[ntp:questions] Second attempt at GPS-18 based NTP server

David Woolley david at ex.djwhome.demon.invalid
Fri Feb 3 08:18:22 UTC 2012

unruh wrote:

> The delays from refclocks are almost always all zero. Thus there will be
> no info in the delay as whther a problem occured. ntpd will simply
> assume it is as good as any other sample, and use it (the clockfilter
> uses delays to select samples)

Even if all the samples are used, taking only one sample within the 
glitch, and using a long time constant, will disturb the clock less than 
taking multiple samples with a short time constant.

>> Offset is not a direct measure of the timekeeping error.
> It my not be a direct measure, but it is the only measure you have. And
> since ntpd is blind to history, it cannot even use history to determine
> such errors. 
The point was that you need to understand whether you are getting high 
offsets because the clock is wrong (e.g. temperature) or because the 
offset measurements are wrong (e.g. interrupt latency).

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