Re: [avr-gcc-list] suggestion

[David Breeze]

Hi,

There are situations, hardware related, where 2 sbi or cbi instructions would 
cause problems as there would be a significant time (clock dependant) between 
setting/clearing the bits.

David

>>> <address@hidden> 05 July 2006 13:27 >>>


that is, just one word to toggle one bit and 3 words to toggle 2+ bits.

My suggestion is to optimize the case when 2 bits are set into 2 sbi
commands, and when 2 bits are cleared into 2 cbi commands. It's quite
easy to count number of 1s or 0s in the mask - and if there are exacly
2, apply this optimization.

I was able to save ~100 bytes and fit my program into 4K, just by optimizing
these often used bit-tweaking places in my program.

If someone would have time to implement this kind of optimization for
I/O ports, that would be really great! I've never dealt with compilers
and just don't know how to do that..







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