hello Nuno (or Nu–o ?),

Thanks for your answer :-)

My first analysis leads to roughly the same approach. But I still have some
inquiries :

> All timers are maintained by an Interrupt timer.
> 
Do you mean you must wait for a timer induced interruption to increment your
several auxilliary timers ?
Remember I must use a 12C509 without an interrupt :-(
Somebody told me I could use a watchdog wakeup ? (but the timing would be :
1st not accurate, 2nd too long)
-> any other idea ?

> Resources are managed through semaphores (which are also used to signal
> end of
> delays.).
> 
By "semaphore", I think you mean 1-bit-"flag" at H or L level ?

> Since, memory is short, all variables are global.
> 
That was also my way of thinking : no need to use stacks !

> Typical cycles are not closed, but can be. It all depends on the timing
> constraints (maximum atomic execution time for each task.).
> 
What do you mean by "cycles are not closed" ?

Thanks for any additional idea ;-)

Jean-Yves