On Mon, 2009-06-08 at 09:45 -0700, wael showair wrote:
>
> wael showair wrote:
> >
> >> > You cannot really rely on getting the exact same number of edge
> >> > interrupts that were emitted. At least not unless you have a hard RT
> >> > system and can guarantee that you'll always dequeue them fast enough.
> >>
> >> Yes, my system is a hard RT & i want to receive all the interrupts that
> >> have been generated exactly
> >
> > No. Linux is not hard RT. You cannot rely on this in a reliable way,
> > if for any reason the kernel masks interrupt for too long, which can
> > happen, you'll see that sort of coalescing happening.
>
> what about using the RT-Preempt Patch? i can see that it will convert Linux
> ti an RTOS.
Not only I don't think it's going to guarantee RT response (just improve
it), that's a pretty big hammer to work around what is a design bug in
your system in the first place :-)
> i have check the function of do_IRQ: there is no ack called b 4 calling the
> handler but actually it does the following:
You haven't read properly :-)
> 1. it gets the irq number using :
> irq = ppc_md.get_irq();
>
> 2. then it calls the handler :
> if (irq != NO_IRQ && irq != NO_IRQ_IGNORE) {
> generic_handle_irq(irq);
> } else if (irq != NO_IRQ_IGNORE)
> /* That's not SMP safe ... but who cares ? */
> ppc_spurious_interrupts++;
>
> i have checked the function of generic_handle_irq where it is defined
> linux/irq.h & it calls the handler
No. It call the -flow- handler, which is a different thing (yes, the
terminology can be a bit confusing). The flow handler is configured
by the interrupt controller itself and will do whatever necessary
ack'ing, masking, EOI'ing etc... for a given PIC around the call to the
actual driver handler.
> so from the previous code the processor or the pic does not ack but they
> call my ISR handler.
They do. You missed it.
> i have also read the specs of my OpenPIC & found that:
>
> "the interrupt handler executing on the processor should then acknowledge
> the interrupt by explicitly reading the IACK register.
Reading the IACK is what get_irq() does on OpenPIC.
> The PIC unit
> interprets this read as an interrupt acknowledge (IACK) cycle; in response,
> the PIC unit returns the vector associated with the
> interrupt source to the interrupt handler routine."
>
> "At the end of the interrupt the End Of Interrupt (EOI) register must be
> set"
Which is done by the flow handler.
> So the processor neither reads this iack register nor the handler set the
> EOI register.
You obviously missed both :-)
Ben.
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