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n65/scroll.asm

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NASM
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;------------------------------------------------------------------------------
; This is a direct port of Michael Martin's tutorial project for NES101
;
; I believe that tutorial can be found here:
; http://hackipedia.org/Platform/Nintendo/NES/tutorial,%20NES%20programming%20101/NES101.html
;
; I just rewrote it to have something interesting to test my assembler on.
; Saf 2015
;
; Create an iNES header
.ines {"prog": 1, "char": 1, "mapper": 0, "mirror": 0}
; SRAM
; I have no way to do this right now, but I need to add
; the ability to simply name parts of memory with a sort
; of alias, specifically in the zero page where memory
; access is quick.
; For now, let's just remember that in the zero page:
; *dx = $00 ; The speed delta x of the sprite
; *a = $01 ; Whether the A button is down
; *scroll = $02 ; The scroll amount
;
; *sprite = $200 ; Some sprite memory
; Actually I can probably do this with a .org and label pair
.org $0200
sprite:
; Main Code Segment
.org $C000
reset:
SEI
CLD
; Wait two VBLANKs.
wait_vb1:
LDA $2002
BPL wait_vb1
wait_vb2:
LDA $2002
BPL wait_vb2
; Clear out RAM.
LDA #$00
LDX #$00
clear_segments:
STA $00, X
STA $0100, X
STA $0200, X
STA $0300, X
STA $0400, X
STA $0500, X
STA $0600, X
STA $0700, X
INX
BNE clear_segments
; Reset the stack pointer.
LDX #$FF
TXS
; Disable all graphics.
LDA #$00
STA $2000
STA $2001
JSR init_graphics
JSR init_input
JSR init_sound
; Set basic PPU registers. Load background from $0000,
; sprites from $1000, and the name table from $2000.
LDA #$88
STA $2000
LDA #$1E
STA $2001
CLI
; Transfer control to the VBLANK routines.
forever:
JMP forever
init_graphics:
JSR init_sprites
JSR load_palette
JSR load_name_tables
JSR init_scrolling
RTS
init_input:
; The A button starts out not-pressed.
LDA #$00
STA $01 ; $01 = A button
RTS
init_sound:
; initialize sound hardware
LDA #$01
STA $4015
LDA #$00
STA $4001
LDA #$40
STA $4017
RTS
init_sprites:
; Clear page #2, which we'll use to hold sprite data
LDA #$00
LDX #$00
sprite_clear1:
STA $0200, X ; $0200 = sprite
INX
BNE sprite_clear1
; initialize Sprite 0
LDA #$70
STA $0200 ; sprite Y coordinate
LDA #$01
STA $0201 ; sprite + 1Pattern number
STA $0203 ; sprite+3 X coordinate
; sprite+2, color, stays 0.
; Set initial value of dx
LDA #$01
STA $00 ; dx = $00
RTS
; Load palette into $3F00
load_palette:
LDA #$3F
LDX #$00
STA $2006
STX $2006
loady_loop:
LDA palette, X
STA $2007
INX
CPX #$20
BNE loady_loop
RTS
; Jam some text into the first name table (at $2400, thanks to mirroring)
load_name_tables:
LDY #$00
LDX #$04
LDA #<bg
STA $10
LDA #>bg
STA $11
LDA #$24
STA $2006
LDA #$00
STA $2006
go_back:
LDA ($10), Y
STA $2007
INY
BNE go_back
INC $11
DEX
BNE go_back
RTS
; Clear out the Name Table at $2800 (where we already are. Yay.)
LDY #$00
LDX #$04
LDA #$00
back:
STA $2007
INY
BNE back
DEX
BNE back
RTS
init_scrolling:
LDA #$F0
STA $02 ; scroll
RTS
update_sprite:
LDA #>sprite
STA $4014 ; Jam page $200-$2FF into SPR-RAM
LDA $05 ; sprite+3 Is this right???
BEQ hit_left
CMP #$F7
BNE edge_done
; Hit right
LDX #$FF
STX $00 ; dx
JSR high_c
JMP edge_done
hit_left:
LDX #$01
STX $00 ; dx
JSR high_c
edge_done: ; update X and store it.
CLC
ADC $00 ; dx
STA $05 ; sprite+3 Is this right?
RTS
react_to_input:
LDA #$01 ; strobe joypad
STA $4016
LDA #$00
STA $4016
LDA $4016 ; Is the A button down?
AND #$01
BEQ not_a
LDX $01 ; a
BNE a_done ; Only react if the A button wasn't down last time.
STA $01 ; Store the 1 in local variable 'a' so that we this is
JSR reverse_dx ; only called once per press.
