Hi guys,

I'm trying to figure out how to use both C and ASM in my programming. I am mainly using PIC18F4550 assembly, but there are things that are just much easier in C that I would eventually just like to code up really quick, and call it from assembly. For example, if you were helping me with my other post, I was trying to do some simple hex to bcd conversions that was just a nightmare for me. Plus, you can't divide or multiply by non-integers.

Anyways, let's get to the point. As a small assignment, I have three .c files named bottom.c, middle.c, and top.c. I need to replace middle.c with middle.asm (I make this).

middle.c:

#include "P18F4550.h" 		//local copy of version found in MCC18 directory


int bottom (int dividend, int divisor);

int middle(int arg1, int arg2)
{
	int middlelocal;

	middlelocal	= arg1;
	middlelocal += bottom(arg1, arg2);

	return middlelocal;
}

As I was starting with my middle.asm file, I kinda realized I don't use arguments in any of my function calls since I store the data all in registers.

This is what I have so far in my middle.asm:

LIST P=18F4550		
	#include "P18F4550.INC"

extern bottom

middle:
        ; Define middlelocal variable (since it's an int, should I res 4 bytes?)
	local middlelocal
        ; Get arg2
        movff	TOSU,arg2U
	movff	TOSH,arg2H
	movff	TOSL,arg2L
	; Get arg1
	pop
	movff	TOSU,arg1U
	movff	TOSH,arg1H
	movff	TOSL,arg1L
	; Set middlelocal = arg1?
	movff	arg1L,middlelocal
        ; TODO: Push variables onto stack, but not sure what to do with middlelocal
     
        return
	end

Here are my questions:
1) When it's just a local variable, is it best to just use "local" or should I just make a variable at the top by doing "middlelocal res 1."
2) How do I call a C function from assembly that has arguments?
3) How do I make a function in assembly language that uses arguments?

I was trying to search for tutorials, but all I can find are tutorials for C or for asm.

 

It would be easier to write the program in C, and make calls to ASM routines....
You will just have to declare the ASM instructions in your C program...
Example;

asm volatile("nop");

or

#define Nop() asm("NOP");
#define Reset() asm("RESET");

B. Morse