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 1.13 2007/04/30 07:18:53 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>
46 #include <sys/thread2.h>
49 * Single-precision macros for 64-bit machines
51 typedef long long l_fp
;
52 #define L_ADD(v, u) ((v) += (u))
53 #define L_SUB(v, u) ((v) -= (u))
54 #define L_ADDHI(v, a) ((v) += (long long)(a) << 32)
55 #define L_NEG(v) ((v) = -(v))
56 #define L_RSHIFT(v, n) \
59 (v) = -(-(v) >> (n)); \
63 #define L_MPY(v, a) ((v) *= (a))
64 #define L_CLR(v) ((v) = 0)
65 #define L_ISNEG(v) ((v) < 0)
66 #define L_LINT(v, a) ((v) = (long long)(a) << 32)
67 #define L_GINT(v) ((v) < 0 ? -(-(v) >> 32) : (v) >> 32)
70 * Generic NTP kernel interface
72 * These routines constitute the Network Time Protocol (NTP) interfaces
73 * for user and daemon application programs. The ntp_gettime() routine
74 * provides the time, maximum error (synch distance) and estimated error
75 * (dispersion) to client user application programs. The ntp_adjtime()
76 * routine is used by the NTP daemon to adjust the system clock to an
77 * externally derived time. The time offset and related variables set by
78 * this routine are used by other routines in this module to adjust the
79 * phase and frequency of the clock discipline loop which controls the
82 * When the kernel time is reckoned directly in nanoseconds (NTP_NANO
83 * defined), the time at each tick interrupt is derived directly from
84 * the kernel time variable. When the kernel time is reckoned in
85 * microseconds, (NTP_NANO undefined), the time is derived from the
86 * kernel time variable together with a variable representing the
87 * leftover nanoseconds at the last tick interrupt. In either case, the
88 * current nanosecond time is reckoned from these values plus an
89 * interpolated value derived by the clock routines in another
90 * architecture-specific module. The interpolation can use either a
91 * dedicated counter or a processor cycle counter (PCC) implemented in
94 * Note that all routines must run at priority splclock or higher.
97 * Phase/frequency-lock loop (PLL/FLL) definitions
99 * The nanosecond clock discipline uses two variable types, time
100 * variables and frequency variables. Both types are represented as 64-
101 * bit fixed-point quantities with the decimal point between two 32-bit
102 * halves. On a 32-bit machine, each half is represented as a single
103 * word and mathematical operations are done using multiple-precision
104 * arithmetic. On a 64-bit machine, ordinary computer arithmetic is
107 * A time variable is a signed 64-bit fixed-point number in ns and
108 * fraction. It represents the remaining time offset to be amortized
109 * over succeeding tick interrupts. The maximum time offset is about
110 * 0.5 s and the resolution is about 2.3e-10 ns.
112 * 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
113 * 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
114 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
116 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
118 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
120 * A frequency variable is a signed 64-bit fixed-point number in ns/s
121 * and fraction. It represents the ns and fraction to be added to the
122 * kernel time variable at each second. The maximum frequency offset is
123 * about +-500000 ns/s and the resolution is about 2.3e-10 ns/s.
125 * 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
126 * 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
127 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
128 * |s s s s s s s s s s s s s| ns/s |
129 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
131 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
134 * The following variables establish the state of the PLL/FLL and the
135 * residual time and frequency offset of the local clock.
137 #define SHIFT_PLL 4 /* PLL loop gain (shift) */
138 #define SHIFT_FLL 2 /* FLL loop gain (shift) */
140 static int time_state
= TIME_OK
; /* clock state */
141 static int time_status
= STA_UNSYNC
; /* clock status bits */
142 static long time_tai
; /* TAI offset (s) */
143 static long time_monitor
; /* last time offset scaled (ns) */
144 static long time_constant
; /* poll interval (shift) (s) */
145 static long time_precision
= 1; /* clock precision (ns) */
146 static long time_maxerror
= MAXPHASE
/ 1000; /* maximum error (us) */
147 static long time_esterror
= MAXPHASE
/ 1000; /* estimated error (us) */
148 static long time_reftime
; /* time at last adjustment (s) */
149 static long time_tick
; /* nanoseconds per tick (ns) */
150 static l_fp time_offset
; /* time offset (ns) */
151 static l_fp time_freq
; /* frequency offset (ns/s) */
152 static l_fp time_adj
; /* tick adjust (ns/s) */
156 * The following variables are used when a pulse-per-second (PPS) signal
157 * is available and connected via a modem control lead. They establish
158 * the engineering parameters of the clock discipline loop when
159 * controlled by the PPS signal.
