kern_ntptime.c revision 45294
1/*********************************************************************** 2 * * 3 * Copyright (c) David L. Mills 1993-1999 * 4 * * 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 * 15 * warranty. * 16 * * 17 **********************************************************************/ 18 19/* 20 * Adapted from the original sources for FreeBSD and timecounters by: 21 * Poul-Henning Kamp <phk@FreeBSD.org>. 22 * 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 25 * in this file. 26 * 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. 30 */ 31 32#include "opt_ntp.h" 33 34#include <sys/param.h> 35#include <sys/systm.h> 36#include <sys/sysproto.h> 37#include <sys/kernel.h> 38#include <sys/proc.h> 39#include <sys/time.h> 40#include <sys/timex.h> 41#include <sys/timepps.h> 42#include <sys/sysctl.h> 43 44/* 45 * Single-precision macros for 64-bit machines 46 */ 47typedef long long l_fp; 48#define L_ADD(v, u) ((v) += (u)) 49#define L_SUB(v, u) ((v) -= (u)) 50#define L_ADDHI(v, a) ((v) += (long long)(a) << 32) 51#define L_NEG(v) ((v) = -(v)) 52#define L_RSHIFT(v, n) \ 53 do { \ 54 if ((v) < 0) \ 55 (v) = -(-(v) >> (n)); \ 56 else \ 57 (v) = (v) >> (n); \ 58 } while (0) 59#define L_MPY(v, a) ((v) *= (a)) 60#define L_CLR(v) ((v) = 0) 61#define L_ISNEG(v) ((v) < 0) 62#define L_LINT(v, a) ((v) = (long long)(a) << 32) 63#define L_GINT(v) ((v) < 0 ? -(-(v) >> 32) : (v) >> 32) 64 65/* 66 * Generic NTP kernel interface 67 * 68 * These routines constitute the Network Time Protocol (NTP) interfaces 69 * for user and daemon application programs. The ntp_gettime() routine 70 * provides the time, maximum error (synch distance) and estimated error 71 * (dispersion) to client user application programs. The ntp_adjtime() 72 * routine is used by the NTP daemon to adjust the system clock to an 73 * externally derived time. The time offset and related variables set by 74 * this routine are used by other routines in this module to adjust the 75 * phase and frequency of the clock discipline loop which controls the 76 * system clock. 77 * 78 * When the kernel time is reckoned directly in nanoseconds (NTP_NANO 79 * defined), the time at each tick interrupt is derived directly from 80 * the kernel time variable. When the kernel time is reckoned in 81 * microseconds, (NTP_NANO undefined), the time is derived from the 82 * kernel time variable together with a variable representing the 83 * leftover nanoseconds at the last tick interrupt. In either case, the 84 * current nanosecond time is reckoned from these values plus an 85 * interpolated value derived by the clock routines in another 86 * architecture-specific module. The interpolation can use either a 87 * dedicated counter or a processor cycle counter (PCC) implemented in 88 * some architectures. 89 * 90 * Note that all routines must run at priority splclock or higher. 91 */ 92 93/* 94 * Phase/frequency-lock loop (PLL/FLL) definitions 95 * 96 * The nanosecond clock discipline uses two variable types, time 97 * variables and frequency variables. Both types are represented as 64- 98 * bit fixed-point quantities with the decimal point between two 32-bit 99 * halves. On a 32-bit machine, each half is represented as a single 100 * word and mathematical operations are done using multiple-precision 101 * arithmetic. On a 64-bit machine, ordinary computer arithmetic is 102 * used. 103 * 104 * A time variable