1 files changed, 132 insertions, 0 deletions
diff --git a/src/btree.s b/src/btree.s
new file mode 100644
index 0000000..2867bf0
--- /dev/null
+++ b/src/btree.s
@@ -0,0 +1,132 @@
+.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"