Re: [avr-libc-dev] Deprecation policy [was: Re: [RFC][PATCH] Deprecate inb / outb.]

[Dmitry K.]

16 Jun 2003 11:45 Russell Shaw wrote:
> Dmitry K. wrote:
> > 16 Jun 2003 06:18 Joerg Wunsch wrote:
> >>Basically, it's now no longer (easily) possible to use one
> >>of the SFRs as the target of an inline asm statement anyway (see bug
> >>ID #2233, we need to update our inline asm docs accordingly).
> >
> > Examples of SFRs usage:
> >
> > //#define _SFR_ASM_COMPAT  1        /* needed for second example only       
> > */
> >
> > #include <avr/io.h>
> >
> > /* Examples of SFRs as the target of an inline asm statements.
> >    For qualitative realization it is necessary to add check:
> >     if (__builtin_constant_p((port)))
> >  */
> > #define cbi_atomic(port,bit)    do {                    \
>
> ...
>
> > } while (0)
>
> What is the do{...} while(0) for?

I shall specify, superfluous here only internal brackets. Removal
"do ... while" is undesirable, as, for example, it will be impossible to 
write:
        if (flag)
                cbi_atomic(PORTB, 2);   /* excess ';'   */
        else
==>  parse error before "else"