So we also do get NMEA messages occasionally. The issue is that it seems to just stop after a couple of seconds.
Having looked into it further we are noticing a couple things
- From a cold boot, for the first 30 seconds or so, if we send !GPSSTATUS we would get Last Fix Status = None. At this point, if we are observing the NMEA port, we would see those no fix NMEA messages I mentioned in the first post
- After 30 seconds, if we send !GPSSTATUS again, we would now get Last Fix Status = Fail, FailCode=4 which we understand to be GPS fix timeout (We would assume it would follow the max time param in our auto start config, which is 50 seconds but it doesn’t). The moment it switched to Fail, we would stop getting NMEA messages
- From this point onwards, the modem will stay on this Last Fix Status = Fail state.
We then tried to force it to get a fix by send !GPSFIX=1,255,1. Sometimes this message will return a ERROR message (But doesn’t return a error code like EM759x AT Reference Manual seems to suggest) but retrying the message a few times eventually returns a OK code.
Once that happens, Last Fix Status would be SUCCESS and we would start seeing NMEA messages again and it will keep sending NMEA messages until it goes back to Last Fix Status is FAIL. Not sure what causes it to go from SUCCESS to FAIL thou because just outright removing the antenna doesn’t seem to cause that, it would just stay on SUCCESS and keep resending the last good position, but we have definitely seen the modem go from SUCCESS to FAIL, which subsequently stops the NMEA messages.
So I guess our question at this point is
- Is the modem supposed to stop sending NMEA messages if Last Fix Status is Failed
- Is there a reason why the modem doesn’t seem to retry getting a fix automatically until we manually send a !GPSFIX message despite !GPSAUTOSTART being set