is a signed 64-bit fixed-point number in ns and 105 * fraction. It represents the remaining time offset to be amortized 106 * over succeeding tick interrupts. The maximum time offset is about 107 * 0.5 s and the resolution is about 2.3e-10 ns. 108 * 109 * 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 110 * 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 1 111 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 112 * |s s s| ns | 113 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 114 * | fraction | 115 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 116 * 117 * A frequency variable is a signed 64-bit fixed-point number in ns/s 118 * and fraction. It represents the ns and fraction to be added to the 119 * kernel time variable at each second. The maximum frequency offset is 120 * about +-500000 ns/s and the resolution is about 2.3e-10 ns/s. 121 * 122 * 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 123 * 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 1 124 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 125 * |s s s s s s s s s s s s s| ns/s | 126 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 127 * | fraction | 128 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 129 */ 130/* 131 * The following variables establish the state of the PLL/FLL and the 132 * residual time and frequency offset of the local clock. 133 */ 134#define SHIFT_PLL 4 /* PLL loop gain (shift) */ 135#define SHIFT_FLL 2 /* FLL loop gain (shift) */ 136 137static int time_state = TIME_OK; /* clock state */ 138static int time_status = STA_UNSYNC; /* clock status bits */ 139static long time_constant; /* poll interval (shift) (s) */ 140static long time_precision = 1; /* clock precision (ns) */ 141static long time_maxerror = MAXPHASE / 1000; /* maximum error (us) */ 142static long time_esterror = MAXPHASE / 1000; /* estimated error (us) */ 143static long time_reftime; /* time at last adjustment (s) */ 144static long time_tick; /* nanoseconds per tick (ns) */ 145static l_fp time_offset; /* time offset (ns) */ 146static l_fp time_freq; /* frequency offset (ns/s) */ 147 148int ntp_mult; 149int ntp_div; 150#ifdef PPS_SYNC 151/* 152 * The following variables are used when a pulse-per-second (PPS) signal 153 * is available and connected via a modem control lead. They establish 154 * the engineering parameters of the clock discipline loop when 155 * controlled by the PPS signal. 156 */ 157#define PPS_FAVG 2 /* min freq avg interval (s) (shift) */ 158#define PPS_FAVGMAX 8 /* max freq avg interval (s) (shift) */ 159#define PPS_PAVG 4 /* phase avg interval (s) (shift) */ 160#define PPS_VALID 120 /* PPS signal watchdog max (s) */ 161#define MAXTIME 500000 /* max PPS error (jitter) (ns) */ 162#define MAXWANDER 500000 /* max PPS wander (ns/s/s) */ 163 164struct ppstime { 165 long sec; /* PPS seconds */ 166 long nsec; /* PPS nanoseconds */ 167}; 168static struct ppstime pps_tf[3]; /* phase median filter */ 169static struct ppstime pps_filt; /* phase offset */ 170static l_fp pps_freq; /* scaled frequency offset (ns/s) */ 171static long pps_offacc; /* offset accumulator */ 172static long pps_fcount; /* frequency accumulator */ 173static long pps_jitter; /* scaled time dispersion (ns) */ 174static long pps_stabil; /* scaled frequency dispersion (ns/s) */ 175static long pps_lastsec; /* time at last calibration (s) */ 176static int pps_valid; /* signal watchdog