[ntp:questions] Re: How to configure gps/pps with ntp?

Richard B. Gilbert rgilbert88 at comcast.net
Sun Mar 26 04:59:57 UTC 2006

Chris Richmond - MD6-FDC ~ wrote:

> Folks,
>    I'm back...  Now that ntp is running, I want to get it going with
> my Garmin gps18lvc.  I've got a 2.4.32 kernel with PPSKit running,
> linked /dev/ttyS0 -> /dev/pps1, and added "server prefer"
> to the config file.  ntpq -p -n reports the .GPS. line, but the data
> isn't updating (all zero's except the last field is 4000.00).  I connected
> to /dev/ttyS0 with minicom, and I'm getting the NEMA sentences, so
> I think the hardware is OK.  I've tried looking through the online
> docs, but among all the words are hardly any examples of what to
> actually *do*.  I've also looked through Terje's notes, but the
> actual configs weren't mentioned.  > ntpq -c rv -p ntp1
> shows that refid= (other box, not GPS).
> Please let me know what else I need to do.
> Thx, Chris

Ooops!!  I missed the fact that, while you have configured the PPS 
driver, you have not yet configured the NMEA driver

The PPS signal should mark the top of the second with accuracy that 
might approach +/- 50ns.  That's ALL it does.  It does NOT tell you 
which second it is.

The GPS18LVC uses the NMEA protocol so you also need to configure the 
NMEA driver (driver 20).  Add a line:
to your ntp.conf

You will still need to create the link that I mentioned in my previous 

That may not be all of it; as I said, I've never configured the Garmin 
GPS18LVC myself and I may have missed things.

Keep good notes of everything you do.  There is no documentation for 
configuring the GPS18LVC and you are being requested to write some to 
help the next guy who needs it.

More information about the questions mailing list