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 */ 47 typedef 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) */ 136 137 static int time_state = TIME_OK; /* clock state */ 138 static int time_status = STA_UNSYNC; /* clock status bits */ 139 static long time_constant; /* poll interval (shift) (s) */ 140 static long time_precision = 1; /* clock precision (ns) */ 141 static long time_maxerror = MAXPHASE / 1000; /* maximum error (us) */ 142 static long time_esterror = MAXPHASE / 1000; /* estimated error (us) */ 143 static long time_reftime; /* time at last adjustment (s) */ 144 static long time_tick; /* nanoseconds per tick (ns) */ 145 static l_fp time_offset; /* time offset (ns) */ 146 static l_fp time_freq; /* frequency offset (ns/s) */ 147 148 int ntp_mult; 149 int 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) */ 163 164 struct ppstime { 165 long sec; /* PPS seconds */ 166 long nsec; /* PPS nanoseconds */ 167 }; 168 static struct ppstime pps_tf[3]; /* phase median filter */ 169 static struct ppstime pps_filt; /* phase offset */ 170 static l_fp pps_freq; /* scaled frequency offset (ns/s) */ 171 static long pps_offacc; /* offset accumulator */ 172 static long pps_fcount; /* frequency accumulator */ 173 static long pps_jitter; /* scaled time dispersion (ns) */ 174 static long pps_stabil; /* scaled frequency dispersion (ns/s) */ 175 static long pps_lastsec; /* time at last calibration (s) */ 176 static int pps_valid; /* signal watchdog counter */ 177 static int pps_shift = PPS_FAVG; /* interval duration (s) (shift) */ 178 static int pps_intcnt; /* wander counter */ 179 static int pps_offcnt; /* offset accumulator counter */ 180 181 /* 182 * PPS signal quality monitors 183 */ 184 static long pps_calcnt; /* calibration intervals */ 185 static long pps_jitcnt; /* jitter limit exceeded */ 186 static long pps_stbcnt; /* stability limit exceeded */ 187 static long pps_errcnt; /* calibration errors */ 188 #endif /* PPS_SYNC */ 189 /* 190 * End of phase/frequency-lock loop (PLL/FLL) definitions 191 */ 192 193 static void ntp_init(void); 194 static 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 */ 201 static int 202 ntp_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 } 246 247 SYSCTL_NODE(_kern, OID_AUTO, ntp_pll, CTLFLAG_RW, 0, ""); 248 SYSCTL_PROC(_kern_ntp_pll, OID_AUTO, gettime, CTLTYPE_OPAQUE|CTLFLAG_RD, 249 0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", ""); 250 251 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, mult, CTLFLAG_RW, &ntp_mult, 0, ""); 252 SYSCTL_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_ 260 struct ntp_adjtime_args { 261 struct timex *tp; 262 }; 263 #endif 264 265 int 266 ntp_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); 286 if (error) 287 return (error); 288 s = splclock(); 289 if (modes & MOD_FREQUENCY) { 290 freq = (ntv.freq * 1000LL) >> 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 / 1000LL) << 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 / 1000LL) << 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 p->p_retval[0] = TIME_ERROR; 382 else 383 p->p_retval[0] = time_state; 384 return (error); 385 } 386 387 /* 388 * second_overflow() - called after ntp_tick_adjust() 389 * 390 * This routine is ordinarily called immediately following the above 391 * routine ntp_tick_adjust(). While these two routines are normally 392 * combined, they are separated here only for the purposes of 393 * simulation. 