[time-nuts] Cheap jitter measurements

[David J Taylor]

Hi,

Yes, but isn't generating pulses OUT of a PC with low latency/jitter one
of the difficult issues?

If we (somebody smarter than me...) flip this around and modify a copy
NTP to grab the QueryPerformanceCounter value when it gets a PPS pulse
and log that count, don't we now have a way to compare the high
resolution uncorrected counter to NTP and the external PPS?

Agreed, not trivial. But maybe fun anyway!

Dan
================================

Dan,

Take a look at Dave Hart's patches to the Microsoft serial port driver, that 
does something similar.  The source may be in the NTP distribution, or 
Meinberg may have a copy.  At one time using the QueryPerfomanceCounter call 
was an option (look for "QPC").  With Windows-8 and later there is a much 
more precise GetSystemTime call which NTP uses.

I played a little with those calls (in a non-serious way) and wrote some 
code:

  http://www.satsignal.eu/ntp/TSCtime.html

based on:

  http://www.lochan.org/2005/keith-cl/useful/win32time.html

and just messing around!  Perhaps it's of interest or use?

Cheers,
David
-- 
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor at blueyonder.co.uk
Twitter: @gm8arv