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 $
36 #include <sys/param.h>
37 #include <sys/systm.h>
38 #include <sys/sysmsg.h>
39 #include <sys/kernel.h>
43 #include <sys/timex.h>
44 #include <sys/timepps.h>
45 #include <sys/sysctl.h>
47 #include <sys/thread2.h>
50 * Single-precision macros for 64-bit machines
52 typedef long long l_fp
;
53 #define L_ADD(v, u) ((v) += (u))
54 #define L_SUB(v, u) ((v) -= (u))
55 #define L_ADDHI(v, a) ((v) += (long long)(a) << 32)
56 #define L_NEG(v) ((v) = -(v))
57 #define L_RSHIFT(v, n) \
60 (v) = -(-(v) >> (n)); \
64 #define L_MPY(v, a) ((v) *= (a))
65 #define L_CLR(v) ((v) = 0)
66 #define L_ISNEG(v) ((v) < 0)
67 #define L_LINT(v, a) ((v) = (long long)(a) << 32)
68 #define L_GINT(v) ((v) < 0 ? -(-(v) >> 32) : (v) >> 32)
71 * Generic NTP kernel interface
73 * These routines constitute the Network Time Protocol (NTP) interfaces
74 * for user and daemon application programs. The ntp_gettime() routine
75 * provides the time, maximum error (synch distance) and estimated error
76 * (dispersion) to client user application programs. The ntp_adjtime()
77 * routine is used by the NTP daemon to adjust the system clock to an
78 * externally derived time. The time offset and related variables set by
79 * this routine are used by other routines in this module to adjust the
80 * phase and frequency of the clock discipline loop which controls the
83 * When the kernel time is reckoned directly in nanoseconds (NTP_NANO
84 * defined), the time at each tick interrupt is derived directly from
85 * the kernel time variable. When the kernel time is reckoned in
86 * microseconds, (NTP_NANO undefined), the time is derived from the
87 * kernel time variable together with a variable representing the
88 * leftover nanoseconds at the last tick interrupt. In either case, the
89 * current nanosecond time is reckoned from these values plus an
90 * interpolated value derived by the clock routines in another
91 * architecture-specific module. The interpolation can use either a
92 * dedicated counter or a processor cycle counter (PCC) implemented in
95 * Note that all routines must run at priority splclock or higher.
98 * Phase/frequency-lock loop (PLL/FLL) definitions
100 * The nanosecond clock discipline uses two variable types, time
101 * variables and frequency variables. Both types are represented as 64-
102 * bit fixed-point quantities with the decimal point between two 32-bit
103 * halves. On a 32-bit machine, each half is represented as a single
104 * word and mathematical operations are done using multiple-precision
105 * arithmetic. On a 64-bit machine, ordinary computer arithmetic is
108 * A time variable is a signed 64-bit fixed-point number in ns and
109 * fraction. It represents the remaining time offset to be amortized
110 * over succeeding tick interrupts. The maximum time offset is about
111 * 0.5 s and the resolution is about 2.3e-10 ns.
113 * 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
114 * 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
115 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
117 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
119 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
121 * A frequency variable is a signed 64-bit fixed-point number in ns/s
122 * and fraction. It represents the ns and fraction to be added to the
123 * kernel time variable at each second. The maximum frequency offset is
124 * about +-500000 ns/s and the resolution is about 2.3e-10 ns/s.
126 * 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
127 * 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
128 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
129 * |s s s s s s s s s s s s s| ns/s |
130 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
132 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
135 * The following variables establish the state of the PLL/FLL and the
136 * residual time and frequency offset of the local clock.
