kern_ntptime.c revision 33388
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) */ 102 103/* 104 * The following variables establish the state of the PLL/FLL and the 105 * residual time and frequency offset of the local clock. The scale 106 * factors are defined in the timex.h header file. 107 * 108 * time_phase and time_freq are the phase increment and the frequency 109 * increment, respectively, of the kernel time variable at each tick of 110 * the clock. 111 * 112 * time_freq is set via ntp_adjtime() from a value stored in a file when 113 * the synchronization daemon is first started. Its value is retrieved 114 * via ntp_adjtime() and written to the file about once per hour by the 115 * daemon. 116 * 117 * time_adj is the adjustment added to the value of tick at each timer 118 * interrupt and is recomputed from time_phase and time_freq at each 119 * seconds rollover. 120 * 121 * time_reftime is the second's portion of the system time on the last 122 * call to ntp_adjtime(). It is used to adjust the time_freq variable 123 * and to increase the time_maxerror as the time since last update 124 * increases. 125 */ 126long time_phase = 0; /* phase offset (scaled us) */ 127static long time_freq = 0; /* frequency offset (scaled ppm) */ 128long time_adj = 0; /* tick adjust (scaled 1 / hz) */ 129static long time_reftime = 0; /* time at last adjustment (s) */ 130 131#ifdef PPS_SYNC 132/* 133 * The following variables are used only if the kernel PPS discipline 134 * code is configured (PPS_SYNC). The scale factors are defined in the 135 * timex.h header file. 136 * 137 * pps_time contains the time at each calibration interval, as read by 138 * microtime(). pps_count counts the seconds of the calibration 139 * interval, the duration of which is nominally pps_shift in powers of 140 * two. 141 * 142 * pps_offset is the time offset produced by the time median filter 143 * pps_tf[], while pps_jitter is the dispersion (jitter) measured by 144 * this filter. 145 * 146 * pps_freq is the frequency offset produced by the frequency median 147 * filter pps_ff[], while pps_stabil is the dispersion (wander) measured 148 * by this filter. 149 * 150 * pps_usec is latched from a high resolution counter or external clock 151 * at pps_time. Here we want the hardware counter contents only, not the 152 * contents plus the time_tv.usec as usual. 153 * 154 * pps_valid counts the number of seconds since the last PPS update. It 155 * is used as a watchdog timer to disable the PPS discipline should the 156 * PPS signal be lost. 157 * 158 * pps_glitch counts the number of seconds since the beginning of an 159 * offset burst more than tick/2 from current nominal offset. It is used 160 * mainly to suppress error bursts due to priority conflicts between the 161 * PPS interrupt and timer interrupt. 162 * 163 * pps_intcnt counts the calibration intervals for use in the interval- 164 * adaptation algorithm. It's just too complicated for words. 