chip-8.s

;-----------------------------------------------------------------------------
; BIOS
;-----------------------------------------------------------------------------

;	.org		0
;	.incbin		../bios.min		; don't need this for real PM

;-----------------------------------------------------------------------------
; Memory addresses
;-----------------------------------------------------------------------------

	.equ		tilemap			$1360	; default location for tilemap?

	.equ		BIOS_SIZE		$1000
	.equ		RAM_SIZE		$1000
	.equ		IO_SIZE			$0100
	.equ		ROM_SIZE		$80000

	.reloc
BIOS_BEGIN:		.ds		BIOS_SIZE
BIOS_END:
RAM_BEGIN:		.ds		RAM_SIZE
RAM_END:
IO_BEGIN:		.ds		IO_SIZE
IO_END:
USER_BEGIN:
	.endreloc

	.equ		NN				IO_BEGIN		; you can use [NN+...] instead of [nn+...] when required

;-----------------------------------------------------------------------------
; I/O address offsets
;-----------------------------------------------------------------------------

	.equ		BUTTONS			$52


	.equ		VIDEO_0			$80
	.equ		VIDEO_1			$81
	.equ		VIDEO_TILEDATA	$82		; word

	.equ		COUNTER2		$08

	.equ		CPU0			$00
	.equ		CPU2			$02

;-----------------------------------------------------------------------------
; I/O bits
;-----------------------------------------------------------------------------

	.equ		BUTTON_A		$01
	.equ		BUTTON_B		$02
	.equ		BUTTON_C		$04
	.equ		BUTTON_UP		$08
	.equ		BUTTON_DOWN		$10
	.equ		BUTTON_LEFT		$20
	.equ		BUTTON_RIGHT	$40
	.equ		BUTTON_POWER	$80

	.equ		CPU2_SPEED		$08

	.equ		COUNTER2_START	$01
	.equ		COUNTER2_RESET	$02
	
	.equ		VIDEO_0_INVERT	$01
	.equ		VIDEO_0_TILED	$02
	.equ		VIDEO_0_ENABLE0	$08
	.equ		VIDEO_0_TSIZE0	$10
	.equ		VIDEO_0_TSIZE1	$20

	.equ		VIDEO_1_ENABLE1	$01
	.equ		VIDEO_1_SLOW0	$02
	.equ		VIDEO_1_SLOW1	$04

;-----------------------------------------------------------------------------
; Interrupt numbers
;-----------------------------------------------------------------------------

	.equ	IntSuspend		0x21
	.equ	IntShutdown		0x24

;-----------------------------------------------------------------------------
; Header
;-----------------------------------------------------------------------------

	.org 0x2100
	.db		"MN"			; cam be anything except 0xBF,0xD9
	jmp		start

	.org 0x2108
	; interrupt handlers come here


	.org	0x21A4
	.db		"NINTENDO"		; magic string
	.db		"CHIP-8____"	; name
	.db		"CH-8"			; 4-character gamecode
	.db		"__"			; ?

;-----------------------------------------------------------------------------
; Start
;-----------------------------------------------------------------------------

	.equ C8_screen	$1000	; TODO change to middle of screen at some point

	; 1300–131F: sprite scratch 32 bits
	; 1320–1327: sprite scratch 16 bits

	.equ C8_I		$1338	; 1328–1329
	.equ C8_PC		$133A	; 132A–132B
	.equ C8_DT		$133C
	.equ C8_ST		$133D

	.equ C8_V		$1340	; V0–VF
	.equ C8_VF		C8_V + $F
	
	.equ C8_SP		$1350	; 1 byte offset for stack
	.equ C8_STACK	$1351	; TODO maybe 16 levels instead?
	.equ C8_ROM 	$1400	; TODO this can be changed to $135A after testing
	.equ C8_OFFSET	C8_ROM - $200 ; offset for CHIP-8 addresses

start:
	call	Init

	call CopyROMtoRAM

	mov hl, C8_ROM
	mov [C8_PC], hl
	mov a, 0
	mov [C8_SP], a

MainLoop:
	mov x, [C8_PC]
	mov h, [x]	; CHIP-8 programs are big-endian
	inc x
	mov l, [x]
	inc x
	mov [C8_PC], x

