sys/kern/kern_ntptime.c

   1 /***********************************************************************
   2  *                                                                     *
   3  * Copyright (c) David L. Mills 1993-2001                              *
   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: src/sys/kern/kern_ntptime.c,v 1.32.2.2 2001/04/22 11:19:46 jhay Exp $
  32  * $DragonFly: src/sys/kern/kern_ntptime.c,v 1.13 2007/04/30 07:18:53 dillon Exp $
  33  */
  34
  35 #include "opt_ntp.h"
  36
  37 #include <sys/param.h>
  38 #include <sys/systm.h>
  39 #include <sys/sysproto.h>
  40 #include <sys/kernel.h>
  41 #include <sys/proc.h>
  42 #include <sys/priv.h>
  43 #include <sys/time.h>
  44 #include <sys/timex.h>
  45 #include <sys/timepps.h>
  46 #include <sys/sysctl.h>
  47
  48 #include <sys/thread2.h>
  49 #include <sys/mplock2.h>
  50
  51 /*
  52  * Single-precision macros for 64-bit machines
  53  */
  54 typedef long long l_fp;
  55 #define L_ADD(v, u)     ((v) += (u))
  56 #define L_SUB(v, u)     ((v) -= (u))
  57 #define L_ADDHI(v, a)   ((v) += (long long)(a) << 32)
  58 #define L_NEG(v)        ((v) = -(v))
  59 #define L_RSHIFT(v, n) \
  60         do { \
  61                 if ((v) < 0) \
  62                         (v) = -(-(v) >> (n)); \
  63                 else \
  64                         (v) = (v) >> (n); \
  65         } while (0)
  66 #define L_MPY(v, a)     ((v) *= (a))
  67 #define L_CLR(v)        ((v) = 0)
  68 #define L_ISNEG(v)      ((v) < 0)
  69 #define L_LINT(v, a)    ((v) = (long long)(a) << 32)
  70 #define L_GINT(v)       ((v) < 0 ? -(-(v) >> 32) : (v) >> 32)
  71
  72 /*
  73  * Generic NTP kernel interface
  74  *
  75  * These routines constitute the Network Time Protocol (NTP) interfaces
  76  * for user and daemon application programs. The ntp_gettime() routine
  77  * provides the time, maximum error (synch distance) and estimated error
  78  * (dispersion) to client user application programs. The ntp_adjtime()
  79  * routine is used by the NTP daemon to adjust the system clock to an
  80  * externally derived time. The time offset and related variables set by
  81  * this routine are used by other routines in this module to adjust the
  82  * phase and frequency of the clock discipline loop which controls the
  83  * system clock.
  84  *
  85  * When the kernel time is reckoned directly in nanoseconds (NTP_NANO
  86  * defined), the time at each tick interrupt is derived directly from
  87  * the kernel time variable. When the kernel time is reckoned in
  88  * microseconds, (NTP_NANO undefined), the time is derived from the
  89  * kernel time variable together with a variable representing the
  90  * leftover nanoseconds at the last tick interrupt. In either case, the
  91  * current nanosecond time is reckoned from these values plus an
  92  * interpolated value derived by the clock routines in another
  93  * architecture-specific module. The interpolation can use either a
  94  * dedicated counter or a processor cycle counter (PCC) implemented in
  95  * some architectures.
  96  *
  97  * Note that all routines must run at priority splclock or higher.
  98  */
  99 /*
 100  * Phase/frequency-lock loop (PLL/FLL) definitions
 101  *
 102  * The nanosecond clock discipline uses two variable types, time
 103  * variables and frequency variables. Both types are represented as 64-
 104  * bit fixed-point quantities with the decimal point between two 32-bit
 105  * halves. On a 32-bit machine, each half is represented as a single
 106  * word and mathematical operations are done using multiple-precision
 107  * arithmetic. On a 64-bit machine, ordinary computer arithmetic is
 108  * used.
 109  *
 110  * A time variable is a signed 64-bit fixed-point number in ns and
 111  * fraction. It represents the remaining time offset to be amortized
 112  * over succeeding tick interrupts. The maximum time offset is about
 113  * 0.5 s and the resolution is about 2.3e-10 ns.
 114  *
 115  *                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
 116  *  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
 117  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 118  * |s s s|                       ns                                |
 119  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 120  * |                        fraction                               |
 121  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 122  *
 123  * A frequency variable is a signed 64-bit fixed-point number in ns/s
 124  * and fraction. It represents the ns and fraction to be added to the
 125  * kernel time variable at each second. The maximum frequency offset is
 126  * about +-500000 ns/s and the resolution is about 2.3e-10 ns/s.
