AT port not attacted with RM520N-GL

Pradeep Gopanapalli pradeep.gopanapalli at
Tue Feb 13 18:00:36 UTC 2024

Hi Aleksander,

Thanks for your reply, I will try out the suggested methods.
And another thing is we are planning to update ModemManager
,currently we are at 1.16.6-2) and we can go to 1.20 stable versions.
Is there any stable version that you can push into ModemManager sources?

Pradeep G

On Tue, Feb 13, 2024 at 3:44 AM Aleksander Morgado <
aleksandermj at> wrote:

> 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",
> > ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0801",
> > ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0801",
> > ATTRS{idVendor}=="2c7c", ATTRS{idProduct}=="0801",
> >
> > 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?
> --
> Aleksander

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