	mov a, h
	tst a, $FF
	jz opcode0

	and a, $F0
	xor a, $10
	jz opcode1

	mov a, h
	and a, $F0
	xor a, $20
	jz opcode2

	mov a, h
	and a, $F0
	xor a, $30
	jz opcode3

	mov a, h
	and a, $F0
	xor a, $40
	jz opcode4

	mov a, h
	and a, $F0
	xor a, $50
	jz opcode5

	mov a, h
	and a, $F0
	xor a, $60
	jz opcode6

	mov a, h
	and a, $F0
	xor a, $70
	jz opcode7

	mov a, h
	and a, $F0
	xor a, $80
	jz opcode8

	mov a, h
	and a, $F0
	xor a, $90
	jz opcode9

	mov a, h
	and a, $F0
	xor a, $A0
	jz opcodeA

	mov a, h
	and a, $F0
	xor a, $B0
	jz opcodeB

	mov a, h
	and a, $F0
	xor a, $C0
	jz opcodeC

	mov a, h
	and a, $F0
	xor a, $D0
	jz opcodeD

	mov a, h
	and a, $F0
	xor a, $E0
	jz opcodeE

	mov a, h
	and a, $F0
	xor a, $F0
	jz opcodeF

	;jmp		MainLoop

opcode0:
	mov a, l
	xor a, $E0
	jz opcode00E0

opcode00E0:
	;memCopy
	mov hl, $1000
_memCopyLoop:
	mov [hl], 0
	inc hl
	cmp l, $13
	jnz _memCopyLoop
	
	jmp MainLoop

opcode1:
	and h, $0F
	add hl, C8_OFFSET
	mov [C8_PC], hl
	jmp MainLoop

opcode2:
	jmp MainLoop

opcode3:
	mov b, 0
	mov a, l
	mov n, a
	mov a, h
	and a, $0F
	mov hl, C8_V
	add hl, ba
	mov a, n
	cmp a, [hl]
	jnz _notEqual

	mov x, C8_PC
	mov hl, [x]
	inc hl
	inc hl
	mov [x], hl

_notEqual:
	jmp MainLoop

opcode4:
	mov b, 0
	mov a, l
	mov n, a
	mov a, h
	and a, $0F
	mov hl, C8_V
	add hl, ba
	mov a, n
	cmp a, [hl]
	jz _equal

	mov x, C8_PC
	mov hl, [x]
	inc hl
	inc hl
	mov [x], hl

_equal:
	jmp MainLoop

opcode5:
	xchg ba, hl
	and b, $0F
	tst a, $0F
	jnz MainLoop
	swap a
	and a, $0F

	push b

	mov hl, C8_V
	mov b, l
	add a, b
	mov l, a
	mov a, [hl]

	pop b
	push hl
	push a

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	mov b, [hl]

	pop a
	pop hl

	cmp a, b
	jnz _notEqual

	mov x, C8_PC
	mov hl, [x]
	inc hl
	inc hl
	mov [x], hl

_notEqual:
	jmp MainLoop

opcode6:
	mov b, 0
	mov a, l
	mov n, a
	mov a, h
	and a, $0F
	mov hl, C8_V
	add hl, ba
	mov a, n
	mov [hl], a
	jmp MainLoop

opcode7:
	mov b, 0
	mov a, l
	mov n, a
	mov a, h
	and a, $0F
	mov hl, C8_V
	add hl, ba
	mov a, n
	add [hl], a
	jmp MainLoop

opcode8:
	mov a, l
	tst a, $0F
	jz opcode8XY0

	and a, $0F
	mov b, a
	
	xor a, $01
	jz opcode8XY1

	mov a, b
	xor a, $02
	jz opcode8XY2

	mov a, b
	xor a, $03
	jz opcode8XY3
	
	mov a, b
	xor a, $04
	jz opcode8XY4
	
	mov a, b
	xor a, $05
	jz opcode8XY5

	mov a, b
	xor a, $06
	jz opcode8XY6
	
	mov a, b
	xor a, $07
	jz opcode8XY7
	
	mov a, b
	xor a, $0E
	jz opcode8XYE

	jmp MainLoop

opcode8XY0:
	mov ba, hl
	and b, $0F
	swap a
	and a, $0F

	push b

	mov hl, C8_V
	mov b, l
	add a, b
	mov l, a
	mov a, [hl]

