RE: AW: [avr-gcc-list] Gcc bug??

[Dave Hansen]

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From: "Dave Hylands" <address@hidden>
[...]
> While we're talking about volatile, here's an example where volatile
> might not help you (I've helped several people with this who had
> misconceptions about what volatile does). Let's say I have a peripheral
> which has a two register interface, the first register being an index
> into an internal register and the second register gets the value.
>
> struct hw
> {
>         uint8_t reg;
>         uint8_t val;
> };
>
> struct hw *p;
>
> void SetReg( uint8_t inReg, uint8_t inVal )
> {
>         p->reg = inReg;
>         p->val = inVal;
> }
>
> It's possible for the compiler to reorder these to set val first and
> then set reg. Declaring p as volatile will NOT change this behaviour.

But declaring what p points to _should_ work, right?  e.g.

  struct hw * volatile p;

makes p volatile, but

  struct hw volatile * p;

makes what p points to volatile.

In any case, I believe you can modify your data structure as follows to make 
it work without a barrier function:

  struct hw
  {
        uint8_t volatile reg;
        uint8_t volatile val;
  };

Regards,
  -=Dave

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