Re: [avr-chat] Missed Optimisation ?

[Graham Davies]

bob wrote:

> I didn't mean to imply 4 read-OR-write cycles, just that with an unknown
> hardware ...

For mercy's sake, the hardware (microcontroller) is not unknown to the 
compiler!

> ... the OR itself (which is a
> read-modify-write operation) could have side effects.

No, no, no, no, no.  The compiler has placed the value in temporary storage 
on which accesses absoluteley cannot have side effects.

> I think Erik is right, in ISRs either inspect the compiler code very
> carefully or write in assembler yourself.

Erik may be right for himself, but he is giving bad advice in general.  Good 
general advise is a) understand the C language and b) make sure you can 
trust your tool chain.

Graham.