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8bitworkshop/presets/nes-conio/ex1.asm

167 lines
3.1 KiB
NASM

;;;;; CONSTANTS
PPU_CTRL equ $2000
PPU_MASK equ $2001
PPU_STATUS equ $2002
OAM_ADDR equ $2003
OAM_DATA equ $2004
PPU_SCROLL equ $2005
PPU_ADDR equ $2006
PPU_DATA equ $2007
PPU_OAM_DMA equ $4014
DMC_FREQ equ $4010
;;;;; ZERO-PAGE VARIABLES
seg.u ZPVars
org $0
ScrollPos byte ; used during NMI
;;;;; CARTRIDGE FILE HEADER
processor 6502
seg Header
org $7FF0
NES_MAPPER equ 0 ;mapper number
NES_PRG_BANKS equ 2 ;number of 16K PRG banks, change to 2 for NROM256
NES_CHR_BANKS equ 1 ;number of 8K CHR banks (0 = RAM)
NES_MIRRORING equ 1 ;0 horizontal, 1 vertical, 8 four screen
.byte $4e,$45,$53,$1a ; header
.byte NES_PRG_BANKS
.byte NES_CHR_BANKS
.byte NES_MIRRORING|(NES_MAPPER<<4)
.byte NES_MAPPER&$f0
;;;;; CODE
seg Code
org $8000
start:
_exit:
sei ;disable IRQs
cld ;decimal mode not supported
ldx #$ff
txs ;set up stack pointer
inx ;increment X to 0
stx PPU_MASK ;disable rendering
stx DMC_FREQ ;disable DMC interrupts
stx PPU_CTRL ;disable NMI interrupts
jsr WaitSyncSafe ;wait for VSYNC
; clear RAM -- not a subroutine because we clear the stack too
lda #0
tax
.clearRAM
sta $0,x
sta $100,x
; skip $200-$2FF, used for OAM display list
sta $300,x
sta $400,x
sta $500,x
sta $600,x
sta $700,x
inx
bne .clearRAM
; end of clear RAM routine
jsr SetPalette ;set colors
jsr FillVRAM ;set PPU RAM
jsr WaitSync ;wait for VSYNC (and PPU warmup)
lda #0
sta PPU_ADDR
sta PPU_ADDR ;PPU addr = 0
sta PPU_SCROLL
sta PPU_SCROLL ;scroll = 0
lda #$90
sta PPU_CTRL ;enable NMI
lda #$1e
sta PPU_MASK ;enable rendering
.endless
jmp .endless ;endless loop
;;;;; SUBROUTINES
; set palette colors
SetPalette: subroutine
ldy #$0
lda #$3f
sta PPU_ADDR
sty PPU_ADDR
ldx #4
.loop:
lda Palette,y
sta PPU_DATA
iny
dex
bne .loop
rts
; fill video RAM
FillVRAM: subroutine
txa
ldy #$20
sty PPU_ADDR
sta PPU_ADDR
ldy #$10
.loop:
sta PPU_DATA
adc #1
inx
bne .loop
dey
bne .loop
rts
; wait for VSYNC to start
WaitSyncSafe: subroutine
bit PPU_STATUS
WaitSync:
bit PPU_STATUS
bpl WaitSync
rts
;;;;; INTERRUPT HANDLERS
nmi:
irq:
; save registers
pha ; save A
; update scroll position
inc ScrollPos
lda ScrollPos
sta PPU_SCROLL
sta PPU_SCROLL
; reload registers
pla ; reload A
rti
;;;;; CONSTANT DATA
Palette:
hex 1f001020 ; black, gray, lt gray, white
TextString:
byte "HELLO WORLD!"
byte 0
;;;;; CPU VECTORS
org $fffa
.word nmi ;$fffa vblank nmi
.word start ;$fffc reset
.word irq ;$fffe irq / brk
;;;;; TILE SETS
REPEAT 64
hex 003c6666766e663c007e181818381818
hex 007e60300c06663c003c66061c06663c
hex 0006067f661e0e06003c6606067c607e
hex 003c66667c60663c00181818180c667e
hex 003c66663c66663c003c66063e66663c
hex 01010101010101010000000000000000
hex ff000000000000000000000000000000
hex 01020408102040800000000000000000
REPEND