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; /* frequency offset (scaled ppm)*/
41 long time_reftime; /* time at last adjustment (s) */
43 long time_next_adjust;
46 * ntp_clear - Clears the NTP state variables
48 * Must be called while holding a write on the xtime_lock
52 time_adjust = 0; /* stop active adjtime() */
53 time_status |= STA_UNSYNC;
54 time_maxerror = NTP_PHASE_LIMIT;
55 time_esterror = NTP_PHASE_LIMIT;
57 ntp_update_frequency();
59 tick_length = tick_length_base;
62 #define CLOCK_TICK_OVERFLOW (LATCH * HZ - CLOCK_TICK_RATE)
63 #define CLOCK_TICK_ADJUST (((s64)CLOCK_TICK_OVERFLOW * NSEC_PER_SEC) / (s64)CLOCK_TICK_RATE)
65 void ntp_update_frequency(void)
67 tick_length_base = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ) << TICK_LENGTH_SHIFT;
68 tick_length_base += (s64)CLOCK_TICK_ADJUST << TICK_LENGTH_SHIFT;
69 tick_length_base += ((s64)time_freq * NSEC_PER_USEC) << (TICK_LENGTH_SHIFT - SHIFT_USEC);
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.
169 * Compensate for (HZ==100) != (1 << SHIFT_HZ). Add 25% and 3.125% to
170 * get 128.125; => only 0.125% error (p. 14)
172 time_adj += shift_right(time_adj, 2) + shift_right(time_adj, 5);
176 * Compensate for (HZ==250) != (1 << SHIFT_HZ). Add 1.5625% and
177 * 0.78125% to get 255.85938; => only 0.05% error (p. 14)
179 time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7);
183 * Compensate for (HZ==1000) != (1 << SHIFT_HZ). Add 1.5625% and
184 * 0.78125% to get 1023.4375; => only 0.05% error (p. 14)
186 time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7);
188 tick_length = tick_length_base;
189 tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - (SHIFT_SCALE - 10));
193 * Returns how many microseconds we need to add to xtime this tick
194 * in doing an adjustment requested with adjtime.
196 static long adjtime_adjustment(void)
198 long time_adjust_step;
200 time_adjust_step = time_adjust;
201 if (time_adjust_step) {
203 * We are doing an adjtime thing. Prepare time_adjust_step to
204 * be within bounds. Note that a positive time_adjust means we
205 * want the clock to run faster.
207 * Limit the amount of the step to be in the range
208 * -tickadj .. +tickadj
210 time_adjust_step = min(time_adjust_step, (long)tickadj);
211 time_adjust_step = max(time_adjust_step, (long)-tickadj);
213 return time_adjust_step;
216 /* in the NTP reference this is called "hardclock()" */
217 void update_ntp_one_tick(void)
219 long time_adjust_step;
221 time_adjust_step = adjtime_adjustment();
222 if (time_adjust_step)
223 /* Reduce by this step the amount of time left */
224 time_adjust -= time_adjust_step;
226 /* Changes by adjtime() do not take effect till next tick. */
227 if (time_next_adjust != 0) {
228 time_adjust = time_next_adjust;
229 time_next_adjust = 0;
234 * Return how long ticks are at the moment, that is, how much time
235 * update_wall_time_one_tick will add to xtime next time we call it
236 * (assuming no calls to do_adjtimex in the meantime).
237 * The return value is in fixed-point nanoseconds shifted by the
238 * specified number of bits to the right of the binary point.
239 * This function has no side-effects.
241 u64 current_tick_length(void)
245 /* calculate the finest interval NTP will allow.
248 ret += (u64)(adjtime_adjustment() * 1000) << TICK_LENGTH_SHIFT;
254 void __attribute__ ((weak)) notify_arch_cmos_timer(void)
259 /* adjtimex mainly allows reading (and writing, if superuser) of
260 * kernel time-keeping variables. used by xntpd.
