🚀 go-pugleaf

In article <1993Jan23.042626.991@verdix.com> scotty@verdix.com (Scott R. Chilcote) writes:
> 
>We're programming a device that has a RAM cache at address 809800H.
>
>Is it legal to address this memory in C as follows?
>
>#define ON_CHIP 0x809800
>
>int main(void)
>{
>
>   float *oc_ptr = (float *) ON_CHIP;

SHORT ANSWER: I don't *know* if this is legal.

LONG ANSWER: if I were the king of the forest, I wouldn't define this
as being legal.  While you can do limited integer arithmetic with
pointers (incrementing or decrementing by a constant integer), the
pointers themselves are manipulated by the integer times the sizeof
the pointer type.

So to my mind, if you declared
   float *oc_ptr = (float *) ON_CHIP;
it seems to me that the pointer would actually point to the 0x809800'th
float in memory starting at the lowest addressable location (not
necessarily NULL, BTW).

So in order to do what you want to do "legally", you'd have to figure
out what the ON_CHIP address would be in terms of a contiguous array
of floats.

- David Andrews
  dandrews@bilver.oau.org