1 /***********************************************************************
3 * Copyright (c) David L. Mills 1993-2001 *
5 * Permission to use, copy, modify, and distribute this software and *
6 * its documentation for any purpose and without fee is hereby *
7 * granted, provided that the above copyright notice appears in all *
8 * copies and that both the copyright notice and this permission *
9 * notice appear in supporting documentation, and that the name *
10 * University of Delaware not be used in advertising or publicity *
11 * pertaining to distribution of the software without specific, *
12 * written prior permission. The University of Delaware makes no *
13 * representations about the suitability this software for any *
14 * purpose. It is provided "as is" without express or implied *
17 **********************************************************************/
20 * Adapted from the original sources for FreeBSD and timecounters by:
21 * Poul-Henning Kamp <phk@FreeBSD.org>.
23 * The 32bit version of the "LP" macros seems a bit past its "sell by"
24 * date so I have retained only the 64bit version and included it directly
27 * Only minor changes done to interface with the timecounters over in
28 * sys/kern/kern_clock.c. Some of the comments below may be (even more)
29 * confusing and/or plain wrong in that context.
31 * $FreeBSD: src/sys/kern/kern_ntptime.c,v 1.32.2.2 2001/04/22 11:19:46 jhay Exp $
32 * $DragonFly: src/sys/kern/kern_ntptime.c,v 1.6 2003/07/26 18:12:44 dillon Exp $
37 #include <sys/param.h>
38 #include <sys/systm.h>
39 #include <sys/sysproto.h>
40 #include <sys/kernel.h>
43 #include <sys/timex.h>
44 #include <sys/timepps.h>
45 #include <sys/sysctl.h>
48 * Single-precision macros for 64-bit machines
50 typedef long long l_fp;
51 #define L_ADD(v, u) ((v) += (u))
52 #define L_SUB(v, u) ((v) -= (u))
53 #define L_ADDHI(v, a) ((v) += (long long)(a) << 32)
54 #define L_NEG(v) ((v) = -(v))
55 #define L_RSHIFT(v, n) \
58 (v) = -(-(v) >> (n)); \
62 #define L_MPY(v, a) ((v) *= (a))
63 #define L_CLR(v) ((v) = 0)
64 #define L_ISNEG(v) ((v) < 0)
65 #define L_LINT(v, a) ((v) = (long long)(a) << 32)
66 #define L_GINT(v) ((v) < 0 ? -(-(v) >> 32) : (v) >> 32)
69 * Generic NTP kernel interface
71 * These routines constitute the Network Time Protocol (NTP) interfaces
72 * for user and daemon application programs. The ntp_gettime() routine
73 * provides the time, maximum error (synch distance) and estimated error
74 * (dispersion) to client user application programs. The ntp_adjtime()
75 * routine is used by the NTP daemon to adjust the system clock to an
76 * externally derived time. The time offset and related variables set by
77 * this routine are used by other routines in this module to adjust the
78 * phase and frequency of the clock discipline loop which controls the
81 * When the kernel time is reckoned directly in nanoseconds (NTP_NANO
82 * defined), the time at each tick interrupt is derived directly from
83 * the kernel time variable. When the kernel time is reckoned in
84 * microseconds, (NTP_NANO undefined), the time is derived from the
85 * kernel time variable together with a variable representing the
86 * leftover nanoseconds at the last tick interrupt. In either case, the
87 * current nanosecond time is reckoned from these values plus an
88 * interpolated value derived by the clock routines in another
89 * architecture-specific module. The interpolation can use either a
90 * dedicated counter or a processor cycle counter (PCC) implemented in
93 * Note that all routines must run at priority splclock or higher.
96 * Phase/frequency-lock loop (PLL/FLL) definitions
98 * The nanosecond clock discipline uses two variable types, time
99 * variables and frequency variables. Both types are represented as 64-
100 * bit fixed-point quantities with the decimal point between two 32-bit
101 * halves. On a 32-bit machine, each half is represented as a single
102 * word and mathematical operations are done using multiple-precision
103 * arithmetic. On a 64-bit machine, ordinary computer arithmetic is
106 * A time variable is a signed 64-bit fixed-point number in ns and
107 * fraction. It represents the remaining time offset to be amortized
108 * over succeeding tick interrupts. The maximum time offset is about
109 * 0.5 s and the resolution is about 2.3e-10 ns.
