Re: [avr-gcc-list] Possibly wrong code generated using _BV macro

[Omar Choudary]

Ups, just seen it (about sbi):
"This instruction operates on the lower 32 I/O Registers – addresses 0-31."

Sorry for writing too early.

Omar

On Wed, Jan 4, 2012 at 9:06 PM, Omar Choudary <address@hidden> wrote:
> Hello,
>
> I wanted to use the _BV macro to set the JTD bit in MCUCR in order to
> disable the JTAG interface and
> allow the PF4-PF7 pins for other use.
>
> The listing result is this:
>
>    MCUCR |= _BV(JTD); // needs to be done twice
>    9cf2:   85 b7           in  r24, 0x35   ; 53
>    9cf4:   80 68           ori r24, 0x80   ; 128
>    9cf6:   85 bf           out 0x35, r24   ; 53
>    MCUCR |= _BV(JTD);
>    9cf8:   85 b7           in  r24, 0x35   ; 53
>    9cfa:   80 68           ori r24, 0x80   ; 128
>    9cfc:   85 bf           out 0x35, r24   ; 53
>
> As you can see the instruction is xoring a temporary value instead of
> using the expected sbi.
>
> On the other hand if I use the same approach for a normal port
> register I get the desired result:
>    DDRF |= _BV(PF4);
>    2d66:   84 9a           sbi 0x10, 4 ; 16
>    PORTF |= _BV(PF4);
>    2d68:   8c 9a           sbi 0x11, 4 ; 17
>
>
> Any ideas why _BV works for a port register but not for MCUCR?
> I'm using AT90USB1287, avr-gcc 4.5.2.
>
> Thanks,
>  Omar