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

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    1 /*      $NetBSD: kern_clock.c,v 1.94 2005/03/02 11:05:34 mycroft Exp $  */
    2 
    3 /*-
    4  * Copyright (c) 2000, 2004 The NetBSD Foundation, Inc.
    5  * All rights reserved.
    6  *
    7  * This code is derived from software contributed to The NetBSD Foundation
    8  * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
    9  * NASA Ames Research Center.
   10  * This code is derived from software contributed to The NetBSD Foundation
   11  * by Charles M. Hannum.
   12  *
   13  * Redistribution and use in source and binary forms, with or without
   14  * modification, are permitted provided that the following conditions
   15  * are met:
   16  * 1. Redistributions of source code must retain the above copyright
   17  *    notice, this list of conditions and the following disclaimer.
   18  * 2. Redistributions in binary form must reproduce the above copyright
   19  *    notice, this list of conditions and the following disclaimer in the
   20  *    documentation and/or other materials provided with the distribution.
   21  * 3. All advertising materials mentioning features or use of this software
   22  *    must display the following acknowledgement:
   23  *      This product includes software developed by the NetBSD
   24  *      Foundation, Inc. and its contributors.
   25  * 4. Neither the name of The NetBSD Foundation nor the names of its
   26  *    contributors may be used to endorse or promote products derived
   27  *    from this software without specific prior written permission.
   28  *
   29  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
   30  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   31  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   32  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
   33  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   34  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   35  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   36  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   37  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   38  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   39  * POSSIBILITY OF SUCH DAMAGE.
   40  */
   41 
   42 /*-
   43  * Copyright (c) 1982, 1986, 1991, 1993
   44  *      The Regents of the University of California.  All rights reserved.
   45  * (c) UNIX System Laboratories, Inc.
   46  * All or some portions of this file are derived from material licensed
   47  * to the University of California by American Telephone and Telegraph
   48  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
   49  * the permission of UNIX System Laboratories, Inc.
   50  *
   51  * Redistribution and use in source and binary forms, with or without
   52  * modification, are permitted provided that the following conditions
   53  * are met:
   54  * 1. Redistributions of source code must retain the above copyright
   55  *    notice, this list of conditions and the following disclaimer.
   56  * 2. Redistributions in binary form must reproduce the above copyright
   57  *    notice, this list of conditions and the following disclaimer in the
   58  *    documentation and/or other materials provided with the distribution.
   59  * 3. Neither the name of the University nor the names of its contributors
   60  *    may be used to endorse or promote products derived from this software
   61  *    without specific prior written permission.
   62  *
   63  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   64  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   65  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   66  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   67  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   68  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   69  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   70  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   71  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   72  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   73  * SUCH DAMAGE.
   74  *
   75  *      @(#)kern_clock.c        8.5 (Berkeley) 1/21/94
   76  */
   77 
   78 #include <sys/cdefs.h>
   79 __KERNEL_RCSID(0, "$NetBSD: kern_clock.c,v 1.94 2005/03/02 11:05:34 mycroft Exp $");
   80 
   81 #include "opt_ntp.h"
   82 #include "opt_multiprocessor.h"
   83 #include "opt_perfctrs.h"
   84 
   85 #include <sys/param.h>
   86 #include <sys/systm.h>
   87 #include <sys/callout.h>
   88 #include <sys/kernel.h>
   89 #include <sys/proc.h>
   90 #include <sys/resourcevar.h>
   91 #include <sys/signalvar.h>
   92 #include <sys/sysctl.h>
   93 #include <sys/timex.h>
   94 #include <sys/sched.h>
   95 #include <sys/time.h>
   96 
   97 #include <machine/cpu.h>
   98 #ifdef __HAVE_GENERIC_SOFT_INTERRUPTS
   99 #include <machine/intr.h>
  100 #endif
  101 
  102 #ifdef GPROF
  103 #include <sys/gmon.h>
  104 #endif
  105 
  106 /*
  107  * Clock handling routines.
  108  *
  109  * This code is written to operate with two timers that run independently of
  110  * each other.  The main clock, running hz times per second, is used to keep
  111  * track of real time.  The second timer handles kernel and user profiling,
  112  * and does resource use estimation.  If the second timer is programmable,
  113  * it is randomized to avoid aliasing between the two clocks.  For example,
  114  * the randomization prevents an adversary from always giving up the CPU
  115  * just before its quantum expires.  Otherwise, it would never accumulate
  116  * CPU ticks.  The mean frequency of the second timer is stathz.
  117  *
  118  * If no second timer exists, stathz will be zero; in this case we drive
  119  * profiling and statistics off the main clock.  This WILL NOT be accurate;
  120  * do not do it unless absolutely necessary.
  121  *
  122  * The statistics clock may (or may not) be run at a higher rate while
  123  * profiling.  This profile clock runs at profhz.  We require that profhz
  124  * be an integral multiple of stathz.
  125  *
  126  * If the statistics clock is running fast, it must be divided by the ratio
  127  * profhz/stathz for statistics.  (For profiling, every tick counts.)
  128  */
  129 
  130 #ifdef NTP      /* NTP phase-locked loop in kernel */
  131 /*
  132  * Phase/frequency-lock loop (PLL/FLL) definitions
  133  *
  134  * The following variables are read and set by the ntp_adjtime() system
  135  * call.
  136  *
  137  * time_state shows the state of the system clock, with values defined
  138  * in the timex.h header file.
  139  *
  140  * time_status shows the status of the system clock, with bits defined
  141  * in the timex.h header file.
  142  *
  143  * time_offset is used by the PLL/FLL to adjust the system time in small
  144  * increments.
  145  *
  146  * time_constant determines the bandwidth or "stiffness" of the PLL.
  147  *
  148  * time_tolerance determines maximum frequency error or tolerance of the
  149  * CPU clock oscillator and is a property of the architecture; however,
  150  * in principle it could change as result of the presence of external
  151  * discipline signals, for instance.
  152  *
  153  * time_precision is usually equal to the kernel tick variable; however,
  154  * in cases where a precision clock counter or external clock is
  155  * available, the resolution can be much less than this and depend on
  156  * whether the external clock is working or not.
  157  *
  158  * time_maxerror is initialized by a ntp_adjtime() call and increased by
  159  * the kernel once each second to reflect the maximum error bound
  160  * growth.
  161  *
  162  * time_esterror is set and read by the ntp_adjtime() call, but
  163  * otherwise not used by the kernel.
  164  */
  165 int time_state = TIME_OK;       /* clock state */
  166 int time_status = STA_UNSYNC;   /* clock status bits */
  167 long time_offset = 0;           /* time offset (us) */
  168 long time_constant = 0;         /* pll time constant */
  169 long time_tolerance = MAXFREQ;  /* frequency tolerance (scaled ppm) */
  170 long time_precision = 1;        /* clock precision (us) */
  171 long time_maxerror = MAXPHASE;  /* maximum error (us) */
  172 long time_esterror = MAXPHASE;  /* estimated error (us) */
  173 
  174 /*
  175  * The following variables establish the state of the PLL/FLL and the
  176  * residual time and frequency offset of the local clock. The scale
  177  * factors are defined in the timex.h header file.
  178  *
  179  * time_phase and time_freq are the phase increment and the frequency
  180  * increment, respectively, of the kernel time variable.
