Useful Code Snippets

Useful code snippets for the 65c816 ASM and general SNES hardware.

65c816 S-CPU

General

Wait for H-Blank

-
BIT $4212
BVS -
-
BIT $4212
BVC -

Inverse the accumulator (8-bit)

EOR #$FF
INC

Inverse the accumulator (16-bit)

EOR #$FFFF
INC

SMW Hacking

Custom block template

by Alcaro Works with SA-1.

db $42 ; or db $37
JMP MarioBelow : JMP MarioAbove : JMP MarioSide
JMP SpriteV : JMP SpriteH : JMP MarioCape : JMP MarioFireball
JMP TopCorner : JMP BodyInside : JMP HeadInside
; JMP WallFeet : JMP WallBody ; if using db $37

MarioBelow:
MarioAbove:
MarioSide:

TopCorner:
BodyInside:
HeadInside:

WallFeet:
WallBody:

SpriteV:
SpriteH:

MarioCape:
MarioFireball:
RTL

Decompress GFX File

by Vitor Vilela Works with SA-1.

; Decompress input GFX file
; Must be called from SNES CPU.
; SA-1 is automatically invoked on SA-1 Pack ROMs.

STZ $00
REP #$20
LDA #$7EAD	; destination buffer = $7EAD00
STA $01
LDA #$0080	; deoompress ExGFX80.bin ..
JSL $0FF900

65c816 SA-1 CPU

Some snippets present on S-CPU section works with SA-1 CPU as well.

General

Unsigned 16 bit x 16 bit = 32 bit multiplication

by Akaginite

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; 16bit * 16bit Multiplication SA-1 version
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Parameters
; $00-$01 : Multiplicand
; $02-$03 : Multiplier
; Return values
; $04-$07 : Product
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

MathMul16_16:	STZ $2250
		REP #$20
		LDA $00
		STA $2251
		ASL A
		LDA $02
		STA $2253
		BCS +
		LDA.w #$0000
+		BIT $02
		BPL +
		CLC
		ADC $00
+		CLC
		ADC $2308
		STA $06
		LDA $2306
		STA $04
		SEP #$20
		RTS