[ntp:questions] Reasons of NTP not to use GPS source
Brian.Inglis at SystematicSw.ab.ca
Tue Sep 17 06:48:22 UTC 2013
On 2013-09-16 01:00, Igor Pavlov wrote:
> I am using GPS-receiver based on Geos-1m chip (
> I connected it to serial port and configured NTP.
> It becomes unused by NTP: when do ntpq -p reuest ti puts "x" near
> "GPS_NMEA(1)" record.
> What reasons can be for this?
> Example of "ntpq -p" output
> remote refid st t when poll reach delay offset
> xGPS_NMEA(1) .GPS. 0 l 14 16 377 0.000 -303.07
> *stratum1.net .PPS. 1 u 62 64 377 62.800 -68.052
> +dl120g7.naviteh 220.127.116.11 2 u 58 64 377 30.151 -100.04
> +18.104.22.168 22.214.171.124 2 u - 64 377 10.006 -105.88
See David Taylor's pages at
and linked pages at top for a lot of details about setup, but keep everything
really simple to start, then change one thing at a time after running for a
while and checking the results.
Check your GPS comms and config using the supplied setup software:
are you seeing NMEA output at your selected 115.2kbps?
which sentences $GPRMC, etc.?
has your receiver completed its initial survey and is it reporting Active, and
reasonable mode, position, altitude, UTC date and time in sentence $GPRMC?
how many satellites is your receiver tracking to what precision in sentences
$GPGGA, $GPGSA, $GPGSV?
is your receiver set to 1Hz PPS rather than 5Hz updates?
is PPS toggling DCD high for about 100ms at the start of ecah second?
Note that Windows recognizes only low to high DCD transitions as PPS.
If your mouse cursor starts jumping around, unplug your RS232 cable, *disable*
the Windows mouse driver which just got loaded on your serial port, plug in your
RS232 cable, and restart if required.
If all that looks good, next try disabling everything but PPS and $GPRMC
sentence output from your receiver config, and use only your server 127.127.20.n
line, without any fudge settings, plus your backup Internet servers, in ntp.conf.
Then restart NTP and see if ntp.log shows something like:
14 Aug 12:50:38 ntpd[####]: GPS_NMEA(#) serial /dev/gps# open at 4800 bps
14 Aug 12:50:38 ntpd[####]: GPS_NMEA(#) 8011 81 mobilize assoc #####
14 Aug 12:50:39 ntpd[####]: GPS_NMEA(#) 802b 8b clock_event clk_no_reply
14 Aug 12:50:39 ntpd[####]: Using user-mode PPS timestamp for GPS_NMEA(#)
14 Aug 12:50:57 ntpd[####]: GPS_NMEA(#) 8034 84 reachable
14 Aug 12:50:57 ntpd[####]: GPS_NMEA(#) 904a 8a sys_peer
Now ntpq -p should show * beside your GPS_NMEA(#) entry:
remote refid st t when poll reach delay offset jitter
*GPS_NMEA(#) .GPS. 0 l 12 16 377 0.000 -0.011 0.021
and if you defined statsdir ... and statistics clockstats in ntp.conf you should
see entries in clockstats.yyyymmdd like:
56512 7.123 127.127.20.# ...
If nothing seems to be working, try restarting the NTP service - at times it
seems to have issues getting going properly in various ways.
More information about the questions