165 */ 166static struct timeval pps_time; /* kernel time at last interval */ 167static long pps_offset = 0; /* pps time offset (us) */ 168static long pps_jitter = MAXTIME; /* pps time dispersion (jitter) (us) */ 169static long pps_tf[] = {0, 0, 0}; /* pps time offset median filter (us) */ 170static long pps_freq = 0; /* frequency offset (scaled ppm) */ 171static long pps_stabil = MAXFREQ; /* frequency dispersion (scaled ppm) */ 172static long pps_ff[] = {0, 0, 0}; /* frequency offset median filter */ 173static long pps_usec = 0; /* microsec counter at last interval */ 174static long pps_valid = PPS_VALID; /* pps signal watchdog counter */ 175static int pps_glitch = 0; /* pps signal glitch counter */ 176static int pps_count = 0; /* calibration interval counter (s) */ 177static int pps_shift = PPS_SHIFT; /* interval duration (s) (shift) */ 178static int pps_intcnt = 0; /* intervals at current duration */ 179 180/* 181 * PPS signal quality monitors 182 * 183 * pps_jitcnt counts the seconds that have been discarded because the 184 * jitter measured by the time median filter exceeds the limit MAXTIME 185 * (100 us). 186 * 187 * pps_calcnt counts the frequency calibration intervals, which are 188 * variable from 4 s to 256 s. 189 * 190 * pps_errcnt counts the calibration intervals which have been discarded 191 * because the wander exceeds the limit MAXFREQ (100 ppm) or where the 192 * calibration interval jitter exceeds two ticks. 193 * 194 * pps_stbcnt counts the calibration intervals that have been discarded 195 * because the frequency wander exceeds the limit MAXFREQ / 4 (25 us). 196 */ 197static long pps_jitcnt = 0; /* jitter limit exceeded */ 198static long pps_calcnt = 0; /* calibration intervals */ 199static long pps_errcnt = 0; /* calibration errors */ 200static long pps_stbcnt = 0; /* stability limit exceeded */ 201#endif /* PPS_SYNC */ 202 203static void hardupdate __P((long offset)); 204 205/* 206 * hardupdate() - local clock update 207 * 208 * This routine is called by ntp_adjtime() to update the local clock 209 * phase and frequency. The implementation is of an adaptive-parameter, 210 * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new 211 * time and frequency offset estimates for each call. If the kernel PPS 212 * discipline code is configured (PPS_SYNC), the PPS signal itself 213 * determines the new time offset, instead of the calling argument. 214 * Presumably, calls to ntp_adjtime() occur only when the caller 215 * believes the local clock is valid within some bound (+-128 ms with 216 * NTP). If the caller's time is far different than the PPS time, an 217 * argument will ensue, and it's not clear who will lose. 218 * 219 * For uncompensated quartz crystal oscillatores and nominal update 220 * intervals less than 1024 s, operation should be in phase-lock mode 221 * (STA_FLL = 0), where the loop is disciplined to phase. For update 222 * intervals greater than thiss, operation should be in frequency-lock 223 * mode (STA_FLL = 1), where the loop is disciplined to frequency. 224 * 225 * Note: splclock() is in effect. 226 */ 227static void 228hardupdate(offset) 229 long offset; 230{ 231 long ltemp, mtemp; 232 233 if (!(time_status & STA_PLL) && !(time_status & STA_PPSTIME)) 234 return; 235 ltemp = offset; 236#ifdef PPS_SYNC 237 if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL) 238 ltemp = pps_offset; 239#endif /* PPS_SYNC */ 240 241 /* 242 * Scale the phase adjustment and clamp to the operating range. 243 */ 244 if (ltemp > MAXPHASE) 245 time_offset = MAXPHASE << SHIFT_UPDATE; 246 else if (ltemp < -MAXPHASE) 247 time_offset = -(MAXPHASE << SHIFT_UPDATE); 248 else 249 time_offset = ltemp << SHIFT_UPDATE; 250 251 /* 252 * Select whether the frequency is to be controlled and in which 253 * mode (PLL or FLL). Clamp to the operating range. Ugly 254 * multiply/divide should be replaced someday. 