[time-nuts] NTP and Oncore UT+

Chris Albertson albertson.chris at gmail.com
Sat Apr 19 23:52:57 UTC 2014

If you are running NTP, always you are going to need the PPS.  This applies
for any GPS receiver.  The data you get over the serial port is never
intended for timing....If you do not use PPS your NTP server will see the
GPS as being such a poor clock that it will likely ignore it in favor of
some Internet time servers.

If you don't understand what data to send to your UT+ to get it started.
 Look at what NTP sends over the serial port.  You can even cheat and let
NTP send whatever it does then disconnect the UT+ from the PC and it will
keep going until you kill the power. (I was so lazy I used this method for
a while.)

Sorry I've forgotten the details but you can look at the code in the ref.
clock driver or simply capture the data off the wire.  It uses a binary
protocol so don't try to capture it with a terminal.

You only really need the PPS if NTP is going to seriously use the UT+ for
timing.    The data comes out the serial port no matter if the PPS is
connected or not.  Who would the GPS know it the PPS was used? PPS is a one
way interface.

On Sat, Apr 19, 2014 at 1:58 PM, Bob Stewart <bob at evoria.net> wrote:

> I've done as much as I can do with my little Adafruit, so I guess it's
> time to move to a timing receiver.  I already have a UT+, so I might as
> well make use of it.  My thought was to use the NTP refclock driver and
> probably take the sawtooth from SHMEM with a simple "C" program to pass to
> my GPSDO.  The reference pages indicate that a PPS interface is
> "required".  Do I need to wire up the PPS just to get access to the
> sawtooth value, or can I just hook up serial access to the UT+ and use NTP
> as an interface to the UT+?  I have no experience with setting up a
> refclock driver, so any help would be appreciated.  Using NTP certainly
> looks a lot easier than figuring out why this UT+ doesn't always like to
> talk on the serial port and writing custom code to do the bits I want.  The
> PPS from the UT+ will, of course, be connected to my GPSDO board.
> From the manual:
> "The driver requires a standard PPS interface for the
> pulse-per-second output from the receiver. The serial data stream alone
> does not provide precision time stamps (0-50msec variance, according to
> the manual), whereas the PPS output is precise down to 50 nsec (1 sigma)
> for the VP/UT models and 25 nsec for the M12 Timing. If you do not have the
> PPS signal available, then you should probably be using the NMEA
> driver rather than the Oncore driver."
> Bob - AE6RV
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Chris Albertson
Redondo Beach, California

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