Add memory module.

src/memory.ml

@@ -0,0 +1,16 @@
+(** http://bgb.bircd.org/pandocs.htm#memorymap
+    http://imrannazar.com/GameBoy-Emulation-in-JavaScript:-Memory *)
+
+type map = {
+  rom_bank_00 : bytes; (* cartridge, 16KB *)
+  rom_bank_01 : bytes; (* additional bank, 16KB *)
+  vram : bytes; (* Video RAM, 8KB *)
+}
+
+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;
+  }

src/oboy.ml

@@ -15,6 +15,7 @@ let power_up cartridge =
     Cartridge.print_info cartridge;
 
     let cpu = Cpu.init_cpu in
+    let mem = Memory.init cartridge in
     run cpu cartridge