We have looked at our GPS on a scope, the PPS it is dead on and the NMEA (just one sentence) is also reliable with about a 680 ms latency and 10 ms jitter.
Here is the configuration file I am now using (any combination of tos entries seems to make no difference). When I start NTP is locks on to the GPS but then it eventually marks both clocks as falsetickers. After a while it regains lock with PPS and then loses it again, and repeats. Seems this is an NTP issue related to having just two clocks? As you can see time is quite precise. Anyone know that is going on? Thanks... ce000:/etc# cat ntp.conf # /etc/ntp.conf, configuration for ntpd driftfile /var/lib/ntp/ntp.drift statsdir /var/log/ntpstats/ statistics loopstats peerstats clockstats filegen loopstats file loopstats type day enable filegen peerstats file peerstats type day enable filegen clockstats file clockstats type day enable #For using GPS NMEA/PPS w/ shared-memory server 127.127.28.0 minpoll 4 maxpoll 4 fudge 127.127.28.0 time1 0.680 refid NMEA server 127.127.28.1 minpoll 4 maxpoll 4 prefer fudge 127.127.28.1 refid PPS #Look for two clocks instead of three for falsetickers - me-07/11 #tos minclock 2 minsane 1 tos mindist 0.015 # By default, exchange time with everybody, but don't allow configuration. # See /usr/share/doc/ntp-doc/html/accopt.html for details. restrict -4 default kod notrap nomodify nopeer noquery restrict -6 default kod notrap nomodify nopeer noquery # Local users may interrogate the ntp server more closely. restrict 127.0.0.1 restrict ::1 ce000:~/current# ./ntpstatus | tee ntplog.txt remote refid st t when poll reach delay offset jitter ============================================================================ == xSHM(0) .NMEA. 0 l 13 16 377 0.000 -74.683 68.862 *SHM(1) .PPS. 0 l 15 16 377 0.000 -0.034 0.061 assID=0 status=09f4 leap_none, sync_telephone, 15 events, event_peer/strat_chg, version="ntpd 4.2.2p4@1.1585-o Sun Nov 22 17:01:18 UTC 2009 (1)", processor="armv4tl", system="Linux/2.6.21-ts", leap=00, stratum=1, precision=-14, rootdelay=0.000, rootdispersion=0.616, peer=58573, refid=PPS, reftime=d1c87c31.39a87bc0 Wed, Jul 13 2011 20:18:57.225, poll=4, clock=d1c87c40.9888f6ef Wed, Jul 13 2011 20:19:12.595, state=4, offset=-0.034, frequency=-63.624, jitter=0.061, noise=0.062, stability=0.015, tai=0 synchronised to modem at stratum 1 time correct to within 0 ms polling server every 16 s ce000:~/current# ./ntpstatus | tee ntplog.txt remote refid st t when poll reach delay offset jitter ============================================================================ == xSHM(0) .NMEA. 0 l 15 16 377 0.000 -74.683 68.862 *SHM(1) .PPS. 0 l 17 16 377 0.000 -0.034 0.061 assID=0 status=09f4 leap_none, sync_telephone, 15 events, event_peer/strat_chg, version="ntpd 4.2.2p4@1.1585-o Sun Nov 22 17:01:18 UTC 2009 (1)", processor="armv4tl", system="Linux/2.6.21-ts", leap=00, stratum=1, precision=-14, rootdelay=0.000, rootdispersion=0.399, peer=58573, refid=PPS, reftime=d1c87c42.38d1c420 Wed, Jul 13 2011 20:19:14.221, poll=4, clock=d1c87c42.51d3869c Wed, Jul 13 2011 20:19:14.319, state=4, offset=-0.036, frequency=-63.624, jitter=0.061, noise=0.062, stability=0.014, tai=0 synchronised to modem at stratum 1 time correct to within 0 ms polling server every 16 s ce000:~/current# ./ntpstatus | tee ntplog.txt remote refid st t when poll reach delay offset jitter ============================================================================ == xSHM(0) .NMEA. 0 l 17 16 377 0.000 -74.683 68.862 *SHM(1) .PPS. 0 l 2 16 377 0.000 -0.036 0.061 assID=0 status=09f4 leap_none, sync_telephone, 15 events, event_peer/strat_chg, version="ntpd 4.2.2p4@1.1585-o Sun Nov 22 17:01:18 UTC 2009 (1)", processor="armv4tl", system="Linux/2.6.21-ts", leap=00, stratum=1, precision=-14, rootdelay=0.000, rootdispersion=0.429, peer=58573, refid=PPS, reftime=d1c87c42.38d1c420 Wed, Jul 13 2011 20:19:14.221, poll=4, clock=d1c87c44.ef2b821c Wed, Jul 13 2011 20:19:16.934, state=4, offset=-0.036, frequency=-63.624, jitter=0.061, noise=0.062, stability=0.014, tai=0 synchronised to modem at stratum 1 time correct to within 0 ms polling server every 16 s ce000:~/current# ./ntpstatus | tee ntplog.txt remote refid st t when poll reach delay offset jitter ============================================================================ == xSHM(0) .NMEA. 0 l 1 16 377 0.000 -101.07 65.086 xSHM(1) .PPS. 0 l 4 16 377 0.000 -0.036 0.061 assID=0 status=00f4 leap_none, sync_unspec, 15 events, event_peer/strat_chg, version="ntpd 4.2.2p4@1.1585-o Sun Nov 22 17:01:18 UTC 2009 (1)", processor="armv4tl", system="Linux/2.6.21-ts", leap=00, stratum=1, precision=-14, rootdelay=0.000, rootdispersion=0.459, peer=0, refid=PPS, reftime=d1c87c42.38d1c420 Wed, Jul 13 2011 20:19:14.221, poll=4, clock=d1c87c46.bf9dd353 Wed, Jul 13 2011 20:19:18.748, state=4, offset=-0.036, frequency=-63.624, jitter=0.061, noise=0.062, stability=0.014, tai=0 synchronised to unspecified at stratum 1 time correct to within 0 ms polling server every 16 s ce000:~/current# ./ntpstatus | tee ntplog.txt remote refid st t when poll reach delay offset jitter ============================================================================ == xSHM(0) .NMEA. 0 l 3 16 377 0.000 -101.07 65.086 xSHM(1) .PPS. 0 l 6 16 377 0.000 -0.036 0.061 assID=0 status=00f4 leap_none, sync_unspec, 15 events, event_peer/strat_chg, version="ntpd 4.2.2p4@1.1585-o Sun Nov 22 17:01:18 UTC 2009 (1)", processor="armv4tl", system="Linux/2.6.21-ts", leap=00, stratum=1, precision=-14, rootdelay=0.000, rootdispersion=0.489, peer=0, refid=PPS, reftime=d1c87c42.38d1c420 Wed, Jul 13 2011 20:19:14.221, poll=4, clock=d1c87c48.da266bef Wed, Jul 13 2011 20:19:20.852, state=4, offset=-0.036, frequency=-63.624, jitter=0.061, noise=0.062, stability=0.014, tai=0 synchronised to unspecified at stratum 1 time correct to within 0 ms polling server every 16 s _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions