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

     /*-
      * Copyright (c) 1997, 1998 Poul-Henning Kamp <phk@FreeBSD.org>
      * Copyright (c) 1982, 1986, 1991, 1993
      *      The Regents of the University of California.  All rights reserved.
      * (c) UNIX System Laboratories, Inc.
      * All or some portions of this file are derived from material licensed
      * to the University of California by American Telephone and Telegraph
      * Co. or Unix System Laboratories, Inc. and are reproduced herein with
      * the permission of UNIX System Laboratories, Inc.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by the University of
     *      California, Berkeley and its contributors.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)kern_clock.c        8.5 (Berkeley) 1/21/94
     * $FreeBSD$
     */
    
    #include "opt_ntp.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/dkstat.h>
    #include <sys/callout.h>
    #include <sys/kernel.h>
    #include <sys/proc.h>
    #include <sys/malloc.h>
    #include <sys/resourcevar.h>
    #include <sys/signalvar.h>
    #include <sys/timex.h>
    #include <sys/timepps.h>
    #include <vm/vm.h>
    #include <sys/lock.h>
    #include <vm/pmap.h>
    #include <vm/vm_map.h>
    #include <sys/sysctl.h>
    
    #include <machine/cpu.h>
    #include <machine/limits.h>
    
    #ifdef GPROF
    #include <sys/gmon.h>
    #endif
    
    #if defined(SMP) && defined(BETTER_CLOCK)
    #include <machine/smp.h>
    #endif
    
    /*
     * Number of timecounters used to implement stable storage
     */
    #ifndef NTIMECOUNTER
    #define NTIMECOUNTER    5
    #endif
    
    static MALLOC_DEFINE(M_TIMECOUNTER, "timecounter", 
            "Timecounter stable storage");
    
    static void initclocks __P((void *dummy));
    SYSINIT(clocks, SI_SUB_CLOCKS, SI_ORDER_FIRST, initclocks, NULL)
    
    static void tco_forward __P((int force));
    static void tco_setscales __P((struct timecounter *tc));
    static __inline unsigned tco_delta __P((struct timecounter *tc));
    
    /* Some of these don't belong here, but it's easiest to concentrate them. */
    #if defined(SMP) && defined(BETTER_CLOCK)
    long cp_time[CPUSTATES];
    #else
    static long cp_time[CPUSTATES];
    #endif
    
    long tk_cancc;
    long tk_nin;
    long tk_nout;
   long tk_rawcc;
   
   time_t time_second;
   
   /*
    * Which update policy to use.
    *   0 - every tick, bad hardware may fail with "calcru negative..."
    *   1 - more resistent to the above hardware, but less efficient.
    */
   static int tco_method;
   
   /*
    * Implement a dummy timecounter which we can use until we get a real one
    * in the air.  This allows the console and other early stuff to use
    * timeservices.
    */
   
   static unsigned 
   dummy_get_timecount(struct timecounter *tc)
   {
           static unsigned now;
           return (++now);
   }
   
   static struct timecounter dummy_timecounter = {
           dummy_get_timecount,
           0,
           ~0u,
           1000000,
           "dummy"
   };
   
   struct timecounter *timecounter = &dummy_timecounter;
   
   /*
    * Clock handling routines.
    *
    * This code is written to operate with two timers that run independently of
    * each other.
    *
    * The main timer, running hz times per second, is used to trigger interval
    * timers, timeouts and rescheduling as needed.
    *
    * The second timer handles kernel and user profiling,
    * and does resource use estimation.  If the second timer is programmable,
    * it is randomized to avoid aliasing between the two clocks.  For example,
    * the randomization prevents an adversary from always giving up the cpu
    * just before its quantum expires.  Otherwise, it would never accumulate
    * cpu ticks.  The mean frequency of the second timer is stathz.
    *
    * If no second timer exists, stathz will be zero; in this case we drive
    * profiling and statistics off the main clock.  This WILL NOT be accurate;
    * do not do it unless absolutely necessary.
    *
    * The statistics clock may (or may not) be run at a higher rate while
    * profiling.  This profile clock runs at profhz.  We require that profhz
    * be an integral multiple of stathz.
    *
    * If the statistics clock is running fast, it must be divided by the ratio
    * profhz/stathz for statistics.  (For profiling, every tick counts.)
    *
    * Time-of-day is maintained using a "timecounter", which may or may
    * not be related to the hardware generating the above mentioned
    * interrupts.
    */
   
