The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_ntptime.c

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    1 /*-
    2  ***********************************************************************
    3  *                                                                     *
    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: releng/6.0/sys/kern/kern_ntptime.c 146722 2005-05-28 14:34:41Z rwatson $");
   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/kernel.h>
   42 #include <sys/proc.h>
   43 #include <sys/lock.h>
   44 #include <sys/mutex.h>
   45 #include <sys/time.h>
   46 #include <sys/timex.h>
   47 #include <sys/timetc.h>
   48 #include <sys/timepps.h>
   49 #include <sys/syscallsubr.h>
   50 #include <sys/sysctl.h>
   51 
   52 /*
   53  * Single-precision macros for 64-bit machines
   54  */
   55 typedef int64_t l_fp;
   56 #define L_ADD(v, u)     ((v) += (u))
   57 #define L_SUB(v, u)     ((v) -= (u))
   58 #define L_ADDHI(v, a)   ((v) += (int64_t)(a) << 32)
   59 #define L_NEG(v)        ((v) = -(v))
   60 #define L_RSHIFT(v, n) \
   61         do { \
   62                 if ((v) < 0) \
   63                         (v) = -(-(v) >> (n)); \
   64                 else \
   65                         (v) = (v) >> (n); \
   66         } while (0)
   67 #define L_MPY(v, a)     ((v) *= (a))
   68 #define L_CLR(v)        ((v) = 0)
   69 #define L_ISNEG(v)      ((v) < 0)
   70 #define L_LINT(v, a)    ((v) = (int64_t)(a) << 32)
   71 #define L_GINT(v)       ((v) < 0 ? -(-(v) >> 32) : (v) >> 32)
   72 
   73 /*
   74  * Generic NTP kernel interface
   75  *
   76  * These routines constitute the Network Time Protocol (NTP) interfaces
   77  * for user and daemon application programs. The ntp_gettime() routine
   78  * provides the time, maximum error (synch distance) and estimated error
   79  * (dispersion) to client user application programs. The ntp_adjtime()
   80  * routine is used by the NTP daemon to adjust the system clock to an
   81  * externally derived time. The time offset and related variables set by
   82  * this routine are used by other routines in this module to adjust the
   83  * phase and frequency of the clock discipline loop which controls the
   84  * system clock.
   85  *
   86  * When the kernel time is reckoned directly in nanoseconds (NTP_NANO
   87  * defined), the time at each tick interrupt is derived directly from
   88  * the kernel time variable. When the kernel time is reckoned in
   89  * microseconds, (NTP_NANO undefined), the time is derived from the
   90  * kernel time variable together with a variable representing the
   91  * leftover nanoseconds at the last tick interrupt. In either case, the
   92  * current nanosecond time is reckoned from these values plus an
   93  * interpolated value derived by the clock routines in another
   94  * architecture-specific module. The interpolation can use either a
   95  * dedicated counter or a processor cycle counter (PCC) implemented in
   96  * some architectures.
   97  *
   98  * Note that all routines must run at priority splclock or higher.
   99  */
  100 /*
  101  * Phase/frequency-lock loop (PLL/FLL) definitions
  102  *
  103  * The nanosecond clock discipline uses two variable types, time
  104  * variables and frequency variables. Both types are represented as 64-
  105  * bit fixed-point quantities with the decimal point between two 32-bit
  106  * halves. On a 32-bit machine, each half is represented as a single
  107  * word and mathematical operations are done using multiple-precision
  108  * arithmetic. On a 64-bit machine, ordinary computer arithmetic is
  109  * used.
  110  *
  111  * A time variable is a signed 64-bit fixed-point number in ns and
  112  * fraction. It represents the remaining time offset to be amortized
  113  * over succeeding tick interrupts. The maximum time offset is about
  114  * 0.5 s and the resolution is about 2.3e-10 ns.
  115  *
  116  *                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
  117  *  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
  118  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  119  * |s s s|                       ns                                |
  120  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  121  * |                        fraction                               |
  122  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  123  *
  124  * A frequency variable is a signed 64-bit fixed-point number in ns/s
  125  * and fraction. It represents the ns and fraction to be added to the
  126  * kernel time variable at each second. The maximum frequency offset is
  127  * about +-500000 ns/s and the resolution is about 2.3e-10 ns/s.
  128  *
  129  *                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
  130  *  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
  131  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  132  * |s s s s s s s s s s s s s|            ns/s                     |
  133  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  134  * |                        fraction                               |
  135  * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  136  */
  137 /*
  138  * The following variables establish the state of the PLL/FLL and the
  139  * residual time and frequency offset of the local clock.
