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|
.segment "HEADER"
.byte 'N', 'E', 'S', $1A
;; We split the PRG-ROM into two 16KB sections, the first fixed (the game
;; itself), and then the second one, which holds the library.
.byte $02
;; We keep the CHR-ROM simple: the most basic one (8KB) and no windows.
.byte $01
;; - bit 1: contains battery-backed PRG RAM ($6000-7FFF)
;; - bit 7-4: the lower nibble of the mapper (#%0001 for MMC1)
.byte $12
;; Blanked out stuff.
.res $09, $00
;; asan:fixed-segments FIXED, LIBTREE
.segment "FIXED"
.asciiz "@mssola"
.include "../include/apu.s"
.include "../include/oam.s"
.include "../include/ppu.s"
.include "../include/mmc1.s"
.include "../include/asm.s"
.include "lib.s"
.include "interrupts.s"
.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 ; asan:stack $80-$FF
;; Disable NMIs and the APU's DMC.
inx
stx PPU::m_control
stx PPU::m_mask
stx APU::m_dmc
;; Reset MMC1 chip.
reset_mmc1:
inc reset_mmc1
;; First PPU wait.
bit PPU::m_status
@vblankwait1:
bit PPU::m_status
bpl @vblankwait1
;; 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
;;;
;; Configure the MMC1 chip.
;; The control register:
;;
;; - bits 0-1: nametable arrangement: horizontal mirroring.
;; - bits 2-3: PRG-ROM fixed at $8000 (game), swappable at $C000 (library).
;; - bit 4: CHR-ROM: 8KB at a time.
lda #%00001011
sta MMC1::m_control
lsr
sta MMC1::m_control
lsr
sta MMC1::m_control
lsr
sta MMC1::m_control
lsr
sta MMC1::m_control
;; CHR bank: 0.
lda #0
sta MMC1::m_chr_bank
sta MMC1::m_chr_bank
sta MMC1::m_chr_bank
sta MMC1::m_chr_bank
sta MMC1::m_chr_bank
;; The swappable bank is 1, which contains the library. Also set PRG-RAM to
;; be enabled.
lda #1
sta MMC1::m_prg_bank
sta MMC1::m_prg_bank
sta MMC1::m_prg_bank
sta MMC1::m_prg_bank
sta MMC1::m_prg_bank
__fallthrough__ main
.endproc
.proc main
jsr Btree::todo
@tbd:
jmp @tbd
.endproc
.segment "VECTORS"
.addr nmi, reset, irq
.segment "CHARS"
.incbin "../assets/btree.chr"
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