Re: [avr-chat] Write sequence

[Eric Weddington]

Keith Gudger wrote:
> I have a macro defined:
>
> #define WRITE_4BYTES(x, y) { CS_LOW \
>             *(BASE + ((y) ))) = (INT8U) (x); \
>             *(BASE + ((y + 1)))) = (INT8U) (x >> 8);\
>             CS_HIGH }
>
> (where BASE is defined as an 8 bit pointer with a value 0x8000 in ext
> ram and the macros CS_LOW and CS_HIGH are predefined to set a pin lo /
> high).
>
> When assembled by avr-gcc (GCC) 3.4.5, avr-libc-1.4.2, binutils-2.16.1, I

Hmm, where'dya get the toolchain? ;-)

> get the following (for the atmega128):
>
>     42f2:       31 83           std     Z+1, r19        ; 0x01
>     42f4:       20 83           st      Z, r18
>
> which means that in reality the write occurs this way:
>
>  *(BASE + ((y + 1)))) = (INT8U) (x >> 8);\
>  *(BASE + ((y) ))) = (INT8U) (x); \
>
> Is there any way I can "force" the write order to be in the order I
> specified (in C), or must I resort to assembly?  Thanks.

Would it help to declare the variable that you're writing to volatile?

--
Eric Weddington