[ntp:questions] Re: How application get precise time from Win NT/XP system time that synchronies to NTP

Bjorn Gabrielsson bg at lysator.liu.se
Sat Mar 26 14:10:35 UTC 2005

Roger Chou <rgr.chou at gmail.com> writes:

> Hi,
> My applications is to do time stamp that need 10 microsecond accuracy. Many
> PCs in network environment will need ssme precise time stamp. 

The requrement of 10us is going to cost you... 

>One way to do
> it is to install Trimble Acutime GPS for each PC. 

>Because of cost
> consideration, I installed a Win NT NTP server that use Trimble Acutime GPS
> as reference clock and the rest of PCs synchronize to the server and I try
> to find a way to get precise time from NT/ XP system.

You might be loosing on 10us on Windows. See table below from


Platform 	Operating System        Accuracy
i386 (PC)  	Linux                   10 us
i386 (PC)  	Windows NT              1 ms
SUN             Solaris 2.x             50 us
Hewlett-Packard HPUX 9, 10, 11          50 us
Various 	Free BSD                20 us

Here is how my Accutime2000 is doing on Linux with nanokernel patch.

You will not be even close to 10us distributing time with NTP over a
network. Relaxing it to 1ms could be done if you stay clear of

# /usr/sbin/ntpq -c pe 
     remote           refid      st t when poll reach   delay   offset  jitter
+GPS_PALISADE(0) .GPS.            0 l   13   16  377    0.000    0.000   0.002
*GPS_JUPITER(0)  .GPS.            0 l   19   64  377    0.000   -0.001   0.002

My guess is that you need some way to distribute a PPS-pulse to all
your computers. Computers might have to run kernel PPS API, which is
available (mostly) on FreeBSD and Linux.

My 2 cents,

-- Björn

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