255 */ 256 if (time_status & STA_FREQHOLD || time_reftime == 0) 257 time_reftime = time.tv_sec; 258 mtemp = time.tv_sec - time_reftime; 259 time_reftime = time.tv_sec; 260 if (time_status & STA_FLL) { 261 if (mtemp >= MINSEC) { 262 ltemp = ((time_offset / mtemp) << (SHIFT_USEC - 263 SHIFT_UPDATE)); 264 if (ltemp < 0) 265 time_freq -= -ltemp >> SHIFT_KH; 266 else 267 time_freq += ltemp >> SHIFT_KH; 268 } 269 } else { 270 if (mtemp < MAXSEC) { 271 ltemp *= mtemp; 272 if (ltemp < 0) 273 time_freq -= -ltemp >> (time_constant + 274 time_constant + SHIFT_KF - 275 SHIFT_USEC); 276 else 277 time_freq += ltemp >> (time_constant + 278 time_constant + SHIFT_KF - 279 SHIFT_USEC); 280 } 281 } 282 if (time_freq > time_tolerance) 283 time_freq = time_tolerance; 284 else if (time_freq < -time_tolerance) 285 time_freq = -time_tolerance; 286} 287 288void 289ntp_update_second(long *newsec) 290{ 291 long ltemp; 292 293 time_maxerror += time_tolerance >> SHIFT_USEC; 294 295 /* 296 * Compute the phase adjustment for the next second. In 297 * PLL mode, the offset is reduced by a fixed factor 298 * times the time constant. In FLL mode the offset is 299 * used directly. In either mode, the maximum phase 300 * adjustment for each second is clamped so as to spread 301 * the adjustment over not more than the number of 302 * seconds between updates. 303 */ 304 if (time_offset < 0) { 305 ltemp = -time_offset; 306 if (!(time_status & STA_FLL)) 307 ltemp >>= SHIFT_KG + time_constant; 308 if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE) 309 ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE; 310 time_offset += ltemp; 311 time_adj = -ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE); 312 } else { 313 ltemp = time_offset; 314 if (!(time_status & STA_FLL)) 315 ltemp >>= SHIFT_KG + time_constant; 316 if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE) 317 ltemp = (MAXPHASE / MINSEC) << SHIFT_UPDATE; 318 time_offset -= ltemp; 319 time_adj = ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE); 320 } 321 322 /* 323 * Compute the frequency estimate and additional phase 324 * adjustment due to frequency error for the next 325 * second. When the PPS signal is engaged, gnaw on the 326 * watchdog counter and update the frequency computed by 327 * the pll and the PPS signal. 328 */ 329#ifdef PPS_SYNC 330 pps_valid++; 331 if (pps_valid == PPS_VALID) { 332 pps_jitter = MAXTIME; 333 pps_stabil = MAXFREQ; 334 time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER | 335 STA_PPSWANDER | STA_PPSERROR); 336 } 337 ltemp = time_freq + pps_freq; 338#else 339 ltemp = time_freq; 340#endif /* PPS_SYNC */ 341 if (ltemp < 0) 342 time_adj -= -ltemp >> (SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE); 343 else 344 time_adj += ltemp >> (SHIFT_USEC + SHIFT_HZ - SHIFT_SCALE); 345 346#if SHIFT_HZ == 7 347 /* 348 * When the CPU clock oscillator frequency is not a 349 * power of two in Hz, the SHIFT_HZ is only an 350 * approximate scale factor. In the SunOS kernel, this 351 * results in a PLL gain factor of 1/1.28 = 0.78 what it 352 * should be. In the following code the overall gain is 353 * increased by a factor of 1.25, which results in a 354 * residual error less than 3 percent. 