Help with translating this assembly into c

Question

Hi. My compiler won't work with an assembly file I have and my other compiler that will won't work with the c files I have. I don't understand assembly. I need to move this over but I'm not getting anywhere fast. Is there someone out there that can help? I can't believe there isn't a translator available. Here is the beginning of the file:

    list  p=18F4480       
    #include <p18F4480.inc> 

    #define _Z  STATUS,2
    #define _C  STATUS,0

    GLOBAL AARGB0,AARGB1,AARGB2,AARGB3  
    GLOBAL BARGB0,BARGB1,BARGB2,BARGB3
    GLOBAL ZARGB0,ZARGB1,ZARGB2
    GLOBAL REMB0,REMB1
    GLOBAL TEMP,TEMPB0,TEMPB1,TEMPB2,TEMPB3
    GLOBAL LOOPCOUNT,AEXP,CARGB2


LSB   equ 0
MSB   equ 7

math_data   UDATA 
AARGB0   RES 1  
AARGB1   RES 1
AARGB2   RES 1
AARGB3   RES 1
BARGB0   RES 1 
BARGB1   RES 1
BARGB2   RES 1
BARGB3   RES 1
REMB0    RES 1 
REMB1    RES 1
REMB2    RES 1
REMB3    RES 1 
TEMP     RES 1
TEMPB0   RES 1
TEMPB1   RES 1
TEMPB2   RES 1
TEMPB3   RES 1
ZARGB0   RES 1
ZARGB1   RES 1
ZARGB2   RES 1
CARGB2   RES 1
AEXP     RES 1
LOOPCOUNT   RES 1


math_code   CODE
;---------------------------------------------------------------------
;    24-BIT ADDITION    
_24_BitAdd
    GLOBAL _24_BitAdd
    movf BARGB2,w
    addwf AARGB2,f

    movf BARGB1,w
    btfsc _C
    incfsz BARGB1,w
    addwf AARGB1,f

    movf BARGB0,w
    btfsc _C
    incfsz BARGB0,w
    addwf AARGB0,f
    return

I get that I can largly exclude the first two lines as the device defines are in my main.c anyway. The two #defines are just that, but the simplest way (I think) is to just replace instances of _Z and _C with STATUS,2 and STATUS,0 accordingly. The next lines (the GLOBALs) are simply variable declarations I'm gathering. Same with LSB and MSB except they also assign values. The next chunck I think I just declare a bunch of integers with those names (AARGB0, etc) and then the chunck after that is a function.

I don't even bother to translate that function, because my compiler has #asm/#end asm directives so I can put it in raw (as long as its wrapped in a function).

I think I have it all... until I build and my compiler screams about STATUS not being defined. And of course its not. But what is it? I read on the net that STATUS registers are something special but I really don't get how it works.

If you haven't noticed, I'm not even sure what it is I'm really asking. I just want the bloody thing to work.

Answer 1

Your compilers are refusing your source?

Either you are using broken tools, or your source files are buggy. In both cases, your problem is not "translating ASM to C" or something like that, but the bugs in your source / toolchain. Do not try to work around problems, solve them.

Answer 2

You can try to reverse-engineer the disassembly. But what will you learn?

You should be able to compile your assembly (using compiler 1) into an object file, and link that to the object file compiled by compiler 2 from your C file.

Answer 3

STATUS is a built-in register in the PIC architecture, that implements the same functionality as the "status" or "condition" flags register in most larger CPU:s. It contains bitflags that are set and cleared by the microcontroller as it executes code, telling you the result of operations.

The Z flag, for instance, is set whenever an arithmetic operation results in a zero, and the C (carry) flag is set when arithmetic overflow is detected.

These are flags that are typically not visible from C, as C doesn't want to require that the host processor even has status bits, so directly translating this code to C will be hard. You will need to figure out a way to include the status-reading bit tests in the C code, and use those instructions when possible. This might be troublesome, as from C you have less control over which registers are being used, which in turn might make it hard to make sure you're checking the proper flags in the right place(s).

Here are a few links to other people's extended precision PIC code. Most seem to remain in assembly, but they might still be useful as references or inspiration.