Majora's Mask Printf

INCLUDE "hardware.inc" ; Hardware definitions
INCLUDE "ibmpc1.inc" ; Font data (from devrs.com)

; Constants not in hardware.inc
SGB_UNSUPPORTED EQU $00
SGB_SUPPORTED EQU $03
DEST_JAPAN EQU $00
DEST_INTERNATIONAL EQU $01

; Interrupt handler routines
; ------
; @abner: Parts of the hardware generate interrupts, and we
;         may use the sections below to handle each one. In
;         other words, the program jumps to the relevant section
;         during an interrupt and executes what's in there (before
;         returning to the main program).
;
SECTION "Vblank", ROM0[$0040]

  ret ; Do nothing (i.e. exit handler and return to where the program was interrupted).

SECTION "LCDC", ROM0[$0048]

  ret ; Do nothing

SECTION "Timer_Overflow", ROM0[$0050]

  ret ; Do nothing

SECTION "Serial", ROM0[$0058]

  ret ; Do nothing

SECTION "p1thru4", ROM0[$0060]

  ret ; Do nothing
; ------

; Boot loader jumps here
; ------
; @abner: On startup, the gameboy executes a small program (256 bytes) that reads
;         memory locations from $100 to $14D -- the area called the ROM header. The
;         info we provide here is used to perform some necessary setup.
;
SECTION "start", ROM0[$0100]
  ; $0100 - $0103: Startup handler -- Once ready, the gameboy will run this part.
  nop ; It's tradition to put a nop here
  jp begin

  ; $0104 - $0133: The Nintendo Logo.
  NINTENDO_LOGO

  ; $0134 - $013E: Cart name, in upper-case letters, followed by zeroes. 15 bytes.
  DB "CHOCOWINE-INSPIRED",0,0,0,0,0,0,0,0,0

  ; $0143: Gameboy Color compatibility flag.
  DB 0

  ; $0144 - $0145: "New" Licensee Code, a two character name.
  DB "OK" ; 0,0 would work too (two bytes)

  ; $0146: Super Gameboy compatibility flag.
  DB SGB_UNSUPPORTED

  ; $0147: Cartridge type. Either no ROM or MBC5 is recommended.
  DB CART_ROM

  ; $0148: Rom size.
  DB CART_ROM_256K

  ; $0149: Ram size.
  DB CART_RAM_NONE

  ; $014A: Destination code.
  DB DEST_INTERNATIONAL

  ; $014B: Old licensee code.
  ; $33 indicates new license code will be used.
  ; $33 must be used for SGB games.
  DB $33

  ; $014C: ROM version number
  DB 0

  ; $014D: Header checksum.
  ; Assembler needs to patch this.
  DB 0

  ; $014E- $014F: Global checksum.
  ; Assembler needs to patch this.
  DW 0
; ------

; $0150: Code!
begin:
  nop
  di ; Disable interrupts
  ld sp, $ffff ; Set stack pointer to highest mem location + 1

init:
  ld a, %1110100 ; Background tile palette (11 - black, 10 - dark grey, 01 - light grey, 00 - white)
  ld [rBGP], a ; Memory location that stores the background tile palette

  ; Set X/Y scroll registers to 0. This sets the screen to upper right hand corner of our canvas.
  ; NOTE: Gameboy has a tile map RAM (256x256) we call the canvas, but remember our screen is 160x144
  ld a,0
  ld [rSCX], a
  ld [rSCY], a

  call StopLCD ; We're about to copy to video RAM. It can be glitchy to do that with the screen on.

  ; Load font data into tile memory. mem_CopyMono relies on the 16-bit HL register as a source
  ; memory location, DE as its destination, and BC is a data length indicator.
  ld hl, TileData
  ld de, _VRAM ; $8000
  ld bc, 8*256 ; ASCII - 256 characters, each having 8 bytes of display data
  call mem_CopyMono ; Load font tiles

  ; Turn LCD on. Parameters explained in the I/O registers section of the Gameboy reference
  ld a, LCDCF_ON|LCDCF_BG8000|LCDCF_BG9800|LCDCF_BGON|LCDCF_OBJ16|LCDCF_OBJOFF
  ld [rLCDC], a

  ; Clear canvas by setting it to ascii character $20 (white space)
  ld a, 32 ; ASCII FOR BLANK SPACE
  ld hl, _SCRN0
  ld bc, SCRN_VX_B * SCRN_VY_B
  call mem_SetVRAM

  ; Print "Knzorb (TM)" to the screen
  ld hl, Title
  ld de, _SCRN0+3+(SCRN_VY_B*7)
  ld bc, TitleEnd-Title
  call mem_CopyVRAM

; Epilogue
wait:
  halt
  nop
  jr wait

; ****************************************************************************************
; Hard-coded Data
; ****************************************************************************************
Title:
  DB "The Melodist"
TitleEnd:
  nop

; ****************************************************************************************
; StopLCD: Turn off LCD if it is on (we wait until we know it's off)
; ****************************************************************************************
StopLCD:
  ld a, [rLCDC]
  rlca ; Put high bit of LCDC into carry flag
  ret nc ; If screen is off just exit

; Loop until we hit VBlank
.wait:
  ld a, [rLY]
  cp 145 ; Screen on scan line 145?
  jr nz, .wait ; No. Wait

  ; Turn off LCD
  ld a, [rLCDC]
  res 7, a ; Reset bit 7
  ld [rLCDC], a

  ret

TileData:
  chr_IBMPC1 1, 8 ; Load entire character set. See ibmpc1.inc for details.