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 /*      $NetBSD: kern_ntptime.c,v 1.64 2022/10/26 23:23:52 riastradh Exp $      */
    2 
    3 /*-
    4  * Copyright (c) 2008 The NetBSD Foundation, Inc.
    5  * All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions and the following disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  *
   16  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
   17  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   18  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   19  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
   20  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   21  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   22  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   23  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   24  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   25  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   26  * POSSIBILITY OF SUCH DAMAGE.
   27  */
   28 
   29 /*-
   30  ***********************************************************************
   31  *                                                                     *
   32  * Copyright (c) David L. Mills 1993-2001                              *
   33  *                                                                     *
   34  * Permission to use, copy, modify, and distribute this software and   *
   35  * its documentation for any purpose and without fee is hereby         *
   36  * granted, provided that the above copyright notice appears in all    *
   37  * copies and that both the copyright notice and this permission       *
   38  * notice appear in supporting documentation, and that the name        *
   39  * University of Delaware not be used in advertising or publicity      *
   40  * pertaining to distribution of the software without specific,        *
   41  * written prior permission. The University of Delaware makes no       *
   42  * representations about the suitability this software for any         *
   43  * purpose. It is provided "as is" without express or implied          *
   44  * warranty.                                                           *
   45  *                                                                     *
   46  **********************************************************************/
   47 
   48 /*
   49  * Adapted from the original sources for FreeBSD and timecounters by:
   50  * Poul-Henning Kamp <phk@FreeBSD.org>.
   51  *
   52  * The 32bit version of the "LP" macros seems a bit past its "sell by" 
   53  * date so I have retained only the 64bit version and included it directly
   54  * in this file.
   55  *
   56  * Only minor changes done to interface with the timecounters over in
   57  * sys/kern/kern_clock.c.   Some of the comments below may be (even more)
   58  * confusing and/or plain wrong in that context.
   59  */
   60 
   61 #include <sys/cdefs.h>
   62 /* __FBSDID("$FreeBSD: src/sys/kern/kern_ntptime.c,v 1.59 2005/05/28 14:34:41 rwatson Exp $"); */
   63 __KERNEL_RCSID(0, "$NetBSD: kern_ntptime.c,v 1.64 2022/10/26 23:23:52 riastradh Exp $");
   64 
   65 #ifdef _KERNEL_OPT
   66 #include "opt_ntp.h"
   67 #endif
   68 
   69 #include <sys/param.h>
   70 #include <sys/resourcevar.h>
   71 #include <sys/systm.h>
   72 #include <sys/kernel.h>
   73 #include <sys/proc.h>
   74 #include <sys/sysctl.h>
   75 #include <sys/timex.h>
   76 #include <sys/vnode.h>
   77 #include <sys/kauth.h>
   78 #include <sys/mount.h>
   79 #include <sys/syscallargs.h>
   80 #include <sys/cpu.h>
   81 
   82 #include <compat/sys/timex.h>
   83 
   84 /*
   85  * Single-precision macros for 64-bit machines
   86  */
   87 typedef int64_t l_fp;
   88 #define L_ADD(v, u)     ((v) += (u))
   89 #define L_SUB(v, u)     ((v) -= (u))
   90 #define L_ADDHI(v, a)   ((v) += (int64_t)(a) << 32)
   91 #define L_NEG(v)        ((v) = -(v))
   92 #define L_RSHIFT(v, n) \
   93         do { \
   94                 if ((v) < 0) \
   95                         (v) = -(-(v) >> (n)); \
   96                 else \
   97                         (v) = (v) >> (n); \
   98         } while (0)
   99 #define L_MPY(v, a)     ((v) *= (a))
  100 #define L_CLR(v)        ((v) = 0)
  101 #define L_ISNEG(v)      ((v) < 0)
  102 #define L_LINT(v, a)    ((v) = (int64_t)((uint64_t)(a) << 32))
  103 #define L_GINT(v)       ((v) < 0 ? -(-(v) >> 32) : (v) >> 32)
  104 
  105 #ifdef NTP
  106 /*
  107  * Generic NTP kernel interface
  108  *
  109  * These routines constitute the Network Time Protocol (NTP) interfaces
  110  * for user and daemon application programs. The ntp_gettime() routine
  111  * provides the time, maximum error (synch distance) and estimated error
  112  * (dispersion) to client user application programs. The ntp_adjtime()
  113  * routine is used by the NTP daemon to adjust the system clock to an
  114  * externally derived time. The time offset and related variables set by
  115  * this routine are used by other routines in this module to adjust the
  116  * phase and frequency of the clock discipline loop which controls the
  117  * system clock.
  118  *
  119  * When the kernel time is reckoned directly in nanoseconds (NTP_NANO
  120  * defined), the time at each tick interrupt is derived directly from
  121  * the kernel time variable. When the kernel time is reckoned in
  122  * microseconds, (NTP_NANO undefined), the time is derived from the
  123  * kernel time variable together with a variable representing the
  124  * leftover nanoseconds at the last tick interrupt. In either case, the
  125  * current nanosecond time is reckoned from these values plus an
  126  * interpolated value derived by the clock routines in another
  127  * architecture-specific module. The interpolation can use either a
  128  * dedicated counter or a processor cycle counter (PCC) implemented in
  129  * some architectures.
