Re: [avr-gcc-list] Inserting code before context save in an ISR (for nested interrupts)

[Klaus Rudolph]

The compiler only save registers which are needed by the isr. Why you 
should do this by your own?


> Hi all,
>
> I'm working on a hard realtime application where I need to keep the time
> where interrupts are disabled as small as possible.  I've noticed that a
> typical ISR can take 40+ cycles to push registers onto the stack before
> executing any user ISR code.  I'd like for interrupts to be re-enabled
> immediately upon entering the ISR (before the context save).
>
> The only way that I can think of to do this is to add the naked attribute
> to my ISRs.  Unfortunately, this is very unattractive because then I have
> to do all context save operations manually.  My ISRs are written in C and
> therefore I wouldn't know which registers would need to be saved and would
> be forced to save all of them --- an expensive proposition.
>
> Is there a way to inject a simple sei() into the start of an ISR before
> the automatic context save?
>
> Thanks,
> David Carr
>
>
>
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