394 */ 395 void 396 ntp_update_second(struct timecounter *tcp) 397 { 398 u_int32_t *newsec; 399 l_fp ftemp, time_adj; /* 32/64-bit temporaries */ 400 401 newsec = &tcp->tc_offset_sec; 402 time_maxerror += MAXFREQ / 1000; 403 404 /* 405 * Leap second processing. If in leap-insert state at 406 * the end of the day, the system clock is set back one 407 * second; if in leap-delete state, the system clock is 408 * set ahead one second. The nano_time() routine or 409 * external clock driver will insure that reported time 410 * is always monotonic. 411 */ 412 switch (time_state) { 413 414 /* 415 * No warning. 416 */ 417 case TIME_OK: 418 if (time_status & STA_INS) 419 time_state = TIME_INS; 420 else if (time_status & STA_DEL) 421 time_state = TIME_DEL; 422 break; 423 424 /* 425 * Insert second 23:59:60 following second 426 * 23:59:59. 427 */ 428 case TIME_INS: 429 if (!(time_status & STA_INS)) 430 time_state = TIME_OK; 431 else if ((*newsec) % 86400 == 0) { 432 (*newsec)--; 433 time_state = TIME_OOP; 434 } 435 break; 436 437 /* 438 * Delete second 23:59:59. 439 */ 440 case TIME_DEL: 441 if (!(time_status & STA_DEL)) 442 time_state = TIME_OK; 443 else if (((*newsec) + 1) % 86400 == 0) { 444 (*newsec)++; 445 time_state = TIME_WAIT; 446 } 447 break; 448 449 /* 450 * Insert second in progress. 451 */ 452 case TIME_OOP: 453 time_state = TIME_WAIT; 454 break; 455 456 /* 457 * Wait for status bits to clear. 458 */ 459 case TIME_WAIT: 460 if (!(time_status & (STA_INS | STA_DEL))) 461 time_state = TIME_OK; 462 } 463 464 /* 465 * Compute the total time adjustment for the next 466 * second in ns. The offset is reduced by a factor 467 * depending on FLL or PLL mode and whether the PPS 468 * signal is operating. Note that the value is in effect 469 * scaled by the clock frequency, since the adjustment 470 * is added at each tick interrupt. 471 */ 472 ftemp = time_offset; 473 #ifdef PPS_SYNC 474 if (time_status & STA_PPSTIME && time_status & 475 STA_PPSSIGNAL) 476 L_RSHIFT(ftemp, PPS_FAVG); 477 else if (time_status & STA_MODE) 478 #else 479 if (time_status & STA_MODE) 480 #endif /* PPS_SYNC */ 481 L_RSHIFT(ftemp, SHIFT_FLL); 482 else 483 L_RSHIFT(ftemp, SHIFT_PLL + time_constant); 484 time_adj = ftemp; 485 L_SUB(time_offset, ftemp); 486 L_ADD(time_adj, time_freq); 487 tcp->tc_adjustment = time_adj; 488 #ifdef PPS_SYNC 489 if (pps_valid > 0) 490 pps_valid--; 491 else 492 time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER | 493 STA_PPSWANDER | STA_PPSERROR); 494 #endif /* PPS_SYNC */ 495 } 496 497 /* 498 * ntp_init() - initialize variables and structures 499 * 500 * This routine must be called after the kernel variables hz and tick 501 * are set or changed and before the next tick interrupt. In this 502 * particular implementation, these values are assumed set elsewhere in 503 * the kernel. The design allows the clock frequency and tick interval 504 * to be changed while the system is running. So, this routine should 505 * probably be integrated with the code that does that. 506 */ 507 static void 508 ntp_init() 509 { 510 511 /* 512 * The following variable must be initialized any time the 513 * kernel variable hz is changed. 514 */ 515 time_tick = NANOSECOND / hz; 516 517 /* 518 * The following variables are initialized only at startup. Only 519 * those structures not cleared by the compiler need to be 520 * initialized, and these only in the simulator. In the actual 521 * kernel, any nonzero values here will quickly evaporate. 