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

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