[ntp:questions] PPS versus serial offset

David Taylor david-taylor at blueyonder.co.uk.invalid
Wed Aug 28 11:38:30 UTC 2013

On 28/08/2013 10:10, Rob wrote:
> detha <detha at foad.co.za> wrote:
>> I have a test setup with a RaspberryPi and a SiRF/gpsd module. All
>> working quite well, but one thing bugs me. Looking at the ntpq -p output
>> the serial port readings seem to drift away slowly but steadily from the
>> PPS, see <http://detha.co.za/ntp/ntpmon.20130828.jpg>.
> It is normal.  The offset between serial data and PPS changes all the time.
> It is often a bit better when you put the GPS in binary mode instead
> of NMEA.

Indeed, or use a very high baud rate for the NMEA.

I would be more worried about the 11 ms step in the PPS at about -155 

Nice graph, though....
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