The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_ntptime.c

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    1 /*-
    2  ***********************************************************************
    3  *                                                                     *
    4  * Copyright (c) David L. Mills 1993-2001                              *
    5  *                                                                     *
    6  * Permission to use, copy, modify, and distribute this software and   *
    7  * its documentation for any purpose and without fee is hereby         *
    8  * granted, provided that the above copyright notice appears in all    *
    9  * copies and that both the copyright notice and this permission       *
   10  * notice appear in supporting documentation, and that the name        *
   11  * University of Delaware not be used in advertising or publicity      *
   12  * pertaining to distribution of the software without specific,        *
   13  * written prior permission. The University of Delaware makes no       *
   14  * representations about the suitability this software for any         *
   15  * purpose. It is provided "as is" without express or implied          *
   16  * warranty.                                                           *
   17  *                                                                     *
   18  **********************************************************************/
   19 
   20 /*
   21  * Adapted from the original sources for FreeBSD and timecounters by:
   22  * Poul-Henning Kamp <phk@FreeBSD.org>.
   23  *
   24  * The 32bit version of the "LP" macros seems a bit past its "sell by" 
   25  * date so I have retained only the 64bit version and included it directly
   26  * in this file.
   27  *
   28  * Only minor changes done to interface with the timecounters over in
   29  * sys/kern/kern_clock.c.   Some of the comments below may be (even more)
   30  * confusing and/or plain wrong in that context.
   31  */
   32 
   33 #include <sys/cdefs.h>
   34 __FBSDID("$FreeBSD: stable/10/sys/kern/kern_ntptime.c 285611 2015-07-15 19:11:43Z delphij $");
   35 
   36 #include "opt_ntp.h"
   37 
   38 #include <sys/param.h>
   39 #include <sys/systm.h>
   40 #include <sys/sysproto.h>
   41 #include <sys/eventhandler.h>
   42 #include <sys/kernel.h>
   43 #include <sys/priv.h>
   44 #include <sys/proc.h>
   45 #include <sys/lock.h>
   46 #include <sys/mutex.h>
   47 #include <sys/time.h>
   48 #include <sys/timex.h>
   49 #include <sys/timetc.h>
   50 #include <sys/timepps.h>
   51 #include <sys/syscallsubr.h>
   52 #include <sys/sysctl.h>
   53 
   54 #ifdef PPS_SYNC
   55 FEATURE(pps_sync, "Support usage of external PPS signal by kernel PLL");
   56 #endif
   57 
   58 /*
   59  * Single-precision macros for 64-bit machines
   60  */
   61 typedef int64_t l_fp;
   62 #define L_ADD(v, u)     ((v) += (u))
   63 #define L_SUB(v, u)     ((v) -= (u))
   64 #define L_ADDHI(v, a)   ((v) += (int64_t)(a) << 32)
   65 #define L_NEG(v)        ((v) = -(v))
   66 #define L_RSHIFT(v, n) \
   67         do { \
   68                 if ((v) < 0) \
   69                         (v) = -(-(v) >> (n)); \
   70                 else \
   71                         (v) = (v) >> (n); \
   72         } while (0)
   73 #define L_MPY(v, a)     ((v) *= (a))
   74 #define L_CLR(v)        ((v) = 0)
   75 #define L_ISNEG(v)      ((v) < 0)
   76 #define L_LINT(v, a)    ((v) = (int64_t)(a) << 32)
   77 #define L_GINT(v)       ((v) < 0 ? -(-(v) >> 32) : (v) >> 32)
   78 
   79 /*
   80  * Generic NTP kernel interface
   81  *
   82  * These routines constitute the Network Time Protocol (NTP) interfaces
   83  * for user and daemon application programs. The ntp_gettime() routine
   84  * provides the time, maximum error (synch distance) and estimated error
   85  * (dispersion) to client user application programs. The ntp_adjtime()
   86  * routine is used by the NTP daemon to adjust the system clock to an
   87  * externally derived time. The time offset and related variables set by
   88  * this routine are used by other routines in this module to adjust the
   89  * phase and frequency of the clock discipline loop which controls the
   90  * system clock.
   91  *
   92  * When the kernel time is reckoned directly in nanoseconds (NTP_NANO
   93  * defined), the time at each tick interrupt is derived directly from
   94  * the kernel time variable. When the kernel time is reckoned in
   95  * microseconds, (NTP_NANO undefined), the time is derived from the
   96  * kernel time variable together with a variable representing the
   97  * leftover nanoseconds at the last tick interrupt. In either case, the
   98  * current nanosecond time is reckoned from these values plus an
   99  * interpolated value derived by the clock routines in another
  100  * architecture-specific module. The interpolation can use either a
  101  * dedicated counter or a processor cycle counter (PCC) implemented in
  102  * some architectures.
  103  *
  104  * Note that all routines must run at priority splclock or higher.
  105  */
  106 /*
  107  * Phase/frequency-lock loop (PLL/FLL) definitions
  108  *
  109  * The nanosecond clock discipline uses two variable types, time
  110  * variables and frequency variables. Both types are represented as 64-
  111  * bit fixed-point quantities with the decimal point between two 32-bit
  112  * halves. On a 32-bit machine, each half is represented as a single
  113  * word and mathematical operations are done using multiple-precision
  114  * arithmetic. On a 64-bit machine, ordinary computer arithmetic is
  115  * used.
  116  *
  117  * A time variable is a signed 64-bit fixed-point number in ns and
  118  * fraction. It represents the remaining time offset to be amortized
  119  * over succeeding tick interrupts. The maximum time offset is about
  120  * 0.5 s and the resolution is about 2.3e-10 ns.