counter */ 177static int pps_shift = PPS_FAVG; /* interval duration (s) (shift) */ 178static int pps_intcnt; /* wander counter */ 179static int pps_offcnt; /* offset accumulator counter */ 180 181/* 182 * PPS signal quality monitors 183 */ 184static long pps_calcnt; /* calibration intervals */ 185static long pps_jitcnt; /* jitter limit exceeded */ 186static long pps_stbcnt; /* stability limit exceeded */ 187static long pps_errcnt; /* calibration errors */ 188#endif /* PPS_SYNC */ 189/* 190 * End of phase/frequency-lock loop (PLL/FLL) definitions 191 */ 192 193static void ntp_init(void); 194static void hardupdate(long offset); 195 196/* 197 * ntp_gettime() - NTP user application interface 198 * 199 * See the timex.h header file for synopsis and API description. 200 */ 201static int 202ntp_sysctl SYSCTL_HANDLER_ARGS 203{ 204 struct ntptimeval ntv; /* temporary structure */ 205 struct timespec atv; /* nanosecond time */ 206 207 nanotime(&atv); 208 ntv.time.tv_sec = atv.tv_sec; 209 ntv.time.tv_nsec = atv.tv_nsec; 210 ntv.maxerror = time_maxerror; 211 ntv.esterror = time_esterror; 212 ntv.time_state = time_state; 213 214 /* 215 * Status word error decode. If any of these conditions occur, 216 * an error is returned, instead of the status word. Most 217 * applications will care only about the fact the system clock 218 * may not be trusted, not about the details. 219 * 220 * Hardware or software error 221 */ 222 if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) || 223 224 /* 225 * PPS signal lost when either time or frequency synchronization 226 * requested 227 */ 228 (time_status & (STA_PPSFREQ | STA_PPSTIME) && 229 !(time_status & STA_PPSSIGNAL)) || 230 231 /* 232 * PPS jitter exceeded when time synchronization requested 233 */ 234 (time_status & STA_PPSTIME && 235 time_status & STA_PPSJITTER) || 236 237 /* 238 * PPS wander exceeded or calibration error when frequency 239 * synchronization requested 240 */ 241 (time_status & STA_PPSFREQ && 242 time_status & (STA_PPSWANDER | STA_PPSERROR))) 243 ntv.time_state = TIME_ERROR; 244 return (sysctl_handle_opaque(oidp, &ntv, sizeof ntv, req)); 245} 246 247SYSCTL_NODE(_kern, OID_AUTO, ntp_pll, CTLFLAG_RW, 0, ""); 248SYSCTL_PROC(_kern_ntp_pll, OID_AUTO, gettime, CTLTYPE_OPAQUE|CTLFLAG_RD, 249 0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", ""); 250 251SYSCTL_INT(_kern_ntp_pll, OID_AUTO, mult, CTLFLAG_RW, &ntp_mult, 0, ""); 252SYSCTL_INT(_kern_ntp_pll, OID_AUTO, div, CTLFLAG_RW, &ntp_div, 0, ""); 253 254/* 255 * ntp_adjtime() - NTP daemon application interface 256 * 257 * See the timex.h header file for synopsis and API description. 258 */ 259#ifndef _SYS_SYSPROTO_H_ 260struct ntp_adjtime_args { 261 struct timex *tp; 262}; 263#endif 264 265int 266ntp_adjtime(struct proc *p, struct ntp_adjtime_args *uap) 267{ 268 struct timex ntv; /* temporary structure */ 269 long freq; /* frequency ns/s) */ 270 int modes; /* mode bits from structure */ 271 int s; /* caller priority */ 272 int error; 273 274 error = copyin((caddr_t)uap->tp, (caddr_t)&ntv, sizeof(ntv)); 275 if (error) 276 return(error); 277 278 /* 279 * Update selected clock variables - only the superuser can 280 * change anything. Note that there is no error checking here on 281 * the assumption the superuser should know what it is doing. 