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.INCLUDE "header.asm".INCLUDE "init.asm".INCLUDE "registers.asm"
; Memory layout:; 0000-000F: scratch space for functions.; 0010-0011: controller state of joypad #1.; 0012-0013: controller state of joypad #2.; 0014-0016: 24-bit counter of vblanks.; 0017-0019: RGB color values to use for background color, from [0-31].; 001A-001B: 16-bit pointer to next random byte.; [gap]; 0020-0021: (x, y) coordinates of player.; 0022: shot cooldown timer.; 0023-0024: index of next shot.; [gap]; 0030-003F: {enable, x, y, unused} per shot (max 4 shots).;; 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).define joy1 $10.define joy2 $12.define vBlankCounter $14.define backgroundRed $17.define backgroundGreen $18.define backgroundBlue $19.define randomBytePtr $1A.define playerX $20.define playerY $21.define shotCooldown $22.define nextShotPtr $23.define shotArray $30.define shotArrayLength 4
; TODO(mcmillen): verify that we can relocate these without messing things up..define spriteTableStart $100.define spriteTable1Size $200.define spriteTable2Start $300 ; TODO(mcmillen): use this..define spriteTableSize $220
; Stores result to A.; Assumes 16-bit X & 8-bit A.; Modifies X.; Updates randomBytePtr..MACRO GetRandomByte ldx randomBytePtr lda $028000, X ; $028000: beginning of ROM bank 2. inx cpx #$8000 ; This is the size of the entire ROM bank. bne + ldx #0+ stx randomBytePtr.ENDM
.BANK 0 SLOT 0.ORG 0.SECTION "MainCode"
Start: InitializeSNES
; By default we assume 16-bit X/Y and 8-bit A. ; If any code wants to change this, it's expected to do so itself, ; and to change them back to the defaults before returning. rep #%00010000 ; 16-bit X/Y. sep #%00100000 ; 8-bit A/B.
; Store zeroes to the controller status registers. ; TODO(mcmillen): is this needed? I think the system will overwrite these ; automatically. stz JOY1H stz JOY1L
jsr LoadPaletteAndTileData jsr InitializeSpriteTables jsr InitializeWorld
; 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
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
; 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. 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. Equal to the size of sprites32.pic. ldx #2048 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. Equal to the size of tiles.pic. ldx #512 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. ldy #0- GetRandomByte sta $00 ldx #$0000 ; This is a blank tile. ; 1 in 8 chance that we choose a non-blank tile. and #%00000111 cmp #%00000111 bne + ldx #$0002 lda $00 and #%10000000 cmp #%10000000 bne + ldx #$8002 ; Flip vertically.+ stx VMDATA iny ; The tile map is 32x32 (1024 entries). cpy #1024 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 #%00100000 ; 16-bit A.
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 spriteTableStart, X .rept 4 inx .endr cpx #spriteTable1Size 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 spriteTableStart, X inx inx cpx #spriteTableSize bne -
sep #%00100000 ; 8-bit A. rts
InitializeWorld: ; Start the background color as a dark blue. lda #4 sta backgroundBlue
; Player's initial starting location. lda #(256 / 4) sta playerX lda #((224 - 32) / 2) sta playerY
; Next shot pointer starts at the beginning. ldx #shotArray stx nextShotPtr rts
MainLoop: wai ; Wait for interrupt. jsr JoypadDebug jsr JoypadHandler jsr UpdateWorld jsr SetBackgroundColor jmp MainLoop
JoypadDebug: ; Load joypad registers into RAM for easier inspection. ldx JOY1L stx joy1 ldx JOY2L stx joy2 rts
JoypadHandler:; TODO(mcmillen): handle joystick using 16-bit loads?JoypadUp: lda JOY1H and #$08 ; Up cmp #$08 bne JoypadDown ; Button not pressed. lda playerY cmp #0 beq JoypadDown ; Value saturated. dec playerY dec playerY
JoypadDown: lda JOY1H and #$04 cmp #$04 bne JoypadLeft ; Button not pressed. lda playerY cmp #(224 - 32) beq JoypadLeft ; Value saturated. inc playerY inc playerY
JoypadLeft: lda JOY1H and #$02 ; Left cmp #$02 bne JoypadRight ; Button not pressed. lda playerX cmp #0 beq JoypadRight ; Value saturated. dec playerX dec playerX
JoypadRight: lda JOY1H and #$01 cmp #$01 ; Right bne JoypadStart ; Button not pressed. lda playerX cmp #(256 - 32) beq JoypadStart ; Value saturated. inc playerX inc playerX
JoypadStart: lda JOY1H and #$10 ; Start cmp #$10 bne JoypadSelect ; Button not pressed. lda backgroundRed cmp #0 beq JoypadSelect ; Value saturated. dec backgroundRed
