UPDATE;
360 * Select whether the frequency is to be controlled
361 * and in which mode (PLL or FLL). Clamp to the operating
362 * range. Ugly multiply/divide should be replaced someday.
365 if (time_status & STA_FREQHOLD || time_reftime == 0)
366 time_reftime = xtime.tv_sec;
367 mtemp = xtime.tv_sec - time_reftime;
368 time_reftime = xtime.tv_sec;
369 if (time_status & STA_FLL) {
370 if (mtemp >= MINSEC) {
371 ltemp = (time_offset / mtemp) << (SHIFT_USEC -
373 time_freq += shift_right(ltemp, SHIFT_KH);
374 } else /* calibration interval too short (p. 12) */
376 } else { /* PLL mode */
377 if (mtemp < MAXSEC) {
379 time_freq += shift_right(ltemp,(time_constant +
381 SHIFT_KF - SHIFT_USEC));
382 } else /* calibration interval too long (p. 12) */
385 time_freq = min(time_freq, time_tolerance);
386 time_freq = max(time_freq, -time_tolerance);
388 } /* txc->modes & ADJ_OFFSET */
389 if (txc->modes & ADJ_TICK)
390 tick_usec = txc->tick;
392 if (txc->modes & ADJ_TICK)
393 ntp_update_frequency();
395 leave: if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
398 if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
399 txc->offset = save_adjust;
401 txc->offset = shift_right(time_offset, SHIFT_UPDATE);
403 txc->freq = time_freq;
404 txc->maxerror = time_maxerror;
405 txc->esterror = time_esterror;
406 txc->status = time_status;
407 txc->constant = time_constant;
408 txc->precision = time_precision;
409 txc->tolerance = time_tolerance;
410 txc->tick = tick_usec;
412 /* PPS is not implemented, so these are zero */
421 write_sequnlock_irq(&xtime_lock);
422 do_gettimeofday(&txc->time);
423 notify_arch_cmos_timer();