  130  *
  131  * Note that all routines must run at priority splclock or higher.
  132  */
  133 /*
  134  * Phase/frequency-lock loop (PLL/FLL) definitions
  135  *
  136  * The nanosecond clock discipline uses two variable types, time
  137  * variables and frequency variables. Both types are represented as 64-
  138  * bit fixed-point quantities with the decimal point between two 32-bit
  139  * halves. On a 32-bit machine, each half is represented as a single
  140  * word and mathematical operations are done using multiple-precision
  141  * arithmetic. On a 64-bit machine, ordinary computer arithmetic is
  142  * used.
  143  *
  144  * A time variable is a signed 64-bit fixed-point number in ns and
  145  * fraction. It represents the remaining time offset to be amortized
  146  * over succeeding tick interrupts. The maximum time offset is about
  147  * 0.5 s and the resolution is about 2.3e-10 ns.
  148  *
  149  *                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
  150  *  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
  151  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  152  * |s s s|                       ns                                |
  153  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  154  * |                        fraction                               |
  155  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  156  *
  157  * A frequency variable is a signed 64-bit fixed-point number in ns/s
  158  * and fraction. It represents the ns and fraction to be added to the
  159  * kernel time variable at each second. The maximum frequency offset is
  160  * about +-500000 ns/s and the resolution is about 2.3e-10 ns/s.
  161  *
  162  *                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
  163  *  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
  164  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  165  * |s s s s s s s s s s s s s|            ns/s                     |
  166  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  167  * |                        fraction                               |
  168  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  169  */
  170 /*
  171  * The following variables establish the state of the PLL/FLL and the
  172  * residual time and frequency offset of the local clock.
  173  */
  174 #define SHIFT_PLL       4               /* PLL loop gain (shift) */
  175 #define SHIFT_FLL       2               /* FLL loop gain (shift) */
  176 
  177 static int time_state = TIME_OK;        /* clock state */
  178 static int time_status = STA_UNSYNC;    /* clock status bits */
  179 static long time_tai;                   /* TAI offset (s) */
  180 static long time_monitor;               /* last time offset scaled (ns) */
  181 static long time_constant;              /* poll interval (shift) (s) */
  182 static long time_precision = 1;         /* clock precision (ns) */
  183 static long time_maxerror = MAXPHASE / 1000; /* maximum error (us) */
  184 static long time_esterror = MAXPHASE / 1000; /* estimated error (us) */
  185 static time_t time_reftime;             /* time at last adjustment (s) */
  186 static l_fp time_offset;                /* time offset (ns) */
  187 static l_fp time_freq;                  /* frequency offset (ns/s) */
  188 #endif /* NTP */
  189 
  190 static l_fp time_adj;                   /* tick adjust (ns/s) */
  191 int64_t time_adjtime;           /* correction from adjtime(2) (usec) */
  192 
  193 #ifdef NTP
  194 #ifdef PPS_SYNC
  195 /*
  196  * The following variables are used when a pulse-per-second (PPS) signal
  197  * is available and connected via a modem control lead. They establish
  198  * the engineering parameters of the clock discipline loop when
  199  * controlled by the PPS signal.
  200  */
  201 #define PPS_FAVG        2               /* min freq avg interval (s) (shift) */
  202 #define PPS_FAVGDEF     8               /* default freq avg int (s) (shift) */
  203 #define PPS_FAVGMAX     15              /* max freq avg interval (s) (shift) */
  204 #define PPS_PAVG        4               /* phase avg interval (s) (shift) */
  205 #define PPS_VALID       120             /* PPS signal watchdog max (s) */
  206 #define PPS_MAXWANDER   100000          /* max PPS wander (ns/s) */
  207 #define PPS_POPCORN     2               /* popcorn spike threshold (shift) */
  208 
  209 static struct timespec pps_tf[3];       /* phase median filter */
  210 static l_fp pps_freq;                   /* scaled frequency offset (ns/s) */
  211 static long pps_fcount;                 /* frequency accumulator */
  212 static long pps_jitter;                 /* nominal jitter (ns) */
  213 static long pps_stabil;                 /* nominal stability (scaled ns/s) */
  214 static long pps_lastsec;                /* time at last calibration (s) */
  215 static int pps_valid;                   /* signal watchdog counter */
  216 static int pps_shift = PPS_FAVG;        /* interval duration (s) (shift) */
  217 static int pps_shiftmax = PPS_FAVGDEF;  /* max interval duration (s) (shift) */
  218 static int pps_intcnt;                  /* wander counter */
  219 
  220 /*
  221  * PPS signal quality monitors
  222  */
  223 static long pps_calcnt;                 /* calibration intervals */
  224 static long pps_jitcnt;                 /* jitter limit exceeded */
  225 static long pps_stbcnt;                 /* stability limit exceeded */
