[time-nuts] PPS offset between GPS receivers

David J Taylor david-taylor at blueyonder.co.uk
Tue Dec 11 14:22:46 UTC 2012


I'm not sure about the jammer but I'm running a timing receiver in
position hold several floors up, I haven't seen dropouts like this.

ntpd is running with a "noselect" NMEA source since I'm having problems
with ntpd marking the PPS and NMEA as falsetickers. The startup sequence
for the server is this:

* run ntpd -g -q with NMEA enabled
* run chronyd for 3 minutes to set the time and frequency offset
* copy the current frequency to ntpd's drift file, then run ntpd with
NMEA disabled

This hack seems to work everytime with ntpd ready in less than 4 minutes
after turning on. I just hope nothing would happen that changes the
time.

I have seen 0.2 us spikes every hour from some unknown task but the
larger spikes are rare. Another device running the same OpenWrt firmware
but with a timing receiver has only the small periodic spikes.
===============================================

Gabs,

Sorry, I'm not familiar enough with Linux to be able to help.  On my systems 
there's just the automated start of ntpd, with no 3rd party software, and 
the PPS is a separate kernel-mode driver, not the one integrated into the 
NMEA driver.  It may be best to ask on the Usenet comp.protocols.time.ntp 
group to get NTP working properly.

Cheers,
David
-- 
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor at blueyonder.co.uk 




More information about the time-nuts mailing list