Olin Lathrop wrote:

>> If task A has equal priority as task B, will CPU time be shared
>> equally among the tasks?
> 
> In theory.

Depends on the scheduler, though, as everything else. There is not "the
RTOS" -- there are RTOS concepts, and their implementations. And pretty
much every implementation is different.

>> 5. If we have two tasks, J and K, which each perform very important
>> protocol operations (such as bitbang 1-wire and RS-485 protocol),
>> and both are set to the highest priority, how should they be set up
>> so that they don't interrupt each other in critical moments,
> 
> It may not be possible.  Essentially you are asking for a way to have
> a particular task declare that it be the only task that gets CPU
> until it says otherwise.  Some real time OSes might support that, but
> no ordinary desktop OS or multi-user system would allow that. 

Typical desktop/multi-user systems do allow this. Most systems have a
means of thread (aka task) synchronization. You can use this to prevent
that two threads interrupt each other in critical moments. Details (and
nomenclature) of course vary widely between systems. 

However on a typical desktop/multi-user system this doesn't mean that
other processes (or the system) won't interrupt your task/thread. But if
that is a requirement, such systems are not suited anyway. I would think
that any OS that can be called a "real-time OS" should have a means to
guarantee this, though.

Gerhard
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