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 #define MAX_TICKADJ 500 /* microsecs */
26 #define MAX_TICKADJ_SCALED (((u64)(MAX_TICKADJ * NSEC_PER_USEC) << \
27 TICK_LENGTH_SHIFT) / HZ)
30 * phase-lock loop variables
32 /* TIME_ERROR prevents overwriting the CMOS clock */
33 int time_state = TIME_OK; /* clock synchronization status */
34 int time_status = STA_UNSYNC; /* clock status bits */
35 long time_offset; /* time adjustment (ns) */
36 long time_constant = 2; /* pll time constant */
37 long time_tolerance = MAXFREQ; /* frequency tolerance (ppm) */
38 long time_precision = 1; /* clock precision (us) */
39 long time_maxerror = NTP_PHASE_LIMIT; /* maximum error (us) */
40 long time_esterror = NTP_PHASE_LIMIT; /* estimated error (us) */
41 long time_freq; /* frequency offset (scaled ppm)*/
42 long time_reftime; /* time at last adjustment (s) */
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;
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;
70 tick_length_base += ((s64)time_freq * NSEC_PER_USEC) << (TICK_LENGTH_SHIFT - SHIFT_USEC);
72 do_div(tick_length_base, HZ);
74 tick_nsec = tick_length_base >> TICK_LENGTH_SHIFT;
78 * this routine handles the overflow of the microsecond field
80 * The tricky bits of code to handle the accurate clock support
81 * were provided by Dave Mills (Mills@UDEL.EDU) of NTP fame.
82 * They were originally developed for SUN and DEC kernels.
83 * All the kudos should go to Dave for this stuff.
85 void second_overflow(void)
89 /* Bump the maxerror field */
90 time_maxerror += time_tolerance >> SHIFT_USEC;
91 if (time_maxerror > NTP_PHASE_LIMIT) {
92 time_maxerror = NTP_PHASE_LIMIT;
93 time_status |= STA_UNSYNC;
97 * Leap second processing. If in leap-insert state at the end of the
98 * day, the system clock is set back one second; if in leap-delete
99 * state, the system clock is set ahead one second. The microtime()
100 * routine or external clock driver will insure that reported time is
101 * always monotonic. The ugly divides should be replaced.
103 switch (time_state) {
105 if (time_status & STA_INS)
106 time_state = TIME_INS;
107 else if (time_status & STA_DEL)
108 time_state = TIME_DEL;
111 if (xtime.tv_sec % 86400 == 0) {
113 wall_to_monotonic.tv_sec++;
115 * The timer interpolator will make time change
116 * gradually instead of an immediate jump by one second
118 time_interpolator_update(-NSEC_PER_SEC);
119 time_state = TIME_OOP;
121 printk(KERN_NOTICE "Clock: inserting leap second "
126 if ((xtime.tv_sec + 1) % 86400 == 0) {
128 wall_to_monotonic.tv_sec--;
130 * Use of time interpolator for a gradual change of
133 time_interpolator_update(NSEC_PER_SEC);
134 time_state = TIME_WAIT;
136 printk(KERN_NOTICE "Clock: deleting leap second "
141 time_state = TIME_WAIT;
144 if (!(time_status & (STA_INS | STA_DEL)))
145 time_state = TIME_OK;
149 * Compute the phase adjustment for the next second. In PLL mode, the
150 * offset is reduced by a fixed factor times the time constant. In FLL
151 * mode the offset is used directly. In either mode, the maximum phase
152 * adjustment for each second is clamped so as to spread the adjustment
153 * over not more than the number of seconds between updates.
155 tick_length = tick_length_base;
156 time_adj = time_offset;
157 if (!(time_status & STA_FLL))
158 time_adj = shift_right(time_adj, SHIFT_KG + time_constant);
159 time_adj = min(time_adj, -((MAXPHASE / HZ) << SHIFT_UPDATE) / MINSEC);
160 time_adj = max(time_adj, ((MAXPHASE / HZ) << SHIFT_UPDATE) / MINSEC);
161 time_offset -= time_adj;
162 tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - SHIFT_UPDATE);
164 if (unlikely(time_adjust)) {
165 if (time_adjust > MAX_TICKADJ) {
166 time_adjust -= MAX_TICKADJ;
167 tick_length += MAX_TICKADJ_SCALED;
168 } else if (time_adjust < -MAX_TICKADJ) {
169 time_adjust += MAX_TICKADJ;
170 tick_length -= MAX_TICKADJ_SCALED;
173 tick_length += (s64)(time_adjust * NSEC_PER_USEC /
174 HZ) << TICK_LENGTH_SHIFT;
180 * Return how long ticks are at the moment, that is, how much time
181 * update_wall_time_one_tick will add to xtime next time we call it
182 * (assuming no calls to do_adjtimex in the meantime).
183 * The return value is in fixed-point nanoseconds shifted by the
184 * specified number of bits to the right of the binary point.
185 * This function has no side-effects.
187 u64 current_tick_length(void)
193 void __attribute__ ((weak)) notify_arch_cmos_timer(void)
198 /* adjtimex mainly allows reading (and writing, if superuser) of
199 * kernel time-keeping variables. used by xntpd.
