Day 23 - Using AS

AS?

	It seems that the Goldroad Assember isn't being updated anymore, so this would be a good
time to talk about using the GNU Assember (AS) instead. 
	
Basic ASM Syntax
	As far as I know, the basic syntax of AS is the same, there aren't any differences in how
the instructions look such as:

	ldr r1,=0x4000000  ; same as before

Defines and The Preprocessor
	One of the main differences are the defines and defining data, to define 
your data use EQU like this:

.equ var, 0x2000000 ; bytes 0-3, (32bits per variable)
.equ another, 0x2000004 ; bytes 4-7

or

.equ REG_DISPCNT, 0x4000000

You might want to go through and convert your headers. However, there is another option.
You can use GCC to assemble your .S files (another assembly extension), if you do this:

	gcc -c test.S
	objcopy -O binary test.o test.gba

You will be able to use #define, so you can might be able to replace '@' with '#' and be
able to use your headers in a snap. (Note that macros are probably different so you might have
to remove them, I'll talk about macros later.)

Day 1 with GNU
Here's a white dot code ready to be assembled by GCC:

@-- CODE START --;
@ comments start with a @ now.
#define REG_DISPCNT 0x4000000

.text @ the text section
start:
	ldr r1,=0x403 @Mode 3 , BG2 enabled
	ldr r2,=REG_DISPCNT
	str r1,[r2]

	ldr r1,=0xFFFF @White, (I know it's really 0x7FFF, but who cares..)
	ldr r2,=0x6000200  @somewhere on the screen
	str r1,[r2]

infin:
	b infin
@-- CODE END --;

To assemble, put into test.S on your desktop, I'll assume C:\devkitadv\ is the right directory:
open a DOS window:

	set path=C:\devkitadv\bin\
	cd PATH_TO_YOUR_DESKTOP_HERE
	gcc -c test.S
	objcopy -O binary test.o test.gba

I hope you have no problems getting the file to assemble, GNU programs tend to have loads of freaky
quirks..

Day In Review

	Eventually, I hope to get to link an ASM file with a C/C++ file.	

	Happy Coding!,
		- GBAGuy

Intro - Day 24