  121  *
  122  *                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
  123  *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  124  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  125  * |s s s|                       ns                                |
  126  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  127  * |                        fraction                               |
  128  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  129  *
  130  * A frequency variable is a signed 64-bit fixed-point number in ns/s
  131  * and fraction. It represents the ns and fraction to be added to the
  132  * kernel time variable at each second. The maximum frequency offset is
  133  * about +-500000 ns/s and the resolution is about 2.3e-10 ns/s.
  134  *
  135  *                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
  136  *  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
  137  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  138  * |s s s s s s s s s s s s s|            ns/s                     |
  139  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  140  * |                        fraction                               |
  141  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  142  */
  143 /*
  144  * The following variables establish the state of the PLL/FLL and the
  145  * residual time and frequency offset of the local clock.
  146  */
  147 #define SHIFT_PLL       4               /* PLL loop gain (shift) */
  148 #define SHIFT_FLL       2               /* FLL loop gain (shift) */
  149 
  150 static int time_state = TIME_OK;        /* clock state */
  151 int time_status = STA_UNSYNC;   /* clock status bits */
  152 static long time_tai;                   /* TAI offset (s) */
  153 static long time_monitor;               /* last time offset scaled (ns) */
  154 static long time_constant;              /* poll interval (shift) (s) */
  155 static long time_precision = 1;         /* clock precision (ns) */
  156 static long time_maxerror = MAXPHASE / 1000; /* maximum error (us) */
  157 long time_esterror = MAXPHASE / 1000; /* estimated error (us) */
  158 static long time_reftime;               /* uptime at last adjustment (s) */
  159 static l_fp time_offset;                /* time offset (ns) */
  160 static l_fp time_freq;                  /* frequency offset (ns/s) */
  161 static l_fp time_adj;                   /* tick adjust (ns/s) */
  162 
  163 static int64_t time_adjtime;            /* correction from adjtime(2) (usec) */
  164 
  165 #ifdef PPS_SYNC
  166 /*
  167  * The following variables are used when a pulse-per-second (PPS) signal
  168  * is available and connected via a modem control lead. They establish
  169  * the engineering parameters of the clock discipline loop when
  170  * controlled by the PPS signal.
  171  */
  172 #define PPS_FAVG        2               /* min freq avg interval (s) (shift) */
  173 #define PPS_FAVGDEF     8               /* default freq avg int (s) (shift) */
  174 #define PPS_FAVGMAX     15              /* max freq avg interval (s) (shift) */
  175 #define PPS_PAVG        4               /* phase avg interval (s) (shift) */
  176 #define PPS_VALID       120             /* PPS signal watchdog max (s) */
  177 #define PPS_MAXWANDER   100000          /* max PPS wander (ns/s) */
  178 #define PPS_POPCORN     2               /* popcorn spike threshold (shift) */
  179 
  180 static struct timespec pps_tf[3];       /* phase median filter */
  181 static l_fp pps_freq;                   /* scaled frequency offset (ns/s) */
  182 static long pps_fcount;                 /* frequency accumulator */
  183 static long pps_jitter;                 /* nominal jitter (ns) */
  184 static long pps_stabil;                 /* nominal stability (scaled ns/s) */
  185 static long pps_lastsec;                /* time at last calibration (s) */
  186 static int pps_valid;                   /* signal watchdog counter */
  187 static int pps_shift = PPS_FAVG;        /* interval duration (s) (shift) */
  188 static int pps_shiftmax = PPS_FAVGDEF;  /* max interval duration (s) (shift) */
  189 static int pps_intcnt;                  /* wander counter */
  190 
  191 /*
  192  * PPS signal quality monitors
  193  */
  194 static long pps_calcnt;                 /* calibration intervals */
  195 static long pps_jitcnt;                 /* jitter limit exceeded */
  196 static long pps_stbcnt;                 /* stability limit exceeded */
  197 static long pps_errcnt;                 /* calibration errors */
  198 #endif /* PPS_SYNC */
  199 /*
  200  * End of phase/frequency-lock loop (PLL/FLL) definitions
  201  */
  202 
  203 static void ntp_init(void);
  204 static void hardupdate(long offset);
  205 static void ntp_gettime1(struct ntptimeval *ntvp);
  206 static int ntp_is_time_error(void);
  207 
  208 static int
  209 ntp_is_time_error(void)
  210 {
  211         /*
  212          * Status word error decode. If any of these conditions occur,
  213          * an error is returned, instead of the status word. Most
  214          * applications will care only about the fact the system clock
  215          * may not be trusted, not about the details.
  216          *
  217          * Hardware or software error
  218          */
  219         if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||
  220 
  221         /*
  222          * PPS signal lost when either time or frequency synchronization
  223          * requested
  224          */
  225             (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
  226             !(time_status & STA_PPSSIGNAL)) ||
  227 
  228         /*
  229          * PPS jitter exceeded when time synchronization requested
  230          */
  231             (time_status & STA_PPSTIME &&
  232             time_status & STA_PPSJITTER) ||
  233 
  234         /*
  235          * PPS wander exceeded or calibration error when frequency
  236          * synchronization requested
  237          */
  238             (time_status & STA_PPSFREQ &&
  239             time_status & (STA_PPSWANDER | STA_PPSERROR)))
  240                 return (1);
  241 
  242         return (0);
  243 }
  244 
  245 static void
  246 ntp_gettime1(struct ntptimeval *ntvp)
  247 {
  248         struct timespec atv;    /* nanosecond time */
  249 
  250         GIANT_REQUIRED;
  251 
  252         nanotime(&atv);
  253         ntvp->time.tv_sec = atv.tv_sec;
  254         ntvp->time.tv_nsec = atv.tv_nsec;
  255         ntvp->maxerror = time_maxerror;
  256         ntvp->esterror = time_esterror;
  257         ntvp->tai = time_tai;
  258         ntvp->time_state = time_state;
  259 
  260         if (ntp_is_time_error())
  261                 ntvp->time_state = TIME_ERROR;
  262 }
  263 
  264 /*
  265  * ntp_gettime() - NTP user application interface
  266  *
  267  * See the timex.h header file for synopsis and API description.  Note that
  268  * the TAI offset is returned in the ntvtimeval.tai structure member.