161 #define PPS_FAVG 2 /* min freq avg interval (s) (shift) */
162 #define PPS_FAVGDEF 8 /* default freq avg int (s) (shift) */
163 #define PPS_FAVGMAX 15 /* max freq avg interval (s) (shift) */
164 #define PPS_PAVG 4 /* phase avg interval (s) (shift) */
165 #define PPS_VALID 120 /* PPS signal watchdog max (s) */
166 #define PPS_MAXWANDER 100000 /* max PPS wander (ns/s) */
167 #define PPS_POPCORN 2 /* popcorn spike threshold (shift) */
169 static struct timespec pps_tf
[3]; /* phase median filter */
170 static l_fp pps_freq
; /* scaled frequency offset (ns/s) */
171 static long pps_fcount
; /* frequency accumulator */
172 static long pps_jitter
; /* nominal jitter (ns) */
173 static long pps_stabil
; /* nominal stability (scaled ns/s) */
174 static long pps_lastsec
; /* time at last calibration (s) */
175 static int pps_valid
; /* signal watchdog counter */
176 static int pps_shift
= PPS_FAVG
; /* interval duration (s) (shift) */
177 static int pps_shiftmax
= PPS_FAVGDEF
; /* max interval duration (s) (shift) */
178 static int pps_intcnt
; /* wander counter */
181 * PPS signal quality monitors
183 static long pps_calcnt
; /* calibration intervals */
184 static long pps_jitcnt
; /* jitter limit exceeded */
185 static long pps_stbcnt
; /* stability limit exceeded */
186 static long pps_errcnt
; /* calibration errors */
187 #endif /* PPS_SYNC */
189 * End of phase/frequency-lock loop (PLL/FLL) definitions
192 static void ntp_init(void);
193 static void hardupdate(long offset
);
196 * ntp_gettime() - NTP user application interface
198 * See the timex.h header file for synopsis and API description. Note
199 * that the TAI offset is returned in the ntvtimeval.tai structure
203 ntp_sysctl(SYSCTL_HANDLER_ARGS
)
205 struct ntptimeval ntv
; /* temporary structure */
206 struct timespec atv
; /* nanosecond time */
209 ntv
.time
.tv_sec
= atv
.tv_sec
;
210 ntv
.time
.tv_nsec
= atv
.tv_nsec
;
211 ntv
.maxerror
= time_maxerror
;
212 ntv
.esterror
= time_esterror
;
214 ntv
.time_state
= time_state
;
217 * Status word error decode. If any of these conditions occur,
218 * an error is returned, instead of the status word. Most
219 * applications will care only about the fact the system clock
220 * may not be trusted, not about the details.