JMP a_done
not_a:
STA $01 ; A has been released, so put that zero into 'a'.
a_done:
LDA $4016 ; B does nothing
LDA $4016 ; Select does nothing
LDA $4016 ; Start does nothing
LDA $4016 ; Up
AND #$01
BEQ not_up
LDX sprite ; Load Y value
CPX #$07
BEQ not_up ; No going past the top of the screen
DEX
STX sprite
not_up: lda $4016 ; Down
AND #$01
BEQ not_dn
LDX sprite
CPX #$DF ; No going past the bottom of the screen.
BEQ not_dn
INX
STX sprite
not_dn:
RTS ; Ignore left and right, we don't use 'em
reverse_dx:
LDA #$FF
EOR $00 ; dx
CLC
ADC #$01
STA $00 ; dx
JSR low_c
RTS
scroll_screen:
LDX #$00 ; Reset VRAM
STX $2006
STX $2006
LDX $02 ; scroll ; Do we need to scroll at all?
BEQ no_scroll
DEX
STX $02 ; scroll
LDA #$00
STA $2005 ; Write 0 for Horiz. Scroll value
STX $2005 ; Write the value of 'scroll' for Vert. Scroll value
no_scroll:
RTS
low_c:
PHA
LDA #$84
STA $4000
LDA #$AA
STA $4002
LDA #$09
STA $4003
PLA
RTS
high_c:
PHA
LDA #$86
STA $4000
LDA #$69
STA $4002
LDA #$08
STA $4003
PLA
RTS
vblank:
JSR scroll_screen
JSR update_sprite
JSR react_to_input
irq:
RTI
; palette data
palette:
.bytes $0E,$00,$0E,$19,$00,$00,$00,$00,$00,$00,$00,$00,$01,$00,$01,$21
.bytes $0E,$20,$22,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00
; Background data
bg:
.ascii " "
.ascii " "
.ascii " SAF'S 6502 NES ASSEMBLER "
.ascii " "
.ascii " "
.ascii " "
.ascii " VSS RES "
.ascii " RDY PHI2 "
.ascii " PH1 S0 "
.ascii " IRQ 6 PHI0 "
.ascii " NC NC "
.ascii " NMI NC "
.ascii " SYNC 5 R/W "
.ascii " VCC D0 "
.ascii " A0 D1 "
.ascii " A1 0 D2 "
.ascii " A2 D3 "
.ascii " A3 D4 "
.ascii " A4 2 D5 "
.ascii " A5 D6 "
.ascii " A6 D7 "
.ascii " A7 A15 "
.ascii " A8 A14 "
.ascii " A9 A13 "
.ascii " A10 A12 "
.ascii " A11 VSS "
.ascii " "
.ascii " "
.ascii " "
.ascii " "
; Attribute table
.bytes $00,$00,$00,$00,$00,$00,$00,$00,
.bytes $00,$00,$FF,$FF,$FF,$00,$00,$00,
.bytes $00,$00,$FF,$FF,$FF,$00,$00,$00,
.bytes $00,$00,$FF,$FF,$FF,$00,$00,$00,
.bytes $00,$00,$FF,$FF,$FF,$00,$00,$00,
.bytes $00,$00,$FF,$FF,$FF,$00,$00,$00,
.bytes $00,$00,$FF,$FF,$FF,$00,$00,$00,
.bytes $00,$00,$00,$00,$00,$00,$00,$00,
; Setup the interrupt vectors
.org $FFFA ;first of the three vectors starts here
.dw vblank ;when an NMI happens (once per frame if enabled) the processor will jump to the label NMI:
.dw reset ;when the processor first turns on or is reset, it will jump to the label RESET:
.dw irq ;external interrupt IRQ is not used in this tutorial
; This is CHR-ROM page 1, which starts at 0x0000, but I'm skipping the first bit
; So this is where tile memory is going to go, this is the commodore 64's character ROM
; mapped to ASCII for tile numbers. We are only using 4KB of this 8KB page.