  269  */
  270 #ifndef _SYS_SYSPROTO_H_
  271 struct ntp_gettime_args {
  272         struct ntptimeval *ntvp;
  273 };
  274 #endif
  275 /* ARGSUSED */
  276 int
  277 sys_ntp_gettime(struct thread *td, struct ntp_gettime_args *uap)
  278 {       
  279         struct ntptimeval ntv;
  280 
  281         mtx_lock(&Giant);
  282         ntp_gettime1(&ntv);
  283         mtx_unlock(&Giant);
  284 
  285         td->td_retval[0] = ntv.time_state;
  286         return (copyout(&ntv, uap->ntvp, sizeof(ntv)));
  287 }
  288 
  289 static int
  290 ntp_sysctl(SYSCTL_HANDLER_ARGS)
  291 {
  292         struct ntptimeval ntv;  /* temporary structure */
  293 
  294         ntp_gettime1(&ntv);
  295 
  296         return (sysctl_handle_opaque(oidp, &ntv, sizeof(ntv), req));
  297 }
  298 
  299 SYSCTL_NODE(_kern, OID_AUTO, ntp_pll, CTLFLAG_RW, 0, "");
  300 SYSCTL_PROC(_kern_ntp_pll, OID_AUTO, gettime, CTLTYPE_OPAQUE|CTLFLAG_RD,
  301         0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", "");
  302 
  303 #ifdef PPS_SYNC
  304 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shiftmax, CTLFLAG_RW,
  305     &pps_shiftmax, 0, "Max interval duration (sec) (shift)");
  306 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shift, CTLFLAG_RW,
  307     &pps_shift, 0, "Interval duration (sec) (shift)");
  308 SYSCTL_LONG(_kern_ntp_pll, OID_AUTO, time_monitor, CTLFLAG_RD,
  309     &time_monitor, 0, "Last time offset scaled (ns)");
  310 
  311 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD,
  312     &pps_freq, sizeof(pps_freq), "I", "Scaled frequency offset (ns/sec)");
  313 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, time_freq, CTLFLAG_RD,
  314     &time_freq, sizeof(time_freq), "I", "Frequency offset (ns/sec)");
  315 #endif
  316 
  317 /*
  318  * ntp_adjtime() - NTP daemon application interface
  319  *
  320  * See the timex.h header file for synopsis and API description.  Note that
  321  * the timex.constant structure member has a dual purpose to set the time
  322  * constant and to set the TAI offset.
  323  */
  324 #ifndef _SYS_SYSPROTO_H_
  325 struct ntp_adjtime_args {
  326         struct timex *tp;
  327 };
  328 #endif
  329 
  330 int
  331 sys_ntp_adjtime(struct thread *td, struct ntp_adjtime_args *uap)
  332 {
  333         struct timex ntv;       /* temporary structure */
  334         long freq;              /* frequency ns/s) */
  335         int modes;              /* mode bits from structure */
  336         int s;                  /* caller priority */
  337         int error;
  338 
  339         error = copyin((caddr_t)uap->tp, (caddr_t)&ntv, sizeof(ntv));
  340         if (error)
  341                 return(error);
  342 
  343         /*
  344          * Update selected clock variables - only the superuser can
  345          * change anything. Note that there is no error checking here on
  346          * the assumption the superuser should know what it is doing.
  347          * Note that either the time constant or TAI offset are loaded
  348          * from the ntv.constant member, depending on the mode bits. If
  349          * the STA_PLL bit in the status word is cleared, the state and
  350          * status words are reset to the initial values at boot.
