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Re: interrupts disabled during DSRs on ARM
- From: Nick Garnett <nickg at calivar dot com>
- To: Andrew Parlane <andrewp at carallon dot com>, ecos-discuss at ecos dot sourceware dot org
- Date: Fri, 01 Nov 2013 17:11:17 +0000
- Subject: Re: interrupts disabled during DSRs on ARM
- Authentication-results: sourceware.org; auth=none
- References: <5273D735 dot 8060505 at carallon dot com>
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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Nick Garnett Kernel Architect
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