 127  *
 128  *                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
 129  *  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
 130  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 131  * |s s s s s s s s s s s s s|            ns/s                     |
 132  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 133  * |                        fraction                               |
 134  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 135  */
 136 /*
 137  * The following variables establish the state of the PLL/FLL and the
 138  * residual time and frequency offset of the local clock.
 139  */
 140 #define SHIFT_PLL       4               /* PLL loop gain (shift) */
 141 #define SHIFT_FLL       2               /* FLL loop gain (shift) */
 142
 143 static int time_state = TIME_OK;        /* clock state */
 144 static int time_status = STA_UNSYNC;    /* clock status bits */
 145 static long time_tai;                   /* TAI offset (s) */
 146 static long time_monitor;               /* last time offset scaled (ns) */
 147 static long time_constant;              /* poll interval (shift) (s) */
 148 static long time_precision = 1;         /* clock precision (ns) */
 149 static long time_maxerror = MAXPHASE / 1000; /* maximum error (us) */
 150 static long time_esterror = MAXPHASE / 1000; /* estimated error (us) */
 151 static long time_reftime;               /* time at last adjustment (s) */
 152 static long time_tick;                  /* nanoseconds per tick (ns) */
 153 static l_fp time_offset;                /* time offset (ns) */
 154 static l_fp time_freq;                  /* frequency offset (ns/s) */
 155 static l_fp time_adj;                   /* tick adjust (ns/s) */
 156
 157 #ifdef PPS_SYNC
 158 /*
 159  * The following variables are used when a pulse-per-second (PPS) signal
 160  * is available and connected via a modem control lead. They establish
 161  * the engineering parameters of the clock discipline loop when
 162  * controlled by the PPS signal.
 163  */
 164 #define PPS_FAVG        2               /* min freq avg interval (s) (shift) */
 165 #define PPS_FAVGDEF     8               /* default freq avg int (s) (shift) */
 166 #define PPS_FAVGMAX     15              /* max freq avg interval (s) (shift) */
 167 #define PPS_PAVG        4               /* phase avg interval (s) (shift) */
 168 #define PPS_VALID       120             /* PPS signal watchdog max (s) */
 169 #define PPS_MAXWANDER   100000          /* max PPS wander (ns/s) */
 170 #define PPS_POPCORN     2               /* popcorn spike threshold (shift) */
 171
 172 static struct timespec pps_tf[3];       /* phase median filter */
 173 static l_fp pps_freq;                   /* scaled frequency offset (ns/s) */
 174 static long pps_fcount;                 /* frequency accumulator */
 175 static long pps_jitter;                 /* nominal jitter (ns) */
 176 static long pps_stabil;                 /* nominal stability (scaled ns/s) */
 177 static long pps_lastsec;                /* time at last calibration (s) */
 178 static int pps_valid;                   /* signal watchdog counter */
 179 static int pps_shift = PPS_FAVG;        /* interval duration (s) (shift) */
 180 static int pps_shiftmax = PPS_FAVGDEF;  /* max interval duration (s) (shift) */
 181 static int pps_intcnt;                  /* wander counter */
 182
 183 /*
 184  * PPS signal quality monitors
 185  */
 186 static long pps_calcnt;                 /* calibration intervals */
 187 static long pps_jitcnt;                 /* jitter limit exceeded */
 188 static long pps_stbcnt;                 /* stability limit exceeded */
 189 static long pps_errcnt;                 /* calibration errors */
 190 #endif /* PPS_SYNC */
 191 /*
 192  * End of phase/frequency-lock loop (PLL/FLL) definitions
 193  */
 194
 195 static void ntp_init(void);
 196 static void hardupdate(long offset);
 197
 198 /*
 199  * ntp_gettime() - NTP user application interface
 200  *
 201  * See the timex.h header file for synopsis and API description. Note
 202  * that the TAI offset is returned in the ntvtimeval.tai structure
 203  * member.
 204  */
 205 static int
 206 ntp_sysctl(SYSCTL_HANDLER_ARGS)
 207 {
 208         struct ntptimeval ntv;  /* temporary structure */
 209         struct timespec atv;    /* nanosecond time */
 210
 211         nanotime(&atv);
 212         ntv.time.tv_sec = atv.tv_sec;
 213         ntv.time.tv_nsec = atv.tv_nsec;
 214         ntv.maxerror = time_maxerror;
 215         ntv.esterror = time_esterror;
 216         ntv.tai = time_tai;
 217         ntv.time_state = time_state;
 218
 219         /*
 220          * Status word error decode. If any of these conditions occur,
 221          * an error is returned, instead of the status word. Most
 222          * applications will care only about the fact the system clock
 223          * may not be trusted, not about the details.
