[ntp:questions] NMEA driver using common PPSAPI code

Dave Hart davehart at gmail.com
Thu Sep 23 16:30:28 UTC 2010


14 seconds is the difference between UTC and GPS time.  The support
you added to refclock_nmea.c for $GPZDG results in running ntpd in GPS
time, not UTC.  That's a pretty unusual thing to do, and requires you
not interact with any "real" NTP servers.  It appears UTC time is
leaking into your setup via the PPS.  I'm not sure how, since the
PPSAPI timestamps should be in GPS time as well, driven by the system
clock which ntpd has moved to GPS time.

It's going to take some debugging by someone who has reason to want to
run a nonstandard NTP service in GPS time.

Cheers,
Dave Hart

On Thu, Sep 23, 2010 at 12:11 PM, Venu Gopal <neo.venu at gmail.com> wrote:
> Dear Friends,
>
> NMEA driver was modified to use common PPSAPI code since 4.2.5p185.
> I see  that NTP exhibits a strange behavior stepping the clock by +/- 7 secs
> and sometimes +/- 14 secs when restarted. This isn't the case with the
> earlier
> versions where the reference clock driver was not using common PPSAPI code.
>
> Let me know if anyone had a similar experience.
>
> Snippets of the ntp.log for reference:
>
> 23 Sep 06:28:26 ntpd[26548]: refclock_nmea: serial /dev/gps0 open at 9600
> bps
> 23 Sep 06:28:26 ntpd[26548]: GPS_NMEA(0) 8011 81 mobilize assoc 45269
> 23 Sep 06:28:26 ntpd[26548]: 0.0.0.0 c016 06 restart
> 23 Sep 06:28:26 ntpd[26548]: 0.0.0.0 c012 02 freq_set kernel 42.388 PPM
> 23 Sep 06:28:27 ntpd[26548]: GPS_NMEA(0) using only $GPZDG
> 23 Sep 06:28:27 ntpd[26548]: GPS_NMEA(0) 8024 84 reachable
> 23 Sep 06:28:27 ntpd[26548]: GPS_NMEA(0) 963a 8a sys_peer
> *23 Sep 06:28:27 ntpd[26548]: 0.0.0.0 c41c 0c clock_step -7.201275 s*
> 23 Sep 06:28:20 ntpd[26548]: 0.0.0.0 c415 05 clock_sync
> 23 Sep 06:28:36 ntpd[26548]: GPS_NMEA(0) 8044 84 reachable
> *23 Sep 06:28:36 ntpd[26548]: 0.0.0.0 c413 03 spike_detect +7.119944 s*
> 23 Sep 06:33:07 ntpd[26548]: ntpd exiting on signal 15
> 23 Sep 06:33:11 ntpd[27041]: refclock_nmea: serial /dev/gps0 open at 9600
> bps
> 23 Sep 06:33:11 ntpd[27041]: GPS_NMEA(0) 8011 81 mobilize assoc 795
> 23 Sep 06:33:11 ntpd[27041]: 0.0.0.0 c016 06 restart
> 23 Sep 06:33:11 ntpd[27041]: 0.0.0.0 c012 02 freq_set kernel 42.388 PPM
> 23 Sep 06:33:12 ntpd[27041]: GPS_NMEA(0) using only $GPZDG
> 23 Sep 06:33:12 ntpd[27041]: GPS_NMEA(0) 8024 84 reachable
> 23 Sep 06:33:12 ntpd[27041]: GPS_NMEA(0) 963a 8a sys_peer
> 23 Sep 06:33:12 ntpd[27041]: 0.0.0.0 c415 05 clock_sync
> *23 Sep 06:33:28 ntpd[27041]: 0.0.0.0 0413 03 spike_detect +0.201292 s*
> *23 Sep 06:48:24 ntpd[27041]: 0.0.0.0 041c 0c clock_step +0.200150 s*
> 23 Sep 06:48:24 ntpd[27041]: 0.0.0.0 0415 05 clock_sync
> 23 Sep 06:48:24 ntpd[27041]: 0.0.0.0 041d 0d kern PPS enabled
> 23 Sep 06:48:40 ntpd[27041]: GPS_NMEA(0) 8044 84 reachable
> 23 Sep 06:54:39 ntpd[27041]: ntpd exiting on signal 15
> 23 Sep 06:54:45 ntpd[29180]: refclock_nmea: serial /dev/gps0 open at 9600
> bps
> 23 Sep 06:54:45 ntpd[29180]: GPS_NMEA(0) 8011 81 mobilize assoc 22732