  140  */
  141 #define SHIFT_PLL       4               /* PLL loop gain (shift) */
  142 #define SHIFT_FLL       2               /* FLL loop gain (shift) */
  143 
  144 static int time_state = TIME_OK;        /* clock state */
  145 static int time_status = STA_UNSYNC;    /* clock status bits */
  146 static long time_tai;                   /* TAI offset (s) */
  147 static long time_monitor;               /* last time offset scaled (ns) */
  148 static long time_constant;              /* poll interval (shift) (s) */
  149 static long time_precision = 1;         /* clock precision (ns) */
  150 static long time_maxerror = MAXPHASE / 1000; /* maximum error (us) */
  151 static long time_esterror = MAXPHASE / 1000; /* estimated error (us) */
  152 static long time_reftime;               /* time at last adjustment (s) */
  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 static int64_t time_adjtime;            /* correction from adjtime(2) (usec) */
  158 
  159 #ifdef PPS_SYNC
  160 /*
  161  * The following variables are used when a pulse-per-second (PPS) signal
  162  * is available and connected via a modem control lead. They establish
  163  * the engineering parameters of the clock discipline loop when
  164  * controlled by the PPS signal.
  165  */
  166 #define PPS_FAVG        2               /* min freq avg interval (s) (shift) */
  167 #define PPS_FAVGDEF     8               /* default freq avg int (s) (shift) */
  168 #define PPS_FAVGMAX     15              /* max freq avg interval (s) (shift) */
  169 #define PPS_PAVG        4               /* phase avg interval (s) (shift) */
  170 #define PPS_VALID       120             /* PPS signal watchdog max (s) */
  171 #define PPS_MAXWANDER   100000          /* max PPS wander (ns/s) */
  172 #define PPS_POPCORN     2               /* popcorn spike threshold (shift) */
  173 
  174 static struct timespec pps_tf[3];       /* phase median filter */
  175 static l_fp pps_freq;                   /* scaled frequency offset (ns/s) */
  176 static long pps_fcount;                 /* frequency accumulator */
  177 static long pps_jitter;                 /* nominal jitter (ns) */
  178 static long pps_stabil;                 /* nominal stability (scaled ns/s) */
  179 static long pps_lastsec;                /* time at last calibration (s) */
  180 static int pps_valid;                   /* signal watchdog counter */
  181 static int pps_shift = PPS_FAVG;        /* interval duration (s) (shift) */
  182 static int pps_shiftmax = PPS_FAVGDEF;  /* max interval duration (s) (shift) */
  183 static int pps_intcnt;                  /* wander counter */
  184 
  185 /*
  186  * PPS signal quality monitors
  187  */
  188 static long pps_calcnt;                 /* calibration intervals */
  189 static long pps_jitcnt;                 /* jitter limit exceeded */
  190 static long pps_stbcnt;                 /* stability limit exceeded */
  191 static long pps_errcnt;                 /* calibration errors */
  192 #endif /* PPS_SYNC */
  193 /*
  194  * End of phase/frequency-lock loop (PLL/FLL) definitions
  195  */
  196 
  197 static void ntp_init(void);
  198 static void hardupdate(long offset);
  199 static void ntp_gettime1(struct ntptimeval *ntvp);
  200 
  201 static void
  202 ntp_gettime1(struct ntptimeval *ntvp)
  203 {
  204         struct timespec atv;    /* nanosecond time */
  205 
  206         GIANT_REQUIRED;
  207 
  208         nanotime(&atv);
  209         ntvp->time.tv_sec = atv.tv_sec;
  210         ntvp->time.tv_nsec = atv.tv_nsec;
  211         ntvp->maxerror = time_maxerror;
  212         ntvp->esterror = time_esterror;
  213         ntvp->tai = time_tai;
  214         ntvp->time_state = time_state;
  215 
  216         /*
  217          * Status word error decode. If any of these conditions occur,
  218          * an error is returned, instead of the status word. Most
  219          * applications will care only about the fact the system clock
  220          * may not be trusted, not about the details.
  221          *
  222          * Hardware or software error
  223          */
  224         if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||
  225 
  226         /*
  227          * PPS signal lost when either time or frequency synchronization
  228          * requested
  229          */
  230             (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
  231             !(time_status & STA_PPSSIGNAL)) ||
  232 
  233         /*
  234          * PPS jitter exceeded when time synchronization requested
  235          */
  236             (time_status & STA_PPSTIME &&
  237             time_status & STA_PPSJITTER) ||
  238 
  239         /*
  240          * PPS wander exceeded or calibration error when frequency
  241          * synchronization requested
  242          */
  243             (time_status & STA_PPSFREQ &&
  244             time_status & (STA_PPSWANDER | STA_PPSERROR)))
  245                 ntvp->time_state = TIME_ERROR;
  246 }
  247 
  248 /*
  249  * ntp_gettime() - NTP user application interface
  250  *
  251  * See the timex.h header file for synopsis and API description. Note
  252  * that the TAI offset is returned in the ntvtimeval.tai structure
  253  * member.