522 */ 523 L_CLR(time_offset); 524 L_CLR(time_freq); 525 #ifdef PPS_SYNC 526 pps_filt.sec = pps_filt.nsec = 0; 527 pps_tf[0] = pps_tf[1] = pps_tf[2] = pps_filt; 528 pps_fcount = 0; 529 L_CLR(pps_freq); 530 #endif /* PPS_SYNC */ 531 } 532 533 SYSINIT(ntpclocks, SI_SUB_CLOCKS, SI_ORDER_FIRST, ntp_init, NULL) 534 535 /* 536 * hardupdate() - local clock update 537 * 538 * This routine is called by ntp_adjtime() to update the local clock 539 * phase and frequency. The implementation is of an adaptive-parameter, 540 * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new 541 * time and frequency offset estimates for each call. If the kernel PPS 542 * discipline code is configured (PPS_SYNC), the PPS signal itself 543 * determines the new time offset, instead of the calling argument. 544 * Presumably, calls to ntp_adjtime() occur only when the caller 545 * believes the local clock is valid within some bound (+-128 ms with 546 * NTP). If the caller's time is far different than the PPS time, an 547 * argument will ensue, and it's not clear who will lose. 548 * 549 * For uncompensated quartz crystal oscillators and nominal update 550 * intervals less than 256 s, operation should be in phase-lock mode, 551 * where the loop is disciplined to phase. For update intervals greater 552 * than 1024 s, operation should be in frequency-lock mode, where the 553 * loop is disciplined to frequency. Between 256 s and 1024 s, the mode 554 * is selected by the STA_MODE status bit. 555 */ 556 static void 557 hardupdate(offset) 558 long offset; /* clock offset (ns) */ 559 { 560 long ltemp, mtemp; 561 l_fp ftemp; 562 563 /* 564 * Select how the phase is to be controlled and from which 565 * source. If the PPS signal is present and enabled to 566 * discipline the time, the PPS offset is used; otherwise, the 567 * argument offset is used. 568 */ 569 ltemp = offset; 570 if (ltemp > MAXPHASE) 571 ltemp = MAXPHASE; 572 else if (ltemp < -MAXPHASE) 573 ltemp = -MAXPHASE; 574 if (!(time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)) 575 L_LINT(time_offset, ltemp); 576 577 /* 578 * Select how the frequency is to be controlled and in which 579 * mode (PLL or FLL). If the PPS signal is present and enabled 580 * to discipline the frequency, the PPS frequency is used; 581 * otherwise, the argument offset is used to compute it. 582 */ 583 if (time_status & STA_PPSFREQ && time_status & STA_PPSSIGNAL) { 584 time_reftime = time_second; 585 return; 586 } 587 if (time_status & STA_FREQHOLD || time_reftime == 0) 588 time_reftime = time_second; 589 mtemp = time_second - time_reftime; 590 if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC) 591 ) { 592 L_LINT(ftemp, (ltemp << 4) / mtemp); 593 L_RSHIFT(ftemp, SHIFT_FLL + 4); 594 L_ADD(time_freq, ftemp); 595 time_status |= STA_MODE; 596 } else { 597 L_LINT(ftemp, ltemp); 598 L_RSHIFT(ftemp, (SHIFT_PLL + 2 + time_constant) << 1); 599 L_MPY(ftemp, mtemp); 600 L_ADD(time_freq, ftemp); 601 time_status &= ~STA_MODE; 602 } 603 time_reftime = time_second; 604 if (L_GINT(time_freq) > MAXFREQ) 605 L_LINT(time_freq, MAXFREQ); 606 else if (L_GINT(time_freq) < -MAXFREQ) 607 L_LINT(time_freq, -MAXFREQ); 608 } 609 610 #ifdef PPS_SYNC 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 the intrinsic frequency error is cancelled 620 * out. The code requires the caller to capture the time and 621 * architecture-dependent hardware counter values in nanoseconds at the 622 * on-time PPS signal transition. 