	pop b
	push hl
	push a

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	pop a
	mov [hl], a

	pop hl

	jmp MainLoop

opcode8XY1:
	mov ba, hl
	and b, $0F
	swap a
	and a, $0F

	push b

	mov hl, C8_V
	mov b, l
	add a, b
	mov l, a
	mov a, [hl]

	pop b
	push hl
	push a

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	mov b, [hl]

	pop a
	or a, b
	mov [hl], a

	pop hl

	jmp MainLoop

opcode8XY2:
	mov ba, hl
	and b, $0F
	swap a
	and a, $0F

	push b

	mov hl, C8_V
	mov b, l
	add a, b
	mov l, a
	mov a, [hl]

	pop b
	push hl
	push a

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	mov b, [hl]

	pop a
	and a, b
	mov [hl], a

	pop hl

	jmp MainLoop

opcode8XY3:
	mov ba, hl
	and b, $0F
	swap a
	and a, $0F

	push b

	mov hl, C8_V
	mov b, l
	add a, b
	mov l, a
	mov a, [hl]

	pop b
	push hl
	push a

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	mov b, [hl]

	pop a
	xor a, b
	mov [hl], a

	pop hl

	jmp MainLoop

opcode8XY4:
	mov ba, hl
	and b, $0F
	swap a
	and a, $0F

	push b

	mov hl, C8_V
	mov b, l
	add a, b
	mov l, a
	mov a, [hl]

	pop b
	push hl
	push a

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	mov b, [hl]

	pop a
	add a, b
	mov [hl], a

	mov hl, C8_VF
	mov a, f
	shr a
	and a, $01
	mov [hl], a

	pop hl

	jmp MainLoop

opcode8XY5:
	mov ba, hl
	and b, $0F
	swap a
	and a, $0F

	push b

	mov hl, C8_V
	mov b, l
	add a, b
	mov l, a
	mov a, [hl]

	pop b
	push hl
	push a

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	mov b, [hl]

	pop a
	xchg a, b
	sub a, b
	mov [hl], a

	mov hl, C8_VF
	mov a, f
	shr a
	and a, $01
	xor a, $01
	mov [hl], a

	pop hl

	jmp MainLoop

opcode8XY6:
	mov ba, hl
	and b, $0F
	;swap a
	;and a, $0F

	;push b

	;mov hl, C8_V
	;mov b, l
	;add a, b
	;mov l, a
	;mov a, [hl]

	;pop b
	;push hl
	;push a

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	mov b, [hl]

	;pop a
	;shl a
	;mov [hl], a

	shr b
	mov [hl], b

	mov hl, C8_VF
	mov a, f
	shr a
	and a, $01
	mov [hl], a

	;pop hl

	jmp MainLoop

opcode8XY7:
	mov ba, hl
	and b, $0F
	swap a
	and a, $0F

	push b

	mov hl, C8_V
	mov b, l
	add a, b
	mov l, a
	mov a, [hl]

	pop b
	push hl
	push a

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	mov b, [hl]

	pop a
	sub a, b
	mov [hl], a

	mov hl, C8_VF
	mov a, f
	shr a
	and a, $01
	xor a, $01
	mov [hl], a

	pop hl

	jmp MainLoop

opcode8XYE:
	mov ba, hl
	and b, $0F
	;swap a
	;and a, $0F

	;push b

	;mov hl, C8_V
	;mov b, l
	;add a, b
	;mov l, a
	;mov a, [hl]

	;pop b
	;push hl
	;push a

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	mov b, [hl]

	;pop a
	;shl a
	;mov [hl], a

	shl b
	mov [hl], b

	mov hl, C8_VF
	mov a, f
	shr a
	and a, $01
	mov [hl], a

	;pop hl

	jmp MainLoop

opcode9:
	xchg ba, hl
	and b, $0F
	tst a, $0F
	jnz MainLoop
	swap a
	and a, $0F

	push b

	mov hl, C8_V
	mov b, l
	add a, b
	mov l, a
	mov a, [hl]

	pop b
	push hl
	push a

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	mov b, [hl]

