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|
.segment "VECTORS"
.addr nmi, reset, irq
.segment "CODE"
;; Debug utilities.
.scope Debug
;; Counter for frame drops.
zp_frame_drops = $90
.endscope
;; Pretty standard reset function, nothing crazy.
.proc reset
;; Disable interrupts and decimal mode.
sei
cld
;; Disable APU frame counter.
ldx #$40
stx APU::FRAME_COUNTER
;; Setup the stack.
ldx #$FF
txs
;; Disable NMIs and the APU's DMC.
inx
stx PPU::CONTROL
stx PPU::MASK
stx APU::DMC
;; First PPU wait.
bit PPU::STATUS
@vblankwait1:
bit PPU::STATUS
bpl @vblankwait1
;; Initialize the counter for frame drops before any NMIs can come in.
.ifdef PARTIAL
lda #0
sta Debug::zp_frame_drops
.endif
;; Reset all sprites by simply moving the Y coordinate out of screen.
lda #$EF
ldx #0
@sprite_reset_loop:
sta $200, x
inx
inx
inx
inx
bne @sprite_reset_loop
;; DMA setup for sprite reset.
lda #$00
sta OAM::ADDRESS
lda #$02
sta OAM::DMA
;; Second PPU wait. After that the PPU is stable.
@vblankwait2:
bit PPU::STATUS
bpl @vblankwait2
;; NOTE: palettes are not initialized here as it's going to be one of the
;; first things done on `main` code.
jmp main
.endproc
.proc nmi
;; Should we skip it?
bit Globals::zp_flags
;; If we are on a dev environment, account for any frame drops.
.ifdef PARTIAL
bpl @account_for_frame_drop
.else
bpl @end
.endif
;; Save registers.
pha
txa
pha
tya
pha
;; Sprite DMA.
lda #$00
sta OAM::ADDRESS
lda #$02
sta OAM::DMA
;; Are we paused? If so skip timers, PAL handler and the likes.
lda #%00001000
and Globals::zp_flags
bne @ppu_registers
;; PAL-specific code
.ifdef PAL
jsr Driver::pal_handler
.endif
;; TODO: some actions here will depend on the status of the game...
lda Globals::zp_flags
and #%00000001
bne @ppu_registers
;; Increase the random seed.
inc Prng::zp_rand
;; Decrease title timer.
lda Title::zp_title_timer
beq @ppu_registers
dec Title::zp_title_timer
@ppu_registers:
;; 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
@account_for_frame_drop:
inc Debug::zp_frame_drops
rti
.endproc
;; Unused.
.proc irq
rti
.endproc
|
