[ntp:questions] Come back PPS I miss you!

David J Taylor david-taylor at blueyonder.co.uk.invalid
Fri Feb 10 16:44:54 UTC 2012

> So.. I am replying to my own posts too..
> Started ntpd in debug and seeing a lot of GPS_NMEA(1) PPS_RELATE_NONE
>>From the source:
> * The function returns PPS_RELATE_NONE (0) if no PPS edge correlation
> * can be fixed; PPS_RELATE_EDGE (1) when a PPS edge could be fixed, but
> * the distance to the reference time stamp is too big (exceeds +/-400ms)
> * and the ATOM driver PLL cannot be used to fix the phase; and
> * PPS_RELATE_PHASE (2) when the ATOM driver PLL code can be used.
> So does this mean basically I am screwed and can get on with life?
> Many thanks,
> Mark


If it were me, I might reduce the complexity of your ntp.conf file, reduce 
it to the basics, and see how NTP worked.  Have two or three Internet 
servers you can trust, and just the minimum needed to get the serial GPS 
and PPS over DCD working.  Remove any keys or peer statements.  Were it my 
own Sure or Garmin GPS 18/x LVC, that configuration might be something 

driftfile "C:\Tools\NTP\etc\ntp.drift"

# ref-clock drivers

# PPS - serialpps.sys
server minpoll 4

# NMEA serial port, 16 = 9600 baud, 2 = $GPGGA
server minpoll 4  mode 18  prefer

server	0.uk.pool.ntp.org
server	1.uk.pool.ntp.org
server	2.uk.pool.ntp.org

enable stats
statsdir "C:\Tools\NTP\etc\"
statistics loopstats

IIRC, you can put noselect against the NMEA source, so the the seconds 
come from the Internet, and the PPS from the GPS device.  Your NMEA mode 
value may be different, of course.  One problem I have seen in the past is 
with NMEA devices which output more than one sentence, but at a baud rate 
which is too slow to accommodate all the sentences in the time available! 
I expect you've check that sort of thing, though.

# Sure GPS board:
server minpoll 4  mode 18  prefer

# Garmin GPS 18 LVC receiver:
server minpoll 4 prefer

# Garmin GPS 18x LVC at 19200bps
server minpoll 4  mode 33While NTP is not running, you might look for a brief pulse on the DCD line 
using my very simple port monitor.

I hope there's something there which helps.


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