  254  */
  255 #ifndef _SYS_SYSPROTO_H_
  256 struct ntp_gettime_args {
  257         struct ntptimeval *ntvp;
  258 };
  259 #endif
  260 /* ARGSUSED */
  261 int
  262 ntp_gettime(struct thread *td, struct ntp_gettime_args *uap)
  263 {       
  264         struct ntptimeval ntv;
  265 
  266         mtx_lock(&Giant);
  267         ntp_gettime1(&ntv);
  268         mtx_unlock(&Giant);
  269 
  270         return (copyout(&ntv, uap->ntvp, sizeof(ntv)));
  271 }
  272 
  273 static int
  274 ntp_sysctl(SYSCTL_HANDLER_ARGS)
  275 {
  276         struct ntptimeval ntv;  /* temporary structure */
  277 
  278         ntp_gettime1(&ntv);
  279 
  280         return (sysctl_handle_opaque(oidp, &ntv, sizeof(ntv), req));
  281 }
  282 
  283 SYSCTL_NODE(_kern, OID_AUTO, ntp_pll, CTLFLAG_RW, 0, "");
  284 SYSCTL_PROC(_kern_ntp_pll, OID_AUTO, gettime, CTLTYPE_OPAQUE|CTLFLAG_RD,
  285         0, sizeof(struct ntptimeval) , ntp_sysctl, "S,ntptimeval", "");
  286 
  287 #ifdef PPS_SYNC
  288 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shiftmax, CTLFLAG_RW, &pps_shiftmax, 0, "");
  289 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, pps_shift, CTLFLAG_RW, &pps_shift, 0, "");
  290 SYSCTL_INT(_kern_ntp_pll, OID_AUTO, time_monitor, CTLFLAG_RD, &time_monitor, 0, "");
  291 
  292 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, pps_freq, CTLFLAG_RD, &pps_freq, sizeof(pps_freq), "I", "");
  293 SYSCTL_OPAQUE(_kern_ntp_pll, OID_AUTO, time_freq, CTLFLAG_RD, &time_freq, sizeof(time_freq), "I", "");
  294 #endif
  295 /*
  296  * ntp_adjtime() - NTP daemon application interface
  297  *
  298  * See the timex.h header file for synopsis and API description. Note
  299  * that the timex.constant structure member has a dual purpose to set
  300  * the time constant and to set the TAI offset.
  301  */
  302 #ifndef _SYS_SYSPROTO_H_
  303 struct ntp_adjtime_args {
  304         struct timex *tp;
  305 };
  306 #endif
  307 
  308 /*
  309  * MPSAFE
  310  */
  311 int
  312 ntp_adjtime(struct thread *td, struct ntp_adjtime_args *uap)
  313 {
  314         struct timex ntv;       /* temporary structure */
  315         long freq;              /* frequency ns/s) */
  316         int modes;              /* mode bits from structure */
  317         int s;                  /* caller priority */
  318         int error;
  319 
  320         error = copyin((caddr_t)uap->tp, (caddr_t)&ntv, sizeof(ntv));
  321         if (error)
  322                 return(error);
  323 
  324         /*
  325          * Update selected clock variables - only the superuser can
  326          * change anything. Note that there is no error checking here on
  327          * the assumption the superuser should know what it is doing.
  328          * Note that either the time constant or TAI offset are loaded
  329          * from the ntv.constant member, depending on the mode bits. If
  330          * the STA_PLL bit in the status word is cleared, the state and
  331          * status words are reset to the initial values at boot.
  332          */
  333         mtx_lock(&Giant);
  334         modes = ntv.modes;
  335         if (modes)
  336                 error = suser(td);
  337         if (error)
  338                 goto done2;
  339         s = splclock();
  340         if (modes & MOD_MAXERROR)
  341                 time_maxerror = ntv.maxerror;
  342         if (modes & MOD_ESTERROR)
  343                 time_esterror = ntv.esterror;
  344         if (modes & MOD_STATUS) {
  345                 if (time_status & STA_PLL && !(ntv.status & STA_PLL)) {
  346                         time_state = TIME_OK;
  347                         time_status = STA_UNSYNC;
  348 #ifdef PPS_SYNC
  349                         pps_shift = PPS_FAVG;
  350 #endif /* PPS_SYNC */
  351                 }
  352                 time_status &= STA_RONLY;
  353                 time_status |= ntv.status & ~STA_RONLY;
  354         }
  355         if (modes & MOD_TIMECONST) {
  356                 if (ntv.constant < 0)
  357                         time_constant = 0;
  358                 else if (ntv.constant > MAXTC)
  359                         time_constant = MAXTC;
  360                 else
  361                         time_constant = ntv.constant;
  362         }
  363         if (modes & MOD_TAI) {
  364                 if (ntv.constant > 0) /* XXX zero & negative numbers ? */
  365                         time_tai = ntv.constant;
  366         }
  367 #ifdef PPS_SYNC
  368         if (modes & MOD_PPSMAX) {
  369                 if (ntv.shift < PPS_FAVG)
  370                         pps_shiftmax = PPS_FAVG;
  371                 else if (ntv.shift > PPS_FAVGMAX)
  372                         pps_shiftmax = PPS_FAVGMAX;
  373                 else
  374                         pps_shiftmax = ntv.shift;
  375         }
  376 #endif /* PPS_SYNC */
  377         if (modes & MOD_NANO)
  378                 time_status |= STA_NANO;
  379         if (modes & MOD_MICRO)
  380                 time_status &= ~STA_NANO;
  381         if (modes & MOD_CLKB)
  382                 time_status |= STA_CLK;
  383         if (modes & MOD_CLKA)
