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.INCLUDE "header.asm".INCLUDE "init.asm".INCLUDE "registers.asm"
.BANK 0 SLOT 0.ORG 0.SECTION "MainCode"
; Memory layout:; 0000-000F: scratch space for functions.; 0010-0011: controller state of joypad #1.; 0012-0013: controller state of joypad #2.; 0014-0017: 32-bit counter of vblanks.; 0020-0021: (x, y) coordinates of player.; 0022-0024: RGB color values to use for background color, from [0-31].;; Sprite table buffers -- copied each frame to OAM during VBlank, using DMA.; 0100-02FF: table 1 (4 bytes each: x/y coord, tile #, flip/priority/palette); 0300-031F: table 2 (2 bits each: high x-coord bit, size)
Start: InitializeSNES
jsr LoadPaletteAndTileData jsr InitializeSpriteTables
; Set screen mode: 16x16 tiles for backgrounds, mode 1. lda #%11000001 sta SCREENMODE
; Set sprite size to 16x16 (small) and 32x32 (large). lda #%01100000 sta OAMSIZE
; Main screen: enable sprites & BG3. lda #%00010100 sta MSENABLE
; Turn on the screen. ; Format: x000bbbb ; x: 0 = screen on, 1 = screen off, bbbb: Brightness ($0-$F) lda #%00001111 sta INIDISP
; Enable NMI interrupt & joypad. ; n-vh---j n: NMI interrupt enable v: vertical counter enable ; h: horizontal counter enable j: joypad enable lda #%10000001 sta NMITIMEN
; Store zeroes to the controller status registers. ; TODO(mcmillen): is this needed? I think the system will overwrite these ; automatically. stz JOY1H stz JOY1L
; Write something recognizable into our scratch space. jsr FillScratch
; Start the background color as a dark blue. lda #8 sta $24
; Player's initial starting location. lda #(256 / 4) sta $20 lda #((224 - 8) / 2) sta $21
MainLoop: wai ; Wait for interrupt. jmp MainLoop
LoadPaletteAndTileData: ; For more details on DMA, see: ; http://wiki.superfamicom.org/snes/show/Grog%27s+Guide+to+DMA+and+HDMA+on+the+SNES ; http://wiki.superfamicom.org/snes/show/Making+a+Small+Game+-+Tic-Tac-Toe ; ; A lot of the graphics-related registers are explained in Qwertie's doc: ; http://emu-docs.org/Super%20NES/General/snesdoc.html ; ... but be careful, because there are some errors in this doc. ; ; bazz's tutorial (available from http://wiki.superfamicom.org/snes/) is ; quite helpful with palette / sprites / DMA, especially starting at ; http://wiki.superfamicom.org/snes/show/Working+with+VRAM+-+Loading+the+Palette
; 16-bit X/Y registers. Used for DMA source address & transfer size, both of ; which want 16-bit values. rep #%00010000 ; 8-bit A/B registers. Used for DMA source bank & destination address. sep #%00100000
; Initialize the palette memory in a loop. ; We could also do this with a DMA transfer (like we do with the tile data ; below), but it seems overkill for just a few bytes. :) ; TODO(mcmillen): do it with a DMA transfer.
