LinuxQuestions.org - Help with ModemManager and modem on UART port

I have a SARA-R52M10 cellular modem attached to a Raspberry Pi CM4 running Ubuntu 24.04 on UART3:

Code:

    root@GATEWAY-0x00000028:~# ll /dev/ttyAMA3

    crw-rw---- 1 root dialout 204, 67 Feb 25 01:21 /dev/ttyAMA3

I can get responses from it fine with

Code:

screen /dev/ttyAMA3 115200

or by running

Code:

stty -F /dev/ttyAMA3 115200 && cat /dev/ttyAMA3

in one terminal and

Code:

echo -e "AT\r" > /dev/ttyAMA3

in another.

But I am trying to get ModemManager to talk to it, and I cannot.

I am running:

Code:

    echo 'ACTION!="add|change|move|bind", GOTO="mm_sara_r52m10_end"

    SUBSYSTEMS=="tty", DEVPATH=="/devices/platform/soc/fe201600.serial/fe201600.serial:0/fe201600.serial:0.0/tty/ttyAMA3"

    LABEL="mm_sara_r52m10_end"



    # Rule for ModemManager to handle the device on ttyAMA3

    ACTION=="add|change|move", SUBSYSTEM=="tty", KERNEL=="ttyAMA3", \

        ENV{ID_MM_DEVICE_PROCESS}="1", \

        ENV{ID_MM_TTY_BAUDRATE}="115200", \

        ENV{ID_MM_PORT_TYPE_AT_PRIMARY}="1", \

        ENV{ID_MM_TTY_FLOW_CONTROL}="rts-cts"

    ' > /etc/udev/rules.d/99-sara-r52m10.rules

    udevadm control --reload && udevadm trigger



    systemctl restart ModemManager

    mmcli --scan-modems

    mmcli --list-modems

and get

Code:

    successfully requested to scan devices

    No modems were found

And

Code:

    journalctl -u ModemManager --no-pager --since "$(systemctl show -p ActiveEnterTimestamp ModemManager | cut -d'=' -f2)"

shows:

Code:

    Feb 25 01:27:02 GATEWAY-0x00000028 systemd[1]: Starting ModemManager.service - Modem Manager...

    Feb 25 01:27:02 GATEWAY-0x00000028 ModemManager[1737]: <msg> ModemManager (version 1.23.4) starting in system bus...

    Feb 25 01:27:02 GATEWAY-0x00000028 systemd[1]: Started ModemManager.service - Modem Manager.

    Feb 25 01:27:09 GATEWAY-0x00000028 ModemManager[1737]: <msg> [base-manager] couldn't check support for device '/sys/devices/platform/scb/fd580000.ethernet': not supported by any plugin

    Feb 25 01:27:09 GATEWAY-0x00000028 ModemManager[1737]: <msg> [base-manager] couldn't check support for device '/sys/devices/platform/soc/fe300000.mmcnr/mmc_host/mmc1/mmc1:0001/mmc1:0001:1': not supported by any plugin

    Feb 25 01:27:18 GATEWAY-0x00000028 ModemManager[1737]: <msg> [device /sys/devices/platform/soc] creating modem with plugin 'generic' and '1' ports

    Feb 25 01:27:18 GATEWAY-0x00000028 ModemManager[1737]: <wrn> [plugin/generic] could not grab port ttyAMA3: Cannot add port 'tty/ttyAMA3', unhandled port type

    Feb 25 01:27:18 GATEWAY-0x00000028 ModemManager[1737]: <wrn> [base-manager] couldn't create modem for device '/sys/devices/platform/soc': Failed to find primary AT port

Do my rules look ok? I am pretty unconfident in them.

How can I resolve the issue shown in the last couple lines of that output and get ModemManager talking to my modem?

Any thoughts are appreciated. Thanks!