355 */ 356 /* Same thing applies for FreeBSD --GAW */ 357 if (hz == 100) { 358 if (time_adj < 0) 359 time_adj -= -time_adj >> 2; 360 else 361 time_adj += time_adj >> 2; 362 } 363#endif /* SHIFT_HZ */ 364 365 /* XXX - this is really bogus, but can't be fixed until 366 xntpd's idea of the system clock is fixed to know how 367 the user wants leap seconds handled; in the mean time, 368 we assume that users of NTP are running without proper 369 leap second support (this is now the default anyway) */ 370 /* 371 * Leap second processing. If in leap-insert state at 372 * the end of the day, the system clock is set back one 373 * second; if in leap-delete state, the system clock is 374 * set ahead one second. The microtime() routine or 375 * external clock driver will insure that reported time 376 * is always monotonic. The ugly divides should be 377 * replaced. 378 */ 379 switch (time_state) { 380 381 case TIME_OK: 382 if (time_status & STA_INS) 383 time_state = TIME_INS; 384 else if (time_status & STA_DEL) 385 time_state = TIME_DEL; 386 break; 387 388 case TIME_INS: 389 if ((*newsec) % 86400 == 0) { 390 (*newsec)--; 391 time_state = TIME_OOP; 392 } 393 break; 394 395 case TIME_DEL: 396 if (((*newsec) + 1) % 86400 == 0) { 397 (*newsec)++; 398 time_state = TIME_WAIT; 399 } 400 break; 401 402 case TIME_OOP: 403 time_state = TIME_WAIT; 404 break; 405 406 case TIME_WAIT: 407 if (!(time_status & (STA_INS | STA_DEL))) 408 time_state = TIME_OK; 409 break; 410 } 411} 412 413static int 414ntp_sysctl SYSCTL_HANDLER_ARGS 415{ 416 struct timeval atv; 417 struct ntptimeval ntv; 418 int s; 419 420 s = splclock(); 421 microtime(&atv); 422 ntv.time = atv; 423 ntv.maxerror = time_maxerror; 424 ntv.esterror = time_esterror; 425 splx(s); 426 427 ntv.time_state = time_state; 428 429 /* 430 * Status word error decode. If any of these conditions 431 * occur, an error is returned, instead of the status 432 * word. Most applications will care only about the fact 433 * the system clock may not be trusted, not about the 434 * details. 435 * 436 * Hardware or software error 437 */ 438 if (time_status & (STA_UNSYNC | STA_CLOCKERR)) { 439 ntv.time_state = TIME_ERROR; 440 } 441 442 /* 443 * PPS signal lost when either time or frequency 444 * synchronization requested 445 */ 446 if (time_status & (STA_PPSFREQ | STA_PPSTIME) && 447 !(time_status & STA_PPSSIGNAL)) { 448 ntv.time_state = TIME_ERROR; 449 } 450 451 /* 452 * PPS jitter exceeded when time synchronization 453 * requested 454 */ 455 if (time_status & STA_PPSTIME && 456 time_status & STA_PPSJITTER) { 457 ntv.time_state = TIME_ERROR; 458 } 459 460 /* 461 * PPS wander exceeded or calibration error when 462 * frequency synchronization requested 463 */ 464 if (time_status & STA_PPSFREQ && 465 time_status & (STA_PPSWANDER | STA_PPSERROR)) { 466 ntv.time_state = TIME_ERROR; 467 } 468 return (sysctl_handle_opaque(oidp, &ntv, sizeof ntv, req)); 469} 470 471SYSCTL_NODE(_kern, KERN_NTP_PLL, ntp_pll, CTLFLAG_RW, 0, 472 "NTP kernel PLL related stuff"); 473SYSCTL_PROC(_kern_ntp_pll, NTP_PLL_GETTIME, gettime, CTLTYPE_OPAQUE|CTLFLAG_RD, 474 0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", ""); 475 476/* 477 * ntp_adjtime() - NTP daemon application interface 478 */ 479#ifndef _SYS_SYSPROTO_H_ 480struct ntp_adjtime_args { 481 struct timex *tp; 482}; 483#endif 484 485int 486ntp_adjtime(struct proc *p, struct ntp_adjtime_args *uap) 487{ 488 struct timex ntv; 489 int modes; 490 int s; 491 int error; 492 493 error = copyin((caddr_t)uap->tp, (caddr_t)&ntv, sizeof(ntv)); 494 if (error) 495 return error; 496 497 /* 498 * Update selected clock variables - only the superuser can 499 * change anything. Note that there is no error checking here on 500 * the assumption the superuser should know what it is doing. 