1 /*- 2 * ---------------------------------------------------------------------------- 3 * "THE BEER-WARE LICENSE" (Revision 42): 4 * <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you 5 * can do whatever you want with this stuff. If we meet some day, and you think 6 * this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp 7 * ---------------------------------------------------------------------------- 8 */ 9 10 #include <sys/cdefs.h> 11 __FBSDID("$FreeBSD$"); 12 13 #include "opt_ntp.h" 14 15 #include <sys/param.h> 16 #include <sys/kernel.h> 17 #include <sys/sysctl.h> 18 #include <sys/systm.h> 19 #include <sys/timepps.h> 20 #include <sys/timetc.h> 21 #include <sys/timex.h> 22 23 /* 24 * A large step happens on boot. This constant detects such steps. 25 * It is relatively small so that ntp_update_second gets called enough 26 * in the typical 'missed a couple of seconds' case, but doesn't loop 27 * forever when the time step is large. 28 */ 29 #define LARGE_STEP 200 30 31 /* 32 * Implement a dummy timecounter which we can use until we get a real one 33 * in the air. This allows the console and other early stuff to use 34 * time services. 35 */ 36 37 static u_int 38 dummy_get_timecount(struct timecounter *tc) 39 { 40 static u_int now; 41 42 return (++now); 43 } 44 45 static struct timecounter dummy_timecounter = { 46 dummy_get_timecount, 0, ~0u, 1000000, "dummy", -1000000 47 }; 48 49 struct timehands { 50 /* These fields must be initialized by the driver. */ 51 struct timecounter *th_counter; 52 int64_t th_adjustment; 53 u_int64_t th_scale; 54 u_int th_offset_count; 55 struct bintime th_offset; 56 struct timeval th_microtime; 57 struct timespec th_nanotime; 58 /* Fields not to be copied in tc_windup start with th_generation. */ 59 volatile u_int th_generation; 60 struct timehands *th_next; 61 }; 62 63 extern struct timehands th0; 64 static struct timehands th9 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th0}; 65 static struct timehands th8 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th9}; 66 static struct timehands th7 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th8}; 67 static struct timehands th6 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th7}; 68 static struct timehands th5 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th6}; 69 static struct timehands th4 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th5}; 70 static struct timehands th3 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th4}; 71 static struct timehands th2 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th3}; 72 static struct timehands th1 = { NULL, 0, 0, 0, {0, 0}, {0, 0}, {0, 0}, 0, &th2}; 73 static struct timehands th0 = { 74 &dummy_timecounter, 75 0, 76 (uint64_t)-1 / 1000000, 77 0, 78 {1, 0}, 79 {0, 0}, 80 {0, 0}, 81 1, 82 &th1 83 }; 84 85 static struct timehands *volatile timehands = &th0; 86 struct timecounter *timecounter = &dummy_timecounter; 87 static struct timecounter *timecounters = &dummy_timecounter; 88 89 time_t time_second = 1; 90 time_t time_uptime = 0; 91 92 static struct bintime boottimebin; 93 struct timeval boottime; 94 SYSCTL_STRUCT(_kern, KERN_BOOTTIME, boottime, CTLFLAG_RD, 95 &boottime, timeval, "System boottime"); 96 97 SYSCTL_NODE(_kern, OID_AUTO, timecounter, CTLFLAG_RW, 0, ""); 98 99 #define TC_STATS(foo) \ 100 static u_int foo; \ 101 SYSCTL_UINT(_kern_timecounter, OID_AUTO, foo, CTLFLAG_RD, &foo, 0, "");\ 102 struct __hack 103 104 TC_STATS(nbinuptime); TC_STATS(nnanouptime); TC_STATS(nmicrouptime); 105 TC_STATS(nbintime); TC_STATS(nnanotime); TC_STATS(nmicrotime); 106 TC_STATS(ngetbinuptime); TC_STATS(ngetnanouptime); TC_STATS(ngetmicrouptime); 107 TC_STATS(ngetbintime); TC_STATS(ngetnanotime); TC_STATS(ngetmicrotime); 108 TC_STATS(nsetclock); 109 110 #undef TC_STATS 111 112 static void tc_windup(void); 113 114 /* 115 * Return the difference between the timehands' counter value now and what 116 * was when we copied it to the timehands' offset_count. 