[ntp:questions] Peer Review of ntpq -c rv

David J Taylor david-taylor at blueyonder.co.uk.invalid
Thu Mar 8 07:42:50 UTC 2012


"Ron Frazier (NTP)" <timekeepingntplist at c3energy.com> wrote in message 
news:4F582243.10406 at c3energy.com...
[]
> At first I was confused and thought he was ms off.  However, if he's 
> within 34 us, that's pretty good.  Sounds like his board is working OK, 
> but could possibly be a bit better.  If he were communicating 
> exclusively on the serial port and the PPS were not working, would he be 
> getting performance this good?

As has been written here many time before - serial NMEA alone is likely to 
about as good as Internet sources (if that) and perhaps three orders or 
magnitude worse than a serial port PPS/DCD connection.  Milliseconds, not 
microseconds.

[]
> However, the manual for the Trimble Resolution T recommends GPZDA for 
> timekeeping.

Strange they do that as that sentence has no information about whether the 
GPS data is valid or whether the GPS is locked.  Until I hear a good 
reason otherwise, that seems to me to be the /worst possible/ single NMEA 
sentence to use!

Cheers,
David 



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