Use memory map instead of cartridge.

src/memory.ml

@@ -1,3 +1,5 @@
+open Bytes
+
 (** http://bgb.bircd.org/pandocs.htm#memorymap
     http://imrannazar.com/GameBoy-Emulation-in-JavaScript:-Memory *)
 
@@ -5,12 +7,31 @@ type map = {
   rom_bank_00 : bytes; (* cartridge, 16KB *)
   rom_bank_01 : bytes; (* additional bank, 16KB *)
   vram : bytes; (* Video RAM, 8KB *)
+  io : bytes; (* I/O ports *)
 }
 
 let init (cartridge: Cartridge.t) =
-  let open Bytes in
   {
     rom_bank_00 = sub cartridge.full_rom 0 0x4000;
     rom_bank_01 = create 0x4000;
     vram = create 0x2000;
+    io = create 0x0080;
   }
+
+let get_mem_bank mem addr =
+  match addr with
+  | x when x < 0x4000 -> mem.rom_bank_00, x
+  | x when x < 0x8000 -> mem.rom_bank_01, (x - 0x4000)
+  | x when x < 0xA000 -> mem.vram,  (x - 0x8000)
+  | x when x < 0xFF00 -> failwith "Unimplemented memory range."
+  | x when x < 0xFF80 -> mem.io, x - 0xFF00
+  | _ -> failwith "Invalid memory range."
+
+
+let get mem addr =
+  let m, x = get_mem_bank mem addr in
+  get m x
+
+let set mem addr c =
+  let m, x = get_mem_bank mem addr in
+  set m x c