How to probe a modem exposing virtual ports (GSM 07.10 muxed ports)

Aleksander Morgado aleksandermj at
Fri Mar 8 09:31:49 UTC 2024

Hey Garfield,

> I have a situation where I have a ublox modem, the LISA u200, wired up using its SPI bus as the communication channel. On the DTE side is a raspberry pi SBC with a custom spi platform driver that exposes a tty device for modem. This driver is not capable of multiplexing and exposing multiple virtual channels.
> To overcome this I have a user mode daemon that performs this function by connection to the single tty port exposed by the spi driver and in turn creating 5 pseudo tty's (/dev/ptty1 -> /dev/ptty5) to interact with. These are actually links to /dev/pts/1 to /dev/pts/5.
> I want the ublox plugin to manage this device but there seems to be no way to filter/grab those ports.

You should be able to add the ID_MM_PHYSDEV_UID udev tags for all
those pseudo TTYs, so that ModemManager can "bind" all those ports
together to the same modem object, see


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