[ntp:questions] Packet timestamps when using Windows-7/Vista

David J Taylor david-taylor at blueyonder.delete-this-bit.and-this-part.co.uk.invalid
Mon Dec 14 15:06:07 UTC 2009

"Martin Burnicki" <> wrote in message 
news:ipkhv6-f29.ln1 at gateway.py.meinberg.de...
> The Windows API call used to slew the system time reports a standard 
> tick
> rate of 15.6001 on a Vista machine here even if the time returned by a 
> loop
> of GetSystemTimeAsFiletime() calls increments in 1.000 ms steps.
> So what happens if the default tick rate of 15.6001 ms is actually 
> modified
> to compensate the clock drift, e.g. by +5 -> 15.6006 to speed up the 
> system
> clock, or e.g. by -5 -> 15.5996 ms to slew it down?
> Can you check if the frequency offset measured by ntpd on the system 
> which
> has a TX time before the RX time has a different sign as the frequency
> offset measured on those systems which work "good"?
> The log_adj utility I've written some time ago
> http://www.meinberg.de/download/utils/windows/log_adj-1.4.zip
> also reports whether the adjustment applied to the standard clock tick 
> is
> positive, or negative, and which magnitude it is. This may be relevant 
> for
> the reason why the problem occurs.
>> I'm quite happy to work with someone offline on this, and my test 
>> program
>> is available.
> If you send me that program (or a link to it) I can give it a try.
> Martin


Thanks for your comments.

I'm not sure what frequency offset you are asking me to check - what NTP 
reports?  The PCs have statistic logging enabled so I can check that.  I'm 
just running log_adj on the two Windows-7 systems to see what there is to 

I'll tidy up the test program I have a little and post back here with a 


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