138 #define SHIFT_PLL 4 /* PLL loop gain (shift) */
139 #define SHIFT_FLL 2 /* FLL loop gain (shift) */
141 static int time_state
= TIME_OK
; /* clock state */
142 static int time_status
= STA_UNSYNC
; /* clock status bits */
143 static long time_tai
; /* TAI offset (s) */
144 static long time_monitor
; /* last time offset scaled (ns) */
145 static long time_constant
; /* poll interval (shift) (s) */
146 static long time_precision
= 1; /* clock precision (ns) */
147 static long time_maxerror
= MAXPHASE
/ 1000; /* maximum error (us) */
148 static long time_esterror
= MAXPHASE
/ 1000; /* estimated error (us) */
149 static time_t time_reftime
; /* time at last adjustment (s) */
150 static long time_tick
; /* nanoseconds per tick (ns) */
151 static l_fp time_offset
; /* time offset (ns) */
152 static l_fp time_freq
; /* frequency offset (ns/s) */
153 static l_fp time_adj
; /* tick adjust (ns/s) */
155 static struct lock ntp_lock
= LOCK_INITIALIZER("ntplk", 0, 0);
159 * The following variables are used when a pulse-per-second (PPS) signal
160 * is available and connected via a modem control lead. They establish
161 * the engineering parameters of the clock discipline loop when
162 * controlled by the PPS signal.
164 #define PPS_FAVG 2 /* min freq avg interval (s) (shift) */
165 #define PPS_FAVGDEF 8 /* default freq avg int (s) (shift) */
166 #define PPS_FAVGMAX 15 /* max freq avg interval (s) (shift) */
167 #define PPS_PAVG 4 /* phase avg interval (s) (shift) */
168 #define PPS_VALID 120 /* PPS signal watchdog max (s) */
169 #define PPS_MAXWANDER 100000 /* max PPS wander (ns/s) */
170 #define PPS_POPCORN 2 /* popcorn spike threshold (shift) */
172 static struct timespec pps_tf
[3]; /* phase median filter */
173 static l_fp pps_freq
; /* scaled frequency offset (ns/s) */
174 static long pps_fcount
; /* frequency accumulator */
175 static long pps_jitter
; /* nominal jitter (ns) */
176 static long pps_stabil
; /* nominal stability (scaled ns/s) */
177 static long pps_lastsec
; /* time at last calibration (s) */
178 static int pps_valid
; /* signal watchdog counter */
179 static int pps_shift
= PPS_FAVG
; /* interval duration (s) (shift) */
180 static int pps_shiftmax
= PPS_FAVGDEF
; /* max interval duration (s) (shift) */
181 static int pps_intcnt
; /* wander counter */
184 * PPS signal quality monitors
186 static long pps_calcnt
; /* calibration intervals */
187 static long pps_jitcnt
; /* jitter limit exceeded */
188 static long pps_stbcnt
; /* stability limit exceeded */
189 static long pps_errcnt
; /* calibration errors */
190 #endif /* PPS_SYNC */
192 * End of phase/frequency-lock loop (PLL/FLL) definitions
195 static void ntp_init(void);
196 static void hardupdate(long offset
);
199 * ntp_gettime() - NTP user application interface
201 * See the timex.h header file for synopsis and API description. Note
202 * that the TAI offset is returned in the ntvtimeval.tai structure
206 ntp_sysctl(SYSCTL_HANDLER_ARGS
)
208 struct ntptimeval ntv
; /* temporary structure */
209 struct timespec atv
; /* nanosecond time */
212 lockmgr(&ntp_lock
, LK_EXCLUSIVE
);
215 ntv
.time
.tv_sec
= atv
.tv_sec
;
216 ntv
.time
.tv_nsec
= atv
.tv_nsec
;
217 ntv
.maxerror
= time_maxerror
;
218 ntv
.esterror
= time_esterror
;
220 ntv
.time_state
= time_state
;
223 * Status word error decode. If any of these conditions occur,
224 * an error is returned, instead of the status word. Most
225 * applications will care only about the fact the system clock
226 * may not be trusted, not about the details.
