kern_ntptime.c revision 36810
1/****************************************************************************** 2 * * 3 * Copyright (c) David L. Mills 1993, 1994 * 4 * * 5 * Permission to use, copy, modify, and distribute this software and its * 6 * documentation for any purpose and without fee is hereby granted, provided * 7 * that the above copyright notice appears in all copies and that both the * 8 * copyright notice and this permission notice appear in supporting * 9 * documentation, and that the name University of Delaware not be used in * 10 * advertising or publicity pertaining to distribution of the software * 11 * without specific, written prior permission. The University of Delaware * 12 * makes no representations about the suitability this software for any * 13 * purpose. It is provided "as is" without express or implied warranty. * 14 * * 15 ******************************************************************************/ 16 17/* 18 * Modification history kern_ntptime.c 19 * 20 * 24 Sep 94 David L. Mills 21 * Tightened code at exits. 22 * 23 * 24 Mar 94 David L. Mills 24 * Revised syscall interface to include new variables for PPS 25 * time discipline. 26 * 27 * 14 Feb 94 David L. Mills 28 * Added code for external clock 29 * 30 * 28 Nov 93 David L. Mills 31 * Revised frequency scaling to conform with adjusted parameters 32 * 33 * 17 Sep 93 David L. Mills 34 * Created file 35 */ 36/* 37 * ntp_gettime(), ntp_adjtime() - precision time interface for SunOS 38 * V4.1.1 and V4.1.3 39 * 40 * These routines consitute the Network Time Protocol (NTP) interfaces 41 * for user and daemon application programs. The ntp_gettime() routine 42 * provides the time, maximum error (synch distance) and estimated error 43 * (dispersion) to client user application programs. The ntp_adjtime() 44 * routine is used by the NTP daemon to adjust the system clock to an 45 * externally derived time. The time offset and related variables set by 46 * this routine are used by hardclock() to adjust the phase and 47 * frequency of the phase-lock loop which controls the system clock. 48 */ 49 50#include "opt_ntp.h" 51 52#include <sys/param.h> 53#include <sys/systm.h> 54#include <sys/sysproto.h> 55#include <sys/kernel.h> 56#include <sys/proc.h> 57#include <sys/timex.h> 58#include <sys/sysctl.h> 59 60/* 61 * Phase/frequency-lock loop (PLL/FLL) definitions 62 * 63 * The following variables are read and set by the ntp_adjtime() system 64 * call. 65 * 66 * time_state shows the state of the system clock, with values defined 67 * in the timex.h header file. 68 * 69 * time_status shows the status of the system clock, with bits defined 70 * in the timex.h header file. 71 * 72 * time_offset is used by the PLL/FLL to adjust the system time in small 73 * increments. 74 * 75 * time_constant determines the bandwidth or "stiffness" of the PLL. 76 * 77 * time_tolerance determines maximum frequency error or tolerance of the 78 * CPU clock oscillator and is a property of the architecture; however, 79 * in principle it could change as result of the presence of external 80 * discipline signals, for instance. 81 * 82 * time_precision is usually equal to the kernel tick variable; however, 83 * in cases where a precision clock counter or external clock is 84 * available, the resolution can be much less than this and depend on 85 * whether the external clock is working or not. 86 * 87 * time_maxerror is initialized by a ntp_adjtime() call and increased by 88 * the kernel once each second to reflect the maximum error 89 * bound growth. 