  351          */
  352         mtx_lock(&Giant);
  353         modes = ntv.modes;
  354         if (modes)
  355                 error = priv_check(td, PRIV_NTP_ADJTIME);
  356         if (error)
  357                 goto done2;
  358         s = splclock();
  359         if (modes & MOD_MAXERROR)
  360                 time_maxerror = ntv.maxerror;
  361         if (modes & MOD_ESTERROR)
  362                 time_esterror = ntv.esterror;
  363         if (modes & MOD_STATUS) {
  364                 if (time_status & STA_PLL && !(ntv.status & STA_PLL)) {
  365                         time_state = TIME_OK;
  366                         time_status = STA_UNSYNC;
  367 #ifdef PPS_SYNC
  368                         pps_shift = PPS_FAVG;
  369 #endif /* PPS_SYNC */
  370                 }
  371                 time_status &= STA_RONLY;
  372                 time_status |= ntv.status & ~STA_RONLY;
  373         }
  374         if (modes & MOD_TIMECONST) {
  375                 if (ntv.constant < 0)
  376                         time_constant = 0;
  377                 else if (ntv.constant > MAXTC)
  378                         time_constant = MAXTC;
  379                 else
  380                         time_constant = ntv.constant;
  381         }
  382         if (modes & MOD_TAI) {
  383                 if (ntv.constant > 0) /* XXX zero & negative numbers ? */
  384                         time_tai = ntv.constant;
  385         }
  386 #ifdef PPS_SYNC
  387         if (modes & MOD_PPSMAX) {
  388                 if (ntv.shift < PPS_FAVG)
  389                         pps_shiftmax = PPS_FAVG;
  390                 else if (ntv.shift > PPS_FAVGMAX)
  391                         pps_shiftmax = PPS_FAVGMAX;
  392                 else
  393                         pps_shiftmax = ntv.shift;
  394         }
  395 #endif /* PPS_SYNC */
  396         if (modes & MOD_NANO)
  397                 time_status |= STA_NANO;
  398         if (modes & MOD_MICRO)
  399                 time_status &= ~STA_NANO;
  400         if (modes & MOD_CLKB)
  401                 time_status |= STA_CLK;
  402         if (modes & MOD_CLKA)
  403                 time_status &= ~STA_CLK;
  404         if (modes & MOD_FREQUENCY) {
  405                 freq = (ntv.freq * 1000LL) >> 16;
  406                 if (freq > MAXFREQ)
  407                         L_LINT(time_freq, MAXFREQ);
  408                 else if (freq < -MAXFREQ)
  409                         L_LINT(time_freq, -MAXFREQ);
  410                 else {
  411                         /*
  412                          * ntv.freq is [PPM * 2^16] = [us/s * 2^16]
  413                          * time_freq is [ns/s * 2^32]
  414                          */
  415                         time_freq = ntv.freq * 1000LL * 65536LL;
  416                 }
  417 #ifdef PPS_SYNC
  418                 pps_freq = time_freq;
  419 #endif /* PPS_SYNC */
  420         }
  421         if (modes & MOD_OFFSET) {
  422                 if (time_status & STA_NANO)
  423                         hardupdate(ntv.offset);
  424                 else
  425                         hardupdate(ntv.offset * 1000);
  426         }
  427 
  428         /*
  429          * Retrieve all clock variables. Note that the TAI offset is
  430          * returned only by ntp_gettime();
  431          */
  432         if (time_status & STA_NANO)
  433                 ntv.offset = L_GINT(time_offset);
  434         else
  435                 ntv.offset = L_GINT(time_offset) / 1000; /* XXX rounding ? */
  436         ntv.freq = L_GINT((time_freq / 1000LL) << 16);
  437         ntv.maxerror = time_maxerror;
  438         ntv.esterror = time_esterror;
  439         ntv.status = time_status;
  440         ntv.constant = time_constant;
  441         if (time_status & STA_NANO)
  442                 ntv.precision = time_precision;
  443         else
  444                 ntv.precision = time_precision / 1000;
  445         ntv.tolerance = MAXFREQ * SCALE_PPM;
  446 #ifdef PPS_SYNC
  447         ntv.shift = pps_shift;
  448         ntv.ppsfreq = L_GINT((pps_freq / 1000LL) << 16);
  449         if (time_status & STA_NANO)
  450                 ntv.jitter = pps_jitter;
  451         else
  452                 ntv.jitter = pps_jitter / 1000;
  453         ntv.stabil = pps_stabil;
  454         ntv.calcnt = pps_calcnt;
  455         ntv.errcnt = pps_errcnt;
  456         ntv.jitcnt = pps_jitcnt;
  457         ntv.stbcnt = pps_stbcnt;
  458 #endif /* PPS_SYNC */
  459         splx(s);
  460 
  461         error = copyout((caddr_t)&ntv, (caddr_t)uap->tp, sizeof(ntv));
  462         if (error)
  463                 goto done2;
  464 
  465         if (ntp_is_time_error())
  466                 td->td_retval[0] = TIME_ERROR;
  467         else
  468                 td->td_retval[0] = time_state;
  469 
  470 done2:
  471         mtx_unlock(&Giant);
  472         return (error);
  473 }
  474 
  475 /*
  476  * second_overflow() - called after ntp_tick_adjust()
  477  *
  478  * This routine is ordinarily called immediately following the above
  479  * routine ntp_tick_adjust(). While these two routines are normally
  480  * combined, they are separated here only for the purposes of
  481  * simulation.
  482  */
  483 void
  484 ntp_update_second(int64_t *adjustment, time_t *newsec)
  485 {
  486         int tickrate;
  487         l_fp ftemp;             /* 32/64-bit temporary */
  488 
  489         /*
  490          * On rollover of the second both the nanosecond and microsecond
  491          * clocks are updated and the state machine cranked as
  492          * necessary. The phase adjustment to be used for the next
  493          * second is calculated and the maximum error is increased by
  494          * the tolerance.
  495          */
  496         time_maxerror += MAXFREQ / 1000;
  497 
  498         /*
  499          * Leap second processing. If in leap-insert state at
  500          * the end of the day, the system clock is set back one
  501          * second; if in leap-delete state, the system clock is
  502          * set ahead one second. The nano_time() routine or
  503          * external clock driver will insure that reported time
  504          * is always monotonic.
  505          */
  506         switch (time_state) {
  507 
  508                 /*
  509                  * No warning.
  510                  */
  511                 case TIME_OK:
  512                 if (time_status & STA_INS)
  513                         time_state = TIME_INS;
  514                 else if (time_status & STA_DEL)
  515                         time_state = TIME_DEL;
  516                 break;
  517 
  518                 /*
  519                  * Insert second 23:59:60 following second
  520                  * 23:59:59.
  521                  */
  522                 case TIME_INS:
  523                 if (!(time_status & STA_INS))
  524                         time_state = TIME_OK;
  525                 else if ((*newsec) % 86400 == 0) {
  526                         (*newsec)--;
  527                         time_state = TIME_OOP;
  528                         time_tai++;
  529                 }
  530                 break;
  531 
  532                 /*
  533                  * Delete second 23:59:59.
