Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_ntptime.c
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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 * $FreeBSD$ 32 */ 33 34 #include "opt_ntp.h" 35 36 #include <sys/param.h> 37 #include <sys/systm.h> 38 #include <sys/sysproto.h> 39 #include <sys/kernel.h> 40 #include <sys/proc.h> 41 #include <sys/time.h> 42 #include <sys/timex.h> 43 #include <sys/timepps.h> 44 #include <sys/sysctl.h> 45 46 /* 47 * Single-precision macros for 64-bit machines 48 */ 49 typedef long long l_fp; 50 #define L_ADD(v, u) ((v) += (u)) 51 #define L_SUB(v, u) ((v) -= (u)) 52 #define L_ADDHI(v, a) ((v) += (long long)(a) << 32) 53 #define L_NEG(v) ((v) = -(v)) 54 #define L_RSHIFT(v, n) \ 55 do { \ 56 if ((v) < 0) \ 57 (v) = -(-(v) >> (n)); \ 58 else \ 59 (v) = (v) >> (n); \ 60 } while (0) 61 #define L_MPY(v, a) ((v) *= (a)) 62 #define L_CLR(v) ((v) = 0) 63 #define L_ISNEG(v) ((v) < 0) 64 #define L_LINT(v, a) ((v) = (long long)(a) << 32) 65 #define L_GINT(v) ((v) < 0 ? -(-(v) >> 32) : (v) >> 32) 66 67 /* 68 * Generic NTP kernel interface 69 * 70 * These routines constitute the Network Time Protocol (NTP) interfaces 71 * for user and daemon application programs. The ntp_gettime() routine 72 * provides the time, maximum error (synch distance) and estimated error 73 * (dispersion) to client user application programs. The ntp_adjtime() 74 * routine is used by the NTP daemon to adjust the system clock to an 75 * externally derived time. The time offset and related variables set by 76 * this routine are used by other routines in this module to adjust the 77 * phase and frequency of the clock discipline loop which controls the 78 * system clock. 79 * 80 * When the kernel time is reckoned directly in nanoseconds (NTP_NANO 81 * defined), the time at each tick interrupt is derived directly from 82 * the kernel time variable. When the kernel time is reckoned in 83 * microseconds, (NTP_NANO undefined), the time is derived from the 84 * kernel time variable together with a variable representing the 85 * leftover nanoseconds at the last tick interrupt. In either case, the 86 * current nanosecond time is reckoned from these values plus an 87 * interpolated value derived by the clock routines in another 88 * architecture-specific module. The interpolation can use either a 89 * dedicated counter or a processor cycle counter (PCC) implemented in 90 * some architectures. 91 * 92 * Note that all routines must run at priority splclock or higher. 93 */ 94 95 /* 96 * Phase/frequency-lock loop (PLL/FLL) definitions 97 * 98 * The nanosecond clock discipline uses two variable types, time 99 * variables and frequency variables. Both types are represented as 64- 100 * bit fixed-point quantities with the decimal point between two 32-bit 101 * halves. On a 32-bit machine, each half is represented as a single 102 * word and mathematical operations are done using multiple-precision 103 * arithmetic. On a 64-bit machine, ordinary computer arithmetic is 104 * used. 105 * 106 * A time variable is a signed 64-bit fixed-point number in ns and 107 * fraction. It represents the remaining time offset to be amortized 108 * over succeeding tick interrupts. The maximum time offset is about 109 * 0.5 s and the resolution is about 2.3e-10 ns. 110 * 111 * 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 