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|
.segment "VECTORS"
.addr nmi, reset, irq
.segment "CODE"
;; Pretty standard reset function, nothing crazy.
.proc reset
sei
cld
ldx #$40
stx APU::FRAME_COUNTER
ldx #$FF
txs
inx
stx PPU::CONTROL
stx PPU::MASK
stx APU::DMC
@vblankwait1:
bit PPU::STATUS
bpl @vblankwait1
ldx #0
lda #0
@ram_reset_loop:
sta $000, x
sta $100, x
sta $300, x
sta $400, x
sta $500, x
sta $600, x
sta $700, x
inx
bne @ram_reset_loop
lda #$EF
@sprite_reset_loop:
sta $200, x
inx
bne @sprite_reset_loop
lda #$00
sta OAM::ADDRESS
lda #$02
sta OAM::DMA
@vblankwait2:
bit PPU::STATUS
bpl @vblankwait2
lda #$3F
sta PPU::ADDRESS
lda #$00
sta PPU::ADDRESS
lda #$0F
ldx #$20
@palettes_reset_loop:
sta PPU::DATA
dex
bne @palettes_reset_loop
jmp main
.endproc
.proc nmi
;; Should we skip it?
bit Globals::zp_flags
bpl @end
;; Save registers.
pha
txa
pha
tya
pha
;; Sprite DMA.
lda #$00
sta OAM::ADDRESS
lda #$02
sta OAM::DMA
;; TODO: some actions here will depend on the status of the game...
;; Decrease title timer.
lda Title::zp_title_timer
beq :+
dec Title::zp_title_timer
:
;; Should we update PPU registers?
bit Globals::zp_flags
bvc @scroll
;; Zero out the `ppu` flag.
lda #%10111111
and Globals::zp_flags
sta Globals::zp_flags
bit PPU::STATUS
;; Update the PPU control/mask registers with shadowed values.
lda PPU::zp_mask
sta PPU::MASK
lda PPU::zp_control
sta PPU::CONTROL
@scroll:
;; Always reset the scroll just in case.
bit PPU::STATUS
lda #$00
sta PPU::SCROLL
sta PPU::SCROLL
;; Unblock the main code.
lda #%01111111
and Globals::zp_flags
sta Globals::zp_flags
;; Restore registers.
pla
tay
pla
tax
pla
@end:
rti
.endproc
;; Unused.
.proc irq
rti
.endproc
|
