[ntp:questions] Assistance with PPS on Windows

David J Taylor david-taylor at blueyonder.co.uk.invalid
Thu May 5 21:48:09 UTC 2011

"Richard B. Gilbert" <rgilbert88 at comcast.net> wrote in message 
news:OJmdnUVxob4WkV7QnZ2dnUVZ_vydnZ2d at giganews.com...
> Getting the time into the computer takes X microseconds where X depends 
> on the hardware and software.  Windows' clock ticks every 17 
> milliseconds or something like that.  Other operating systems also take 
> a toll!

Recent version of Windows tend to run at ~1KHz, and you can set that for 
Windows XP as well.

> If you *really* care about the nanoseconds, you don't feed them to the 
> computer!  If you must, please don't step in what comes out the other 
> end! ;-)

Indeed!  Windows with a serial PPS source can achieve offsets well under 
250 microseconds - see:


Ken is reporting offsets of nearly 5 milliseconds, so there's something 
else going on.  I wonder what the spec of that PPS signal is, and how all 
the other stuff is multiplexed onto that cable?  Worth a look with the 
'scope, methinks.


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