  534                  */
  535                 case TIME_DEL:
  536                 if (!(time_status & STA_DEL))
  537                         time_state = TIME_OK;
  538                 else if (((*newsec) + 1) % 86400 == 0) {
  539                         (*newsec)++;
  540                         time_tai--;
  541                         time_state = TIME_WAIT;
  542                 }
  543                 break;
  544 
  545                 /*
  546                  * Insert second in progress.
  547                  */
  548                 case TIME_OOP:
  549                         time_state = TIME_WAIT;
  550                 break;
  551 
  552                 /*
  553                  * Wait for status bits to clear.
  554                  */
  555                 case TIME_WAIT:
  556                 if (!(time_status & (STA_INS | STA_DEL)))
  557                         time_state = TIME_OK;
  558         }
  559 
  560         /*
  561          * Compute the total time adjustment for the next second
  562          * in ns. The offset is reduced by a factor depending on
  563          * whether the PPS signal is operating. Note that the
  564          * value is in effect scaled by the clock frequency,
  565          * since the adjustment is added at each tick interrupt.
  566          */
  567         ftemp = time_offset;
  568 #ifdef PPS_SYNC
  569         /* XXX even if PPS signal dies we should finish adjustment ? */
  570         if (time_status & STA_PPSTIME && time_status &
  571             STA_PPSSIGNAL)
  572                 L_RSHIFT(ftemp, pps_shift);
  573         else
  574                 L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
  575 #else
  576                 L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
  577 #endif /* PPS_SYNC */
  578         time_adj = ftemp;
  579         L_SUB(time_offset, ftemp);
  580         L_ADD(time_adj, time_freq);
  581         
  582         /*
  583          * Apply any correction from adjtime(2).  If more than one second
  584          * off we slew at a rate of 5ms/s (5000 PPM) else 500us/s (500PPM)
  585          * until the last second is slewed the final < 500 usecs.
  586          */
  587         if (time_adjtime != 0) {
  588                 if (time_adjtime > 1000000)
  589                         tickrate = 5000;
  590                 else if (time_adjtime < -1000000)
  591                         tickrate = -5000;
  592                 else if (time_adjtime > 500)
  593                         tickrate = 500;
  594                 else if (time_adjtime < -500)
  595                         tickrate = -500;
  596                 else
  597                         tickrate = time_adjtime;
  598                 time_adjtime -= tickrate;
  599                 L_LINT(ftemp, tickrate * 1000);
  600                 L_ADD(time_adj, ftemp);
  601         }
  602         *adjustment = time_adj;
  603                 
  604 #ifdef PPS_SYNC
  605         if (pps_valid > 0)
  606                 pps_valid--;
  607         else
  608                 time_status &= ~STA_PPSSIGNAL;
  609 #endif /* PPS_SYNC */
  610 }
  611 
  612 /*
  613  * ntp_init() - initialize variables and structures
  614  *
  615  * This routine must be called after the kernel variables hz and tick
  616  * are set or changed and before the next tick interrupt. In this
  617  * particular implementation, these values are assumed set elsewhere in
  618  * the kernel. The design allows the clock frequency and tick interval
  619  * to be changed while the system is running. So, this routine should
  620  * probably be integrated with the code that does that.
  621  */
  622 static void
  623 ntp_init()
  624 {
  625 
  626         /*
  627          * The following variables are initialized only at startup. Only
  628          * those structures not cleared by the compiler need to be
  629          * initialized, and these only in the simulator. In the actual
  630          * kernel, any nonzero values here will quickly evaporate.
  631          */
  632         L_CLR(time_offset);
  633         L_CLR(time_freq);
  634 #ifdef PPS_SYNC
  635         pps_tf[0].tv_sec = pps_tf[0].tv_nsec = 0;
  636         pps_tf[1].tv_sec = pps_tf[1].tv_nsec = 0;
  637         pps_tf[2].tv_sec = pps_tf[2].tv_nsec = 0;
  638         pps_fcount = 0;
  639         L_CLR(pps_freq);
  640 #endif /* PPS_SYNC */      
  641 }
  642 
  643 SYSINIT(ntpclocks, SI_SUB_CLOCKS, SI_ORDER_MIDDLE, ntp_init, NULL);
  644 
  645 /*
  646  * hardupdate() - local clock update
  647  *
  648  * This routine is called by ntp_adjtime() to update the local clock
  649  * phase and frequency. The implementation is of an adaptive-parameter,
  650  * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
  651  * time and frequency offset estimates for each call. If the kernel PPS
  652  * discipline code is configured (PPS_SYNC), the PPS signal itself
  653  * determines the new time offset, instead of the calling argument.
  654  * Presumably, calls to ntp_adjtime() occur only when the caller
  655  * believes the local clock is valid within some bound (+-128 ms with
  656  * NTP). If the caller's time is far different than the PPS time, an
  657  * argument will ensue, and it's not clear who will lose.
  658  *
  659  * For uncompensated quartz crystal oscillators and nominal update
  660  * intervals less than 256 s, operation should be in phase-lock mode,
  661  * where the loop is disciplined to phase. For update intervals greater
  662  * than 1024 s, operation should be in frequency-lock mode, where the
  663  * loop is disciplined to frequency. Between 256 s and 1024 s, the mode
  664  * is selected by the STA_MODE status bit.
  665  */
  666 static void
  667 hardupdate(offset)
  668         long offset;            /* clock offset (ns) */
  669 {
  670         long mtemp;
  671         l_fp ftemp;
  672 
  673         /*
  674          * Select how the phase is to be controlled and from which
  675          * source. If the PPS signal is present and enabled to
  676          * discipline the time, the PPS offset is used; otherwise, the
  677          * argument offset is used.
