[ntp:questions] NTP with GPS and RTC

David Woolley david at ex.djwhome.demon.invalid
Fri Apr 26 13:31:29 UTC 2013


[ Long lines repaired. ]
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.  Assuming the machine temperature was 
reasonably stable, you would need to to trim hte DS3231 several times a 
year to be sure of bettering a coasting local clock.  (2ppm per year, 
maximum of 5ppm over first 10 years.)

> - the kernel stops updating the RTC

No.

> - there is no other existing mechanism that disciplines the local system clock

You have provided insufficient information about your system to answer this.



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