[ntp:questions] 64-bit serialpps.sys despite unsigned?

David J Taylor david-taylor at blueyonder.co.uk
Thu Mar 17 15:32:47 UTC 2011

> Yes, it looks good, and thanks for clarifying the "before" was using
> the user-mode PPS hack in the Windows port of ntpd.
>> However, it doesn't seem to be working anything like as well as 
>> nominally
>> the same software installed in 32-bit Windows on PC Stamsund.  Compare 
>> the
>> offsets of 32-bit PC Stamsund (well under 50 microseconds) with 64-bit 
>> PC
>> Alta (well over 500 microseconds and somewhat periodic).
> My guess:  the key difference is the one you already identified,
> Stamsund is using a precision around -20 (microseconds) while Alta is
> stuck with precision -10 and the resulting minimum 0.977 ms jitter.
> If you manage to get Alta's system clock to tick 64 times per seconds
> instead of 500, 1000, or 2000 times per second, the interpolation code
> can correctly correlate the high-resolution counter and system clock
> given the 1000 Hz scheduler resolution.  Things to try would include
> remove -M from ntpd options, prevent Flash or Java or media player
> apps from being run.
> Cheers,
> Dave Hart


Looking in even more detail, I found that....

PC Stamsund had set, from 2009 Aug 23:

PC Alta had set, from 2010 Dec 19:

I should have seen that before!  Removing the system_clock and adding the 
interp_dangerous from Alta has resulted in an immediate improvement.

Thanks for encouraging me to look further!

Case solved (I hope) and 64-bit PPS working on Windows-7.  My thanks for 
your work on this.

SatSignal software - quality software written to your requirements
Web:  http://www.satsignal.eu
Email:  david-taylor at blueyonder.co.uk 

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