[ntp:questions] What is the NTP recovery time from 16s step in GPS server?
david-taylor at blueyonder.co.uk.invalid
Tue Oct 30 19:28:26 UTC 2012
On 30/10/2012 17:59, Rob wrote:
> When I wrote that part of gpsd, I implemented the proper checks so
> that the time is only put in the SHM after the GPS receiver has
> indicated that it has a valid fix on the satellites.
THanks for this information, Rob. In this case the GPS appears to have
a valid fix, but it is outting GPS time and not UTC. There must be a
flag in the Trimble TSIP which tells you this, as I've seen the same
when monitoring with the Trimble Studio software. It takes some time
for the switch-over to occur.
> I would hope that the receiver has collected the GPS offset by that
> time, so that it will not put the wrong time value in SHM during a
> short interval.
For this receiver that hope is not applicable. Perhaps gpsd should only
show UTC, or have a flag to indicate between GPS time and UTC?
> However, it has been a couple of years and many changes have been
> made to the code, I cannot tell you if it may have been broken.
> Do you really see the problem you describe above, or is it only a
> hypothesis of what might happen?
Oh, I really see this. I had occasion to restart my Raspberry Pi NTP
server and the gpsd source was off by 16.0 seconds for a few minutes
after booting. The GPS receiver is powered from the PC. At the moment
it has multiple Internet servers as well as the gpsd/ATOM reclocks.
More information about the questions