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

Richard B. Gilbert rgilbert88 at comcast.net
Fri Oct 24 01:55:52 UTC 2008

David Woolley wrote:
> Richard B. Gilbert wrote:
>> To turn your equipment on after months of downtime and expect it to 
>> lock on to the correct time with millisecond accuracy within seconds 
>> is asking for a hell of a lot.
> Not really.  He's starting a GPS receiver at the same time and that has 
> to lock to 50ns.
> Doing it on a general purpose computer is more difficult, but not 
> particularly impossible.

Even with GPS and a full four satellite fix, ten seconds to synchronize 
is extremely ambitious!!  You can set the time to within whatever 
precision the hardware and software support but that is only half the 
problem.  You also need to set the correct clock frequency.  On a cold 
start, the clock frequency is a moving target as the hardware warms up.

I would expect to wait at least thirty minutes for the system to 
stabilize with both the correct phase (time) and frequency.

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