  181  *
  182  * time_freq is set via ntp_adjtime() from a value stored in a file when
  183  * the synchronization daemon is first started. Its value is retrieved
  184  * via ntp_adjtime() and written to the file about once per hour by the
  185  * daemon.
  186  *
  187  * time_adj is the adjustment added to the value of tick at each timer
  188  * interrupt and is recomputed from time_phase and time_freq at each
  189  * seconds rollover.
  190  *
  191  * time_reftime is the second's portion of the system time at the last
  192  * call to ntp_adjtime(). It is used to adjust the time_freq variable
  193  * and to increase the time_maxerror as the time since last update
  194  * increases.
  195  */
  196 long time_phase = 0;            /* phase offset (scaled us) */
  197 long time_freq = 0;             /* frequency offset (scaled ppm) */
  198 long time_adj = 0;              /* tick adjust (scaled 1 / hz) */
  199 long time_reftime = 0;          /* time at last adjustment (s) */
  200 
  201 #ifdef PPS_SYNC
  202 /*
  203  * The following variables are used only if the kernel PPS discipline
  204  * code is configured (PPS_SYNC). The scale factors are defined in the
  205  * timex.h header file.
  206  *
  207  * pps_time contains the time at each calibration interval, as read by
  208  * microtime(). pps_count counts the seconds of the calibration
  209  * interval, the duration of which is nominally pps_shift in powers of
  210  * two.
  211  *
  212  * pps_offset is the time offset produced by the time median filter
  213  * pps_tf[], while pps_jitter is the dispersion (jitter) measured by
  214  * this filter.
  215  *
  216  * pps_freq is the frequency offset produced by the frequency median
  217  * filter pps_ff[], while pps_stabil is the dispersion (wander) measured
  218  * by this filter.
  219  *
  220  * pps_usec is latched from a high resolution counter or external clock
  221  * at pps_time. Here we want the hardware counter contents only, not the
  222  * contents plus the time_tv.usec as usual.
  223  *
  224  * pps_valid counts the number of seconds since the last PPS update. It
  225  * is used as a watchdog timer to disable the PPS discipline should the
  226  * PPS signal be lost.
  227  *
  228  * pps_glitch counts the number of seconds since the beginning of an
  229  * offset burst more than tick/2 from current nominal offset. It is used
  230  * mainly to suppress error bursts due to priority conflicts between the
  231  * PPS interrupt and timer interrupt.
  232  *
  233  * pps_intcnt counts the calibration intervals for use in the interval-
  234  * adaptation algorithm. It's just too complicated for words.
  235  *
  236  * pps_kc_hardpps_source contains an arbitrary value that uniquely
  237  * identifies the currently bound source of the PPS signal, or NULL
  238  * if no source is bound.
  239  *
  240  * pps_kc_hardpps_mode indicates which transitions, if any, of the PPS
  241  * signal should be reported.
  242  */
  243 struct timeval pps_time;        /* kernel time at last interval */
  244 long pps_tf[] = {0, 0, 0};      /* pps time offset median filter (us) */
  245 long pps_offset = 0;            /* pps time offset (us) */
  246 long pps_jitter = MAXTIME;      /* time dispersion (jitter) (us) */
  247 long pps_ff[] = {0, 0, 0};      /* pps frequency offset median filter */
  248 long pps_freq = 0;              /* frequency offset (scaled ppm) */
  249 long pps_stabil = MAXFREQ;      /* frequency dispersion (scaled ppm) */
  250 long pps_usec = 0;              /* microsec counter at last interval */
  251 long pps_valid = PPS_VALID;     /* pps signal watchdog counter */
  252 int pps_glitch = 0;             /* pps signal glitch counter */
  253 int pps_count = 0;              /* calibration interval counter (s) */
  254 int pps_shift = PPS_SHIFT;      /* interval duration (s) (shift) */
  255 int pps_intcnt = 0;             /* intervals at current duration */
  256 void *pps_kc_hardpps_source = NULL; /* current PPS supplier's identifier */
  257 int pps_kc_hardpps_mode = 0;    /* interesting edges of PPS signal */
  258 
  259 /*
  260  * PPS signal quality monitors
  261  *
  262  * pps_jitcnt counts the seconds that have been discarded because the
  263  * jitter measured by the time median filter exceeds the limit MAXTIME
  264  * (100 us).
  265  *
  266  * pps_calcnt counts the frequency calibration intervals, which are
  267  * variable from 4 s to 256 s.
  268  *
  269  * pps_errcnt counts the calibration intervals which have been discarded
  270  * because the wander exceeds the limit MAXFREQ (100 ppm) or where the
  271  * calibration interval jitter exceeds two ticks.
  272  *
  273  * pps_stbcnt counts the calibration intervals that have been discarded
  274  * because the frequency wander exceeds the limit MAXFREQ / 4 (25 us).
  275  */
  276 long pps_jitcnt = 0;            /* jitter limit exceeded */
  277 long pps_calcnt = 0;            /* calibration intervals */
  278 long pps_errcnt = 0;            /* calibration errors */
  279 long pps_stbcnt = 0;            /* stability limit exceeded */
  280 #endif /* PPS_SYNC */
  281 
  282 #ifdef EXT_CLOCK
  283 /*
  284  * External clock definitions
  285  *
  286  * The following definitions and declarations are used only if an
  287  * external clock is configured on the system.
  288  */
  289 #define CLOCK_INTERVAL 30       /* CPU clock update interval (s) */
  290 
  291 /*
  292  * The clock_count variable is set to CLOCK_INTERVAL at each PPS
  293  * interrupt and decremented once each second.
  294  */
  295 int clock_count = 0;            /* CPU clock counter */
  296 
  297 #ifdef HIGHBALL
  298 /*
  299  * The clock_offset and clock_cpu variables are used by the HIGHBALL
  300  * interface. The clock_offset variable defines the offset between
  301  * system time and the HIGBALL counters. The clock_cpu variable contains
  302  * the offset between the system clock and the HIGHBALL clock for use in
  303  * disciplining the kernel time variable.
  304  */
  305 extern struct timeval clock_offset; /* Highball clock offset */
  306 long clock_cpu = 0;             /* CPU clock adjust */
  307 #endif /* HIGHBALL */
  308 #endif /* EXT_CLOCK */
  309 #endif /* NTP */
  310 
  311 
  312 /*
  313  * Bump a timeval by a small number of usec's.
  314  */
  315 #define BUMPTIME(t, usec) { \
  316         volatile struct timeval *tp = (t); \
  317         long us; \
  318  \
  319         tp->tv_usec = us = tp->tv_usec + (usec); \
  320         if (us >= 1000000) { \
  321                 tp->tv_usec = us - 1000000; \
  322                 tp->tv_sec++; \
  323         } \
  324 }
  325 
  326 int     stathz;
  327 int     profhz;
  328 int     profsrc;
  329 int     schedhz;
  330 int     profprocs;
  331 int     hardclock_ticks;
  332 static int statscheddiv; /* stat => sched divider (used if schedhz == 0) */
  333 static int psdiv;                       /* prof => stat divider */
  334 int     psratio;                        /* ratio: prof / stat */
  335 int     tickfix, tickfixinterval;       /* used if tick not really integral */
  336 #ifndef NTP
  337 static int tickfixcnt;                  /* accumulated fractional error */
  338 #else
  339 int     fixtick;                        /* used by NTP for same */
  340 int     shifthz;
  341 #endif
  342 
  343 /*
  344  * We might want ldd to load the both words from time at once.