228 * Hardware or software error
230 if ((time_status
& (STA_UNSYNC
| STA_CLOCKERR
)) ||
233 * PPS signal lost when either time or frequency synchronization
236 (time_status
& (STA_PPSFREQ
| STA_PPSTIME
) &&
237 !(time_status
& STA_PPSSIGNAL
)) ||
240 * PPS jitter exceeded when time synchronization requested
242 (time_status
& STA_PPSTIME
&&
243 time_status
& STA_PPSJITTER
) ||
246 * PPS wander exceeded or calibration error when frequency
247 * synchronization requested
249 (time_status
& STA_PPSFREQ
&&
250 time_status
& (STA_PPSWANDER
| STA_PPSERROR
))) {
251 ntv
.time_state
= TIME_ERROR
;
254 error
= sysctl_handle_opaque(oidp
, &ntv
, sizeof ntv
, req
);
255 lockmgr(&ntp_lock
, LK_RELEASE
);
260 SYSCTL_NODE(_kern
, OID_AUTO
, ntp_pll
, CTLFLAG_RW
, 0, "");
261 SYSCTL_PROC(_kern_ntp_pll
, OID_AUTO
, gettime
, CTLTYPE_OPAQUE
|CTLFLAG_RD
,
262 0, sizeof(struct ntptimeval
) , ntp_sysctl
, "S,ntptimeval", "");
265 SYSCTL_INT(_kern_ntp_pll
, OID_AUTO
, pps_shiftmax
, CTLFLAG_RW
, &pps_shiftmax
, 0, "");
266 SYSCTL_INT(_kern_ntp_pll
, OID_AUTO
, pps_shift
, CTLFLAG_RW
, &pps_shift
, 0, "");
267 SYSCTL_INT(_kern_ntp_pll
, OID_AUTO
, time_monitor
, CTLFLAG_RD
, &time_monitor
, 0, "");
269 SYSCTL_OPAQUE(_kern_ntp_pll
, OID_AUTO
, pps_freq
, CTLFLAG_RD
, &pps_freq
, sizeof(pps_freq
), "I", "");
270 SYSCTL_OPAQUE(_kern_ntp_pll
, OID_AUTO
, time_freq
, CTLFLAG_RD
, &time_freq
, sizeof(time_freq
), "I", "");
273 * ntp_adjtime() - NTP daemon application interface
275 * See the timex.h header file for synopsis and API description. Note
276 * that the timex.constant structure member has a dual purpose to set
277 * the time constant and to set the TAI offset.
282 sys_ntp_adjtime(struct sysmsg
*sysmsg
, const struct ntp_adjtime_args
*uap
)
284 struct timex ntv
; /* temporary structure */
285 long freq
; /* frequency ns/s) */
286 int modes
; /* mode bits from structure */
289 error
= copyin((caddr_t
)uap
->tp
, (caddr_t
)&ntv
, sizeof(ntv
));
294 * Update selected clock variables - only the superuser can
295 * change anything. Note that there is no error checking here on
296 * the assumption the superuser should know what it is doing.
297 * Note that either the time constant or TAI offset are loaded
298 * from the ntv.constant member, depending on the mode bits. If
299 * the STA_PLL bit in the status word is cleared, the state and
300 * status words are reset to the initial values at boot.
