Re: [Sdcc-user] SDCC should not otimize!

[Bernhard H. <ber...@be...>]

>   dummy = graRD1;      //Dummy Read
>   grafik_wbusy();
>   dummy = graRD1;
>   grafik_wbusy();
>
> graRD1 is a XRAM location declared as:
>
> volatile xdata at 0xF003 unsigned char graRD1;
>
> Now the asm file look's like the optimizer only use:
>
>   dummy = graRD1;
>   grafik_wbusy();

I can't reproduce this. The output of the latest SDCC corresponds to:

   grafik_wbusy();
   grafik_wbusy();

The read access on graRD1 is twice omitted.

> one time. The second read is optimized. I understand why this is so but i
> have to do a dummy read before the normal read. The compiler always
otimize
> the second read away. I can define a variable and do something with it.
>
>   temp = graRD1;      //Dummy Read
>   grafik_wbusy();
>   dummy = graRD1;
>   grafik_wbusy();
>
> /*do something with dummy*/
>
> dummy = dummy | temp;
>
> But this can't be the right way to do that. Is there a statement or
> something to tell the compiler not to otimize these four lines?

This could be a bug in SDCC, but I don't know exactly. A "workaround" is to
define dummy as volatile:

volatile unsigned char dummy;

Bernhard