  226 static long pps_errcnt;                 /* calibration errors */
  227 #endif /* PPS_SYNC */
  228 /*
  229  * End of phase/frequency-lock loop (PLL/FLL) definitions
  230  */
  231 
  232 static void hardupdate(long offset);
  233 
  234 /*
  235  * ntp_gettime() - NTP user application interface
  236  */
  237 void
  238 ntp_gettime(struct ntptimeval *ntv)
  239 {
  240         memset(ntv, 0, sizeof(*ntv));
  241 
  242         mutex_spin_enter(&timecounter_lock);
  243         nanotime(&ntv->time);
  244         ntv->maxerror = time_maxerror;
  245         ntv->esterror = time_esterror;
  246         ntv->tai = time_tai;
  247         ntv->time_state = time_state;
  248         mutex_spin_exit(&timecounter_lock);
  249 }
  250 
  251 /* ARGSUSED */
  252 /*
  253  * ntp_adjtime() - NTP daemon application interface
  254  */
  255 int
  256 sys_ntp_adjtime(struct lwp *l, const struct sys_ntp_adjtime_args *uap, register_t *retval)
  257 {
  258         /* {
  259                 syscallarg(struct timex *) tp;
  260         } */
  261         struct timex ntv;
  262         int error;
  263 
  264         error = copyin((void *)SCARG(uap, tp), (void *)&ntv, sizeof(ntv));
  265         if (error != 0)
  266                 return (error);
  267 
  268         if (ntv.modes != 0 && (error = kauth_authorize_system(l->l_cred,
  269             KAUTH_SYSTEM_TIME, KAUTH_REQ_SYSTEM_TIME_NTPADJTIME, NULL,
  270             NULL, NULL)) != 0)
  271                 return (error);
  272 
  273         ntp_adjtime1(&ntv);
  274 
  275         error = copyout((void *)&ntv, (void *)SCARG(uap, tp), sizeof(ntv));
  276         if (!error)
  277                 *retval = ntp_timestatus();
  278 
  279         return error;
  280 }
  281 
  282 void
  283 ntp_adjtime1(struct timex *ntv)
  284 {
  285         long freq;
  286         int modes;
  287 
  288         /*
  289          * Update selected clock variables - only the superuser can
  290          * change anything. Note that there is no error checking here on
  291          * the assumption the superuser should know what it is doing.
  292          * Note that either the time constant or TAI offset are loaded
  293          * from the ntv.constant member, depending on the mode bits. If
  294          * the STA_PLL bit in the status word is cleared, the state and
  295          * status words are reset to the initial values at boot.
  296          */
  297         mutex_spin_enter(&timecounter_lock);
  298         modes = ntv->modes;
  299         if (modes != 0)
  300                 /* We need to save the system time during shutdown */
  301                 time_adjusted |= 2;
  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                 if (time_status & STA_PLL && !(ntv->status & STA_PLL)) {
  308                         time_state = TIME_OK;
  309                         time_status = STA_UNSYNC;
  310 #ifdef PPS_SYNC
  311                         pps_shift = PPS_FAVG;
  312 #endif /* PPS_SYNC */
  313                 }
  314                 time_status &= STA_RONLY;
  315                 time_status |= ntv->status & ~STA_RONLY;
  316         }
  317         if (modes & MOD_TIMECONST) {
  318                 if (ntv->constant < 0)
  319                         time_constant = 0;
  320                 else if (ntv->constant > MAXTC)
  321                         time_constant = MAXTC;
  322                 else
  323                         time_constant = ntv->constant;
  324         }
  325         if (modes & MOD_TAI) {
  326                 if (ntv->constant > 0)  /* XXX zero & negative numbers ? */
  327                         time_tai = ntv->constant;
  328         }
  329 #ifdef PPS_SYNC
  330         if (modes & MOD_PPSMAX) {
  331                 if (ntv->shift < PPS_FAVG)
  332                         pps_shiftmax = PPS_FAVG;
  333                 else if (ntv->shift > PPS_FAVGMAX)
  334                         pps_shiftmax = PPS_FAVGMAX;
  335                 else
  336                         pps_shiftmax = ntv->shift;
  337         }
  338 #endif /* PPS_SYNC */
  339         if (modes & MOD_NANO)
  340                 time_status |= STA_NANO;
  341         if (modes & MOD_MICRO)
  342                 time_status &= ~STA_NANO;
  343         if (modes & MOD_CLKB)
  344                 time_status |= STA_CLK;
  345         if (modes & MOD_CLKA)
  346                 time_status &= ~STA_CLK;
  347         if (modes & MOD_FREQUENCY) {
  348                 freq = MIN(INT32_MAX, MAX(INT32_MIN, ntv->freq));
  349                 freq = (freq * (int64_t)1000) >> 16;
  350                 if (freq > MAXFREQ)
  351                         L_LINT(time_freq, MAXFREQ);
  352                 else if (freq < -MAXFREQ)
  353                         L_LINT(time_freq, -MAXFREQ);
  354                 else {
  355                         /*
  356                          * ntv.freq is [PPM * 2^16] = [us/s * 2^16]
  357                          * time_freq is [ns/s * 2^32]
  358                          */
  359                         time_freq = ntv->freq * 1000LL * 65536LL;
  360                 }
  361 #ifdef PPS_SYNC
  362                 pps_freq = time_freq;
  363 #endif /* PPS_SYNC */
  364         }
  365         if (modes & MOD_OFFSET) {
  366                 if (time_status & STA_NANO) {
  367                         hardupdate(ntv->offset);
  368                 } else {
  369                         long offset = ntv->offset;
  370                         offset = MIN(offset, MAXPHASE/1000);
