[ntp:questions] setting the time using gps-time and pps without ntpd?

Unruh unruh-spam at physics.ubc.ca
Thu Apr 24 06:35:32 UTC 2008

nb at komeda-berlin.de (Nicola Berndt) writes:


>recently I tried building a microsecond precision timeserver using a 
>gps-device with pps signal.

>The gps-data is transmitted via usb, the pps signal via the rs232 
>carrier detect line.

>I tried several drivers and they all worked, but I had to figure that 
>obviously my mainboard (via epia en12000EG) has terrible jitter. - unusable!

Are you sure that it is not the reading of the time that is the problem.
What gps do you use? Are you sure it really has and is using PPS?
And what do you call "terrible"

>To solve the problem I think about simply setting the time every n 
>seconds according to the collected gps time and the pps-signal. My 
>system will run off for far less than a microsecond in an interval of 
>let's say, 20 seconds or so. Like this I would implement a constantly 
>jumping time, but the amount of jumps would be extremely small.

Just use ntp to discipline your clock. No need to try to bacly reinvent

>Since I learned that timekeeping is a very complex topic, I thought, I'd 
>better ask on this list, before I build something troublesome without 
>even knowing..

More information about the questions mailing list