BPI R3 Mini with disappearing Quectel RM520N-GLAA

Banana Pi Router design BPI-R3/R3 Mini(MT7986)
1

Hi!

I’m having some issues with my BPI R3 Mini and a Quectel RM520N-GLAA where the Quectel modem is no longer accessible or visible as a USB device after the system has been shut down uncleanly (power outage or pulling the power plug).

The Problem:

The Quectel modem is always visible and accessible at least once after reinstalling OpenWRT 24.10.0/24.10.1, but after the first shutdown after it was first visible it will not be accessible anymore. Rebooting the system via the reboot command or via the web UI usually keeps the modem accessible.

When the modem disappears it’s no longer visible through lsusb or in cat /sys/kernel/debug/usb/devices until I reinstall OpenWRT and unplug the power cord once, then it will become available again. The Quectel modem itself seems to work just fine when plugged in to a Windows computer via a USB adapter, then there are no problems when it loses power etc. The modem is always detected and reconnects once plugged back in again to the Windows computer.

The setup:

  • BPI R3 Mini with a Quectel RM520N-GLAA connected via the internal M.2 B key slot with the Quectel modem set to QMI USB mode. The modem is running the latest RM520NGLAAR03A04M4G_01.204.01.204 firmware.
  • OpenWRT 24.10.0/24.10.1 installed on the eMMC. Clean install with only qmi-utils and luci-proto-qmi installed.

What I’ve tried so far:

  • Reinstalled OpenWRT 24.10.0/24.10.1 multiple times.
  • Tested the Quectel modem connected via a USB adapter. When it’s connected to my Windows computer it works really well, no problems here at all. When connected to the USB 2.0 port of the BPI R3 Mini it maxes out the bandwidth of the USB 2.0 port but sometimes resets itself, maybe it’s using too much power?
  • Tried running the echo 544 > /sys/class/gpio/export command and rebooting when the modem disappears. This seems to fix the problem for a single reboot or so, but the issue will return as soon as soon as the power cord is unplugged once and then the command doesn’t seem to fix the issue any more? When running the echo 544 > /sys/class/gpio/export command in “Local startup” it doesn’t seem to work at all.
  • Replaced the power adapter with a different one that has 12V PD support and sufficient power.

I participated in a similar discussion here [BPi-R3 mini] RM520N-GL not detected with OpenWRT 24.10.0-rc5 where some suggestions were made on how to make the modem available as a USB device. I just don’t really understand why this is a problem only after shutting down the system.

I’m not really sure how to proceed from here. Does anyone have any idea of what I should try next? I guess trawling through some logs is a reasonable next step. I’m just a bit unsure of what to look for.

I’m thankful for any new ideas on how to proceed. Thanks!