Reply by Leighton Rowe April 12, 20072007-04-12
Question...

For AT91SAM7S mcu's, is it possible to make an IRQ source - basically
one of the peripherals (Timer0, SPI, etc.) - behave like an FIQ
interrupt? If yes, then how? If not, then why?

I'm aware that IRQs on AT91SAM7S mcus have a priority scheme. However,
I'm somewhat concerned about sharing ISRs over the IRQ level,
especially if one of the ISRs must execute immediately once called.

For example, if a higher priority IRQ source triggers just after a
lower priority ISR begins execution, then most likely the higher IRQ
source will be pending until the lower ISR completes.

I'd prefer avoiding this scenario my making time critcal ISRs be
FIQs...if possible on AT91SAM7S mcu's.

Many thanks,
Leighton