[ntp:questions] Stabilizing the drift file?

David L. Mills mills at udel.edu
Fri Nov 24 20:27:04 UTC 2006


Assuming your system specification allows for up to 10 ms measurement 
error over two seconds, your script can result in a maximum frequency 
error of 5000 PPM. Golly.


Juergen.Salm at siemens.com wrote:
> Hi Dave.
>>This could be avoided by forcefully setting the clock at initial
> That's exactly what we do.
> You have to know that Robert an I are working on the same project.
> Robert is a systems engineer of the platform we use to build our
> device.
> The requirements of max. 100ms external offset, max. 10ms internal
> offset an 5 minutes until service availability are coming from our
> requirement specification. ;-)
> And we are always talking about a reboot scenario. So we don't need to
> compensate large offsets.
> What we do now during reboot is
> a) Measure the drift with my script for 2 seconds
> b) Set the time with ntpdate -b
> c) start ntpd with "iburst burst minpoll 4 maxpoll 6" for the
> controller blades requiring  <100ms offfset and with "iburst burst
> minpoll 4 maxpoll 4" for those blades requiring <10ms among themselves
> So ntpd can start its operation with (almost) no initial offset and a
> drift that is +-2ppm away from the long-term value.
> This gives us a max. offset of <<1 ms right from the start.
> And that's what we were looking for. :-)
> Bye
>  Juergen

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