282 */ 283 modes = ntv.modes; 284 if (modes) 285 error = suser(p->p_cred->pc_ucred, &p->p_acflag); 286 if (error) 287 return (error); 288 s = splclock(); 289 if (modes & MOD_FREQUENCY) { 290 freq = (ntv.freq * 1000) << 16; 291 if (freq > MAXFREQ) 292 L_LINT(time_freq, MAXFREQ); 293 else if (freq < -MAXFREQ) 294 L_LINT(time_freq, -MAXFREQ); 295 else 296 L_LINT(time_freq, freq); 297 298#ifdef PPS_SYNC 299 pps_freq = time_freq; 300#endif /* PPS_SYNC */ 301 } 302 if (modes & MOD_MAXERROR) 303 time_maxerror = ntv.maxerror; 304 if (modes & MOD_ESTERROR) 305 time_esterror = ntv.esterror; 306 if (modes & MOD_STATUS) { 307 time_status &= STA_RONLY; 308 time_status |= ntv.status & ~STA_RONLY; 309 } 310 if (modes & MOD_TIMECONST) { 311 if (ntv.constant < 0) 312 time_constant = 0; 313 else if (ntv.constant > MAXTC) 314 time_constant = MAXTC; 315 else 316 time_constant = ntv.constant; 317 } 318 if (modes & MOD_NANO) 319 time_status |= STA_NANO; 320 if (modes & MOD_MICRO) 321 time_status &= ~STA_NANO; 322 if (modes & MOD_CLKB) 323 time_status |= STA_CLK; 324 if (modes & MOD_CLKA) 325 time_status &= ~STA_CLK; 326 if (modes & MOD_OFFSET) { 327 if (time_status & STA_NANO) 328 hardupdate(ntv.offset); 329 else 330 hardupdate(ntv.offset * 1000); 331 } 332 333 /* 334 * Retrieve all clock variables 335 */ 336 if (time_status & STA_NANO) 337 ntv.offset = L_GINT(time_offset); 338 else 339 ntv.offset = L_GINT(time_offset) / 1000; 340 ntv.freq = L_GINT((time_freq / 1000) << 16); 341 ntv.maxerror = time_maxerror; 342 ntv.esterror = time_esterror; 343 ntv.status = time_status; 344 ntv.constant = time_constant; 345 if (time_status & STA_NANO) 346 ntv.precision = time_precision; 347 else 348 ntv.precision = time_precision / 1000; 349 ntv.tolerance = MAXFREQ * SCALE_PPM; 350#ifdef PPS_SYNC 351 ntv.shift = pps_shift; 352 ntv.ppsfreq = L_GINT((pps_freq / 1000) << 16); 353 ntv.jitter = pps_jitter; 354 if (time_status & STA_NANO) 355 ntv.jitter = pps_jitter; 356 else 357 ntv.jitter = pps_jitter / 1000; 358 ntv.stabil = pps_stabil; 359 ntv.calcnt = pps_calcnt; 360 ntv.errcnt = pps_errcnt; 361 ntv.jitcnt = pps_jitcnt; 362 ntv.stbcnt = pps_stbcnt; 363#endif /* PPS_SYNC */ 364 splx(s); 365 366 error = copyout((caddr_t)&ntv, (caddr_t)uap->tp, sizeof(ntv)); 367 if (error) 368 return (error); 369 370 /* 371 * Status word error decode. See comments in 372 * ntp_gettime() routine. 373 */ 374 if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) || 375 (time_status & (STA_PPSFREQ | STA_PPSTIME) && 376 !(time_status & STA_PPSSIGNAL)) || 377 (time_status & STA_PPSTIME && 378 time_status & STA_PPSJITTER) || 379 (time_status & STA_PPSFREQ && 380 time_status & (STA_PPSWANDER | STA_PPSERROR))) 381 return (TIME_ERROR); 382 return (time_state); 383} 384 385/* 386 * second_overflow() - called after ntp_tick_adjust() 387 * 388 * This routine is ordinarily called immediately following the above 389 * routine ntp_tick_adjust(). While these two routines are normally 390 * combined, they are separated here only for the purposes of 391 * simulation. 392 */ 393void 394ntp_update_second(struct timecounter *tcp) 395{ 396 u_int32_t *newsec; 397 l_fp ftemp, time_adj; /* 32/64-bit temporaries */ 398 399 newsec = &tcp->tc_offset_sec; 400 time_maxerror += MAXFREQ / 1000; 401 402 /* 403 * Leap second processing. If in leap-insert state at 404 * the end of the day, the system clock is set back one 405 * second; if in leap-delete state, the system clock is 406 * set ahead one second. The nano_time() routine or 407 * external clock driver will insure that reported time 408 * is always monotonic. 