   int     stathz;
   int     profhz;
   static int profprocs;
   int     ticks;
   static int psdiv, pscnt;                /* prof => stat divider */
   int     psratio;                        /* ratio: prof / stat */
   
   /*
    * Initialize clock frequencies and start both clocks running.
    */
   /* ARGSUSED*/
   static void
   initclocks(dummy)
           void *dummy;
   {
           register int i;
   
           /*
            * Set divisors to 1 (normal case) and let the machine-specific
            * code do its bit.
            */
           psdiv = pscnt = 1;
           cpu_initclocks();
   
           /*
            * Compute profhz/stathz, and fix profhz if needed.
            */
           i = stathz ? stathz : hz;
           if (profhz == 0)
                   profhz = i;
           psratio = profhz / i;
   }
   
   /*
    * The real-time timer, interrupting hz times per second.
    */
   void
   hardclock(frame)
           register struct clockframe *frame;
   {
           register struct proc *p;
   
           p = curproc;
           if (p) {
                   register struct pstats *pstats;
   
                   /*
                    * Run current process's virtual and profile time, as needed.
                    */
                   pstats = p->p_stats;
                   if (CLKF_USERMODE(frame) &&
                       timevalisset(&pstats->p_timer[ITIMER_VIRTUAL].it_value) &&
                       itimerdecr(&pstats->p_timer[ITIMER_VIRTUAL], tick) == 0)
                           psignal(p, SIGVTALRM);
                   if (timevalisset(&pstats->p_timer[ITIMER_PROF].it_value) &&
                       itimerdecr(&pstats->p_timer[ITIMER_PROF], tick) == 0)
                           psignal(p, SIGPROF);
           }
   
   #if defined(SMP) && defined(BETTER_CLOCK)
           forward_hardclock(pscnt);
   #endif
   
           /*
            * If no separate statistics clock is available, run it from here.
            */
           if (stathz == 0)
                   statclock(frame);
   
           tco_forward(0);
           ticks++;
   
           /*
            * Process callouts at a very low cpu priority, so we don't keep the
            * relatively high clock interrupt priority any longer than necessary.
            */
           if (TAILQ_FIRST(&callwheel[ticks & callwheelmask]) != NULL) {
                   if (CLKF_BASEPRI(frame)) {
                           /*
                            * Save the overhead of a software interrupt;
                            * it will happen as soon as we return, so do it now.
                            */
                           (void)splsoftclock();
                           softclock();
                   } else
                           setsoftclock();
           } else if (softticks + 1 == ticks)
                   ++softticks;
   }
   
   /*
    * Compute number of ticks in the specified amount of time.
    */
   int
   tvtohz(tv)
           struct timeval *tv;
   {
           register unsigned long ticks;
           register long sec, usec;
   