  345  * To succeed we need to be quadword aligned.
  346  * The sparc already does that, and that it has worked so far is a fluke.
  347  */
  348 volatile struct timeval time  __attribute__((__aligned__(__alignof__(quad_t))));
  349 volatile struct timeval mono_time;
  350 
  351 void    *softclock_si;
  352 
  353 /*
  354  * Initialize clock frequencies and start both clocks running.
  355  */
  356 void
  357 initclocks(void)
  358 {
  359         int i;
  360 
  361 #ifdef __HAVE_GENERIC_SOFT_INTERRUPTS
  362         softclock_si = softintr_establish(IPL_SOFTCLOCK, softclock, NULL);
  363         if (softclock_si == NULL)
  364                 panic("initclocks: unable to register softclock intr");
  365 #endif
  366 
  367         /*
  368          * Set divisors to 1 (normal case) and let the machine-specific
  369          * code do its bit.
  370          */
  371         psdiv = 1;
  372         cpu_initclocks();
  373 
  374         /*
  375          * Compute profhz/stathz/rrticks, and fix profhz if needed.
  376          */
  377         i = stathz ? stathz : hz;
  378         if (profhz == 0)
  379                 profhz = i;
  380         psratio = profhz / i;
  381         rrticks = hz / 10;
  382         if (schedhz == 0) {
  383                 /* 16Hz is best */
  384                 statscheddiv = i / 16;
  385                 if (statscheddiv <= 0)
  386                         panic("statscheddiv");
  387         }
  388 
  389 #ifdef NTP
  390         switch (hz) {
  391         case 1:
  392                 shifthz = SHIFT_SCALE - 0;
  393                 break;
  394         case 2:
  395                 shifthz = SHIFT_SCALE - 1;
  396                 break;
  397         case 4:
  398                 shifthz = SHIFT_SCALE - 2;
  399                 break;
  400         case 8:
  401                 shifthz = SHIFT_SCALE - 3;
  402                 break;
  403         case 16:
  404                 shifthz = SHIFT_SCALE - 4;
  405                 break;
  406         case 32:
  407                 shifthz = SHIFT_SCALE - 5;
  408                 break;
  409         case 50:
  410         case 60:
  411         case 64:
  412                 shifthz = SHIFT_SCALE - 6;
  413                 break;
  414         case 96:
  415         case 100:
  416         case 128:
  417                 shifthz = SHIFT_SCALE - 7;
  418                 break;
  419         case 256:
  420                 shifthz = SHIFT_SCALE - 8;
  421                 break;
  422         case 512:
  423                 shifthz = SHIFT_SCALE - 9;
  424                 break;
  425         case 1000:
  426         case 1024:
  427                 shifthz = SHIFT_SCALE - 10;
  428                 break;
  429         case 1200:
  430         case 2048:
  431                 shifthz = SHIFT_SCALE - 11;
  432                 break;
  433         case 4096:
  434                 shifthz = SHIFT_SCALE - 12;
  435                 break;
  436         case 8192:
  437                 shifthz = SHIFT_SCALE - 13;
  438                 break;
  439         case 16384:
  440                 shifthz = SHIFT_SCALE - 14;
  441                 break;
  442         case 32768:
  443                 shifthz = SHIFT_SCALE - 15;
  444                 break;
  445         case 65536:
  446                 shifthz = SHIFT_SCALE - 16;
  447                 break;
  448         default:
  449                 panic("weird hz");
  450         }
  451         if (fixtick == 0) {
  452                 /*
  453                  * Give MD code a chance to set this to a better
  454                  * value; but, if it doesn't, we should.
  455                  */
  456                 fixtick = (1000000 - (hz*tick));
  457         }
  458 #endif
  459 }
  460 
  461 /*
  462  * The real-time timer, interrupting hz times per second.
  463  */
  464 void
  465 hardclock(struct clockframe *frame)
  466 {
  467         struct lwp *l;
  468         struct proc *p;
  469         int delta;
  470         extern int tickdelta;
  471         extern long timedelta;
  472         struct cpu_info *ci = curcpu();
  473         struct ptimer *pt;
  474 #ifdef NTP
  475         int time_update;
  476         int ltemp;
  477 #endif
  478 
  479         l = curlwp;
  480         if (l) {
  481                 p = l->l_proc;
  482                 /*
  483                  * Run current process's virtual and profile time, as needed.
  484                  */
  485                 if (CLKF_USERMODE(frame) && p->p_timers &&
  486                     (pt = LIST_FIRST(&p->p_timers->pts_virtual)) != NULL)
  487                         if (itimerdecr(pt, tick) == 0)
  488                                 itimerfire(pt);
  489                 if (p->p_timers &&
  490                     (pt = LIST_FIRST(&p->p_timers->pts_prof)) != NULL)
  491                         if (itimerdecr(pt, tick) == 0)
  492                                 itimerfire(pt);
  493         }
  494 
  495         /*
  496          * If no separate statistics clock is available, run it from here.
  497          */
  498         if (stathz == 0)
  499                 statclock(frame);
  500         if ((--ci->ci_schedstate.spc_rrticks) <= 0)
  501                 roundrobin(ci);
  502 
  503 #if defined(MULTIPROCESSOR)
  504         /*
  505          * If we are not the primary CPU, we're not allowed to do
  506          * any more work.
  507          */
  508         if (CPU_IS_PRIMARY(ci) == 0)
  509                 return;
  510 #endif
  511 
  512         /*
  513          * Increment the time-of-day.  The increment is normally just
  514          * ``tick''.  If the machine is one which has a clock frequency
  515          * such that ``hz'' would not divide the second evenly into
  516          * milliseconds, a periodic adjustment must be applied.  Finally,
  517          * if we are still adjusting the time (see adjtime()),
  518          * ``tickdelta'' may also be added in.
  519          */
  520         hardclock_ticks++;
  521         delta = tick;
  522 
  523 #ifndef NTP
  524         if (tickfix) {
  525                 tickfixcnt += tickfix;
  526                 if (tickfixcnt >= tickfixinterval) {
  527                         delta++;
  528                         tickfixcnt -= tickfixinterval;
  529                 }
  530         }
  531 #endif /* !NTP */
  532         /* Imprecise 4bsd adjtime() handling */
  533         if (timedelta != 0) {
  534                 delta += tickdelta;
  535                 timedelta -= tickdelta;
  536         }
  537 
  538 #ifdef notyet
  539         microset();
  540 #endif
  541 
  542 #ifndef NTP
  543         BUMPTIME(&time, delta);         /* XXX Now done using NTP code below */
  544 #endif
  545         BUMPTIME(&mono_time, delta);
  546 
  547 #ifdef NTP
  548         time_update = delta;
  549 
  550         /*
  551          * Compute the phase adjustment. If the low-order bits
  552          * (time_phase) of the update overflow, bump the high-order bits
  553          * (time_update).
