[time-nuts] M12+T more confusion

[Hal Murray]

> I hear SiRF's ZDA message is supposed to be sync'd with the top of the
> second.

The manual says something like that.

I've been searching for inexpensive GPS units that work well with ntp.  The 
SiRF sets are inexpensive, but the timing on their NMEA messages sucks.  
There is a lot of jitter and wander.  By wander I mean offset that changes 
slowly so you can't filter it out, hanging bridges.
  http://www.megapathdsl.net/~hmurray/ntp/GPSSiRF-off.gif

They also have a leap second bug that makes the answer off by a second some 
of the time in some strange pattern over a week.  I assume that's what caused 
it.  It was working OK until the GPS satellites started announcing the next 
leap second.
  http://www.megapathdsl.net/~hmurray/ntp/leap-gps2.gif
(I'll bet there is a good story behind that one.)


The NMEA driver in ntpd defaults to expecting RMC, so that's what I normally 
use.

A while ago, somebody mentioned that ZDA should be better, so I tried it.  I 
couldn't see any difference.





-- 
These are my opinions, not necessarily my employer's.  I hate spam.