112 * 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 1 113 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 114 * |s s s| ns | 115 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 116 * | fraction | 117 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 118 * 119 * A frequency variable is a signed 64-bit fixed-point number in ns/s 120 * and fraction. It represents the ns and fraction to be added to the 121 * kernel time variable at each second. The maximum frequency offset is 122 * about +-500000 ns/s and the resolution is about 2.3e-10 ns/s. 123 * 124 * 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 125 * 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 1 126 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 127 * |s s s s s s s s s s s s s| ns/s | 128 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 129 * | fraction | 130 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 131 */ 132 /* 133 * The following variables establish the state of the PLL/FLL and the 134 * residual time and frequency offset of the local clock. 135 */ 136 #define SHIFT_PLL 4 /* PLL loop gain (shift) */ 137 #define SHIFT_FLL 2 /* FLL loop gain (shift) */ 138 139 static int time_state = TIME_OK; /* clock state */ 140 static int time_status = STA_UNSYNC; /* clock status bits */ 141 static long time_constant; /* poll interval (shift) (s) */ 142 static long time_precision = 1; /* clock precision (ns) */ 143 static long time_maxerror = MAXPHASE / 1000; /* maximum error (us) */ 144 static long time_esterror = MAXPHASE / 1000; /* estimated error (us) */ 145 static long time_reftime; /* time at last adjustment (s) */ 146 static long time_tick; /* nanoseconds per tick (ns) */ 147 static l_fp time_offset; /* time offset (ns) */ 148 static l_fp time_freq; /* frequency offset (ns/s) */ 149 150 #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_FAVGDEF 7 /* default freq avg int (s) (shift) */ 159 #define PPS_FAVGMAX 15 /* max freq avg interval (s) (shift) */ 160 #define PPS_PAVG 4 /* phase avg interval (s) (shift) */ 161 #define PPS_VALID 120 /* PPS signal watchdog max (s) */ 162 #define PPS_MAXWANDER 100000 /* max PPS wander (ns/s) */ 163 #define PPS_POPCORN 2 /* popcorn spike threshold (shift) */ 164 165 static struct timespec pps_tf[3]; /* phase median filter */ 166 static l_fp pps_freq; /* scaled frequency offset (ns/s) */ 167 static long pps_fcount; /* frequency accumulator */ 168 static long pps_jitter; /* nominal jitter (ns) */ 169 static long pps_stabil; /* nominal stability (scaled ns/s) */ 170 static long pps_lastsec; /* time at last calibration (s) */ 171 static int pps_valid; /* signal watchdog counter */ 172 static int pps_shift = PPS_FAVG; /* interval duration (s) (shift) */ 173 static int pps_shiftmax = PPS_FAVGDEF; /* max interval duration (s) (shift) */ 174 static int pps_intcnt; /* wander counter */ 175 176 /* 177 * PPS signal quality monitors 178 */ 179 static long pps_calcnt; /* calibration intervals */ 180 static long pps_jitcnt; /* jitter limit exceeded */ 181 static long pps_stbcnt; /* stability limit exceeded */ 182 static long pps_errcnt; /* calibration errors */ 183 #endif /* PPS_SYNC */ 184 /* 185 * End of phase/frequency-lock loop (PLL/FLL) definitions 186 */ 187 188 static void ntp_init(void); 189 static void hardupdate(long offset); 190 191 /* 192 * ntp_gettime() - NTP user application interface 193 * 194 * See the timex.h header file for synopsis and API description. 