; First, sprite palette data: ldx #0 lda #128 ; Palette entries for sprites start at 128. sta CGADDR- lda.l SpritePalette, X sta CGDATA inx cpx #32 ; 32 bytes of palette data. bne -
; Now, BG3 palette data. ; Palette entries for BG3 start at 0. ; TODO(mcmillen): BG2 started at 32, but maybe that's only in mode 0? ldx #0 lda #0 sta CGADDR- lda.l TilePalette, X sta CGDATA inx cpx #8 ; 8 bytes of palette data. bne -
; TODO(mcmillen): make the "DMA stuff into VRAM" a macro or function. ; Set VMADDR to where we want the DMA to start. We'll store sprite data ; at the beginning of VRAM. ldx #$0000 stx VMADDR ; DMA 0 source address & bank. ldx #SpriteData stx DMA0SRC lda #:SpriteData sta DMA0SRCBANK ; DMA 0 transfer size. ; See the helpful comment in sprites.asm to find the size of the tile data. ldx #640 stx DMA0SIZE ; DMA 0 control register. ; Transfer type 001 = 2 addresses, LH. lda #%00000001 sta DMA0CTRL ; DMA 0 destination. lda #$18 ; The upper byte is assumed to be $21, so this is $2118 & $2119. sta DMA0DST ; Enable DMA channel 0. lda #%00000001 sta DMAENABLE
; Store background tile data at byte $2000 of VRAM. ; (VMADDR is a word address, so multiply by 2 to get the byte address.) ldx #$1000 stx VMADDR ; DMA 0 source address & bank. ldx #TileData stx DMA0SRC lda #:TileData sta DMA0SRCBANK ; DMA 0 transfer size. ; See the helpful comment in tiles.asm to find the size of the tile data. ldx #384 stx DMA0SIZE ; DMA 0 control register. ; Transfer type 001 = 2 addresses, LH. lda #%00000001 sta DMA0CTRL ; DMA 0 destination. lda #$18 ; The upper byte is assumed to be $21, so this is $2118 & $2119. sta DMA0DST ; Enable DMA channel 0. lda #%00000001 sta DMAENABLE
; Tell the system that the BG3 tilemap starts at $4000. lda #%00100000 sta BG3TILEMAP ; ... and that the background tile data for BG3 starts at $2000. lda #%00000001 sta BG34NBA
; Set up the BG3 tilemap. ; VRAM write mode: increments the address every time we write a word. lda #%10000000 sta VMAIN ; Set word address for accessing VRAM. ldx #$2000 ; BG 3 tilemap starts here. (Byte address $4000.) stx VMADDR ; Now write entries into the tile map. ; We have only a couple tiles, but we set the invert horizontal/vertical ; bits so that we get more variation. We also do 7 tiles per loop -- since ; the tile map is 32 entries wide, this means that successive rows end up ; looking different. ldy #0- ldx #$0000 stx VMDATA iny ldx #$0000 stx VMDATA iny ldx #$0000 stx VMDATA iny ldx #$0000 stx VMDATA iny ldx #$0002 stx VMDATA iny ldx #$0000 stx VMDATA iny ldx #$8004 stx VMDATA iny ldx #$0000 stx VMDATA iny ldx #$0000 stx VMDATA iny ldx #$0000 stx VMDATA iny ldx #$4002 stx VMDATA iny ldx #$0000 stx VMDATA iny ldx #$0000 stx VMDATA iny ldx #$A004 stx VMDATA iny ; The tile map is 32x32 (1024 entries). ; This is the next multiple of 14 above that. cpy #(74 * 14) bne -
rts
InitializeSpriteTables: ; This page is a good reference on SNES sprite formats: ; http://wiki.superfamicom.org/snes/show/SNES+Sprites ; It uses the same approach we're using, in which we keep a buffer of the ; sprite tables in RAM, and DMA the sprite tables to the system's OAM ; during VBlank. rep #%00110000 ; 16-bit A/X/Y.
ldx #$0000 ; Fill sprite table 1. 4 bytes per sprite, laid out as follows: ; Byte 1: xxxxxxxx x: X coordinate ; Byte 2: yyyyyyyy y: Y coordinate ; Byte 3: cccccccc c: Starting tile # ; Byte 4: vhoopppc v: vertical flip h: horizontal flip o: priority bits ; p: palette # lda #$01- sta $0100, X ; We keep our sprite table at $0100 and DMA it to OAM later. inx inx inx inx cpx #$0200 bne -
; Fill sprite table 2. 2 bits per sprite, like so: ; bits 0,2,4,6 - High bit of the sprite's x-coordinate. ; bits 1,3,5,7 - Toggle Sprite size: 0 - small size 1 - large size ; Setting all the high bits keeps the sprites offscreen. lda #%0101010101010101- sta $0100, X inx inx cpx #$0220 bne -
