[ntp:questions] NMEA ref.clock better than my ISP's timeserver?

David Lord snews at lordynet.org
Fri Jun 12 20:39:12 UTC 2009

Unruh wrote:
> David Lord <snews at lordynet.org> writes:
>> David J Taylor wrote:
>>> David Lord wrote:


> I get an average of 2usec from pps driving the parallel interrupt ( with
> "myown" interupt service daemon). I think much of that is a) ntp's
> handling of rate fluctuations, and b)natural variation in the interrupt
> handling due to computer issues. My gps 18 has about a 20m run to the
> computer, and is simply a "bar wire ( well one of the Cat5e twisted pair
> wires) connection.

Thanks for that Bill, to both you and David, I'll still make up
the pcbs but will first try connecting with straight through cable.


> Putting in a thermistor on top of the clock crystal and read the
> temperature and use it to predict the rate variation. That will probably
> give far better results than using a temperature controll. Also using
> chrony ( which now has an shm refclock input at least in beta). will
> give better results than ntp. 

 From my searches I had opposite impression, that patches to ntp
for temperature compensation were good but not anywhere near as
good as keeping crystal at constant temperature.

Add to that a pps source probably takes system clocks largely
out of the equation.

I'm very happy to give chrony another try. I used it for a few
years without problems when on dialup. I'm thinking of
notebook rather than servers but I'd be happy to try on one of
servers (webserver uses ntpd but has chrony-1.20nb3 which I
guess is old).


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