A trivial example of how to mix GBDK C and Assembly....

Written by Ken Jenks



mix_c_asm.c:



/*

     mix_c_asm.c

     An example of how to mix C and assembly -- Ken Jenks, 1999



     There are actually three files of interest:

     This one (mix_c_asm.c), mix_c_asm_add.s and mix_c_asm_make.bat.



     Based on main.c

     http://www.gbdev.org/gbdk/guidelines.html

     Michael Hope, 1999.



     Also based on fonts.c

     Simple example of how to use multiple fonts on the GB

     Michael Hope, 1999.

*/



#include <stdio.h>

#include <font.h>

#include <console.h>

#include <drawing.h>



void main(void)

{

     font_t ibm_font, italic_font, min_font;



     /* The following three lines are from main.c, demonstrating

        how to call a function, mix_c_asm_add(), which is defined

        in assembly language. See file mix_c_asm_add.s. -- KJ

     */

     WORD i;

     WORD mix_c_asm_add(WORD, WORD);



     i = mix_c_asm_add(1, 3);



     /* The rest of this code is from fonts.c -- KJ */



     /* First, init the font system */

     font_init();



     /* Load all the fonts that we can */

     ibm_font = font_load(font_ibm);  /* 96 tiles */

     italic_font = font_load(font_italic);   /* 93 tiles */



     /* Load this one with dk grey background and white foreground */

     color(WHITE, DKGREY, SOLID);



     min_font = font_load(font_min);



     /* Turn scrolling off (why not?) */

     mode(get_mode() | M_NO_SCROLL);



     /* Print some text! */



     /* IBM font */

     font_set(ibm_font);



     /* In italic */

     font_set(italic_font);

     printf("The result was: %d\n",i);



     /* Done */

     font_set(ibm_font);

     printf("\nDone!");

}





mix_c_asm_add.s:



.globl _mix_c_asm_add

_mix_c_asm_add:	; WORD mix_c_asm_add(WORD a, WORD b)

      		; There is no register to save:

		;  BC is not used

		;  DE is the return register

		;  HL needs never to be saved



	LDA  HL,2(SP)

	LD   E,(HL)	; Get a in DE

	INC  HL

	LD   D,(HL)

	INC  HL

	LD   A,(HL)	; Get b in HL

	INC  HL

	LD   H,(HL)

	LD   L,A

	ADD  HL,DE	; Add DE to HL

	LD   D,H

	LD   E,L

			; There is no register to restore

	RET		; Return result in DE





mix_c_asm_make.bat:



..\bin\lcc -Wa-l -Wl-m -o mix_c_asm.gb mix_c_asm.c mix_c_asm_add.s



rem Assuming you installed GBDK in the default directory, C:\SDK\

rem this file and its two friends should be located in

rem   C:\sdk\gbz80-gb\2-1-5\examples

rem or a directory at a similar level.

rem See http://www.gbdev.org/gbdk/tools.html

rem -- KJ