Pytrack only receive empty nmea messages



  • Hi,

    I currently work with the LoPy4 (1.18.0.r1) and the pytrack shield (0.0.8), and everything worked fine until the pytrack started receiving only empty nmea messages (things like "$GNGLL,,,,,,,"), some are not completly empty (the total number of satellites in viex in GSV messages is never empty) and some are have wrong informations in the fiew fields not empty (the date in RMC messages often give a date in january 1980 when it's not empty).

    This issue did not happen after a firmware or software upgrade, simply from one day to another and on several devices at the same time.

    Has anyone a clue on what is happening and on how to fix this ?

    Thanks.



  • Going back to the 1.18.0.r1 and reseting the GPS did not help.
    The firmware updater (1.15.2.b1) installs the 1.18.1.r10 version of the firmware and I'm unable to find the 1.20.rc4 version of the firmware.



  • @emmanuel-florent said in [Pytrack only receive empty nmea messages]

    With previous 1.20 rc3 I got some Guru mediations, problems that has been fixed.

    How have you got them? I didn't get Guru meditaitons with LoPy (without a number) and WiPy 3


  • Global Moderator

    @daraujo I have been able to acquire a valid GPS location on the current lastest development firmware. It is available throught firmware-updater 1.20 rc4. With previous 1.20 rc3 I got some Guru mediations, problems that has been fixed.



  • @daraujo

    Should I go back to the 1.18.0.r1 version and try reseting the GPS ?

    Yes, give it a try.

    If it is invalid it doesn't get a fix. In my street I have a time frame for getting fixes in the window. I will not get them in the evening hours. That's one reason why I am adding on my system a feature to read a stream from SD card.



  • Thanks for the quick answer.

    All the checksums are correct and i2c connections were already secured with locks.
    However every GLL and RMC messages are invalid.

    I tried to update the firmware to 1.20 rc3 (I could not find rc4) but there is a "Guru Meditation Error: Core 1 panic'ed (LoadProhibited)." every time I run the script.
    Should I go back to the 1.18.0.r1 version and try reseting the GPS ?



  • The min date ist not the one of Unix.

    • Check the valid flag of the sentence. Note that V means invalid :-|
    • Check the checksum.
      If you do not receive the stream fast enough, you will mix more than one sentences into one. The buffer of the i2c is not large. So delaying the i2c read will drop some chars. You will not be noticed about that. Therefore you have to check the checksum. It is an xor of all bytes between $ and * (without these two tokens)

    You may mix it up with the end of the GSA sentence without a fix:

    $GPGSA,A,1,,,,,,,,,,,,,,,*1E
    

    You may also get in trouble with other i2c connection running in parallel. Secure them with a lock so, that i2c reads are serialized.

    My problems stoped with firmware 1.20 rc4. It is worth to update one of your devices and test it.

    If you have done all that, reseting the GPS with an MTK message can be helpful. But check first that you don't drop chars of the stream.


 

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