409 */ 410 switch (time_state) { 411 412 /* 413 * No warning. 414 */ 415 case TIME_OK: 416 if (time_status & STA_INS) 417 time_state = TIME_INS; 418 else if (time_status & STA_DEL) 419 time_state = TIME_DEL; 420 break; 421 422 /* 423 * Insert second 23:59:60 following second 424 * 23:59:59. 425 */ 426 case TIME_INS: 427 if (!(time_status & STA_INS)) 428 time_state = TIME_OK; 429 else if ((*newsec) % 86400 == 0) { 430 (*newsec)--; 431 time_state = TIME_OOP; 432 } 433 break; 434 435 /* 436 * Delete second 23:59:59. 437 */ 438 case TIME_DEL: 439 if (!(time_status & STA_DEL)) 440 time_state = TIME_OK; 441 else if (((*newsec) + 1) % 86400 == 0) { 442 (*newsec)++; 443 time_state = TIME_WAIT; 444 } 445 break; 446 447 /* 448 * Insert second in progress. 449 */ 450 case TIME_OOP: 451 time_state = TIME_WAIT; 452 break; 453 454 /* 455 * Wait for status bits to clear. 456 */ 457 case TIME_WAIT: 458 if (!(time_status & (STA_INS | STA_DEL))) 459 time_state = TIME_OK; 460 } 461 462 /* 463 * Compute the total time adjustment for the next 464 * second in ns. The offset is reduced by a factor 465 * depending on FLL or PLL mode and whether the PPS 466 * signal is operating. Note that the value is in effect 467 * scaled by the clock frequency, since the adjustment 468 * is added at each tick interrupt. 469 */ 470 ftemp = time_offset; 471#ifdef PPS_SYNC 472 if (time_status & STA_PPSTIME && time_status & 473 STA_PPSSIGNAL) 474 L_RSHIFT(ftemp, PPS_FAVG); 475 else if (time_status & STA_MODE) 476#else 477 if (time_status & STA_MODE) 478#endif /* PPS_SYNC */ 479 L_RSHIFT(ftemp, SHIFT_FLL); 480 else 481 L_RSHIFT(ftemp, SHIFT_PLL + time_constant); 482 time_adj = ftemp; 483 L_SUB(time_offset, ftemp); 484 L_ADD(time_adj, time_freq); 485 tcp->tc_adjustment = time_adj; 486#ifdef PPS_SYNC 487 if (pps_valid > 0) 488 pps_valid--; 489 else 490 time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER | 491 STA_PPSWANDER | STA_PPSERROR); 492#endif /* PPS_SYNC */ 493} 494 495/* 496 * ntp_init() - initialize variables and structures 497 * 498 * This routine must be called after the kernel variables hz and tick 499 * are set or changed and before the next tick interrupt. In this 500 * particular implementation, these values are assumed set elsewhere in 501 * the kernel. The design allows the clock frequency and tick interval 502 * to be changed while the system is running. So, this routine should 503 * probably be integrated with the code that does that. 504 */ 505static void 506ntp_init() 507{ 508 509 /* 510 * The following variable must be initialized any time the 511 * kernel variable hz is changed. 512 */ 513 time_tick = NANOSECOND / hz; 514 515 /* 516 * The following variables are initialized only at startup. Only 517 * those structures not cleared by the compiler need to be 518 * initialized, and these only in the simulator. In the actual 519 * kernel, any nonzero values here will quickly evaporate. 520 */ 521 L_CLR(time_offset); 522 L_CLR(time_freq); 523#ifdef PPS_SYNC 524 pps_filt.sec = pps_filt.nsec = 0; 525 pps_tf[0] = pps_tf[1] = pps_tf[2] = pps_filt; 526 pps_fcount = 0; 527 L_CLR(pps_freq); 528#endif /* PPS_SYNC */ 529} 530 531SYSINIT(ntpclocks, SI_SUB_CLOCKS, SI_ORDER_FIRST, ntp_init, NULL) 532 533/* 534 * hardupdate() - local clock update 535 * 536 * This routine is called by ntp_adjtime() to update the local clock 537 * phase and frequency. The implementation is of an adaptive-parameter, 538 * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new 539 * time and frequency offset estimates for each call. If the kernel PPS 540 * discipline code is configured (PPS_SYNC), the PPS signal itself 541 * determines the new time offset, instead of the calling argument. 