195 */ 196 static int 197 ntp_sysctl SYSCTL_HANDLER_ARGS 198 { 199 struct ntptimeval ntv; /* temporary structure */ 200 struct timespec atv; /* nanosecond time */ 201 202 nanotime(&atv); 203 ntv.time.tv_sec = atv.tv_sec; 204 ntv.time.tv_nsec = atv.tv_nsec; 205 ntv.maxerror = time_maxerror; 206 ntv.esterror = time_esterror; 207 ntv.time_state = time_state; 208 209 /* 210 * Status word error decode. If any of these conditions occur, 211 * an error is returned, instead of the status word. Most 212 * applications will care only about the fact the system clock 213 * may not be trusted, not about the details. 214 * 215 * Hardware or software error 216 */ 217 if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) || 218 219 /* 220 * PPS signal lost when either time or frequency synchronization 221 * requested 222 */ 223 (time_status & (STA_PPSFREQ | STA_PPSTIME) && 224 !(time_status & STA_PPSSIGNAL)) || 225 226 /* 227 * PPS jitter exceeded when time synchronization requested 228 */ 229 (time_status & STA_PPSTIME && 230 time_status & STA_PPSJITTER) || 231 232 /* 233 * PPS wander exceeded or calibration error when frequency 234 * synchronization requested 235 */ 236 (time_status & STA_PPSFREQ && 237 time_status & (STA_PPSWANDER | STA_PPSERROR))) 238 ntv.time_state = TIME_ERROR; 239 return (sysctl_handle_opaque(oidp, &ntv, sizeof ntv, req)); 240 } 241 242 SYSCTL_NODE(_kern, OID_AUTO, ntp_pll, CTLFLAG_RW, 0, ""); 243 SYSCTL_PROC(_kern_ntp_pll, OID_AUTO, gettime, CTLTYPE_OPAQUE|CTLFLAG_RD, 244 0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", ""); 245 246 #ifdef PPS_SYNC 247 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shiftmax, CTLFLAG_RW, &pps_shiftmax, 0, ""); 248 #endif 249 /* 250 * ntp_adjtime() - NTP daemon application interface 251 * 252 * See the timex.h header file for synopsis and API description. 253 */ 254 #ifndef _SYS_SYSPROTO_H_ 255 struct ntp_adjtime_args { 256 struct timex *tp; 257 }; 258 #endif 259 260 int 261 ntp_adjtime(struct proc *p, struct ntp_adjtime_args *uap) 262 { 263 struct timex ntv; /* temporary structure */ 264 long freq; /* frequency ns/s) */ 265 int modes; /* mode bits from structure */ 266 int s; /* caller priority */ 267 int error; 268 269 error = copyin((caddr_t)uap->tp, (caddr_t)&ntv, sizeof(ntv)); 270 if (error) 271 return(error); 272 273 /* 274 * Update selected clock variables - only the superuser can 275 * change anything. Note that there is no error checking here on 276 * the assumption the superuser should know what it is doing. 277 */ 278 modes = ntv.modes; 279 if (modes) 280 error = suser(p->p_cred->pc_ucred, &p->p_acflag); 281 if (error) 282 return (error); 283 s = splclock(); 284 if (modes & MOD_FREQUENCY) { 285 freq = (ntv.freq * 1000LL) >> 16; 286 if (freq > MAXFREQ) 287 L_LINT(time_freq, MAXFREQ); 288 else if (freq < -MAXFREQ) 289 L_LINT(time_freq, -MAXFREQ); 290 else 291 L_LINT(time_freq, freq); 292 293 #ifdef PPS_SYNC 294 pps_freq = time_freq; 295 #endif /* PPS_SYNC */ 296 } 297 if (modes & MOD_MAXERROR) 298 time_maxerror = ntv.maxerror; 299 if (modes & MOD_ESTERROR) 300 time_esterror = ntv.esterror; 301 if (modes & MOD_STATUS) { 302 time_status &= STA_RONLY; 303 time_status |= ntv.status & ~STA_RONLY; 304 } 305 if (modes & MOD_TIMECONST) { 