623 * 624 * Note that, on some Unix systems this routine runs at an interrupt 625 * priority level higher than the timer interrupt routine hardclock(). 626 * Therefore, the variables used are distinct from the hardclock() 627 * variables, except for the actual time and frequency variables, which 628 * are determined by this routine and updated atomically. 629 */ 630 void 631 hardpps(tsp, nsec) 632 struct timespec *tsp; /* time at PPS */ 633 long nsec; /* hardware counter at PPS */ 634 { 635 long u_sec, u_nsec, v_nsec; /* temps */ 636 l_fp ftemp; 637 638 /* 639 * The signal is first processed by a frequency discriminator 640 * which rejects noise and input signals with frequencies 641 * outside the range 1 +-MAXFREQ PPS. If two hits occur in the 642 * same second, we ignore the later hit; if not and a hit occurs 643 * outside the range gate, keep the later hit but do not 644 * process it. 645 */ 646 time_status |= STA_PPSSIGNAL | STA_PPSJITTER; 647 time_status &= ~(STA_PPSWANDER | STA_PPSERROR); 648 pps_valid = PPS_VALID; 649 u_sec = tsp->tv_sec; 650 u_nsec = tsp->tv_nsec; 651 if (u_nsec >= (NANOSECOND >> 1)) { 652 u_nsec -= NANOSECOND; 653 u_sec++; 654 } 655 v_nsec = u_nsec - pps_tf[0].nsec; 656 if (u_sec == pps_tf[0].sec && v_nsec < -MAXFREQ) { 657 return; 658 } 659 pps_tf[2] = pps_tf[1]; 660 pps_tf[1] = pps_tf[0]; 661 pps_tf[0].sec = u_sec; 662 pps_tf[0].nsec = u_nsec; 663 664 /* 665 * Compute the difference between the current and previous 666 * counter values. If the difference exceeds 0.5 s, assume it 667 * has wrapped around, so correct 1.0 s. If the result exceeds 668 * the tick interval, the sample point has crossed a tick 669 * boundary during the last second, so correct the tick. Very 670 * intricate. 671 */ 672 u_nsec = nsec; 673 if (u_nsec > (NANOSECOND >> 1)) 674 u_nsec -= NANOSECOND; 675 else if (u_nsec < -(NANOSECOND >> 1)) 676 u_nsec += NANOSECOND; 677 pps_fcount += u_nsec; 678 if (v_nsec > MAXFREQ) { 679 return; 680 } 681 time_status &= ~STA_PPSJITTER; 682 683 /* 684 * A three-stage median filter is used to help denoise the PPS 685 * time. The median sample becomes the time offset estimate; the 686 * difference between the other two samples becomes the time 687 * dispersion (jitter) estimate. 688 */ 689 if (pps_tf[0].nsec > pps_tf[1].nsec) { 690 if (pps_tf[1].nsec > pps_tf[2].nsec) { 691 pps_filt = pps_tf[1]; /* 0 1 2 */ 692 u_nsec = pps_tf[0].nsec - pps_tf[2].nsec; 693 } else if (pps_tf[2].nsec > pps_tf[0].nsec) { 694 pps_filt = pps_tf[0]; /* 2 0 1 */ 695 u_nsec = pps_tf[2].nsec - pps_tf[1].nsec; 696 } else { 697 pps_filt = pps_tf[2]; /* 0 2 1 */ 698 u_nsec = pps_tf[0].nsec - pps_tf[1].nsec; 699 } 700 } else { 701 if (pps_tf[1].nsec < pps_tf[2].nsec) { 702 pps_filt = pps_tf[1]; /* 2 1 0 */ 703 u_nsec = pps_tf[2].nsec - pps_tf[0].nsec; 704 } else if (pps_tf[2].nsec < pps_tf[0].nsec) { 705 pps_filt = pps_tf[0]; /* 1 0 2 */ 706 u_nsec = pps_tf[1].nsec - pps_tf[2].nsec; 707 } else { 708 pps_filt = pps_tf[2]; /* 1 2 0 */ 709 u_nsec = pps_tf[1].nsec - pps_tf[0].nsec; 710 } 711 } 712 713 /* 714 * Nominal jitter is due to PPS signal noise and interrupt 715 * latency. If it exceeds the jitter limit, the sample is 716 * discarded. otherwise, if so enabled, the time offset is 717 * updated. The offsets are accumulated over the phase averaging 718 * interval to improve accuracy. The jitter is averaged only for 719 * performance monitoring. We can tolerate a modest loss of data 720 * here without degrading time accuracy. 