On Fri, 30 Mar 2001 16:55:07 +0000, you wrote:

>I am not an expert on this, but I would tend to believe that since PICC
>keeps hands-off anything in an asm block, and since you don't use the
>variables source and result other than in the assembler block, that it
>just figures it doesn't need those two variables, so they don't exist =
for
>the assembler block to use. (W is used for passed values).
>
>As a test, perhaps add some do-nothing code that uses those variables
>within the function, or use static variables.
>
>Cheers,
>
>Bob
>
>> char reverse_bits(char source)// reverses bits 0 to 6 - source =3D =
0ABCDEFG
>> {
>> char result;
>> #asm
>>         swapf   _source,w       ;W=3D DEFG0ABC
>>         btfsc   _source,3        ; If D =3D 1,
>>         xorlw  0x88                ;convert now sure W=3D 0EFGDABC
>>
>>         btfsc   _source,6        ;Test bit A
>>          xorlw  0x05               ;Invert bits A and C
>>         btfsc   _source,4        ;Test bit C
>>          xorlw  0x05             ;Invert bits A and C
>>                                        ;now W =3D 0EFGDCBA
>>         btfsc   _source,2        ;Do the same with E and G
>>          xorlw  0x50
>>         btfsc   _source,0
>>          xorlw  0x50
>>         movwf _result          ;so now W =3D 0GFEDCBA (done)
>> #endasm
>> return(result);
>> }
>>
>> But, on building, the linker says that _source and _result are =
undefined variables. I thought that, to use a C variable in a piece of =
assembler code, you simply prepend an underscore to it. Anyone know what =
I'm doing wrong?
>>
I found that Hi-Tech had a nasty habit of optimising out vars that
were only used inside ASM blocks.=20
I can't remember If I found a solution to this situation for return
vars.=20
I think doing something like=20
result=3Dresult;
outside the #asm can fix it, but can also generate unnecessary code.=20

The other problems is that with full optimisation on. it will
'helpfully' optimise out all your assembler code! I found it to be
much less hassle to put asm stuff in a seperate .as file.=20
Under MPLAB this is relatively painless to do.=20

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