...I need because I have to do things that should happen separate from the application (i.e. special processing and radio transmission like repeating).

And these things HAVE to run paralel. I really can't see any other option as doing some kind of cooperative tasks with the help of timer.

+the whole implementation is stucked into an API so the scheduller is running there, without any knowledge what the mighty application is doing.

And I pray that '51 architecture can live with it. Have no other options it's the core of an ASIC, and trust me it was not my decission to use it (although I like this micro very much).

Anyway if Keil managed to do an RTOS with scheduller for '51, why wouldn't it work for me if I build one (without preemtion, context switch etc.)?

To Jan:
p.s. Slovak beer is good enough for me, but I decided, why not to learn German :)

And yeah unfortunately I had to leave C and dive into ASM after realising the fact that a C compiler lives his own life and it must not always be in a way I want. So any asm vs C commentars are welcome.