Create src/lib

src/lib/memory.ml

@@ -0,0 +1,109 @@
+(**
+ * Copyright (c) 2015, Fabien Freling
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD 2-clause license found in the
+ * LICENSE file at the top level directory of this source tree.
+ *)
+
+open Bytes
+open Printf
+
+(** @see http://bgb.bircd.org/pandocs.htm#memorymap
+    @see http://imrannazar.com/GameBoy-Emulation-in-JavaScript:-Memory *)
+
+(** Common addresses *)
+let gDIV  = 0xFF04 (** divider register *)
+let gTIMA = 0xFF05 (** timer counter *)
+let gTMA  = 0xFF06 (** timer modulo *)
+let gTAC  = 0xFF07 (** timer control *)
+
+type map = {
+  rom_bank_00 : bytes; (* cartridge, 16KB *)
+  rom_bank_01 : bytes; (* additional bank, 16KB *)
+  vram        : bytes; (* Video RAM, 8KB *)
+  wram_bank_0 : bytes; (* work RAM, 4KB *)
+  wram_bank_1 : bytes; (* work RAM, 4KB *)
+  io          : bytes; (* I/O ports *)
+  hram        : bytes; (* High RAM, 8KB *)
+  interrupt   : bytes; (* Interrupt Enable Register *)
+}
+
+type t = {
+  map       : map;
+  timer_div : Timer.t;
+  tima      : Timer.t;
+}
+
+let init (cartridge: Cartridge.t) =
+  let map = {
+    rom_bank_00 = sub cartridge.full_rom 0 0x4000;
+    rom_bank_01 = create 0x4000;
+    vram = create 0x2000;
+    wram_bank_0 = create 0x1000;
+    wram_bank_1 = create 0x1000;
+    io = create 0x0080;
+    hram = create 0x2000;
+    interrupt = create 1
+  } in
+
+  (** Init register values
+      @see http://bgb.bircd.org/pandocs.htm#powerupsequence *)
+  let zero = char_of_int 0 in
+  set map.io 0x05 zero; (* TIMA, 0xFF05 *)
+  set map.io 0x06 zero; (* TMA,  0xFF06 *)
+  set map.io 0x07 zero; (* TAC,  0xFF07 *)
+
+  let timer_div = Timer.create 16384 true in
+  let tima = Timer.create_tima 0 in
+
+  { map; timer_div; tima; }
+
+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 < 0xC000 -> failwith "Unimplemented memory range."
+  | x when x < 0xD000 -> mem.wram_bank_0,  (x - 0xC000)
+  | x when x < 0xE000 -> mem.wram_bank_1,  (x - 0xD000)
+  | x when x < 0xFF00 -> failwith "Unimplemented memory range."
+  | x when x < 0xFF80 -> mem.io, x - 0xFF00
+  | x when x < 0xFFFF -> mem.hram, x - 0xFF80
+  | 0xFFFF -> mem.interrupt, 0
+  | x -> eprintf "Memory access 0x%06X\n" x;
+         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
+
+(** Increment byte in memory, wrap value in case of overflow *)
+let inc mem addr = 
+  let m, x = get_mem_bank mem addr in
+  let value = Bytes.get m x |> int_of_char in
+  let inc_value = value + 1 in
+  let overflow = inc_value > 0xFF in
+  let c = inc_value mod 0x01FF |> char_of_int in
+  Bytes.set m x c;
+  overflow
+
+
+let update_timers mem cycles =
+  let should_inc_div = Timer.update mem.timer_div cycles in
+  if should_inc_div then ignore (inc mem.map gDIV);
+
+  let should_inc_tima = Timer.update mem.tima cycles in
+  if should_inc_tima then begin
+    let overflow = inc mem.map gTIMA in
+    if overflow then begin
+      let tma = get mem.map gTMA in
+      set mem.map gTIMA tma
+      (* TODO: INT 50 - Timer interupt *)
+    end
+  end