542 * Presumably, calls to ntp_adjtime() occur only when the caller 543 * believes the local clock is valid within some bound (+-128 ms with 544 * NTP). If the caller's time is far different than the PPS time, an 545 * argument will ensue, and it's not clear who will lose. 546 * 547 * For uncompensated quartz crystal oscillators and nominal update 548 * intervals less than 256 s, operation should be in phase-lock mode, 549 * where the loop is disciplined to phase. For update intervals greater 550 * than 1024 s, operation should be in frequency-lock mode, where the 551 * loop is disciplined to frequency. Between 256 s and 1024 s, the mode 552 * is selected by the STA_MODE status bit. 553 */ 554static void 555hardupdate(offset) 556 long offset; /* clock offset (ns) */ 557{ 558 long ltemp, mtemp; 559 l_fp ftemp; 560 561 /* 562 * Select how the phase is to be controlled and from which 563 * source. If the PPS signal is present and enabled to 564 * discipline the time, the PPS offset is used; otherwise, the 565 * argument offset is used. 566 */ 567 ltemp = offset; 568 if (ltemp > MAXPHASE) 569 ltemp = MAXPHASE; 570 else if (ltemp < -MAXPHASE) 571 ltemp = -MAXPHASE; 572 if (!(time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)) 573 L_LINT(time_offset, ltemp); 574 575 /* 576 * Select how the frequency is to be controlled and in which 577 * mode (PLL or FLL). If the PPS signal is present and enabled 578 * to discipline the frequency, the PPS frequency is used; 579 * otherwise, the argument offset is used to compute it. 580 */ 581 if (time_status & STA_PPSFREQ && time_status & STA_PPSSIGNAL) { 582 time_reftime = time_second; 583 return; 584 } 585 if (time_status & STA_FREQHOLD || time_reftime == 0) 586 time_reftime = time_second; 587 mtemp = time_second - time_reftime; 588 if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC) 589 ) { 590 L_LINT(ftemp, (ltemp << 4) / mtemp); 591 L_RSHIFT(ftemp, SHIFT_FLL + 4); 592 L_ADD(time_freq, ftemp); 593 time_status |= STA_MODE; 594 } else { 595 L_LINT(ftemp, ltemp); 596 L_RSHIFT(ftemp, (SHIFT_PLL + 2 + time_constant) << 1); 597 L_MPY(ftemp, mtemp); 598 L_ADD(time_freq, ftemp); 599 time_status &= ~STA_MODE; 600 } 601 time_reftime = time_second; 602 if (L_GINT(time_freq) > MAXFREQ) 603 L_LINT(time_freq, MAXFREQ); 604 else if (L_GINT(time_freq) < -MAXFREQ) 605 L_LINT(time_freq, -MAXFREQ); 606} 607 608#ifdef PPS_SYNC 609/* 610 * hardpps() - discipline CPU clock oscillator to external PPS signal 611 * 612 * This routine is called at each PPS interrupt in order to discipline 613 * the CPU clock oscillator to the PPS signal. It measures the PPS phase 614 * and leaves it in a handy spot for the hardclock() routine. It 615 * integrates successive PPS phase differences and calculates the 616 * frequency offset. This is used in hardclock() to discipline the CPU 617 * clock oscillator so that the intrinsic frequency error is cancelled 618 * out. The code requires the caller to capture the time and 619 * architecture-dependent hardware counter values in nanoseconds at the 620 * on-time PPS signal transition. 