mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-11-23 06:32:11 +00:00
147 lines
2.2 KiB
NASM
147 lines
2.2 KiB
NASM
|
|
include "nesdefs.asm"
|
|
|
|
;;;;; VARIABLES
|
|
|
|
seg.u RAM
|
|
org $0
|
|
|
|
ScrollPos byte ; used during NMI
|
|
Rand byte
|
|
Temp1 byte
|
|
|
|
SpriteBuf equ $200
|
|
|
|
;;;;; NES CARTRIDGE HEADER
|
|
|
|
NES_HEADER 0,2,1,0 ; mapper 0, 2 PRGs, 1 CHR, horiz. mirror
|
|
|
|
;;;;; START OF CODE
|
|
|
|
Start:
|
|
NES_INIT ; set up stack pointer, turn off PPU
|
|
jsr WaitSync
|
|
jsr WaitSync
|
|
jsr ClearRAM
|
|
jsr WaitSync ;wait for VSYNC
|
|
jsr SetPalette ;set colors
|
|
jsr FillVRAM ;set PPU RAM
|
|
jsr WaitSync ;wait for VSYNC (and PPU warmup)
|
|
jsr InitSprites
|
|
lda #0
|
|
sta PPU_ADDR
|
|
sta PPU_ADDR ;PPU addr = 0
|
|
sta PPU_SCROLL
|
|
sta PPU_SCROLL ;scroll = 0
|
|
lda #CTRL_NMI
|
|
sta PPU_CTRL ; enable NMI
|
|
lda #MASK_BG|MASK_SPR
|
|
sta PPU_MASK ; enable rendering
|
|
.endless
|
|
jmp .endless ;endless loop
|
|
|
|
; fill video RAM
|
|
FillVRAM: subroutine
|
|
txa
|
|
ldy #$20
|
|
sty PPU_ADDR
|
|
sta PPU_ADDR
|
|
ldy #$10
|
|
.loop:
|
|
stx PPU_DATA
|
|
inx
|
|
bne .loop
|
|
dey
|
|
bne .loop
|
|
rts
|
|
|
|
;
|
|
InitSprites: subroutine
|
|
lda #1
|
|
ldx #0
|
|
.loop
|
|
sta SpriteBuf,x
|
|
jsr NextRandom
|
|
inx
|
|
bne .loop
|
|
rts
|
|
|
|
;
|
|
MoveSprites: subroutine
|
|
lda #1
|
|
ldx #0
|
|
.loop
|
|
sta Temp1
|
|
and #3
|
|
clc
|
|
adc SpriteBuf,x
|
|
sta SpriteBuf,x
|
|
lda Temp1
|
|
jsr NextRandom
|
|
inx
|
|
bne .loop
|
|
rts
|
|
|
|
; set palette colors
|
|
|
|
SetPalette: subroutine
|
|
ldy #$00
|
|
lda #$3f
|
|
sta PPU_ADDR
|
|
sty PPU_ADDR
|
|
ldx #32
|
|
.loop:
|
|
lda Palette,y
|
|
sta PPU_DATA
|
|
iny
|
|
dex
|
|
bne .loop
|
|
rts
|
|
|
|
|
|
;;;;; COMMON SUBROUTINES
|
|
|
|
include "nesppu.asm"
|
|
|
|
;;;;; INTERRUPT HANDLERS
|
|
|
|
NMIHandler:
|
|
SAVE_REGS
|
|
; load sprites
|
|
lda #$02
|
|
sta PPU_OAM_DMA
|
|
; update scroll position (must be done after VRAM updates)
|
|
inc ScrollPos
|
|
lda ScrollPos
|
|
sta PPU_SCROLL
|
|
lda #0
|
|
sta PPU_SCROLL
|
|
; move sprites
|
|
jsr MoveSprites
|
|
; reload registers
|
|
RESTORE_REGS
|
|
rti
|
|
|
|
;;;;; CONSTANT DATA
|
|
|
|
align $100
|
|
Palette:
|
|
hex 1f ;background
|
|
hex 09090000 ;bg0
|
|
hex 09090c00 ;bg1
|
|
hex 09091c00 ;bg2
|
|
hex 09092c00 ;bg3
|
|
hex 14243400 ;sp0
|
|
hex 15253500 ;sp1
|
|
hex 16263600 ;sp2
|
|
hex 17273700 ;sp3
|
|
|
|
;;;;; CPU VECTORS
|
|
|
|
NES_VECTORS
|
|
|
|
;;;;; TILE SETS
|
|
|
|
org $10000
|
|
incbin "jroatch.chr"
|