306 if (ntv.constant < 0) 307 time_constant = 0; 308 else if (ntv.constant > MAXTC) 309 time_constant = MAXTC; 310 else 311 time_constant = ntv.constant; 312 } 313 #ifdef PPS_SYNC 314 if (modes & MOD_PPSMAX) { 315 if (ntv.shift < PPS_FAVG) 316 pps_shiftmax = PPS_FAVG; 317 else if (ntv.shift > PPS_FAVGMAX) 318 pps_shiftmax = PPS_FAVGMAX; 319 else 320 pps_shiftmax = ntv.shift; 321 } 322 #endif /* PPS_SYNC */ 323 if (modes & MOD_NANO) 324 time_status |= STA_NANO; 325 if (modes & MOD_MICRO) 326 time_status &= ~STA_NANO; 327 if (modes & MOD_CLKB) 328 time_status |= STA_CLK; 329 if (modes & MOD_CLKA) 330 time_status &= ~STA_CLK; 331 if (modes & MOD_OFFSET) { 332 if (time_status & STA_NANO) 333 hardupdate(ntv.offset); 334 else 335 hardupdate(ntv.offset * 1000); 336 } 337 338 /* 339 * Retrieve all clock variables 340 */ 341 if (time_status & STA_NANO) 342 ntv.offset = L_GINT(time_offset); 343 else 344 ntv.offset = L_GINT(time_offset) / 1000; 345 ntv.freq = L_GINT((time_freq / 1000LL) << 16); 346 ntv.maxerror = time_maxerror; 347 ntv.esterror = time_esterror; 348 ntv.status = time_status; 349 ntv.constant = time_constant; 350 if (time_status & STA_NANO) 351 ntv.precision = time_precision; 352 else 353 ntv.precision = time_precision / 1000; 354 ntv.tolerance = MAXFREQ * SCALE_PPM; 355 #ifdef PPS_SYNC 356 ntv.shift = pps_shift; 357 ntv.ppsfreq = L_GINT((pps_freq / 1000LL) << 16); 358 if (time_status & STA_NANO) 359 ntv.jitter = pps_jitter; 360 else 361 ntv.jitter = pps_jitter / 1000; 362 ntv.stabil = pps_stabil; 363 ntv.calcnt = pps_calcnt; 364 ntv.errcnt = pps_errcnt; 365 ntv.jitcnt = pps_jitcnt; 366 ntv.stbcnt = pps_stbcnt; 367 #endif /* PPS_SYNC */ 368 splx(s); 369 370 error = copyout((caddr_t)&ntv, (caddr_t)uap->tp, sizeof(ntv)); 371 if (error) 372 return (error); 373 374 /* 375 * Status word error decode. See comments in 376 * ntp_gettime() routine. 377 */ 378 if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) || 379 (time_status & (STA_PPSFREQ | STA_PPSTIME) && 380 !(time_status & STA_PPSSIGNAL)) || 381 (time_status & STA_PPSTIME && 382 time_status & STA_PPSJITTER) || 383 (time_status & STA_PPSFREQ && 384 time_status & (STA_PPSWANDER | STA_PPSERROR))) 385 p->p_retval[0] = TIME_ERROR; 386 else 387 p->p_retval[0] = time_state; 388 return (error); 389 } 390 391 /* 392 * second_overflow() - called after ntp_tick_adjust() 393 * 394 * This routine is ordinarily called immediately following the above 395 * routine ntp_tick_adjust(). While these two routines are normally 396 * combined, they are separated here only for the purposes of 397 * simulation. 398 */ 399 void 400 ntp_update_second(struct timecounter *tcp) 401 { 402 u_int32_t *newsec; 403 l_fp ftemp, time_adj; /* 32/64-bit temporaries */ 404 405 newsec = &tcp->tc_offset_sec; 406 /* 407 * On rollover of the second both the nanosecond and microsecond 408 * clocks are updated and the state machine cranked as 409 * necessary. The phase adjustment to be used for the next 410 * second is calculated and the maximum error is increased by 411 * the tolerance. 412 */ 413 time_maxerror += MAXFREQ / 1000; 414 415 /* 416 * Leap second processing. If in leap-insert state at 417 * the end of the day, the system clock is set back one 418 * second; if in leap-delete state, the system clock is 419 * set ahead one second. The nano_time() routine or 420 * external clock driver will insure that reported time 421 * is always monotonic. 