 224          *
 225          * Hardware or software error
 226          */
 227         if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||
 228
 229         /*
 230          * PPS signal lost when either time or frequency synchronization
 231          * requested
 232          */
 233             (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
 234             !(time_status & STA_PPSSIGNAL)) ||
 235
 236         /*
 237          * PPS jitter exceeded when time synchronization requested
 238          */
 239             (time_status & STA_PPSTIME &&
 240             time_status & STA_PPSJITTER) ||
 241
 242         /*
 243          * PPS wander exceeded or calibration error when frequency
 244          * synchronization requested
 245          */
 246             (time_status & STA_PPSFREQ &&
 247             time_status & (STA_PPSWANDER | STA_PPSERROR)))
 248                 ntv.time_state = TIME_ERROR;
 249         return (sysctl_handle_opaque(oidp, &ntv, sizeof ntv, req));
 250 }
 251
 252 SYSCTL_NODE(_kern, OID_AUTO, ntp_pll, CTLFLAG_RW, 0, "");
 253 SYSCTL_PROC(_kern_ntp_pll, OID_AUTO, gettime, CTLTYPE_OPAQUE|CTLFLAG_RD,
 254         0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", "");
 255
 256 #ifdef PPS_SYNC
 257 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shiftmax, CTLFLAG_RW, &pps_shiftmax, 0, "");
 258 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shift, CTLFLAG_RW, &pps_shift, 0, "");
 259 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, time_monitor, CTLFLAG_RD, &time_monitor, 0, "");
 260
 261 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, &pps_freq, sizeof(pps_freq), "I", "");
 262 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, time_freq, CTLFLAG_RD, &time_freq, sizeof(time_freq), "I", "");
 263 #endif
 264 /*
 265  * ntp_adjtime() - NTP daemon application interface
 266  *
 267  * See the timex.h header file for synopsis and API description. Note
 268  * that the timex.constant structure member has a dual purpose to set
 269  * the time constant and to set the TAI offset.
 270  *
 271  * MPALMOSTSAFE
 272  */
 273 int
 274 sys_ntp_adjtime(struct ntp_adjtime_args *uap)
 275 {
 276         struct thread *td = curthread;
 277         struct timex ntv;       /* temporary structure */
 278         long freq;              /* frequency ns/s) */
 279         int modes;              /* mode bits from structure */
 280         int error;
 281
 282         error = copyin((caddr_t)uap->tp, (caddr_t)&ntv, sizeof(ntv));
 283         if (error)
 284                 return(error);
 285
 286         /*
 287          * Update selected clock variables - only the superuser can
 288          * change anything. Note that there is no error checking here on
 289          * the assumption the superuser should know what it is doing.
 290          * Note that either the time constant or TAI offset are loaded
 291          * from the ntv.constant member, depending on the mode bits. If
 292          * the STA_PLL bit in the status word is cleared, the state and
 293          * status words are reset to the initial values at boot.
 294          */
 295         modes = ntv.modes;
 296         if (modes)
 297                 error = priv_check(td, PRIV_NTP_ADJTIME);
 298         if (error)
 299                 return (error);
 300
 301         get_mplock();
 302         crit_enter();
 303         if (modes & MOD_MAXERROR)
 304                 time_maxerror = ntv.maxerror;
 305         if (modes & MOD_ESTERROR)
 306                 time_esterror = ntv.esterror;
 307         if (modes & MOD_STATUS) {
 308                 if (time_status & STA_PLL && !(ntv.status & STA_PLL)) {
 309                         time_state = TIME_OK;
 310                         time_status = STA_UNSYNC;
 311 #ifdef PPS_SYNC
 312                         pps_shift = PPS_FAVG;
 313 #endif /* PPS_SYNC */
 314                 }
 315                 time_status &= STA_RONLY;
 316                 time_status |= ntv.status & ~STA_RONLY;
 317         }
 318         if (modes & MOD_TIMECONST) {
 319                 if (ntv.constant < 0)
 320                         time_constant = 0;
 321                 else if (ntv.constant > MAXTC)
 322                         time_constant = MAXTC;
 323                 else
 324                         time_constant = ntv.constant;
 325         }
 326         if (modes & MOD_TAI) {
 327                 if (ntv.constant > 0) /* XXX zero & negative numbers ? */
 328                         time_tai = ntv.constant;
 329         }
 330 #ifdef PPS_SYNC
 331         if (modes & MOD_PPSMAX) {
 332                 if (ntv.shift < PPS_FAVG)
 333                         pps_shiftmax = PPS_FAVG;
 334                 else if (ntv.shift > PPS_FAVGMAX)
 335                         pps_shiftmax = PPS_FAVGMAX;
 336                 else
 337                         pps_shiftmax = ntv.shift;
 338         }
 339 #endif /* PPS_SYNC */
 340         if (modes & MOD_NANO)
 341                 time_status |= STA_NANO;
 342         if (modes & MOD_MICRO)
 343                 time_status &= ~STA_NANO;
 344         if (modes & MOD_CLKB)
 345                 time_status |= STA_CLK;
 346         if (modes & MOD_CLKA)
 347                 time_status &= ~STA_CLK;
 348         if (modes & MOD_OFFSET) {
 349                 if (time_status & STA_NANO)
 350                         hardupdate(ntv.offset);
 351                 else
 352                         hardupdate(ntv.offset * 1000);
 353         }
 354         /*
 355          * Note: the userland specified frequency is in seconds per second
 356          * times 65536e+6.  Multiply by a thousand and divide by 65336 to
 357          * get nanoseconds.