90 * 91 * time_esterror is set and read by the ntp_adjtime() call, but 92 * otherwise not used by the kernel. 93 */ 94static int time_status = STA_UNSYNC; /* clock status bits */ 95static int time_state = TIME_OK; /* clock state */ 96static long time_offset = 0; /* time offset (us) */ 97static long time_constant = 0; /* pll time constant */ 98static long time_tolerance = MAXFREQ; /* frequency tolerance (scaled ppm) */ 99static long time_precision = 1; /* clock precision (us) */ 100static long time_maxerror = MAXPHASE; /* maximum error (us) */ 101static long time_esterror = MAXPHASE; /* estimated error (us) */ 102static int time_daemon = 0; /* No timedaemon active */ 103 104/* 105 * The following variables establish the state of the PLL/FLL and the 106 * residual time and frequency offset of the local clock. The scale 107 * factors are defined in the timex.h header file. 108 * 109 * time_phase and time_freq are the phase increment and the frequency 110 * increment, respectively, of the kernel time variable at each tick of 111 * the clock. 112 * 113 * time_freq is set via ntp_adjtime() from a value stored in a file when 114 * the synchronization daemon is first started. Its value is retrieved 115 * via ntp_adjtime() and written to the file about once per hour by the 116 * daemon. 117 * 118 * time_adj is the adjustment added to the value of tick at each timer 119 * interrupt and is recomputed from time_phase and time_freq at each 120 * seconds rollover. 121 * 122 * time_reftime is the second's portion of the system time on the last 123 * call to ntp_adjtime(). It is used to adjust the time_freq variable 124 * and to increase the time_maxerror as the time since last update 125 * increases. 126 */ 127long time_phase = 0; /* phase offset (scaled us) */ 128static long time_freq = 0; /* frequency offset (scaled ppm) */ 129long time_adj = 0; /* tick adjust (scaled 1 / hz) */ 130static long time_reftime = 0; /* time at last adjustment (s) */ 131 132#ifdef PPS_SYNC 133/* 134 * The following variables are used only if the kernel PPS discipline 135 * code is configured (PPS_SYNC). The scale factors are defined in the 136 * timex.h header file. 137 * 138 * pps_time contains the time at each calibration interval, as read by 139 * microtime(). pps_count counts the seconds of the calibration 140 * interval, the duration of which is nominally pps_shift in powers of 141 * two. 142 * 143 * pps_offset is the time offset produced by the time median filter 144 * pps_tf[], while pps_jitter is the dispersion (jitter) measured by 145 * this filter. 146 * 147 * pps_freq is the frequency offset produced by the frequency median 148 * filter pps_ff[], while pps_stabil is the dispersion (wander) measured 149 * by this filter. 150 * 151 * pps_usec is latched from a high resolution counter or external clock 152 * at pps_time. Here we want the hardware counter contents only, not the 153 * contents plus the time_tv.usec as usual. 154 * 155 * pps_valid counts the number of seconds since the last PPS update. It 156 * is used as a watchdog timer to disable the PPS discipline should the 157 * PPS signal be lost. 158 * 159 * pps_glitch counts the number of seconds since the beginning of an 160 * offset burst more than tick/2 from current nominal offset. It is used 161 * mainly to suppress error bursts due to priority conflicts between the 162 * PPS interrupt and timer interrupt. 