111 * 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
112 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
113 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
115 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
117 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
119 * A frequency variable is a signed 64-bit fixed-point number in ns/s
120 * and fraction. It represents the ns and fraction to be added to the
121 * kernel time variable at each second. The maximum frequency offset is
122 * about +-500000 ns/s and the resolution is about 2.3e-10 ns/s.
124 * 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
125 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
126 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
127 * |s s s s s s s s s s s s s| ns/s |
128 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
130 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
133 * The following variables establish the state of the PLL/FLL and the
134 * residual time and frequency offset of the local clock.
136 #define SHIFT_PLL 4 /* PLL loop gain (shift) */
137 #define SHIFT_FLL 2 /* FLL loop gain (shift) */
139 static int time_state = TIME_OK; /* clock state */
140 static int time_status = STA_UNSYNC; /* clock status bits */
141 static long time_tai; /* TAI offset (s) */
142 static long time_monitor; /* last time offset scaled (ns) */
143 static long time_constant; /* poll interval (shift) (s) */
144 static long time_precision = 1; /* clock precision (ns) */
145 static long time_maxerror = MAXPHASE / 1000; /* maximum error (us) */
146 static long time_esterror = MAXPHASE / 1000; /* estimated error (us) */
147 static long time_reftime; /* time at last adjustment (s) */
148 static long time_tick; /* nanoseconds per tick (ns) */
149 static l_fp time_offset; /* time offset (ns) */
150 static l_fp time_freq; /* frequency offset (ns/s) */
151 static l_fp time_adj; /* tick adjust (ns/s) */
155 * The following variables are used when a pulse-per-second (PPS) signal
156 * is available and connected via a modem control lead. They establish
157 * the engineering parameters of the clock discipline loop when
158 * controlled by the PPS signal.
160 #define PPS_FAVG 2 /* min freq avg interval (s) (shift) */
161 #define PPS_FAVGDEF 8 /* default freq avg int (s) (shift) */
162 #define PPS_FAVGMAX 15 /* max freq avg interval (s) (shift) */
163 #define PPS_PAVG 4 /* phase avg interval (s) (shift) */
164 #define PPS_VALID 120 /* PPS signal watchdog max (s) */
165 #define PPS_MAXWANDER 100000 /* max PPS wander (ns/s) */
166 #define PPS_POPCORN 2 /* popcorn spike threshold (shift) */
168 static struct timespec pps_tf[3]; /* phase median filter */
169 static l_fp pps_freq; /* scaled frequency offset (ns/s) */
170 static long pps_fcount; /* frequency accumulator */
171 static long pps_jitter; /* nominal jitter (ns) */
172 static long pps_stabil; /* nominal stability (scaled ns/s) */
173 static long pps_lastsec; /* time at last calibration (s) */
174 static int pps_valid; /* signal watchdog counter */
175 static int pps_shift = PPS_FAVG; /* interval duration (s) (shift) */
176 static int pps_shiftmax = PPS_FAVGDEF; /* max interval duration (s) (shift) */
177 static int pps_intcnt; /* wander counter */
180 * PPS signal quality monitors
182 static long pps_calcnt; /* calibration intervals */
183 static long pps_jitcnt; /* jitter limit exceeded */
184 static long pps_stbcnt; /* stability limit exceeded */
185 static long pps_errcnt; /* calibration errors */
186 #endif /* PPS_SYNC */
188 * End of phase/frequency-lock loop (PLL/FLL) definitions
191 static void ntp_init(void);
192 static void hardupdate(long offset);
195 * ntp_gettime() - NTP user application interface
197 * See the timex.h header file for synopsis and API description. Note
198 * that the TAI offset is returned in the ntvtimeval.tai structure
202 ntp_sysctl(SYSCTL_HANDLER_ARGS)
204 struct ntptimeval ntv; /* temporary structure */
205 struct timespec atv; /* nanosecond time */
208 ntv.time.tv_sec = atv.tv_sec;
209 ntv.time.tv_nsec = atv.tv_nsec;
210 ntv.maxerror = time_maxerror;
211 ntv.esterror = time_esterror;
213 ntv.time_state = time_state;
216 * Status word error decode. If any of these conditions occur,
217 * an error is returned, instead of the status word. Most
218 * applications will care only about the fact the system clock
219 * may not be trusted, not about the details.
