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https://github.com/sehugg/8bitworkshop.git
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65 lines
1.4 KiB
NASM
65 lines
1.4 KiB
NASM
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processor 6502
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;;;;; CONSTANTS
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PPU_CTRL equ $2000
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PPU_MASK equ $2001
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PPU_STATUS equ $2002
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OAM_ADDR equ $2003
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OAM_DATA equ $2004
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PPU_SCROLL equ $2005
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PPU_ADDR equ $2006
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PPU_DATA equ $2007
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PPU_OAM_DMA equ $4014
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DMC_FREQ equ $4010
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APU_STATUS equ $4015
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;;;;; CARTRIDGE FILE HEADER
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NES_MIRR_HORIZ equ 0
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NES_MIRR_VERT equ 1
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NES_MIRR_QUAD equ 8
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MAC NES_HEADER
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seg Header
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org $7ff0
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.NES_MAPPER SET {1} ;mapper number
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.NES_PRG_BANKS SET {2} ;number of 16K PRG banks, change to 2 for NROM256
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.NES_CHR_BANKS SET {3} ;number of 8K CHR banks (0 = RAM)
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.NES_MIRRORING SET {4} ;0 horizontal, 1 vertical, 8 four screen
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byte $4e,$45,$53,$1a ; header
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byte .NES_PRG_BANKS
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byte .NES_CHR_BANKS
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byte .NES_MIRRORING|(.NES_MAPPER<<4)
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byte .NES_MAPPER&$f0
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byte 0,0,0,0,0,0,0,0 ; reserved, set to zero
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seg Code
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org $8000
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ENDM
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;;;;; NES_INIT SETUP MACRO (place at start)
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MAC NES_INIT
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sei ;disable IRQs
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cld ;decimal mode not supported
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ldx #$ff
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txs ;set up stack pointer
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inx ;increment X to 0
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stx PPU_MASK ;disable rendering
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stx DMC_FREQ ;disable DMC interrupts
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stx PPU_CTRL ;disable NMI interrupts
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bit PPU_STATUS ;clear VBL flag
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ENDM
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;;;;; NES_VECTORS - CPU vectors at end of address space
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MAC NES_VECTORS
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seg Vectors
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org $fffa
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.word NMIHandler ;$fffa vblank nmi
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.word Start ;$fffc reset
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.word NMIHandler ;$fffe irq / brk (not used)
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ENDM
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