On Apr 14, 2011, at 8:50 PM, Eric Decker wrote:
>> And yes, if you did it in assembler, you could use a 20-bit
>> immediate.
>
>
>> Anyone know how to get 20 bit immediate in gcc extended asm?
>>
>> ie.
>>
>> __asm__ __volatile__ ("movx.a %1,%0":"=m" (DMA0SA):"i" (0xefefeUL));
>
> Note the immediate field is 0xefefe (20 bits).
>
>>
>> which unfortunately generates...
>>
>> __asm__ __volatile__ ("movx.a %1,%0":"=m" (DMA0SA):"i" (0xefefeUL));
>> 3b12: 00 18 f2 40 fe fe d2 01 movx.a
>> #65278,&0x001d2;#0x0fefe
I think what Peter was saying is that this is a limitation of C
inlining not being able to pass a 20bit constant to the assembler,
rather than the assembler not being able to use the 20-bit immediate
value. It's the compiler side that handles all those magic "-m" and
"i" modifiers.
You can probably fake it with something like:
#define mov20(dest, srcconst) \
__asm__ __volatile__ ("movx.a (%1<<16)+%2,
%0":"=m" (dest):"i" (srcconst>>16): "i"(srcconst & 0xFFFF));
(I'm not familiar enough with the extended MSP430's to actually give
it a try...)
BillW
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