[ntp:questions] Remarkably good CPU oscillators?

David L. Mills mills at udel.edu
Sun Nov 5 18:28:47 UTC 2006


Very dangerous to clamp the frequency. In the normal course the time 
constant ramps up to 1024 s, which makes the loop very, very stiff and 
changes exceeding 0.1 PPM are very unlikely.


David Woolley wrote:

> In article <1162738456.358848.206590 at h48g2000cwc.googlegroups.com>,
> shoppa at trailing-edge.com wrote:
>>Is this statistic just "too good to be true"? Or did I luck out when I
>>bought this box many years ago?
> No. If anything it is bordering on the too big to be good.  This is
> one of the main reasons why I think that ntpd should be much more reluctant
> to apply corrections of more than about 3 to 5 ppm, once the frequency has
> been calibrated.  My feeling is that it should limit the corrections to
> this range unless there is an extended period indicative of a different
> frequency.  It might be reasonable to allow, say, 0.1ppm per day to 
> account for long term drift.

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