501 */ 502 modes = ntv.modes; 503 if ((modes != 0) 504 && (error = suser(p->p_cred->pc_ucred, &p->p_acflag))) 505 return error; 506 507 s = splclock(); 508 if (modes & MOD_FREQUENCY) 509#ifdef PPS_SYNC 510 time_freq = ntv.freq - pps_freq; 511#else /* PPS_SYNC */ 512 time_freq = ntv.freq; 513#endif /* PPS_SYNC */ 514 if (modes & MOD_MAXERROR) 515 time_maxerror = ntv.maxerror; 516 if (modes & MOD_ESTERROR) 517 time_esterror = ntv.esterror; 518 if (modes & MOD_STATUS) { 519 time_status &= STA_RONLY; 520 time_status |= ntv.status & ~STA_RONLY; 521 } 522 if (modes & MOD_TIMECONST) 523 time_constant = ntv.constant; 524 if (modes & MOD_OFFSET) 525 hardupdate(ntv.offset); 526 527 /* 528 * Retrieve all clock variables 529 */ 530 if (time_offset < 0) 531 ntv.offset = -(-time_offset >> SHIFT_UPDATE); 532 else 533 ntv.offset = time_offset >> SHIFT_UPDATE; 534#ifdef PPS_SYNC 535 ntv.freq = time_freq + pps_freq; 536#else /* PPS_SYNC */ 537 ntv.freq = time_freq; 538#endif /* PPS_SYNC */ 539 ntv.maxerror = time_maxerror; 540 ntv.esterror = time_esterror; 541 ntv.status = time_status; 542 ntv.constant = time_constant; 543 ntv.precision = time_precision; 544 ntv.tolerance = time_tolerance; 545#ifdef PPS_SYNC 546 ntv.shift = pps_shift; 547 ntv.ppsfreq = pps_freq; 548 ntv.jitter = pps_jitter >> PPS_AVG; 549 ntv.stabil = pps_stabil; 550 ntv.calcnt = pps_calcnt; 551 ntv.errcnt = pps_errcnt; 552 ntv.jitcnt = pps_jitcnt; 553 ntv.stbcnt = pps_stbcnt; 554#endif /* PPS_SYNC */ 555 (void)splx(s); 556 557 error = copyout((caddr_t)&ntv, (caddr_t)uap->tp, sizeof(ntv)); 558 if (!error) { 559 /* 560 * Status word error decode. See comments in 561 * ntp_gettime() routine. 562 */ 563 p->p_retval[0] = time_state; 564 if (time_status & (STA_UNSYNC | STA_CLOCKERR)) 565 p->p_retval[0] = TIME_ERROR; 566 if (time_status & (STA_PPSFREQ | STA_PPSTIME) && 567 !(time_status & STA_PPSSIGNAL)) 568 p->p_retval[0] = TIME_ERROR; 569 if (time_status & STA_PPSTIME && 570 time_status & STA_PPSJITTER) 571 p->p_retval[0] = TIME_ERROR; 572 if (time_status & STA_PPSFREQ && 573 time_status & (STA_PPSWANDER | STA_PPSERROR)) 574 p->p_retval[0] = TIME_ERROR; 575 } 576 return error; 577} 578 579#ifdef PPS_SYNC 580 581/* We need this ugly monster twice, so let's macroize it. */ 582 583#define MEDIAN3X(a, m, s, i1, i2, i3) \ 584 do { \ 585 m = a[i2]; \ 586 s = a[i1] - a[i3]; \ 587 } while (0) 588 589#define MEDIAN3(a, m, s) \ 590 do { \ 591 if (a[0] > a[1]) { \ 592 if (a[1] > a[2]) \ 593 MEDIAN3X(a, m, s, 0, 1, 2); \ 594 else if (a[2] > a[0]) \ 595 MEDIAN3X(a, m, s, 2, 0, 1); \ 596 else \ 597 MEDIAN3X(a, m, s, 0, 2, 1); \ 598 } else { \ 599 if (a[2] > a[1]) \ 600 MEDIAN3X(a, m, s, 2, 1, 0); \ 601 else if (a[0] > a[2]) \ 602 MEDIAN3X(a, m, s, 1, 0, 2); \ 603 else \ 604 MEDIAN3X(a, m, s, 1, 2, 0); \ 605 } \ 606 } while (0) 607 608/* 609 * hardpps() - discipline CPU clock oscillator to external PPS signal 610 * 611 * This routine is called at each PPS interrupt in