[ntp:questions] Re: ntpd PLL and clock overshoot

user at domain.invalid user at domain.invalid
Wed Oct 18 15:52:51 UTC 2006


I put a good deal of effort in the detailed calculations, especially the 
rounding issues. Even with uninterpolated 10-ms tick interval, the 
results are surprisingly good. In fact, I have tested it with tinkered 
1-s tick (!) and it ain't half bad.


Terje Mathisen wrote:

> Martin Burnicki wrote:
>> Then ntpd starts to correct the initial offset properly in less than 300
>> seconds. This looks like it was going to converge properly. However,
>> unfortunately at a 10 ms offset the filter algorithm seems to switch and
>> the following correction is still very poor compared to the initial
>> correction.
> Martin, the 10 ms behavior is pretty much a given, since the OS clock 
> works at the same 10 ms resolution!
> The realtime thread hack to interpolate between OS ticks does help, but 
> NTPD still needs a lot of statistical data to be able to settle down at 
> offset values well below the OS tick!
> Terje

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