 358          */
 359         if (modes & MOD_FREQUENCY) {
 360                 freq = (ntv.freq * 1000LL) >> 16;
 361                 if (freq > MAXFREQ)
 362                         L_LINT(time_freq, MAXFREQ);
 363                 else if (freq < -MAXFREQ)
 364                         L_LINT(time_freq, -MAXFREQ);
 365                 else
 366                         L_LINT(time_freq, freq);
 367 #ifdef PPS_SYNC
 368                 pps_freq = time_freq;
 369 #endif /* PPS_SYNC */
 370         }
 371
 372         /*
 373          * Retrieve all clock variables. Note that the TAI offset is
 374          * returned only by ntp_gettime();
 375          */
 376         if (time_status & STA_NANO)
 377                 ntv.offset = time_monitor;
 378         else
 379                 ntv.offset = time_monitor / 1000; /* XXX rounding ? */
 380         ntv.freq = L_GINT((time_freq / 1000LL) << 16);
 381         ntv.maxerror = time_maxerror;
 382         ntv.esterror = time_esterror;
 383         ntv.status = time_status;
 384         ntv.constant = time_constant;
 385         if (time_status & STA_NANO)
 386                 ntv.precision = time_precision;
 387         else
 388                 ntv.precision = time_precision / 1000;
 389         ntv.tolerance = MAXFREQ * SCALE_PPM;
 390 #ifdef PPS_SYNC
 391         ntv.shift = pps_shift;
 392         ntv.ppsfreq = L_GINT((pps_freq / 1000LL) << 16);
 393         if (time_status & STA_NANO)
 394                 ntv.jitter = pps_jitter;
 395         else
 396                 ntv.jitter = pps_jitter / 1000;
 397         ntv.stabil = pps_stabil;
 398         ntv.calcnt = pps_calcnt;
 399         ntv.errcnt = pps_errcnt;
 400         ntv.jitcnt = pps_jitcnt;
 401         ntv.stbcnt = pps_stbcnt;
 402 #endif /* PPS_SYNC */
 403         crit_exit();
 404         rel_mplock();
 405
 406         error = copyout((caddr_t)&ntv, (caddr_t)uap->tp, sizeof(ntv));
 407         if (error)
 408                 return (error);
 409
 410         /*
 411          * Status word error decode. See comments in
 412          * ntp_gettime() routine.
 413          */
 414         if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||
 415             (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
 416             !(time_status & STA_PPSSIGNAL)) ||
 417             (time_status & STA_PPSTIME &&
 418             time_status & STA_PPSJITTER) ||
 419             (time_status & STA_PPSFREQ &&
 420             time_status & (STA_PPSWANDER | STA_PPSERROR))) {
 421                 uap->sysmsg_result = TIME_ERROR;
 422         } else {
 423                 uap->sysmsg_result = time_state;
 424         }
 425         return (error);
 426 }
 427
 428 /*
 429  * second_overflow() - called after ntp_tick_adjust()
 430  *
 431  * This routine is ordinarily called from hardclock() whenever the seconds
 432  * hand rolls over.  It returns leap seconds to add or drop, and sets nsec_adj
 433  * to the total adjustment to make over the next second in (ns << 32).
 434  *
 435  * This routine is only called by cpu #0.
 436  */
 437 int
 438 ntp_update_second(time_t newsec, int64_t *nsec_adj)
 439 {
 440         l_fp ftemp;             /* 32/64-bit temporary */
 441         int  adjsec = 0;
 442
 443         /*
 444          * On rollover of the second both the nanosecond and microsecond
 445          * clocks are updated and the state machine cranked as
 446          * necessary. The phase adjustment to be used for the next
 447          * second is calculated and the maximum error is increased by
 448          * the tolerance.