304 error
= caps_priv_check_self(SYSCAP_NOSETTIME
);
308 lockmgr(&ntp_lock
, LK_EXCLUSIVE
);
310 if (modes
& MOD_MAXERROR
)
311 time_maxerror
= ntv
.maxerror
;
312 if (modes
& MOD_ESTERROR
)
313 time_esterror
= ntv
.esterror
;
314 if (modes
& MOD_STATUS
) {
315 if (time_status
& STA_PLL
&& !(ntv
.status
& STA_PLL
)) {
316 time_state
= TIME_OK
;
317 time_status
= STA_UNSYNC
;
319 pps_shift
= PPS_FAVG
;
320 #endif /* PPS_SYNC */
322 time_status
&= STA_RONLY
;
323 time_status
|= ntv
.status
& ~STA_RONLY
;
325 if (modes
& MOD_TIMECONST
) {
326 if (ntv
.constant
< 0)
328 else if (ntv
.constant
> MAXTC
)
329 time_constant
= MAXTC
;
331 time_constant
= ntv
.constant
;
333 if (modes
& MOD_TAI
) {
334 if (ntv
.constant
> 0) /* XXX zero & negative numbers ? */
335 time_tai
= ntv
.constant
;
338 if (modes
& MOD_PPSMAX
) {
339 if (ntv
.shift
< PPS_FAVG
)
340 pps_shiftmax
= PPS_FAVG
;
341 else if (ntv
.shift
> PPS_FAVGMAX
)
342 pps_shiftmax
= PPS_FAVGMAX
;
344 pps_shiftmax
= ntv
.shift
;
346 #endif /* PPS_SYNC */
347 if (modes
& MOD_NANO
)
348 time_status
|= STA_NANO
;
349 if (modes
& MOD_MICRO
)
350 time_status
&= ~STA_NANO
;
351 if (modes
& MOD_CLKB
)
352 time_status
|= STA_CLK
;
353 if (modes
& MOD_CLKA
)
354 time_status
&= ~STA_CLK
;
355 if (modes
& MOD_OFFSET
) {
356 if (time_status
& STA_NANO
)
357 hardupdate(ntv
.offset
);
359 hardupdate(ntv
.offset
* 1000);
362 * Note: the userland specified frequency is in seconds per second
363 * times 65536e+6. Multiply by a thousand and divide by 65336 to
366 if (modes
& MOD_FREQUENCY
) {
367 freq
= (ntv
.freq
* 1000LL) >> 16;
369 L_LINT(time_freq
, MAXFREQ
);
370 else if (freq
< -MAXFREQ
)
371 L_LINT(time_freq
, -MAXFREQ
);
373 L_LINT(time_freq
, freq
);
375 pps_freq
= time_freq
;
376 #endif /* PPS_SYNC */
380 * Retrieve all clock variables. Note that the TAI offset is
381 * returned only by ntp_gettime();
383 if (time_status
& STA_NANO
)
384 ntv
.offset
= time_monitor
;
386 ntv
.offset
= time_monitor
/ 1000; /* XXX rounding ? */
387 ntv
.freq
= L_GINT((time_freq
/ 1000LL) << 16);
388 ntv
.maxerror
= time_maxerror
;
389 ntv
.esterror
= time_esterror
;
390 ntv
.status
= time_status
;
391 ntv
.constant
= time_constant
;
392 if (time_status
& STA_NANO
)
393 ntv
.precision
= time_precision
;
395 ntv
.precision
= time_precision
/ 1000;
396 ntv
.tolerance
= MAXFREQ
* SCALE_PPM
;
398 ntv
.shift
= pps_shift
;
399 ntv
.ppsfreq
= L_GINT((pps_freq
/ 1000LL) << 16);
400 if (time_status
& STA_NANO
)
401 ntv
.jitter
= pps_jitter
;
403 ntv
.jitter
= pps_jitter
/ 1000;
404 ntv
.stabil
= pps_stabil
;
405 ntv
.calcnt
= pps_calcnt
;
406 ntv
.errcnt
= pps_errcnt
;
407 ntv
.jitcnt
= pps_jitcnt
;
408 ntv
.stbcnt
= pps_stbcnt
;
409 #endif /* PPS_SYNC */
411 lockmgr(&ntp_lock
, LK_RELEASE
);
413 error
= copyout((caddr_t
)&ntv
, (caddr_t
)uap
->tp
, sizeof(ntv
));
418 * Status word error decode. See comments in
419 * ntp_gettime() routine.
421 if ((time_status
& (STA_UNSYNC
| STA_CLOCKERR
)) ||
422 (time_status
& (STA_PPSFREQ
| STA_PPSTIME
) &&
423 !(time_status
& STA_PPSSIGNAL
)) ||
424 (time_status
& STA_PPSTIME
&&
425 time_status
& STA_PPSJITTER
) ||
426 (time_status
& STA_PPSFREQ
&&
427 time_status
& (STA_PPSWANDER
| STA_PPSERROR
))) {
428 sysmsg
->sysmsg_result
= TIME_ERROR
;
430 sysmsg
->sysmsg_result
= time_state
;
436 * second_overflow() - called after ntp_tick_adjust()
438 * This routine is ordinarily called from hardclock() whenever the seconds
439 * hand rolls over. It returns leap seconds to add or drop, and sets nsec_adj
440 * to the total adjustment to make over the next second in (ns << 32).
