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FIQ interrupts on LP23xx

Posted by torginus on April 25, 2009

I'd like to ask a techincal a question.

I'm using a Philips LPC2378 microcontroller, which has a separate register set for handling FIQ interrupts.

Does it mean, that this makes context saving upon entry unnecessary, so I needn't (and shouldn't) use portSAVE_CONTEXT(), and portRESTORE_CONTEXT() upon entry, and exit from the interrupt handler?
Or are there parts of the context that still need to be saved?
Is it safe to call FreeRTOS functions from such a 'plain' FIQ interrupt?

Btw, what's the difference between the portSAVE/RESTORE combo and using GCC's builtin __attribute("IRQ"/"FIQ")__ function attributes?

RE: FIQ interrupts on LP23xx

Posted by Richard on April 25, 2009
Best not to call API function from the FIQ, and use the standard GCC method of entering the function, not the portSAVE/RESTORE_CONTEXT macros.

You might like to check the implementation of the portENTER_CRITICAL() and portEXIT_CRITICAL() macros to ensure they don't disable and enable FIQ interrupts - unless you want them to.

The __attribute__ method does not save the entire context, often contains bugs (depending on the GCC version) and does not save the context in the form expected by the kernel.


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