222 * Hardware or software error
224 if ((time_status
& (STA_UNSYNC
| STA_CLOCKERR
)) ||
227 * PPS signal lost when either time or frequency synchronization
230 (time_status
& (STA_PPSFREQ
| STA_PPSTIME
) &&
231 !(time_status
& STA_PPSSIGNAL
)) ||
234 * PPS jitter exceeded when time synchronization requested
236 (time_status
& STA_PPSTIME
&&
237 time_status
& STA_PPSJITTER
) ||
240 * PPS wander exceeded or calibration error when frequency
241 * synchronization requested
243 (time_status
& STA_PPSFREQ
&&
244 time_status
& (STA_PPSWANDER
| STA_PPSERROR
)))
245 ntv
.time_state
= TIME_ERROR
;
246 return (sysctl_handle_opaque(oidp
, &ntv
, sizeof ntv
, req
));
249 SYSCTL_NODE(_kern
, OID_AUTO
, ntp_pll
, CTLFLAG_RW
, 0, "");
250 SYSCTL_PROC(_kern_ntp_pll
, OID_AUTO
, gettime
, CTLTYPE_OPAQUE
|CTLFLAG_RD
,
251 0, sizeof(struct ntptimeval
) , ntp_sysctl
, "S,ntptimeval", "");
254 SYSCTL_INT(_kern_ntp_pll
, OID_AUTO
, pps_shiftmax
, CTLFLAG_RW
, &pps_shiftmax
, 0, "");
255 SYSCTL_INT(_kern_ntp_pll
, OID_AUTO
, pps_shift
, CTLFLAG_RW
, &pps_shift
, 0, "");
256 SYSCTL_INT(_kern_ntp_pll
, OID_AUTO
, time_monitor
, CTLFLAG_RD
, &time_monitor
, 0, "");
258 SYSCTL_OPAQUE(_kern_ntp_pll
, OID_AUTO
, pps_freq
, CTLFLAG_RD
, &pps_freq
, sizeof(pps_freq
), "I", "");
259 SYSCTL_OPAQUE(_kern_ntp_pll
, OID_AUTO
, time_freq
, CTLFLAG_RD
, &time_freq
, sizeof(time_freq
), "I", "");
262 * ntp_adjtime() - NTP daemon application interface
264 * See the timex.h header file for synopsis and API description. Note
265 * that the timex.constant structure member has a dual purpose to set
266 * the time constant and to set the TAI offset.
269 sys_ntp_adjtime(struct ntp_adjtime_args
*uap
)
271 struct thread
*td
= curthread
;
272 struct timex ntv
; /* temporary structure */
273 long freq
; /* frequency ns/s) */
274 int modes
; /* mode bits from structure */
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);
348 * Note: the userland specified frequency is in seconds per second
349 * times 65536e+6. Multiply by a thousand and divide by 65336 to
352 if (modes
& MOD_FREQUENCY
) {
353 freq
= (ntv
.freq
* 1000LL) >> 16;
355 L_LINT(time_freq
, MAXFREQ
);
356 else if (freq
< -MAXFREQ
)
357 L_LINT(time_freq
, -MAXFREQ
);
359 L_LINT(time_freq
, freq
);
361 pps_freq
= time_freq
;
362 #endif /* PPS_SYNC */
366 * Retrieve all clock variables. Note that the TAI offset is
367 * returned only by ntp_gettime();
369 if (time_status
& STA_NANO
)
370 ntv
.offset
= time_monitor
;
372 ntv
.offset
= time_monitor
/ 1000; /* XXX rounding ? */
373 ntv
.freq
= L_GINT((time_freq
/ 1000LL) << 16);
374 ntv
.maxerror
= time_maxerror
;
375 ntv
.esterror
= time_esterror
;
376 ntv
.status
= time_status
;
377 ntv
.constant
= time_constant
;
378 if (time_status
& STA_NANO
)
379 ntv
.precision
= time_precision
;
381 ntv
.precision
= time_precision
/ 1000;
382 ntv
.tolerance
= MAXFREQ
* SCALE_PPM
;
384 ntv
.shift
= pps_shift
;
385 ntv
.ppsfreq
= L_GINT((pps_freq
/ 1000LL) << 16);
386 if (time_status
& STA_NANO
)
387 ntv
.jitter
= pps_jitter
;
389 ntv
.jitter
= pps_jitter
/ 1000;
390 ntv
.stabil
= pps_stabil
;
391 ntv
.calcnt
= pps_calcnt
;
392 ntv
.errcnt
= pps_errcnt
;
393 ntv
.jitcnt
= pps_jitcnt
;
394 ntv
.stbcnt
= pps_stbcnt
;
395 #endif /* PPS_SYNC */
398 error
= copyout((caddr_t
)&ntv
, (caddr_t
)uap
->tp
, sizeof(ntv
));
403 * Status word error decode. See comments in
404 * ntp_gettime() routine.