  384                 time_status &= ~STA_CLK;
  385         if (modes & MOD_FREQUENCY) {
  386                 freq = (ntv.freq * 1000LL) >> 16;
  387                 if (freq > MAXFREQ)
  388                         L_LINT(time_freq, MAXFREQ);
  389                 else if (freq < -MAXFREQ)
  390                         L_LINT(time_freq, -MAXFREQ);
  391                 else {
  392                         /*
  393                          * ntv.freq is [PPM * 2^16] = [us/s * 2^16]
  394                          * time_freq is [ns/s * 2^32]
  395                          */
  396                         time_freq = ntv.freq * 1000LL * 65536LL;
  397                 }
  398 #ifdef PPS_SYNC
  399                 pps_freq = time_freq;
  400 #endif /* PPS_SYNC */
  401         }
  402         if (modes & MOD_OFFSET) {
  403                 if (time_status & STA_NANO)
  404                         hardupdate(ntv.offset);
  405                 else
  406                         hardupdate(ntv.offset * 1000);
  407         }
  408 
  409         /*
  410          * Retrieve all clock variables. Note that the TAI offset is
  411          * returned only by ntp_gettime();
  412          */
  413         if (time_status & STA_NANO)
  414                 ntv.offset = L_GINT(time_offset);
  415         else
  416                 ntv.offset = L_GINT(time_offset) / 1000; /* XXX rounding ? */
  417         ntv.freq = L_GINT((time_freq / 1000LL) << 16);
  418         ntv.maxerror = time_maxerror;
  419         ntv.esterror = time_esterror;
  420         ntv.status = time_status;
  421         ntv.constant = time_constant;
  422         if (time_status & STA_NANO)
  423                 ntv.precision = time_precision;
  424         else
  425                 ntv.precision = time_precision / 1000;
  426         ntv.tolerance = MAXFREQ * SCALE_PPM;
  427 #ifdef PPS_SYNC
  428         ntv.shift = pps_shift;
  429         ntv.ppsfreq = L_GINT((pps_freq / 1000LL) << 16);
  430         if (time_status & STA_NANO)
  431                 ntv.jitter = pps_jitter;
  432         else
  433                 ntv.jitter = pps_jitter / 1000;
  434         ntv.stabil = pps_stabil;
  435         ntv.calcnt = pps_calcnt;
  436         ntv.errcnt = pps_errcnt;
  437         ntv.jitcnt = pps_jitcnt;
  438         ntv.stbcnt = pps_stbcnt;
  439 #endif /* PPS_SYNC */
  440         splx(s);
  441 
  442         error = copyout((caddr_t)&ntv, (caddr_t)uap->tp, sizeof(ntv));
  443         if (error)
  444                 goto done2;
  445 
  446         /*
  447          * Status word error decode. See comments in
  448          * ntp_gettime() routine.
  449          */
  450         if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||
  451             (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
  452             !(time_status & STA_PPSSIGNAL)) ||
  453             (time_status & STA_PPSTIME &&
  454             time_status & STA_PPSJITTER) ||
  455             (time_status & STA_PPSFREQ &&
  456             time_status & (STA_PPSWANDER | STA_PPSERROR))) {
  457                 td->td_retval[0] = TIME_ERROR;
  458         } else {
  459                 td->td_retval[0] = time_state;
  460         }
  461 done2:
  462         mtx_unlock(&Giant);
  463         return (error);
  464 }
  465 
  466 /*
  467  * second_overflow() - called after ntp_tick_adjust()
  468  *
  469  * This routine is ordinarily called immediately following the above
  470  * routine ntp_tick_adjust(). While these two routines are normally
  471  * combined, they are separated here only for the purposes of
  472  * simulation.
  473  */
  474 void
  475 ntp_update_second(int64_t *adjustment, time_t *newsec)
  476 {
  477         int tickrate;
  478         l_fp ftemp;             /* 32/64-bit temporary */
  479 
  480         /*
  481          * On rollover of the second both the nanosecond and microsecond
  482          * clocks are updated and the state machine cranked as
  483          * necessary. The phase adjustment to be used for the next
  484          * second is calculated and the maximum error is increased by
  485          * the tolerance.
  486          */
  487         time_maxerror += MAXFREQ / 1000;
  488 
  489         /*
  490          * Leap second processing. If in leap-insert state at
  491          * the end of the day, the system clock is set back one
  492          * second; if in leap-delete state, the system clock is
  493          * set ahead one second. The nano_time() routine or
  494          * external clock driver will insure that reported time
  495          * is always monotonic.
  496          */
  497         switch (time_state) {
  498 
  499                 /*
  500                  * No warning.
  501                  */
  502                 case TIME_OK:
  503                 if (time_status & STA_INS)
  504                         time_state = TIME_INS;
  505                 else if (time_status & STA_DEL)
  506                         time_state = TIME_DEL;
  507                 break;
  508 
  509                 /*
  510                  * Insert second 23:59:60 following second
  511                  * 23:59:59.