117 */ 118 static __inline u_int 119 tc_delta(struct timehands *th) 120 { 121 struct timecounter *tc; 122 123 tc = th->th_counter; 124 return ((tc->tc_get_timecount(tc) - th->th_offset_count) & 125 tc->tc_counter_mask); 126 } 127 128 /* 129 * Functions for reading the time. We have to loop until we are sure that 130 * the timehands that we operated on was not updated under our feet. See 131 * the comment in <sys/time.h> for a description of these 12 functions. 132 */ 133 134 void 135 binuptime(struct bintime *bt) 136 { 137 struct timehands *th; 138 u_int gen; 139 140 nbinuptime++; 141 do { 142 th = timehands; 143 gen = th->th_generation; 144 *bt = th->th_offset; 145 bintime_addx(bt, th->th_scale * tc_delta(th)); 146 } while (gen == 0 || gen != th->th_generation); 147 } 148 149 void 150 nanouptime(struct timespec *tsp) 151 { 152 struct bintime bt; 153 154 nnanouptime++; 155 binuptime(&bt); 156 bintime2timespec(&bt, tsp); 157 } 158 159 void 160 microuptime(struct timeval *tvp) 161 { 162 struct bintime bt; 163 164 nmicrouptime++; 165 binuptime(&bt); 166 bintime2timeval(&bt, tvp); 167 } 168 169 void 170 bintime(struct bintime *bt) 171 { 172 173 nbintime++; 174 binuptime(bt); 175 bintime_add(bt, &boottimebin); 176 } 177 178 void 179 nanotime(struct timespec *tsp) 180 { 181 struct bintime bt; 182 183 nnanotime++; 184 bintime(&bt); 185 bintime2timespec(&bt, tsp); 186 } 187 188 void 189 microtime(struct timeval *tvp) 190 { 191 struct bintime bt; 192 193 nmicrotime++; 194 bintime(&bt); 195 bintime2timeval(&bt, tvp); 196 } 197 198 void 199 getbinuptime(struct bintime *bt) 200 { 201 struct timehands *th; 202 u_int gen; 203 204 ngetbinuptime++; 205 do { 206 th = timehands; 207 gen = th->th_generation; 208 *bt = th->th_offset; 209 } while (gen == 0 || gen != th->th_generation); 210 } 211 212 void 213 getnanouptime(struct timespec *tsp) 214 { 215 struct timehands *th; 216 u_int gen; 217 218 ngetnanouptime++; 219 do { 220 th = timehands; 221 gen = th->th_generation; 222 bintime2timespec(&th->th_offset, tsp); 223 } while (gen == 0 || gen != th->th_generation); 224 } 225 226 void 227 getmicrouptime(struct timeval *tvp) 228 { 229 struct timehands *th; 230 u_int gen; 231 232 ngetmicrouptime++; 233 do { 234 th = timehands; 235 gen = th->th_generation; 236 bintime2timeval(&th->th_offset, tvp); 237 } while (gen == 0 || gen != th->th_generation); 238 } 239 240 void 241 getbintime(struct bintime *bt) 242 { 243 struct timehands *th; 244 u_int gen; 245 246 ngetbintime++; 247 do { 248 th = timehands; 249 gen = th->th_generation; 250 *bt = th->th_offset; 251 } while (gen == 0 || gen != th->th_generation); 252 bintime_add(bt, &boottimebin); 253 } 254 255 void 256 getnanotime(struct timespec *tsp) 257 { 258 struct timehands *th; 259 u_int gen; 260 261 ngetnanotime++; 262 do { 263 th = timehands; 264 gen = th->th_generation; 265 *tsp = th->th_nanotime; 266 } while (gen == 0 || gen != th->th_generation); 267 } 268 269 void 270 getmicrotime(struct timeval *tvp) 271 { 272 struct timehands *th; 273 u_int gen; 274 275 ngetmicrotime++; 