Re: interrupts disabled during DSRs on ARM

[Andrew Parlane <andrewp at carallon dot com>]

Hi,

Thanks for your reply. You are correct. I had 
CYGIMP_HAL_COMMON_INTERRUPTS_USE_INTERRUPT_STACK turned off, which meant 
that the HAL_INTERRUPT_STACK_CALL_PENDING_DSRS macro pointed to 
Cyg_interrupt::call_pending_DSRs_inner() ie. skipping the re-enable 
interrupts bit. Which seems valid in the case you don't have a separate 
interrupt stack.

Thanks for your help,
Andrew
Carallon ltd.

On 01/11/2013 17:11, Nick Garnett wrote:
> On 01/11/13 16:30, Andrew Parlane wrote:
> > Hi,
> >
> > Another question regarding the ARM interrupt handling code.
> >
> > When an IRQ occurs we jump to IRQ: in hal\arm\arch\current\src\vectors.s
> > we save the previous state, potentially switch stack, take the scheduler
> > lock, find the IRQ number, call the ISR, and then call interrupt_end.
> >
> > interrupt_end() in kernel\current\src\intr\intr.cxx queues up the DSR if
> > asked to, and then unlocks the scheduler. As long as the scheduler
> > wasn't locked before the IRQ, this causes the scheduler to call any DSRs
> > that are queued up. This happens in call_pending_DSRs_inner() in the
> > same file. We disable interrupts, get the pointer to the DSR to call,
> > restore interrupts and call the DSR.
> >
> > In the case I've been describing we are still in the IRQ handler, and as
> > such the interrupts are disabled throughout the entirety of this, and
> > hence disabled in the DSR.
> >
> > Looking at: http://ecos.sourceware.org/docs-1.3.1/ref/ecos-ref.c.html in
> > the first paragraph it states: "This separation explicitly allows for
> > the DSRs to be run with interrupts enabled, thus allowing other
> > potentially higher priority interrupts to occur and be processed while
> > processing a lower priority interrupt."
> >
> > Am I missing something here?
> call_pending_DSRs_inner() is called via
> cyg_interrupt_call_pending_DSRs() which is itself called by
> hal_interrupt_stack_call_pending_DSRs() in vectors.S. This last routine
> switches to the interrupt stack and enables interrupts before calling
> cyg_interrupt_call_pending_DSRs().



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