  512                  */
  513                 case TIME_INS:
  514                 if (!(time_status & STA_INS))
  515                         time_state = TIME_OK;
  516                 else if ((*newsec) % 86400 == 0) {
  517                         (*newsec)--;
  518                         time_state = TIME_OOP;
  519                         time_tai++;
  520                 }
  521                 break;
  522 
  523                 /*
  524                  * Delete second 23:59:59.
  525                  */
  526                 case TIME_DEL:
  527                 if (!(time_status & STA_DEL))
  528                         time_state = TIME_OK;
  529                 else if (((*newsec) + 1) % 86400 == 0) {
  530                         (*newsec)++;
  531                         time_tai--;
  532                         time_state = TIME_WAIT;
  533                 }
  534                 break;
  535 
  536                 /*
  537                  * Insert second in progress.
  538                  */
  539                 case TIME_OOP:
  540                         time_state = TIME_WAIT;
  541                 break;
  542 
  543                 /*
  544                  * Wait for status bits to clear.
  545                  */
  546                 case TIME_WAIT:
  547                 if (!(time_status & (STA_INS | STA_DEL)))
  548                         time_state = TIME_OK;
  549         }
  550 
  551         /*
  552          * Compute the total time adjustment for the next second
  553          * in ns. The offset is reduced by a factor depending on
  554          * whether the PPS signal is operating. Note that the
  555          * value is in effect scaled by the clock frequency,
  556          * since the adjustment is added at each tick interrupt.
  557          */
  558         ftemp = time_offset;
  559 #ifdef PPS_SYNC
  560         /* XXX even if PPS signal dies we should finish adjustment ? */
  561         if (time_status & STA_PPSTIME && time_status &
  562             STA_PPSSIGNAL)
  563                 L_RSHIFT(ftemp, pps_shift);
  564         else
  565                 L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
  566 #else
  567                 L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
  568 #endif /* PPS_SYNC */
  569         time_adj = ftemp;
  570         L_SUB(time_offset, ftemp);
  571         L_ADD(time_adj, time_freq);
  572         
  573         /*
  574          * Apply any correction from adjtime(2).  If more than one second
  575          * off we slew at a rate of 5ms/s (5000 PPM) else 500us/s (500PPM)
  576          * until the last second is slewed the final < 500 usecs.
  577          */
  578         if (time_adjtime != 0) {
  579                 if (time_adjtime > 1000000)
  580                         tickrate = 5000;
  581                 else if (time_adjtime < -1000000)
  582                         tickrate = -5000;
  583                 else if (time_adjtime > 500)
  584                         tickrate = 500;
  585                 else if (time_adjtime < -500)
  586                         tickrate = -500;
  587                 else
  588                         tickrate = time_adjtime;
  589                 time_adjtime -= tickrate;
  590                 L_LINT(ftemp, tickrate * 1000);
  591                 L_ADD(time_adj, ftemp);
  592         }
  593         *adjustment = time_adj;
  594                 
  595 #ifdef PPS_SYNC
  596         if (pps_valid > 0)
  597                 pps_valid--;
  598         else
  599                 time_status &= ~STA_PPSSIGNAL;
  600 #endif /* PPS_SYNC */
  601 }
  602 
  603 /*
  604  * ntp_init() - initialize variables and structures
  605  *
  606  * This routine must be called after the kernel variables hz and tick
  607  * are set or changed and before the next tick interrupt. In this
  608  * particular implementation, these values are assumed set elsewhere in
  609  * the kernel. The design allows the clock frequency and tick interval
  610  * to be changed while the system is running. So, this routine should
  611  * probably be integrated with the code that does that.
  612  */
  613 static void
  614 ntp_init()
  615 {
  616 
  617         /*
  618          * The following variables are initialized only at startup. Only
  619          * those structures not cleared by the compiler need to be
  620          * initialized, and these only in the simulator. In the actual
  621          * kernel, any nonzero values here will quickly evaporate.
  622          */
  623         L_CLR(time_offset);
  624         L_CLR(time_freq);
  625 #ifdef PPS_SYNC
  626         pps_tf[0].tv_sec = pps_tf[0].tv_nsec = 0;
  627         pps_tf[1].tv_sec = pps_tf[1].tv_nsec = 0;
  628         pps_tf[2].tv_sec = pps_tf[2].tv_nsec = 0;
  629         pps_fcount = 0;
  630         L_CLR(pps_freq);
  631 #endif /* PPS_SYNC */      
  632 }
  633 
  634 SYSINIT(ntpclocks, SI_SUB_CLOCKS, SI_ORDER_MIDDLE, ntp_init, NULL)
  635 
  636 /*
  637  * hardupdate() - local clock update
  638  *
  639  * This routine is called by ntp_adjtime() to update the local clock
  640  * phase and frequency. The implementation is of an adaptive-parameter,
  641  * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
  642  * time and frequency offset estimates for each call. If the kernel PPS
  643  * discipline code is configured (PPS_SYNC), the PPS signal itself
  644  * determines the new time offset, instead of the calling argument.
