Preventing modem-manager from accessing specific serial ports?

[Volker Kuhlmann <list0570 paradise net nz>]

I have a bunch of Arduino hardware that connects with emulated serial
ports using FTDI chips (there are other possibilities for serial port
emulation too, e.g. CP2102 or microcontroller based ones).

As soon as I plug one of these devices in, modem-manager becomes active
and probes the devices, timing out each time (of course) and retrying
that about 3 times. This interferes with the serial port being used by
Arduino or terminal software.

What is the mechanism to tell modem-manager to keep its hands off
FTDI-based serial ports? I have used udev rules to create
constant-name device symlinks based on the devices USB IDs and serial
number. I realise that modems use emulated serial ports too so there is
always conflict, but I am not sure whether there are modems using
devices for which the device name is /dev/ttyUSBN. I'd be happy to
configure exclusion lists, but how do I do this?

There also seems to be a difference between desktop and laptop
computers. Modem-manager activates only on the laptop.

Thanks,

Volker

-- 
Volker Kuhlmann
http://volker.dnsalias.net/     Please do not CC list postings to me.