This topic summarizes how to setup an NMEA port on the AR755x platform.

Setup Target

To setup an AR755x target, run the follow commands (only once):

AT!ENTERCND="A710"
AT!CUSTOM="GPSENABLE",1
AT!CUSTOM="NMEAENABLE",1
AT!CUSTOM="GPSSEL",1
AT!GPSQMICONFIG=1
AT!GPSNMEA=1
AT!GPSNMEACONFIG=1,1
AT!GPSNMEASENTENCE=29FF
AT!GPSONLY=0
AT!RESET

Start NMEA

Once, the target is setup, run this on the AR755x Linux console:

 start NMEA device:
echo '$GPS_START' > /dev/nmea

Then "/dev/nmea" file can be open in order to parse the NMEA frames.

Warning

If you need to use Legato positioning service in parallel, you can't use this command; you have to use le_posCtrl_Request().

Stop NMEA

To stop the NMEA, run this on the AR755x Linux console:

echo '$GPS_STOP' > /dev/nmea

Warning

If you need to use Legato positioning service in parallel, you can't use this command; you have to use le_posCtrl_Release().

Get NMEA stream

Here's an example of a dump of GNSS NMEA frames (here only $GNxxx frames):

echo '$GPS_START' > /dev/nmea
cat /dev/nmea | grep '$GN'
 
$GNGNS,094821.0,4849.931307,N,00216.053323,E,AA,14,0.6,161.5,48.0,,*6D
$GNGSA,A,2,05,13,18,21,27,29,31,,,,,,1.0,0.6,0.7*2C
$GNGSA,A,2,68,69,74,75,76,84,86,,,,,,1.0,0.6,0.7*2E
$GNGNS,094822.0,4849.931277,N,00216.053326,E,AA,15,0.6,161.5,48.0,,*6C
$GNGSA,A,2,05,13,16,18,21,27,29,31,,,,,0.9,0.6,0.7*23
$GNGSA,A,2,68,69,74,75,76,84,86,,,,,,0.9,0.6,0.7*26
$GNGNS,094823.0,4849.931249,N,00216.053330,E,AA,15,0.6,161.5,48.0,,*67
$GNGSA,A,2,05,13,16,18,21,27,29,31,,,,,0.9,0.6,0.7*23
$GNGSA,A,2,68,69,74,75,76,84,86,,,,,,0.9,0.6,0.7*26
$GNGNS,094824.0,4849.931225,N,00216.053333,E,AA,15,0.6,161.5,48.0,,*69
$GNGSA,A,2,05,13,16,18,21,27,29,31,,,,,0.9,0.6,0.7*23
$GNGSA,A,2,68,69,74,75,76,84,86,,,,,,0.9,0.6,0.7*26
 
 
Decoding...
 
$GNGNS: GNSS Fix data
http://www.catb.org/gpsd/NMEA.html#_gns_fix_data
 
$GNGSA: GNSS Active Satellites + Dilution of precision
http://www.catb.org/gpsd/NMEA.html#_gsa_gps_dop_and_active_satellites
 
2D-Fix with:
- 8 GPS Satellites: 05,13,16,18,21,27,29,31
- 7 Glonass Satellites: 68,69,74,75,76,84,86
 
Time: 094824.0 --> 09:48:24 (UTC)
Latitude: 4849.931225,N --> 48 + (49.931225 / 60) = 48.83218708333333
Longitude: 00216.053333,E  --> 002 + (16.053333 / 60) = 2.26755555
https://www.google.fr/maps/@48.8321871,2.2675556,17z​

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