221 * Hardware or software error
223 if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||
226 * PPS signal lost when either time or frequency synchronization
229 (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
230 !(time_status & STA_PPSSIGNAL)) ||
233 * PPS jitter exceeded when time synchronization requested
235 (time_status & STA_PPSTIME &&
236 time_status & STA_PPSJITTER) ||
239 * PPS wander exceeded or calibration error when frequency
240 * synchronization requested
242 (time_status & STA_PPSFREQ &&
243 time_status & (STA_PPSWANDER | STA_PPSERROR)))
244 ntv.time_state = TIME_ERROR;
245 return (sysctl_handle_opaque(oidp, &ntv, sizeof ntv, req));
248 SYSCTL_NODE(_kern, OID_AUTO, ntp_pll, CTLFLAG_RW, 0, "");
249 SYSCTL_PROC(_kern_ntp_pll, OID_AUTO, gettime, CTLTYPE_OPAQUE|CTLFLAG_RD,
250 0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", "");
253 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shiftmax, CTLFLAG_RW, &pps_shiftmax, 0, "");
254 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shift, CTLFLAG_RW, &pps_shift, 0, "");
255 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, time_monitor, CTLFLAG_RD, &time_monitor, 0, "");
257 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, &pps_freq, sizeof(pps_freq), "I", "");
258 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, time_freq, CTLFLAG_RD, &time_freq, sizeof(time_freq), "I", "");
261 * ntp_adjtime() - NTP daemon application interface
263 * See the timex.h header file for synopsis and API description. Note
264 * that the timex.constant structure member has a dual purpose to set
265 * the time constant and to set the TAI offset.
268 ntp_adjtime(struct ntp_adjtime_args *uap)
270 struct thread *td = curthread;
271 struct timex ntv; /* temporary structure */
272 long freq; /* frequency ns/s) */
273 int modes; /* mode bits from structure */
274 int s; /* caller priority */
277 error = copyin((caddr_t)uap->tp, (caddr_t)&ntv, sizeof(ntv));
282 * Update selected clock variables - only the superuser can
283 * change anything. Note that there is no error checking here on
284 * the assumption the superuser should know what it is doing.
285 * Note that either the time constant or TAI offset are loaded
286 * from the ntv.constant member, depending on the mode bits. If
287 * the STA_PLL bit in the status word is cleared, the state and
288 * status words are reset to the initial values at boot.
296 if (modes & MOD_MAXERROR)
297 time_maxerror = ntv.maxerror;
298 if (modes & MOD_ESTERROR)
299 time_esterror = ntv.esterror;
300 if (modes & MOD_STATUS) {
301 if (time_status & STA_PLL && !(ntv.status & STA_PLL)) {
302 time_state = TIME_OK;
303 time_status = STA_UNSYNC;
305 pps_shift = PPS_FAVG;
306 #endif /* PPS_SYNC */
308 time_status &= STA_RONLY;
309 time_status |= ntv.status & ~STA_RONLY;
311 if (modes & MOD_TIMECONST) {
312 if (ntv.constant < 0)
314 else if (ntv.constant > MAXTC)
315 time_constant = MAXTC;
317 time_constant = ntv.constant;
319 if (modes & MOD_TAI) {
320 if (ntv.constant > 0) /* XXX zero & negative numbers ? */
321 time_tai = ntv.constant;
324 if (modes & MOD_PPSMAX) {
325 if (ntv.shift < PPS_FAVG)
326 pps_shiftmax = PPS_FAVG;
327 else if (ntv.shift > PPS_FAVGMAX)
328 pps_shiftmax = PPS_FAVGMAX;
330 pps_shiftmax = ntv.shift;
332 #endif /* PPS_SYNC */
333 if (modes & MOD_NANO)
334 time_status |= STA_NANO;
335 if (modes & MOD_MICRO)
336 time_status &= ~STA_NANO;
337 if (modes & MOD_CLKB)
338 time_status |= STA_CLK;
339 if (modes & MOD_CLKA)
340 time_status &= ~STA_CLK;
341 if (modes & MOD_OFFSET) {
342 if (time_status & STA_NANO)
343 hardupdate(ntv.offset);
345 hardupdate(ntv.offset * 1000);