406 if ((time_status
& (STA_UNSYNC
| STA_CLOCKERR
)) ||
407 (time_status
& (STA_PPSFREQ
| STA_PPSTIME
) &&
408 !(time_status
& STA_PPSSIGNAL
)) ||
409 (time_status
& STA_PPSTIME
&&
410 time_status
& STA_PPSJITTER
) ||
411 (time_status
& STA_PPSFREQ
&&
412 time_status
& (STA_PPSWANDER
| STA_PPSERROR
))) {
413 uap
->sysmsg_result
= TIME_ERROR
;
415 uap
->sysmsg_result
= time_state
;
421 * second_overflow() - called after ntp_tick_adjust()
423 * This routine is ordinarily called from hardclock() whenever the seconds
424 * hand rolls over. It returns leap seconds to add or drop, and sets nsec_adj
425 * to the total adjustment to make over the next second in (ns << 32).
427 * This routine is only called by cpu #0.
430 ntp_update_second(time_t newsec
, int64_t *nsec_adj
)
432 l_fp ftemp
; /* 32/64-bit temporary */
436 * On rollover of the second both the nanosecond and microsecond
437 * clocks are updated and the state machine cranked as
438 * necessary. The phase adjustment to be used for the next
439 * second is calculated and the maximum error is increased by
442 time_maxerror
+= MAXFREQ
/ 1000;
445 * Leap second processing. If in leap-insert state at
446 * the end of the day, the system clock is set back one
447 * second; if in leap-delete state, the system clock is
448 * set ahead one second. The nano_time() routine or
449 * external clock driver will insure that reported time
450 * is always monotonic.
452 switch (time_state
) {
458 if (time_status
& STA_INS
)
459 time_state
= TIME_INS
;
460 else if (time_status
& STA_DEL
)
461 time_state
= TIME_DEL
;
465 * Insert second 23:59:60 following second
469 if (!(time_status
& STA_INS
))
470 time_state
= TIME_OK
;
471 else if ((newsec
) % 86400 == 0) {
473 time_state
= TIME_OOP
;
478 * Delete second 23:59:59.
481 if (!(time_status
& STA_DEL
))
482 time_state
= TIME_OK
;
483 else if (((newsec
) + 1) % 86400 == 0) {
486 time_state
= TIME_WAIT
;
491 * Insert second in progress.
495 time_state
= TIME_WAIT
;
499 * Wait for status bits to clear.
502 if (!(time_status
& (STA_INS
| STA_DEL
)))
503 time_state
= TIME_OK
;
507 * time_offset represents the total time adjustment we wish to
508 * make (over no particular period of time). time_freq represents
509 * the frequency compensation we wish to apply.
511 * time_adj represents the total adjustment we wish to make over
512 * one full second. hardclock usually applies this adjustment in
513 * time_adj / hz jumps, hz times a second.
517 /* XXX even if PPS signal dies we should finish adjustment ? */
518 if ((time_status
& STA_PPSTIME
) && (time_status
& STA_PPSSIGNAL
))
519 L_RSHIFT(ftemp
, pps_shift
);
521 L_RSHIFT(ftemp
, SHIFT_PLL
+ time_constant
);
523 L_RSHIFT(ftemp
, SHIFT_PLL
+ time_constant
);
524 #endif /* PPS_SYNC */
525 time_adj
= ftemp
; /* adjustment for part of the offset */
526 L_SUB(time_offset
, ftemp
);
527 L_ADD(time_adj
, time_freq
); /* add frequency correction */
528 *nsec_adj
= time_adj
;
533 time_status
&= ~STA_PPSSIGNAL
;
534 #endif /* PPS_SYNC */
539 * ntp_init() - initialize variables and structures
541 * This routine must be called after the kernel variables hz and tick
542 * are set or changed and before the next tick interrupt. In this
543 * particular implementation, these values are assumed set elsewhere in
544 * the kernel. The design allows the clock frequency and tick interval
545 * to be changed while the system is running. So, this routine should
546 * probably be integrated with the code that does that.
553 * The following variable must be initialized any time the
554 * kernel variable hz is changed.
556 time_tick
= NANOSECOND
/ hz
;
559 * The following variables are initialized only at startup. Only
560 * those structures not cleared by the compiler need to be
561 * initialized, and these only in the simulator. In the actual
562 * kernel, any nonzero values here will quickly evaporate.