442 * This routine is only called by cpu #0.
445 ntp_update_second(time_t newsec
, int64_t *nsec_adj
)
447 l_fp ftemp
; /* 32/64-bit temporary */
451 * On rollover of the second both the nanosecond and microsecond
452 * clocks are updated and the state machine cranked as
453 * necessary. The phase adjustment to be used for the next
454 * second is calculated and the maximum error is increased by
457 time_maxerror
+= MAXFREQ
/ 1000;
460 * Leap second processing. If in leap-insert state at
461 * the end of the day, the system clock is set back one
462 * second; if in leap-delete state, the system clock is
463 * set ahead one second. The nano_time() routine or
464 * external clock driver will insure that reported time
465 * is always monotonic.
467 switch (time_state
) {
473 if (time_status
& STA_INS
)
474 time_state
= TIME_INS
;
475 else if (time_status
& STA_DEL
)
476 time_state
= TIME_DEL
;
480 * Insert second 23:59:60 following second
484 if (!(time_status
& STA_INS
))
485 time_state
= TIME_OK
;
486 else if ((newsec
) % 86400 == 0) {
488 time_state
= TIME_OOP
;
493 * Delete second 23:59:59.
496 if (!(time_status
& STA_DEL
))
497 time_state
= TIME_OK
;
498 else if (((newsec
) + 1) % 86400 == 0) {
501 time_state
= TIME_WAIT
;
506 * Insert second in progress.
510 time_state
= TIME_WAIT
;
514 * Wait for status bits to clear.
517 if (!(time_status
& (STA_INS
| STA_DEL
)))
518 time_state
= TIME_OK
;
522 * time_offset represents the total time adjustment we wish to
523 * make (over no particular period of time). time_freq represents
524 * the frequency compensation we wish to apply.
526 * time_adj represents the total adjustment we wish to make over
527 * one full second. hardclock usually applies this adjustment in
528 * time_adj / hz jumps, hz times a second.
532 /* XXX even if PPS signal dies we should finish adjustment ? */
533 if ((time_status
& STA_PPSTIME
) && (time_status
& STA_PPSSIGNAL
))
534 L_RSHIFT(ftemp
, pps_shift
);
536 L_RSHIFT(ftemp
, SHIFT_PLL
+ time_constant
);
538 L_RSHIFT(ftemp
, SHIFT_PLL
+ time_constant
);
539 #endif /* PPS_SYNC */
540 time_adj
= ftemp
; /* adjustment for part of the offset */
541 L_SUB(time_offset
, ftemp
);
542 L_ADD(time_adj
, time_freq
); /* add frequency correction */
543 *nsec_adj
= time_adj
;
548 time_status
&= ~STA_PPSSIGNAL
;
549 #endif /* PPS_SYNC */
554 * ntp_init() - initialize variables and structures
556 * This routine must be called after the kernel variables hz and tick
557 * are set or changed and before the next tick interrupt. In this
558 * particular implementation, these values are assumed set elsewhere in
559 * the kernel. The design allows the clock frequency and tick interval
560 * to be changed while the system is running. So, this routine should
561 * probably be integrated with the code that does that.
568 * The following variable must be initialized any time the
569 * kernel variable hz is changed.
571 time_tick
= NANOSECOND
/ hz
;
574 * The following variables are initialized only at startup. Only
575 * those structures not cleared by the compiler need to be
576 * initialized, and these only in the simulator. In the actual
577 * kernel, any nonzero values here will quickly evaporate.
