Hi There are a pretty small number of things that a GPSDO worries about that are not in the standard NMEA data structures:
1) DAC 2) Temperature 3) Lock state 4) Time error 5) Maybe a “quality of lock” metric A lot of GPSDO’s put out more than that in their status messages. There is a lot of repetition between NMEA messages and that carries over to the custom stuff. More or less anything that starts with $P is considered a specialized / custom message. You could easily have a $PTNT (for TimeNuts of course not for blowing things up) message or set of messages. If you added a “version” field to the list above, and a “number of fields to follow”, you probably would have a useful string to use. $PTNT,1,5,32768,27.232,1.1.3,+22.868, -13.45,100 would be version 1, 5 fields, DAC 32768 out of who knows how many (hmm…), State 1.1.3 (out of how many), Temp 22.868 C, time error -13.45 ns, lock quality 100%. You could take care of the dac issue by going to a float with a defied range of 0 to 1. State is a bit more difficult. It depends a lot on how things are implemented. We probably would need it a bit better defined or put it in another message. Bob > On Dec 17, 2016, at 2:22 PM, Jim Harman <[email protected]> wrote: > > Hi all, > > I have experimented with LH 5 just monitoring a GPS receiver and am very > impressed with the results. > > As a next step, I would like to use LH to monitor a homebrew GPSDO, and I > think it would be easier to modify the GPSDO firmware to emulate an > existing device rather than customize LH to work with the logging data that > my system currently produces. > > In addition to NMEA data from the GPS, my system can output the DAC and TIC > (phase error) values as well as the temperature, Since I control the > firmware, I can produce pretty much any data format as long as it is > clearly documented, but I would prefer a text-based rather than binary > protocol and not to have to reformat all the NMEA data. > > Does this approach make sense, and if so which of the several standard > GPSDOs would it be best to emulate? > > Thanks in advance for your insights > > -- > > --Jim Harman > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