163 * 164 * pps_intcnt counts the calibration intervals for use in the interval- 165 * adaptation algorithm. It's just too complicated for words. 166 */ 167static struct timeval pps_time; /* kernel time at last interval */ 168static long pps_offset = 0; /* pps time offset (us) */ 169static long pps_jitter = MAXTIME; /* pps time dispersion (jitter) (us) */ 170static long pps_tf[] = {0, 0, 0}; /* pps time offset median filter (us) */ 171static long pps_freq = 0; /* frequency offset (scaled ppm) */ 172static long pps_stabil = MAXFREQ; /* frequency dispersion (scaled ppm) */ 173static long pps_ff[] = {0, 0, 0}; /* frequency offset median filter */ 174static long pps_usec = 0; /* microsec counter at last interval */ 175static long pps_valid = PPS_VALID; /* pps signal watchdog counter */ 176static int pps_glitch = 0; /* pps signal glitch counter */ 177static int pps_count = 0; /* calibration interval counter (s) */ 178static int pps_shift = PPS_SHIFT; /* interval duration (s) (shift) */ 179static int pps_intcnt = 0; /* intervals at current duration */ 180 181/* 182 * PPS signal quality monitors 183 * 184 * pps_jitcnt counts the seconds that have been discarded because the 185 * jitter measured by the time median filter exceeds the limit MAXTIME 186 * (100 us). 187 * 188 * pps_calcnt counts the frequency calibration intervals, which are 189 * variable from 4 s to 256 s. 190 * 191 * pps_errcnt counts the calibration intervals which have been discarded 192 * because the wander exceeds the limit MAXFREQ (100 ppm) or where the 193 * calibration interval jitter exceeds two ticks. 194 * 195 * pps_stbcnt counts the calibration intervals that have been discarded 196 * because the frequency wander exceeds the limit MAXFREQ / 4 (25 us). 197 */ 198static long pps_jitcnt = 0; /* jitter limit exceeded */ 199static long pps_calcnt = 0; /* calibration intervals */ 200static long pps_errcnt = 0; /* calibration errors */ 201static long pps_stbcnt = 0; /* stability limit exceeded */ 202#endif /* PPS_SYNC */ 203 204static void hardupdate __P((long offset)); 205 206/* 207 * hardupdate() - local clock update 208 * 209 * This routine is called by ntp_adjtime() to update the local clock 210 * phase and frequency. The implementation is of an adaptive-parameter, 211 * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new 212 * time and frequency offset estimates for each call. If the kernel PPS 213 * discipline code is configured (PPS_SYNC), the PPS signal itself 214 * determines the new time offset, instead of the calling argument. 215 * Presumably, calls to ntp_adjtime() occur only when the caller 216 * believes the local clock is valid within some bound (+-128 ms with 217 * NTP). If the caller's time is far different than the PPS time, an 218 * argument will ensue, and it's not clear who will lose. 219 * 220 * For uncompensated quartz crystal oscillatores and nominal update 221 * intervals less than 1024 s, operation should be in phase-lock mode 222 * (STA_FLL = 0), where the loop is disciplined to phase. For update 223 * intervals greater than thiss, operation should be in frequency-lock 224 * mode (STA_FLL = 1), where the loop is disciplined to frequency. 225 * 226 * Note: splclock() is in effect. 227 */ 228static void 229hardupdate(offset) 230 long offset; 231{ 232 long ltemp, mtemp; 233 234 if (!(time_status & STA_PLL) && !