[ntp:questions] Slow convergence of NTP with GPS/PPS

Nicola Berndt nb at komeda-berlin.de
Mon Oct 20 12:40:13 UTC 2008


just found this thread, after having not studied the list for quite a 
while. I have the exact same problem (have to be ready within minutes) 
and I also have an accurate (and meanwhile excellently working) PPS signal.

I understand that ntp is not designed for wild and fast changes, but to 
my understanding these are not always necessary, given pretty well 
defined startup-conditions like a reboot. Well, when I reboot my VIA 
epia 12000EG I experience right the phenomenon David described: ntpd 
sets the time pretty fast initially using the -g switch but then 
increases the offset a lot, turns around, shoots over 0 again and after 
a long time finally reaches a very high precision. This happens with and 
without a driftfile.

My plan was (well, IS - I just ordered it today..) to get a Soekris net 
4501 and maybe even an ovenized oscilator on an external board, since we 
have some tasks that simply depend on very precise time.

The option to just use an application that simply reads NMEA and PPS is 
of no use for me anymore (I had that plan in the very beginning), since 
we have to sync several devices to the GPS/PPS equipped unit.

So my question actually is: Is this initial variance part of the plan or 
do I have a chance to get around it with the Soekris board?

Best regards,
./nico berndt

More information about the questions mailing list