We can't help with this RTOS, however; you should focus on
something that has open standards so you aren't locked in.
The Linux/POSIX community is the most common standard although not
the only one.
For m16c try:
Using these open standards and off the shelf I/O support with a
tiny tiny Linux compatible rtos will get you the best solution
overall and the development is FREE, the source code is FREE and
non commercial development is FREE.