  554          */
  555         time_phase += time_adj;
  556         if (time_phase <= -FINEUSEC) {
  557                 ltemp = -time_phase >> SHIFT_SCALE;
  558                 time_phase += ltemp << SHIFT_SCALE;
  559                 time_update -= ltemp;
  560         } else if (time_phase >= FINEUSEC) {
  561                 ltemp = time_phase >> SHIFT_SCALE;
  562                 time_phase -= ltemp << SHIFT_SCALE;
  563                 time_update += ltemp;
  564         }
  565 
  566 #ifdef HIGHBALL
  567         /*
  568          * If the HIGHBALL board is installed, we need to adjust the
  569          * external clock offset in order to close the hardware feedback
  570          * loop. This will adjust the external clock phase and frequency
  571          * in small amounts. The additional phase noise and frequency
  572          * wander this causes should be minimal. We also need to
  573          * discipline the kernel time variable, since the PLL is used to
  574          * discipline the external clock. If the Highball board is not
  575          * present, we discipline kernel time with the PLL as usual. We
  576          * assume that the external clock phase adjustment (time_update)
  577          * and kernel phase adjustment (clock_cpu) are less than the
  578          * value of tick.
  579          */
  580         clock_offset.tv_usec += time_update;
  581         if (clock_offset.tv_usec >= 1000000) {
  582                 clock_offset.tv_sec++;
  583                 clock_offset.tv_usec -= 1000000;
  584         }
  585         if (clock_offset.tv_usec < 0) {
  586                 clock_offset.tv_sec--;
  587                 clock_offset.tv_usec += 1000000;
  588         }
  589         time.tv_usec += clock_cpu;
  590         clock_cpu = 0;
  591 #else
  592         time.tv_usec += time_update;
  593 #endif /* HIGHBALL */
  594 
  595         /*
  596          * On rollover of the second the phase adjustment to be used for
  597          * the next second is calculated. Also, the maximum error is
  598          * increased by the tolerance. If the PPS frequency discipline
  599          * code is present, the phase is increased to compensate for the
  600          * CPU clock oscillator frequency error.
  601          *
  602          * On a 32-bit machine and given parameters in the timex.h
  603          * header file, the maximum phase adjustment is +-512 ms and
  604          * maximum frequency offset is a tad less than) +-512 ppm. On a
  605          * 64-bit machine, you shouldn't need to ask.
  606          */
  607         if (time.tv_usec >= 1000000) {
  608                 time.tv_usec -= 1000000;
  609                 time.tv_sec++;
  610                 time_maxerror += time_tolerance >> SHIFT_USEC;
  611 
  612                 /*
  613                  * Leap second processing. If in leap-insert state at
  614                  * the end of the day, the system clock is set back one
  615                  * second; if in leap-delete state, the system clock is
  616                  * set ahead one second. The microtime() routine or
  617                  * external clock driver will insure that reported time
  618                  * is always monotonic. The ugly divides should be
  619                  * replaced.
  620                  */
  621                 switch (time_state) {
  622                 case TIME_OK:
  623                         if (time_status & STA_INS)
  624                                 time_state = TIME_INS;
  625                         else if (time_status & STA_DEL)
  626                                 time_state = TIME_DEL;
  627                         break;
  628 
  629                 case TIME_INS:
  630                         if (time.tv_sec % 86400 == 0) {
  631                                 time.tv_sec--;
  632                                 time_state = TIME_OOP;
  633                         }
  634                         break;
  635 
  636                 case TIME_DEL:
  637                         if ((time.tv_sec + 1) % 86400 == 0) {
  638                                 time.tv_sec++;
  639                                 time_state = TIME_WAIT;
  640                         }
  641                         break;
  642 
  643                 case TIME_OOP:
  644                         time_state = TIME_WAIT;
  645                         break;
  646 
  647                 case TIME_WAIT:
  648                         if (!(time_status & (STA_INS | STA_DEL)))
  649                                 time_state = TIME_OK;
  650                         break;
  651                 }
  652 
  653                 /*
  654                  * Compute the phase adjustment for the next second. In
  655                  * PLL mode, the offset is reduced by a fixed factor
  656                  * times the time constant. In FLL mode the offset is
  657                  * used directly. In either mode, the maximum phase
  658                  * adjustment for each second is clamped so as to spread
  659                  * the adjustment over not more than the number of
  660                  * seconds between updates.
  661                  */
  662                 if (time_offset < 0) {
  663                         ltemp = -time_offset;
  664                         if (!(time_status & STA_FLL))
  665                                 ltemp >>= SHIFT_KG + time_constant;
  666                         if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE)
  667                                 ltemp = (MAXPHASE / MINSEC) <<
  668                                     SHIFT_UPDATE;
  669                         time_offset += ltemp;
  670                         time_adj = -ltemp << (shifthz - SHIFT_UPDATE);
  671                 } else if (time_offset > 0) {
  672                         ltemp = time_offset;
  673                         if (!(time_status & STA_FLL))
  674                                 ltemp >>= SHIFT_KG + time_constant;
  675                         if (ltemp > (MAXPHASE / MINSEC) << SHIFT_UPDATE)
  676                                 ltemp = (MAXPHASE / MINSEC) <<
  677                                     SHIFT_UPDATE;
  678                         time_offset -= ltemp;
  679                         time_adj = ltemp << (shifthz - SHIFT_UPDATE);
  680                 } else
  681                         time_adj = 0;
  682 
  683                 /*
  684                  * Compute the frequency estimate and additional phase
  685                  * adjustment due to frequency error for the next
  686                  * second. When the PPS signal is engaged, gnaw on the
  687                  * watchdog counter and update the frequency computed by
  688                  * the pll and the PPS signal.
  689                  */
  690 #ifdef PPS_SYNC
  691                 pps_valid++;
  692                 if (pps_valid == PPS_VALID) {
  693                         pps_jitter = MAXTIME;
  694                         pps_stabil = MAXFREQ;
  695                         time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
  696                             STA_PPSWANDER | STA_PPSERROR);
  697                 }
  698                 ltemp = time_freq + pps_freq;
  699 #else
  700                 ltemp = time_freq;
  701 #endif /* PPS_SYNC */
  702 
  703                 if (ltemp < 0)
  704                         time_adj -= -ltemp >> (SHIFT_USEC - shifthz);
  705                 else
  706                         time_adj += ltemp >> (SHIFT_USEC - shifthz);
  707                 time_adj += (long)fixtick << shifthz;
  708 
  709                 /*
  710                  * When the CPU clock oscillator frequency is not a
  711                  * power of 2 in Hz, shifthz is only an approximate
  712                  * scale factor.
  713                  *
  714                  * To determine the adjustment, you can do the following:
  715                  *   bc -q
  716                  *   scale=24
  717                  *   obase=2
  718                  *   idealhz/realhz
  719                  * where `idealhz' is the next higher power of 2, and `realhz'
  720                  * is the actual value.  You may need to factor this result
  721                  * into a sequence of 2 multipliers to get better precision.
  722                  *
  723                  * Likewise, the error can be calculated with (e.g. for 100Hz):
  724                  *   bc -q
  725                  *   scale=24
  726                  *   ((1+2^-2+2^-5)*(1-2^-10)*realhz-idealhz)/idealhz
  727                  * (and then multiply by 1000000 to get ppm).