           /*
            * If the number of usecs in the whole seconds part of the time
            * difference fits in a long, then the total number of usecs will
            * fit in an unsigned long.  Compute the total and convert it to
            * ticks, rounding up and adding 1 to allow for the current tick
            * to expire.  Rounding also depends on unsigned long arithmetic
            * to avoid overflow.
            *
            * Otherwise, if the number of ticks in the whole seconds part of
            * the time difference fits in a long, then convert the parts to
            * ticks separately and add, using similar rounding methods and
            * overflow avoidance.  This method would work in the previous
            * case but it is slightly slower and assumes that hz is integral.
            *
            * Otherwise, round the time difference down to the maximum
            * representable value.
            *
            * If ints have 32 bits, then the maximum value for any timeout in
            * 10ms ticks is 248 days.
            */
           sec = tv->tv_sec;
           usec = tv->tv_usec;
           if (usec < 0) {
                   sec--;
                   usec += 1000000;
           }
           if (sec < 0) {
   #ifdef DIAGNOSTIC
                   if (usec > 0) {
                           sec++;
                           usec -= 1000000;
                   }
                   printf("tvotohz: negative time difference %ld sec %ld usec\n",
                          sec, usec);
   #endif
                   ticks = 1;
           } else if (sec <= LONG_MAX / 1000000)
                   ticks = (sec * 1000000 + (unsigned long)usec + (tick - 1))
                           / tick + 1;
           else if (sec <= LONG_MAX / hz)
                   ticks = sec * hz
                           + ((unsigned long)usec + (tick - 1)) / tick + 1;
           else
                   ticks = LONG_MAX;
           if (ticks > INT_MAX)
                   ticks = INT_MAX;
           return ((int)ticks);
   }
   
   /*
    * Start profiling on a process.
    *
    * Kernel profiling passes proc0 which never exits and hence
    * keeps the profile clock running constantly.
    */
   void
   startprofclock(p)
           register struct proc *p;
   {
           int s;
   
           if ((p->p_flag & P_PROFIL) == 0) {
                   p->p_flag |= P_PROFIL;
                   if (++profprocs == 1 && stathz != 0) {
                           s = splstatclock();
                           psdiv = pscnt = psratio;
                           setstatclockrate(profhz);
                           splx(s);
                   }
           }
   }
   
   /*
    * Stop profiling on a process.
    */
   void
   stopprofclock(p)
           register struct proc *p;
   {
           int s;
   
           if (p->p_flag & P_PROFIL) {
                   p->p_flag &= ~P_PROFIL;
                   if (--profprocs == 0 && stathz != 0) {
                           s = splstatclock();
                           psdiv = pscnt = 1;
                           setstatclockrate(stathz);
                           splx(s);
                   }
           }
   }
   
   /*
    * Statistics clock.  Grab profile sample, and if divider reaches 0,
    * do process and kernel statistics.
    */
   void
   statclock(frame)
           register struct clockframe *frame;
   {
   #ifdef GPROF
           register struct gmonparam *g;
           int i;
   #endif
           register struct proc *p;
           struct pstats *pstats;
           long rss;
           struct rusage *ru;
           struct vmspace *vm;
   
           if (curproc != NULL && CLKF_USERMODE(frame)) {
                   p = curproc;
                   if (p->p_flag & P_PROFIL)
                           addupc_intr(p, CLKF_PC(frame), 1);
   #if defined(SMP) && defined(BETTER_CLOCK)
                   if (stathz != 0)
                           forward_statclock(pscnt);
   #endif
                   if (--pscnt > 0)
                           return;
                   /*
                    * Came from user mode; CPU was in user state.
                    * If this process is being profiled record the tick.
                    */
                   p->p_uticks++;
                   if (p->p_nice > NZERO)
                           cp_time[CP_NICE]++;
                   else
                           cp_time[CP_USER]++;
           } else {
   #ifdef GPROF
                   /*
                    * Kernel statistics are just like addupc_intr, only easier.
                    */
                   g = &_gmonparam;
                   if (g->state == GMON_PROF_ON) {
                           i = CLKF_PC(frame) - g->lowpc;
                           if (i < g->textsize) {
                                   i /= HISTFRACTION * sizeof(*g->kcount);
                                   g->kcount[i]++;
                           }
                   }
   #endif
   #if defined(SMP) && defined(BETTER_CLOCK)
                   if (stathz != 0)
                           forward_statclock(pscnt);
   #endif
                   if (--pscnt > 0)
                           return;
                   /*
                    * Came from kernel mode, so we were:
                    * - handling an interrupt,
                    * - doing syscall or trap work on behalf of the current
                    *   user process, or
                    * - spinning in the idle loop.
                    * Whichever it is, charge the time as appropriate.
                    * Note that we charge interrupts to the current process,
                    * regardless of whether they are ``for'' that process,
                    * so that we know how much of its real time was spent
                    * in ``non-process'' (i.e., interrupt) work.
                    */
                   p = curproc;
                   if (CLKF_INTR(frame)) {
                           if (p != NULL)
                                   p->p_iticks++;
                           cp_time[CP_INTR]++;
                   } else if (p != NULL) {
                           p->p_sticks++;
                           cp_time[CP_SYS]++;
                   } else
                           cp_time[CP_IDLE]++;
           }
           pscnt = psdiv;
   
