mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-11-28 23:49:20 +00:00
198 lines
4.2 KiB
NASM
198 lines
4.2 KiB
NASM
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include "nesdefs.asm"
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;;;;; ZERO-PAGE VARIABLES
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seg.u ZEROPAGE
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org $0
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;;;;; OTHER VARIABLES
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seg.u RAM
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org $300
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LineXLo ds 224
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LineXHi ds 224
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;;;;; NES CARTRIDGE HEADER
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NES_HEADER 0,2,1,0 ; mapper 0, 2 PRGs, 1 CHR, horiz. mirror
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;;;;; START OF CODE
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Start:
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NES_INIT ; set up stack pointer, turn off PPU
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jsr WaitSync ; wait for VSYNC
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jsr ClearRAM ; clear RAM
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jsr WaitSync ; wait for VSYNC (and PPU warmup)
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jsr SetPalette ; set palette colors
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jsr FillVRAM ; set PPU video RAM
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lda #0
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sta PPU_ADDR
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sta PPU_ADDR ; PPU addr = $0000
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sta PPU_SCROLL
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sta PPU_SCROLL ; scroll = $0000
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lda #CTRL_NMI
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sta PPU_CTRL ; enable NMI
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lda #MASK_BG|MASK_SPR
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sta PPU_MASK ; enable rendering
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.endless
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jmp .endless ; endless loop
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; fill video RAM
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FillVRAM: subroutine
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txa
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ldy #$20
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sty PPU_ADDR
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sta PPU_ADDR
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ldy #$10
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.loop:
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sta PPU_DATA
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adc #7
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inx
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bne .loop
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dey
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bne .loop
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rts
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; set palette colors
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SetPalette: subroutine
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ldy #$00
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lda #$3f
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sta PPU_ADDR
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sty PPU_ADDR
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ldx #32
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.loop:
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lda Palette,y
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sta PPU_DATA
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iny
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dex
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bne .loop
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rts
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; set sprite 0
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SetSprite0: subroutine
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sta $200 ;y
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lda #1 ;code
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sta $201
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lda #0 ;flags
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sta $202
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lda #8 ;xpos
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sta $203
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rts
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;;;;; COMMON SUBROUTINES
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include "nesppu.asm"
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;;;;; INTERRUPT HANDLERS
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NMIHandler: subroutine
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SAVE_REGS
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lda #112
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jsr SetSprite0
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; load sprites
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lda #$02
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sta PPU_OAM_DMA
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; wait for sprite 0
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.wait0 bit PPU_STATUS
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bvs .wait0
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.wait1 bit PPU_STATUS
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bvc .wait1
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; alter horiz. scroll position for each scanline
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ldy #0
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.loop
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tya
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sec
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adc LineXLo,y
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sta LineXLo,y
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lda LineXHi,y
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adc #0
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sta LineXHi,y
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sta PPU_SCROLL ; horiz byte
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lda #0
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sta PPU_SCROLL ; vert byte
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REPEAT 25
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bit $0000
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REPEND
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iny
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cpy #224
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bne .loop
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RESTORE_REGS
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rti
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;;;;; CONSTANT DATA
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align $100
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Palette:
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hex 1f ;background
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hex 09092c00 ;bg0
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hex 09091900 ;bg1
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hex 09091500 ;bg2
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hex 09092500 ;bg3
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;;;;; CPU VECTORS
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NES_VECTORS
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;;;;; TILE SETS
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org $10000
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; background (tile) pattern table
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REPEAT 10
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;;{w:8,h:8,bpp:1,count:48,brev:1,np:2,pofs:8,remap:[0,1,2,4,5,6,7,8,9,10,11,12]};;
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hex 00000000000000000000000000000000
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hex 7e42424646467e007e42424646467e00
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hex 08080818181818000808081818181800
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hex 3e22023e30303e003e22023e30303e00
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hex 3c24041e06263e003c24041e06263e00
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hex 4444447e0c0c0c004444447e0c0c0c00
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hex 3c20203e06263e003c20203e06263e00
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hex 3e22203e26263e003e22203e26263e00
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hex 3e020206060606003e02020606060600
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hex 3c24247e46467e003c24247e46467e00
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hex 3e22223e060606003e22223e06060600
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hex 3c24247e626262003c24247e62626200
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hex 7c44447e62627e007c44447e62627e00
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hex 7e42406060627e007e42406060627e00
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hex 7e42426262627e007e42426262627e00
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hex 7c40407c60607c007c40407c60607c00
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hex 3c20203c303030003c20203c30303000
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hex 7e42406e62627e007e42406e62627e00
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hex 4242427e626262004242427e62626200
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hex 10101018181818001010101818181800
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hex 0404040606467e000404040606467e00
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hex 4444447e626262004444447e62626200
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hex 2020203030303e002020203030303e00
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hex fe9292d2d2d2d200fe9292d2d2d2d200
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hex 7e424262626262007e42426262626200
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hex 7e46464242427e007e46464242427e00
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hex 7e42427e606060007e42427e60606000
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hex 7e424242424e7e007e424242424e7e00
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hex 7c44447e626262007c44447e62626200
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hex 7e42407e06467e007e42407e06467e00
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hex 7e101018181818007e10101818181800
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hex 4242426262627e004242426262627e00
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hex 646464642c2c3c00646464642c2c3c00
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hex 4949494969697f004949494969697f00
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hex 4242423c626262004242423c62626200
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hex 4242427e181818004242427e18181800
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hex 7e42027e60627e007e42027e60427e00
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hex 10101818180018001010181818001800
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hex 187e407e067e1800187e407e067e1800
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hex 00180018180000000018001818000000
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hex 00003c3c0000000000003c3c00000000
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hex 00000018180000000000001818000000
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hex 18180810000000001818081000000000
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hex 00000018180810000000001818081000
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hex 7c7c7c7c7c7c7c007c7c7c7c7c7c7c00
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hex 0000000000007c000000000000007c00
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hex 00000000000000000000000000000000
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hex 00000000000000000000000000000000
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;;
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REPEND
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REPEAT 32
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hex 00000000000000000000000000000000
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REPEND
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