[ntp:questions] pps breaks when nmea is enabled for ntpd

Mike S mikes at flatsurface.com
Sat Jun 15 18:22:33 UTC 2013

On 6/14/2013 9:03 PM, Richard Cagley wrote:
> If I enable an internet server and pps, then pps works great
> server clock.redhat.com iburst prefer minpoll 4 maxpoll 4
> server minpoll 4 maxpoll 4
> fudge flag3 1
> However, if I add an NMEA server to my ntp.conf file like this
> server mode 1
> fudge flag1 1
> server minpoll 4 maxpoll 4
> fudge flag3 1
> then pps stops working.

You don't say otherwise, so I assume this is all on the same serial 
port. I think what's happening is that NMEA grabs the serial port first, 
so the separate Atom (PPS) driver doesn't have access.

Don't use the Atom ( driver, you don't need it. The NMEA 
driver has its own PPS capabilities. You used "flag1 1", which enables 
that support - what did you think that was doing? It doesn't make sense 
to have two different PPS drivers, both driven by the same signal.

This is what I use for a Garmin 18x-LVC.

#       flag1 1 = enable PPS
#       flag2 0 = PPS on assert
server    mode 1 minpoll 4 maxpoll 4 prefer
fudge    time2 0.470 flag1 1 refid gPPS

This works better than using both drivers with different serial ports, 
in my experience.

BTW, you should stop abusing redhat. It's rude to hit a public NTP 
server at maxpoll 4.

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