[time-nuts] PPS offset between GPS receivers
lists at rtty.us
Sat Dec 8 03:28:20 UTC 2012
A lot depends on exactly what the interrupt structure is. It may also depend on the phase of the cpu clock relative to the pps signal. What's reasonably sure is that there is indeed some offset between the two where the answer is indeed "ft's" random. Another thing to check - how wide is the random region?
On Dec 7, 2012, at 9:19 PM, Chris Albertson <albertson.chris at gmail.com> wrote:
> One more test to try. Connect one PPS signal to both GPIO ports and see
> how close to zero offset you get. It would likely be random which gets
> read first.
> On Wed, Dec 5, 2012 at 5:37 AM, Gabs Ricalde <gsricalde at gmail.com> wrote:
>> Hi everyone,
>> As Tom suggested, I redid the test with less than 1 ft. of wire from the
>> PPS output to the GPIO without any logic gates or line receivers. Same
>> the SKG25A1 was 2 microseconds ahead of the 58534A. Without any other way
>> testing, I would probably trust the output of the timing receiver more
>> than the SkyNav module. Anyway the SkyNav board is an inexpensive unit and
>> I wouldn't mind setting an offset in ntpd.
>> I don't have a scope yet, and a low jitter PPS GPIO is the closest thing I
>> to a TIC.
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> Chris Albertson
> Redondo Beach, California
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