347 if (modes & MOD_FREQUENCY) {
348 freq = (ntv.freq * 1000LL) >> 16;
350 L_LINT(time_freq, MAXFREQ);
351 else if (freq < -MAXFREQ)
352 L_LINT(time_freq, -MAXFREQ);
354 L_LINT(time_freq, freq);
356 pps_freq = time_freq;
357 #endif /* PPS_SYNC */
361 * Retrieve all clock variables. Note that the TAI offset is
362 * returned only by ntp_gettime();
364 if (time_status & STA_NANO)
365 ntv.offset = time_monitor;
367 ntv.offset = time_monitor / 1000; /* XXX rounding ? */
368 ntv.freq = L_GINT((time_freq / 1000LL) << 16);
369 ntv.maxerror = time_maxerror;
370 ntv.esterror = time_esterror;
371 ntv.status = time_status;
372 ntv.constant = time_constant;
373 if (time_status & STA_NANO)
374 ntv.precision = time_precision;
376 ntv.precision = time_precision / 1000;
377 ntv.tolerance = MAXFREQ * SCALE_PPM;
379 ntv.shift = pps_shift;
380 ntv.ppsfreq = L_GINT((pps_freq / 1000LL) << 16);
381 if (time_status & STA_NANO)
382 ntv.jitter = pps_jitter;
384 ntv.jitter = pps_jitter / 1000;
385 ntv.stabil = pps_stabil;
386 ntv.calcnt = pps_calcnt;
387 ntv.errcnt = pps_errcnt;
388 ntv.jitcnt = pps_jitcnt;
389 ntv.stbcnt = pps_stbcnt;
390 #endif /* PPS_SYNC */
393 error = copyout((caddr_t)&ntv, (caddr_t)uap->tp, sizeof(ntv));
398 * Status word error decode. See comments in
399 * ntp_gettime() routine.
401 if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||
402 (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
403 !(time_status & STA_PPSSIGNAL)) ||
404 (time_status & STA_PPSTIME &&
405 time_status & STA_PPSJITTER) ||
406 (time_status & STA_PPSFREQ &&
407 time_status & (STA_PPSWANDER | STA_PPSERROR))) {
408 uap->lmsg.u.ms_result = TIME_ERROR;
410 uap->lmsg.u.ms_result = time_state;
416 * second_overflow() - called after ntp_tick_adjust()
418 * This routine is ordinarily called immediately following the above
419 * routine ntp_tick_adjust(). While these two routines are normally
420 * combined, they are separated here only for the purposes of
424 ntp_update_second(struct timecounter *tcp)
427 l_fp ftemp; /* 32/64-bit temporary */
429 newsec = &tcp->tc_offset_sec;
431 * On rollover of the second both the nanosecond and microsecond
432 * clocks are updated and the state machine cranked as
433 * necessary. The phase adjustment to be used for the next
434 * second is calculated and the maximum error is increased by
437 time_maxerror += MAXFREQ / 1000;
440 * Leap second processing. If in leap-insert state at
441 * the end of the day, the system clock is set back one
442 * second; if in leap-delete state, the system clock is
443 * set ahead one second. The nano_time() routine or
444 * external clock driver will insure that reported time
445 * is always monotonic.
447 switch (time_state) {
453 if (time_status & STA_INS)
454 time_state = TIME_INS;
455 else if (time_status & STA_DEL)
456 time_state = TIME_DEL;
460 * Insert second 23:59:60 following second
464 if (!(time_status & STA_INS))
465 time_state = TIME_OK;
466 else if ((*newsec) % 86400 == 0) {
468 time_state = TIME_OOP;
473 * Delete second 23:59:59.
476 if (!(time_status & STA_DEL))
477 time_state = TIME_OK;
478 else if (((*newsec) + 1) % 86400 == 0) {
481 time_state = TIME_WAIT;
486 * Insert second in progress.
490 time_state = TIME_WAIT;
494 * Wait for status bits to clear.
497 if (!(time_status & (STA_INS | STA_DEL)))
498 time_state = TIME_OK;
502 * Compute the total time adjustment for the next second
503 * in ns. The offset is reduced by a factor depending on
504 * whether the PPS signal is operating. Note that the
505 * value is in effect scaled by the clock frequency,
506 * since the adjustment is added at each tick interrupt.
