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

Richard B. Gilbert rgilbert88 at comcast.net
Fri Oct 24 12:47:23 UTC 2008


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.
> 
> David 
> 
> 

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 
correct time.




More information about the questions mailing list