  371                         offset = MAX(offset, -MAXPHASE/1000);
  372                         hardupdate(offset * 1000);
  373                 }
  374         }
  375 
  376         /*
  377          * Retrieve all clock variables. Note that the TAI offset is
  378          * returned only by ntp_gettime();
  379          */
  380         if (time_status & STA_NANO)
  381                 ntv->offset = L_GINT(time_offset);
  382         else
  383                 ntv->offset = L_GINT(time_offset) / 1000; /* XXX rounding ? */
  384         if (time_freq < 0)
  385                 ntv->freq = L_GINT(-((-time_freq / 1000LL) << 16));
  386         else
  387                 ntv->freq = L_GINT((time_freq / 1000LL) << 16);
  388         ntv->maxerror = time_maxerror;
  389         ntv->esterror = time_esterror;
  390         ntv->status = time_status;
  391         ntv->constant = time_constant;
  392         if (time_status & STA_NANO)
  393                 ntv->precision = time_precision;
  394         else
  395                 ntv->precision = time_precision / 1000;
  396         ntv->tolerance = MAXFREQ * SCALE_PPM;
  397 #ifdef PPS_SYNC
  398         ntv->shift = pps_shift;
  399         ntv->ppsfreq = L_GINT((pps_freq / 1000LL) << 16);
  400         if (time_status & STA_NANO)
  401                 ntv->jitter = pps_jitter;
  402         else
  403                 ntv->jitter = pps_jitter / 1000;
  404         ntv->stabil = pps_stabil;
  405         ntv->calcnt = pps_calcnt;
  406         ntv->errcnt = pps_errcnt;
  407         ntv->jitcnt = pps_jitcnt;
  408         ntv->stbcnt = pps_stbcnt;
  409 #endif /* PPS_SYNC */
  410         mutex_spin_exit(&timecounter_lock);
  411 }
  412 #endif /* NTP */
  413 
  414 /*
  415  * second_overflow() - called after ntp_tick_adjust()
  416  *
  417  * This routine is ordinarily called immediately following the above
  418  * routine ntp_tick_adjust(). While these two routines are normally
  419  * combined, they are separated here only for the purposes of
  420  * simulation.
  421  */
  422 void
  423 ntp_update_second(int64_t *adjustment, time_t *newsec)
  424 {
  425         int tickrate;
  426         l_fp ftemp;             /* 32/64-bit temporary */
  427 
  428         KASSERT(mutex_owned(&timecounter_lock));
  429 
  430 #ifdef NTP
  431 
  432         /*
  433          * On rollover of the second both the nanosecond and microsecond
  434          * clocks are updated and the state machine cranked as
  435          * necessary. The phase adjustment to be used for the next
  436          * second is calculated and the maximum error is increased by
  437          * the tolerance.
  438          */
  439         time_maxerror += MAXFREQ / 1000;
  440 
  441         /*
  442          * Leap second processing. If in leap-insert state at
  443          * the end of the day, the system clock is set back one
  444          * second; if in leap-delete state, the system clock is
  445          * set ahead one second. The nano_time() routine or
  446          * external clock driver will insure that reported time
  447          * is always monotonic.
  448          */
  449         switch (time_state) {
  450 
  451                 /*
  452                  * No warning.
  453                  */
  454                 case TIME_OK:
  455                 if (time_status & STA_INS)
  456                         time_state = TIME_INS;
  457                 else if (time_status & STA_DEL)
  458                         time_state = TIME_DEL;
  459                 break;
  460 
  461                 /*
  462                  * Insert second 23:59:60 following second
  463                  * 23:59:59.
  464                  */
  465                 case TIME_INS:
  466                 if (!(time_status & STA_INS))
  467                         time_state = TIME_OK;
  468                 else if ((*newsec) % 86400 == 0) {
  469                         (*newsec)--;
  470                         time_state = TIME_OOP;
  471                         time_tai++;
  472                 }
  473                 break;
  474 
  475                 /*
  476                  * Delete second 23:59:59.
  477                  */
  478                 case TIME_DEL:
  479                 if (!(time_status & STA_DEL))
  480                         time_state = TIME_OK;
  481                 else if (((*newsec) + 1) % 86400 == 0) {
  482                         (*newsec)++;
  483                         time_tai--;
  484                         time_state = TIME_WAIT;
  485                 }
  486                 break;
  487 
  488                 /*
  489                  * Insert second in progress.
  490                  */
  491                 case TIME_OOP:
  492                         time_state = TIME_WAIT;
  493                 break;
  494 
  495                 /*
  496                  * Wait for status bits to clear.
  497                  */
  498                 case TIME_WAIT:
  499                 if (!(time_status & (STA_INS | STA_DEL)))
  500                         time_state = TIME_OK;
  501         }
  502 
  503         /*
  504          * Compute the total time adjustment for the next second
  505          * in ns. The offset is reduced by a factor depending on
  506          * whether the PPS signal is operating. Note that the
  507          * value is in effect scaled by the clock frequency,
  508          * since the adjustment is added at each tick interrupt.