           /*
            * We maintain statistics shown by user-level statistics
            * programs:  the amount of time in each cpu state.
            */
   
           /*
            * We adjust the priority of the current process.  The priority of
            * a process gets worse as it accumulates CPU time.  The cpu usage
            * estimator (p_estcpu) is increased here.  The formula for computing
            * priorities (in kern_synch.c) will compute a different value each
            * time p_estcpu increases by 4.  The cpu usage estimator ramps up
            * quite quickly when the process is running (linearly), and decays
            * away exponentially, at a rate which is proportionally slower when
            * the system is busy.  The basic principal is that the system will
            * 90% forget that the process used a lot of CPU time in 5 * loadav
            * seconds.  This causes the system to favor processes which haven't
            * run much recently, and to round-robin among other processes.
            */
           if (p != NULL) {
                   p->p_cpticks++;
                   if (++p->p_estcpu == 0)
                           p->p_estcpu--;
                   if ((p->p_estcpu & 3) == 0) {
                           resetpriority(p);
                           if (p->p_priority >= PUSER)
                                   p->p_priority = p->p_usrpri;
                   }
   
                   /* Update resource usage integrals and maximums. */
                   if ((pstats = p->p_stats) != NULL &&
                       (ru = &pstats->p_ru) != NULL &&
                       (vm = p->p_vmspace) != NULL) {
                           ru->ru_ixrss += vm->vm_tsize * PAGE_SIZE / 1024;
                           ru->ru_idrss += vm->vm_dsize * PAGE_SIZE / 1024;
                           ru->ru_isrss += vm->vm_ssize * PAGE_SIZE / 1024;
                           rss = vm->vm_pmap.pm_stats.resident_count *
                                 PAGE_SIZE / 1024;
                           if (ru->ru_maxrss < rss)
                                   ru->ru_maxrss = rss;
                   }
           }
   }
   
   /*
    * Return information about system clocks.
    */
   static int
   sysctl_kern_clockrate SYSCTL_HANDLER_ARGS
   {
           struct clockinfo clkinfo;
           /*
            * Construct clockinfo structure.
            */
           clkinfo.hz = hz;
           clkinfo.tick = tick;
           clkinfo.tickadj = tickadj;
           clkinfo.profhz = profhz;
           clkinfo.stathz = stathz ? stathz : hz;
           return (sysctl_handle_opaque(oidp, &clkinfo, sizeof clkinfo, req));
   }
   
   SYSCTL_PROC(_kern, KERN_CLOCKRATE, clockrate, CTLTYPE_STRUCT|CTLFLAG_RD,
           0, 0, sysctl_kern_clockrate, "S,clockinfo","");
   
   static __inline unsigned
   tco_delta(struct timecounter *tc)
   {
   
           return ((tc->tc_get_timecount(tc) - tc->tc_offset_count) & 
               tc->tc_counter_mask);
   }
   