582 pps_tf
[0].tv_sec
= pps_tf
[0].tv_nsec
= 0;
583 pps_tf
[1].tv_sec
= pps_tf
[1].tv_nsec
= 0;
584 pps_tf
[2].tv_sec
= pps_tf
[2].tv_nsec
= 0;
587 #endif /* PPS_SYNC */
590 SYSINIT(ntpclocks
, SI_BOOT2_CLOCKS
, SI_ORDER_FIRST
, ntp_init
, NULL
);
593 * hardupdate() - local clock update
595 * This routine is called by ntp_adjtime() to update the local clock
596 * phase and frequency. The implementation is of an adaptive-parameter,
597 * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
598 * time and frequency offset estimates for each call. If the kernel PPS
599 * discipline code is configured (PPS_SYNC), the PPS signal itself
600 * determines the new time offset, instead of the calling argument.
601 * Presumably, calls to ntp_adjtime() occur only when the caller
602 * believes the local clock is valid within some bound (+-128 ms with
603 * NTP). If the caller's time is far different than the PPS time, an
604 * argument will ensue, and it's not clear who will lose.
606 * For uncompensated quartz crystal oscillators and nominal update
607 * intervals less than 256 s, operation should be in phase-lock mode,
608 * where the loop is disciplined to phase. For update intervals greater
609 * than 1024 s, operation should be in frequency-lock mode, where the
610 * loop is disciplined to frequency. Between 256 s and 1024 s, the mode
611 * is selected by the STA_MODE status bit.
614 hardupdate(long offset
)
620 * Select how the phase is to be controlled and from which
621 * source. If the PPS signal is present and enabled to
622 * discipline the time, the PPS offset is used; otherwise, the
623 * argument offset is used.
625 if (!(time_status
& STA_PLL
))
627 if (!((time_status
& STA_PPSTIME
) && (time_status
& STA_PPSSIGNAL
))) {
628 if (offset
> MAXPHASE
)
629 time_monitor
= MAXPHASE
;
630 else if (offset
< -MAXPHASE
)
631 time_monitor
= -MAXPHASE
;
633 time_monitor
= offset
;
634 L_LINT(time_offset
, time_monitor
);
638 * Select how the frequency is to be controlled and in which
639 * mode (PLL or FLL). If the PPS signal is present and enabled
640 * to discipline the frequency, the PPS frequency is used;
641 * otherwise, the argument offset is used to compute it.
643 if ((time_status
& STA_PPSFREQ
) && time_status
& STA_PPSSIGNAL
) {
644 time_reftime
= time_uptime
;
647 if ((time_status
& STA_FREQHOLD
) || time_reftime
== 0)
648 time_reftime
= time_uptime
;
649 mtemp
= time_uptime
- time_reftime
;
650 L_LINT(ftemp
, time_monitor
);
651 L_RSHIFT(ftemp
, (SHIFT_PLL
+ 2 + time_constant
) << 1);
653 L_ADD(time_freq
, ftemp
);
654 time_status
&= ~STA_MODE
;
655 if (mtemp
>= MINSEC
&& (time_status
& STA_FLL
|| mtemp
> MAXSEC
)) {
656 L_LINT(ftemp
, (time_monitor
<< 4) / mtemp
);
657 L_RSHIFT(ftemp
, SHIFT_FLL
+ 4);
658 L_ADD(time_freq
, ftemp
);
659 time_status
|= STA_MODE
;
661 time_reftime
= time_uptime
;
662 if (L_GINT(time_freq
) > MAXFREQ
)
663 L_LINT(time_freq
, MAXFREQ
);
664 else if (L_GINT(time_freq
) < -MAXFREQ
)
665 L_LINT(time_freq
, -MAXFREQ
);
670 * hardpps() - discipline CPU clock oscillator to external PPS signal
672 * This routine is called at each PPS interrupt in order to discipline
673 * the CPU clock oscillator to the PPS signal. There are two independent
674 * first-order feedback loops, one for the phase, the other for the
675 * frequency. The phase loop measures and grooms the PPS phase offset
676 * and leaves it in a handy spot for the seconds overflow routine. The
677 * frequency loop averages successive PPS phase differences and
678 * calculates the PPS frequency offset, which is also processed by the
679 * seconds overflow routine. The code requires the caller to capture the
680 * time and architecture-dependent hardware counter values in
681 * nanoseconds at the on-time PPS signal transition.