  509          */
  510         ftemp = time_offset;
  511 #ifdef PPS_SYNC
  512         /* XXX even if PPS signal dies we should finish adjustment ? */
  513         if (time_status & STA_PPSTIME && time_status &
  514             STA_PPSSIGNAL)
  515                 L_RSHIFT(ftemp, pps_shift);
  516         else
  517                 L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
  518 #else
  519                 L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
  520 #endif /* PPS_SYNC */
  521         time_adj = ftemp;
  522         L_SUB(time_offset, ftemp);
  523         L_ADD(time_adj, time_freq);
  524         
  525 #ifdef PPS_SYNC
  526         if (pps_valid > 0)
  527                 pps_valid--;
  528         else
  529                 time_status &= ~STA_PPSSIGNAL;
  530 #endif /* PPS_SYNC */
  531 #else  /* !NTP */
  532         L_CLR(time_adj);
  533 #endif /* !NTP */
  534 
  535         /*
  536          * Apply any correction from adjtime(2).  If more than one second
  537          * off we slew at a rate of 5ms/s (5000 PPM) else 500us/s (500PPM)
  538          * until the last second is slewed the final < 500 usecs.
  539          */
  540         if (time_adjtime != 0) {
  541                 if (time_adjtime > 1000000)
  542                         tickrate = 5000;
  543                 else if (time_adjtime < -1000000)
  544                         tickrate = -5000;
  545                 else if (time_adjtime > 500)
  546                         tickrate = 500;
  547                 else if (time_adjtime < -500)
  548                         tickrate = -500;
  549                 else
  550                         tickrate = time_adjtime;
  551                 time_adjtime -= tickrate;
  552                 L_LINT(ftemp, tickrate * 1000);
  553                 L_ADD(time_adj, ftemp);
  554         }
  555         *adjustment = time_adj;
  556 }
  557 
  558 /*
  559  * ntp_init() - initialize variables and structures
  560  *
  561  * This routine must be called after the kernel variables hz and tick
  562  * are set or changed and before the next tick interrupt. In this
  563  * particular implementation, these values are assumed set elsewhere in
  564  * the kernel. The design allows the clock frequency and tick interval
  565  * to be changed while the system is running. So, this routine should
  566  * probably be integrated with the code that does that.
  567  */
  568 void
  569 ntp_init(void)
  570 {
  571 
  572         /*
  573          * The following variables are initialized only at startup. Only
  574          * those structures not cleared by the compiler need to be
  575          * initialized, and these only in the simulator. In the actual
  576          * kernel, any nonzero values here will quickly evaporate.
  577          */
  578         L_CLR(time_adj);
  579 #ifdef NTP
  580         L_CLR(time_offset);
  581         L_CLR(time_freq);
  582 #ifdef PPS_SYNC
  583         pps_tf[0].tv_sec = pps_tf[0].tv_nsec = 0;
  584         pps_tf[1].tv_sec = pps_tf[1].tv_nsec = 0;
  585         pps_tf[2].tv_sec = pps_tf[2].tv_nsec = 0;
  586         pps_fcount = 0;
  587         L_CLR(pps_freq);
  588 #endif /* PPS_SYNC */
  589 #endif
  590 }
  591 
  592 #ifdef NTP
  593 /*
  594  * hardupdate() - local clock update
  595  *
  596  * This routine is called by ntp_adjtime() to update the local clock
  597  * phase and frequency. The implementation is of an adaptive-parameter,
  598  * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
  599  * time and frequency offset estimates for each call. If the kernel PPS
  600  * discipline code is configured (PPS_SYNC), the PPS signal itself
  601  * determines the new time offset, instead of the calling argument.
  602  * Presumably, calls to ntp_adjtime() occur only when the caller
  603  * believes the local clock is valid within some bound (+-128 ms with
  604  * NTP). If the caller's time is far different than the PPS time, an
  605  * argument will ensue, and it's not clear who will lose.
  606  *
  607  * For uncompensated quartz crystal oscillators and nominal update
  608  * intervals less than 256 s, operation should be in phase-lock mode,
  609  * where the loop is disciplined to phase. For update intervals greater
  610  * than 1024 s, operation should be in frequency-lock mode, where the
  611  * loop is disciplined to frequency. Between 256 s and 1024 s, the mode
  612  * is selected by the STA_MODE status bit.
  613  *
  614  * Note: splclock() is in effect.
  615  */
  616 void
  617 hardupdate(long offset)
  618 {
  619         long mtemp;
  620         l_fp ftemp;
  621 
  622         KASSERT(mutex_owned(&timecounter_lock));
  623 
  624         /*
  625          * Select how the phase is to be controlled and from which
  626          * source. If the PPS signal is present and enabled to
  627          * discipline the time, the PPS offset is used; otherwise, the
  628          * argument offset is used.