422 */ 423 switch (time_state) { 424 425 /* 426 * No warning. 427 */ 428 case TIME_OK: 429 if (time_status & STA_INS) 430 time_state = TIME_INS; 431 else if (time_status & STA_DEL) 432 time_state = TIME_DEL; 433 break; 434 435 /* 436 * Insert second 23:59:60 following second 437 * 23:59:59. 438 */ 439 case TIME_INS: 440 if (!(time_status & STA_INS)) 441 time_state = TIME_OK; 442 else if ((*newsec) % 86400 == 0) { 443 (*newsec)--; 444 time_state = TIME_OOP; 445 } 446 break; 447 448 /* 449 * Delete second 23:59:59. 450 */ 451 case TIME_DEL: 452 if (!(time_status & STA_DEL)) 453 time_state = TIME_OK; 454 else if (((*newsec) + 1) % 86400 == 0) { 455 (*newsec)++; 456 time_state = TIME_WAIT; 457 } 458 break; 459 460 /* 461 * Insert second in progress. 462 */ 463 case TIME_OOP: 464 time_state = TIME_WAIT; 465 break; 466 467 /* 468 * Wait for status bits to clear. 469 */ 470 case TIME_WAIT: 471 if (!(time_status & (STA_INS | STA_DEL))) 472 time_state = TIME_OK; 473 } 474 475 /* 476 * Compute the total time adjustment for the next second 477 * in ns. The offset is reduced by a factor depending on 478 * whether the PPS signal is operating. Note that the 479 * value is in effect scaled by the clock frequency, 480 * since the adjustment is added at each tick interrupt. 481 */ 482 ftemp = time_offset; 483 #ifdef PPS_SYNC 484 if (time_status & STA_PPSTIME && time_status & 485 STA_PPSSIGNAL) 486 L_RSHIFT(ftemp, PPS_FAVG); 487 else 488 L_RSHIFT(ftemp, SHIFT_PLL + time_constant); 489 #else 490 L_RSHIFT(ftemp, SHIFT_PLL + time_constant); 491 #endif /* PPS_SYNC */ 492 time_adj = ftemp; 493 L_SUB(time_offset, ftemp); 494 L_ADD(time_adj, time_freq); 495 tcp->tc_adjustment = time_adj; 496 #ifdef PPS_SYNC 497 if (pps_valid > 0) 498 pps_valid--; 499 else 500 time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER | 501 STA_PPSWANDER | STA_PPSERROR); 502 #endif /* PPS_SYNC */ 503 } 504 505 /* 506 * ntp_init() - initialize variables and structures 507 * 508 * This routine must be called after the kernel variables hz and tick 509 * are set or changed and before the next tick interrupt. In this 510 * particular implementation, these values are assumed set elsewhere in 511 * the kernel. The design allows the clock frequency and tick interval 512 * to be changed while the system is running. So, this routine should 513 * probably be integrated with the code that does that. 514 */ 515 static void 516 ntp_init() 517 { 518 519 /* 520 * The following variable must be initialized any time the 521 * kernel variable hz is changed. 522 */ 523 time_tick = NANOSECOND / hz; 524 525 /* 526 * The following variables are initialized only at startup. Only 527 * those structures not cleared by the compiler need to be 528 * initialized, and these only in the simulator. In the actual 529 * kernel, any nonzero values here will quickly evaporate. 530 */ 531 L_CLR(time_offset); 532 L_CLR(time_freq); 533 #ifdef PPS_SYNC 534 pps_tf[0].tv_sec = pps_tf[0].tv_nsec = 0; 535 pps_tf[1].tv_sec = pps_tf[1].tv_nsec = 0; 536 pps_tf[2].tv_sec = pps_tf[2].tv_nsec = 0; 537 pps_fcount = 0; 538 L_CLR(pps_freq); 539 #endif /* PPS_SYNC */ 540 } 541 542 SYSINIT(ntpclocks, SI_SUB_CLOCKS, SI_ORDER_FIRST, ntp_init, NULL) 543 544 /* 545 * hardupdate() - local clock update 546 * 547 * This routine is called by ntp_adjtime() to update the local clock 548 * phase and frequency. The implementation is of an adaptive-parameter, 549 * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new 550 * time and frequency offset estimates for each call. If the kernel PPS 551 * discipline code is configured (PPS_SYNC), the PPS signal itself 552 * determines the new time offset, instead of the calling argument. 