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

David Lord Wed, 13 Jul 2011 18:34:12 -0700

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

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