[ntp:questions] custom NMEA messages

Leon McCalla leonmccalla at hotmail.com
Thu Dec 24 20:43:43 UTC 2015

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.


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