276 do { 277 th = timehands; 278 gen = th->th_generation; 279 *tvp = th->th_microtime; 280 } while (gen == 0 || gen != th->th_generation); 281 } 282 283 /* 284 * Initialize a new timecounter and possibly use it. 285 */ 286 void 287 tc_init(struct timecounter *tc) 288 { 289 unsigned u; 290 291 u = tc->tc_frequency / tc->tc_counter_mask; 292 if (u > hz && tc->tc_quality >= 0) { 293 tc->tc_quality = -2000; 294 if (bootverbose) { 295 printf("Timecounter \"%s\" frequency %ju Hz", 296 tc->tc_name, (intmax_t)tc->tc_frequency); 297 printf(" -- Insufficient hz, needs at least %u\n", u); 298 } 299 } else if (tc->tc_quality >= 0 || bootverbose) { 300 printf("Timecounter \"%s\" frequency %ju Hz quality %d", 301 tc->tc_name, (intmax_t)tc->tc_frequency, 302 tc->tc_quality); 303 } 304 305 printf("\n"); 306 tc->tc_next = timecounters; 307 timecounters = tc; 308 (void)tc->tc_get_timecount(tc); 309 (void)tc->tc_get_timecount(tc); 310 /* Never automatically use a timecounter with negative quality */ 311 if (tc->tc_quality < 0) 312 return; 313 if (tc->tc_quality < timecounter->tc_quality) 314 return; 315 timecounter = tc; 316 } 317 318 /* Report the frequency of the current timecounter. */ 319 u_int64_t 320 tc_getfrequency(void) 321 { 322 323 return (timehands->th_counter->tc_frequency); 324 } 325 326 /* 327 * Step our concept of UTC. This is done by modifying our estimate of 328 * when we booted. XXX: needs further work. 329 */ 330 void 331 tc_setclock(struct timespec *ts) 332 { 333 struct timespec ts2; 334 335 nsetclock++; 336 nanouptime(&ts2); 337 boottime.tv_sec = ts->tv_sec - ts2.tv_sec; 338 /* XXX boottime should probably be a timespec. */ 339 boottime.tv_usec = (ts->tv_nsec - ts2.tv_nsec) / 1000; 340 if (boottime.tv_usec < 0) { 341 boottime.tv_usec += 1000000; 342 boottime.tv_sec--; 343 } 344 timeval2bintime(&boottime, &boottimebin); 345 346 /* XXX fiddle all the little crinkly bits around the fiords... */ 347 tc_windup(); 348 } 349 350 /* 351 * Initialize the next struct timehands in the ring and make 352 * it the active timehands. Along the way we might switch to a different 353 * timecounter and/or do seconds processing in NTP. Slightly magic. 354 */ 355 static void 356 tc_windup(void) 357 { 358 struct bintime bt; 359 struct timehands *th, *tho; 360 u_int64_t scale; 361 u_int delta, ncount, ogen; 362 int i; 363 time_t t; 364 365 /* 366 * Make the next timehands a copy of the current one, but do not 367 * overwrite the generation or next pointer. While we update 368 * the contents, the generation must be zero. 369 */ 370 tho = timehands; 371 th = tho->th_next; 372 ogen = th->th_generation; 373 th->th_generation = 0; 374 bcopy(tho, th, offsetof(struct timehands, th_generation)); 375 376 /* 377 * Capture a timecounter delta on the current timecounter and if 378 * changing timecounters, a counter value from the new timecounter. 379 * Update the offset fields accordingly. 380 */ 381 delta = tc_delta(th); 382 if (th->th_counter != timecounter) 383 ncount = timecounter->tc_get_timecount(timecounter); 384 else 385 ncount = 0; 386 th->th_offset_count += delta; 387 th->th_offset_count &= th->th_counter->tc_counter_mask; 388 bintime_addx(&th->th_offset, th->th_scale * delta); 389 390 /* 391 * Hardware latching timecounters may not generate interrupts on 392 * PPS events, so instead we poll them. There is a finite risk that 393 * the hardware might capture a count which is later than the one we 394 * got above, and therefore possibly in the next NTP second which might 395 * have a different rate than the current NTP second. It doesn't 396 * matter in practice. 