Re: [avr-gcc-list] volatile...

[Dave Hansen]

From: Paulo Marques <address@hidden>

> Dave Hansen wrote:

[...]

> > You've opened some new cans of worms here, but I'll only make one small 
> > comment
>
> I was afraid of that (the cans of worms, not your comment) ;)

Thanks for noticing the implied smiley.  Looking at what I wrote, I'm not 
sure it has the tone that was intended...

> > [...]
> >
> > > static uint16_t atomic_read_16(uint16_t *ptr)
> > > {
> > >     uint16_t ret;
> > >
> > >     cli();
> > >     ret = (volatile)(*ptr);
> >
> > Your cast to volatile here is not only unnecessary, it's wrong.

[...]

> But you're actually wrong about the volatile not being needed. Because the 
> "sei" instruction doesn't claim anything about memory clobbers, without 
> volatile the compiler would be free to re-order instructions and do the 
> "sei" before the assignment.

Ouch.  I would have thought the "volatile" int the sei macro would have 
taken care of this.

> This is no theoretical scenario. Just search the archives for previous 
> threads over this.

I didn't find anything in a quick search, but I believe you.

Would declaring the variable (ret) 'volatile' let us remove the cast?

Regards,

  -=Dave

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