Basic support for CPU opcodes.

Support for 2 opcodes: nop and jump.
These are the first opcodes encountered in Super Mario Land.

src/cpu.ml

@@ -1,26 +1,68 @@
-(** http://bgb.bircd.org/pandocs.htm#cpuregistersandflags *)
+open Printf
+
+(** http://bgb.bircd.org/pandocs.htm#cpuregistersandflags
+    http://gameboy.mongenel.com/dmg/lesson1.html *)
 
 type registers = {
-  a : char; (* accumulator *)
-  b : char;
-  c : char;
-  d : char;
-  e : char;
-  h : char;
-  l : char;
+  mutable a : char; (* accumulator *)
+  mutable f : char; (* flags *)
+  mutable b : char;
+  mutable c : char;
+  mutable d : char;
+  mutable e : char;
+  mutable h : char;
+  mutable l : char;
 
-  sp : int; (* stack pointer *)
-  pc : int; (* program counter *)
+  mutable sp : int; (* stack pointer *)
+  mutable pc : int; (* program counter *)
 }
 
-type flags = {
+(* type flags = {
   z  : bool; (* zero *)
   n  : bool; (* substraction *)
   h  : bool; (* half-carry *)
   cy : bool; (* carry *)
-}
+} *)
 
 type t = {
   reg : registers;
-  flags : flags;
+  mutable cycles : int;
 }
+
+(** http://bgb.bircd.org/pandocs.htm#powerupsequence *)
+let init_registers =
+  {
+    a = '\x00';
+    f = '\x00';
+    b = '\x00';
+    c = '\x00';
+    d = '\x00';
+    e = '\x00';
+    h = '\x00';
+    l = '\x00';
+    sp = 0xFFFE;
+    pc = 0x0100;
+  }
+
+let init_cpu =
+  { reg = init_registers; cycles = 0 }
+
+let inc_pc cpu count =
+  cpu.reg.pc <- cpu.reg.pc + count
+
+let inc_cycles cpu count =
+  cpu.cycles <- cpu.cycles + count
+
+let read_2B b addr =
+  let low = Bytes.get b addr in
+  let high = Bytes.get b (addr + 1) in
+  (int_of_char high) * 256 + (int_of_char low)
+
+(** http://imrannazar.com/GameBoy-Z80-Opcode-Map *)
+let run cpu (cartridge: Cartridge.t) =
+(*  Hexa.print_slice cartridge.full_rom cpu.reg.pc (cpu.reg.pc + 7) ~width:16; *)
+  match Bytes.get cartridge.full_rom cpu.reg.pc with
+  | '\x00' -> printf "  nop\n"; inc_pc cpu 1; inc_cycles cpu 4
+  | '\xC3' -> let addr = read_2B cartridge.full_rom (cpu.reg.pc + 1) in
+              printf "  jp 0x%02x\n" addr; cpu.reg.pc <- addr; inc_cycles cpu 16
+  | _ as x -> eprintf "OpCode %02X\n" (int_of_char x); failwith "Unimplemented opcode."

src/hexa.ml

@@ -1,14 +1,14 @@
 open Printf
 
-let print_bytes b ?(width=8) =
-  let l = Bytes.length b in
-  let rec print_line b start last =
+let rec print_slice ?(width=8) 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
+    print_slice ~width b (start + width) last
+
+let print_bytes ?(width=8) b width =
+  let l = Bytes.length b in
+  print_slice ~width b 0 l

src/oboy.ml

@@ -1,5 +1,9 @@
 open Printf
 
+let rec run (cpu: Cpu.t) (cartridge: Cartridge.t) =
+  Cpu.run cpu cartridge;
+  run cpu cartridge
+
 (** Power up sequence
     http://bgb.bircd.org/pandocs.htm#powerupsequence *)
 let power_up cartridge =
@@ -10,12 +14,19 @@ let power_up cartridge =
     print_endline "Valid ROM.";
     printf "Title: %s\n" cartridge.title;
     printf "ROM size: %iKB\n" cartridge.rom_size;
-    printf "RAM size: %iKB\n" cartridge.ram_size
+    printf "RAM size: %iKB\n" cartridge.ram_size;
+
+    let cpu = Cpu.init_cpu in
+    run cpu cartridge
 
 
 let () =
-  if Array.length Sys.argv < 2
-  then print_endline "Please specify a ROM.";
+  if Array.length Sys.argv < 2 then
+  begin
+    prerr_endline "Please specify a ROM.";
+    eprintf "Usage: %s path/to/rom\n" Sys.argv.(0);
+    exit 1;
+  end;
 
   let cartridge = Cartridge.read_cartridge Sys.argv.(1) in
   match cartridge with