  645  * Presumably, calls to ntp_adjtime() occur only when the caller
  646  * believes the local clock is valid within some bound (+-128 ms with
  647  * NTP). If the caller's time is far different than the PPS time, an
  648  * argument will ensue, and it's not clear who will lose.
  649  *
  650  * For uncompensated quartz crystal oscillators and nominal update
  651  * intervals less than 256 s, operation should be in phase-lock mode,
  652  * where the loop is disciplined to phase. For update intervals greater
  653  * than 1024 s, operation should be in frequency-lock mode, where the
  654  * loop is disciplined to frequency. Between 256 s and 1024 s, the mode
  655  * is selected by the STA_MODE status bit.
  656  */
  657 static void
  658 hardupdate(offset)
  659         long offset;            /* clock offset (ns) */
  660 {
  661         long mtemp;
  662         l_fp ftemp;
  663 
  664         /*
  665          * Select how the phase is to be controlled and from which
  666          * source. If the PPS signal is present and enabled to
  667          * discipline the time, the PPS offset is used; otherwise, the
  668          * argument offset is used.
  669          */
  670         if (!(time_status & STA_PLL))
  671                 return;
  672         if (!(time_status & STA_PPSTIME && time_status &
  673             STA_PPSSIGNAL)) {
  674                 if (offset > MAXPHASE)
  675                         time_monitor = MAXPHASE;
  676                 else if (offset < -MAXPHASE)
  677                         time_monitor = -MAXPHASE;
  678                 else
  679                         time_monitor = offset;
  680                 L_LINT(time_offset, time_monitor);
  681         }
  682 
  683         /*
  684          * Select how the frequency is to be controlled and in which
  685          * mode (PLL or FLL). If the PPS signal is present and enabled
  686          * to discipline the frequency, the PPS frequency is used;
  687          * otherwise, the argument offset is used to compute it.
  688          */
  689         if (time_status & STA_PPSFREQ && time_status & STA_PPSSIGNAL) {
  690                 time_reftime = time_second;
  691                 return;
  692         }
  693         if (time_status & STA_FREQHOLD || time_reftime == 0)
  694                 time_reftime = time_second;
  695         mtemp = time_second - time_reftime;
  696         L_LINT(ftemp, time_monitor);
  697         L_RSHIFT(ftemp, (SHIFT_PLL + 2 + time_constant) << 1);
  698         L_MPY(ftemp, mtemp);
  699         L_ADD(time_freq, ftemp);
  700         time_status &= ~STA_MODE;
  701         if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp >
  702             MAXSEC)) {
  703                 L_LINT(ftemp, (time_monitor << 4) / mtemp);
  704                 L_RSHIFT(ftemp, SHIFT_FLL + 4);
  705                 L_ADD(time_freq, ftemp);
  706                 time_status |= STA_MODE;
  707         }
  708         time_reftime = time_second;
  709         if (L_GINT(time_freq) > MAXFREQ)
  710                 L_LINT(time_freq, MAXFREQ);
  711         else if (L_GINT(time_freq) < -MAXFREQ)
  712                 L_LINT(time_freq, -MAXFREQ);
  713 }
  714 
  715 #ifdef PPS_SYNC
  716 /*
  717  * hardpps() - discipline CPU clock oscillator to external PPS signal
  718  *
  719  * This routine is called at each PPS interrupt in order to discipline
  720  * the CPU clock oscillator to the PPS signal. There are two independent
  721  * first-order feedback loops, one for the phase, the other for the
  722  * frequency. The phase loop measures and grooms the PPS phase offset
  723  * and leaves it in a handy spot for the seconds overflow routine. The
  724  * frequency loop averages successive PPS phase differences and
  725  * calculates the PPS frequency offset, which is also processed by the
  726  * seconds overflow routine. The code requires the caller to capture the
  727  * time and architecture-dependent hardware counter values in
  728  * nanoseconds at the on-time PPS signal transition.
  729  *
  730  * Note that, on some Unix systems this routine runs at an interrupt
  731  * priority level higher than the timer interrupt routine hardclock().
  732  * Therefore, the variables used are distinct from the hardclock()
  733  * variables, except for the actual time and frequency variables, which
  734  * are determined by this routine and updated atomically.
  735  */
  736 void
  737 hardpps(tsp, nsec)
  738         struct timespec *tsp;   /* time at PPS */
  739         long nsec;              /* hardware counter at PPS */
  740 {
  741         long u_sec, u_nsec, v_nsec; /* temps */
  742         l_fp ftemp;
  743 
  744         /*
  745          * The signal is first processed by a range gate and frequency
  746          * discriminator. The range gate rejects noise spikes outside
  747          * the range +-500 us. The frequency discriminator rejects input
  748          * signals with apparent frequency outside the range 1 +-500
  749          * PPM. If two hits occur in the same second, we ignore the
  750          * later hit; if not and a hit occurs outside the range gate,
  751          * keep the later hit for later comparison, but do not process
  752          * it.
