RE: [avr-gcc-list] Problem with timer0 overflow interrupt in clanguage..

[Schwichtenberg, Knut]

On Friday, December 07, 2007 5:24 PM, David Kelly wrote:
> The compiler won't read PINB using the above.
> 
> In general on AVR when one reads PORTB one reads the output latchs, in
> other words the last value written. On other CPU's this same 
> action may
> read the input buffers. AVR provids PIN ports for specifically reading
> the state of the external pins.
> 
> Using -O1 the above exclusive-or-equals generates exactly the 
> same code
> as the OP first wrote:
> 
>         PORTB = ~PORTB;
>  3ee:   85 b1           in      r24, 0x05       ; 5
>  3f0:   80 95           com     r24
>  3f2:   85 b9           out     0x05, r24       ; 5
>         PORTB ^= 0xff;
>  3f4:   85 b1           in      r24, 0x05       ; 5
>  3f6:   80 95           com     r24
>  3f8:   85 b9           out     0x05, r24       ; 5
This result is unambiguous. The question is: Is this a bug which means a
bug report is necessary or is it a feature that needs to be described?
It would be comfortable if GCC could distinguish between the IO-ports
and other IO-variables were the in and out address are identical.

Knut