[ntp:questions] custom NMEA messages

Mike Cook michael.cook at sfr.fr
Sat Dec 26 20:55:04 UTC 2015

If you look at the doc <<https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver20.html>> you will see that your message is not supported, so you would have to modify the driver.
However I suspect that you also have some standard sentences as well as these beast are supposed to work with GPSD under linux. I haven’t looked in detail but I found a link to <<http://raspberrypi.stackexchange.com/questions/547/how-do-i-attach-a-gps-receiver>> which may help.
It is possible that your device was configured for a particular application and you will need to reset it to its defaults to get the common NMEA sentences. 

Hope the helps.

Le 24 déc. 2015 à 21:43, Leon McCalla <leonmccalla at hotmail.com> a écrit :
> Hi,
> I have a globalsat BU-353-S4 GPS receiver that I would lie to use as a source for NTPd.  When looking at the messages that it produces, unlike the periodic messages I would expect every second, I get messages in bursts of threes followed by a pause. If the face of an analog clock represented a 3 second window I receive messages at 12,1,4,8.
> One option is to use the UTC messages as an estimate to set the clock initially then NEVER use the gps again but this defeats the purpose of using a GPS for NTPd.  My alternative is to try to find some stability in the madness before subjecting NTPd to these seemingly unstable messages.
> looking at the messages in detail, I can see that a GPGBS message is produced in the middle of the burst and based on wireshark messages, this single message appears every 3.000 seconds. While this is not every second as a traditional PPS message is expected, I would like to see if NTPd can work with something less frequent but highly stable.
> how do I compile a custom driver to read NMEA messages that are not part of the default NMEA driver? The GPGBS message looks like this... http://www.trimble.com/OEM_ReceiverHelp/V4.44/en/NMEA-0183messages_GBS.html
> PS if im going crazy for no reason and NTPd is capable of working with this garbage please let me know.
> Leon
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