Local variables (even if designated as xdata) are in code space

I verified that the code I posted reproduces the issue. It's not the code from my program, as I can't post that code here. Reposting with the proper formatting...

#define BASE 0x1000

void blah (unsigned char Offset)
{
        unsigned char xdata *Address;
        Address = (BASE + Offset);
        SPXB_MSTR_DATA1 = *(Address+3);
        SPXB_MSTR_DATA2 = *(Address+2);
        SPXB_MSTR_DATA3 = *(Address+1);
}

I verified that the code I posted reproduces the issue. It's not the code from my program, as I can't post that code here. Reposting with the proper formatting...

#define BASE 0x1000

void blah (unsigned char Offset)
{
        unsigned char xdata *Address;
        Address = (BASE + Offset);
        SPXB_MSTR_DATA1 = *(Address+3);
        SPXB_MSTR_DATA2 = *(Address+2);
        SPXB_MSTR_DATA3 = *(Address+1);
}

.

There you go again erik. Looking into that assembly.

.

(I was being sarcastic... remember? from a thread where some ppl didn't think looking into the underlying assembly was 'needed')

I knew that, but the eaters of fried pigeons that flew in through the window would not

Erik

It appears to be an issue with pointer + fixed offset. If I actually modify the pointer instead, I get the correct behavior. Though I still can't inspect the pointer or its target. I think that's due to optimizations, which is fairly reasonable. I'll respond again if I find out more.

Thanks all.

So, have you looked at the generated assembler code?

A lot of compilers would ignore your pointer variable, and just evaluate the real address for the individual memory accesses - all depending on how good the processor is at doing pointer manipulation.

In this case, it is porbably as cheap - or cheaper - for the compiler to join (BASE plus a constant offset) in the individual accesses (or as an decremented temp variable) and then add the Offset parameter before making the memory access.