567 pps_tf
[0].tv_sec
= pps_tf
[0].tv_nsec
= 0;
568 pps_tf
[1].tv_sec
= pps_tf
[1].tv_nsec
= 0;
569 pps_tf
[2].tv_sec
= pps_tf
[2].tv_nsec
= 0;
572 #endif /* PPS_SYNC */
575 SYSINIT(ntpclocks
, SI_BOOT2_CLOCKS
, SI_ORDER_FIRST
, ntp_init
, NULL
)
578 * hardupdate() - local clock update
580 * This routine is called by ntp_adjtime() to update the local clock
581 * phase and frequency. The implementation is of an adaptive-parameter,
582 * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
583 * time and frequency offset estimates for each call. If the kernel PPS
584 * discipline code is configured (PPS_SYNC), the PPS signal itself
585 * determines the new time offset, instead of the calling argument.
586 * Presumably, calls to ntp_adjtime() occur only when the caller
587 * believes the local clock is valid within some bound (+-128 ms with
588 * NTP). If the caller's time is far different than the PPS time, an
589 * argument will ensue, and it's not clear who will lose.
591 * For uncompensated quartz crystal oscillators and nominal update
592 * intervals less than 256 s, operation should be in phase-lock mode,
593 * where the loop is disciplined to phase. For update intervals greater
594 * than 1024 s, operation should be in frequency-lock mode, where the
595 * loop is disciplined to frequency. Between 256 s and 1024 s, the mode
596 * is selected by the STA_MODE status bit.
599 hardupdate(long offset
)
608 * Select how the phase is to be controlled and from which
609 * source. If the PPS signal is present and enabled to
610 * discipline the time, the PPS offset is used; otherwise, the
611 * argument offset is used.
613 if (!(time_status
& STA_PLL
))
615 if (!((time_status
& STA_PPSTIME
) && (time_status
& STA_PPSSIGNAL
))) {
616 if (offset
> MAXPHASE
)
617 time_monitor
= MAXPHASE
;
618 else if (offset
< -MAXPHASE
)
619 time_monitor
= -MAXPHASE
;
621 time_monitor
= offset
;
622 L_LINT(time_offset
, time_monitor
);
626 * Select how the frequency is to be controlled and in which
627 * mode (PLL or FLL). If the PPS signal is present and enabled
628 * to discipline the frequency, the PPS frequency is used;
629 * otherwise, the argument offset is used to compute it.
631 * gd_time_seconds is basically an uncompensated uptime. We use
632 * this for consistency.
634 if (time_status
& STA_PPSFREQ
&& time_status
& STA_PPSSIGNAL
) {
635 time_reftime
= time_second
;
638 if (time_status
& STA_FREQHOLD
|| time_reftime
== 0)
639 time_reftime
= time_second
;
640 mtemp
= time_second
- time_reftime
;
641 L_LINT(ftemp
, time_monitor
);
642 L_RSHIFT(ftemp
, (SHIFT_PLL
+ 2 + time_constant
) << 1);
644 L_ADD(time_freq
, ftemp
);
645 time_status
&= ~STA_MODE
;
646 if (mtemp
>= MINSEC
&& (time_status
& STA_FLL
|| mtemp
> MAXSEC
)) {
647 L_LINT(ftemp
, (time_monitor
<< 4) / mtemp
);
648 L_RSHIFT(ftemp
, SHIFT_FLL
+ 4);
649 L_ADD(time_freq
, ftemp
);
650 time_status
|= STA_MODE
;
652 time_reftime
= time_second
;
653 if (L_GINT(time_freq
) > MAXFREQ
)
654 L_LINT(time_freq
, MAXFREQ
);
655 else if (L_GINT(time_freq
) < -MAXFREQ
)
656 L_LINT(time_freq
, -MAXFREQ
);
661 * hardpps() - discipline CPU clock oscillator to external PPS signal
663 * This routine is called at each PPS interrupt in order to discipline
664 * the CPU clock oscillator to the PPS signal. There are two independent
665 * first-order feedback loops, one for the phase, the other for the
666 * frequency. The phase loop measures and grooms the PPS phase offset
667 * and leaves it in a handy spot for the seconds overflow routine. The
668 * frequency loop averages successive PPS phase differences and
669 * calculates the PPS frequency offset, which is also processed by the
670 * seconds overflow routine. The code requires the caller to capture the
671 * time and architecture-dependent hardware counter values in
672 * nanoseconds at the on-time PPS signal transition.
