[Bug 1001572] Separate FIQ and IRQ management

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--- Comment #3 from Nick Garnett <nickg@ecoscentric.com> 2012-04-24 10:53:38 BST ---
(In reply to comment #2)
> I notice that FUNC_START_ARM does not put the new functions in a different
> section, so they won't be GC'd, so will be in all programs, whether used or
> not. It looks like I was going to do something about this in the eCosCentric
> sources, but then it seems I commented it out (changeset 371380826e8c). Hmm,
> can't remember why now.

That is true of a number of asm utility routines. Something for a different
checkin to deal with.



> Thanks for incorporating the fix from bug 1001160.

Frankly, I had forgotten that was the source of that particular change.


> But that bug also mentions a third possibility, that it might be useful for
> some users to do their own FIQ handling (and not use the FIQ->IRQ kludge), but
> for FIQs to still be disabled when handling IRQs. This can have benefits for
> some people. In particular, you would no longer need a separate FIQ interrupt
> stack, but could share one with IRQ again, which could be an important memory
> saver.
> 
> I think all it would need is one more CDL option controlling the CPSR_INTR_MASK
> define, which CYGOPT_HAL_ARM_FIQ_DISABLE can use 'requires' on to set. And also
> then that lets us avoid defining __fiq_stack in that case. Thoughts?

I'm not convinced. It seems to be a rather nasty subversion of the way in which
the architecture is intended to work. I suspect that the IRQ entry code would
need to be rejigged a little to ensure there are no races.

For now I think we want to check this in as it stands. If there is any demand
for what you suggest above then it can be added at a later date.

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