  753          */
  754         time_status |= STA_PPSSIGNAL | STA_PPSJITTER;
  755         time_status &= ~(STA_PPSWANDER | STA_PPSERROR);
  756         pps_valid = PPS_VALID;
  757         u_sec = tsp->tv_sec;
  758         u_nsec = tsp->tv_nsec;
  759         if (u_nsec >= (NANOSECOND >> 1)) {
  760                 u_nsec -= NANOSECOND;
  761                 u_sec++;
  762         }
  763         v_nsec = u_nsec - pps_tf[0].tv_nsec;
  764         if (u_sec == pps_tf[0].tv_sec && v_nsec < NANOSECOND -
  765             MAXFREQ)
  766                 return;
  767         pps_tf[2] = pps_tf[1];
  768         pps_tf[1] = pps_tf[0];
  769         pps_tf[0].tv_sec = u_sec;
  770         pps_tf[0].tv_nsec = u_nsec;
  771 
  772         /*
  773          * Compute the difference between the current and previous
  774          * counter values. If the difference exceeds 0.5 s, assume it
  775          * has wrapped around, so correct 1.0 s. If the result exceeds
  776          * the tick interval, the sample point has crossed a tick
  777          * boundary during the last second, so correct the tick. Very
  778          * intricate.
  779          */
  780         u_nsec = nsec;
  781         if (u_nsec > (NANOSECOND >> 1))
  782                 u_nsec -= NANOSECOND;
  783         else if (u_nsec < -(NANOSECOND >> 1))
  784                 u_nsec += NANOSECOND;
  785         pps_fcount += u_nsec;
  786         if (v_nsec > MAXFREQ || v_nsec < -MAXFREQ)
  787                 return;
  788         time_status &= ~STA_PPSJITTER;
  789 
  790         /*
  791          * A three-stage median filter is used to help denoise the PPS
  792          * time. The median sample becomes the time offset estimate; the
  793          * difference between the other two samples becomes the time
  794          * dispersion (jitter) estimate.
  795          */
  796         if (pps_tf[0].tv_nsec > pps_tf[1].tv_nsec) {
  797                 if (pps_tf[1].tv_nsec > pps_tf[2].tv_nsec) {
  798                         v_nsec = pps_tf[1].tv_nsec;     /* 0 1 2 */
  799                         u_nsec = pps_tf[0].tv_nsec - pps_tf[2].tv_nsec;
  800                 } else if (pps_tf[2].tv_nsec > pps_tf[0].tv_nsec) {
  801                         v_nsec = pps_tf[0].tv_nsec;     /* 2 0 1 */
  802                         u_nsec = pps_tf[2].tv_nsec - pps_tf[1].tv_nsec;
  803                 } else {
  804                         v_nsec = pps_tf[2].tv_nsec;     /* 0 2 1 */
  805                         u_nsec = pps_tf[0].tv_nsec - pps_tf[1].tv_nsec;
  806                 }
  807         } else {
  808                 if (pps_tf[1].tv_nsec < pps_tf[2].tv_nsec) {
  809                         v_nsec = pps_tf[1].tv_nsec;     /* 2 1 0 */
  810                         u_nsec = pps_tf[2].tv_nsec - pps_tf[0].tv_nsec;
  811                 } else if (pps_tf[2].tv_nsec < pps_tf[0].tv_nsec) {
  812                         v_nsec = pps_tf[0].tv_nsec;     /* 1 0 2 */
  813                         u_nsec = pps_tf[1].tv_nsec - pps_tf[2].tv_nsec;
  814                 } else {
  815                         v_nsec = pps_tf[2].tv_nsec;     /* 1 2 0 */
  816                         u_nsec = pps_tf[1].tv_nsec - pps_tf[0].tv_nsec;
  817                 }
  818         }
  819 
  820         /*
  821          * Nominal jitter is due to PPS signal noise and interrupt
  822          * latency. If it exceeds the popcorn threshold, the sample is
  823          * discarded. otherwise, if so enabled, the time offset is
  824          * updated. We can tolerate a modest loss of data here without
  825          * much degrading time accuracy.
  826          */
  827         if (u_nsec > (pps_jitter << PPS_POPCORN)) {
  828                 time_status |= STA_PPSJITTER;
  829                 pps_jitcnt++;
  830         } else if (time_status & STA_PPSTIME) {
  831                 time_monitor = -v_nsec;
  832                 L_LINT(time_offset, time_monitor);
  833         }
  834         pps_jitter += (u_nsec - pps_jitter) >> PPS_FAVG;
  835         u_sec = pps_tf[0].tv_sec - pps_lastsec;
  836         if (u_sec < (1 << pps_shift))
  837                 return;
  838 
  839         /*
  840          * At the end of the calibration interval the difference between
  841          * the first and last counter values becomes the scaled
  842          * frequency. It will later be divided by the length of the
  843          * interval to determine the frequency update. If the frequency
  844          * exceeds a sanity threshold, or if the actual calibration
  845          * interval is not equal to the expected length, the data are
  846          * discarded. We can tolerate a modest loss of data here without
  847          * much degrading frequency accuracy.