  728                  */
  729                 switch (hz) {
  730                 case 60:
  731                         /* A factor of 1.000100010001 gives about 15ppm
  732                            error. */
  733                         if (time_adj < 0) {
  734                                 time_adj -= (-time_adj >> 4);
  735                                 time_adj -= (-time_adj >> 8);
  736                         } else {
  737                                 time_adj += (time_adj >> 4);
  738                                 time_adj += (time_adj >> 8);
  739                         }
  740                         break;
  741 
  742                 case 96:
  743                         /* A factor of 1.0101010101 gives about 244ppm error. */
  744                         if (time_adj < 0) {
  745                                 time_adj -= (-time_adj >> 2);
  746                                 time_adj -= (-time_adj >> 4) + (-time_adj >> 8);
  747                         } else {
  748                                 time_adj += (time_adj >> 2);
  749                                 time_adj += (time_adj >> 4) + (time_adj >> 8);
  750                         }
  751                         break;
  752 
  753                 case 50:
  754                 case 100:
  755                         /* A factor of 1.010001111010111 gives about 1ppm
  756                            error. */
  757                         if (time_adj < 0) {
  758                                 time_adj -= (-time_adj >> 2) + (-time_adj >> 5);
  759                                 time_adj += (-time_adj >> 10);
  760                         } else {
  761                                 time_adj += (time_adj >> 2) + (time_adj >> 5);
  762                                 time_adj -= (time_adj >> 10);
  763                         }
  764                         break;
  765 
  766                 case 1000:
  767                         /* A factor of 1.000001100010100001 gives about 50ppm
  768                            error. */
  769                         if (time_adj < 0) {
  770                                 time_adj -= (-time_adj >> 6) + (-time_adj >> 11);
  771                                 time_adj -= (-time_adj >> 7);
  772                         } else {
  773                                 time_adj += (time_adj >> 6) + (time_adj >> 11);
  774                                 time_adj += (time_adj >> 7);
  775                         }
  776                         break;
  777 
  778                 case 1200:
  779                         /* A factor of 1.1011010011100001 gives about 64ppm
  780                            error. */
  781                         if (time_adj < 0) {
  782                                 time_adj -= (-time_adj >> 1) + (-time_adj >> 6);
  783                                 time_adj -= (-time_adj >> 3) + (-time_adj >> 10);
  784                         } else {
  785                                 time_adj += (time_adj >> 1) + (time_adj >> 6);
  786                                 time_adj += (time_adj >> 3) + (time_adj >> 10);
  787                         }
  788                         break;
  789                 }
  790 
  791 #ifdef EXT_CLOCK
  792                 /*
  793                  * If an external clock is present, it is necessary to
  794                  * discipline the kernel time variable anyway, since not
  795                  * all system components use the microtime() interface.
  796                  * Here, the time offset between the external clock and
  797                  * kernel time variable is computed every so often.
  798                  */
  799                 clock_count++;
  800                 if (clock_count > CLOCK_INTERVAL) {
  801                         clock_count = 0;
  802                         microtime(&clock_ext);
  803                         delta.tv_sec = clock_ext.tv_sec - time.tv_sec;
  804                         delta.tv_usec = clock_ext.tv_usec -
  805                             time.tv_usec;
  806                         if (delta.tv_usec < 0)
  807                                 delta.tv_sec--;
  808                         if (delta.tv_usec >= 500000) {
  809                                 delta.tv_usec -= 1000000;
  810                                 delta.tv_sec++;
  811                         }
  812                         if (delta.tv_usec < -500000) {
  813                                 delta.tv_usec += 1000000;
  814                                 delta.tv_sec--;
  815                         }
  816                         if (delta.tv_sec > 0 || (delta.tv_sec == 0 &&
  817                             delta.tv_usec > MAXPHASE) ||
  818                             delta.tv_sec < -1 || (delta.tv_sec == -1 &&
  819                             delta.tv_usec < -MAXPHASE)) {
  820                                 time = clock_ext;
  821                                 delta.tv_sec = 0;
  822                                 delta.tv_usec = 0;
  823                         }
  824 #ifdef HIGHBALL
  825                         clock_cpu = delta.tv_usec;
  826 #else /* HIGHBALL */
  827                         hardupdate(delta.tv_usec);
  828 #endif /* HIGHBALL */
  829                 }
  830 #endif /* EXT_CLOCK */
  831         }
  832 
  833 #endif /* NTP */
  834 
  835         /*
  836          * Update real-time timeout queue.
  837          * Process callouts at a very low CPU priority, so we don't keep the
  838          * relatively high clock interrupt priority any longer than necessary.
  839          */
  840         if (callout_hardclock()) {
  841                 if (CLKF_BASEPRI(frame)) {
  842                         /*
  843                          * Save the overhead of a software interrupt;
  844                          * it will happen as soon as we return, so do
  845                          * it now.
  846                          */
  847                         spllowersoftclock();
  848                         KERNEL_LOCK(LK_CANRECURSE|LK_EXCLUSIVE);
  849                         softclock(NULL);
  850                         KERNEL_UNLOCK();
  851                 } else {
  852 #ifdef __HAVE_GENERIC_SOFT_INTERRUPTS
  853                         softintr_schedule(softclock_si);
  854 #else
  855                         setsoftclock();
  856 #endif
  857                 }
  858         }
  859 }
  860 
  861 /*
  862  * Compute number of hz until specified time.  Used to compute second
  863  * argument to callout_reset() from an absolute time.
  864  */
  865 int
  866 hzto(struct timeval *tv)
  867 {
  868         unsigned long ticks;
  869         long sec, usec;
  870         int s;
  871 
  872         /*
  873          * If the number of usecs in the whole seconds part of the time
  874          * difference fits in a long, then the total number of usecs will
  875          * fit in an unsigned long.  Compute the total and convert it to
  876          * ticks, rounding up and adding 1 to allow for the current tick
  877          * to expire.  Rounding also depends on unsigned long arithmetic
  878          * to avoid overflow.
  879          *
  880          * Otherwise, if the number of ticks in the whole seconds part of
  881          * the time difference fits in a long, then convert the parts to
  882          * ticks separately and add, using similar rounding methods and
  883          * overflow avoidance.  This method would work in the previous
  884          * case, but it is slightly slower and assume that hz is integral.
  885          *
  886          * Otherwise, round the time difference down to the maximum
  887          * representable value.
  888          *
  889          * If ints are 32-bit, then the maximum value for any timeout in
  890          * 10ms ticks is 248 days.
  891          */
  892         s = splclock();
  893         sec = tv->tv_sec - time.tv_sec;
  894         usec = tv->tv_usec - time.tv_usec;
  895         splx(s);
  896 
  897         if (usec < 0) {
  898                 sec--;
  899                 usec += 1000000;
  900         }
  901 
  902         if (sec < 0 || (sec == 0 && usec <= 0)) {
  903                 /*
  904                  * Would expire now or in the past.  Return 0 ticks.
  905                  * This is different from the legacy hzto() interface,
  906                  * and callers need to check for it.
  907                  */
  908                 ticks = 0;
  909         } else if (sec <= (LONG_MAX / 1000000))
  910                 ticks = (((sec * 1000000) + (unsigned long)usec + (tick - 1))
  911                     / tick) + 1;
  912         else if (sec <= (LONG_MAX / hz))
  913                 ticks = (sec * hz) +
  914                     (((unsigned long)usec + (tick - 1)) / tick) + 1;
  915         else
  916                 ticks = LONG_MAX;
  917 
  918         if (ticks > INT_MAX)
  919                 ticks = INT_MAX;
  920 
  921         return ((int)ticks);
  922 }
  923 
  924 /*
  925  * Start profiling on a process.