   /*
    * We have eight functions for looking at the clock, four for
    * microseconds and four for nanoseconds.  For each there is fast
    * but less precise version "get{nano|micro}[up]time" which will
    * return a time which is up to 1/HZ previous to the call, whereas
    * the raw version "{nano|micro}[up]time" will return a timestamp
    * which is as precise as possible.  The "up" variants return the
    * time relative to system boot, these are well suited for time
    * interval measurements.
    */
   
   void
   getmicrotime(struct timeval *tvp)
   {
           struct timecounter *tc;
   
           if (!tco_method) {
                   tc = timecounter;
                   *tvp = tc->tc_microtime;
           } else {
                   microtime(tvp);
           }
   }
   
   void
   getnanotime(struct timespec *tsp)
   {
           struct timecounter *tc;
   
           if (!tco_method) {
                   tc = timecounter;
                   *tsp = tc->tc_nanotime;
           } else {
                   nanotime(tsp);
           }
   }
   
   void
   microtime(struct timeval *tv)
   {
           struct timecounter *tc;
   
           tc = (struct timecounter *)timecounter;
           tv->tv_sec = tc->tc_offset_sec;
           tv->tv_usec = tc->tc_offset_micro;
           tv->tv_usec += ((u_int64_t)tco_delta(tc) * tc->tc_scale_micro) >> 32;
           tv->tv_usec += boottime.tv_usec;
           tv->tv_sec += boottime.tv_sec;
           while (tv->tv_usec >= 1000000) {
                   tv->tv_usec -= 1000000;
                   tv->tv_sec++;
           }
   }
   
   void
   nanotime(struct timespec *ts)
   {
           unsigned count;
           u_int64_t delta;
           struct timecounter *tc;
   
           tc = (struct timecounter *)timecounter;
           ts->tv_sec = tc->tc_offset_sec;
           count = tco_delta(tc);
           delta = tc->tc_offset_nano;
           delta += ((u_int64_t)count * tc->tc_scale_nano_f);
           delta >>= 32;
           delta += ((u_int64_t)count * tc->tc_scale_nano_i);
           delta += boottime.tv_usec * 1000;
           ts->tv_sec += boottime.tv_sec;
           while (delta >= 1000000000) {
                   delta -= 1000000000;
                   ts->tv_sec++;
           }
           ts->tv_nsec = delta;
   }
   
   void
   getmicrouptime(struct timeval *tvp)
   {
           struct timecounter *tc;
   
           if (!tco_method) {
                   tc = timecounter;
                   tvp->tv_sec = tc->tc_offset_sec;
                   tvp->tv_usec = tc->tc_offset_micro;
           } else {
                   microuptime(tvp);
           }
   }
   
   void
   getnanouptime(struct timespec *tsp)
   {
           struct timecounter *tc;
   
           if (!tco_method) {
                   tc = timecounter;
                   tsp->tv_sec = tc->tc_offset_sec;
                   tsp->tv_nsec = tc->tc_offset_nano >> 32;
           } else {
                   nanouptime(tsp);
           }
   }
   
   void
   microuptime(struct timeval *tv)
   {
           struct timecounter *tc;
   
           tc = (struct timecounter *)timecounter;
           tv->tv_sec = tc->tc_offset_sec;
           tv->tv_usec = tc->tc_offset_micro;
           tv->tv_usec += ((u_int64_t)tco_delta(tc) * tc->tc_scale_micro) >> 32;
           if (tv->tv_usec >= 1000000) {
                   tv->tv_usec -= 1000000;
                   tv->tv_sec++;
           }
   }
   
   void
   nanouptime(struct timespec *ts)
   {
           unsigned count;
           u_int64_t delta;
           struct timecounter *tc;
   
           tc = (struct timecounter *)timecounter;
           ts->tv_sec = tc->tc_offset_sec;
           count = tco_delta(tc);
           delta = tc->tc_offset_nano;
           delta += ((u_int64_t)count * tc->tc_scale_nano_f);
           delta >>= 32;
           delta += ((u_int64_t)count * tc->tc_scale_nano_i);
           if (delta >= 1000000000) {
                   delta -= 1000000000;
                   ts->tv_sec++;
           }
           ts->tv_nsec = delta;
   }
   
   static void
   tco_setscales(struct timecounter *tc)
   {
           u_int64_t scale;
   
