[ntp:questions] Slow convergence of NTP with GPS/PPS
unruh-spam at physics.ubc.ca
Fri Oct 24 17:34:17 UTC 2008
"Richard B. Gilbert" <rgilbert88 at comcast.net> writes:
>David J Taylor wrote:
>> Unruh wrote:
>>> With a minpoll of 4, just setting the phase correctly with zero drift
>>> compensation would at worst be out by 1ms by the next reading. And
>>> you can get a pretty good estimate of the drift, even if it is
>>> changing. The temp coefficient is not 10PPM/degree C. More like 1 or
>>> less. That means the first few measurements gives a pretty good
>>> estimate of the drift ( ie to a few PPM) and then the finer
>>> corrections can come while things settle down.
>> It isn't NTP which is the limit, but the GPS receiver acquiring lock from
>> scratch after an indeterminate period of being switched off. The GPS
>> could take minutes to lock and declare that it has valid time.
>And ntpd could take many minutes to bludgeon the local clock into
>submission! It's easy to determine and set the correct time. It's less
>easy to determine and set the correct frequency and thus KEEP the
Actually it is relatively easy to determine the frequency as well in a
short time. and then refine it. It is NOT easy if you use a Markovian strategy
like ntp uses.
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