Vault 7: Projects
This publication series is about specific projects related to the Vault 7 main publication.
MPLAB
®
XC16 C Compiler Users Guide
DS50002071C-page 206 2012-2013 Microchip Technology Inc.
Examples in this Section:
Mixing C and Assembly
Calling an Assembly Function in C
EXAMPLE 16-1: MIXING C AND ASSEMBLY
/*
** file: ex1.c
*/
extern unsigned int asmVariable;
extern void asmFunction(void);
unsigned int cVariable;
void foo(void)
{
asmFunction();
asmVariable = 0x1234;
}
The file ex2.s defines asmFunction and asmVariable as required for use in a
linked application. The assembly file also shows how to call a C function, foo, and how
to access a C defined variable, cVariable.
;
; file: ex2.s
;
.text
.global _asmFunction
_asmFunction:
mov #0,w0
mov w0,_cVariable
return
.global _main
_main:
call _foo
return
.bss
.global _asmVariable
.align 2
_asmVariable: .space 2
.end
In the C file, ex1.c, external references to symbols declared in an assembly file are
declared using the standard extern keyword; note that asmFunction, or
_asmFunction in the assembly source, is a void function and is declared
accordingly.
In the assembly file, ex1.s, the symbols _asmFunction, _main and _asmVariable
are made globally visible through the use of the .global assembler directive and can
be accessed by any other source file. The symbol _main is only referenced and not
declared; therefore, the assembler takes this to be an external reference.
The following compiler example shows how to call an assembly function with two
parameters. The C function main in call1.c calls the asmFunction in call2.s
with two parameters.
Protego_Release_01_05-Related-OEM-Documentation-MPLAB-XC16-C-Compiler.pdf