  629          */
  630         if (!(time_status & STA_PLL))
  631                 return;
  632         if (!(time_status & STA_PPSTIME && time_status &
  633             STA_PPSSIGNAL)) {
  634                 if (offset > MAXPHASE)
  635                         time_monitor = MAXPHASE;
  636                 else if (offset < -MAXPHASE)
  637                         time_monitor = -MAXPHASE;
  638                 else
  639                         time_monitor = offset;
  640                 L_LINT(time_offset, time_monitor);
  641         }
  642 
  643         /*
  644          * Select how the frequency is to be controlled and in which
  645          * mode (PLL or FLL). If the PPS signal is present and enabled
  646          * to discipline the frequency, the PPS frequency is used;
  647          * otherwise, the argument offset is used to compute it.
  648          */
  649         if (time_status & STA_PPSFREQ && time_status & STA_PPSSIGNAL) {
  650                 time_reftime = time_second;
  651                 return;
  652         }
  653         if (time_status & STA_FREQHOLD || time_reftime == 0)
  654                 time_reftime = time_second;
  655         mtemp = time_second - time_reftime;
  656         L_LINT(ftemp, time_monitor);
  657         L_RSHIFT(ftemp, (SHIFT_PLL + 2 + time_constant) << 1);
  658         L_MPY(ftemp, mtemp);
  659         L_ADD(time_freq, ftemp);
  660         time_status &= ~STA_MODE;
  661         if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp >
  662             MAXSEC)) {
  663                 L_LINT(ftemp, (time_monitor << 4) / mtemp);
  664                 L_RSHIFT(ftemp, SHIFT_FLL + 4);
  665                 L_ADD(time_freq, ftemp);
  666                 time_status |= STA_MODE;
  667         }
  668         time_reftime = time_second;
  669         if (L_GINT(time_freq) > MAXFREQ)
  670                 L_LINT(time_freq, MAXFREQ);
  671         else if (L_GINT(time_freq) < -MAXFREQ)
  672                 L_LINT(time_freq, -MAXFREQ);
  673 }
  674 
  675 #ifdef PPS_SYNC
  676 /*
  677  * hardpps() - discipline CPU clock oscillator to external PPS signal
  678  *
  679  * This routine is called at each PPS interrupt in order to discipline
  680  * the CPU clock oscillator to the PPS signal. It measures the PPS phase
  681  * and leaves it in a handy spot for the hardclock() routine. It
  682  * integrates successive PPS phase differences and calculates the
  683  * frequency offset. This is used in hardclock() to discipline the CPU
  684  * clock oscillator so that intrinsic frequency error is cancelled out.
  685  * The code requires the caller to capture the time and hardware counter
  686  * value at the on-time PPS signal transition.
  687  *
  688  * Note that, on some Unix systems, this routine runs at an interrupt
  689  * priority level higher than the timer interrupt routine hardclock().
  690  * Therefore, the variables used are distinct from the hardclock()
  691  * variables, except for certain exceptions: The PPS frequency pps_freq
  692  * and phase pps_offset variables are determined by this routine and
  693  * updated atomically. The time_tolerance variable can be considered a
  694  * constant, since it is infrequently changed, and then only when the
  695  * PPS signal is disabled. The watchdog counter pps_valid is updated
  696  * once per second by hardclock() and is atomically cleared in this
  697  * routine.
  698  */
  699 void
  700 hardpps(struct timespec *tsp,           /* time at PPS */
  701         long nsec                       /* hardware counter at PPS */)
  702 {
  703         long u_sec, u_nsec, v_nsec; /* temps */
  704         l_fp ftemp;
  705 
  706         KASSERT(mutex_owned(&timecounter_lock));
  707 
  708         /*
  709          * The signal is first processed by a range gate and frequency
  710          * discriminator. The range gate rejects noise spikes outside
  711          * the range +-500 us. The frequency discriminator rejects input
  712          * signals with apparent frequency outside the range 1 +-500
  713          * PPM. If two hits occur in the same second, we ignore the
  714          * later hit; if not and a hit occurs outside the range gate,
  715          * keep the later hit for later comparison, but do not process
  716          * it.
  717          */
  718         time_status |= STA_PPSSIGNAL | STA_PPSJITTER;
  719         time_status &= ~(STA_PPSWANDER | STA_PPSERROR);
  720         pps_valid = PPS_VALID;
  721         u_sec = tsp->tv_sec;
  722         u_nsec = tsp->tv_nsec;
  723         if (u_nsec >= (NANOSECOND >> 1)) {
  724                 u_nsec -= NANOSECOND;
  725                 u_sec++;
  726         }
  727         v_nsec = u_nsec - pps_tf[0].tv_nsec;
  728         if (u_sec == pps_tf[0].tv_sec && v_nsec < NANOSECOND -
  729             MAXFREQ)
  730                 return;
  731         pps_tf[2] = pps_tf[1];
  732         pps_tf[1] = pps_tf[0];
  733         pps_tf[0].tv_sec = u_sec;
  734         pps_tf[0].tv_nsec = u_nsec;
  735 
  736         /*
  737          * Compute the difference between the current and previous
  738          * counter values. If the difference exceeds 0.5 s, assume it
  739          * has wrapped around, so correct 1.0 s. If the result exceeds
  740          * the tick interval, the sample point has crossed a tick
  741          * boundary during the last second, so correct the tick. Very
  742          * intricate.