(time_status & STA_PPSTIME)) 235 return; 236 ltemp = offset; 237#ifdef PPS_SYNC 238 if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL) 239 ltemp = pps_offset; 240#endif /* PPS_SYNC */ 241 242 /* 243 * Scale the phase adjustment and clamp to the operating range. 244 */ 245 if (ltemp > MAXPHASE) 246 time_offset = MAXPHASE << SHIFT_UPDATE; 247 else if (ltemp < -MAXPHASE) 248 time_offset = -(MAXPHASE << SHIFT_UPDATE); 249 else 250 time_offset = ltemp << SHIFT_UPDATE; 251 252 /* 253 * Select whether the frequency is to be controlled and in which 254 * mode (PLL or FLL). Clamp to the operating range. Ugly 255 * multiply/divide should be replaced someday. 256 */ 257 if (time_status & STA_FREQHOLD || time_reftime == 0) 258 time_reftime = time_second; 259 mtemp = time_second - time_reftime; 260 time_reftime = time_second; 261 if (time_status & STA_FLL) { 262 if (mtemp >= MINSEC) { 263 ltemp = ((time_offset / mtemp) << (SHIFT_USEC - 264 SHIFT_UPDATE)); 265 if (ltemp < 0) 266 time_freq -= -ltemp >> SHIFT_KH; 267 else 268 time_freq += ltemp >> SHIFT_KH; 269 } 270 } else { 271 if (mtemp < MAXSEC) { 272 ltemp *= mtemp; 273 if (ltemp < 0) 274 time_freq -= -ltemp >> (time_constant + 275 time_constant + SHIFT_KF - 276 SHIFT_USEC); 277 else 278 time_freq += ltemp >> (time_constant + 279 time_constant + SHIFT_KF - 280 SHIFT_USEC); 281 } 282 } 283 if (time_freq > time_tolerance) 284 time_freq = time_tolerance; 285 else if (time_freq < -time_tolerance) 286 time_freq = -time_tolerance; 287} 288 289/* 290 * On rollover of the second the phase adjustment to be used for 291 * the next second is calculated. Also, the maximum error is 292 * increased by the tolerance. If the PPS frequency discipline 293 * code is present, the phase is increased to compensate for the 294 * CPU clock oscillator frequency error. 295 * 296 * On a 32-bit machine and given parameters in the timex.h 297 * header file, the maximum phase adjustment is +-512 ms and 298 * maximum frequency offset is a tad less than) +-512 ppm. On a 299 * 64-bit machine, you shouldn't need to ask. 300 */ 301void 302ntp_update_second(struct timecounter *tc) 303{ 304 u_int32_t *newsec; 305 long ltemp; 306 307 if (!time_daemon) 308 return; 309 310 newsec = &tc->tc_offset_sec; 311 time_maxerror += time_tolerance >> SHIFT_USEC; 312 313 /* 314 * Compute the phase adjustment for the next second. In 315 * PLL mode, the offset is reduced by a fixed factor 316 * times the time constant. In FLL mode the offset is 317 * used directly. In either mode, the maximum phase 318 * adjustment for each second is clamped so as to spread 319 * the adjustment over not more than the number of 320 * seconds between updates. 321 */ 322 if (time_offset < 0) { 323 ltemp = -time_offset; 324 if (!(time_status & STA_FLL)) 325 ltemp >>= SHIFT_KG + time_constant; 326 if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE) 327 ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE; 328 time_offset += ltemp; 329 time_adj = -ltemp << (SHIFT_SCALE - SHIFT_UPDATE); 330 } else { 331 ltemp = time_offset; 332 if (!(time_status & STA_FLL)) 333 ltemp >>= SHIFT_KG + time_constant; 334 if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE) 335 ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE; 336 time_offset -= ltemp; 337 time_adj = ltemp << (SHIFT_SCALE - SHIFT_UPDATE); 338 } 339 340 /* 341 * Compute the frequency estimate and additional phase 342 * adjustment due to frequency error for the next 343 * second. When the PPS signal is engaged, gnaw on the 344 * watchdog counter and update the frequency computed by 345 * the pll and the PPS signal. 