	pop a
	pop hl

	cmp a, b
	jz _equal

	mov x, C8_PC
	mov hl, [x]
	inc hl
	inc hl
	mov [x], hl

_equal:
	jmp MainLoop

opcodeA:
	and h, $0F
	add hl, C8_OFFSET
	mov [C8_I], hl
	jmp MainLoop

opcodeB:
	jmp MainLoop

opcodeC:
	jmp MainLoop

opcodeD:
	mov x, [C8_I]
	call CopySpriteToScreen
	jmp MainLoop

opcodeE:
	jmp MainLoop

opcodeF:
	mov a, l
	xor a, $1E
	jz opcodeFX1E

	mov a, l
	xor a, $29
	jz opcodeFX29

	mov a, l
	xor a, $33
	jz opcodeFX33

	mov a, l
	xor a, $55
	jz opcodeFX55

	mov a, l
	xor a, $65
	jz opcodeFX65

	jmp MainLoop

opcodeFX1E:
	mov b, 0
	mov a, h
	and a, $0F
	mov hl, C8_V
	add hl, ba

	mov a, [hl]
	mov hl, C8_I
	add [hl], a
	jmp MainLoop

opcodeFX29:
	mov b, 0
	mov a, h
	and a, $0F
	mov hl, C8_V
	add hl, ba

	mov a, [hl]
	mov l, 5
	mul l, a
	add hl, font
	mov x, C8_I
	mov [x], hl
	jmp MainLoop

opcodeFX33:
	mov b, h
	and b, $0F

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	mov l, [hl]
	mov h, 0

	mov x, [C8_I]

	push hl
	mov a, 100
	div hl, a
	mov [x], l

	inc x

	pop hl
	push hl
	mov a, 10
	div hl, a
	mov h, 0
	div hl, a
	mov [x], h

	inc x

	pop hl
	mov a, 100
	div hl, a
	mov a, 10
	mov l, h
	mov h, 0
	div hl, a
	mov [x], h

	jmp MainLoop

opcodeFX55:
	mov b, h
	and b, $0F
	inc b

	mov hl, C8_V
	mov x, [C8_I]

_storeLoop:
	mov [x], [hl]
	inc x
	inc hl
	jdbnz _storeLoop

	;mov [C8_I], x

	jmp MainLoop

opcodeFX65:
	mov b, h
	and b, $0F
	inc b

	mov hl, C8_V
	mov x, [C8_I]

_storeLoop:
	mov [hl], [x]
	inc x
	inc hl
	jdbnz _storeLoop

	;mov [C8_I], x

	jmp MainLoop

;-----------------------------------------------------------------------------
; Delay
;-----------------------------------------------------------------------------

Delay:
	push	x
	mov		x, 0
_loop:

	test	[nn+BUTTONS], BUTTON_POWER
	jnz		_dont_suspend
	int		IntSuspend
_dont_suspend:

	dec		x
	jnz		_loop
	pop		x
	ret

;-----------------------------------------------------------------------------
; Init
; init display to blit mode
;-----------------------------------------------------------------------------

Init:
	movw	nn, IO_BEGIN

	movb	[nn+VIDEO_0], $01+$08	# set blit mode
	movb	[nn+VIDEO_1], $01+$08	# enable video

	ret

CopyROMtoRAM:
	mov x, gameROM
	mov y, C8_ROM
	mov hl, endGameROM - gameROM
_loop:
	mov [y], [x]
	inc x
	inc y
	dec hl
	jnzb _loop

	ret

;-----------------------------------------------------------------------------
; CopySpriteToScreen
; display sprite from x
;-----------------------------------------------------------------------------

RotateSprite:
	push hl
	;memCopy
	mov b, l
	and b, $0F
	mov hl, $1310
_memCopyLoop:
	mov [hl], [x]
	inc hl
	inc x
	jdbnz _memCopyLoop

	pop hl
	push hl

	mov x, $1317
	mov hl, $1300
	mov n, 8
_sprite_row_loop:
	mov		b, 8
_sprite_bit_loop:
	mov a, [x]
	shl a
	mov [x], a
	rolc [hl]
	inc hl
	jdbnz _sprite_bit_loop

