Dennis Clark wrote:
Rather than hijack a thread I'll start my own.
How does everyone lean out an ISR? I too have been appalled at the
preamble/postamble code GCC puts into the ISR.
I always put ISR variables in global space to avoid stack issues, but the
heap access registers still need push/popped. I tried using register
variables to avoid heap access and found that there is no way to know if a
library call is using that register - The compiler does NOT guarantee
exclusive access. Can you actually get away with a "NAKID" attribute on
the ISR?
How have others dealt with ISR bloat reduction?
Many thanks,
DLC
Use local variables rather than global ones where you can - it is always
more efficient.
The biggest cost to the ISR preamble and postamble comes if the ISR
makes a function call - all registers that the function *might* use have
to be stacked for safety. So in general, avoid function calls (inlined
functions are fine).
However, if you have a very complex ISR (which is generally a bad idea -
it's better to keep ISR's short and simple) so that your preamble is
already fairly long, then any rarely-executed sequences can be put in a
function (perhaps declared "noinline"), so that any additional pushing
and popping is only done when that function actually runs.
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