  678          */
  679         if (!(time_status & STA_PLL))
  680                 return;
  681         if (!(time_status & STA_PPSTIME && time_status &
  682             STA_PPSSIGNAL)) {
  683                 if (offset > MAXPHASE)
  684                         time_monitor = MAXPHASE;
  685                 else if (offset < -MAXPHASE)
  686                         time_monitor = -MAXPHASE;
  687                 else
  688                         time_monitor = offset;
  689                 L_LINT(time_offset, time_monitor);
  690         }
  691 
  692         /*
  693          * Select how the frequency is to be controlled and in which
  694          * mode (PLL or FLL). If the PPS signal is present and enabled
  695          * to discipline the frequency, the PPS frequency is used;
  696          * otherwise, the argument offset is used to compute it.
  697          */
  698         if (time_status & STA_PPSFREQ && time_status & STA_PPSSIGNAL) {
  699                 time_reftime = time_uptime;
  700                 return;
  701         }
  702         if (time_status & STA_FREQHOLD || time_reftime == 0)
  703                 time_reftime = time_uptime;
  704         mtemp = time_uptime - time_reftime;
  705         L_LINT(ftemp, time_monitor);
  706         L_RSHIFT(ftemp, (SHIFT_PLL + 2 + time_constant) << 1);
  707         L_MPY(ftemp, mtemp);
  708         L_ADD(time_freq, ftemp);
  709         time_status &= ~STA_MODE;
  710         if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp >
  711             MAXSEC)) {
  712                 L_LINT(ftemp, (time_monitor << 4) / mtemp);
  713                 L_RSHIFT(ftemp, SHIFT_FLL + 4);
  714                 L_ADD(time_freq, ftemp);
  715                 time_status |= STA_MODE;
  716         }
  717         time_reftime = time_uptime;
  718         if (L_GINT(time_freq) > MAXFREQ)
  719                 L_LINT(time_freq, MAXFREQ);
  720         else if (L_GINT(time_freq) < -MAXFREQ)
  721                 L_LINT(time_freq, -MAXFREQ);
  722 }
  723 
  724 #ifdef PPS_SYNC
  725 /*
  726  * hardpps() - discipline CPU clock oscillator to external PPS signal
  727  *
  728  * This routine is called at each PPS interrupt in order to discipline
  729  * the CPU clock oscillator to the PPS signal. There are two independent
  730  * first-order feedback loops, one for the phase, the other for the
  731  * frequency. The phase loop measures and grooms the PPS phase offset
  732  * and leaves it in a handy spot for the seconds overflow routine. The
  733  * frequency loop averages successive PPS phase differences and
  734  * calculates the PPS frequency offset, which is also processed by the
  735  * seconds overflow routine. The code requires the caller to capture the
  736  * time and architecture-dependent hardware counter values in
  737  * nanoseconds at the on-time PPS signal transition.
  738  *
  739  * Note that, on some Unix systems this routine runs at an interrupt
  740  * priority level higher than the timer interrupt routine hardclock().
  741  * Therefore, the variables used are distinct from the hardclock()
  742  * variables, except for the actual time and frequency variables, which
  743  * are determined by this routine and updated atomically.
  744  */
  745 void
  746 hardpps(tsp, nsec)
  747         struct timespec *tsp;   /* time at PPS */
  748         long nsec;              /* hardware counter at PPS */
  749 {
  750         long u_sec, u_nsec, v_nsec; /* temps */
  751         l_fp ftemp;
  752 
  753         /*
  754          * The signal is first processed by a range gate and frequency
  755          * discriminator. The range gate rejects noise spikes outside
  756          * the range +-500 us. The frequency discriminator rejects input
  757          * signals with apparent frequency outside the range 1 +-500
  758          * PPM. If two hits occur in the same second, we ignore the
  759          * later hit; if not and a hit occurs outside the range gate,
  760          * keep the later hit for later comparison, but do not process
  761          * it.
  762          */
  763         time_status |= STA_PPSSIGNAL | STA_PPSJITTER;
  764         time_status &= ~(STA_PPSWANDER | STA_PPSERROR);
  765         pps_valid = PPS_VALID;
  766         u_sec = tsp->tv_sec;
  767         u_nsec = tsp->tv_nsec;
  768         if (u_nsec >= (NANOSECOND >> 1)) {
  769                 u_nsec -= NANOSECOND;
  770                 u_sec++;
  771         }
  772         v_nsec = u_nsec - pps_tf[0].tv_nsec;
  773         if (u_sec == pps_tf[0].tv_sec && v_nsec < NANOSECOND -
  774             MAXFREQ)
  775                 return;
  776         pps_tf[2] = pps_tf[1];
  777         pps_tf[1] = pps_tf[0];
  778         pps_tf[0].tv_sec = u_sec;
  779         pps_tf[0].tv_nsec = u_nsec;
  780 
  781         /*
  782          * Compute the difference between the current and previous
  783          * counter values. If the difference exceeds 0.5 s, assume it
  784          * has wrapped around, so correct 1.0 s. If the result exceeds
  785          * the tick interval, the sample point has crossed a tick
  786          * boundary during the last second, so correct the tick. Very
  787          * intricate.
  788          */
  789         u_nsec = nsec;
  790         if (u_nsec > (NANOSECOND >> 1))
  791                 u_nsec -= NANOSECOND;
  792         else if (u_nsec < -(NANOSECOND >> 1))
  793                 u_nsec += NANOSECOND;
  794         pps_fcount += u_nsec;
  795         if (v_nsec > MAXFREQ || v_nsec < -MAXFREQ)
  796                 return;
  797         time_status &= ~STA_PPSJITTER;
  798 
  799         /*
  800          * A three-stage median filter is used to help denoise the PPS
  801          * time. The median sample becomes the time offset estimate; the
  802          * difference between the other two samples becomes the time
  803          * dispersion (jitter) estimate.
