Re: [gpsd-dev] Draft Time Service HOWTO is beginning to approach final form

[Eric S. Raymond]

Andy Walls <address@hidden>:
> In gpsd's ntpshm.c, setting
> 
>       shmTime->leap = LEAP_NOTINSYNC;
> 
> tells ntpd that the shared memory clock is in alarm.  ntpd essentially
> ignores clocks that are in alarm.
> 
> I am hoping that while a clock is in alarm status, ntpd won't declare it
> a falseticker, so that when it comes out of alarm, it will be
> immediately useful to ntpd.

That is interesting.  Comment added:

static int ntpshm_alloc(struct gps_context_t *context)
/* allocate NTP SHM segment.  return its segment number, or -1 */
{
    int i;

    for (i = 0; i < NTPSHMSEGS; i++)
        if (context->shmTime[i] != NULL && !context->shmTimeInuse[i]) {
            context->shmTimeInuse[i] = true;

            /*
             * In case this segment gets sent to ntpd before an
             * ephemeris is available, the LEAP_NOTINSYNC value will
             * tell ntpd that this source is in a "clock alarm" state
             * and should be ignored.  The goal is to prevent ntpd
             * from declaring the GPS a falseticker before it gets
             * all its marbles together.
             */
            memset((void *)context->shmTime[i], 0, sizeof(struct shmTime));
            context->shmTime[i]->mode = 1;
            context->shmTime[i]->leap = LEAP_NOTINSYNC;
            context->shmTime[i]->precision = -1;        /* initially 0.5 sec */
            context->shmTime[i]->nsamples = 3;  /* stages of median filter */

            return i;
        }

    return -1;
}

 
-- 
                <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>