346 */ 347#ifdef PPS_SYNC 348 pps_valid++; 349 if (pps_valid == PPS_VALID) { 350 pps_jitter = MAXTIME; 351 pps_stabil = MAXFREQ; 352 time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER | 353 STA_PPSWANDER | STA_PPSERROR); 354 } 355 ltemp = time_freq + pps_freq; 356#else 357 ltemp = time_freq; 358#endif /* PPS_SYNC */ 359 if (ltemp < 0) 360 time_adj -= -ltemp << (SHIFT_SCALE - SHIFT_USEC); 361 else 362 time_adj += ltemp << (SHIFT_SCALE - SHIFT_USEC); 363 364 tc->tc_adjustment = time_adj; 365 366 /* XXX - this is really bogus, but can't be fixed until 367 xntpd's idea of the system clock is fixed to know how 368 the user wants leap seconds handled; in the mean time, 369 we assume that users of NTP are running without proper 370 leap second support (this is now the default anyway) */ 371 /* 372 * Leap second processing. If in leap-insert state at 373 * the end of the day, the system clock is set back one 374 * second; if in leap-delete state, the system clock is 375 * set ahead one second. The microtime() routine or 376 * external clock driver will insure that reported time 377 * is always monotonic. The ugly divides should be 378 * replaced. 379 */ 380 switch (time_state) { 381 382 case TIME_OK: 383 if (time_status & STA_INS) 384 time_state = TIME_INS; 385 else if (time_status & STA_DEL) 386 time_state = TIME_DEL; 387 break; 388 389 case TIME_INS: 390 if ((*newsec) % 86400 == 0) { 391 (*newsec)--; 392 time_state = TIME_OOP; 393 } 394 break; 395 396 case TIME_DEL: 397 if (((*newsec) + 1) % 86400 == 0) { 398 (*newsec)++; 399 time_state = TIME_WAIT; 400 } 401 break; 402 403 case TIME_OOP: 404 time_state = TIME_WAIT; 405 break; 406 407 case TIME_WAIT: 408 if (!(time_status & (STA_INS | STA_DEL))) 409 time_state = TIME_OK; 410 break; 411 } 412} 413 414static int 415ntp_sysctl SYSCTL_HANDLER_ARGS 416{ 417 struct timeval atv; 418 struct ntptimeval ntv; 419 int s; 420 421 s = splclock(); 422 microtime(&atv); 423 ntv.time = atv; 424 ntv.maxerror = time_maxerror; 425 ntv.esterror = time_esterror; 426 splx(s); 427 428 ntv.time_state = time_state; 429 430 /* 431 * Status word error decode. If any of these conditions 432 * occur, an error is returned, instead of the status 433 * word. Most applications will care only about the fact 434 * the system clock may not be trusted, not about the 435 * details. 436 * 437 * Hardware or software error 438 */ 439 if (time_status & (STA_UNSYNC | STA_CLOCKERR)) { 440 ntv.time_state = TIME_ERROR; 441 } 442 443 /* 444 * PPS signal lost when either time or frequency 445 * synchronization requested 446 */ 447 if (time_status & (STA_PPSFREQ | STA_PPSTIME) && 448 !(time_status & STA_PPSSIGNAL)) { 449 ntv.time_state = TIME_ERROR; 450 } 451 452 /* 453 * PPS jitter exceeded when time synchronization 454 * requested 455 */ 456 if (time_status & STA_PPSTIME && 457 time_status & STA_PPSJITTER) { 458 ntv.time_state = TIME_ERROR; 459 } 460 461 /* 462 * PPS wander exceeded or calibration error when 463 * frequency synchronization requested 464 */ 465 if (time_status & STA_PPSFREQ && 466 time_status & (STA_PPSWANDER | STA_PPSERROR)) { 467 ntv.time_state = TIME_ERROR; 468 } 469 return (sysctl_handle_opaque(oidp, &ntv, sizeof ntv, req)); 470} 471 472SYSCTL_NODE(_kern, KERN_NTP_PLL, ntp_pll, CTLFLAG_RW, 0, 473 "NTP kernel PLL related stuff"); 474SYSCTL_PROC(_kern_ntp_pll, NTP_PLL_GETTIME, gettime, CTLTYPE_OPAQUE|CTLFLAG_RD, 