[ntp:questions] NTP with GPS and RTC

unruh unruh at invalid.ca
Fri Apr 26 01:21:31 UTC 2013

On 2013-04-25, Harlan Stenn <stenn at ntp.org> wrote:
> I gather it returns time to the nearest second - that will not be very
> useful for OS or NTP timestamps.  If you have to set the time to the
> nearest second you will also need to take special care to make sure that
> you set the clock at the "correct" moment of the second in order to get
> the "seconds" transition to happen ar the right time.

Well, actually, If you could set it so that it really kept the second
properly, and it had an interrupt when the second turned, that would be
just like a PPs clock with the seconds also delivered. Of course those
careates are pretty big ones. I know with the normal rtc, you have to
send it the set signal exactly .5 sec before the second transition
actually occurs.

> As I said above, I do not know if the OS is that careful about setting
> the time of the RTC every 11 minutes.

That of course makes is a very jumpy clock. every second its time
suddenly jumps. You would be far better off disabling the 11 min process
(chrony does that for you for example). 

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