.org $0200
.bytes $00,$00,$00,$00,$00,$00,$00,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 32
.bytes $18,$18,$18,$18,$00,$00,$18,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 33
.bytes $66,$66,$66,$00,$00,$00,$00,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 34
.bytes $66,$66,$FF,$66,$FF,$66,$66,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 35
.bytes $18,$3E,$60,$3C,$06,$7C,$18,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 36
.bytes $62,$66,$0C,$18,$30,$66,$46,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 37
.bytes $3C,$66,$3C,$38,$67,$66,$3F,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 38
.bytes $06,$0C,$18,$00,$00,$00,$00,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 39
.bytes $0C,$18,$30,$30,$30,$18,$0C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 40
.bytes $30,$18,$0C,$0C,$0C,$18,$30,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 41
.bytes $00,$66,$3C,$FF,$3C,$66,$00,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 42
.bytes $00,$18,$18,$7E,$18,$18,$00,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 43
.bytes $00,$00,$00,$00,$00,$18,$18,$30,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 44
.bytes $00,$00,$00,$7E,$00,$00,$00,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 45
.bytes $00,$00,$00,$00,$00,$18,$18,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 46
.bytes $00,$03,$06,$0C,$18,$30,$60,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 47
.bytes $3C,$66,$6E,$76,$66,$66,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 48
.bytes $18,$18,$38,$18,$18,$18,$7E,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 49
.bytes $3C,$66,$06,$0C,$30,$60,$7E,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 50
.bytes $3C,$66,$06,$1C,$06,$66,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 51
.bytes $06,$0E,$1E,$66,$7F,$06,$06,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 52
.bytes $7E,$60,$7C,$06,$06,$66,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 53
.bytes $3C,$66,$60,$7C,$66,$66,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 54
.bytes $7E,$66,$0C,$18,$18,$18,$18,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 55
.bytes $3C,$66,$66,$3C,$66,$66,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 56
.bytes $3C,$66,$66,$3E,$06,$66,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 57
.bytes $00,$00,$18,$00,$00,$18,$00,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 58
.bytes $00,$00,$18,$00,$00,$18,$18,$30,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 59
.bytes $0E,$18,$30,$60,$30,$18,$0E,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 60
.bytes $00,$00,$7E,$00,$7E,$00,$00,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 61
.bytes $70,$18,$0C,$06,$0C,$18,$70,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 62
.bytes $3C,$66,$06,$0C,$18,$00,$18,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 63
.bytes $3C,$66,$6E,$6E,$60,$62,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 64
.bytes $18,$3C,$66,$7E,$66,$66,$66,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 65
.bytes $7C,$66,$66,$7C,$66,$66,$7C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 66
.bytes $3C,$66,$60,$60,$60,$66,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 67
.bytes $78,$6C,$66,$66,$66,$6C,$78,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 68
.bytes $7E,$60,$60,$78,$60,$60,$7E,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 69
.bytes $7E,$60,$60,$78,$60,$60,$60,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 70
.bytes $3C,$66,$60,$6E,$66,$66,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 71
.bytes $66,$66,$66,$7E,$66,$66,$66,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 72
.bytes $3C,$18,$18,$18,$18,$18,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 73
.bytes $1E,$0C,$0C,$0C,$0C,$6C,$38,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 74
.bytes $66,$6C,$78,$70,$78,$6C,$66,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 75
.bytes $60,$60,$60,$60,$60,$60,$7E,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 76
.bytes $63,$77,$7F,$6B,$63,$63,$63,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 77
.bytes $66,$76,$7E,$7E,$6E,$66,$66,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 78
.bytes $3C,$66,$66,$66,$66,$66,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 79
.bytes $7C,$66,$66,$7C,$60,$60,$60,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 80
.bytes $3C,$66,$66,$66,$66,$3C,$0E,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 81
.bytes $7C,$66,$66,$7C,$78,$6C,$66,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 82
.bytes $3C,$66,$60,$3C,$06,$66,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 83
.bytes $7E,$18,$18,$18,$18,$18,$18,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 84
.bytes $66,$66,$66,$66,$66,$66,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 85
.bytes $66,$66,$66,$66,$66,$3C,$18,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 86
.bytes $63,$63,$63,$6B,$7F,$77,$63,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 87
.bytes $66,$66,$3C,$18,$3C,$66,$66,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 88
.bytes $66,$66,$66,$3C,$18,$18,$18,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 89
.bytes $7E,$06,$0C,$18,$30,$60,$7E,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 90
.bytes $3C,$30,$30,$30,$30,$30,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 91
.bytes $0C,$12,$30,$7C,$30,$62,$FC,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 92
.bytes $3C,$0C,$0C,$0C,$0C,$0C,$3C,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 93
.bytes $00,$18,$3C,$7E,$18,$18,$18,$18,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 94
.bytes $00,$10,$30,$7F,$7F,$30,$10,$00,$FF,$FF,$FF,$FF,$FF,$FF,$FF,$FF ; Character 95
; This is CHR-ROM page 2, which starts at 0x2000, and we put the sprite data here.
.org $1000
.bytes $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00 ; Character 0: Blank
.bytes $18,$24,$66,$99,$99,$66,$24,$18,$00,$18,$18,$66,$66,$18,$18,$00 ; Character 1: Diamond sprite
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