 449          */
 450         time_maxerror += MAXFREQ / 1000;
 451
 452         /*
 453          * Leap second processing. If in leap-insert state at
 454          * the end of the day, the system clock is set back one
 455          * second; if in leap-delete state, the system clock is
 456          * set ahead one second. The nano_time() routine or
 457          * external clock driver will insure that reported time
 458          * is always monotonic.
 459          */
 460         switch (time_state) {
 461
 462                 /*
 463                  * No warning.
 464                  */
 465                 case TIME_OK:
 466                 if (time_status & STA_INS)
 467                         time_state = TIME_INS;
 468                 else if (time_status & STA_DEL)
 469                         time_state = TIME_DEL;
 470                 break;
 471
 472                 /*
 473                  * Insert second 23:59:60 following second
 474                  * 23:59:59.
 475                  */
 476                 case TIME_INS:
 477                 if (!(time_status & STA_INS))
 478                         time_state = TIME_OK;
 479                 else if ((newsec) % 86400 == 0) {
 480                         --adjsec;
 481                         time_state = TIME_OOP;
 482                 }
 483                 break;
 484
 485                 /*
 486                  * Delete second 23:59:59.
 487                  */
 488                 case TIME_DEL:
 489                 if (!(time_status & STA_DEL))
 490                         time_state = TIME_OK;
 491                 else if (((newsec) + 1) % 86400 == 0) {
 492                         ++adjsec;
 493                         time_tai--;
 494                         time_state = TIME_WAIT;
 495                 }
 496                 break;
 497
 498                 /*
 499                  * Insert second in progress.
 500                  */
 501                 case TIME_OOP:
 502                         time_tai++;
 503                         time_state = TIME_WAIT;
 504                 break;
 505
 506                 /*
 507                  * Wait for status bits to clear.
 508                  */
 509                 case TIME_WAIT:
 510                 if (!(time_status & (STA_INS | STA_DEL)))
 511                         time_state = TIME_OK;
 512         }
 513
 514         /*
 515          * time_offset represents the total time adjustment we wish to
 516          * make (over no particular period of time).  time_freq represents
 517          * the frequency compensation we wish to apply.
 518          *
 519          * time_adj represents the total adjustment we wish to make over
 520          * one full second.  hardclock usually applies this adjustment in
 521          * time_adj / hz jumps, hz times a second.
 522          */
 523         ftemp = time_offset;
 524 #ifdef PPS_SYNC
 525         /* XXX even if PPS signal dies we should finish adjustment ? */
 526         if ((time_status & STA_PPSTIME) && (time_status & STA_PPSSIGNAL))
 527                 L_RSHIFT(ftemp, pps_shift);
 528         else
 529                 L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
 530 #else
 531                 L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
 532 #endif /* PPS_SYNC */
 533         time_adj = ftemp;               /* adjustment for part of the offset */
 534         L_SUB(time_offset, ftemp);
 535         L_ADD(time_adj, time_freq);     /* add frequency correction */
 536         *nsec_adj = time_adj;
 537 #ifdef PPS_SYNC
 538         if (pps_valid > 0)
 539                 pps_valid--;
 540         else
 541                 time_status &= ~STA_PPSSIGNAL;
 542 #endif /* PPS_SYNC */
 543         return(adjsec);
 544 }
 545
 546 /*
 547  * ntp_init() - initialize variables and structures
 548  *
 549  * This routine must be called after the kernel variables hz and tick
 550  * are set or changed and before the next tick interrupt. In this
 551  * particular implementation, these values are assumed set elsewhere in
 552  * the kernel. The design allows the clock frequency and tick interval
 553  * to be changed while the system is running. So, this routine should
 554  * probably be integrated with the code that does that.
 555  */
 556 static void
 557 ntp_init(void)
 558 {
 559
 560         /*
 561          * The following variable must be initialized any time the
 562          * kernel variable hz is changed.
 563          */
 564         time_tick = NANOSECOND / hz;
 565
 566         /*
 567          * The following variables are initialized only at startup. Only
 568          * those structures not cleared by the compiler need to be
 569          * initialized, and these only in the simulator. In the actual
 570          * kernel, any nonzero values here will quickly evaporate.