553 * Presumably, calls to ntp_adjtime() occur only when the caller 554 * believes the local clock is valid within some bound (+-128 ms with 555 * NTP). If the caller's time is far different than the PPS time, an 556 * argument will ensue, and it's not clear who will lose. 557 * 558 * For uncompensated quartz crystal oscillators and nominal update 559 * intervals less than 256 s, operation should be in phase-lock mode, 560 * where the loop is disciplined to phase. For update intervals greater 561 * than 1024 s, operation should be in frequency-lock mode, where the 562 * loop is disciplined to frequency. Between 256 s and 1024 s, the mode 563 * is selected by the STA_MODE status bit. 564 */ 565 static void 566 hardupdate(offset) 567 long offset; /* clock offset (ns) */ 568 { 569 long ltemp, mtemp; 570 l_fp ftemp; 571 572 /* 573 * Select how the phase is to be controlled and from which 574 * source. If the PPS signal is present and enabled to 575 * discipline the time, the PPS offset is used; otherwise, the 576 * argument offset is used. 577 */ 578 if (!(time_status & STA_PLL)) 579 return; 580 ltemp = offset; 581 if (ltemp > MAXPHASE) 582 ltemp = MAXPHASE; 583 else if (ltemp < -MAXPHASE) 584 ltemp = -MAXPHASE; 585 if (!(time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)) 586 L_LINT(time_offset, ltemp); 587 588 /* 589 * Select how the frequency is to be controlled and in which 590 * mode (PLL or FLL). If the PPS signal is present and enabled 591 * to discipline the frequency, the PPS frequency is used; 592 * otherwise, the argument offset is used to compute it. 593 */ 594 if (time_status & STA_PPSFREQ && time_status & STA_PPSSIGNAL) { 595 time_reftime = time_second; 596 return; 597 } 598 if (time_status & STA_FREQHOLD || time_reftime == 0) 599 time_reftime = time_second; 600 mtemp = time_second - time_reftime; 601 L_LINT(ftemp, ltemp); 602 L_RSHIFT(ftemp, (SHIFT_PLL + 2 + time_constant) << 1); 603 L_MPY(ftemp, mtemp); 604 L_ADD(time_freq, ftemp); 605 time_status &= ~STA_MODE; 606 if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) { 607 L_LINT(ftemp, (ltemp << 4) / mtemp); 608 L_RSHIFT(ftemp, SHIFT_FLL + 4); 609 L_ADD(time_freq, ftemp); 610 time_status |= STA_MODE; 611 } 612 time_reftime = time_second; 613 if (L_GINT(time_freq) > MAXFREQ) 614 L_LINT(time_freq, MAXFREQ); 615 else if (L_GINT(time_freq) < -MAXFREQ) 616 L_LINT(time_freq, -MAXFREQ); 617 } 618 619 #ifdef PPS_SYNC 620 /* 621 * hardpps() - discipline CPU clock oscillator to external PPS signal 622 * 623 * This routine is called at each PPS interrupt in order to discipline 624 * the CPU clock oscillator to the PPS signal. It measures the PPS phase 625 * and leaves it in a handy spot for the hardclock() routine. It 626 * integrates successive PPS phase differences and calculates the 627 * frequency offset. This is used in hardclock() to discipline the CPU 628 * clock oscillator so that the intrinsic frequency error is cancelled 629 * out. The code requires the caller to capture the time and 630 * architecture-dependent hardware counter values in nanoseconds at the 631 * on-time PPS signal transition. 