  926  *
  927  * Kernel profiling passes proc0 which never exits and hence
  928  * keeps the profile clock running constantly.
  929  */
  930 void
  931 startprofclock(struct proc *p)
  932 {
  933 
  934         if ((p->p_flag & P_PROFIL) == 0) {
  935                 p->p_flag |= P_PROFIL;
  936                 /*
  937                  * This is only necessary if using the clock as the
  938                  * profiling source.
  939                  */
  940                 if (++profprocs == 1 && stathz != 0)
  941                         psdiv = psratio;
  942         }
  943 }
  944 
  945 /*
  946  * Stop profiling on a process.
  947  */
  948 void
  949 stopprofclock(struct proc *p)
  950 {
  951 
  952         if (p->p_flag & P_PROFIL) {
  953                 p->p_flag &= ~P_PROFIL;
  954                 /*
  955                  * This is only necessary if using the clock as the
  956                  * profiling source.
  957                  */
  958                 if (--profprocs == 0 && stathz != 0)
  959                         psdiv = 1;
  960         }
  961 }
  962 
  963 #if defined(PERFCTRS)
  964 /*
  965  * Independent profiling "tick" in case we're using a separate
  966  * clock or profiling event source.  Currently, that's just
  967  * performance counters--hence the wrapper.
  968  */
  969 void
  970 proftick(struct clockframe *frame)
  971 {
  972 #ifdef GPROF
  973         struct gmonparam *g;
  974         intptr_t i;
  975 #endif
  976         struct proc *p;
  977 
  978         p = curproc;
  979         if (CLKF_USERMODE(frame)) {
  980                 if (p->p_flag & P_PROFIL)
  981                         addupc_intr(p, CLKF_PC(frame));
  982         } else {
  983 #ifdef GPROF
  984                 g = &_gmonparam;
  985                 if (g->state == GMON_PROF_ON) {
  986                         i = CLKF_PC(frame) - g->lowpc;
  987                         if (i < g->textsize) {
  988                                 i /= HISTFRACTION * sizeof(*g->kcount);
  989                                 g->kcount[i]++;
  990                         }
  991                 }
  992 #endif
  993 #ifdef PROC_PC
  994                 if (p && p->p_flag & P_PROFIL)
  995                         addupc_intr(p, PROC_PC(p));
  996 #endif
  997         }
  998 }
  999 #endif
 1000 
 1001 /*
 1002  * Statistics clock.  Grab profile sample, and if divider reaches 0,
 1003  * do process and kernel statistics.
 1004  */
 1005 void
 1006 statclock(struct clockframe *frame)
 1007 {
 1008 #ifdef GPROF
 1009         struct gmonparam *g;
 1010         intptr_t i;
 1011 #endif
 1012         struct cpu_info *ci = curcpu();
 1013         struct schedstate_percpu *spc = &ci->ci_schedstate;
 1014         struct lwp *l;
 1015         struct proc *p;
 1016 
 1017         /*
 1018          * Notice changes in divisor frequency, and adjust clock
 1019          * frequency accordingly.
 1020          */
 1021         if (spc->spc_psdiv != psdiv) {
 1022                 spc->spc_psdiv = psdiv;
 1023                 spc->spc_pscnt = psdiv;
 1024                 if (psdiv == 1) {
 1025                         setstatclockrate(stathz);
 1026                 } else {
 1027                         setstatclockrate(profhz);
 1028                 }
 1029         }
 1030         l = curlwp;
 1031         p = (l ? l->l_proc : 0);
 1032         if (CLKF_USERMODE(frame)) {
 1033                 if (p->p_flag & P_PROFIL && profsrc == PROFSRC_CLOCK)
 1034                         addupc_intr(p, CLKF_PC(frame));
 1035                 if (--spc->spc_pscnt > 0)
 1036                         return;
 1037                 /*
 1038                  * Came from user mode; CPU was in user state.
 1039                  * If this process is being profiled record the tick.
 1040                  */
 1041                 p->p_uticks++;
 1042                 if (p->p_nice > NZERO)
 1043                         spc->spc_cp_time[CP_NICE]++;
 1044                 else
 1045                         spc->spc_cp_time[CP_USER]++;
 1046         } else {
 1047 #ifdef GPROF
 1048                 /*
 1049                  * Kernel statistics are just like addupc_intr, only easier.
 1050                  */
 1051                 g = &_gmonparam;
 1052                 if (profsrc == PROFSRC_CLOCK && g->state == GMON_PROF_ON) {
 1053                         i = CLKF_PC(frame) - g->lowpc;
 1054                         if (i < g->textsize) {
 1055                                 i /= HISTFRACTION * sizeof(*g->kcount);
 1056                                 g->kcount[i]++;
 1057                         }
 1058                 }
 1059 #endif
 1060 #ifdef LWP_PC
 1061                 if (p && profsrc == PROFSRC_CLOCK && p->p_flag & P_PROFIL)
 1062                         addupc_intr(p, LWP_PC(l));
 1063 #endif
 1064                 if (--spc->spc_pscnt > 0)
 1065                         return;
 1066                 /*
 1067                  * Came from kernel mode, so we were:
 1068                  * - handling an interrupt,
 1069                  * - doing syscall or trap work on behalf of the current
 1070                  *   user process, or
 1071                  * - spinning in the idle loop.
 1072                  * Whichever it is, charge the time as appropriate.
 1073                  * Note that we charge interrupts to the current process,
 1074                  * regardless of whether they are ``for'' that process,
 1075                  * so that we know how much of its real time was spent
 1076                  * in ``non-process'' (i.e., interrupt) work.
 1077                  */
 1078                 if (CLKF_INTR(frame)) {
 1079                         if (p != NULL)
 1080                                 p->p_iticks++;
 1081                         spc->spc_cp_time[CP_INTR]++;
 1082                 } else if (p != NULL) {
 1083                         p->p_sticks++;
 1084                         spc->spc_cp_time[CP_SYS]++;
 1085                 } else
 1086                         spc->spc_cp_time[CP_IDLE]++;
 1087         }
 1088         spc->spc_pscnt = psdiv;
 1089 
 1090         if (l != NULL) {
 1091                 ++p->p_cpticks;
 1092                 /*
 1093                  * If no separate schedclock is provided, call it here
 1094                  * at about 16 Hz.
 1095                  */
 1096                 if (schedhz == 0)
 1097                         if ((int)(--ci->ci_schedstate.spc_schedticks) <= 0) {
 1098                                 schedclock(l);
 1099                                 ci->ci_schedstate.spc_schedticks = statscheddiv;
 1100                         }
 1101         }
 1102 }
 1103 
 1104 
 1105 #ifdef NTP      /* NTP phase-locked loop in kernel */
 1106 
 1107 /*
 1108  * hardupdate() - local clock update
 1109  *
 1110  * This routine is called by ntp_adjtime() to update the local clock
 1111  * phase and frequency. The implementation is of an adaptive-parameter,
 1112  * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
 1113  * time and frequency offset estimates for each call. If the kernel PPS
 1114  * discipline code is configured (PPS_SYNC), the PPS signal itself
 1115  * determines the new time offset, instead of the calling argument.
 1116  * Presumably, calls to ntp_adjtime() occur only when the caller
 1117  * believes the local clock is valid within some bound (+-128 ms with
 1118  * NTP). If the caller's time is far different than the PPS time, an
 1119  * argument will ensue, and it's not clear who will lose.