	dec x
	sub hl, 8
	dec n
	jnz _sprite_row_loop

	cmp x, $1317
	jz _done

	mov x, $131F
	mov hl, $1308
	mov n, 8
	jmp _sprite_row_loop

_done:
	pop ba
	ret

DoSpriteAttributeStuff:
	and b, $0F
	;mov n, a
	swap a
	and a, $0F

	; B X
	; A Y

	push b

	mov hl, C8_V
	mov b, l
	add a, b
	mov l, a
	mov a, [hl]
	and a, $1F

	mov h, a
	and h, $07
	
	; H is now bit offset/counter

	pop b
	push hl
	push a

	mov hl, C8_V
	mov a, l
	add a, b
	mov l, a
	mov b, [hl]
	and b, $3F

	pop a
	pop hl

	shr a
	shr a
	shr a

	xchg ba, hl

	; B is now bit offset/counter
	; HL is XY

	;mov a, n
	;and a, $0F
	;mov n, a

	; N is now row counter TODO not actually needed

	; get bit offset, Y AND 7: B
	; display row counter: N

	ret

OffsetSprite:

	; OK now we push HL so we can retrieve it as XY later
	push hl

	; TODO save N???

	; and try to do this

	; byte 0 = hl
	; byte 1 = x
	; byte 2 = y
	; for 8 bytes:
	;	for bit offset > 0:
	;		shift byte 0 left
	;		rolc byte 1
	;		rolc byte 2
	;		dec bit offset
	;	inc byte 0
	;	inc byte 1
	;	inc byte 2

	mov hl, $1300
	mov x, $1308
	mov y, $1310

	push ba

	tst b, $FF
	jz loop_done

	mov n, 8
	
for_bit_offset_lt_zero:
	shl [hl]
	mov a, [x]
	rolc a
	mov [x], a
	mov a, [y]
	rolc a
	mov [y], a
	jdbnz for_bit_offset_lt_zero

	dec n
	jz loop_done

	pop ba
	push ba
	inc hl
	inc x
	inc y
	jmp for_bit_offset_lt_zero

loop_done:
	pop ba
	pop hl

	ret


CopySpriteToScreen:

	mov y, C8_VF
	mov [y], 0

	; here:
	; x = sprite
	; hl = DXYN

	call RotateSprite

	; here:
	; $1300 = rotated sprite
	; ba = DXYN

	call DoSpriteAttributeStuff

	; $1300 = rotated sprite
	; B = offset

	call OffsetSprite

	; here:
	; $1300 = rotated and offset sprite

	xchg ba, hl
	mov l, 96
	mul l, a
	mov a, l
	add a, b
	mov l, a
	mov a, h
	add a, $10
	mov h, a	

	;memCopy
	mov b, 8
	mov n, 3
	mov x, $1300
_memCopyLoop2:
	mov a, [x]
	and a, [hl]
	jz _noCollision

	mov y, C8_VF
	mov [y], 1

_noCollision:
	xor [hl], [x] ; TODO xor
	inc hl
	inc x
	jdbnz _memCopyLoop2
	dec n
	jz memcpy_done
	add hl, 88
	mov b, 8
	jmp _memCopyLoop2

memcpy_done:
	ret


;-----------------------------------------------------------------------------
; Data
;-----------------------------------------------------------------------------

	.align	8
font8x8:
	.incbin font8x8.bin

gameROM:
	.incbin BC_test.ch8 ;test_opcode.ch8
endGameROM:

font:
	.db    0xF0, 0x90, 0x90, 0x90, 0xF0
    .db    0x20, 0x60, 0x20, 0x20, 0x70
    .db    0xF0, 0x10, 0xF0, 0x80, 0xF0
    .db    0xF0, 0x10, 0xF0, 0x10, 0xF0
    .db    0x90, 0x90, 0xF0, 0x10, 0x10
    .db    0xF0, 0x80, 0xF0, 0x10, 0xF0
    .db    0xF0, 0x80, 0xF0, 0x90, 0xF0
    .db    0xF0, 0x10, 0x20, 0x40, 0x40
    .db    0xF0, 0x90, 0xF0, 0x90, 0xF0
    .db    0xF0, 0x90, 0xF0, 0x10, 0xF0
    .db    0xF0, 0x90, 0xF0, 0x90, 0x90
    .db    0xE0, 0x90, 0xE0, 0x90, 0xE0
    .db    0xF0, 0x80, 0x80, 0x80, 0xF0
    .db    0xE0, 0x90, 0x90, 0x90, 0xE0
    .db    0xF0, 0x80, 0xF0, 0x80, 0xF0
    .db    0xF0, 0x80, 0xF0, 0x80, 0x80 

;-----------------------------------------------------------------------------
; End
;-----------------------------------------------------------------------------

	.end