  804          */
  805         if (pps_tf[0].tv_nsec > pps_tf[1].tv_nsec) {
  806                 if (pps_tf[1].tv_nsec > pps_tf[2].tv_nsec) {
  807                         v_nsec = pps_tf[1].tv_nsec;     /* 0 1 2 */
  808                         u_nsec = pps_tf[0].tv_nsec - pps_tf[2].tv_nsec;
  809                 } else if (pps_tf[2].tv_nsec > pps_tf[0].tv_nsec) {
  810                         v_nsec = pps_tf[0].tv_nsec;     /* 2 0 1 */
  811                         u_nsec = pps_tf[2].tv_nsec - pps_tf[1].tv_nsec;
  812                 } else {
  813                         v_nsec = pps_tf[2].tv_nsec;     /* 0 2 1 */
  814                         u_nsec = pps_tf[0].tv_nsec - pps_tf[1].tv_nsec;
  815                 }
  816         } else {
  817                 if (pps_tf[1].tv_nsec < pps_tf[2].tv_nsec) {
  818                         v_nsec = pps_tf[1].tv_nsec;     /* 2 1 0 */
  819                         u_nsec = pps_tf[2].tv_nsec - pps_tf[0].tv_nsec;
  820                 } else if (pps_tf[2].tv_nsec < pps_tf[0].tv_nsec) {
  821                         v_nsec = pps_tf[0].tv_nsec;     /* 1 0 2 */
  822                         u_nsec = pps_tf[1].tv_nsec - pps_tf[2].tv_nsec;
  823                 } else {
  824                         v_nsec = pps_tf[2].tv_nsec;     /* 1 2 0 */
  825                         u_nsec = pps_tf[1].tv_nsec - pps_tf[0].tv_nsec;
  826                 }
  827         }
  828 
  829         /*
  830          * Nominal jitter is due to PPS signal noise and interrupt
  831          * latency. If it exceeds the popcorn threshold, the sample is
  832          * discarded. otherwise, if so enabled, the time offset is
  833          * updated. We can tolerate a modest loss of data here without
  834          * much degrading time accuracy.
  835          *
  836          * The measurements being checked here were made with the system
  837          * timecounter, so the popcorn threshold is not allowed to fall below
  838          * the number of nanoseconds in two ticks of the timecounter.  For a
  839          * timecounter running faster than 1 GHz the lower bound is 2ns, just
  840          * to avoid a nonsensical threshold of zero.
  841         */
  842         if (u_nsec > lmax(pps_jitter << PPS_POPCORN, 
  843             2 * (NANOSECOND / (long)qmin(NANOSECOND, tc_getfrequency())))) {
  844                 time_status |= STA_PPSJITTER;
  845                 pps_jitcnt++;
  846         } else if (time_status & STA_PPSTIME) {
  847                 time_monitor = -v_nsec;
  848                 L_LINT(time_offset, time_monitor);
  849         }
  850         pps_jitter += (u_nsec - pps_jitter) >> PPS_FAVG;
  851         u_sec = pps_tf[0].tv_sec - pps_lastsec;
  852         if (u_sec < (1 << pps_shift))
  853                 return;
  854 
  855         /*
  856          * At the end of the calibration interval the difference between
  857          * the first and last counter values becomes the scaled
  858          * frequency. It will later be divided by the length of the
  859          * interval to determine the frequency update. If the frequency
  860          * exceeds a sanity threshold, or if the actual calibration
  861          * interval is not equal to the expected length, the data are
  862          * discarded. We can tolerate a modest loss of data here without
  863          * much degrading frequency accuracy.
  864          */
  865         pps_calcnt++;
  866         v_nsec = -pps_fcount;
  867         pps_lastsec = pps_tf[0].tv_sec;
  868         pps_fcount = 0;
  869         u_nsec = MAXFREQ << pps_shift;
  870         if (v_nsec > u_nsec || v_nsec < -u_nsec || u_sec != (1 <<
  871             pps_shift)) {
  872                 time_status |= STA_PPSERROR;
  873                 pps_errcnt++;
  874                 return;
  875         }
  876 
  877         /*
  878          * Here the raw frequency offset and wander (stability) is
  879          * calculated. If the wander is less than the wander threshold
  880          * for four consecutive averaging intervals, the interval is
  881          * doubled; if it is greater than the threshold for four
  882          * consecutive intervals, the interval is halved. The scaled
  883          * frequency offset is converted to frequency offset. The
  884          * stability metric is calculated as the average of recent
  885          * frequency changes, but is used only for performance
  886          * monitoring.
  887          */
  888         L_LINT(ftemp, v_nsec);
  889         L_RSHIFT(ftemp, pps_shift);
  890         L_SUB(ftemp, pps_freq);
  891         u_nsec = L_GINT(ftemp);
  892         if (u_nsec > PPS_MAXWANDER) {
  893                 L_LINT(ftemp, PPS_MAXWANDER);
  894                 pps_intcnt--;
  895                 time_status |= STA_PPSWANDER;
  896                 pps_stbcnt++;
  897         } else if (u_nsec < -PPS_MAXWANDER) {
  898                 L_LINT(ftemp, -PPS_MAXWANDER);
  899                 pps_intcnt--;
  900                 time_status |= STA_PPSWANDER;
  901                 pps_stbcnt++;
  902         } else {
  903                 pps_intcnt++;
  904         }
  905         if (pps_intcnt >= 4) {
  906                 pps_intcnt = 4;
  907                 if (pps_shift < pps_shiftmax) {
  908                         pps_shift++;
  909                         pps_intcnt = 0;
  910                 }
  911         } else if (pps_intcnt <= -4 || pps_shift > pps_shiftmax) {
  912                 pps_intcnt = -4;
  913                 if (pps_shift > PPS_FAVG) {
  914                         pps_shift--;
  915                         pps_intcnt = 0;
  916                 }
  917         }
  918         if (u_nsec < 0)
  919                 u_nsec = -u_nsec;
  920         pps_stabil += (u_nsec * SCALE_PPM - pps_stabil) >> PPS_FAVG;
  921 
  922         /*
  923          * The PPS frequency is recalculated and clamped to the maximum
  924          * MAXFREQ. If enabled, the system clock frequency is updated as
  925          * well.