 571          */
 572         L_CLR(time_offset);
 573         L_CLR(time_freq);
 574 #ifdef PPS_SYNC
 575         pps_tf[0].tv_sec = pps_tf[0].tv_nsec = 0;
 576         pps_tf[1].tv_sec = pps_tf[1].tv_nsec = 0;
 577         pps_tf[2].tv_sec = pps_tf[2].tv_nsec = 0;
 578         pps_fcount = 0;
 579         L_CLR(pps_freq);
 580 #endif /* PPS_SYNC */
 581 }
 582
 583 SYSINIT(ntpclocks, SI_BOOT2_CLOCKS, SI_ORDER_FIRST, ntp_init, NULL)
 584
 585 /*
 586  * hardupdate() - local clock update
 587  *
 588  * This routine is called by ntp_adjtime() to update the local clock
 589  * phase and frequency. The implementation is of an adaptive-parameter,
 590  * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
 591  * time and frequency offset estimates for each call. If the kernel PPS
 592  * discipline code is configured (PPS_SYNC), the PPS signal itself
 593  * determines the new time offset, instead of the calling argument.
 594  * Presumably, calls to ntp_adjtime() occur only when the caller
 595  * believes the local clock is valid within some bound (+-128 ms with
 596  * NTP). If the caller's time is far different than the PPS time, an
 597  * argument will ensue, and it's not clear who will lose.
 598  *
 599  * For uncompensated quartz crystal oscillators and nominal update
 600  * intervals less than 256 s, operation should be in phase-lock mode,
 601  * where the loop is disciplined to phase. For update intervals greater
 602  * than 1024 s, operation should be in frequency-lock mode, where the
 603  * loop is disciplined to frequency. Between 256 s and 1024 s, the mode
 604  * is selected by the STA_MODE status bit.
 605  */
 606 static void
 607 hardupdate(long offset)
 608 {
 609         long mtemp;
 610         l_fp ftemp;
 611         globaldata_t gd;
 612
 613         gd = mycpu;
 614
 615         /*
 616          * Select how the phase is to be controlled and from which
 617          * source. If the PPS signal is present and enabled to
 618          * discipline the time, the PPS offset is used; otherwise, the
 619          * argument offset is used.
 620          */
 621         if (!(time_status & STA_PLL))
 622                 return;
 623         if (!((time_status & STA_PPSTIME) && (time_status & STA_PPSSIGNAL))) {
 624                 if (offset > MAXPHASE)
 625                         time_monitor = MAXPHASE;
 626                 else if (offset < -MAXPHASE)
 627                         time_monitor = -MAXPHASE;
 628                 else
 629                         time_monitor = offset;
 630                 L_LINT(time_offset, time_monitor);
 631         }
 632
 633         /*
 634          * Select how the frequency is to be controlled and in which
 635          * mode (PLL or FLL). If the PPS signal is present and enabled
 636          * to discipline the frequency, the PPS frequency is used;
 637          * otherwise, the argument offset is used to compute it.
 638          *
 639          * gd_time_seconds is basically an uncompensated uptime.  We use
 640          * this for consistency.
 641          */
 642         if (time_status & STA_PPSFREQ && time_status & STA_PPSSIGNAL) {
 643                 time_reftime = time_second;
 644                 return;
 645         }
 646         if (time_status & STA_FREQHOLD || time_reftime == 0)
 647                 time_reftime = time_second;
 648         mtemp = time_second - time_reftime;
 649         L_LINT(ftemp, time_monitor);
 650         L_RSHIFT(ftemp, (SHIFT_PLL + 2 + time_constant) << 1);
 651         L_MPY(ftemp, mtemp);
 652         L_ADD(time_freq, ftemp);
 653         time_status &= ~STA_MODE;
 654         if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
 655                 L_LINT(ftemp, (time_monitor << 4) / mtemp);
 656                 L_RSHIFT(ftemp, SHIFT_FLL + 4);
 657                 L_ADD(time_freq, ftemp);
 658                 time_status |= STA_MODE;
 659         }
 660         time_reftime = time_second;
 661         if (L_GINT(time_freq) > MAXFREQ)
 662                 L_LINT(time_freq, MAXFREQ);
 663         else if (L_GINT(time_freq) < -MAXFREQ)
 664                 L_LINT(time_freq, -MAXFREQ);
 665 }
 666
 667 #ifdef PPS_SYNC
 668 /*
 669  * hardpps() - discipline CPU clock oscillator to external PPS signal
 670  *
 671  * This routine is called at each PPS interrupt in order to discipline
 672  * the CPU clock oscillator to the PPS signal. There are two independent
 673  * first-order feedback loops, one for the phase, the other for the
 674  * frequency. The phase loop measures and grooms the PPS phase offset
 675  * and leaves it in a handy spot for the seconds overflow routine. The
 676  * frequency loop averages successive PPS phase differences and
 677  * calculates the PPS frequency offset, which is also processed by the
 678  * seconds overflow routine. The code requires the caller to capture the
 679  * time and architecture-dependent hardware counter values in
 680  * nanoseconds at the on-time PPS signal transition.