632 * 633 * Note that, on some Unix systems this routine runs at an interrupt 634 * priority level higher than the timer interrupt routine hardclock(). 635 * Therefore, the variables used are distinct from the hardclock() 636 * variables, except for the actual time and frequency variables, which 637 * are determined by this routine and updated atomically. 638 */ 639 void 640 hardpps(tsp, nsec) 641 struct timespec *tsp; /* time at PPS */ 642 long nsec; /* hardware counter at PPS */ 643 { 644 long u_sec, u_nsec, v_nsec; /* temps */ 645 l_fp ftemp; 646 647 /* 648 * The signal is first processed by a frequency discriminator 649 * which rejects noise and input signals with frequencies 650 * outside the range 1 +-MAXFREQ PPS. If two hits occur in the 651 * same second, we ignore the later hit; if not and a hit occurs 652 * outside the range gate, keep the later hit but do not 653 * process it. 654 */ 655 time_status |= STA_PPSSIGNAL | STA_PPSJITTER; 656 time_status &= ~(STA_PPSWANDER | STA_PPSERROR); 657 pps_valid = PPS_VALID; 658 u_sec = tsp->tv_sec; 659 u_nsec = tsp->tv_nsec; 660 if (u_nsec >= (NANOSECOND >> 1)) { 661 u_nsec -= NANOSECOND; 662 u_sec++; 663 } 664 v_nsec = u_nsec - pps_tf[0].tv_nsec; 665 if (u_sec == pps_tf[0].tv_sec && v_nsec < -MAXFREQ) { 666 return; 667 } 668 pps_tf[2] = pps_tf[1]; 669 pps_tf[1] = pps_tf[0]; 670 pps_tf[0].tv_sec = u_sec; 671 pps_tf[0].tv_nsec = u_nsec; 672 673 /* 674 * Compute the difference between the current and previous 675 * counter values. If the difference exceeds 0.5 s, assume it 676 * has wrapped around, so correct 1.0 s. If the result exceeds 677 * the tick interval, the sample point has crossed a tick 678 * boundary during the last second, so correct the tick. Very 679 * intricate. 680 */ 681 u_nsec = nsec; 682 if (u_nsec > (NANOSECOND >> 1)) 683 u_nsec -= NANOSECOND; 684 else if (u_nsec < -(NANOSECOND >> 1)) 685 u_nsec += NANOSECOND; 686 pps_fcount += u_nsec; 687 if (v_nsec > MAXFREQ || v_nsec < -MAXFREQ) { 688 return; 689 } 690 time_status &= ~STA_PPSJITTER; 691 692 /* 693 * A three-stage median filter is used to help denoise the PPS 694 * time. The median sample becomes the time offset estimate; the 695 * difference between the other two samples becomes the time 696 * dispersion (jitter) estimate. 697 */ 698 if (pps_tf[0].tv_nsec > pps_tf[1].tv_nsec) { 699 if (pps_tf[1].tv_nsec > pps_tf[2].tv_nsec) { 700 v_nsec = pps_tf[1].tv_nsec; /* 0 1 2 */ 701 u_nsec = pps_tf[0].tv_nsec - pps_tf[2].tv_nsec; 702 } else if (pps_tf[2].tv_nsec > pps_tf[0].tv_nsec) { 703 v_nsec = pps_tf[0].tv_nsec; /* 2 0 1 */ 704 u_nsec = pps_tf[2].tv_nsec - pps_tf[1].tv_nsec; 705 } else { 706 v_nsec = pps_tf[2].tv_nsec; /* 0 2 1 */ 707 u_nsec = pps_tf[0].tv_nsec - pps_tf[1].tv_nsec; 708 } 709 } else { 710 if (pps_tf[1].tv_nsec < pps_tf[2].tv_nsec) { 711 v_nsec = pps_tf[1].tv_nsec; /* 2 1 0 */ 712 u_nsec = pps_tf[2].tv_nsec - pps_tf[0].tv_nsec; 713 } else if (pps_tf[2].tv_nsec < pps_tf[0].tv_nsec) { 714 v_nsec = pps_tf[0].tv_nsec; /* 1 0 2 */ 715 u_nsec = pps_tf[1].tv_nsec - pps_tf[2].tv_nsec; 716 } else { 717 v_nsec = pps_tf[2].tv_nsec; /* 1 2 0 */ 718 u_nsec = pps_tf[1].tv_nsec - pps_tf[0].tv_nsec; 719 } 720 } 721 722 /* 723 * Nominal jitter is due to PPS signal noise and interrupt 724 * latency. If it exceeds the popcorn threshold, 725 * the sample is discarded. otherwise, if so enabled, the time 726 * offset is updated. We can tolerate a modest loss of data here 727 * without degrading time accuracy. 