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|
;; NOTE: automatically generated by the build system.
.include "../config/generated.s"
.segment "HEADER"
;; Bytes 0-3: NES\0 magic header.
.byte 'N', 'E', 'S', $1A
;; Standard 32KB + 8KB NROM cartridge.
.byte $02, $01
;; Horizontal mirroring, no battery.
.byte $00
;; We use the NES 2.0 header mainly to differentiate between NTSC vs PAL in
;; a way that emulators won't ignore it.
.byte $08
;; Blanked out stuff.
.res $04, $00
;; NTSC vs PAL
.ifdef PAL
.byte $01
.else
.byte $00
.endif
;; Blanked out stuff.
.res $03, $00
.segment "CODE"
.include "../include/apu.s"
.include "../include/oam.s"
.include "../include/ppu.s"
.include "../include/asm.s"
.include "../include/joypad.s"
.include "../include/globals.s"
.include "../include/debug.s"
.include "assets.s"
.include "background.s"
.include "prng.s"
.include "explosions.s"
.include "items.s"
.include "player.s"
.include "enemies.s"
.include "bullets.s"
.include "title.s"
.include "over.s"
.include "driver.s"
.include "interrupts.s"
;; Pretty standard reset function, nothing crazy.
.proc reset
;; Disable interrupts and decimal mode.
sei
cld
;; Disable APU frame counter.
ldx #$40
stx APU::m_frame_counter
;; Setup the stack.
ldx #$FF
txs
;; Disable NMIs and the APU's DMC.
inx
stx PPU::m_control
stx PPU::m_mask
stx APU::m_dmc
;; First PPU wait.
bit PPU::m_status
@vblankwait1:
bit PPU::m_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 OAM::m_sprites, x
inx
inx
inx
inx
bne @sprite_reset_loop
;; DMA setup for sprite reset.
lda #$00
sta OAM::m_address
lda #$02
sta OAM::m_dma
;; Second PPU wait. After that the PPU is stable.
@vblankwait2:
bit PPU::m_status
bpl @vblankwait2
;; NOTE: palettes are not initialized here as it's going to be one of the
;; first things done on `main` code.
__fallthrough__ main
.endproc
.proc main
;; TODO: high score initialization has to happen here.
@init:
;; Disable the PPU and zero out variables which shadow PPU registers.
lda #0
sta PPU::m_mask
sta PPU::zp_mask
sta PPU::zp_control
;; Initialize other global variables which the rest of the game assume to
;; have zero as their initial values. Note that it's important to have these
;; variables defined before
sta Globals::zp_flags
sta Globals::zp_multiplayer
sta Joypad::zp_buttons
sta Joypad::zp_prev
sta Player::zp_state
sta Items::zp_state
;; Initialize the level. We allow the build system to pass its own value for
;; this in `LEVEL`, just in case we want to debug the enemy of a specific
;; level.
.ifdef LEVEL
lda #LEVEL
sta Globals::zp_level
and #%00000111
sta Globals::zp_level_kind
.else
sta Globals::zp_level
sta Globals::zp_level_kind
.endif
;; Initialize the assets for the game. If the first sprite is not
;; initialized to zero, then we are not coming from reset() but from
;; starting after a "Game over". In this case skip this initialization.
lda OAM::m_address
bne @skip_assets
jsr Assets::init
@skip_assets:
;; Initialize some variables from the "Game Over" side of the game.
jsr Over::init
;; Initialize variables from the game's driver that need to be set before
;; NMIs start ticking.
jsr Driver::init_before_nmi
;; Initialize some PAL-specific constants.
.ifdef PAL
lda #0
sta Driver::zp_pal_counter
.endif
;; We shadow the PPU control register in memory. Otherwise we go into the
;; title as expected.
jsr Title::init
lda #%10001000
sta PPU::zp_control
sta PPU::m_control
cli
;; Enable back the PPU
lda #%00011110
sta PPU::zp_mask
sta PPU::m_mask
@main_game_loop:
;; Select the joypad from the active player and read it.
lda Globals::zp_multiplayer
and #$01
tax
READ_JOYPAD_X
lda Globals::zp_flags
and #%00000011
beq @title_screen
cmp #1
beq @game_screen
jmp @over
@title_screen:
;; If we are in a transitioning state, avoid the update from the title.
lda Globals::zp_flags
and #%00000100
bne @do_switch
jsr Title::update
beq @set_flags
@do_switch:
;; Start was pressed by the player, switch to the main game.
jsr Driver::switch
jmp @set_flags
@game_screen:
jsr Driver::update
__fallthrough__ @set_flags
@set_flags:
lda #%10000000
ora Globals::zp_flags
sta Globals::zp_flags
@wait_for_render:
bit Globals::zp_flags
bmi @wait_for_render
;; Rendering is done, we can perform another iteration of the loop!
jmp @main_game_loop
@over:
;; Display the "Game over" screen if it hasn't been displayed yet. After
;; that, if we detect that the user wants to go back to the title screen we
;; go back to @init to initialize everything again except for the score
;; which should be preserved. Otherwise we go back to the main game loop,
;; which effectively means to just sit and wait until for the right player
;; input.
jsr Over::handle
pha
;; Wait for the PPU to render the screen.
@set_flags_over:
lda #%10000000
ora Globals::zp_flags
sta Globals::zp_flags
@wait_for_render_over:
bit Globals::zp_flags
bmi @wait_for_render_over
;; Can the player start over?
pla
beq @main_game_loop
;; We will skip the initialization of the assets so to avoid writing into
;; the first nametable when it's just fine. That being said, we still need
;; to prepare palettes for the title screen. Do it now before starting over.
jsr Assets::prepare_for_title_screen
jmp @init
.endproc
.segment "VECTORS"
.addr nmi, reset, irq
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