510 /* XXX even if PPS signal dies we should finish adjustment ? */
511 if (time_status & STA_PPSTIME && time_status &
513 L_RSHIFT(ftemp, pps_shift);
515 L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
517 L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
518 #endif /* PPS_SYNC */
520 L_SUB(time_offset, ftemp);
521 L_ADD(time_adj, time_freq);
522 tcp->tc_adjustment = time_adj;
527 time_status &= ~STA_PPSSIGNAL;
528 #endif /* PPS_SYNC */
532 * ntp_init() - initialize variables and structures
534 * This routine must be called after the kernel variables hz and tick
535 * are set or changed and before the next tick interrupt. In this
536 * particular implementation, these values are assumed set elsewhere in
537 * the kernel. The design allows the clock frequency and tick interval
538 * to be changed while the system is running. So, this routine should
539 * probably be integrated with the code that does that.
546 * The following variable must be initialized any time the
547 * kernel variable hz is changed.
549 time_tick = NANOSECOND / hz;
552 * The following variables are initialized only at startup. Only
553 * those structures not cleared by the compiler need to be
554 * initialized, and these only in the simulator. In the actual
555 * kernel, any nonzero values here will quickly evaporate.
560 pps_tf[0].tv_sec = pps_tf[0].tv_nsec = 0;
561 pps_tf[1].tv_sec = pps_tf[1].tv_nsec = 0;
562 pps_tf[2].tv_sec = pps_tf[2].tv_nsec = 0;
565 #endif /* PPS_SYNC */
568 SYSINIT(ntpclocks, SI_SUB_CLOCKS, SI_ORDER_FIRST, ntp_init, NULL)
571 * hardupdate() - local clock update
573 * This routine is called by ntp_adjtime() to update the local clock
574 * phase and frequency. The implementation is of an adaptive-parameter,
575 * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
576 * time and frequency offset estimates for each call. If the kernel PPS
577 * discipline code is configured (PPS_SYNC), the PPS signal itself
578 * determines the new time offset, instead of the calling argument.
579 * Presumably, calls to ntp_adjtime() occur only when the caller
580 * believes the local clock is valid within some bound (+-128 ms with
581 * NTP). If the caller's time is far different than the PPS time, an
582 * argument will ensue, and it's not clear who will lose.
584 * For uncompensated quartz crystal oscillators and nominal update
585 * intervals less than 256 s, operation should be in phase-lock mode,
586 * where the loop is disciplined to phase. For update intervals greater
587 * than 1024 s, operation should be in frequency-lock mode, where the
588 * loop is disciplined to frequency. Between 256 s and 1024 s, the mode
589 * is selected by the STA_MODE status bit.
593 long offset; /* clock offset (ns) */
599 * Select how the phase is to be controlled and from which
600 * source. If the PPS signal is present and enabled to
601 * discipline the time, the PPS offset is used; otherwise, the
602 * argument offset is used.
604 if (!(time_status & STA_PLL))
606 if (!(time_status & STA_PPSTIME && time_status &
608 if (offset > MAXPHASE)
609 time_monitor = MAXPHASE;
610 else if (offset < -MAXPHASE)
611 time_monitor = -MAXPHASE;
613 time_monitor = offset;
614 L_LINT(time_offset, time_monitor);
618 * Select how the frequency is to be controlled and in which
619 * mode (PLL or FLL). If the PPS signal is present and enabled
620 * to discipline the frequency, the PPS frequency is used;
621 * otherwise, the argument offset is used to compute it.