475 0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", ""); 476 477/* 478 * ntp_adjtime() - NTP daemon application interface 479 */ 480#ifndef _SYS_SYSPROTO_H_ 481struct ntp_adjtime_args { 482 struct timex *tp; 483}; 484#endif 485 486int 487ntp_adjtime(struct proc *p, struct ntp_adjtime_args *uap) 488{ 489 struct timex ntv; 490 int modes; 491 int s; 492 int error; 493 494 time_daemon = 1; 495 496 error = copyin((caddr_t)uap->tp, (caddr_t)&ntv, sizeof(ntv)); 497 if (error) 498 return error; 499 500 /* 501 * Update selected clock variables - only the superuser can 502 * change anything. Note that there is no error checking here on 503 * the assumption the superuser should know what it is doing. 504 */ 505 modes = ntv.modes; 506 if ((modes != 0) 507 && (error = suser(p->p_cred->pc_ucred, &p->p_acflag))) 508 return error; 509 510 s = splclock(); 511 if (modes & MOD_FREQUENCY) 512#ifdef PPS_SYNC 513 time_freq = ntv.freq - pps_freq; 514#else /* PPS_SYNC */ 515 time_freq = ntv.freq; 516#endif /* PPS_SYNC */ 517 if (modes & MOD_MAXERROR) 518 time_maxerror = ntv.maxerror; 519 if (modes & MOD_ESTERROR) 520 time_esterror = ntv.esterror; 521 if (modes & MOD_STATUS) { 522 time_status &= STA_RONLY; 523 time_status |= ntv.status & ~STA_RONLY; 524 } 525 if (modes & MOD_TIMECONST) 526 time_constant = ntv.constant; 527 if (modes & MOD_OFFSET) 528 hardupdate(ntv.offset); 529 530 /* 531 * Retrieve all clock variables 532 */ 533 if (time_offset < 0) 534 ntv.offset = -(-time_offset >> SHIFT_UPDATE); 535 else 536 ntv.offset = time_offset >> SHIFT_UPDATE; 537#ifdef PPS_SYNC 538 ntv.freq = time_freq + pps_freq; 539#else /* PPS_SYNC */ 540 ntv.freq = time_freq; 541#endif /* PPS_SYNC */ 542 ntv.maxerror = time_maxerror; 543 ntv.esterror = time_esterror; 544 ntv.status = time_status; 545 ntv.constant = time_constant; 546 ntv.precision = time_precision; 547 ntv.tolerance = time_tolerance; 548#ifdef PPS_SYNC 549 ntv.shift = pps_shift; 550 ntv.ppsfreq = pps_freq; 551 ntv.jitter = pps_jitter >> PPS_AVG; 552 ntv.stabil = pps_stabil; 553 ntv.calcnt = pps_calcnt; 554 ntv.errcnt = pps_errcnt; 555 ntv.jitcnt = pps_jitcnt; 556 ntv.stbcnt = pps_stbcnt; 557#endif /* PPS_SYNC */ 558 (void)splx(s); 559 560 error = copyout((caddr_t)&ntv, (caddr_t)uap->tp, sizeof(ntv)); 561 if (!error) { 562 /* 563 * Status word error decode. See comments in 564 * ntp_gettime() routine. 565 */ 566 p->p_retval[0] = time_state; 567 if (time_status & (STA_UNSYNC | STA_CLOCKERR)) 568 p->p_retval[0] = TIME_ERROR; 569 if (time_status & (STA_PPSFREQ | STA_PPSTIME) && 570 !(time_status & STA_PPSSIGNAL)) 571 p->p_retval[0] = TIME_ERROR; 572 if (time_status & STA_PPSTIME && 573 time_status & STA_PPSJITTER) 574 p->p_retval[0] = TIME_ERROR; 575 if (time_status & STA_PPSFREQ && 576 time_status & (STA_PPSWANDER | STA_PPSERROR)) 577 p->p_retval[0] = TIME_ERROR; 578 } 579 return error; 580} 581 582#ifdef PPS_SYNC 583 584/* We need this ugly monster twice, so let's macroize it. */ 585 586#define MEDIAN3X(a, m, s, i1, i2, i3) \ 587 do { \ 588 m = a[i2]; \ 589 s = a[i1] - a[i3]; \ 590 } while (0) 591 592#define MEDIAN3(a, m, s) \ 593 do { \ 594 if (a[0] > a[1]) { \ 595 if (a[1] > a[2]) \ 596 MEDIAN3X(a, m, s, 0, 1, 2); \ 597 else if (a[2] > a[0]) \ 598 MEDIAN3X(a, m, s, 2, 0, 1); \ 599 else \ 600 MEDIAN3X(a, m, s, 0, 2, 1); \ 601 } else { \ 602 if (a[2] > a[1]) \ 603 MEDIAN3X(a, m, s, 2, 1, 0); \ 604 else if (a[0] > a[2]) \ 605 MEDIAN3X(a, m, s, 1, 0, 2); \ 