  743          */
  744         u_nsec = nsec;
  745         if (u_nsec > (NANOSECOND >> 1))
  746                 u_nsec -= NANOSECOND;
  747         else if (u_nsec < -(NANOSECOND >> 1))
  748                 u_nsec += NANOSECOND;
  749         pps_fcount += u_nsec;
  750         if (v_nsec > MAXFREQ || v_nsec < -MAXFREQ)
  751                 return;
  752         time_status &= ~STA_PPSJITTER;
  753 
  754         /*
  755          * A three-stage median filter is used to help denoise the PPS
  756          * time. The median sample becomes the time offset estimate; the
  757          * difference between the other two samples becomes the time
  758          * dispersion (jitter) estimate.
  759          */
  760         if (pps_tf[0].tv_nsec > pps_tf[1].tv_nsec) {
  761                 if (pps_tf[1].tv_nsec > pps_tf[2].tv_nsec) {
  762                         v_nsec = pps_tf[1].tv_nsec;     /* 0 1 2 */
  763                         u_nsec = pps_tf[0].tv_nsec - pps_tf[2].tv_nsec;
  764                 } else if (pps_tf[2].tv_nsec > pps_tf[0].tv_nsec) {
  765                         v_nsec = pps_tf[0].tv_nsec;     /* 2 0 1 */
  766                         u_nsec = pps_tf[2].tv_nsec - pps_tf[1].tv_nsec;
  767                 } else {
  768                         v_nsec = pps_tf[2].tv_nsec;     /* 0 2 1 */
  769                         u_nsec = pps_tf[0].tv_nsec - pps_tf[1].tv_nsec;
  770                 }
  771         } else {
  772                 if (pps_tf[1].tv_nsec < pps_tf[2].tv_nsec) {
  773                         v_nsec = pps_tf[1].tv_nsec;     /* 2 1 0 */
  774                         u_nsec = pps_tf[2].tv_nsec - pps_tf[0].tv_nsec;
  775                 } else if (pps_tf[2].tv_nsec < pps_tf[0].tv_nsec) {
  776                         v_nsec = pps_tf[0].tv_nsec;     /* 1 0 2 */
  777                         u_nsec = pps_tf[1].tv_nsec - pps_tf[2].tv_nsec;
  778                 } else {
  779                         v_nsec = pps_tf[2].tv_nsec;     /* 1 2 0 */
  780                         u_nsec = pps_tf[1].tv_nsec - pps_tf[0].tv_nsec;
  781                 }
  782         }
  783 
  784         /*
  785          * Nominal jitter is due to PPS signal noise and interrupt
  786          * latency. If it exceeds the popcorn threshold, the sample is
  787          * discarded. otherwise, if so enabled, the time offset is
  788          * updated. We can tolerate a modest loss of data here without
  789          * much degrading time accuracy.
  790          */
  791         if (u_nsec > (pps_jitter << PPS_POPCORN)) {
  792                 time_status |= STA_PPSJITTER;
  793                 pps_jitcnt++;
  794         } else if (time_status & STA_PPSTIME) {
  795                 time_monitor = -v_nsec;
  796                 L_LINT(time_offset, time_monitor);
  797         }
  798         pps_jitter += (u_nsec - pps_jitter) >> PPS_FAVG;
  799         u_sec = pps_tf[0].tv_sec - pps_lastsec;
  800         if (u_sec < (1 << pps_shift))
  801                 return;
  802 
  803         /*
  804          * At the end of the calibration interval the difference between
  805          * the first and last counter values becomes the scaled
  806          * frequency. It will later be divided by the length of the
  807          * interval to determine the frequency update. If the frequency
  808          * exceeds a sanity threshold, or if the actual calibration
  809          * interval is not equal to the expected length, the data are
  810          * discarded. We can tolerate a modest loss of data here without
  811          * much degrading frequency accuracy.
  812          */
  813         pps_calcnt++;
  814         v_nsec = -pps_fcount;
  815         pps_lastsec = pps_tf[0].tv_sec;
  816         pps_fcount = 0;
  817         u_nsec = MAXFREQ << pps_shift;
  818         if (v_nsec > u_nsec || v_nsec < -u_nsec || u_sec != (1 <<
  819             pps_shift)) {
  820                 time_status |= STA_PPSERROR;
  821                 pps_errcnt++;
  822                 return;
  823         }
  824 
  825         /*
  826          * Here the raw frequency offset and wander (stability) is
  827          * calculated. If the wander is less than the wander threshold
  828          * for four consecutive averaging intervals, the interval is
  829          * doubled; if it is greater than the threshold for four
  830          * consecutive intervals, the interval is halved. The scaled
  831          * frequency offset is converted to frequency offset. The
  832          * stability metric is calculated as the average of recent
  833          * frequency changes, but is used only for performance
  834          * monitoring.