623 if (time_status & STA_PPSFREQ && time_status & STA_PPSSIGNAL) {
624 time_reftime = time_second;
627 if (time_status & STA_FREQHOLD || time_reftime == 0)
628 time_reftime = time_second;
629 mtemp = time_second - time_reftime;
630 L_LINT(ftemp, time_monitor);
631 L_RSHIFT(ftemp, (SHIFT_PLL + 2 + time_constant) << 1);
633 L_ADD(time_freq, ftemp);
634 time_status &= ~STA_MODE;
635 if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp >
637 L_LINT(ftemp, (time_monitor << 4) / mtemp);
638 L_RSHIFT(ftemp, SHIFT_FLL + 4);
639 L_ADD(time_freq, ftemp);
640 time_status |= STA_MODE;
642 time_reftime = time_second;
643 if (L_GINT(time_freq) > MAXFREQ)
644 L_LINT(time_freq, MAXFREQ);
645 else if (L_GINT(time_freq) < -MAXFREQ)
646 L_LINT(time_freq, -MAXFREQ);
651 * hardpps() - discipline CPU clock oscillator to external PPS signal
653 * This routine is called at each PPS interrupt in order to discipline
654 * the CPU clock oscillator to the PPS signal. There are two independent
655 * first-order feedback loops, one for the phase, the other for the
656 * frequency. The phase loop measures and grooms the PPS phase offset
657 * and leaves it in a handy spot for the seconds overflow routine. The
658 * frequency loop averages successive PPS phase differences and
659 * calculates the PPS frequency offset, which is also processed by the
660 * seconds overflow routine. The code requires the caller to capture the
661 * time and architecture-dependent hardware counter values in
662 * nanoseconds at the on-time PPS signal transition.
664 * Note that, on some Unix systems this routine runs at an interrupt
665 * priority level higher than the timer interrupt routine hardclock().
666 * Therefore, the variables used are distinct from the hardclock()
667 * variables, except for the actual time and frequency variables, which
668 * are determined by this routine and updated atomically.
672 struct timespec *tsp; /* time at PPS */
673 long nsec; /* hardware counter at PPS */
675 long u_sec, u_nsec, v_nsec; /* temps */
679 * The signal is first processed by a range gate and frequency
680 * discriminator. The range gate rejects noise spikes outside
681 * the range +-500 us. The frequency discriminator rejects input
682 * signals with apparent frequency outside the range 1 +-500
683 * PPM. If two hits occur in the same second, we ignore the
684 * later hit; if not and a hit occurs outside the range gate,
685 * keep the later hit for later comparison, but do not process
688 time_status |= STA_PPSSIGNAL | STA_PPSJITTER;
689 time_status &= ~(STA_PPSWANDER | STA_PPSERROR);
690 pps_valid = PPS_VALID;
692 u_nsec = tsp->tv_nsec;
693 if (u_nsec >= (NANOSECOND >> 1)) {
694 u_nsec -= NANOSECOND;
697 v_nsec = u_nsec - pps_tf[0].tv_nsec;
698 if (u_sec == pps_tf[0].tv_sec && v_nsec < NANOSECOND -
701 pps_tf[2] = pps_tf[1];
702 pps_tf[1] = pps_tf[0];
703 pps_tf[0].tv_sec = u_sec;
704 pps_tf[0].tv_nsec = u_nsec;
707 * Compute the difference between the current and previous
708 * counter values. If the difference exceeds 0.5 s, assume it
709 * has wrapped around, so correct 1.0 s. If the result exceeds
710 * the tick interval, the sample point has crossed a tick
711 * boundary during the last second, so correct the tick. Very
715 if (u_nsec > (NANOSECOND >> 1))
716 u_nsec -= NANOSECOND;
717 else if (u_nsec < -(NANOSECOND >> 1))
718 u_nsec += NANOSECOND;
719 pps_fcount += u_nsec;
720 if (v_nsec > MAXFREQ || v_nsec < -MAXFREQ)
722 time_status &= ~STA_PPSJITTER;
725 * A three-stage median filter is used to help denoise the PPS
726 * time. The median sample becomes the time offset estimate; the
727 * difference between the other two samples becomes the time
728 * dispersion (jitter) estimate.