JoypadSelect: lda JOY1H and #$20 ; Select cmp #$20 bne JoypadY ; Button not pressed. lda backgroundRed cmp #31 beq JoypadY ; Value saturated. inc backgroundRed
JoypadY: lda JOY1H and #$40 ; Y cmp #$40 bne JoypadX ; Button not pressed. lda backgroundGreen cmp #0 beq JoypadX ; Value saturated. dec backgroundGreen
JoypadX: lda JOY1L and #$40 ; X cmp #$40 bne JoypadL ; Button not pressed. lda backgroundGreen cmp #31 beq JoypadL ; Value saturated. inc backgroundGreen
JoypadL: lda JOY1L and #$20 ; L cmp #$20 bne JoypadR ; Button not pressed. lda backgroundBlue cmp #0 beq JoypadR ; Value saturated. dec backgroundBlue
JoypadR: lda JOY1L and #$10 ; R cmp #$10 bne JoypadB ; Button not pressed. lda backgroundBlue cmp #31 beq JoypadB ; Value saturated. inc backgroundBlue
JoypadB: lda JOY1H and #$80 ; B cmp #$80 bne JoypadDone jsr MaybeShoot
JoypadDone: rts
MaybeShoot: ; If the cooldown timer is non-zero, don't shoot. lda shotCooldown cmp #0 bne ++ ldx nextShotPtr stx $0060 ; Enable shot; set its position to player position. lda #1 sta 0, X lda playerX sta 1, X lda playerY sta 2, X ; Update nextShotPtr. .rept 4 inx .endr cpx #(shotArray + shotArrayLength * 4) bne + ldx #shotArray+ stx nextShotPtr
; Set cooldown timer. lda #16 sta shotCooldown++ rts
UpdateWorld: ; TODO(mcmillen): separate out "update world" from "update sprite table".
; Update shot cooldown. lda shotCooldown cmp #0 beq + dea sta shotCooldown+
; Copy player coords into sprite table. lda playerX sta $0100 lda playerY sta $0101 ; Set the sprite. lda #0 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 spriteTable2Start and #%11111110 ora #%00000010 ; ... and make it the large size. (32x32) sta spriteTable2Start
; Move shot coords and copy into sprite table. ldx #0 ; To modify sprite table 2 - one bit set for each active shot. ; These bits will be *removed* from the sprite table entry. stz $00UpdateShot: lsr $00 lsr $00 lda shotArray, X cmp #1 bne DisableShot ; Add to the x-coordinate. If the carry bit is set, we went off the edge ; of the screen, so disable the shot. lda shotArray + 1, X clc adc #6 ; x velocity bcs DisableShot sta shotArray + 1, X ; Store new x-coord.
; Set up shot in sprite table. lda shotArray + 1, X ; x ; TODO(mcmillen): document that shots start at $110? sta $0110, X lda shotArray + 2, X ; y sta $0111, X lda #8 ; which sprite? sta $0112, X
lda $00 ora #%01000000 sta $00 jmp ShotDone
DisableShot: ; Disable it by setting x-position to 1 and setting the high x-bit. lda #1 sta $110, X
ShotDone: ; TODO(mcmillen): in places where we .rept inx (etc), is it faster to use ; actual addition? .rept 4 inx .endr cpx #16 bne UpdateShot ; Set the enable/disable (and size) bits of the shot sprites. lda #$ff eor $00 sta $0301
; Make the background scroll. Horizontal over time; vertical depending on ; player's y-coordinate. lda vBlankCounter sta BG3HOFS lda vBlankCounter + 1 sta BG3HOFS lda playerY .rept 3 lsr .endr sta BG3VOFS stz BG3VOFS
rts
SetBackgroundColor: ; The background-color bytes 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 backgroundGreen .rept 5 asl .endr ora backgroundRed sta CGDATA
; Compute the high-order byte and store it in CGDATA. lda backgroundBlue .rept 2 asl .endr sta $00 lda backgroundGreen .rept 3 lsr .endr ora $00 sta CGDATA rts
VBlankHandler: jsr VBlankCounter jsr DMASpriteTables rti
VBlankCounter: ; Increment a counter of how many VBlanks we've done. ; This is a 24-bit counter. At 60 vblanks/second, this will take ; 77 hours to wrap around; that's good enough for me :) inc vBlankCounter lda vBlankCounter cmp #$00 bne VBlankCounterDone inc vBlankCounter + 1 lda vBlankCounter + 1 cmp #$00 bne VBlankCounterDone inc vBlankCounter + 2VBlankCounterDone: rts
DMASpriteTables: ; 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 #spriteTableStart stx DMA0SRC stz DMA0SRCBANK ldx #spriteTableSize stx DMA0SIZE ; Kick off the DMA transfer. lda #%00000001 sta DMAENABLE rts
.ENDS
; Bank 1 is used for our graphics assets..BANK 1 SLOT 0.ORG 0.SECTION "GraphicsData"
SpriteData: .INCBIN "sprites32.pic"SpritePalette: .INCBIN "sprites32.clr"
TileData: .INCBIN "tiles.pic"TilePalette: .INCBIN "tiles.clr"
.ENDS
; Fill an entire bank with random numbers..SEED 1.BANK 2 SLOT 0.ORG 0.SECTION "RandomBytes".DBRND 32 * 1024, 0, 255.ENDS
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