[ntp:questions] GPS NG type 46 refclock tests

juergen perlinger juergen.perlinger at t-online.de
Sun Dec 7 09:44:07 UTC 2014

On 12/06/2014 09:50 PM, Paul wrote:
> [I just don't understand why NTP people like GPSD]
Well, they have a decent code base for dealing with a number of GPS
devices, and they have hardware PPS support. And using GPSD as a time
source makes more sense than using NTPD as source for position

There has been the idea to support the chrony pipe model as an
alternative to the shared memory clocks to couple GPSD and NTPD, but
that would probably have required work on both sides. I found the idea
of using the JSON GPSD client protocol  more appealing and wrote a
simple driver as  a proof of concept.

> On Sat, Dec 6, 2014 at 4:29 AM, David Taylor <
> david-taylor at blueyonder.co.uk.invalid> wrote:
>>   ln -s /dev/ttyAMA0 /dev/gps0
> Sure that can work.  I haven't looked at Refclock 46 in any detail though.
That's indeed the way it is intended to work. The GPSD-JSON driver uses
the same naming scheme as the NMEA driver -- It makes switching between
NMEA and GPSD a bit more easy while experimenting.

NOTE:  You must also start GPSD on the same link (like 'gpsd -n
/dev/gps0') or the driver will not find its device.

If there is need for it, I'm willing to do the necessary stuff to let
the driver do the link evaluation. Then the native device name would be
used by the driver. This would still require the link for NTPDs sake,
but GPSD could use ttySxy or whatever.

Feel free to file a bug (well, a feature requirement) against the driver
if you feel hampered by the current setup!
>> Secondly, in the documentation "TVP" is mentioned.  It would be helpful if
>> it were defined, but is not.  I guess time-velocity-position?  As I have
>> those in cgps -s I appear to be covered, but what about the other objects?
>> WATCH, PPS and version are listed.  How you I know whether I have these?
> It's TPV not TVP and yes it's time-position-velocity.  This is all
> "explained" here: <http://www.catb.org/gpsd/gpsd_json.html>
> WATCH and VERSION are commands sent by the client to the server.  TPV and
> PPS are responses sent by the server to the client.  I'm sure they're fully
> supported in your instance.
I'd call it 'briefly described' -- an explanation would go far beyond
that, IMHO. But I've seen worse also.

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