[ntp:questions] Making ntpd tweak a TCXO

Mike S mikes at flatsurface.com
Fri Feb 5 15:36:55 UTC 2016


On 1/27/2016 11:55 AM, Mark Haun wrote:
> Does the NTP software provide any hooks that could be used to accomplish
> this?  I thought of a crude approach, simply writing a program to examine
> the drift file periodically, and using that information to adjust the TCXO. 
> But that (a) fails to stop ntpd from adjusting the virtual clock frequency
> within the OS, and (b) isn't really a proper control loop.  I guess it would
> work, sort of, as a last resort.

Just a thought - monitor the ntpd loopstats log, and adjust your tcxo
based on the frequency offset. That's updated much more frequently than
the drift file, so would be more responsive than using the drift file.
You'd probably want something like a PID loop to filter jitter and avoid
chasing.

It doesn't stop ntpd from adjusting the clock, but it would minimize the
size of the adjustment, which should long term average to 0.

---
Mike



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