262 int do_adjtimex(struct timex *txc)
264 long ltemp, mtemp, save_adjust;
267 /* In order to modify anything, you gotta be super-user! */
268 if (txc->modes && !capable(CAP_SYS_TIME))
271 /* Now we validate the data before disabling interrupts */
273 if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
274 /* singleshot must not be used with any other mode bits */
275 if (txc->modes != ADJ_OFFSET_SINGLESHOT)
278 if (txc->modes != ADJ_OFFSET_SINGLESHOT && (txc->modes & ADJ_OFFSET))
279 /* adjustment Offset limited to +- .512 seconds */
280 if (txc->offset <= - MAXPHASE || txc->offset >= MAXPHASE )
283 /* if the quartz is off by more than 10% something is VERY wrong ! */
284 if (txc->modes & ADJ_TICK)
285 if (txc->tick < 900000/USER_HZ ||
286 txc->tick > 1100000/USER_HZ)
289 write_seqlock_irq(&xtime_lock);
290 result = time_state; /* mostly `TIME_OK' */
292 /* Save for later - semantics of adjtime is to return old value */
293 save_adjust = time_next_adjust ? time_next_adjust : time_adjust;
295 #if 0 /* STA_CLOCKERR is never set yet */
296 time_status &= ~STA_CLOCKERR; /* reset STA_CLOCKERR */
298 /* If there are input parameters, then process them */
301 if (txc->modes & ADJ_STATUS) /* only set allowed bits */
302 time_status = (txc->status & ~STA_RONLY) |
303 (time_status & STA_RONLY);
305 if (txc->modes & ADJ_FREQUENCY) { /* p. 22 */
306 if (txc->freq > MAXFREQ || txc->freq < -MAXFREQ) {
310 time_freq = txc->freq;
313 if (txc->modes & ADJ_MAXERROR) {
314 if (txc->maxerror < 0 || txc->maxerror >= NTP_PHASE_LIMIT) {
318 time_maxerror = txc->maxerror;
321 if (txc->modes & ADJ_ESTERROR) {
322 if (txc->esterror < 0 || txc->esterror >= NTP_PHASE_LIMIT) {
326 time_esterror = txc->esterror;
329 if (txc->modes & ADJ_TIMECONST) { /* p. 24 */
330 if (txc->constant < 0) { /* NTP v4 uses values > 6 */
334 time_constant = txc->constant;
337 if (txc->modes & ADJ_OFFSET) { /* values checked earlier */
338 if (txc->modes == ADJ_OFFSET_SINGLESHOT) {
339 /* adjtime() is independent from ntp_adjtime() */
340 if ((time_next_adjust = txc->offset) == 0)
343 else if (time_status & STA_PLL) {
347 * Scale the phase adjustment and
348 * clamp to the operating range.
350 if (ltemp > MAXPHASE)
351 time_offset = MAXPHASE << SHIFT_UPDATE;
352 else if (ltemp < -MAXPHASE)
353 time_offset = -(MAXPHASE << SHIFT_UPDATE);
355 time_offset = ltemp << SHIFT_UPDATE;
358 * Select whether the frequency is to be controlled
359 * and in which mode (PLL or FLL). Clamp to the operating
360 * range. Ugly multiply/divide should be replaced someday.
363 if (time_status & STA_FREQHOLD || time_reftime == 0)
364 time_reftime = xtime.tv_sec;
365 mtemp = xtime.tv_sec - time_reftime;
366 time_reftime = xtime.tv_sec;
367 if (time_status & STA_FLL) {
368 if (mtemp >= MINSEC) {
369 ltemp = (time_offset / mtemp) << (SHIFT_USEC -
371 time_freq += shift_right(ltemp, SHIFT_KH);
372 } else /* calibration interval too short (p. 12) */
374 } else { /* PLL mode */
375 if (mtemp < MAXSEC) {
377 time_freq += shift_right(ltemp,(time_constant +
379 SHIFT_KF - SHIFT_USEC));
380 } else /* calibration interval too long (p. 12) */
383 time_freq = min(time_freq, time_tolerance);
384 time_freq = max(time_freq, -time_tolerance);
386 } /* txc->modes & ADJ_OFFSET */
387 if (txc->modes & ADJ_TICK)
388 tick_usec = txc->tick;
390 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
391 ntp_update_frequency();
393 leave: if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
396 if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
397 txc->offset = save_adjust;
399 txc->offset = shift_right(time_offset, SHIFT_UPDATE);
401 txc->freq = time_freq;
402 txc->maxerror = time_maxerror;
403 txc->esterror = time_esterror;
404 txc->status = time_status;
405 txc->constant = time_constant;
406 txc->precision = time_precision;
407 txc->tolerance = time_tolerance;
408 txc->tick = tick_usec;
410 /* PPS is not implemented, so these are zero */
419 write_sequnlock_irq(&xtime_lock);
420 do_gettimeofday(&txc->time);
421 notify_arch_cmos_timer();