 681  *
 682  * Note that, on some Unix systems this routine runs at an interrupt
 683  * priority level higher than the timer interrupt routine hardclock().
 684  * Therefore, the variables used are distinct from the hardclock()
 685  * variables, except for the actual time and frequency variables, which
 686  * are determined by this routine and updated atomically.
 687  */
 688 void
 689 hardpps(struct timespec *tsp, long nsec)
 690 {
 691         long u_sec, u_nsec, v_nsec; /* temps */
 692         l_fp ftemp;
 693
 694         /*
 695          * The signal is first processed by a range gate and frequency
 696          * discriminator. The range gate rejects noise spikes outside
 697          * the range +-500 us. The frequency discriminator rejects input
 698          * signals with apparent frequency outside the range 1 +-500
 699          * PPM. If two hits occur in the same second, we ignore the
 700          * later hit; if not and a hit occurs outside the range gate,
 701          * keep the later hit for later comparison, but do not process
 702          * it.
 703          */
 704         time_status |= STA_PPSSIGNAL | STA_PPSJITTER;
 705         time_status &= ~(STA_PPSWANDER | STA_PPSERROR);
 706         pps_valid = PPS_VALID;
 707         u_sec = tsp->tv_sec;
 708         u_nsec = tsp->tv_nsec;
 709         if (u_nsec >= (NANOSECOND >> 1)) {
 710                 u_nsec -= NANOSECOND;
 711                 u_sec++;
 712         }
 713         v_nsec = u_nsec - pps_tf[0].tv_nsec;
 714         if (u_sec == pps_tf[0].tv_sec && v_nsec < NANOSECOND -
 715             MAXFREQ)
 716                 return;
 717         pps_tf[2] = pps_tf[1];
 718         pps_tf[1] = pps_tf[0];
 719         pps_tf[0].tv_sec = u_sec;
 720         pps_tf[0].tv_nsec = u_nsec;
 721
 722         /*
 723          * Compute the difference between the current and previous
 724          * counter values. If the difference exceeds 0.5 s, assume it
 725          * has wrapped around, so correct 1.0 s. If the result exceeds
 726          * the tick interval, the sample point has crossed a tick
 727          * boundary during the last second, so correct the tick. Very
 728          * intricate.
 729          */
 730         u_nsec = nsec;
 731         if (u_nsec > (NANOSECOND >> 1))
 732                 u_nsec -= NANOSECOND;
 733         else if (u_nsec < -(NANOSECOND >> 1))
 734                 u_nsec += NANOSECOND;
 735         pps_fcount += u_nsec;
 736         if (v_nsec > MAXFREQ || v_nsec < -MAXFREQ)
 737                 return;
 738         time_status &= ~STA_PPSJITTER;
 739
 740         /*
 741          * A three-stage median filter is used to help denoise the PPS
 742          * time. The median sample becomes the time offset estimate; the
 743          * difference between the other two samples becomes the time
 744          * dispersion (jitter) estimate.
 745          */
 746         if (pps_tf[0].tv_nsec > pps_tf[1].tv_nsec) {
 747                 if (pps_tf[1].tv_nsec > pps_tf[2].tv_nsec) {
 748                         v_nsec = pps_tf[1].tv_nsec;     /* 0 1 2 */
 749                         u_nsec = pps_tf[0].tv_nsec - pps_tf[2].tv_nsec;
 750                 } else if (pps_tf[2].tv_nsec > pps_tf[0].tv_nsec) {
 751                         v_nsec = pps_tf[0].tv_nsec;     /* 2 0 1 */
 752                         u_nsec = pps_tf[2].tv_nsec - pps_tf[1].tv_nsec;
 753                 } else {
 754                         v_nsec = pps_tf[2].tv_nsec;     /* 0 2 1 */
 755                         u_nsec = pps_tf[0].tv_nsec - pps_tf[1].tv_nsec;
 756                 }
 757         } else {
 758                 if (pps_tf[1].tv_nsec < pps_tf[2].tv_nsec) {
 759                         v_nsec = pps_tf[1].tv_nsec;     /* 2 1 0 */
 760                         u_nsec = pps_tf[2].tv_nsec - pps_tf[0].tv_nsec;
 761                 } else if (pps_tf[2].tv_nsec < pps_tf[0].tv_nsec) {
 762                         v_nsec = pps_tf[0].tv_nsec;     /* 1 0 2 */
 763                         u_nsec = pps_tf[1].tv_nsec - pps_tf[2].tv_nsec;
 764                 } else {
 765                         v_nsec = pps_tf[2].tv_nsec;     /* 1 2 0 */
 766                         u_nsec = pps_tf[1].tv_nsec - pps_tf[0].tv_nsec;
 767                 }
 768         }
 769
 770         /*
 771          * Nominal jitter is due to PPS signal noise and interrupt
 772          * latency. If it exceeds the popcorn threshold, the sample is
 773          * discarded. otherwise, if so enabled, the time offset is
 774          * updated. We can tolerate a modest loss of data here without
 775          * much degrading time accuracy.
