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83 lines
1.9 KiB
NASM
83 lines
1.9 KiB
NASM
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processor 6502
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;;;;; CONSTANTS
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PPU_CTRL = $2000
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PPU_MASK = $2001
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PPU_STATUS = $2002
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OAM_ADDR = $2003
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OAM_DATA = $2004
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PPU_SCROLL = $2005
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PPU_ADDR = $2006
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PPU_DATA = $2007
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PPU_OAM_DMA = $4014
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DMC_FREQ = $4010
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APU_STATUS = $4015
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APU_NOISE_VOL = $400C
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APU_NOISE_FREQ = $400E
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APU_NOISE_TIMER = $400F
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APU_DMC_CTRL = $4010
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APU_CHAN_CTRL = $4015
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APU_FRAME = $4017
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; NOTE: I've put this outside of the PPU & APU, because it is a feature
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; of the APU that is primarily of use to the PPU.
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OAM_DMA = $4014
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; OAM local RAM copy goes from $0200-$02FF:
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OAM_RAM = $0200
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;;;;; CARTRIDGE FILE HEADER
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NES_MIRR_HORIZ = 0
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NES_MIRR_VERT = 1
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NES_MIRR_QUAD = 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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bit APU_CHAN_CTRL ;ack DMC IRQ bit 7
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lda #$40
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sta APU_FRAME ;disable APU Frame IRQ
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lda #$0F
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sta APU_CHAN_CTRL ;disable DMC, enable/init other channels.
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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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