APU4D4 and mPCIe LTE modem in slot 3

  • I am attempting to enable 3 x mPCIe LTE modems using a APU4D4 board running Ubuntu 20.04.

    I am aware the SIM slots relate to mPCI slots 2 and 3. I have fitted a SIM carrier to one of the LTE modems in slot 1 and this appears to work. The modem in slot 2 also works and I can query the devices via the USB serial ports that appear in /dev

    However, although the activity LED lights up for the modem in slot 3, I do not see any USB serial ports appearing in /dev for this device and so cannot connect to it. Swapping the modems results in the same issue with no connectivity to the device in slot 3. If I remove the device in slot 3 and place it in an external USB carrier plugged into one of the external USB ports, I can then get all 3 devices to work.

    Is there something I need to do with this slot position (3) in order to enable mPCI functionality as opposed to mSATA? The modem is powered and operating but I don't get any USB connectivity with it when it's in this slot.

    1) The operating system is installed on the SD card, so I don’t need SATA/mSATA

    2) The modems are Simcom SIM7600G-H (1e0e:9001)

    3) The Qualcomm Option driver is installed for these modems

    Thanks Alan