slightlynybbled slightlynybbled - 4 days ago 5
C Question

MPLAB XC16: Mixing C and Assembly

I am attempting to mix some C and assembly language and I am having a bear of a time. I am experienced with C, somewhat with assembly, but I haven't used them on the same project before.

At the moment, I am attempting to compile the simplest possible project, which is a Q1.15 fixed-point multiplication. I don't actually care about the code output, I just needed something to compile so that I could build off of it.

myq15.h:

#ifndef _Q15_MATH
#define _Q15_MATH

#include <stdint.h>

typedef int16_t q15_t;

extern q15_t q15_mul(q15_t multiplicand, q15_t multiplier);
q15_t q15_add(q15_t addend, q15_t adder);

#endif


myq15.c

#include "myq15.h"

q15_t q15_add(q15_t addend, q15_t adder){
int32_t result = (uint32_t)addend + (uint32_t)adder;

if(result > 32767) result = 32767;
else if(result < -32768) result = -32768;

return (q15_t)result;
}


myq15.s:

.include "xc.inc"

.text
.global _q15_mul

_q15_mul:
; w3:w2 = w1 * w0
mul.ss w0, w1, w2

; w0 = (w3:w2) >> 15
rlc w2, w2
rlc w3, w3

; w0 = w3
mov w3, w0

return

.end


My 'main' file simply calls a q15_add() and q15_mul() instance.

On compile, The linker states:

build/default/production/_ext/608098890/myq15.o(.text+0x0): In function `_q15_mul':
: multiple definition of `_q15_mul'


Again, I am trying to figure out how to mix the assembly and C file for other purposes, but if I can't get this simple program to work, I'm hopeless!

Thanks,

Answer

It's a bad idea to name your files the same, the toolchain might confuse them, given that both myq15.c and myq15.s compile to myq15.o by default.

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