order to discipline 612 * the CPU clock oscillator to the PPS signal. It measures the PPS phase 613 * and leaves it in a handy spot for the hardclock() routine. It 614 * integrates successive PPS phase differences and calculates the 615 * frequency offset. This is used in hardclock() to discipline the CPU 616 * clock oscillator so that intrinsic frequency error is cancelled out. 617 * The code requires the caller to capture the time and hardware counter 618 * value at the on-time PPS signal transition. 619 * 620 * Note that, on some Unix systems, this routine runs at an interrupt 621 * priority level higher than the timer interrupt routine hardclock(). 622 * Therefore, the variables used are distinct from the hardclock() 623 * variables, except for certain exceptions: The PPS frequency pps_freq 624 * and phase pps_offset variables are determined by this routine and 625 * updated atomically. The time_tolerance variable can be considered a 626 * constant, since it is infrequently changed, and then only when the 627 * PPS signal is disabled. The watchdog counter pps_valid is updated 628 * once per second by hardclock() and is atomically cleared in this 629 * routine. 630 */ 631void 632hardpps(tvp, p_usec) 633 struct timeval *tvp; /* time at PPS */ 634 long p_usec; /* hardware counter at PPS */ 635{ 636 long u_usec, v_usec, bigtick; 637 long cal_sec, cal_usec; 638 639 /* 640 * An occasional glitch can be produced when the PPS interrupt 641 * occurs in the hardclock() routine before the time variable is 642 * updated. Here the offset is discarded when the difference 643 * between it and the last one is greater than tick/2, but not 644 * if the interval since the first discard exceeds 30 s. 645 */ 646 time_status |= STA_PPSSIGNAL; 647 time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR); 648 pps_valid = 0; 649 u_usec = -tvp->tv_usec; 650 if (u_usec < -500000) 651 u_usec += 1000000; 652 v_usec = pps_offset - u_usec; 653 if (v_usec < 0) 654 v_usec = -v_usec; 655 if (v_usec > (tick >> 1)) { 656 if (pps_glitch > MAXGLITCH) { 657 pps_glitch = 0; 658 pps_tf[2] = u_usec; 659 pps_tf[1] = u_usec; 660 } else { 661 pps_glitch++; 662 u_usec = pps_offset; 663 } 664 } else 665 pps_glitch = 0; 666 667 /* 668 * A three-stage median filter is used to help deglitch the pps 669 * time. The median sample becomes the time offset estimate; the 670 * difference between the other two samples becomes the time 671 * dispersion (jitter) estimate. 672 */ 673 pps_tf[2] = pps_tf[1]; 674 pps_tf[1] = pps_tf[0]; 675 pps_tf[0] = u_usec; 676 MEDIAN3(pps_tf, pps_offset, v_usec); 677 if (v_usec > MAXTIME) 678 pps_jitcnt++; 679 v_usec = (v_usec << PPS_AVG) - pps_jitter; 680 if (v_usec < 0) 681 pps_jitter -= -v_usec >> PPS_AVG; 682 else 683 pps_jitter += v_usec >> PPS_AVG; 684 if (pps_jitter > (MAXTIME >> 1)) 685 time_status |= STA_PPSJITTER; 686 687 /* 688 * During the calibration interval adjust the starting time when 689 * the tick overflows. At the end of the interval compute the 690 * duration of the interval and the difference of the hardware 691 * counters at the beginning and end of the interval. This code 692 * is deliciously complicated by the fact valid differences may 693 * exceed the value of tick when using long calibration 694 * intervals and small ticks. Note that the counter can be 695 * greater than tick if caught at just the wrong instant, but 696 * the values returned and used here are correct. 