Re: [avr-chat] question about _SFR_IO8() and friends

[Michael Hennebry]

On Fri, 19 Sep 2014, Joerg Wunsch wrote:

> What you need is basically explained in the FAQ:
>
> http://www.nongnu.org/avr-libc/user-manual/FAQ.html#faq_port_pass
>
> const volatile uint8_t *dir_reg = &DDRD;
>
> If you can manage to declare it "const", there are chances
> the compiler can really generate optimal code (using IN/OUT,
> rather than memory access instructions) when your macro uses
> it.

The pointer is what needs to be const:
volatile uint8_t * const dir_reg = &DDRD;

That said, why not
#define reg (DDRD)
or
#define dir_reg (&(DDRD()
?


--
Michael   address@hidden
"SCSI is NOT magic. There are *fundamental technical
reasons* why it is necessary to sacrifice a young
goat to your SCSI chain now and then."   --   John Woods