           scale = 1000000000LL << 32;
           scale += tc->tc_adjustment;
           scale /= tc->tc_tweak->tc_frequency;
           tc->tc_scale_micro = scale / 1000;
           tc->tc_scale_nano_f = scale & 0xffffffff;
           tc->tc_scale_nano_i = scale >> 32;
   }
   
   void
   update_timecounter(struct timecounter *tc)
   {
           tco_setscales(tc);
   }
   
   void
   init_timecounter(struct timecounter *tc)
   {
           struct timespec ts1;
           struct timecounter *t1, *t2, *t3;
           int i;
   
           tc->tc_adjustment = 0;
           tc->tc_tweak = tc;
           tco_setscales(tc);
           tc->tc_offset_count = tc->tc_get_timecount(tc);
           MALLOC(t1, struct timecounter *, sizeof *t1, M_TIMECOUNTER, M_WAITOK);
           *t1 = *tc;
           t2 = t1;
           for (i = 1; i < NTIMECOUNTER; i++) {
                   MALLOC(t3, struct timecounter *, sizeof *t3,
                       M_TIMECOUNTER, M_WAITOK);
                   *t3 = *tc;
                   t3->tc_other = t2;
                   t2 = t3;
           }
           t1->tc_other = t3;
           tc = t1;
   
           printf("Timecounter \"%s\"  frequency %lu Hz\n", 
               tc->tc_name, (u_long)tc->tc_frequency);
   
           /* XXX: For now always start using the counter. */
           tc->tc_offset_count = tc->tc_get_timecount(tc);
           nanouptime(&ts1);
           tc->tc_offset_nano = (u_int64_t)ts1.tv_nsec << 32;
           tc->tc_offset_micro = ts1.tv_nsec / 1000;
           tc->tc_offset_sec = ts1.tv_sec;
           timecounter = tc;
   }
   
   void
   set_timecounter(struct timespec *ts)
   {
           struct timespec ts2;
   
           nanouptime(&ts2);
           boottime.tv_sec = ts->tv_sec - ts2.tv_sec;
           boottime.tv_usec = (ts->tv_nsec - ts2.tv_nsec) / 1000;
           if (boottime.tv_usec < 0) {
                   boottime.tv_usec += 1000000;
                   boottime.tv_sec--;
           }
           /* fiddle all the little crinkly bits around the fiords... */
           tco_forward(1);
   }
   
   
   #if 0 /* Currently unused */
   void
   switch_timecounter(struct timecounter *newtc)
   {
           int s;
           struct timecounter *tc;
           struct timespec ts;
   
           s = splclock();
           tc = timecounter;
           if (newtc == tc || newtc == tc->tc_other) {
                   splx(s);
                   return;
           }
           nanouptime(&ts);
           newtc->tc_offset_sec = ts.tv_sec;
           newtc->tc_offset_nano = (u_int64_t)ts.tv_nsec << 32;
           newtc->tc_offset_micro = ts.tv_nsec / 1000;
           newtc->tc_offset_count = newtc->tc_get_timecount(newtc);
           timecounter = newtc;
           splx(s);
   }
   #endif
   
   static struct timecounter *
   sync_other_counter(void)
   {
           struct timecounter *tc, *tcn, *tco;
           unsigned delta;
   
           tco = timecounter;
           tc = tco->tc_other;
           tcn = tc->tc_other;
           *tc = *tco;
           tc->tc_other = tcn;
           delta = tco_delta(tc);
           tc->tc_offset_count += delta;
           tc->tc_offset_count &= tc->tc_counter_mask;
           tc->tc_offset_nano += (u_int64_t)delta * tc->tc_scale_nano_f;
           tc->tc_offset_nano += (u_int64_t)delta * tc->tc_scale_nano_i << 32;
           return (tc);
   }
   
   static void
   tco_forward(int force)
   {
           struct timecounter *tc, *tco;
   
