[ntp:questions] serialPPS+gpsd+ntpd large offset & jitter

Miroslav Lichvar mlichvar at redhat.com
Wed Oct 20 14:34:32 UTC 2010

On Wed, Oct 20, 2010 at 07:00:50AM -0700, M Z wrote:
> I have another question. The fudge in ntp.conf for the GPS is suggested to be 
> set at .420 - how can
> I calculate the best value? gpsd gives all kinds of debug information but what 
> numbers tell me how delayed the GPS signal is compared to the pps? Or is the 
> 'offset' from ntpq the key?

Yes, add or substract (I'm never sure which one is correct) the offset
reported by ntpq to the fudge value, so it will be close to zero.

However, in my experience the NMEA sources tend to be quite bad. If
you are not planning to run without PPS or would rather use an NTP
source as a backup, remove the line and use gpsd just for
the PPS source.

Miroslav Lichvar

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