AT port not attacted with RM520N-GL

Aleksander Morgado aleksandermj at
Tue Feb 13 11:44:46 UTC 2024

Hey Pradeep!

> We are using RM520N-GL in our SD-WAN edge device in USB mode on M.2 Slot.
> We are facing an issue where AT USB ports(ttyUSB2, ttyUSB3) are not enumerated .
> We are using "modemmanager - 1.16.6-2" and also added RM520 blob to " /lib/udev/rules.d/77-mm-quectel-port-types.rules" but still the AT port is not attached .
> Please advise any changes needed to resolve this issue.
> # Quectel RM520
> # #  ttyUSB0 (if #0): QCDM/DIAG port
> # #  ttyUSB1 (if #1): GPS data port
> # #  ttyUSB2 (if #2): AT primary port
> # #  ttyUSB3 (if #3): AT secondary port
> ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0801", ENV{.MM_USBIFNUM}=="00", ENV{ID_MM_PORT_TYPE_QCDM}="1"
> ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0801", ENV{.MM_USBIFNUM}=="01", ENV{ID_MM_PORT_TYPE_GPS}="1"
> ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0801", ENV{.MM_USBIFNUM}=="02", ENV{ID_MM_PORT_TYPE_AT_PRIMARY}="1"
> ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0801", ENV{.MM_USBIFNUM}=="03", ENV{ID_MM_PORT_TYPE_AT_SECONDARY}="1"
> In debug message there is log about "port is not AT-capable"
> >>
> 2024-01-25T16:45:52.070 DEBUG  daemon ModemManager[8350]: <debug> [ttyUSB3/probe] port is not AT-capable
> 2024-01-25T16:45:52.070 DEBUG  daemon ModemManager[8350]: <debug> [ttyUSB2/probe] port is not AT-capable

If the USB ports are exposed by the kernel, but they are not
responsive by the time MM tries to use them, it may be that MM didn't
wait long enough. I know we have updated those timeouts many times in
past releases, and you may be using an older value of the timeout. It
could also be that MM cannot, for some reason, communicate properly
with the device.

You should investigate a bit more:

1) Let it detect the modem without AT ports, wait some minutes, then
restart ModemManager. Does MM use the AT ports in that case? If it
doesn't process them yet, then it's not a timing issue.

2) Try to ignore only one of the TTYs:

Edit 77-mm-quectel-port-types.rules and add:
ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0801",

Then reboot the system. Does MM try to probe and process the non-ignored TTY?


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