606 else \ 607 MEDIAN3X(a, m, s, 1, 2, 0); \ 608 } \ 609 } while (0) 610 611/* 612 * hardpps() - discipline CPU clock oscillator to external PPS signal 613 * 614 * This routine is called at each PPS interrupt in order to discipline 615 * the CPU clock oscillator to the PPS signal. It measures the PPS phase 616 * and leaves it in a handy spot for the hardclock() routine. It 617 * integrates successive PPS phase differences and calculates the 618 * frequency offset. This is used in hardclock() to discipline the CPU 619 * clock oscillator so that intrinsic frequency error is cancelled out. 620 * The code requires the caller to capture the time and hardware counter 621 * value at the on-time PPS signal transition. 622 * 623 * Note that, on some Unix systems, this routine runs at an interrupt 624 * priority level higher than the timer interrupt routine hardclock(). 625 * Therefore, the variables used are distinct from the hardclock() 626 * variables, except for certain exceptions: The PPS frequency pps_freq 627 * and phase pps_offset variables are determined by this routine and 628 * updated atomically. The time_tolerance variable can be considered a 629 * constant, since it is infrequently changed, and then only when the 630 * PPS signal is disabled. The watchdog counter pps_valid is updated 631 * once per second by hardclock() and is atomically cleared in this 632 * routine. 633 */ 634void 635hardpps(tvp, p_usec) 636 struct timeval *tvp; /* time at PPS */ 637 long p_usec; /* hardware counter at PPS */ 638{ 639 long u_usec, v_usec, bigtick; 640 long cal_sec, cal_usec; 641 642 /* 643 * An occasional glitch can be produced when the PPS interrupt 644 * occurs in the hardclock() routine before the time variable is 645 * updated. Here the offset is discarded when the difference 646 * between it and the last one is greater than tick/2, but not 647 * if the interval since the first discard exceeds 30 s. 648 */ 649 time_status |= STA_PPSSIGNAL; 650 time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR); 651 pps_valid = 0; 652 u_usec = -tvp->tv_usec; 653 if (u_usec < -500000) 654 u_usec += 1000000; 655 v_usec = pps_offset - u_usec; 656 if (v_usec < 0) 657 v_usec = -v_usec; 658 if (v_usec > (tick >> 1)) { 659 if (pps_glitch > MAXGLITCH) { 660 pps_glitch = 0; 661 pps_tf[2] = u_usec; 662 pps_tf[1] = u_usec; 663 } else { 664 pps_glitch++; 665 u_usec = pps_offset; 666 } 667 } else 668 pps_glitch = 0; 669 670 /* 671 * A three-stage median filter is used to help deglitch the pps 672 * time. The median sample becomes the time offset estimate; the 673 * difference between the other two samples becomes the time 674 * dispersion (jitter) estimate. 675 */ 676 pps_tf[2] = pps_tf[1]; 677 pps_tf[1] = pps_tf[0]; 678 pps_tf[0] = u_usec; 679 MEDIAN3(pps_tf, pps_offset, v_usec); 680 if (v_usec > MAXTIME) 681 pps_jitcnt++; 682 v_usec = (v_usec << PPS_AVG) - pps_jitter; 683 if (v_usec < 0) 684 pps_jitter -= -v_usec >> PPS_AVG; 685 else 686 pps_jitter += v_usec >> PPS_AVG; 687 if (pps_jitter > (MAXTIME >> 1)) 688 time_status |= STA_PPSJITTER; 689 690 /* 691 * During the calibration interval adjust the starting time when 692 * the tick overflows. At the end of the interval compute the 693 * duration of the interval and the difference of the hardware 694 * counters at the beginning and end of the interval. This code 695 * is deliciously complicated by the fact valid differences may 696 * exceed the value of tick when using long calibration 697 * intervals and small ticks. Note that the counter can be 698 * greater than tick if caught at just the wrong instant, but 699 * the values returned and used here are correct. 