683 * Note that, on some Unix systems this routine runs at an interrupt
684 * priority level higher than the timer interrupt routine hardclock().
685 * Therefore, the variables used are distinct from the hardclock()
686 * variables, except for the actual time and frequency variables, which
687 * are determined by this routine and updated atomically.
690 hardpps(struct timespec
*tsp
, long nsec
)
692 long u_sec
, u_nsec
, v_nsec
; /* temps */
696 * The signal is first processed by a range gate and frequency
697 * discriminator. The range gate rejects noise spikes outside
698 * the range +-500 us. The frequency discriminator rejects input
699 * signals with apparent frequency outside the range 1 +-500
700 * PPM. If two hits occur in the same second, we ignore the
701 * later hit; if not and a hit occurs outside the range gate,
702 * keep the later hit for later comparison, but do not process
705 time_status
|= STA_PPSSIGNAL
| STA_PPSJITTER
;
706 time_status
&= ~(STA_PPSWANDER
| STA_PPSERROR
);
707 pps_valid
= PPS_VALID
;
709 u_nsec
= tsp
->tv_nsec
;
710 if (u_nsec
>= (NANOSECOND
>> 1)) {
711 u_nsec
-= NANOSECOND
;
714 v_nsec
= u_nsec
- pps_tf
[0].tv_nsec
;
715 if (u_sec
== pps_tf
[0].tv_sec
&& v_nsec
< NANOSECOND
-
718 pps_tf
[2] = pps_tf
[1];
719 pps_tf
[1] = pps_tf
[0];
720 pps_tf
[0].tv_sec
= u_sec
;
721 pps_tf
[0].tv_nsec
= u_nsec
;
724 * Compute the difference between the current and previous
725 * counter values. If the difference exceeds 0.5 s, assume it
726 * has wrapped around, so correct 1.0 s. If the result exceeds
727 * the tick interval, the sample point has crossed a tick
728 * boundary during the last second, so correct the tick. Very
732 if (u_nsec
> (NANOSECOND
>> 1))
733 u_nsec
-= NANOSECOND
;
734 else if (u_nsec
< -(NANOSECOND
>> 1))
735 u_nsec
+= NANOSECOND
;
736 pps_fcount
+= u_nsec
;
737 if (v_nsec
> MAXFREQ
|| v_nsec
< -MAXFREQ
)
739 time_status
&= ~STA_PPSJITTER
;
742 * A three-stage median filter is used to help denoise the PPS
743 * time. The median sample becomes the time offset estimate; the
744 * difference between the other two samples becomes the time
745 * dispersion (jitter) estimate.
747 if (pps_tf
[0].tv_nsec
> pps_tf
[1].tv_nsec
) {
748 if (pps_tf
[1].tv_nsec
> pps_tf
[2].tv_nsec
) {
749 v_nsec
= pps_tf
[1].tv_nsec
; /* 0 1 2 */
750 u_nsec
= pps_tf
[0].tv_nsec
- pps_tf
[2].tv_nsec
;
751 } else if (pps_tf
[2].tv_nsec
> pps_tf
[0].tv_nsec
) {
752 v_nsec
= pps_tf
[0].tv_nsec
; /* 2 0 1 */
753 u_nsec
= pps_tf
[2].tv_nsec
- pps_tf
[1].tv_nsec
;
755 v_nsec
= pps_tf
[2].tv_nsec
; /* 0 2 1 */
756 u_nsec
= pps_tf
[0].tv_nsec
- pps_tf
[1].tv_nsec
;
759 if (pps_tf
[1].tv_nsec
< pps_tf
[2].tv_nsec
) {
760 v_nsec
= pps_tf
[1].tv_nsec
; /* 2 1 0 */
761 u_nsec
= pps_tf
[2].tv_nsec
- pps_tf
[0].tv_nsec
;
762 } else if (pps_tf
[2].tv_nsec
< pps_tf
[0].tv_nsec
) {
763 v_nsec
= pps_tf
[0].tv_nsec
; /* 1 0 2 */
764 u_nsec
= pps_tf
[1].tv_nsec
- pps_tf
[2].tv_nsec
;
766 v_nsec
= pps_tf
[2].tv_nsec
; /* 1 2 0 */
767 u_nsec
= pps_tf
[1].tv_nsec
- pps_tf
[0].tv_nsec
;
772 * Nominal jitter is due to PPS signal noise and interrupt
773 * latency. If it exceeds the popcorn threshold, the sample is
774 * discarded. otherwise, if so enabled, the time offset is
775 * updated. We can tolerate a modest loss of data here without
776 * much degrading time accuracy.