397 */ 398 if (tho->th_counter->tc_poll_pps) 399 tho->th_counter->tc_poll_pps(tho->th_counter); 400 401 /* 402 * Deal with NTP second processing. The for loop normally 403 * iterates at most once, but in extreme situations it might 404 * keep NTP sane if timeouts are not run for several seconds. 405 * At boot, the time step can be large when the TOD hardware 406 * has been read, so on really large steps, we call 407 * ntp_update_second only twice. We need to call it twice in 408 * case we missed a leap second. 409 */ 410 bt = th->th_offset; 411 bintime_add(&bt, &boottimebin); 412 i = bt.sec - tho->th_microtime.tv_sec; 413 if (i > LARGE_STEP) 414 i = 2; 415 for (; i > 0; i--) { 416 t = bt.sec; 417 ntp_update_second(&th->th_adjustment, &bt.sec); 418 if (bt.sec != t) 419 boottimebin.sec += bt.sec - t; 420 } 421 /* Update the UTC timestamps used by the get*() functions. */ 422 /* XXX shouldn't do this here. Should force non-`get' versions. */ 423 bintime2timeval(&bt, &th->th_microtime); 424 bintime2timespec(&bt, &th->th_nanotime); 425 426 /* Now is a good time to change timecounters. */ 427 if (th->th_counter != timecounter) { 428 th->th_counter = timecounter; 429 th->th_offset_count = ncount; 430 } 431 432 /*- 433 * Recalculate the scaling factor. We want the number of 1/2^64 434 * fractions of a second per period of the hardware counter, taking 435 * into account the th_adjustment factor which the NTP PLL/adjtime(2) 436 * processing provides us with. 437 * 438 * The th_adjustment is nanoseconds per second with 32 bit binary 439 * fraction and we want 64 bit binary fraction of second: 440 * 441 * x = a * 2^32 / 10^9 = a * 4.294967296 442 * 443 * The range of th_adjustment is +/- 5000PPM so inside a 64bit int 444 * we can only multiply by about 850 without overflowing, but that 445 * leaves suitably precise fractions for multiply before divide. 446 * 447 * Divide before multiply with a fraction of 2199/512 results in a 448 * systematic undercompensation of 10PPM of th_adjustment. On a 449 * 5000PPM adjustment this is a 0.05PPM error. This is acceptable. 450 * 451 * We happily sacrifice the lowest of the 64 bits of our result 452 * to the goddess of code clarity. 453 * 454 */ 455 scale = (u_int64_t)1 << 63; 456 scale += (th->th_adjustment / 1024) * 2199; 457 scale /= th->th_counter->tc_frequency; 458 th->th_scale = scale * 2; 459 460 /* 461 * Now that the struct timehands is again consistent, set the new 462 * generation number, making sure to not make it zero. 463 */ 464 if (++ogen == 0) 465 ogen = 1; 466 th->th_generation = ogen; 467 468 /* Go live with the new struct timehands. */ 469 time_second = th->th_microtime.tv_sec; 470 time_uptime = th->th_offset.sec; 471 timehands = th; 472 } 473 474 /* Report or change the active timecounter hardware. */ 475 static int 476 sysctl_kern_timecounter_hardware(SYSCTL_HANDLER_ARGS) 477 { 478 char newname[32]; 479 struct timecounter *newtc, *tc; 480 int error; 481 482 tc = timecounter; 483 strlcpy(newname, tc->tc_name, sizeof(newname)); 484 485 error = sysctl_handle_string(oidp, &newname[0], sizeof(newname), req); 486 if (error != 0 || req->newptr == NULL || 487 strcmp(newname, tc->tc_name) == 0) 488 return (error); 489 for (newtc = timecounters; newtc != NULL; newtc = newtc->tc_next) { 490 if (strcmp(newname, newtc->tc_name) != 0) 491 continue; 492 493 /* Warm up new timecounter. */ 494 (void)newtc->tc_get_timecount(newtc); 495 (void)newtc->tc_get_timecount(newtc); 496 497 timecounter = newtc; 498 return (0); 499 } 500 return (EINVAL); 501 } 502 503 SYSCTL_PROC(_kern_timecounter, OID_AUTO, hardware, CTLTYPE_STRING | CTLFLAG_RW, 504 0, 0, sysctl_kern_timecounter_hardware, "A", ""); 505 506 507 /* Report or change the active timecounter hardware. */ 508 static int 509 sysctl_kern_timecounter_choice(SYSCTL_HANDLER_ARGS) 510 { 511 char buf[32], *spc; 512 struct timecounter *tc; 513 int error; 514 515 spc = ""; 516 error = 0; 517 for (tc = timecounters; error == 0 && tc != NULL; tc = tc->tc_next) { 518 sprintf(buf, "%s%s(%d)", 519 spc, tc->tc_name, tc->tc_quality); 520 error = SYSCTL_OUT(req, buf, strlen(buf)); 521 spc = " "; 522 } 523 return (error); 524 } 525 526 SYSCTL_PROC(_kern_timecounter, OID_AUTO, choice, CTLTYPE_STRING | CTLFLAG_RD, 527 0, 0, sysctl_kern_timecounter_choice, "A", ""); 528 529 /* 530 * RFC 2783 PPS-API implementation. 531 */ 532 533 int 534 pps_ioctl(u_long cmd, caddr_t data, struct pps_state *pps) 535 { 536 pps_params_t *app; 537 struct pps_fetch_args *fapi; 538 #ifdef PPS_SYNC 539 struct pps_kcbind_args *kapi; 540 #endif 541 542 switch (cmd) { 543 case PPS_IOC_CREATE: 544 return (0); 545 case PPS_IOC_DESTROY: 546 return (0); 547 case PPS_IOC_SETPARAMS: 548 app = (pps_params_t *)data; 549 if (app->mode & ~pps->ppscap) 550 return (EINVAL); 551 pps->ppsparam = *app; 552 return (0); 553 case PPS_IOC_GETPARAMS: 554 app = (pps_params_t *)data; 555 *app = pps->ppsparam; 556 app->api_version = PPS_API_VERS_1; 557 return (0); 558 case PPS_IOC_GETCAP: 559 *(int*)data = pps->ppscap; 560 return (0); 561 case PPS_IOC_FETCH: 562 fapi = (struct pps_fetch_args *)data; 563 if (fapi->tsformat && fapi->tsformat != PPS_TSFMT_TSPEC) 564 return (EINVAL); 565 if (fapi->timeout.tv_sec || fapi->timeout.tv_nsec) 566 return (EOPNOTSUPP); 567 pps->ppsinfo.current_mode = pps->ppsparam.mode; 568 fapi->pps_info_buf = pps->ppsinfo; 569 return (0); 570 case PPS_IOC_KCBIND: 571 #ifdef PPS_SYNC 572 kapi = (struct pps_kcbind_args *)data; 573 /* XXX Only root should be able to do this */ 574 if (kapi->tsformat && kapi->tsformat != PPS_TSFMT_TSPEC) 575 return (EINVAL); 576 if (kapi->kernel_consumer != PPS_KC_HARDPPS) 577 return (EINVAL); 578 if (kapi->edge & ~pps->ppscap) 579 return (EINVAL); 580 pps->kcmode = kapi->edge; 581 return (0); 582 #else 583 return (EOPNOTSUPP); 584 #endif 585 default: 586 return (ENOTTY); 587 } 588 } 589 590 void 591 pps_init(struct pps_state *pps) 592 { 593 pps->ppscap |= PPS_TSFMT_TSPEC; 594 if (pps->ppscap & PPS_CAPTUREASSERT) 595 pps->ppscap |= PPS_OFFSETASSERT; 596 if (pps->ppscap & PPS_CAPTURECLEAR) 597 pps->ppscap |= PPS_OFFSETCLEAR; 598 } 599 600 void 601 pps_capture(struct pps_state *pps) 602 { 603 struct timehands *th; 604 605 th = timehands; 606 pps->capgen = th->th_generation; 607 pps->capth = th; 608 pps->capcount = th->th_counter->tc_get_timecount(th->th_counter); 609 if (pps->capgen != th->th_generation) 610 pps->capgen = 0; 611 } 612 613 void 614 pps_event(struct pps_state *pps, int event) 615 { 616 struct bintime bt; 617 struct timespec ts, *tsp, *osp; 618 u_int tcount, *pcount; 619 int foff, fhard; 620 pps_seq_t *pseq; 621 622 /* If the timecounter was wound up underneath us, bail out. */ 623 if (pps->capgen == 0 || pps->capgen != pps->capth->th_generation) 624 return; 625 626 /* Things would be easier with arrays. */ 627 if (event == PPS_CAPTUREASSERT) { 628 tsp = &pps->ppsinfo.assert_timestamp; 629 osp = &pps->ppsparam.assert_offset; 630 foff = pps->ppsparam.mode & PPS_OFFSETASSERT; 631 fhard = pps->kcmode & PPS_CAPTUREASSERT; 632 pcount = &pps->ppscount[0]; 633 pseq = &pps->ppsinfo.assert_sequence; 634 } else { 635 tsp = &pps->ppsinfo.clear_timestamp; 636 osp = &pps->ppsparam.clear_offset; 637 foff = pps->ppsparam.mode & PPS_OFFSETCLEAR; 638 fhard = pps->kcmode & PPS_CAPTURECLEAR; 639 pcount = &pps->ppscount[1]; 640 pseq = &pps->ppsinfo.clear_sequence; 641 } 642 643 /* 644 * If the timecounter changed, we cannot compare the count values, so 645 * we have to drop the rest of the PPS-stuff until the next event. 646 */ 647 if (pps->ppstc != pps->capth->th_counter) { 648 pps->ppstc = pps->capth->th_counter; 649 *pcount = pps->capcount; 650 pps->ppscount[2] = pps->capcount; 651 return; 652 } 653 654 /* Return if nothing really happened. */ 655 if (*pcount == pps->capcount) 656 return; 657 658 /* Convert the count to a timespec. */ 659 tcount = pps->capcount - pps->capth->th_offset_count; 660 tcount &= pps->capth->th_counter->tc_counter_mask; 661 bt = pps->capth->th_offset; 662 bintime_addx(&bt, pps->capth->th_scale * tcount); 663 bintime_add(&bt, &boottimebin); 664 bintime2timespec(&bt, &ts); 665 666 /* If the timecounter was wound up underneath us, bail out. */ 667 if (pps->capgen != pps->capth->th_generation) 668 return; 669 670 *pcount = pps->capcount; 671 (*pseq)++; 672 *tsp = ts; 673 674 if (foff) { 675 timespecadd(tsp, osp); 676 if (tsp->tv_nsec < 0) { 677 tsp->tv_nsec += 1000000000; 678 tsp->tv_sec -= 1; 679 } 680 } 681 #ifdef PPS_SYNC 682 if (fhard) { 683 u_int64_t scale; 684 685 /* 686 * Feed the NTP PLL/FLL. 687 * The FLL wants to know how many (hardware) nanoseconds 688 * elapsed since the previous event. 689 */ 690 tcount = pps->capcount - pps->ppscount[2]; 691 pps->ppscount[2] = pps->capcount; 692 tcount &= pps->capth->th_counter->tc_counter_mask; 693 scale = (u_int64_t)1 << 63; 694 scale /= pps->capth->th_counter->tc_frequency; 695 scale *= 2; 696 bt.sec = 0; 697 bt.frac = 0; 698 bintime_addx(&bt, scale * tcount); 699 bintime2timespec(&bt, &ts); 700 hardpps(tsp, ts.tv_nsec + 1000000000 * ts.tv_sec); 701 } 702 #endif 703 } 704 705 /* 706 * Timecounters need to be updated every so often to prevent the hardware 707 * counter from overflowing. Updating also recalculates the cached values 708 * used by the get*() family of functions, so their precision depends on 709 * the update frequency. 710 */ 711 712 static int tc_tick; 713 SYSCTL_INT(_kern_timecounter, OID_AUTO, tick, CTLFLAG_RD, &tc_tick, 0, ""); 714 715 void 716 tc_ticktock(void) 717 { 718 static int count; 719 720 if (++count < tc_tick) 721 return; 722 count = 0; 723 tc_windup(); 724 } 725 726 static void 727 inittimecounter(void *dummy) 728 { 729 u_int p; 730 731 /* 732 * Set the initial timeout to 733 * max(1, <approx. number of hardclock ticks in a millisecond>). 734 * People should probably not use the sysctl to set the timeout 735 * to smaller than its inital value, since that value is the 736 * smallest reasonable one. If they want better timestamps they 737 * should use the non-"get"* functions. 738 */ 739 if (hz > 1000) 740 tc_tick = (hz + 500) / 1000; 741 else 742 tc_tick = 1; 743 p = (tc_tick * 1000000) / hz; 744 printf("Timecounters tick every %d.%03u msec\n", p / 1000, p % 1000); 745 746 /* warm up new timecounter (again) and get rolling. */ 747 (void)timecounter->tc_get_timecount(timecounter); 748 (void)timecounter->tc_get_timecount(timecounter); 749 } 750 751 SYSINIT(timecounter, SI_SUB_CLOCKS, SI_ORDER_SECOND, inittimecounter, NULL) 752