gb-tarot/main.asm

; FF80 CALL
; FF81 LOW
; FF82 HIGH
; FF83 RET
; pattern repeats for the first 16 bytes so we can have some call vectors for the scene system
DEF SCENE_SETUP EQU $FF81
DEF SCENE_UPDATE EQU SCENE_SETUP + 4 ; call then ret is 3+1 bytes
DEF SCENE_DRAW EQU SCENE_UPDATE + 4
DEF SCENE_TEARDOWN EQU SCENE_DRAW + 4

DEF INTERRUPT_LCD EQU $FF91

DEF rMYBTN EQU $FFA8
DEF rMYBTNP EQU rMYBTN + 1

INCLUDE "hardware.inc"
SECTION "Interrupts", ROM0[$0]
  ds $48 - @, 0
  call INTERRUPT_LCD - 1
  ret

SECTION "Header", ROM0[$100]

  jp EntryPoint

  ds $150 - @, 0 ; Make room for the header

EntryPoint:
  ; Shut down audio circuitry
  ld a, 0
  ld [rNR52], a

  ld a, [Instructions] ; get the value of a call instruction so we can shove it into our handles
  ld hl, SCENE_SETUP - 1
  ld [hl], a
  ld hl, SCENE_UPDATE - 1
  ld [hl], a
  ld hl, SCENE_DRAW - 1
  ld [hl], a
  ld hl, SCENE_TEARDOWN - 1
  ld [hl], a
  ld hl, INTERRUPT_LCD - 1
  ld [hl], a 

  ld a, [Instructions + 3] ; get the value of a ret instruction
  ld hl, SCENE_SETUP + 2
  ld [hl], a
  ld hl, SCENE_UPDATE + 2
  ld [hl], a
  ld hl, SCENE_DRAW + 2
  ld [hl], a
  ld hl, SCENE_TEARDOWN + 2
  ld [hl], a
  ld hl, INTERRUPT_LCD + 2
  ld [hl], a 

  ; set up our scene vectors
  ld hl, SCENE_SETUP
  ld de, CardReadSetup
  ld a, e
  ld [hl+], a
  ld a, d
  ld [hl+], a
  ld hl, SCENE_UPDATE
  ld de, CardReadUpdate
  ld a, e
  ld [hl+], a
  ld a, d
  ld [hl+], a
  ld hl, SCENE_DRAW
  ld de, CardReadDraw
  ld a, e
  ld [hl+], a
  ld a, d
  ld [hl+], a
  ld hl, SCENE_TEARDOWN
  ld de, CardReadTeardown
  ld a, e
  ld [hl+], a
  ld a, d
  ld [hl+], a
  
  ; set up the interrupt vector to just be ret.
  ld hl, INTERRUPT_LCD
  ld de, INTERRUPT_LCD + 2
  ld a, e
  ld [hl+], a
  ld a, d
  ld [hl+], a

  ; Do not turn the LCD off outside of VBlank
WaitVBlank:
  ld a, [rLY]
  cp 144
  jp c, WaitVBlank

  call SCENE_SETUP - 1

Loop:
  di
  ld hl, rP1
  ld [hl], P1F_GET_DPAD
  ld a, [hl]
  ld a, [hl]
  ld a, [hl]
  ld a, [hl]
  cpl
  and a, %00001111
  ld b, a
  ld [hl], P1F_GET_BTN
  ld a, [hl]
  ld a, [hl]
  ld a, [hl]
  ld a, [hl]
  cpl
  and a, %00001111
  swap a
  or a, b
  ld b, a
  ld a, [rMYBTN]
  cpl
  and a, b
  ld [rMYBTNP], a
  ld a, b
  ld [rMYBTN], a

  call SCENE_UPDATE - 1
  
  ld b, 144
  call AwaitLine

  call SCENE_DRAW - 1
  jp Loop

AwaitLine: ; put the line you want to reach in b
  ld a, [rLY]
  cp b
  jp nz, AwaitLine
  ret

PrintString: ; write ascii string which has been prefixed by its length.
  ld b, [hl]
  inc hl
PrintBChars: ;write ascii characters. will not respect newlines or anything like that
  ; hl should be the source of ascii text
  ; de should be the location in the tile map to start writing at
  ; b should be the length
  ld a, [hli]
  or a, %10000000
  ld [de], a
  inc de
  dec b
  jp nz, PrintBChars
  ret
  
INCLUDE "CardReadScreen.inc"

Instructions:
  call Instructions + 2
  ret