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

src/hexa.ml

@@ -0,0 +1,14 @@
+open Printf
+
+let print_bytes b ?(width=8) =
+  let l = Bytes.length b in
+  let rec print_line b start last =
+    if start < last then
+      let max = min (start + width - 1) last in
+      for i = start to max do
+        printf "%02X " (Bytes.get b i |> int_of_char)
+      done;
+      print_newline ();
+      print_line b (start + width) last
+  in
+  print_line b 0 l

src/oboy.ml

@@ -0,0 +1,4 @@
+let () =
+  if Array.length Sys.argv < 2
+  then print_endline "Please specify a ROM."
+  else Cartridge.read_cartridge Sys.argv.(1)