mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-12-23 18:31:08 +00:00
100 lines
1.5 KiB
Plaintext
100 lines
1.5 KiB
Plaintext
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;#define LIBARGS ,
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;
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; iNES header
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;
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.segment "HEADER"
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INES_MAPPER = 0 ; 0 = NROM
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INES_MIRROR = 1 ; 0 = horizontal mirroring, 1 = vertical mirroring
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INES_SRAM = 0 ; 1 = battery backed SRAM at $6000-7FFF
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.byte 'N', 'E', 'S', $1A ; ID
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.byte $02 ; 16k PRG chunk count
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.byte $01 ; 8k CHR chunk count
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.byte INES_MIRROR | (INES_SRAM << 1) | ((INES_MAPPER & $f) << 4)
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.byte (INES_MAPPER & %11110000)
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.byte $0, $0, $0, $0, $0, $0, $0, $0 ; padding
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;;;;; START OF CODE
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.segment "CODE"
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Start:
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sei ; mask interrupts
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lda #0
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sta $2000 ; disable NMI
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sta $2001 ; disable rendering
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sta $4015 ; disable APU sound
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sta $4010 ; disable DMC IRQ
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lda #$40
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sta $4017 ; disable APU IRQ
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cld ; disable decimal mode
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ldx #$FF
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txs ; initialize stack
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; wait for first vblank
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bit $2002
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:
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bit $2002
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bpl :-
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; clear all RAM to 0
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lda #0
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ldx #0
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:
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sta $0000, X
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sta $0100, X
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sta $0200, X
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sta $0300, X
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sta $0400, X
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sta $0500, X
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sta $0600, X
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sta $0700, X
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inx
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bne :-
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; place all sprites offscreen at Y=255
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lda #255
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ldx #0
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:
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sta $200, X
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inx
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inx
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inx
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inx
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bne :-
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; wait for second vblank
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:
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bit $2002
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bpl :-
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; NES is initialized, ready to begin!
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; enable the NMI for graphical updates, and jump to our main program
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lda #%10001000
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sta $2000
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Endless:
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jmp Endless ; endless loop
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;;;;; INTERRUPT HANDLERS
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NMIHandler:
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rti
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;;;;; CPU VECTORS
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.segment "VECTORS"
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.word NMIHandler
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.word Start
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.word NMIHandler
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;
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; CHR ROM
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;
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.segment "CHARS"
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.incbin "jroatch.chr"
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;
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; .etc
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;
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.segment "STARTUP"
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.segment "SAMPLES"
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