[Update: Mar 25th] Testing Quectel EM12-G WWAN 4G Modem on Librem 5

Hardware Librem 5
21

I didn’t have much to go on (I’d need journalctl logs at least) but I did post this question to AI and it suggested some things to try:

"When using a Quectel EM12-G WWAN 4G Modem on Librem 5 Linux phone running PureOS, there’s an error or bug that makes the audio distorted and with lots of static when making and audio phone call. What is needed to make this modem work, how to troubleshoot and fix? Also, suggest terminal commands to get relevant information to understand better what may be wrong and to verify what the problem is."

Suggestions

To troubleshoot and fix the audio distortion and static issue with the Quectel EM12-G WWAN 4G Modem on a Librem 5 Linux phone running PureOS, you can follow these steps:

  1. Check the Modem Configuration: Use the command sudo mmcli -m any | grep -v 'imei\\ |Numbers\\ |equipment id\\ |device id: ' to get the modem configuration1.
  2. Check the Firmware Version: Ensure that the firmware version of the modem is EM12GPAR01A21M4G1. If not, you may need to update the firmware.
  3. Check the Serial Configuration: The expected modem serial configuration is as follows1:
  • /dev/ttyUSB0 - DM
  • /dev/ttyUSB1 - For GPS NMEA message output
  • /dev/ttyUSB2 - For AT command communication
  • /dev/ttyUSB3 - For PPP connection or AT command communication
  1. Check the Kernel Version: Test the modem with kernel 5.19.0 on Ubuntu using a M.2 to USB3 adapter to see if there is any difference in functionality that may point to required kernel updates on pureos101.
  2. Check the Modem Rules: Ensure that the modem rules are updated1.
  3. Check the Error Log: Repeat the following steps to get the error log1:
  • Turn the modem off
  • Turn the modem on
  • Wait for 4G bars to show in UI
  • Toggle mobile data
  • Send a message, or try to place a call
    [edit: use journalctl commands to select the relevant lines / timeframe of this step]
  1. Check the AT Commands: Use the command ATE in /dev/ttyUSB3 to see if it works with AT commands consistently2.
  2. Check the Network Connection: Use the command AT+CEREG? and AT+CGPADDR to check the current state2.

If the issue persists, you may need to downgrade the firmware to EM12GPAR01A20M4G3. If you’re still experiencing issues, it’s recommended to reach out to Quectel support for further assistance4.

Also, if you already get already some audio through it and are able to place a call - Hurray!! :boom:

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22

Try using a headset with a built-in microphone inserted into the 3.5mm port.

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23

Same issue. It’s not an issue with the speakers but the PCM audio source decoding/encoding

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Quick question, how did you get it to work? Can you share the pm rules, and commands? For me it certainly did not work out of the box.

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25

It’s just the default udev rules shipped with MM. I generally had to restart ModemManager, but otherwise it all worked. Note that I use pmOS not PureOS. PureOS might need some packages updated

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Ah ok that would be the difference, I will give it a try again in pmOS and see what happens.

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