778 if (u_nsec
> (pps_jitter
<< PPS_POPCORN
)) {
779 time_status
|= STA_PPSJITTER
;
781 } else if (time_status
& STA_PPSTIME
) {
782 time_monitor
= -v_nsec
;
783 L_LINT(time_offset
, time_monitor
);
785 pps_jitter
+= (u_nsec
- pps_jitter
) >> PPS_FAVG
;
786 u_sec
= pps_tf
[0].tv_sec
- pps_lastsec
;
787 if (u_sec
< (1 << pps_shift
))
791 * At the end of the calibration interval the difference between
792 * the first and last counter values becomes the scaled
793 * frequency. It will later be divided by the length of the
794 * interval to determine the frequency update. If the frequency
795 * exceeds a sanity threshold, or if the actual calibration
796 * interval is not equal to the expected length, the data are
797 * discarded. We can tolerate a modest loss of data here without
798 * much degrading frequency accuracy.
801 v_nsec
= -pps_fcount
;
802 pps_lastsec
= pps_tf
[0].tv_sec
;
804 u_nsec
= MAXFREQ
<< pps_shift
;
805 if (v_nsec
> u_nsec
|| v_nsec
< -u_nsec
|| u_sec
!= (1 <<
807 time_status
|= STA_PPSERROR
;
813 * Here the raw frequency offset and wander (stability) is
814 * calculated. If the wander is less than the wander threshold
815 * for four consecutive averaging intervals, the interval is
816 * doubled; if it is greater than the threshold for four
817 * consecutive intervals, the interval is halved. The scaled
818 * frequency offset is converted to frequency offset. The
819 * stability metric is calculated as the average of recent
820 * frequency changes, but is used only for performance
823 L_LINT(ftemp
, v_nsec
);
824 L_RSHIFT(ftemp
, pps_shift
);
825 L_SUB(ftemp
, pps_freq
);
826 u_nsec
= L_GINT(ftemp
);
827 if (u_nsec
> PPS_MAXWANDER
) {
828 L_LINT(ftemp
, PPS_MAXWANDER
);
830 time_status
|= STA_PPSWANDER
;
832 } else if (u_nsec
< -PPS_MAXWANDER
) {
833 L_LINT(ftemp
, -PPS_MAXWANDER
);
835 time_status
|= STA_PPSWANDER
;
840 if (pps_intcnt
>= 4) {
842 if (pps_shift
< pps_shiftmax
) {
846 } else if (pps_intcnt
<= -4 || pps_shift
> pps_shiftmax
) {
848 if (pps_shift
> PPS_FAVG
) {
855 pps_stabil
+= (u_nsec
* SCALE_PPM
- pps_stabil
) >> PPS_FAVG
;
858 * The PPS frequency is recalculated and clamped to the maximum
859 * MAXFREQ. If enabled, the system clock frequency is updated as
862 L_ADD(pps_freq
, ftemp
);
863 u_nsec
= L_GINT(pps_freq
);
864 if (u_nsec
> MAXFREQ
)
865 L_LINT(pps_freq
, MAXFREQ
);
866 else if (u_nsec
< -MAXFREQ
)
867 L_LINT(pps_freq
, -MAXFREQ
);
868 if (time_status
& STA_PPSFREQ
)
869 time_freq
= pps_freq
;
871 #endif /* PPS_SYNC */