Day 24 - Compiling With C

Compiling With C?

	Yep, today we will use both ASM and C++ functions in seperate files and compile
them both.
	
The C++ File
	In test.cpp :

/* CODE START */
#include "C:\devkitadv\include\gba.h"

extern "C" {
void SetThePixel(); /* ASM function uses C conventions */
}

int main() {
	REG_DISPCNT = 0x403; /* mode 3 */
	SetThePixel(); /* our ASM function */
	while((*KEYS)&KEY_START);  /* Wait for start key */
	REG_DISPCNT = 0; /* no mode (dot will disappear) */
	while(1);
	return 0;
}
/* CODE END */

The ASM File
	In test.S :

@-- CODE START --@
	.global SetThePixel
SetThePixel:
	ldr r1,=0x6000200 
	ldr r2,=0x00FF    
	str r2,[r1]      @ red dot somewhere on the screen
	bx lr  @return;
@-- CODE END --@

Note: Put a new line at the end of both of the files.
Note2: Having the char '\' in a comment assembles, but the ROM doesn't run then, wierd...

Compiling
Assuming both code files are in the same dir and C:\devkitadv\bin\ is in your path.
To compile:

	gcc test.S test.cpp
	objcopy -O binary a.out test.gba

Then run TEST.GBA to make sure it works.

Day In Review

	References:
		GBADev.ORG Forum Post on this topic
		Link from that post about why
		the "extern "C"" is needed.

	Hope you liked it!,
		- GBAGuy

Intro - Day 25