On 11 February 2011 22:26, JMGross <[email protected]> wrote:
> Hi!
>
Gidday!
> You're right, that writing to MPY isn't necessary if the write is
> redundant, but writing to OP2 is. But in this specific case, writing to MPY
> isn't redundant while OP2 is superfluous. So the code exactly does what it
> should.
> Why?
> Because you don't use b after doing the math.
>
Oh, sorry. I should have changed the test code to return a+b instead of
returning a. I was going for the simplest possible test program.
The exact same problem happens:
push r2
dint
nop
mov.b @r15, &__MPY
mov.b #llo(100), &__OP2
mov &__RESLO, r14
pop r2
push r2
dint
nop
mov.b 1(r15), &__MPY
mov &__RESLO, r15
pop r2
add r14, r15
Now b is used, and is part of the expression returned in r15.
This problem is fixed in mspgcc4. Unfortunately, with mspgcc4 I then run
into other problems, with interrupt vectors not handled correctly for the
msp430x247 chip. This is apparently going to be fixed next release, due in a
few days. In the meantime, I have an ugly workaround for mspgcc3.
- Mike
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