ppu writes to dispcnt

src/crab/bus.cr

@@ -1,6 +1,14 @@
 class Bus
   WRAM_BOARD   = 0x02000000..0x0203FFFF
   WRAM_CHIP    = 0x03000000..0x03007FFF
+  PPU_IO       = 0x04000000..0x0400005F
+  SOUND_IO     = 0x04000060..0x040000AF
+  DMA_IO       = 0x040000B0..0x040000FF
+  TIMER_IO     = 0x04000100..0x0400011F
+  SERIAL_IO_1  = 0x04000120..0x0400012F
+  KEYPAD_IO    = 0x04000130..0x04000133
+  SERIAL_IO_2  = 0x04000134..0x040001FF
+  INTERRUPT_IO = 0x04000200..0x0400FFFF
   CARTRIDGE    = 0x08000000..0x0FFFFFFF
   UNUSED       = 0x10000000..0xFFFFFFFF
 
@@ -15,6 +23,7 @@ class Bus
     case index
     when WRAM_BOARD then @wram_board[index - WRAM_BOARD.begin]
     when WRAM_CHIP  then @wram_chip[index - WRAM_CHIP.begin]
+    when PPU_IO then @gba.ppu[index]
     when CARTRIDGE  then @gba.cartridge[index - CARTRIDGE.begin]
     when UNUSED     then 0xFF
     else                 0xFF
@@ -38,6 +47,7 @@ class Bus
     case index
     when WRAM_BOARD then @wram_board[index - WRAM_BOARD.begin] = value
     when WRAM_CHIP  then @wram_chip[index - WRAM_CHIP.begin] = value
+    when PPU_IO then @gba.ppu[index] = value
     when CARTRIDGE  then @gba.cartridge[index - CARTRIDGE.begin] = value # todo is this meant to be writable?
     when UNUSED     then nil
     else                 raise "Unimplemented write ~ addr:#{hex_str index.to_u32}, val:#{value}"

src/crab/gba.cr

@@ -3,11 +3,13 @@ require "./util"
 require "./cartridge"
 require "./bus"
 require "./cpu"
+require "./ppu"
 
 class GBA
   getter cartridge : Cartridge
   getter bus : Bus { Bus.new self }
   getter cpu : CPU { CPU.new self }
+  getter ppu : PPU { PPU.new self }
 
   def initialize(rom_path : String)
     @cartridge = Cartridge.new rom_path

src/crab/ppu.cr

@@ -0,0 +1,44 @@
+class PPU
+  # LCD Control
+  class DISPCNT < BitField(UInt16)
+    bool obj_window_display
+    bool window_1_display
+    bool window_0_display
+    bool screen_display_obj
+    bool screen_display_bg3
+    bool screen_display_bg2
+    bool screen_display_bg1
+    bool screen_display_bg0
+    bool forced_blank               # (1=Allow access to VRAM,Palette,OAM)
+    bool obj_character_vram_mapping # (0=Two dimensional, 1=One dimensional)
+    bool hblank_interval_free       # (1=Allow access to OAM during H-Blank)
+    bool display_frame_select       # (0-1=Frame 0-1) (for BG Modes 4,5 only)
+    bool reserved_for_bios          # todo update bitfield macro to support overwriting/locking values
+    num bg_mode, 3                  # (0-5=Video Mode 0-5, 6-7=Prohibited)
+  end
+
+  @dispcnt : DISPCNT = DISPCNT.new 0
+
+  def initialize(@gba : GBA)
+  end
+
+  def [](index : Int) : Byte
+    case index
+    when 0x04000000 then (@dispcnt.value >> 8).to_u8
+    when 0x04000001 then @dispcnt.value.to_u8!
+    when 0x04000002 then 0_u8
+    when 0x04000003 then 0_u8
+    else raise "Unimplemented PPU read ~ addr:#{hex_str index.to_u32}"
+    end
+  end
+
+  def []=(index : Int, value : Byte) : Nil
+    case index
+    when 0x04000000 then @dispcnt.value = (@dispcnt.value & 0x00FF) | value.to_u16 << 8
+    when 0x04000001 then @dispcnt.value = (@dispcnt.value & 0xFF00) | value
+    when 0x04000002
+    when 0x04000003
+    else raise "Unimplemented PPU write ~ addr:#{hex_str index.to_u32}, val:#{value}"
+    end
+  end
+end