> When an interrupt is serviced a means
>must be found to save the context of the currently running code and restore the
>execution context at the end of an interrupt. That means any resource that the
>interrupt needs has to be accounted for, condition codes, registers, sometimes
>state information RAM and all functions that the interrupt and main line both can
>call simultaneously  must be re-entrant.

Well, this is what I assumed the compiler would do..
Scan the int code, find out what is used/needed, and only push what is needed.
In the case of the AVR, pushing 32 registers is enormously expensive in a machine with 192 bytes of ram or less.

I have a few situations where I use very fast int code, that doesn't even preserve the status reg, because it doesn't need to. (the int code doesn't affect the flags.) 

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