[ECOS] Multiple runnable DSR's

Gary D. Thomas gary.thomas@mind.be
Fri Jan 24 14:21:00 GMT 2003


On Fri, 2003-01-24 at 04:00, Ian Gilmour wrote:
> 
> My copy of "Embedded Software Development with ECOS" dropped on my desk
> yesterday. I've started skimming through it and I've already got a question
> that hopefully one of you can answer. 
> 
> It isn't clear from the book (or maybe I just haven't hit the relevant bit
> of text yet :-)) but from the email archive it appears as though a DSR
> associated with a low priority ISR can hold up the execution of a DSR
> associated with a high priority ISR.
> 
> Is this correct?
> 
> Are DSR's assigned priorities (presumably they could be based on ISR
> priorities in some way)?
> 
> If yes - do higher prioritised DSR's run ahead of lower priority DSR's if
> both are runnable?
> 
> Or are DSR's simply shoved on a time ordered pending DSR queue and processed
> in time order ahead of any user threads?

Correct.  We discussed having prioritized DSRs (years ago),
but decided that the most correct way to handle this is to
use threads.  This implies that DSR processing should be
short - if a "low priority" DSR is getting in the way of
a "higher priority" one, then that processing should really
be deferred to a thread which can be scheduled as necessary.

-- 
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|       Mind: Embedded Linux and eCos Development        |
|--------------------------------------------------------|
| Gary Thomas              email:  gary.thomas@mind.be   |
| Mind ( http://mind.be )  tel:    +1 (970) 229-1963     |
| gpg: http://www.chez-thomas.org/gary/gpg_key.asc       |
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