Read Nintendo checksum in cartridge header.

This first commit parses the ROM to extract the Nintendo Logo and
display it on stdout.

src/cartridge.ml

@@ -0,0 +1,28 @@
+open Unix
+open Printf
+
+(** http://bgb.bircd.org/pandocs.htm#thecartridgeheader *)
+
+type memory_bank_controller =
+  | ROM_ONLY
+  | MBC1
+
+type t = {
+  nintendo_logo : bytes;
+  title : string;
+  mem_type : memory_bank_controller;
+  rom_size : int;
+  ram_size : int;
+  header_checksum : bytes;
+  global_checksum : bytes;
+}
+
+let read_cartridge file =
+  print_endline file;
+  let fd = openfile file [Unix.O_RDONLY] 0o644 in
+  let n_logo = Bytes.create 48 in
+  let _ = lseek fd 0x0104 SEEK_SET in
+  let _ = read fd n_logo 0 48 in
+  print_endline "Nintendo logo:";
+  Hexa.print_bytes n_logo ~width:16;
+  Unix.close fd