From: Nick Garnett <nickg@calivar.com>
To: Andrew Parlane <andrewp@carallon.com>, ecos-discuss@ecos.sourceware.org
Subject: Re: [ECOS] interrupts disabled during DSRs on ARM
Date: Fri, 01 Nov 2013 17:11:00 -0000 [thread overview]
Message-ID: <5273E0B5.4090000@calivar.com> (raw)
In-Reply-To: <5273D735.8060505@carallon.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().
--
Nick Garnett Kernel Architect
eCosCentric Limited http://www.eCosCentric.com The eCos experts
Barnwell House, Barnwell Drive, Cambridge, UK. Tel: +44 1223 245571
Registered in England and Wales: Reg No: 4422071
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next prev parent reply other threads:[~2013-11-01 17:11 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-01 16:30 Andrew Parlane
2013-11-01 17:11 ` Nick Garnett [this message]
2013-11-01 17:43 ` Andrew Parlane
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