  835          */
  836         L_LINT(ftemp, v_nsec);
  837         L_RSHIFT(ftemp, pps_shift);
  838         L_SUB(ftemp, pps_freq);
  839         u_nsec = L_GINT(ftemp);
  840         if (u_nsec > PPS_MAXWANDER) {
  841                 L_LINT(ftemp, PPS_MAXWANDER);
  842                 pps_intcnt--;
  843                 time_status |= STA_PPSWANDER;
  844                 pps_stbcnt++;
  845         } else if (u_nsec < -PPS_MAXWANDER) {
  846                 L_LINT(ftemp, -PPS_MAXWANDER);
  847                 pps_intcnt--;
  848                 time_status |= STA_PPSWANDER;
  849                 pps_stbcnt++;
  850         } else {
  851                 pps_intcnt++;
  852         }
  853         if (pps_intcnt >= 4) {
  854                 pps_intcnt = 4;
  855                 if (pps_shift < pps_shiftmax) {
  856                         pps_shift++;
  857                         pps_intcnt = 0;
  858                 }
  859         } else if (pps_intcnt <= -4 || pps_shift > pps_shiftmax) {
  860                 pps_intcnt = -4;
  861                 if (pps_shift > PPS_FAVG) {
  862                         pps_shift--;
  863                         pps_intcnt = 0;
  864                 }
  865         }
  866         if (u_nsec < 0)
  867                 u_nsec = -u_nsec;
  868         pps_stabil += (u_nsec * SCALE_PPM - pps_stabil) >> PPS_FAVG;
  869 
  870         /*
  871          * The PPS frequency is recalculated and clamped to the maximum
  872          * MAXFREQ. If enabled, the system clock frequency is updated as
  873          * well.
  874          */
  875         L_ADD(pps_freq, ftemp);
  876         u_nsec = L_GINT(pps_freq);
  877         if (u_nsec > MAXFREQ)
  878                 L_LINT(pps_freq, MAXFREQ);
  879         else if (u_nsec < -MAXFREQ)
  880                 L_LINT(pps_freq, -MAXFREQ);
  881         if (time_status & STA_PPSFREQ)
  882                 time_freq = pps_freq;
  883 }
  884 #endif /* PPS_SYNC */
  885 #endif /* NTP */
  886 
  887 #ifdef NTP
  888 int
  889 ntp_timestatus(void)
  890 {
  891         int rv;
  892 
  893         /*
  894          * Status word error decode. If any of these conditions
  895          * occur, an error is returned, instead of the status
  896          * word. Most applications will care only about the fact
  897          * the system clock may not be trusted, not about the
  898          * details.
  899          *
  900          * Hardware or software error
  901          */
  902         mutex_spin_enter(&timecounter_lock);
  903         if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||
  904 
  905         /*
  906          * PPS signal lost when either time or frequency
  907          * synchronization requested
  908          */
  909             (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
  910              !(time_status & STA_PPSSIGNAL)) ||
  911 
  912         /*
  913          * PPS jitter exceeded when time synchronization
  914          * requested
  915          */
  916             (time_status & STA_PPSTIME &&
  917              time_status & STA_PPSJITTER) ||
  918 
  919         /*
  920          * PPS wander exceeded or calibration error when
  921          * frequency synchronization requested
  922          */
  923             (time_status & STA_PPSFREQ &&
  924              time_status & (STA_PPSWANDER | STA_PPSERROR)))
  925                 rv = TIME_ERROR;
  926         else
  927                 rv = time_state;
  928         mutex_spin_exit(&timecounter_lock);
  929 
  930         return rv;
  931 }
  932 
  933 /*ARGSUSED*/
  934 /*
  935  * ntp_gettime() - NTP user application interface
  936  */
  937 int
  938 sys___ntp_gettime50(struct lwp *l, const struct sys___ntp_gettime50_args *uap, register_t *retval)
  939 {
  940         /* {
  941                 syscallarg(struct ntptimeval *) ntvp;
  942         } */
  943         struct ntptimeval ntv;
  944         int error = 0;
  945 
  946         if (SCARG(uap, ntvp)) {
  947                 ntp_gettime(&ntv);
  948 
  949                 error = copyout((void *)&ntv, (void *)SCARG(uap, ntvp),
  950                                 sizeof(ntv));
  951         }
  952         if (!error) {
  953                 *retval = ntp_timestatus();
  954         }
  955         return(error);
  956 }
  957 
  958 /*
  959  * return information about kernel precision timekeeping
  960  */
  961 static int
  962 sysctl_kern_ntptime(SYSCTLFN_ARGS)
  963 {
  964         struct sysctlnode node;
  965         struct ntptimeval ntv;
  966 
  967         ntp_gettime(&ntv);
  968 
  969         node = *rnode;
  970         node.sysctl_data = &ntv;
  971         node.sysctl_size = sizeof(ntv);
  972         return (sysctl_lookup(SYSCTLFN_CALL(&node)));
  973 }
  974 
  975 SYSCTL_SETUP(sysctl_kern_ntptime_setup, "sysctl kern.ntptime node setup")
  976 {
  977 
  978         sysctl_createv(clog, 0, NULL, NULL,
  979                        CTLFLAG_PERMANENT,
  980                        CTLTYPE_STRUCT, "ntptime",
  981                        SYSCTL_DESCR("Kernel clock values for NTP"),
  982                        sysctl_kern_ntptime, 0, NULL,
  983                        sizeof(struct ntptimeval),
  984                        CTL_KERN, KERN_NTPTIME, CTL_EOL);
  985 }
  986 #endif /* !NTP */

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