721 */ 722 if (u_nsec > MAXTIME) { 723 time_status |= STA_PPSJITTER; 724 pps_jitcnt++; 725 } else if (time_status & STA_PPSTIME) { 726 pps_offacc -= pps_filt.nsec; 727 pps_offcnt++; 728 } 729 if (pps_offcnt >= (1 << PPS_PAVG)) { 730 if (time_status & STA_PPSTIME) { 731 L_LINT(time_offset, pps_offacc); 732 L_RSHIFT(time_offset, PPS_PAVG); 733 } 734 pps_offacc = 0; 735 pps_offcnt = 0; 736 } 737 pps_jitter += (u_nsec - pps_jitter) >> PPS_FAVG; 738 u_sec = pps_tf[0].sec - pps_lastsec; 739 if (ntp_div && ntp_mult) { 740 L_LINT(ftemp, (pps_filt.nsec)); 741 L_RSHIFT(ftemp, ntp_div); 742 L_MPY(ftemp, ntp_mult); 743 L_ADD(pps_freq, ftemp); 744 if (time_status & STA_PPSFREQ) 745 time_freq = pps_freq; 746 return; 747 } 748 if (u_sec < (1 << pps_shift)) 749 return; 750 751 /* 752 * At the end of the calibration interval the difference between 753 * the first and last counter values becomes the scaled 754 * frequency. It will later be divided by the length of the 755 * interval to determine the frequency update. If the frequency 756 * exceeds a sanity threshold, or if the actual calibration 757 * interval is not equal to the expected length, the data are 758 * discarded. We can tolerate a modest loss of data here without 759 * degrading frequency ccuracy. 760 */ 761 pps_calcnt++; 762 v_nsec = -pps_fcount; 763 pps_lastsec = pps_tf[0].sec; 764 pps_fcount = 0; 765 u_nsec = MAXFREQ << pps_shift; 766 if (v_nsec > u_nsec || v_nsec < -u_nsec || u_sec != (1 << 767 pps_shift)) { 768 time_status |= STA_PPSERROR; 769 pps_errcnt++; 770 return; 771 } 772 773 /* 774 * If the actual calibration interval is not equal to the 775 * expected length, the data are discarded. If the wander is 776 * less than the wander threshold for four consecutive 777 * intervals, the interval is doubled; if it is greater than the 778 * threshold for four consecutive intervals, the interval is 779 * halved. The scaled frequency offset is converted to frequency 780 * offset. The stability metric is calculated as the average of 781 * recent frequency changes, but is used only for performance 782 * monitoring. 783 */ 784 L_LINT(ftemp, v_nsec); 785 L_RSHIFT(ftemp, pps_shift); 786 L_SUB(ftemp, pps_freq); 787 u_nsec = L_GINT(ftemp); 788 if (u_nsec > MAXWANDER) { 789 L_LINT(ftemp, MAXWANDER); 790 pps_intcnt--; 791 time_status |= STA_PPSWANDER; 792 pps_stbcnt++; 793 } else if (u_nsec < -MAXWANDER) { 794 L_LINT(ftemp, -MAXWANDER); 795 pps_intcnt--; 796 time_status |= STA_PPSWANDER; 797 pps_stbcnt++; 798 } else { 799 pps_intcnt++; 800 } 801 if (pps_intcnt >= 4) { 802 pps_intcnt = 4; 803 if (pps_shift < PPS_FAVGMAX) { 804 pps_shift++; 805 pps_intcnt = 0; 806 } 807 } else if (pps_intcnt <= -4) { 808 pps_intcnt = -4; 809 if (pps_shift > PPS_FAVG) { 810 pps_shift--; 811 pps_intcnt = 0; 812 } 813 } 814 if (u_nsec < 0) 815 u_nsec = -u_nsec; 816 pps_stabil += (u_nsec * SCALE_PPM - pps_stabil) >> PPS_FAVG; 817 818 /* 819 * The frequency offset is averaged into the PPS frequency. If 820 * enabled, the system clock frequency is updated as well. 821 */ 822 L_RSHIFT(ftemp, PPS_FAVG); 823 L_ADD(pps_freq, ftemp); 824 u_nsec = L_GINT(pps_freq); 825 if (u_nsec > MAXFREQ) 826 L_LINT(pps_freq, MAXFREQ); 827 else if (u_nsec < -MAXFREQ) 828 L_LINT(pps_freq, -MAXFREQ); 829 if (time_status & STA_PPSFREQ) 830 time_freq = pps_freq; 831 } 832 #endif /* PPS_SYNC */ 833