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Re: Hard-Realtime behaviour


On Tue, May 30, 2006 at 10:09:21AM +0200, Fabian Scheler wrote:
> >Disable the caches. How long something takes to execute will depend on
> >what is in the cache. If the code to be executed is still in the cache
> >from the last time it was executied, it will execute a lot quicker
> >than if it has to be fetches from RAM/ROM. The same applies to the
> >data to be processed. So to be deterministic, you need to disable
> >caches.
> 
> In order to guarantee deadlines, the worst case has to be
> deterministic, not the average case! In event-driven systems
> everything should be fine as long as your worst case response time is
> beneath your deadline, things get problematic when you use
> time-discrete algorithms, of course, but in this case you are better
> of using a time-driven approach, anyway.

So you at least need to disable caches when you determine what the
worst case is, assuming the cache is actually helping you.

      Andrew


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