110 lines
3.1 KiB
OCaml
110 lines
3.1 KiB
OCaml
(**
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* Copyright (c) 2015, Fabien Freling
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* All rights reserved.
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*
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* This source code is licensed under the BSD 2-clause license found in the
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* LICENSE file at the top level directory of this source tree.
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*)
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open Bytes
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open Printf
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(** @see http://bgb.bircd.org/pandocs.htm#memorymap
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@see http://imrannazar.com/GameBoy-Emulation-in-JavaScript:-Memory *)
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(** Common addresses *)
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let gDIV = 0xFF04 (* divider register *)
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let gTIMA = 0xFF05 (* timer counter *)
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let gTMA = 0xFF06 (* timer modulo *)
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let gTAC = 0xFF07 (* timer control *)
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type map = {
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rom_bank_00 : bytes; (* cartridge, 16KB *)
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rom_bank_01 : bytes; (* additional bank, 16KB *)
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vram : bytes; (* Video RAM, 8KB *)
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wram_bank_0 : bytes; (* work RAM, 4KB *)
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wram_bank_1 : bytes; (* work RAM, 4KB *)
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io : bytes; (* I/O ports *)
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hram : bytes; (* High RAM, 8KB *)
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interrupt : bytes; (* Interrupt Enable Register *)
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}
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type t = {
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map : map;
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timer_div : Timer.t;
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tima : Timer.t;
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}
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let init (cartridge: Cartridge.t) =
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let map = {
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rom_bank_00 = sub cartridge.full_rom 0 0x4000;
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rom_bank_01 = create 0x4000;
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vram = create 0x2000;
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wram_bank_0 = create 0x1000;
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wram_bank_1 = create 0x1000;
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io = create 0x0080;
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hram = create 0x2000;
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interrupt = create 1
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} in
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(** Init register values
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@see http://bgb.bircd.org/pandocs.htm#powerupsequence *)
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let zero = char_of_int 0 in
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set map.io 0x05 zero; (* TIMA, 0xFF05 *)
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set map.io 0x06 zero; (* TMA, 0xFF06 *)
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set map.io 0x07 zero; (* TAC, 0xFF07 *)
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let timer_div = Timer.create 16384 true in
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let tima = Timer.create_tima 0 in
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{ map; timer_div; tima; }
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let get_mem_bank mem addr =
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match addr with
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| x when x < 0x4000 -> mem.rom_bank_00, x
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| x when x < 0x8000 -> mem.rom_bank_01, (x - 0x4000)
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| x when x < 0xA000 -> mem.vram, (x - 0x8000)
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| x when x < 0xC000 -> failwith "Unimplemented memory range."
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| x when x < 0xD000 -> mem.wram_bank_0, (x - 0xC000)
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| x when x < 0xE000 -> mem.wram_bank_1, (x - 0xD000)
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| x when x < 0xFF00 -> failwith "Unimplemented memory range."
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| x when x < 0xFF80 -> mem.io, x - 0xFF00
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| x when x < 0xFFFF -> mem.hram, x - 0xFF80
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| 0xFFFF -> mem.interrupt, 0
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| x -> eprintf "Memory access 0x%06X\n" x;
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failwith "Invalid memory range."
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let get mem addr =
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let m, x = get_mem_bank mem addr in
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get m x
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let set mem addr c =
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let m, x = get_mem_bank mem addr in
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set m x c
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(** Increment byte in memory, wrap value in case of overflow *)
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let inc mem addr =
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let m, x = get_mem_bank mem addr in
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let value = Bytes.get m x |> int_of_char in
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let inc_value = value + 1 in
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let overflow = inc_value > 0xFF in
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let c = inc_value mod 0x01FF |> char_of_int in
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Bytes.set m x c;
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overflow
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let update_timers mem cycles =
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let should_inc_div = Timer.update mem.timer_div cycles in
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if should_inc_div then ignore (inc mem.map gDIV);
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let should_inc_tima = Timer.update mem.tima cycles in
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if should_inc_tima then begin
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let overflow = inc mem.map gTIMA in
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if overflow then begin
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let tma = get mem.map gTMA in
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set mem.map gTIMA tma
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(* TODO: INT 50 - Timer interupt *)
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end
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end
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