621 * 622 * Note that, on some Unix systems this routine runs at an interrupt 623 * priority level higher than the timer interrupt routine hardclock(). 624 * Therefore, the variables used are distinct from the hardclock() 625 * variables, except for the actual time and frequency variables, which 626 * are determined by this routine and updated atomically. 627 */ 628void 629hardpps(tsp, nsec) 630 struct timespec *tsp; /* time at PPS */ 631 long nsec; /* hardware counter at PPS */ 632{ 633 long u_sec, u_nsec, v_nsec; /* temps */ 634 l_fp ftemp; 635 636 /* 637 * The signal is first processed by a frequency discriminator 638 * which rejects noise and input signals with frequencies 639 * outside the range 1 +-MAXFREQ PPS. If two hits occur in the 640 * same second, we ignore the later hit; if not and a hit occurs 641 * outside the range gate, keep the later hit but do not 642 * process it. 643 */ 644 time_status |= STA_PPSSIGNAL | STA_PPSJITTER; 645 time_status &= ~(STA_PPSWANDER | STA_PPSERROR); 646 pps_valid = PPS_VALID; 647 u_sec = tsp->tv_sec; 648 u_nsec = tsp->tv_nsec; 649 if (u_nsec >= (NANOSECOND >> 1)) { 650 u_nsec -= NANOSECOND; 651 u_sec++; 652 } 653 v_nsec = u_nsec - pps_tf[0].nsec; 654 if (u_sec == pps_tf[0].sec && v_nsec < -MAXFREQ) { 655 return; 656 } 657 pps_tf[2] = pps_tf[1]; 658 pps_tf[1] = pps_tf[0]; 659 pps_tf[0].sec = u_sec; 660 pps_tf[0].nsec = u_nsec; 661 662 /* 663 * Compute the difference between the current and previous 664 * counter values. If the difference exceeds 0.5 s, assume it 665 * has wrapped around, so correct 1.0 s. If the result exceeds 666 * the tick interval, the sample point has crossed a tick 667 * boundary during the last second, so correct the tick. Very 668 * intricate. 669 */ 670 u_nsec = nsec; 671 if (u_nsec > (NANOSECOND >> 1)) 672 u_nsec -= NANOSECOND; 673 else if (u_nsec < -(NANOSECOND >> 1)) 674 u_nsec += NANOSECOND; 675 pps_fcount += u_nsec; 676 if (v_nsec > MAXFREQ) { 677 return; 678 } 679 time_status &= ~STA_PPSJITTER; 680 681 /* 682 * A three-stage median filter is used to help denoise the PPS 683 * time. The median sample becomes the time offset estimate; the 684 * difference between the other two samples becomes the time 685 * dispersion (jitter) estimate. 686 */ 687 if (pps_tf[0].nsec > pps_tf[1].nsec) { 688 if (pps_tf[1].nsec > pps_tf[2].nsec) { 689 pps_filt = pps_tf[1]; /* 0 1 2 */ 690 u_nsec = pps_tf[0].nsec - pps_tf[2].nsec; 691 } else if (pps_tf[2].nsec > pps_tf[0].nsec) { 692 pps_filt = pps_tf[0]; /* 2 0 1 */ 693 u_nsec = pps_tf[2].nsec - pps_tf[1].nsec; 694 } else { 695 pps_filt = pps_tf[2]; /* 0 2 1 */ 696 u_nsec = pps_tf[0].nsec - pps_tf[1].nsec; 697 } 698 } else { 699 if (pps_tf[1].nsec < pps_tf[2].nsec) { 700 pps_filt = pps_tf[1]; /* 2 1 0 */ 701 u_nsec = pps_tf[2].nsec - pps_tf[0].nsec; 702 } else if (pps_tf[2].nsec < pps_tf[0].nsec) { 703 pps_filt = pps_tf[0]; /* 1 0 2 */ 704 u_nsec = pps_tf[1].nsec - pps_tf[2].nsec; 705 } else { 706 pps_filt = pps_tf[2]; /* 1 2 0 */ 707 u_nsec = pps_tf[1].nsec - pps_tf[0].nsec; 708 } 709 } 710 711 /* 712 * Nominal jitter is due to PPS signal noise and interrupt 713 * latency. If it exceeds the jitter limit, the sample is 714 * discarded. otherwise, if so enabled, the time offset is 715 * updated. The offsets are accumulated over the phase averaging 716 * interval to improve accuracy. The jitter is averaged only for 717 * performance monitoring. We can tolerate a modest loss of data 718 * here without degrading time accuracy. 