Re: [avr-libc-dev] "cli" and "sei" should clobber memory

[Eric Weddington]

Joerg Wunsch wrote:

> Sure, the memory clobber causes something like a "global volatile"
> effective for *all* memory variables at these sequence points.  IOW,
> it's a huge pessimization, and (IMHO) *way* worse than declaring your
> single variable to be volatile, and shadow its value where the
> volatileness isn't needed.
>
> The original author of that bug report has meanwhile analyzed the
> behaviour he saw as a bug in his respective version of GCC, and IIRC
> admitted that no memory clobber for sei/cli is really needed.  At
> least, that's what I've gathered from the previous discussion (I only
> kept in mind that the bug report could basically be closed now).
>
>
> > This seems like the correct thing to do since we want to make sure
> > that accesses to variables between "cli" and "sei" are not affect by
> > interrupts.
>
>
> No, please mark these variables as volatile.  Sure, you might need to
> interrupt-protect them anyway, depending on your application.

Another possible way is to do this:

dword atomic_get_dword(volatile dword *ptr)
{
    dword ret;
    cli();
    ret = *ptr;
    sei();
    return ret;
}

Untested of course.



--
Eric Weddington