Serial Port Device Driver for Pistachio?

Hi!
How do I write a simple device driver for Pistachio, such as a serial
port driver? I was looking in the L4Ka::Pistachio sources and in the
IDL4 sources, but didn't find anything. At the moment I'm using the KDB
IO, for which I've written the getc(), putc() functions. But I would
like to have a "real" serial port driver. It should:
a) run in User Mode
b) register for an interrupt, that is received if a char arrives
c) should implement the getc(), putc()

Is there some example code (IDL, C)? Or is there maybe a device driver
tutorial? I'm sure someone has done something like this already.

Thanks,

Martin.