201 int do_adjtimex(struct timex *txc)
203 long ltemp, mtemp, save_adjust;
206 /* In order to modify anything, you gotta be super-user! */
207 if (txc->modes && !capable(CAP_SYS_TIME))
210 /* Now we validate the data before disabling interrupts */
212 if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
213 /* singleshot must not be used with any other mode bits */
214 if (txc->modes != ADJ_OFFSET_SINGLESHOT)
217 if (txc->modes != ADJ_OFFSET_SINGLESHOT && (txc->modes & ADJ_OFFSET))
218 /* adjustment Offset limited to +- .512 seconds */
219 if (txc->offset <= - MAXPHASE || txc->offset >= MAXPHASE )
222 /* if the quartz is off by more than 10% something is VERY wrong ! */
223 if (txc->modes & ADJ_TICK)
224 if (txc->tick < 900000/USER_HZ ||
225 txc->tick > 1100000/USER_HZ)
228 write_seqlock_irq(&xtime_lock);
229 result = time_state; /* mostly `TIME_OK' */
231 /* Save for later - semantics of adjtime is to return old value */
232 save_adjust = time_adjust;
234 #if 0 /* STA_CLOCKERR is never set yet */
235 time_status &= ~STA_CLOCKERR; /* reset STA_CLOCKERR */
237 /* If there are input parameters, then process them */
240 if (txc->modes & ADJ_STATUS) /* only set allowed bits */
241 time_status = (txc->status & ~STA_RONLY) |
242 (time_status & STA_RONLY);
244 if (txc->modes & ADJ_FREQUENCY) { /* p. 22 */
245 if (txc->freq > MAXFREQ || txc->freq < -MAXFREQ) {
249 time_freq = txc->freq;
252 if (txc->modes & ADJ_MAXERROR) {
253 if (txc->maxerror < 0 || txc->maxerror >= NTP_PHASE_LIMIT) {
257 time_maxerror = txc->maxerror;
260 if (txc->modes & ADJ_ESTERROR) {
261 if (txc->esterror < 0 || txc->esterror >= NTP_PHASE_LIMIT) {
265 time_esterror = txc->esterror;
268 if (txc->modes & ADJ_TIMECONST) { /* p. 24 */
269 if (txc->constant < 0) { /* NTP v4 uses values > 6 */
273 time_constant = txc->constant;
276 if (txc->modes & ADJ_OFFSET) { /* values checked earlier */
277 if (txc->modes == ADJ_OFFSET_SINGLESHOT) {
278 /* adjtime() is independent from ntp_adjtime() */
279 time_adjust = txc->offset;
281 else if (time_status & STA_PLL) {
285 * Scale the phase adjustment and
286 * clamp to the operating range.
288 time_offset = min(ltemp, MAXPHASE);
289 time_offset = max(time_offset, -MAXPHASE);
292 * Select whether the frequency is to be controlled
293 * and in which mode (PLL or FLL). Clamp to the operating
294 * range. Ugly multiply/divide should be replaced someday.
297 if (time_status & STA_FREQHOLD || time_reftime == 0)
298 time_reftime = xtime.tv_sec;
299 mtemp = xtime.tv_sec - time_reftime;
300 time_reftime = xtime.tv_sec;
301 if (time_status & STA_FLL) {
302 if (mtemp >= MINSEC) {
303 ltemp = ((time_offset << 12) / mtemp) << (SHIFT_USEC - 12);
304 time_freq += shift_right(ltemp, SHIFT_KH);
305 } else /* calibration interval too short (p. 12) */
307 } else { /* PLL mode */
308 if (mtemp < MAXSEC) {
310 time_freq += shift_right(ltemp,(time_constant +
312 SHIFT_KF - SHIFT_USEC));
313 } else /* calibration interval too long (p. 12) */
316 time_freq = min(time_freq, time_tolerance);
317 time_freq = max(time_freq, -time_tolerance);
318 time_offset = (time_offset * NSEC_PER_USEC / HZ) << SHIFT_UPDATE;
320 } /* txc->modes & ADJ_OFFSET */
321 if (txc->modes & ADJ_TICK)
322 tick_usec = txc->tick;
324 if (txc->modes & (ADJ_TICK|ADJ_FREQUENCY|ADJ_OFFSET))
325 ntp_update_frequency();
327 leave: if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
330 if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
331 txc->offset = save_adjust;
333 txc->offset = shift_right(time_offset, SHIFT_UPDATE) * HZ / 1000;
334 txc->freq = time_freq;
335 txc->maxerror = time_maxerror;
336 txc->esterror = time_esterror;
337 txc->status = time_status;
338 txc->constant = time_constant;
339 txc->precision = time_precision;
340 txc->tolerance = time_tolerance;
341 txc->tick = tick_usec;
343 /* PPS is not implemented, so these are zero */
352 write_sequnlock_irq(&xtime_lock);
353 do_gettimeofday(&txc->time);
354 notify_arch_cmos_timer();