730 if (pps_tf[0].tv_nsec > pps_tf[1].tv_nsec) {
731 if (pps_tf[1].tv_nsec > pps_tf[2].tv_nsec) {
732 v_nsec = pps_tf[1].tv_nsec; /* 0 1 2 */
733 u_nsec = pps_tf[0].tv_nsec - pps_tf[2].tv_nsec;
734 } else if (pps_tf[2].tv_nsec > pps_tf[0].tv_nsec) {
735 v_nsec = pps_tf[0].tv_nsec; /* 2 0 1 */
736 u_nsec = pps_tf[2].tv_nsec - pps_tf[1].tv_nsec;
738 v_nsec = pps_tf[2].tv_nsec; /* 0 2 1 */
739 u_nsec = pps_tf[0].tv_nsec - pps_tf[1].tv_nsec;
742 if (pps_tf[1].tv_nsec < pps_tf[2].tv_nsec) {
743 v_nsec = pps_tf[1].tv_nsec; /* 2 1 0 */
744 u_nsec = pps_tf[2].tv_nsec - pps_tf[0].tv_nsec;
745 } else if (pps_tf[2].tv_nsec < pps_tf[0].tv_nsec) {
746 v_nsec = pps_tf[0].tv_nsec; /* 1 0 2 */
747 u_nsec = pps_tf[1].tv_nsec - pps_tf[2].tv_nsec;
749 v_nsec = pps_tf[2].tv_nsec; /* 1 2 0 */
750 u_nsec = pps_tf[1].tv_nsec - pps_tf[0].tv_nsec;
755 * Nominal jitter is due to PPS signal noise and interrupt
756 * latency. If it exceeds the popcorn threshold, the sample is
757 * discarded. otherwise, if so enabled, the time offset is
758 * updated. We can tolerate a modest loss of data here without
759 * much degrading time accuracy.
761 if (u_nsec > (pps_jitter << PPS_POPCORN)) {
762 time_status |= STA_PPSJITTER;
764 } else if (time_status & STA_PPSTIME) {
765 time_monitor = -v_nsec;
766 L_LINT(time_offset, time_monitor);
768 pps_jitter += (u_nsec - pps_jitter) >> PPS_FAVG;
769 u_sec = pps_tf[0].tv_sec - pps_lastsec;
770 if (u_sec < (1 << pps_shift))
774 * At the end of the calibration interval the difference between
775 * the first and last counter values becomes the scaled
776 * frequency. It will later be divided by the length of the
777 * interval to determine the frequency update. If the frequency
778 * exceeds a sanity threshold, or if the actual calibration
779 * interval is not equal to the expected length, the data are
780 * discarded. We can tolerate a modest loss of data here without
781 * much degrading frequency accuracy.
784 v_nsec = -pps_fcount;
785 pps_lastsec = pps_tf[0].tv_sec;
787 u_nsec = MAXFREQ << pps_shift;
788 if (v_nsec > u_nsec || v_nsec < -u_nsec || u_sec != (1 <<
790 time_status |= STA_PPSERROR;
796 * Here the raw frequency offset and wander (stability) is
797 * calculated. If the wander is less than the wander threshold
798 * for four consecutive averaging intervals, the interval is
799 * doubled; if it is greater than the threshold for four
800 * consecutive intervals, the interval is halved. The scaled
801 * frequency offset is converted to frequency offset. The
802 * stability metric is calculated as the average of recent
803 * frequency changes, but is used only for performance
806 L_LINT(ftemp, v_nsec);
807 L_RSHIFT(ftemp, pps_shift);
808 L_SUB(ftemp, pps_freq);
809 u_nsec = L_GINT(ftemp);
810 if (u_nsec > PPS_MAXWANDER) {
811 L_LINT(ftemp, PPS_MAXWANDER);
813 time_status |= STA_PPSWANDER;
815 } else if (u_nsec < -PPS_MAXWANDER) {
816 L_LINT(ftemp, -PPS_MAXWANDER);
818 time_status |= STA_PPSWANDER;
823 if (pps_intcnt >= 4) {
825 if (pps_shift < pps_shiftmax) {
829 } else if (pps_intcnt <= -4 || pps_shift > pps_shiftmax) {
831 if (pps_shift > PPS_FAVG) {
838 pps_stabil += (u_nsec * SCALE_PPM - pps_stabil) >> PPS_FAVG;
841 * The PPS frequency is recalculated and clamped to the maximum
842 * MAXFREQ. If enabled, the system clock frequency is updated as
845 L_ADD(pps_freq, ftemp);
846 u_nsec = L_GINT(pps_freq);
847 if (u_nsec > MAXFREQ)
848 L_LINT(pps_freq, MAXFREQ);
849 else if (u_nsec < -MAXFREQ)
850 L_LINT(pps_freq, -MAXFREQ);
851 if (time_status & STA_PPSFREQ)
852 time_freq = pps_freq;
854 #endif /* PPS_SYNC */