700 */ 701 bigtick = (long)tick << SHIFT_USEC; 702 pps_usec -= pps_freq; 703 if (pps_usec >= bigtick) 704 pps_usec -= bigtick; 705 if (pps_usec < 0) 706 pps_usec += bigtick; 707 pps_time.tv_sec++; 708 pps_count++; 709 if (pps_count < (1 << pps_shift)) 710 return; 711 pps_count = 0; 712 pps_calcnt++; 713 u_usec = p_usec << SHIFT_USEC; 714 v_usec = pps_usec - u_usec; 715 if (v_usec >= bigtick >> 1) 716 v_usec -= bigtick; 717 if (v_usec < -(bigtick >> 1)) 718 v_usec += bigtick; 719 if (v_usec < 0) 720 v_usec = -(-v_usec >> pps_shift); 721 else 722 v_usec = v_usec >> pps_shift; 723 pps_usec = u_usec; 724 cal_sec = tvp->tv_sec; 725 cal_usec = tvp->tv_usec; 726 cal_sec -= pps_time.tv_sec; 727 cal_usec -= pps_time.tv_usec; 728 if (cal_usec < 0) { 729 cal_usec += 1000000; 730 cal_sec--; 731 } 732 pps_time = *tvp; 733 734 /* 735 * Check for lost interrupts, noise, excessive jitter and 736 * excessive frequency error. The number of timer ticks during 737 * the interval may vary +-1 tick. Add to this a margin of one 738 * tick for the PPS signal jitter and maximum frequency 739 * deviation. If the limits are exceeded, the calibration 740 * interval is reset to the minimum and we start over. 741 */ 742 u_usec = (long)tick << 1; 743 if (!((cal_sec == -1 && cal_usec > (1000000 - u_usec)) 744 || (cal_sec == 0 && cal_usec < u_usec)) 745 || v_usec > time_tolerance || v_usec < -time_tolerance) { 746 pps_errcnt++; 747 pps_shift = PPS_SHIFT; 748 pps_intcnt = 0; 749 time_status |= STA_PPSERROR; 750 return; 751 } 752 753 /* 754 * A three-stage median filter is used to help deglitch the pps 755 * frequency. The median sample becomes the frequency offset 756 * estimate; the difference between the other two samples 757 * becomes the frequency dispersion (stability) estimate. 758 */ 759 pps_ff[2] = pps_ff[1]; 760 pps_ff[1] = pps_ff[0]; 761 pps_ff[0] = v_usec; 762 MEDIAN3(pps_ff, u_usec, v_usec); 763 764 /* 765 * Here the frequency dispersion (stability) is updated. If it 766 * is less than one-fourth the maximum (MAXFREQ), the frequency 767 * offset is updated as well, but clamped to the tolerance. It 768 * will be processed later by the hardclock() routine. 769 */ 770 v_usec = (v_usec >> 1) - pps_stabil; 771 if (v_usec < 0) 772 pps_stabil -= -v_usec >> PPS_AVG; 773 else 774 pps_stabil += v_usec >> PPS_AVG; 775 if (pps_stabil > MAXFREQ >> 2) { 776 pps_stbcnt++; 777 time_status |= STA_PPSWANDER; 778 return; 779 } 780 if (time_status & STA_PPSFREQ) { 781 if (u_usec < 0) { 782 pps_freq -= -u_usec >> PPS_AVG; 783 if (pps_freq < -time_tolerance) 784 pps_freq = -time_tolerance; 785 u_usec = -u_usec; 786 } else { 787 pps_freq += u_usec >> PPS_AVG; 788 if (pps_freq > time_tolerance) 789 pps_freq = time_tolerance; 790 } 791 } 792 793 /* 794 * Here the calibration interval is adjusted. If the maximum 795 * time difference is greater than tick / 4, reduce the interval 796 * by half. If this is not the case for four consecutive 797 * intervals, double the interval. 798 */ 799 if (u_usec << pps_shift > bigtick >> 2) { 800 pps_intcnt = 0; 801 if (pps_shift > PPS_SHIFT) 802 pps_shift--; 803 } else if (pps_intcnt >= 4) { 804 pps_intcnt = 0; 805 if (pps_shift < PPS_SHIFTMAX) 806 pps_shift++; 807 } else 808 pps_intcnt++; 809} 810 811#endif /* PPS_SYNC */ 812