[Bug c/17336] AVRGCC ignores "volatile" keyword for "register" variables

["m_klokov at mail dot ru" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From m_klokov at mail dot ru  2004-09-27 16:17 -------
(In reply to comment #4)
> Not a bug, volatile on global registers means nothing.

Volatile means volatile...

Let me explain more... There are 32 registers in AVR-core. GCC uses only 16.
So other registers I can use in asm-code. As you know asm-routines are usually
high-speed low-level drivers, interrupt handlers, often with some "tricks"
(like fixed execution time or something like this - something you can't
do with C). 

OK. Lets say asm-code is the interrupt handler and it use free register to
notify the main C-program about some event. It uses register because it's much 
faster then RAM, and much more comfortable.
So how can i define such register to allow C-code to access it ???

I should use the "register" keyword obviously...
AND I should use the "volatile" keyword to say compiler that value
can be changed by interrupt handler... (not by C-sentence)
and the code MUST reread the value in a manner I wrote in my C-code
(i.e. don't optimize it). 

It's THE STANDARD MEANINGS of theese keywords...

You must be assuming that C-compiler must use all the available registers?
Or hardware always has small number of registers? 

If so, you make GCC-compiler HARDWARE-DEPENDENT... 

My english is not so good, Sorry.
Please ask if you have any questions.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17336