[ntp:questions] Single GPS/PPS time source gets marked as a falseticker

David Lord snews at lordynet.org
Wed Jul 13 23:42:11 UTC 2011


Michael Eder wrote:
> 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

for my GPS I used:
GPS 18X-LVC
server 127.127.20.2 mode 1 prefer
fudge  127.127.20.2 time2 0.660 refid GPSb
server 127.127.22.2
fudge  127.127.22.2 refid PPSb

Sure-Electronics
server 127.127.20.2 mode 18 prefer
fudge  127.127.20.2 time2 0.350 refid GPSb
server 127.127.22.2
fudge  127.127.22.2 flag2 0 flag3 1 refid PPSb

Note I use the prefer against the NMEA rather than PPS but
I don't use the SHM driver which might be different.

loopstats.20110712:
loop 1350, 7+/-19.0, rms 2.6, freq -35.02+/-0.208, var 0.125

peerstats.20110712:
ident            mean     rms     max
127.127.22.2    0.000   0.003   0.026
127.127.20.2  -64.821  15.543  52.689

This would be better if there wasn't a blip each night
from the change in system load due to the cron jobs.


David


> #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 at 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 at 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 at 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 at 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 at 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




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