sep #%00100000 ; 8-bit A. rts
VBlankHandler: jsr VBlankCounter ; DEBUG jsr JoypadHandler jsr SetBackgroundColor jsr UpdateGraphics jsr DMASpriteTables rti
VBlankCounter: ; Increment a counter of how many VBlanks we've done. inc $14 lda $14 cmp #$00 bne VBlankCounterDone inc $15 lda $15 cmp #$00 bne VBlankCounterDone inc $16 lda $16 cmp #$00 bne VBlankCounterDone inc $17VBlankCounterDone: rts
JoypadHandler: jsr JoypadDebug ; DEBUG
JoypadUp: lda JOY1H and #$08 ; Up cmp #$08 bne JoypadDown ; Button not pressed. lda $21 cmp #0 beq JoypadDown ; Value saturated. dec $21 dec $21
JoypadDown: lda JOY1H and #$04 cmp #$04 bne JoypadLeft ; Button not pressed. lda $21 cmp #(224 - 16) beq JoypadLeft ; Value saturated. inc $21 inc $21
JoypadLeft: lda JOY1H and #$02 ; Left cmp #$02 bne JoypadRight ; Button not pressed. lda $20 cmp #0 beq JoypadRight ; Value saturated. dec $20 dec $20
JoypadRight: lda JOY1H and #$01 cmp #$01 ; Right bne JoypadB ; Button not pressed. lda $20 cmp #(256 - 16) beq JoypadB ; Value saturated. inc $20 inc $20
JoypadB: lda JOY1H and #$80 ; B cmp #$80 bne JoypadA ; Button not pressed. lda $22 cmp #0 beq JoypadA ; Value saturated. dec $22
JoypadA: lda JOY1L and #$80 ; A cmp #$80 bne JoypadY ; Button not pressed. lda $22 cmp #31 beq JoypadY ; Value saturated. inc $22
JoypadY: lda JOY1H and #$40 ; Y cmp #$40 bne JoypadX ; Button not pressed. lda $23 cmp #0 beq JoypadX ; Value saturated. dec $23
JoypadX: lda JOY1L and #$40 ; X cmp #$40 bne JoypadL ; Button not pressed. lda $23 cmp #31 beq JoypadL ; Value saturated. inc $23
JoypadL: lda JOY1L and #$20 ; L cmp #$20 bne JoypadR ; Button not pressed. lda $24 cmp #0 beq JoypadR ; Value saturated. dec $24
JoypadR: lda JOY1L and #$10 ; R cmp #$10 bne JoypadDone ; Button not pressed. lda $24 cmp #31 beq JoypadDone ; Value saturated. inc $24
; TODO(mcmillen): have Start and Select do something too.
JoypadDone: rts
JoypadDebug: ; Load joypad registers into RAM for easier inspection. lda JOY1L sta $10 lda JOY1H sta $11 lda JOY2L sta $12 lda JOY2H sta $13 rts
SetBackgroundColor: ; $22 $23 $24 are (R, G, B), each ranging from [0-31]. ; The palette color format is 15-bit: [0bbbbbgg][gggrrrrr] ; Set the background color. ; Entry 0 corresponds to the SNES background color. stz CGADDR
; Compute and the low-order byte and store it in CGDATA. lda $23 ; Green. .rept 5 asl .endr ora $22 ; Red. sta CGDATA
; Compute the high-order byte and store it in CGDATA. lda $24 ; Blue. .rept 2 asl .endr sta $00 lda $23 ; Green. .rept 3 lsr .endr ora $00 sta CGDATA rts
UpdateGraphics: ; Copy player coords into sprite table. lda $0020 sta $0100 lda $0021 sta $0101 ; Choose which sprite based on frame count. lda $14 and #%00000100 lsr sta $0102 ; Set priority bits so that the sprite is drawn in front. lda #%00110000 sta $0103 ; Clear x-MSB so that the sprite is displayed. lda $0300 and #%11111110 sta $0300
; Make the background scroll. Horizontal over time; vertical depending on ; player's y-coordinate. lda $14 sta BG3HOFS lda $15 sta BG3HOFS lda $21 .rept 3 lsr .endr sta BG3VOFS stz BG3VOFS
rts
DMASpriteTables: rep #%00010000 ; 16-bit X/Y. sep #%00100000 ; 8-bit A. ; Store at the base OAM address. ldx #$0000 stx OAMADDR ; Default DMA control; destination $2104 (OAM data register). stz DMA0CTRL lda #$04 sta DMA0DST ; Our sprites start at $0100 in bank 0 and are #$220 bytes long. ldx #$0100 stx DMA0SRC stz DMA0SRCBANK ldx #$0220 stx DMA0SIZE ; Kick off the DMA transfer. lda #%00000001 sta DMAENABLE rts
FillScratch: lda #$42 ; ASCII "B" ldx #0- sta $00, X inx cpx #$10 bne - rts
.ENDS
.BANK 1 SLOT 0.ORG 0.SECTION "SpriteData".INCLUDE "sprites.asm".ENDS
.BANK 2 SLOT 0.ORG 0.SECTION "TileData".INCLUDE "tiles.asm".ENDS
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