697 */ 698 bigtick = (long)tick << SHIFT_USEC; 699 pps_usec -= pps_freq; 700 if (pps_usec >= bigtick) 701 pps_usec -= bigtick; 702 if (pps_usec < 0) 703 pps_usec += bigtick; 704 pps_time.tv_sec++; 705 pps_count++; 706 if (pps_count < (1 << pps_shift)) 707 return; 708 pps_count = 0; 709 pps_calcnt++; 710 u_usec = p_usec << SHIFT_USEC; 711 v_usec = pps_usec - u_usec; 712 if (v_usec >= bigtick >> 1) 713 v_usec -= bigtick; 714 if (v_usec < -(bigtick >> 1)) 715 v_usec += bigtick; 716 if (v_usec < 0) 717 v_usec = -(-v_usec >> pps_shift); 718 else 719 v_usec = v_usec >> pps_shift; 720 pps_usec = u_usec; 721 cal_sec = tvp->tv_sec; 722 cal_usec = tvp->tv_usec; 723 cal_sec -= pps_time.tv_sec; 724 cal_usec -= pps_time.tv_usec; 725 if (cal_usec < 0) { 726 cal_usec += 1000000; 727 cal_sec--; 728 } 729 pps_time = *tvp; 730 731 /* 732 * Check for lost interrupts, noise, excessive jitter and 733 * excessive frequency error. The number of timer ticks during 734 * the interval may vary +-1 tick. Add to this a margin of one 735 * tick for the PPS signal jitter and maximum frequency 736 * deviation. If the limits are exceeded, the calibration 737 * interval is reset to the minimum and we start over. 738 */ 739 u_usec = (long)tick << 1; 740 if (!((cal_sec == -1 && cal_usec > (1000000 - u_usec)) 741 || (cal_sec == 0 && cal_usec < u_usec)) 742 || v_usec > time_tolerance || v_usec < -time_tolerance) { 743 pps_errcnt++; 744 pps_shift = PPS_SHIFT; 745 pps_intcnt = 0; 746 time_status |= STA_PPSERROR; 747 return; 748 } 749 750 /* 751 * A three-stage median filter is used to help deglitch the pps 752 * frequency. The median sample becomes the frequency offset 753 * estimate; the difference between the other two samples 754 * becomes the frequency dispersion (stability) estimate. 755 */ 756 pps_ff[2] = pps_ff[1]; 757 pps_ff[1] = pps_ff[0]; 758 pps_ff[0] = v_usec; 759 MEDIAN3(pps_ff, u_usec, v_usec); 760 761 /* 762 * Here the frequency dispersion (stability) is updated. If it 763 * is less than one-fourth the maximum (MAXFREQ), the frequency 764 * offset is updated as well, but clamped to the tolerance. It 765 * will be processed later by the hardclock() routine. 766 */ 767 v_usec = (v_usec >> 1) - pps_stabil; 768 if (v_usec < 0) 769 pps_stabil -= -v_usec >> PPS_AVG; 770 else 771 pps_stabil += v_usec >> PPS_AVG; 772 if (pps_stabil > MAXFREQ >> 2) { 773 pps_stbcnt++; 774 time_status |= STA_PPSWANDER; 775 return; 776 } 777 if (time_status & STA_PPSFREQ) { 778 if (u_usec < 0) { 779 pps_freq -= -u_usec >> PPS_AVG; 780 if (pps_freq < -time_tolerance) 781 pps_freq = -time_tolerance; 782 u_usec = -u_usec; 783 } else { 784 pps_freq += u_usec >> PPS_AVG; 785 if (pps_freq > time_tolerance) 786 pps_freq = time_tolerance; 787 } 788 } 789 790 /* 791 * Here the calibration interval is adjusted. If the maximum 792 * time difference is greater than tick / 4, reduce the interval 793 * by half. If this is not the case for four consecutive 794 * intervals, double the interval. 795 */ 796 if (u_usec << pps_shift > bigtick >> 2) { 797 pps_intcnt = 0; 798 if (pps_shift > PPS_SHIFT) 799 pps_shift--; 800 } else if (pps_intcnt >= 4) { 801 pps_intcnt = 0; 802 if (pps_shift < PPS_SHIFTMAX) 803 pps_shift++; 804 } else 805 pps_intcnt++; 806} 807 808#endif /* PPS_SYNC */ 809