 1120  *
 1121  * For uncompensated quartz crystal oscillatores and nominal update
 1122  * intervals less than 1024 s, operation should be in phase-lock mode
 1123  * (STA_FLL = 0), where the loop is disciplined to phase. For update
 1124  * intervals greater than thiss, operation should be in frequency-lock
 1125  * mode (STA_FLL = 1), where the loop is disciplined to frequency.
 1126  *
 1127  * Note: splclock() is in effect.
 1128  */
 1129 void
 1130 hardupdate(long offset)
 1131 {
 1132         long ltemp, mtemp;
 1133 
 1134         if (!(time_status & STA_PLL) && !(time_status & STA_PPSTIME))
 1135                 return;
 1136         ltemp = offset;
 1137 #ifdef PPS_SYNC
 1138         if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)
 1139                 ltemp = pps_offset;
 1140 #endif /* PPS_SYNC */
 1141 
 1142         /*
 1143          * Scale the phase adjustment and clamp to the operating range.
 1144          */
 1145         if (ltemp > MAXPHASE)
 1146                 time_offset = MAXPHASE << SHIFT_UPDATE;
 1147         else if (ltemp < -MAXPHASE)
 1148                 time_offset = -(MAXPHASE << SHIFT_UPDATE);
 1149         else
 1150                 time_offset = ltemp << SHIFT_UPDATE;
 1151 
 1152         /*
 1153          * Select whether the frequency is to be controlled and in which
 1154          * mode (PLL or FLL). Clamp to the operating range. Ugly
 1155          * multiply/divide should be replaced someday.
 1156          */
 1157         if (time_status & STA_FREQHOLD || time_reftime == 0)
 1158                 time_reftime = time.tv_sec;
 1159         mtemp = time.tv_sec - time_reftime;
 1160         time_reftime = time.tv_sec;
 1161         if (time_status & STA_FLL) {
 1162                 if (mtemp >= MINSEC) {
 1163                         ltemp = ((time_offset / mtemp) << (SHIFT_USEC -
 1164                             SHIFT_UPDATE));
 1165                         if (ltemp < 0)
 1166                                 time_freq -= -ltemp >> SHIFT_KH;
 1167                         else
 1168                                 time_freq += ltemp >> SHIFT_KH;
 1169                 }
 1170         } else {
 1171                 if (mtemp < MAXSEC) {
 1172                         ltemp *= mtemp;
 1173                         if (ltemp < 0)
 1174                                 time_freq -= -ltemp >> (time_constant +
 1175                                     time_constant + SHIFT_KF -
 1176                                     SHIFT_USEC);
 1177                         else
 1178                                 time_freq += ltemp >> (time_constant +
 1179                                     time_constant + SHIFT_KF -
 1180                                     SHIFT_USEC);
 1181                 }
 1182         }
 1183         if (time_freq > time_tolerance)
 1184                 time_freq = time_tolerance;
 1185         else if (time_freq < -time_tolerance)
 1186                 time_freq = -time_tolerance;
 1187 }
 1188 
 1189 #ifdef PPS_SYNC
 1190 /*
 1191  * hardpps() - discipline CPU clock oscillator to external PPS signal
 1192  *
 1193  * This routine is called at each PPS interrupt in order to discipline
 1194  * the CPU clock oscillator to the PPS signal. It measures the PPS phase
 1195  * and leaves it in a handy spot for the hardclock() routine. It
 1196  * integrates successive PPS phase differences and calculates the
 1197  * frequency offset. This is used in hardclock() to discipline the CPU
 1198  * clock oscillator so that intrinsic frequency error is cancelled out.
 1199  * The code requires the caller to capture the time and hardware counter
 1200  * value at the on-time PPS signal transition.
 1201  *
 1202  * Note that, on some Unix systems, this routine runs at an interrupt
 1203  * priority level higher than the timer interrupt routine hardclock().
 1204  * Therefore, the variables used are distinct from the hardclock()
 1205  * variables, except for certain exceptions: The PPS frequency pps_freq
 1206  * and phase pps_offset variables are determined by this routine and
 1207  * updated atomically. The time_tolerance variable can be considered a
 1208  * constant, since it is infrequently changed, and then only when the
 1209  * PPS signal is disabled. The watchdog counter pps_valid is updated
 1210  * once per second by hardclock() and is atomically cleared in this
 1211  * routine.
 1212  */
 1213 void
 1214 hardpps(struct timeval *tvp,            /* time at PPS */
 1215         long usec                       /* hardware counter at PPS */)
 1216 {
 1217         long u_usec, v_usec, bigtick;
 1218         long cal_sec, cal_usec;
 1219 
 1220         /*
 1221          * An occasional glitch can be produced when the PPS interrupt
 1222          * occurs in the hardclock() routine before the time variable is
 1223          * updated. Here the offset is discarded when the difference
 1224          * between it and the last one is greater than tick/2, but not
 1225          * if the interval since the first discard exceeds 30 s.
 1226          */
 1227         time_status |= STA_PPSSIGNAL;
 1228         time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
 1229         pps_valid = 0;
 1230         u_usec = -tvp->tv_usec;
 1231         if (u_usec < -500000)
 1232                 u_usec += 1000000;
 1233         v_usec = pps_offset - u_usec;
 1234         if (v_usec < 0)
 1235                 v_usec = -v_usec;
 1236         if (v_usec > (tick >> 1)) {
 1237                 if (pps_glitch > MAXGLITCH) {
 1238                         pps_glitch = 0;
 1239                         pps_tf[2] = u_usec;
 1240                         pps_tf[1] = u_usec;
 1241                 } else {
 1242                         pps_glitch++;
 1243                         u_usec = pps_offset;
 1244                 }
 1245         } else
 1246                 pps_glitch = 0;
 1247 
 1248         /*
 1249          * A three-stage median filter is used to help deglitch the pps
 1250          * time. The median sample becomes the time offset estimate; the
 1251          * difference between the other two samples becomes the time
 1252          * dispersion (jitter) estimate.
 1253          */
 1254         pps_tf[2] = pps_tf[1];
 1255         pps_tf[1] = pps_tf[0];
 1256         pps_tf[0] = u_usec;
 1257         if (pps_tf[0] > pps_tf[1]) {
 1258                 if (pps_tf[1] > pps_tf[2]) {
 1259                         pps_offset = pps_tf[1];         /* 0 1 2 */
 1260                         v_usec = pps_tf[0] - pps_tf[2];
 1261                 } else if (pps_tf[2] > pps_tf[0]) {
 1262                         pps_offset = pps_tf[0];         /* 2 0 1 */
 1263                         v_usec = pps_tf[2] - pps_tf[1];
 1264                 } else {
 1265                         pps_offset = pps_tf[2];         /* 0 2 1 */
 1266                         v_usec = pps_tf[0] - pps_tf[1];
 1267                 }
 1268         } else {
 1269                 if (pps_tf[1] < pps_tf[2]) {
 1270                         pps_offset = pps_tf[1];         /* 2 1 0 */
 1271                         v_usec = pps_tf[2] - pps_tf[0];
 1272                 } else  if (pps_tf[2] < pps_tf[0]) {
 1273                         pps_offset = pps_tf[0];         /* 1 0 2 */
 1274                         v_usec = pps_tf[1] - pps_tf[2];
 1275                 } else {
 1276                         pps_offset = pps_tf[2];         /* 1 2 0 */
 1277                         v_usec = pps_tf[1] - pps_tf[0];
 1278                 }
 1279         }
 1280         if (v_usec > MAXTIME)
 1281                 pps_jitcnt++;
 1282         v_usec = (v_usec << PPS_AVG) - pps_jitter;
 1283         if (v_usec < 0)
 1284                 pps_jitter -= -v_usec >> PPS_AVG;
 1285         else
 1286                 pps_jitter += v_usec >> PPS_AVG;
 1287         if (pps_jitter > (MAXTIME >> 1))
 1288                 time_status |= STA_PPSJITTER;
 1289 
 1290         /*
 1291          * During the calibration interval adjust the starting time when
 1292          * the tick overflows. At the end of the interval compute the
 1293          * duration of the interval and the difference of the hardware
 1294          * counters at the beginning and end of the interval. This code
 1295          * is deliciously complicated by the fact valid differences may
 1296          * exceed the value of tick when using long calibration
 1297          * intervals and small ticks. Note that the counter can be
 1298          * greater than tick if caught at just the wrong instant, but
 1299          * the values returned and used here are correct.