719 */ 720 if (u_nsec > MAXTIME) { 721 time_status |= STA_PPSJITTER; 722 pps_jitcnt++; 723 } else if (time_status & STA_PPSTIME) { 724 pps_offacc -= pps_filt.nsec; 725 pps_offcnt++; 726 } 727 if (pps_offcnt >= (1 << PPS_PAVG)) { 728 if (time_status & STA_PPSTIME) { 729 L_LINT(time_offset, pps_offacc); 730 L_RSHIFT(time_offset, PPS_PAVG); 731 } 732 pps_offacc = 0; 733 pps_offcnt = 0; 734 } 735 pps_jitter += (u_nsec - pps_jitter) >> PPS_FAVG; 736 u_sec = pps_tf[0].sec - pps_lastsec; 737 if (ntp_div && ntp_mult) { 738 L_LINT(ftemp, (pps_filt.nsec)); 739 L_RSHIFT(ftemp, ntp_div); 740 L_MPY(ftemp, ntp_mult); 741 L_ADD(pps_freq, ftemp); 742 if (time_status & STA_PPSFREQ) 743 time_freq = pps_freq; 744 return; 745 } 746 if (u_sec < (1 << pps_shift)) 747 return; 748 749 /* 750 * At the end of the calibration interval the difference between 751 * the first and last counter values becomes the scaled 752 * frequency. It will later be divided by the length of the 753 * interval to determine the frequency update. If the frequency 754 * exceeds a sanity threshold, or if the actual calibration 755 * interval is not equal to the expected length, the data are 756 * discarded. We can tolerate a modest loss of data here without 757 * degrading frequency ccuracy. 758 */ 759 pps_calcnt++; 760 v_nsec = -pps_fcount; 761 pps_lastsec = pps_tf[0].sec; 762 pps_fcount = 0; 763 u_nsec = MAXFREQ << pps_shift; 764 if (v_nsec > u_nsec || v_nsec < -u_nsec || u_sec != (1 << 765 pps_shift)) { 766 time_status |= STA_PPSERROR; 767 pps_errcnt++; 768 return; 769 } 770 771 /* 772 * If the actual calibration interval is not equal to the 773 * expected length, the data are discarded. If the wander is 774 * less than the wander threshold for four consecutive 775 * intervals, the interval is doubled; if it is greater than the 776 * threshold for four consecutive intervals, the interval is 777 * halved. The scaled frequency offset is converted to frequency 778 * offset. The stability metric is calculated as the average of 779 * recent frequency changes, but is used only for performance 780 * monitoring. 781 */ 782 L_LINT(ftemp, v_nsec); 783 L_RSHIFT(ftemp, pps_shift); 784 L_SUB(ftemp, pps_freq); 785 u_nsec = L_GINT(ftemp); 786 if (u_nsec > MAXWANDER) { 787 L_LINT(ftemp, MAXWANDER); 788 pps_intcnt--; 789 time_status |= STA_PPSWANDER; 790 pps_stbcnt++; 791 } else if (u_nsec < -MAXWANDER) { 792 L_LINT(ftemp, -MAXWANDER); 793 pps_intcnt--; 794 time_status |= STA_PPSWANDER; 795 pps_stbcnt++; 796 } else { 797 pps_intcnt++; 798 } 799 if (pps_intcnt >= 4) { 800 pps_intcnt = 4; 801 if (pps_shift < PPS_FAVGMAX) { 802 pps_shift++; 803 pps_intcnt = 0; 804 } 805 } else if (pps_intcnt <= -4) { 806 pps_intcnt = -4; 807 if (pps_shift > PPS_FAVG) { 808 pps_shift--; 809 pps_intcnt = 0; 810 } 811 } 812 if (u_nsec < 0) 813 u_nsec = -u_nsec; 814 pps_stabil += (u_nsec * SCALE_PPM - pps_stabil) >> PPS_FAVG; 815 816 /* 817 * The frequency offset is averaged into the PPS frequency. If 818 * enabled, the system clock frequency is updated as well. 819 */ 820 L_RSHIFT(ftemp, PPS_FAVG); 821 L_ADD(pps_freq, ftemp); 822 u_nsec = L_GINT(pps_freq); 823 if (u_nsec > MAXFREQ) 824 L_LINT(pps_freq, MAXFREQ); 825 else if (u_nsec < -MAXFREQ) 826 L_LINT(pps_freq, -MAXFREQ); 827 if (time_status & STA_PPSFREQ) 828 time_freq = pps_freq; 829} 830#endif /* PPS_SYNC */ 831