Thanks for all your kind comments. OK, I'm not really afraid, just more suspicious about using an OS.

In fact this is a small project which cannot afford an OS, and probably there is no need for such a complex and professional OS.

I was thinking to develop a simple os (maybe it should not be called as OS) which supports basic task scheduling and some sort of signalling. I was trying to learn the basics by reading uc/OS for Philips XA and Mike Koller's RTOS. I think there will be small number of (<10) C routines and a few assembly code at most.

Is this a bad idea?

(Sorry for insufficient information...)