[ntp:questions] high precision tracking: trying to understand sudden jumps

David Woolley david at ex.djwhome.demon.co.uk.invalid
Tue Apr 1 10:19:44 UTC 2008

starlight at binnacle.cx wrote:
> The generic version of 'ntpd' has some sophisticated code that 
> handles interpolation.  See the source.  Power management is 

I know that.  But the problem is that normal applications just get a 
more accurate time for the most recent tick, but still don't see any 
times between ticks.

> Pings are consistently 400 microseconds and 'ntpq -p' reports 800 

Which is excessive for 1GHz network doing essentially nothing but NTP.

> probably have make use of PTP (precision timing protocol).
> Still très expensive.

I assume by PTP you mean ethernet cards that extract a timestamp with a 
very low latency.  I doubt that this will help with lost interrutps.  If 
you really want extreme accuracy for applications you need to:

1) use hardware that maintains a high resolution time completely 
independent of the software and is directly readable by application code 
(I'm not sure if Windows supports such direct reading).

2) you will need to add code to the device drivers that actually 
communicate the real world events that you interested in to the 
software, to read from that special clock very early in their ISR 
(better still devices that will read it using DMA).

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