[BPI-R4] CN14 doesn't initialize M2-modem as a modem

[JohnSpen]

Hello! I’m setting up a Banana Pi BPI-R4 with OpenWRT 24.10.2 installed.

I’m a newbie and don’t know OpenWRT well. I’ve mostly been configuring router using AI (and I’ll share below some of the steps that I took with Claude), but at a some point AI hit a dead end and start going in circles. That’s why I’m looking for help here

I inserted two Foxconn-T77W968 (DW5821e) modems into the Mini-PCIe slot on the back of the board (using a Mini-PCIe to M2 Key-B adapter without SIM).

Adapter photo

Backplate photo

The LEDs for SIM-2 and SIM-3 are not blinking, but both modems are detected by lsusb command:

Bus 001 Device 003: ID 413c:81d6 DELL DW5821e Snapdragon X20 LTE
Bus 001 Device 004: ID 413c:81d6 DELL DW5821e Snapdragon X20 LTE

No ports were created in the /dev/ttyUSB* path. Installing the packages kmod-usb-serial kmod-usb-serial-option kmod-usb-serial-wwan didn’t help either. At this stage, Claude (as I understand it) suggests adding the drivers manually by command echo "413c 81d6" > /sys/bus/usb-serial/drivers/option1/new_id . Two ports were created automatically:

crw-rw---- 1 root dialout 188, 0 Sep 26 10:45 /dev/ttyUSB0
crw-rw---- 1 root dialout 188, 1 Sep 26 10:45 /dev/ttyUSB1

By command lsusb -v -d 413c:81d6 | grep -A 5 -B 5 "bNumEndpoints\|bInterfaceClass", I get the following information about the modems:

Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 2
bInterfaceClass 255 [unknown]
bInterfaceSubClass 66 [unknown]
bInterfaceProtocol 3
iInterface 7 fastboot

Endpoint Descriptor:
bLength 7

--

Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 2
bInterfaceClass 255 [unknown]
bInterfaceSubClass 66 [unknown]
bInterfaceProtocol 3
iInterface 7 fastboot

Endpoint Descriptor:
bLength 7

But the modems are still not being detected in any way:

1. Using the ModemManager tool mmcli -L returns “No modems were found”
2. Created ttyUSB0 and ttyUSB1 ports don’t respond to AT commands.

At this point AI start going in circles. What can be done with this modems? And is it even possible to set up them? Thanks

[Rup]

Hello,

I did not used modems on R4, but could this help? DW5821e Modem no CDC MBIM interface - #3 by ilya.rocket - Hardware Questions and Recommendations - OpenWrt Forum

[JohnSpen]

I have localized the problem. By resetting OpenWRT now one of the modems initializes correctly - as a modem (and create ports), not as a storage device. However, the modem connected to the second Mini-PCIe slot (CN14 mPCIE – SIM3) does not initialize as a modem.

I have tried three different modems and swapped adapters between them - the issue is definitely with the slot itself, because on all other slots (CN16 – SIM1 and CN12 – SIM2) the modems initialize and work correctly.

I am currently still searching for a solution. Thanks.