674 * Note that, on some Unix systems this routine runs at an interrupt
675 * priority level higher than the timer interrupt routine hardclock().
676 * Therefore, the variables used are distinct from the hardclock()
677 * variables, except for the actual time and frequency variables, which
678 * are determined by this routine and updated atomically.
681 hardpps(struct timespec
*tsp
, long nsec
)
683 long u_sec
, u_nsec
, v_nsec
; /* temps */
687 * The signal is first processed by a range gate and frequency
688 * discriminator. The range gate rejects noise spikes outside
689 * the range +-500 us. The frequency discriminator rejects input
690 * signals with apparent frequency outside the range 1 +-500
691 * PPM. If two hits occur in the same second, we ignore the
692 * later hit; if not and a hit occurs outside the range gate,
693 * keep the later hit for later comparison, but do not process
696 time_status
|= STA_PPSSIGNAL
| STA_PPSJITTER
;
697 time_status
&= ~(STA_PPSWANDER
| STA_PPSERROR
);
698 pps_valid
= PPS_VALID
;
700 u_nsec
= tsp
->tv_nsec
;
701 if (u_nsec
>= (NANOSECOND
>> 1)) {
702 u_nsec
-= NANOSECOND
;
705 v_nsec
= u_nsec
- pps_tf
[0].tv_nsec
;
706 if (u_sec
== pps_tf
[0].tv_sec
&& v_nsec
< NANOSECOND
-
709 pps_tf
[2] = pps_tf
[1];
710 pps_tf
[1] = pps_tf
[0];
711 pps_tf
[0].tv_sec
= u_sec
;
712 pps_tf
[0].tv_nsec
= u_nsec
;
715 * Compute the difference between the current and previous
716 * counter values. If the difference exceeds 0.5 s, assume it
717 * has wrapped around, so correct 1.0 s. If the result exceeds
718 * the tick interval, the sample point has crossed a tick
719 * boundary during the last second, so correct the tick. Very
723 if (u_nsec
> (NANOSECOND
>> 1))
724 u_nsec
-= NANOSECOND
;
725 else if (u_nsec
< -(NANOSECOND
>> 1))
726 u_nsec
+= NANOSECOND
;
727 pps_fcount
+= u_nsec
;
728 if (v_nsec
> MAXFREQ
|| v_nsec
< -MAXFREQ
)
730 time_status
&= ~STA_PPSJITTER
;
733 * A three-stage median filter is used to help denoise the PPS
734 * time. The median sample becomes the time offset estimate; the
735 * difference between the other two samples becomes the time
736 * dispersion (jitter) estimate.
738 if (pps_tf
[0].tv_nsec
> pps_tf
[1].tv_nsec
) {
739 if (pps_tf
[1].tv_nsec
> pps_tf
[2].tv_nsec
) {
740 v_nsec
= pps_tf
[1].tv_nsec
; /* 0 1 2 */
741 u_nsec
= pps_tf
[0].tv_nsec
- pps_tf
[2].tv_nsec
;
742 } else if (pps_tf
[2].tv_nsec
> pps_tf
[0].tv_nsec
) {
743 v_nsec
= pps_tf
[0].tv_nsec
; /* 2 0 1 */
744 u_nsec
= pps_tf
[2].tv_nsec
- pps_tf
[1].tv_nsec
;
746 v_nsec
= pps_tf
[2].tv_nsec
; /* 0 2 1 */
747 u_nsec
= pps_tf
[0].tv_nsec
- pps_tf
[1].tv_nsec
;
750 if (pps_tf
[1].tv_nsec
< pps_tf
[2].tv_nsec
) {
751 v_nsec
= pps_tf
[1].tv_nsec
; /* 2 1 0 */
752 u_nsec
= pps_tf
[2].tv_nsec
- pps_tf
[0].tv_nsec
;
753 } else if (pps_tf
[2].tv_nsec
< pps_tf
[0].tv_nsec
) {
754 v_nsec
= pps_tf
[0].tv_nsec
; /* 1 0 2 */
755 u_nsec
= pps_tf
[1].tv_nsec
- pps_tf
[2].tv_nsec
;
757 v_nsec
= pps_tf
[2].tv_nsec
; /* 1 2 0 */
758 u_nsec
= pps_tf
[1].tv_nsec
- pps_tf
[0].tv_nsec
;
763 * Nominal jitter is due to PPS signal noise and interrupt
764 * latency. If it exceeds the popcorn threshold, the sample is
765 * discarded. otherwise, if so enabled, the time offset is
766 * updated. We can tolerate a modest loss of data here without
767 * much degrading time accuracy.