  848          */
  849         pps_calcnt++;
  850         v_nsec = -pps_fcount;
  851         pps_lastsec = pps_tf[0].tv_sec;
  852         pps_fcount = 0;
  853         u_nsec = MAXFREQ << pps_shift;
  854         if (v_nsec > u_nsec || v_nsec < -u_nsec || u_sec != (1 <<
  855             pps_shift)) {
  856                 time_status |= STA_PPSERROR;
  857                 pps_errcnt++;
  858                 return;
  859         }
  860 
  861         /*
  862          * Here the raw frequency offset and wander (stability) is
  863          * calculated. If the wander is less than the wander threshold
  864          * for four consecutive averaging intervals, the interval is
  865          * doubled; if it is greater than the threshold for four
  866          * consecutive intervals, the interval is halved. The scaled
  867          * frequency offset is converted to frequency offset. The
  868          * stability metric is calculated as the average of recent
  869          * frequency changes, but is used only for performance
  870          * monitoring.
  871          */
  872         L_LINT(ftemp, v_nsec);
  873         L_RSHIFT(ftemp, pps_shift);
  874         L_SUB(ftemp, pps_freq);
  875         u_nsec = L_GINT(ftemp);
  876         if (u_nsec > PPS_MAXWANDER) {
  877                 L_LINT(ftemp, PPS_MAXWANDER);
  878                 pps_intcnt--;
  879                 time_status |= STA_PPSWANDER;
  880                 pps_stbcnt++;
  881         } else if (u_nsec < -PPS_MAXWANDER) {
  882                 L_LINT(ftemp, -PPS_MAXWANDER);
  883                 pps_intcnt--;
  884                 time_status |= STA_PPSWANDER;
  885                 pps_stbcnt++;
  886         } else {
  887                 pps_intcnt++;
  888         }
  889         if (pps_intcnt >= 4) {
  890                 pps_intcnt = 4;
  891                 if (pps_shift < pps_shiftmax) {
  892                         pps_shift++;
  893                         pps_intcnt = 0;
  894                 }
  895         } else if (pps_intcnt <= -4 || pps_shift > pps_shiftmax) {
  896                 pps_intcnt = -4;
  897                 if (pps_shift > PPS_FAVG) {
  898                         pps_shift--;
  899                         pps_intcnt = 0;
  900                 }
  901         }
  902         if (u_nsec < 0)
  903                 u_nsec = -u_nsec;
  904         pps_stabil += (u_nsec * SCALE_PPM - pps_stabil) >> PPS_FAVG;
  905 
  906         /*
  907          * The PPS frequency is recalculated and clamped to the maximum
  908          * MAXFREQ. If enabled, the system clock frequency is updated as
  909          * well.
  910          */
  911         L_ADD(pps_freq, ftemp);
  912         u_nsec = L_GINT(pps_freq);
  913         if (u_nsec > MAXFREQ)
  914                 L_LINT(pps_freq, MAXFREQ);
  915         else if (u_nsec < -MAXFREQ)
  916                 L_LINT(pps_freq, -MAXFREQ);
  917         if (time_status & STA_PPSFREQ)
  918                 time_freq = pps_freq;
  919 }
  920 #endif /* PPS_SYNC */
  921 
  922 #ifndef _SYS_SYSPROTO_H_
  923 struct adjtime_args {
  924         struct timeval *delta;
  925         struct timeval *olddelta;
  926 };
  927 #endif
  928 /*
  929  * MPSAFE
  930  */
  931 /* ARGSUSED */
  932 int
  933 adjtime(struct thread *td, struct adjtime_args *uap)
  934 {
  935         struct timeval delta, olddelta, *deltap;
  936         int error;
  937 
  938         if (uap->delta) {
  939                 error = copyin(uap->delta, &delta, sizeof(delta));
  940                 if (error)
  941                         return (error);
  942                 deltap = &delta;
  943         } else
  944                 deltap = NULL;
  945         error = kern_adjtime(td, deltap, &olddelta);
  946         if (uap->olddelta && error == 0)
  947                 error = copyout(&olddelta, uap->olddelta, sizeof(olddelta));
  948         return (error);
  949 }
  950 
  951 int
  952 kern_adjtime(struct thread *td, struct timeval *delta, struct timeval *olddelta)
  953 {
  954         struct timeval atv;
  955         int error;
  956 
  957         if ((error = suser(td)))
  958                 return (error);
  959 
  960         mtx_lock(&Giant);
  961         if (olddelta) {
  962                 atv.tv_sec = time_adjtime / 1000000;
  963                 atv.tv_usec = time_adjtime % 1000000;
  964                 if (atv.tv_usec < 0) {
  965                         atv.tv_usec += 1000000;
  966                         atv.tv_sec--;
  967                 }
  968                 *olddelta = atv;
  969         }
  970         if (delta)
  971                 time_adjtime = (int64_t)delta->tv_sec * 1000000 +
  972                     delta->tv_usec;
  973         mtx_unlock(&Giant);
  974         return (error);
  975 }
  976 

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