[ntp:questions] NTP with GPS and RTC

Steve Kostecke kostecke at ntp.org
Fri Apr 26 16:33:49 UTC 2013

On 2013-04-26, Biebaut Sven <sven.biebaut at be.thalesgroup.com> wrote:

>>Biebaut Sven wrote:
>>> If I drop the idea of the RTC as a reference clock, am I correct in
>>+ stating that, when there is no external synchronisation:
>>> - my local clock and my RTC will drift away from each other, but at
>>+ least my RTC will be closer to the mark (the DS3231 is chosen for its
>>+ precision)
>>Probably not.  ntpd will continue to apply first order frequency 
>>correction to the local clock.  
> Ah, I did not realise that. So a system with ntpd but without an external 
> reference clock would still be more accurate than a system without ntpd 
> at all ?

Only if ntpd has had access to a real local reference clock, or to
remote time servers, for a long enough period of time to calculate the
frequency correction. And the ambient conditions and system load match
that which existed when the correction was determined.

Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/

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