769 if (u_nsec
> (pps_jitter
<< PPS_POPCORN
)) {
770 time_status
|= STA_PPSJITTER
;
772 } else if (time_status
& STA_PPSTIME
) {
773 time_monitor
= -v_nsec
;
774 L_LINT(time_offset
, time_monitor
);
776 pps_jitter
+= (u_nsec
- pps_jitter
) >> PPS_FAVG
;
777 u_sec
= pps_tf
[0].tv_sec
- pps_lastsec
;
778 if (u_sec
< (1 << pps_shift
))
782 * At the end of the calibration interval the difference between
783 * the first and last counter values becomes the scaled
784 * frequency. It will later be divided by the length of the
785 * interval to determine the frequency update. If the frequency
786 * exceeds a sanity threshold, or if the actual calibration
787 * interval is not equal to the expected length, the data are
788 * discarded. We can tolerate a modest loss of data here without
789 * much degrading frequency accuracy.
792 v_nsec
= -pps_fcount
;
793 pps_lastsec
= pps_tf
[0].tv_sec
;
795 u_nsec
= MAXFREQ
<< pps_shift
;
796 if (v_nsec
> u_nsec
|| v_nsec
< -u_nsec
|| u_sec
!= (1 <<
798 time_status
|= STA_PPSERROR
;
804 * Here the raw frequency offset and wander (stability) is
805 * calculated. If the wander is less than the wander threshold
806 * for four consecutive averaging intervals, the interval is
807 * doubled; if it is greater than the threshold for four
808 * consecutive intervals, the interval is halved. The scaled
809 * frequency offset is converted to frequency offset. The
810 * stability metric is calculated as the average of recent
811 * frequency changes, but is used only for performance
814 L_LINT(ftemp
, v_nsec
);
815 L_RSHIFT(ftemp
, pps_shift
);
816 L_SUB(ftemp
, pps_freq
);
817 u_nsec
= L_GINT(ftemp
);
818 if (u_nsec
> PPS_MAXWANDER
) {
819 L_LINT(ftemp
, PPS_MAXWANDER
);
821 time_status
|= STA_PPSWANDER
;
823 } else if (u_nsec
< -PPS_MAXWANDER
) {
824 L_LINT(ftemp
, -PPS_MAXWANDER
);
826 time_status
|= STA_PPSWANDER
;
831 if (pps_intcnt
>= 4) {
833 if (pps_shift
< pps_shiftmax
) {
837 } else if (pps_intcnt
<= -4 || pps_shift
> pps_shiftmax
) {
839 if (pps_shift
> PPS_FAVG
) {
846 pps_stabil
+= (u_nsec
* SCALE_PPM
- pps_stabil
) >> PPS_FAVG
;
849 * The PPS frequency is recalculated and clamped to the maximum
850 * MAXFREQ. If enabled, the system clock frequency is updated as
853 L_ADD(pps_freq
, ftemp
);
854 u_nsec
= L_GINT(pps_freq
);
855 if (u_nsec
> MAXFREQ
)
856 L_LINT(pps_freq
, MAXFREQ
);
857 else if (u_nsec
< -MAXFREQ
)
858 L_LINT(pps_freq
, -MAXFREQ
);
859 if (time_status
& STA_PPSFREQ
)
860 time_freq
= pps_freq
;
862 #endif /* PPS_SYNC */