[ntp:questions] nmea and initial large offset

unruh unruh at wormhole.physics.ubc.ca
Mon May 10 05:11:05 UTC 2010


On 2010-05-09, Rob <nomail at example.com> wrote:
> unruh <unruh at wormhole.physics.ubc.ca> wrote:
>>> Maybe the chrony people should have started with a fork from ntpd.
>>> Then I would probably be using it now.
>>
>> I doubt it. chrony was largely written by one person, Richard Curnow.
>> His philosophy on how to control clocks was completely different from
>> Mill's and has been shown to work much better. It has now been taken
>> over by a small group with M Lichvar contributing most to the
>> development. It is a well developed program, different from ntpd in many
>> many ways, and experimentally much better in many many ways. It needs
>> theoretical work (eg are there conditions in which it becomes unstable?
>> Are there conditions under which it performes worse than a simply
>> Markovian feedback device that ntpd uses? Are there conditions in which
>> the clock filter algorithm of ntpd might be useful, and how can one
>> recognize them automatically. etc) and implimentational ideas. 
>>
>> But as to you using it, I have no idea why, if it were called a fork of
>> ntpd you would be more likely to use it. 
>
> I have heard that it does not support local reference clocks.

It does now. Lichvar added support.   shm in particular. PPS support.



> I have a DCF-77 receiver and a GPS receiver which is interfaced via gpsd.
> My understanding is that chrony cannot use those, and uses only other
> servers via the network.
> That is not very useful for me.

Well you should now be happy.

> When it had started as a fork from ntpd, this issue would probably not
> exist (because ntpd supports both my local reference clocks).

You can actually use a modified ntpd to feed any of the ntpd reference
sources to chrony.




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