728 */ 729 if (u_nsec > (pps_jitter << PPS_POPCORN)) { 730 time_status |= STA_PPSJITTER; 731 pps_jitcnt++; 732 } else if (time_status & STA_PPSTIME) { 733 L_LINT(ftemp, v_nsec); 734 L_SUB(ftemp, time_offset); 735 L_RSHIFT(ftemp, pps_shift); 736 L_SUB(time_offset, ftemp); 737 } 738 pps_jitter += (u_nsec - pps_jitter) >> PPS_FAVG; 739 u_sec = pps_tf[0].tv_sec - pps_lastsec; 740 if (u_sec < (1 << pps_shift)) 741 return; 742 743 /* 744 * At the end of the calibration interval the difference between 745 * the first and last counter values becomes the scaled 746 * frequency. It will later be divided by the length of the 747 * interval to determine the frequency update. If the frequency 748 * exceeds a sanity threshold, or if the actual calibration 749 * interval is not equal to the expected length, the data are 750 * discarded. We can tolerate a modest loss of data here without 751 * degrading frequency ccuracy. 752 */ 753 pps_calcnt++; 754 v_nsec = -pps_fcount; 755 pps_lastsec = pps_tf[0].tv_sec; 756 pps_fcount = 0; 757 u_nsec = MAXFREQ << pps_shift; 758 if (v_nsec > u_nsec || v_nsec < -u_nsec || u_sec != (1 << 759 pps_shift)) { 760 time_status |= STA_PPSERROR; 761 pps_errcnt++; 762 return; 763 } 764 765 /* 766 * Here the raw frequency offset and wander (stability) is 767 * calculated. If the wander is less than the wander threshold 768 * for four consecutive averaging intervals, the interval is 769 * doubled; if it is greater than the threshold for four 770 * consecutive intervals, the interval is halved. The scaled 771 * frequency offset is converted to frequency offset. The 772 * stability metric is calculated as the average of recent 773 * frequency changes, but is used only for performance 774 * monitoring. 775 */ 776 L_LINT(ftemp, v_nsec); 777 L_RSHIFT(ftemp, pps_shift); 778 L_SUB(ftemp, pps_freq); 779 u_nsec = L_GINT(ftemp); 780 if (u_nsec > PPS_MAXWANDER) { 781 L_LINT(ftemp, PPS_MAXWANDER); 782 pps_intcnt--; 783 time_status |= STA_PPSWANDER; 784 pps_stbcnt++; 785 } else if (u_nsec < -PPS_MAXWANDER) { 786 L_LINT(ftemp, -PPS_MAXWANDER); 787 pps_intcnt--; 788 time_status |= STA_PPSWANDER; 789 pps_stbcnt++; 790 } else { 791 pps_intcnt++; 792 } 793 if (pps_intcnt >= 4) { 794 pps_intcnt = 4; 795 if (pps_shift < pps_shiftmax) { 796 pps_shift++; 797 pps_intcnt = 0; 798 } 799 } else if (pps_intcnt <= -4) { 800 pps_intcnt = -4; 801 if (pps_shift > PPS_FAVG) { 802 pps_shift--; 803 pps_intcnt = 0; 804 } 805 } 806 if (u_nsec < 0) 807 u_nsec = -u_nsec; 808 pps_stabil += (u_nsec * SCALE_PPM - pps_stabil) >> PPS_FAVG; 809 810 /* 811 * The PPS frequency is recalculated and clamped to the maximum 812 * MAXFREQ. If enabled, the system clock frequency is updated as 813 * well. 814 */ 815 L_ADD(pps_freq, ftemp); 816 u_nsec = L_GINT(pps_freq); 817 if (u_nsec > MAXFREQ) 818 L_LINT(pps_freq, MAXFREQ); 819 else if (u_nsec < -MAXFREQ) 820 L_LINT(pps_freq, -MAXFREQ); 821 if (time_status & STA_PPSFREQ) 822 time_freq = pps_freq; 823 } 824 #endif /* PPS_SYNC */
Cache object: 2d743630f5df79d707af98a23bdd1997
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