           tco = timecounter;
           tc = sync_other_counter();
           /*
            * We may be inducing a tiny error here, the tc_poll_pps() may
            * process a latched count which happens after the tco_delta()
            * in sync_other_counter(), which would extend the previous
            * counters parameters into the domain of this new one.
            * Since the timewindow is very small for this, the error is
            * going to be only a few weenieseconds (as Dave Mills would
            * say), so lets just not talk more about it, OK ?
            */
           if (tco->tc_poll_pps) 
                   tco->tc_poll_pps(tco);
           if (timedelta != 0) {
                   tc->tc_offset_nano += (u_int64_t)(tickdelta * 1000) << 32;
                   timedelta -= tickdelta;
                   force++;
           }
   
           while (tc->tc_offset_nano >= 1000000000ULL << 32) {
                   tc->tc_offset_nano -= 1000000000ULL << 32;
                   tc->tc_offset_sec++;
                   ntp_update_second(tc);  /* XXX only needed if xntpd runs */
                   tco_setscales(tc);
                   force++;
           }
   
           if (tco_method && !force)
                   return;
   
           tc->tc_offset_micro = (tc->tc_offset_nano / 1000) >> 32;
   
           /* Figure out the wall-clock time */
           tc->tc_nanotime.tv_sec = tc->tc_offset_sec + boottime.tv_sec;
           tc->tc_nanotime.tv_nsec = 
               (tc->tc_offset_nano >> 32) + boottime.tv_usec * 1000;
           tc->tc_microtime.tv_usec = tc->tc_offset_micro + boottime.tv_usec;
           if (tc->tc_nanotime.tv_nsec >= 1000000000) {
                   tc->tc_nanotime.tv_nsec -= 1000000000;
                   tc->tc_microtime.tv_usec -= 1000000;
                   tc->tc_nanotime.tv_sec++;
           }
           time_second = tc->tc_microtime.tv_sec = tc->tc_nanotime.tv_sec;
   
           timecounter = tc;
   }
   
   SYSCTL_NODE(_kern, OID_AUTO, timecounter, CTLFLAG_RW, 0, "");
   
   SYSCTL_INT(_kern_timecounter, OID_AUTO, method, CTLFLAG_RW, &tco_method, 0,
       "This variable determines the method used for updating timecounters. "
       "If the default algorithm (0) fails with \"calcru negative...\" messages "
       "try the alternate algorithm (1) which handles bad hardware better."
   
   );
   
   
   int
   pps_ioctl(u_long cmd, caddr_t data, struct pps_state *pps)
   {
           pps_params_t *app;
           struct pps_fetch_args *fapi;
   #ifdef PPS_SYNC
           struct pps_kcbind_args *kapi;
   #endif
   
           switch (cmd) {
           case PPS_IOC_CREATE:
                   return (0);
           case PPS_IOC_DESTROY:
                   return (0);
           case PPS_IOC_SETPARAMS:
                   app = (pps_params_t *)data;
                   if (app->mode & ~pps->ppscap)
                           return (EINVAL);
                   pps->ppsparam = *app;         
                   return (0);
           case PPS_IOC_GETPARAMS:
                   app = (pps_params_t *)data;
                   *app = pps->ppsparam;
                   app->api_version = PPS_API_VERS_1;
                   return (0);
           case PPS_IOC_GETCAP:
                   *(int*)data = pps->ppscap;
                   return (0);
           case PPS_IOC_FETCH:
                   fapi = (struct pps_fetch_args *)data;
                   if (fapi->tsformat && fapi->tsformat != PPS_TSFMT_TSPEC)
                           return (EINVAL);
                   if (fapi->timeout.tv_sec || fapi->timeout.tv_nsec)
                           return (EOPNOTSUPP);
                   pps->ppsinfo.current_mode = pps->ppsparam.mode;         
                   fapi->pps_info_buf = pps->ppsinfo;
                   return (0);
           case PPS_IOC_KCBIND:
   #ifdef PPS_SYNC
                   kapi = (struct pps_kcbind_args *)data;
                   /* XXX Only root should be able to do this */
                   if (kapi->tsformat && kapi->tsformat != PPS_TSFMT_TSPEC)
                           return (EINVAL);
                   if (kapi->kernel_consumer != PPS_KC_HARDPPS)
                           return (EINVAL);
                   if (kapi->edge & ~pps->ppscap)
                           return (EINVAL);
                   pps->kcmode = kapi->edge;
                   return (0);
   #else
                   return (EOPNOTSUPP);
   #endif
           default:
                   return (ENOTTY);
           }
   }
   
