[ntp:questions] System time ramps forcing step correction?
snews at lordynet.org
Mon Sep 10 11:40:20 UTC 2012
A C wrote:
> On 9/9/2012 15:41, E-Mail Sent to this address will be added to the
> BlackLists wrote:
>> A C wrote:
>>> Has anyone seen a system with GPS/PPS have its system
>>> time ramp/slew ahead by over a second requiring a step
>> Prefer the PPS source?
>> GPS time is usually only second relative without the PPS,
>> and will sometimes drift around a lot within the second
>> on non timing GPSes.
>> I have GPS chips on embedded systems that the serial sentence
>> always seems to wander around 20ms to 50ms.
> NTP doesn't let me prefer the PPS source (ATOM). I'm forced to prefer
> some other source and let PPS activate on its own.
When atom driver was working reliably I had both type-20
and type-22 drivers specified, the type-20 NMEA gave the
"second" and PPS sync was from type-22 atom.
Because of the wander of the nmea value it was also
required that I had "tos mindist 0.5" and used a large
fudge time for the nmea. Both required values depended on
the particular make and firmware revision of the GPS unit.
More information about the questions