  926          */
  927         L_ADD(pps_freq, ftemp);
  928         u_nsec = L_GINT(pps_freq);
  929         if (u_nsec > MAXFREQ)
  930                 L_LINT(pps_freq, MAXFREQ);
  931         else if (u_nsec < -MAXFREQ)
  932                 L_LINT(pps_freq, -MAXFREQ);
  933         if (time_status & STA_PPSFREQ)
  934                 time_freq = pps_freq;
  935 }
  936 #endif /* PPS_SYNC */
  937 
  938 #ifndef _SYS_SYSPROTO_H_
  939 struct adjtime_args {
  940         struct timeval *delta;
  941         struct timeval *olddelta;
  942 };
  943 #endif
  944 /* ARGSUSED */
  945 int
  946 sys_adjtime(struct thread *td, struct adjtime_args *uap)
  947 {
  948         struct timeval delta, olddelta, *deltap;
  949         int error;
  950 
  951         if (uap->delta) {
  952                 error = copyin(uap->delta, &delta, sizeof(delta));
  953                 if (error)
  954                         return (error);
  955                 deltap = &delta;
  956         } else
  957                 deltap = NULL;
  958         error = kern_adjtime(td, deltap, &olddelta);
  959         if (uap->olddelta && error == 0)
  960                 error = copyout(&olddelta, uap->olddelta, sizeof(olddelta));
  961         return (error);
  962 }
  963 
  964 int
  965 kern_adjtime(struct thread *td, struct timeval *delta, struct timeval *olddelta)
  966 {
  967         struct timeval atv;
  968         int error;
  969 
  970         mtx_lock(&Giant);
  971         if (olddelta) {
  972                 atv.tv_sec = time_adjtime / 1000000;
  973                 atv.tv_usec = time_adjtime % 1000000;
  974                 if (atv.tv_usec < 0) {
  975                         atv.tv_usec += 1000000;
  976                         atv.tv_sec--;
  977                 }
  978                 *olddelta = atv;
  979         }
  980         if (delta) {
  981                 if ((error = priv_check(td, PRIV_ADJTIME))) {
  982                         mtx_unlock(&Giant);
  983                         return (error);
  984                 }
  985                 time_adjtime = (int64_t)delta->tv_sec * 1000000 +
  986                     delta->tv_usec;
  987         }
  988         mtx_unlock(&Giant);
  989         return (0);
  990 }
  991 
  992 static struct callout resettodr_callout;
  993 static int resettodr_period = 1800;
  994 
  995 static void
  996 periodic_resettodr(void *arg __unused)
  997 {
  998 
  999         if (!ntp_is_time_error()) {
 1000                 mtx_lock(&Giant);
 1001                 resettodr();
 1002                 mtx_unlock(&Giant);
 1003         }
 1004         if (resettodr_period > 0)
 1005                 callout_schedule(&resettodr_callout, resettodr_period * hz);
 1006 }
 1007 
 1008 static void
 1009 shutdown_resettodr(void *arg __unused, int howto __unused)
 1010 {
 1011 
 1012         callout_drain(&resettodr_callout);
 1013         if (resettodr_period > 0 && !ntp_is_time_error()) {
 1014                 mtx_lock(&Giant);
 1015                 resettodr();
 1016                 mtx_unlock(&Giant);
 1017         }
 1018 }
 1019 
 1020 static int
 1021 sysctl_resettodr_period(SYSCTL_HANDLER_ARGS)
 1022 {
 1023         int error;
 1024 
 1025         error = sysctl_handle_int(oidp, oidp->oid_arg1, oidp->oid_arg2, req);
 1026         if (error || !req->newptr)
 1027                 return (error);
 1028         if (resettodr_period == 0)
 1029                 callout_stop(&resettodr_callout);
 1030         else
 1031                 callout_reset(&resettodr_callout, resettodr_period * hz,
 1032                     periodic_resettodr, NULL);
 1033         return (0);
 1034 }
 1035 
 1036 SYSCTL_PROC(_machdep, OID_AUTO, rtc_save_period, CTLTYPE_INT|CTLFLAG_RW,
 1037         &resettodr_period, 1800, sysctl_resettodr_period, "I",
 1038         "Save system time to RTC with this period (in seconds)");
 1039 TUNABLE_INT("machdep.rtc_save_period", &resettodr_period);
 1040 
 1041 static void
 1042 start_periodic_resettodr(void *arg __unused)
 1043 {
 1044 
 1045         EVENTHANDLER_REGISTER(shutdown_pre_sync, shutdown_resettodr, NULL,
 1046             SHUTDOWN_PRI_FIRST);
 1047         callout_init(&resettodr_callout, 1);
 1048         if (resettodr_period == 0)
 1049                 return;
 1050         callout_reset(&resettodr_callout, resettodr_period * hz,
 1051             periodic_resettodr, NULL);
 1052 }
 1053 
 1054 SYSINIT(periodic_resettodr, SI_SUB_LAST, SI_ORDER_MIDDLE,
 1055         start_periodic_resettodr, NULL);

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