 776          */
 777         if (u_nsec > (pps_jitter << PPS_POPCORN)) {
 778                 time_status |= STA_PPSJITTER;
 779                 pps_jitcnt++;
 780         } else if (time_status & STA_PPSTIME) {
 781                 time_monitor = -v_nsec;
 782                 L_LINT(time_offset, time_monitor);
 783         }
 784         pps_jitter += (u_nsec - pps_jitter) >> PPS_FAVG;
 785         u_sec = pps_tf[0].tv_sec - pps_lastsec;
 786         if (u_sec < (1 << pps_shift))
 787                 return;
 788
 789         /*
 790          * At the end of the calibration interval the difference between
 791          * the first and last counter values becomes the scaled
 792          * frequency. It will later be divided by the length of the
 793          * interval to determine the frequency update. If the frequency
 794          * exceeds a sanity threshold, or if the actual calibration
 795          * interval is not equal to the expected length, the data are
 796          * discarded. We can tolerate a modest loss of data here without
 797          * much degrading frequency accuracy.
 798          */
 799         pps_calcnt++;
 800         v_nsec = -pps_fcount;
 801         pps_lastsec = pps_tf[0].tv_sec;
 802         pps_fcount = 0;
 803         u_nsec = MAXFREQ << pps_shift;
 804         if (v_nsec > u_nsec || v_nsec < -u_nsec || u_sec != (1 <<
 805             pps_shift)) {
 806                 time_status |= STA_PPSERROR;
 807                 pps_errcnt++;
 808                 return;
 809         }
 810
 811         /*
 812          * Here the raw frequency offset and wander (stability) is
 813          * calculated. If the wander is less than the wander threshold
 814          * for four consecutive averaging intervals, the interval is
 815          * doubled; if it is greater than the threshold for four
 816          * consecutive intervals, the interval is halved. The scaled
 817          * frequency offset is converted to frequency offset. The
 818          * stability metric is calculated as the average of recent
 819          * frequency changes, but is used only for performance
 820          * monitoring.
 821          */
 822         L_LINT(ftemp, v_nsec);
 823         L_RSHIFT(ftemp, pps_shift);
 824         L_SUB(ftemp, pps_freq);
 825         u_nsec = L_GINT(ftemp);
 826         if (u_nsec > PPS_MAXWANDER) {
 827                 L_LINT(ftemp, PPS_MAXWANDER);
 828                 pps_intcnt--;
 829                 time_status |= STA_PPSWANDER;
 830                 pps_stbcnt++;
 831         } else if (u_nsec < -PPS_MAXWANDER) {
 832                 L_LINT(ftemp, -PPS_MAXWANDER);
 833                 pps_intcnt--;
 834                 time_status |= STA_PPSWANDER;
 835                 pps_stbcnt++;
 836         } else {
 837                 pps_intcnt++;
 838         }
 839         if (pps_intcnt >= 4) {
 840                 pps_intcnt = 4;
 841                 if (pps_shift < pps_shiftmax) {
 842                         pps_shift++;
 843                         pps_intcnt = 0;
 844                 }
 845         } else if (pps_intcnt <= -4 || pps_shift > pps_shiftmax) {
 846                 pps_intcnt = -4;
 847                 if (pps_shift > PPS_FAVG) {
 848                         pps_shift--;
 849                         pps_intcnt = 0;
 850                 }
 851         }
 852         if (u_nsec < 0)
 853                 u_nsec = -u_nsec;
 854         pps_stabil += (u_nsec * SCALE_PPM - pps_stabil) >> PPS_FAVG;
 855
 856         /*
 857          * The PPS frequency is recalculated and clamped to the maximum
 858          * MAXFREQ. If enabled, the system clock frequency is updated as
 859          * well.
 860          */
 861         L_ADD(pps_freq, ftemp);
 862         u_nsec = L_GINT(pps_freq);
 863         if (u_nsec > MAXFREQ)
 864                 L_LINT(pps_freq, MAXFREQ);
 865         else if (u_nsec < -MAXFREQ)
 866                 L_LINT(pps_freq, -MAXFREQ);
 867         if (time_status & STA_PPSFREQ)
 868                 time_freq = pps_freq;
 869 }
 870 #endif /* PPS_SYNC */