mirror of
https://github.com/sehugg/8bitworkshop.git
synced 2024-11-12 10:07:00 +00:00
152 lines
2.5 KiB
Plaintext
152 lines
2.5 KiB
Plaintext
|
|
include "nesdefs.dasm"
|
|
|
|
;;;;; ZERO-PAGE VARIABLES
|
|
|
|
seg.u ZEROPAGE
|
|
org $0
|
|
|
|
ScrollX ds 1
|
|
ScrollY ds 1
|
|
Temp ds 1
|
|
|
|
;;;;; OTHER VARIABLES
|
|
|
|
seg.u RAM
|
|
org $300
|
|
|
|
;;;;; 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 ; wait for VSYNC
|
|
jsr ClearRAM ; clear RAM
|
|
jsr WaitSync ; wait for VSYNC (and PPU warmup)
|
|
|
|
jsr SetPalette ; set palette colors
|
|
jsr FillVRAM ; set PPU video RAM
|
|
lda #0
|
|
sta PPU_ADDR
|
|
sta PPU_ADDR ; PPU addr = $0000
|
|
sta PPU_SCROLL
|
|
sta PPU_SCROLL ; scroll = $0000
|
|
lda #MASK_BG|MASK_SPR
|
|
sta PPU_MASK ; enable rendering
|
|
lda #CTRL_NMI
|
|
sta PPU_CTRL ; enable NMI
|
|
.endless
|
|
jmp .endless ; endless loop
|
|
|
|
; fill video RAM
|
|
FillVRAM: subroutine
|
|
PPU_SETADDR $2000
|
|
ldy #$10
|
|
.loop:
|
|
sta PPU_DATA
|
|
adc #7
|
|
inx
|
|
bne .loop
|
|
dey
|
|
bne .loop
|
|
rts
|
|
|
|
; set palette colors
|
|
SetPalette: subroutine
|
|
PPU_SETADDR $3f00
|
|
ldx #32
|
|
.loop:
|
|
lda Palette,y
|
|
sta PPU_DATA
|
|
iny
|
|
dex
|
|
bne .loop
|
|
rts
|
|
|
|
; set sprite 0
|
|
SetSprite0: subroutine
|
|
sta $200 ;y
|
|
lda #$01 ;code
|
|
sta $201
|
|
lda #$20 ;flags
|
|
sta $202
|
|
lda #$fe ;xpos
|
|
sta $203
|
|
rts
|
|
|
|
;;;;; COMMON SUBROUTINES
|
|
|
|
include "nesppu.dasm"
|
|
|
|
;;;;; INTERRUPT HANDLERS
|
|
|
|
NMIHandler: subroutine
|
|
SAVE_REGS
|
|
lda #0
|
|
sta PPU_SCROLL
|
|
sta PPU_SCROLL
|
|
lda #111
|
|
jsr SetSprite0
|
|
; load sprites
|
|
lda #$02
|
|
sta PPU_OAM_DMA
|
|
; set XY scroll
|
|
; compute second PPU_ADDR write
|
|
lda ScrollX
|
|
tax ; ScrollX -> X
|
|
lsr
|
|
lsr
|
|
lsr
|
|
sta Temp
|
|
lda ScrollY
|
|
tay ; ScrollY -> Y
|
|
and #$38
|
|
asl
|
|
asl
|
|
ora Temp ; (ScrollX >> 3) | ((ScrollY & 0x38) << 2)
|
|
pha ; push onto stack
|
|
; wait for sprite 0
|
|
.wait0 bit PPU_STATUS
|
|
bvs .wait0
|
|
.wait1 bit PPU_STATUS
|
|
bvc .wait1
|
|
; set PPU_ADDR.1
|
|
lda #0
|
|
sta PPU_ADDR
|
|
; set PPU_SCROLL.1
|
|
sty PPU_SCROLL
|
|
; set PPU_SCROLL.2
|
|
stx PPU_SCROLL
|
|
; set PPU_ADDR.2
|
|
pla
|
|
sta PPU_ADDR
|
|
; modify scroll positions
|
|
inc ScrollX
|
|
inc ScrollY
|
|
; restore registers and return
|
|
RESTORE_REGS
|
|
rti
|
|
|
|
;;;;; CONSTANT DATA
|
|
|
|
align $100
|
|
Palette:
|
|
hex 1f ;background
|
|
hex 09092c00 ;bg0
|
|
hex 09091900 ;bg1
|
|
hex 09091500 ;bg2
|
|
hex 09092500 ;bg3
|
|
|
|
;;;;; CPU VECTORS
|
|
|
|
NES_VECTORS
|
|
|
|
;;;;; TILE SETS
|
|
|
|
org $10000
|
|
incbin "jroatch.chr"
|
|
incbin "jroatch.chr"
|