[ECOS] On ARM7 can one of FIQ/IRQ be used for non-eCos stuff?

Grant Edwards grante@visi.com
Wed Apr 2 16:48:00 GMT 2008

I've got an application where some low-level interrupt driven
stuff needs to happen with minimal latency (a hard deadline of
20us). It's an ARM7 running at 22Mhz, and preliminary
measurements indicate that the eCos ISR latency is going to be
too large.

One thought was to use IRQ for normal eCos stuff, and dedicate
FIQ to the low-latency stuff.  The theory was that since the
FIQ service routine wouldn't do anything with any eCos data
structures, it would be allowed to interrupt normal eCos ISRs.
That would allow the FIQ latency to be kept low.

>From looking at the ARM/arch hal stuff, it looks like eCos
expects to handle both IRQ and FIQ interrupts.  AFAICT, all of
the interrupt sources in my part (Samsung S3C4530) can be
assigned to either IRQ or FIQ.

Is there any reason why eCos has to have control of both
interrupt sources if all of the peripherals which eCos is
handling are on just one of them?

Grant Edwards                   grante             Yow! Nipples, dimples,
                                  at               knuckles, NICKLES,
                               visi.com            wrinkles, pimples!!

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