Question

volatile uint32_t * sdramData = (volatile uint32_t *)0x30000100;


#define WIDTH  800


volatile uint32_t * im[WIDTH/4] = (volatile uint32_t **)sdramData;

The third line is the one giving me an error. I’m trying to make an array of int pointers that start at the location of sdramData. It’s saying an invalid initializer error. Thanks for any help.

Answer 1

The initializer notation needs to be enclosed in braces and the values in the braces must be constants:

volatile uint32_t * im[WIDTH/4] = { sdramData };

This would initialize the first element of the array if sdramData was a constant (it isn’t within the meaning of the term) and leave the others zeroed.

If you really want 200 consecutive 4-byte locations (about which I have my doubts — see below), you’re going to have to produce 200 values to initialize the list (as standard C still doesn’t have a repeat-count option for array initializers, sadly — GCC does, as an extension).

#define SDRAMBASE 0x30000100

#define INIT_x(x)  (SDRAMBASE + (x) * sizeof(uint32_t))
#define INIT_5(x)  INIT_x(x+0), INIT_x(x+1), INIT_x(x+2), INIT_x(x+3), INIT_x(x+4)
#define INIT_10(x) INIT_5(x+0), INIT_5(x+5)
#define INIT_50(x) INIT_10(x+0), INIT_10(x+10), INIT_10(x+20), INIT_10(x+30), INIT_10(x+40)

volatile uint32_t *im[WIDTH/4] =
{
    INIT_50(  0),
    INIT_50( 50),
    INIT_50(100),
    INIT_50(150),
};

Not pretty, but saves a lot of typing. You can insert a (volatile uint32_t *) cast on the INIT_x expansion if you need it — you likely do.

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An alternative interpretation

On the other hand, you can probably write an expression that simply uses SDRAMBASE to do the job without the array im:

#define im_ARRAY(i)  (*(volatile uint32_t *)(SDRAMBASE + (i) * sizeof(uint32_t)))

Now you can write (round brackets instead of square):

uint32_t x = im_ARRAY(43);

instead of:

uint32_t x = im[43];

In fact, you might even use:

#define im_ARRAY   ((volatile uint32_t *)SDRAMBASE)

and then you can write (square brackets as usual):

uint32_t x = im_ARRAY[43];

This looks more plausible as the desired effect. Still not entirely nice, but relatively clean.