> 23 Sep 06:54:45 ntpd[29180]: 0.0.0.0 c016 06 restart
> 23 Sep 06:54:45 ntpd[29180]: 0.0.0.0 c012 02 freq_set kernel 42.388 PPM
> 23 Sep 06:54:46 ntpd[29180]: GPS_NMEA(0) using only $GPZDG
> 23 Sep 06:54:46 ntpd[29180]: GPS_NMEA(0) 8024 84 reachable
> 23 Sep 06:54:46 ntpd[29180]: GPS_NMEA(0) 963a 8a sys_peer
> *23 Sep 06:54:46 ntpd[29180]: 0.0.0.0 c41c 0c clock_step -0.194161 s*
> 23 Sep 06:54:46 ntpd[29180]: 0.0.0.0 c415 05 clock_sync
> 23 Sep 06:55:02 ntpd[29180]: GPS_NMEA(0) 8044 84 reachable
> *23 Sep 06:55:02 ntpd[29180]: 0.0.0.0 c413 03 spike_detect +7.119955 s*
> 23 Sep 07:01:55 ntpd[29180]: ntpd exiting on signal 15
> 23 Sep 07:02:01 ntpd[29924]: refclock_nmea: serial /dev/gps0 open at 9600
> bps
> 23 Sep 07:02:01 ntpd[29924]: GPS_NMEA(0) 8011 81 mobilize assoc 48993
> 23 Sep 07:02:01 ntpd[29924]: 0.0.0.0 c016 06 restart
> 23 Sep 07:02:01 ntpd[29924]: 0.0.0.0 c012 02 freq_set kernel 42.388 PPM
> 23 Sep 07:02:02 ntpd[29924]: GPS_NMEA(0) using only $GPZDG
> 23 Sep 07:02:02 ntpd[29924]: GPS_NMEA(0) 8024 84 reachable
> 23 Sep 07:02:02 ntpd[29924]: GPS_NMEA(0) 963a 8a sys_peer
> *23 Sep 07:02:02 ntpd[29924]: 0.0.0.0 c41c 0c clock_step +7.120941 s*
> 23 Sep 07:02:09 ntpd[29924]: 0.0.0.0 c415 05 clock_sync
> 23 Sep 07:02:25 ntpd[29924]: GPS_NMEA(0) 8044 84 reachable
> 23 Sep 07:02:41 ntpd[29924]: 0.0.0.0 041d 0d kern PPS enabled
> *23 Sep 09:36:50 ntpd[29924]: 0.0.0.0 0413 03 spike_detect -0.134541 s*
> 23 Sep 09:37:06 ntpd[29924]: 0.0.0.0 0415 05 clock_sync
> 23 Sep 11:15:56 ntpd[29924]: ntpd exiting on signal 15
> 23 Sep 11:32:32 ntpd[24273]: refclock_nmea: serial /dev/gps0 open at 9600
> bps
> 23 Sep 11:32:32 ntpd[24273]: GPS_NMEA(0) 8011 81 mobilize assoc 30790
> 23 Sep 11:32:32 ntpd[24273]: 0.0.0.0 c016 06 restart
> 23 Sep 11:32:32 ntpd[24273]: 0.0.0.0 c012 02 freq_set kernel 42.745 PPM
> 23 Sep 11:32:33 ntpd[24273]: GPS_NMEA(0) using only $GPZDG
> 23 Sep 11:32:33 ntpd[24273]: GPS_NMEA(0) 8024 84 reachable
> 23 Sep 11:32:33 ntpd[24273]: GPS_NMEA(0) 963a 8a sys_peer
> *23 Sep 11:32:33 ntpd[24273]: 0.0.0.0 c41c 0c clock_step -7.223907 s*
> 23 Sep 11:32:26 ntpd[24273]: 0.0.0.0 c415 05 clock_sync
> 23 Sep 11:32:36 ntpd[24273]: ntpd exiting on signal 15
> 23 Sep 11:32:37 ntpd[24297]: refclock_nmea: serial /dev/gps0 open at 9600
> bps
> 23 Sep 11:32:37 ntpd[24297]: GPS_NMEA(0) 8011 81 mobilize assoc 51204
> 23 Sep 11:32:37 ntpd[24297]: 0.0.0.0 c016 06 restart
> 23 Sep 11:32:37 ntpd[24297]: 0.0.0.0 c012 02 freq_set kernel 42.745 PPM
> 23 Sep 11:32:37 ntpd[24297]: GPS_NMEA(0) using only $GPZDG
> 23 Sep 11:32:38 ntpd[24297]: GPS_NMEA(0) 8024 84 reachable
> 23 Sep 11:32:38 ntpd[24297]: GPS_NMEA(0) 963a 8a sys_peer
> *23 Sep 11:32:38 ntpd[24297]: 0.0.0.0 c41c 0c clock_step +7.119892 s*
> 23 Sep 11:32:45 ntpd[24297]: 0.0.0.0 c415 05 clock_sync
> 23 Sep 11:33:01 ntpd[24297]: GPS_NMEA(0) 8044 84 reachable
> 23 Sep 11:33:03 ntpd[24297]: ntpd exiting on signal 15
>
>
> Thanks & Kind Regards,
> _Venu
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