That means FP2 has to support host mode since it is easier. And then connect a device with USB CDC or HID so that kernel detect is as a serial port (/dev/ttyUSBx or /dev/ttyACMx).

For example would be cool connect a STM32 or similar MCU to FP2.

There is a STM32F042(ARM CortexM0) smallest LQFP is 32 pin package with builtin USB(this 32 pin variant is USB device only there is variants with Host mode also but it is a bit more complex). there is also a 20pin TSSOP variant with USB.

STM32 has USB CDC and HID drivers for its MCU's.

With such MCU we could do much cool sensor stuff
http://www.st.com/content/st_com/en/...oductId=LN1823

Btw to Dirkvl https://github.com/dirkvl/FairPhone/...vertingTOHtoFP

do not use FTDI. Here is one of the reasons:

https://www.youtube.com/watch?v=eU66as4Bbds

Also FTDI is to high price. You get a real MCU like STM32 for similar price.

I personally will not support any OTH with FTDI hell.