   void
   pps_init(struct pps_state *pps)
   {
           pps->ppscap |= PPS_TSFMT_TSPEC;
           if (pps->ppscap & PPS_CAPTUREASSERT)
                   pps->ppscap |= PPS_OFFSETASSERT;
           if (pps->ppscap & PPS_CAPTURECLEAR)
                   pps->ppscap |= PPS_OFFSETCLEAR;
   }
   
   void
   pps_event(struct pps_state *pps, struct timecounter *tc, unsigned count, int event)
   {
           struct timespec ts, *tsp, *osp;
           u_int64_t delta;
           unsigned tcount, *pcount;
           int foff, fhard;
           pps_seq_t       *pseq;
   
           /* Things would be easier with arrays... */
           if (event == PPS_CAPTUREASSERT) {
                   tsp = &pps->ppsinfo.assert_timestamp;
                   osp = &pps->ppsparam.assert_offset;
                   foff = pps->ppsparam.mode & PPS_OFFSETASSERT;
                   fhard = pps->kcmode & PPS_CAPTUREASSERT;
                   pcount = &pps->ppscount[0];
                   pseq = &pps->ppsinfo.assert_sequence;
           } else {
                   tsp = &pps->ppsinfo.clear_timestamp;
                   osp = &pps->ppsparam.clear_offset;
                   foff = pps->ppsparam.mode & PPS_OFFSETCLEAR;
                   fhard = pps->kcmode & PPS_CAPTURECLEAR;
                   pcount = &pps->ppscount[1];
                   pseq = &pps->ppsinfo.clear_sequence;
           }
   
           /* The timecounter changed: bail */
           if (!pps->ppstc || 
               pps->ppstc->tc_name != tc->tc_name || 
               tc->tc_name != timecounter->tc_name) {
                   pps->ppstc = tc;
                   *pcount = count;
                   return;
           }
   
           /* Nothing really happened */
           if (*pcount == count)
                   return;
   
           *pcount = count;
   
           /* Convert the count to timespec */
           ts.tv_sec = tc->tc_offset_sec;
           tcount = count - tc->tc_offset_count;
           tcount &= tc->tc_counter_mask;
           delta = tc->tc_offset_nano;
           delta += ((u_int64_t)tcount * tc->tc_scale_nano_f);
           delta >>= 32;
           delta += ((u_int64_t)tcount * tc->tc_scale_nano_i);
           delta += boottime.tv_usec * 1000;
           ts.tv_sec += boottime.tv_sec;
           while (delta >= 1000000000) {
                   delta -= 1000000000;
                   ts.tv_sec++;
           }
           ts.tv_nsec = delta;
   
           (*pseq)++;
           *tsp = ts;
   
           if (foff) {
                   timespecadd(tsp, osp);
                   if (tsp->tv_nsec < 0) {
                           tsp->tv_nsec += 1000000000;
                           tsp->tv_sec -= 1;
                   }
           }
   #ifdef PPS_SYNC
           if (fhard) {
                   /* magic, at its best... */
                   tcount = count - pps->ppscount[2];
                   pps->ppscount[2] = count;
                   tcount &= tc->tc_counter_mask;
                   delta = ((u_int64_t)tcount * tc->tc_tweak->tc_scale_nano_f);
                   delta >>= 32;
                   delta += ((u_int64_t)tcount * tc->tc_tweak->tc_scale_nano_i);
                   hardpps(tsp, delta);
           }
   #endif
   }

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