[ntp:questions] Assistance with PPS on Windows

Chris Albertson albertson.chris at gmail.com
Thu May 5 22:35:26 UTC 2011

On Thu, May 5, 2011 at 1:13 PM, Terje Mathisen <"terje.mathisen at
tmsw.no"@ntp.org> wrote:
> unruh wrote:

> Add some extra hw, in the form of a very good crystal (surplus Rb) and a hw
> counter which starts to run on the PPS signal, so that the sw can query it
> to determine how much interrupt latency we got this time, and you get a
> FreeBSD box down in the dual-digit nanoseconds.

yes, FreeBSD and now Linux do run on a nanosecond clock and it's not
at all hard to measure interrupt latency once per second.

If you don't like designing you own electronics use the "pictic".
(Google pictic) it can measure the time from PPS to the interrupt
being serviced  to much better then a nanosecond.  Costs about $50 to
build and a PCBs are available.    But this level of precision is not
needed by most users.  Some do.  My goal is to to learn about the
ionosphere by measuring how radio waves reflect off of it.

Even though I have some of this equipment I'm still astonished that
measurement at the sub-nanosecond level is both possible and
affordable on a hobbyist budget.  Not to long ago this was only
possible in large university or government labs.

Chris Albertson
Redondo Beach, California

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