 1300          */
 1301         bigtick = (long)tick << SHIFT_USEC;
 1302         pps_usec -= pps_freq;
 1303         if (pps_usec >= bigtick)
 1304                 pps_usec -= bigtick;
 1305         if (pps_usec < 0)
 1306                 pps_usec += bigtick;
 1307         pps_time.tv_sec++;
 1308         pps_count++;
 1309         if (pps_count < (1 << pps_shift))
 1310                 return;
 1311         pps_count = 0;
 1312         pps_calcnt++;
 1313         u_usec = usec << SHIFT_USEC;
 1314         v_usec = pps_usec - u_usec;
 1315         if (v_usec >= bigtick >> 1)
 1316                 v_usec -= bigtick;
 1317         if (v_usec < -(bigtick >> 1))
 1318                 v_usec += bigtick;
 1319         if (v_usec < 0)
 1320                 v_usec = -(-v_usec >> pps_shift);
 1321         else
 1322                 v_usec = v_usec >> pps_shift;
 1323         pps_usec = u_usec;
 1324         cal_sec = tvp->tv_sec;
 1325         cal_usec = tvp->tv_usec;
 1326         cal_sec -= pps_time.tv_sec;
 1327         cal_usec -= pps_time.tv_usec;
 1328         if (cal_usec < 0) {
 1329                 cal_usec += 1000000;
 1330                 cal_sec--;
 1331         }
 1332         pps_time = *tvp;
 1333 
 1334         /*
 1335          * Check for lost interrupts, noise, excessive jitter and
 1336          * excessive frequency error. The number of timer ticks during
 1337          * the interval may vary +-1 tick. Add to this a margin of one
 1338          * tick for the PPS signal jitter and maximum frequency
 1339          * deviation. If the limits are exceeded, the calibration
 1340          * interval is reset to the minimum and we start over.
 1341          */
 1342         u_usec = (long)tick << 1;
 1343         if (!((cal_sec == -1 && cal_usec > (1000000 - u_usec))
 1344             || (cal_sec == 0 && cal_usec < u_usec))
 1345             || v_usec > time_tolerance || v_usec < -time_tolerance) {
 1346                 pps_errcnt++;
 1347                 pps_shift = PPS_SHIFT;
 1348                 pps_intcnt = 0;
 1349                 time_status |= STA_PPSERROR;
 1350                 return;
 1351         }
 1352 
 1353         /*
 1354          * A three-stage median filter is used to help deglitch the pps
 1355          * frequency. The median sample becomes the frequency offset
 1356          * estimate; the difference between the other two samples
 1357          * becomes the frequency dispersion (stability) estimate.
 1358          */
 1359         pps_ff[2] = pps_ff[1];
 1360         pps_ff[1] = pps_ff[0];
 1361         pps_ff[0] = v_usec;
 1362         if (pps_ff[0] > pps_ff[1]) {
 1363                 if (pps_ff[1] > pps_ff[2]) {
 1364                         u_usec = pps_ff[1];             /* 0 1 2 */
 1365                         v_usec = pps_ff[0] - pps_ff[2];
 1366                 } else if (pps_ff[2] > pps_ff[0]) {
 1367                         u_usec = pps_ff[0];             /* 2 0 1 */
 1368                         v_usec = pps_ff[2] - pps_ff[1];
 1369                 } else {
 1370                         u_usec = pps_ff[2];             /* 0 2 1 */
 1371                         v_usec = pps_ff[0] - pps_ff[1];
 1372                 }
 1373         } else {
 1374                 if (pps_ff[1] < pps_ff[2]) {
 1375                         u_usec = pps_ff[1];             /* 2 1 0 */
 1376                         v_usec = pps_ff[2] - pps_ff[0];
 1377                 } else  if (pps_ff[2] < pps_ff[0]) {
 1378                         u_usec = pps_ff[0];             /* 1 0 2 */
 1379                         v_usec = pps_ff[1] - pps_ff[2];
 1380                 } else {
 1381                         u_usec = pps_ff[2];             /* 1 2 0 */
 1382                         v_usec = pps_ff[1] - pps_ff[0];
 1383                 }
 1384         }
 1385 
 1386         /*
 1387          * Here the frequency dispersion (stability) is updated. If it
 1388          * is less than one-fourth the maximum (MAXFREQ), the frequency
 1389          * offset is updated as well, but clamped to the tolerance. It
 1390          * will be processed later by the hardclock() routine.
 1391          */
 1392         v_usec = (v_usec >> 1) - pps_stabil;
 1393         if (v_usec < 0)
 1394                 pps_stabil -= -v_usec >> PPS_AVG;
 1395         else
 1396                 pps_stabil += v_usec >> PPS_AVG;
 1397         if (pps_stabil > MAXFREQ >> 2) {
 1398                 pps_stbcnt++;
 1399                 time_status |= STA_PPSWANDER;
 1400                 return;
 1401         }
 1402         if (time_status & STA_PPSFREQ) {
 1403                 if (u_usec < 0) {
 1404                         pps_freq -= -u_usec >> PPS_AVG;
 1405                         if (pps_freq < -time_tolerance)
 1406                                 pps_freq = -time_tolerance;
 1407                         u_usec = -u_usec;
 1408                 } else {
 1409                         pps_freq += u_usec >> PPS_AVG;
 1410                         if (pps_freq > time_tolerance)
 1411                                 pps_freq = time_tolerance;
 1412                 }
 1413         }
 1414 
 1415         /*
 1416          * Here the calibration interval is adjusted. If the maximum
 1417          * time difference is greater than tick / 4, reduce the interval
 1418          * by half. If this is not the case for four consecutive
 1419          * intervals, double the interval.
 1420          */
 1421         if (u_usec << pps_shift > bigtick >> 2) {
 1422                 pps_intcnt = 0;
 1423                 if (pps_shift > PPS_SHIFT)
 1424                         pps_shift--;
 1425         } else if (pps_intcnt >= 4) {
 1426                 pps_intcnt = 0;
 1427                 if (pps_shift < PPS_SHIFTMAX)
 1428                         pps_shift++;
 1429         } else
 1430                 pps_intcnt++;
 1431 }
 1432 #endif /* PPS_SYNC */
 1433 #endif /* NTP  */

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