[ntp:questions] Slow convergence of NTP with GPS/PPS

Terje Mathisen terje.mathisen at hda.hydro.com
Wed Oct 1 12:09:57 UTC 2008

Unruh wrote:
> David Woolley <david at ex.djwhome.demon.co.uk.invalid> writes:
>> My understanding was that -g turns off the 1000 second check for the 
>> first step, but still leaves the time within +/- 128ms, which will still 
>> take an unacceptable time to converge to +/- 5ms.  Certainly the 4.2.4p4 
>> documentation makes no claims for it beyond once only disabling the 1000 
>> second check.
> 128ms at 500PPM is 250sec or 4 min. It will take longer than that since the
> rate will not peg out, but it should not be hours.
> Maybe it is best to set the clock initiallly so that it is out by by more
> than 128ms (Eg advance it by 10 sec) and then use -g.

Afair the 128 ms is also a 'tinker' configuration parameter, i.e. it 
should be possible to reduce it to 10 or 15 ms, at the cost of getting a 
few more steps during runtime.


- <Terje.Mathisen at hda.hydro.com>
"almost all programming can be viewed as an exercise in caching"

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