Implement timers

This commit is contained in:
Fabien Freling 2016-01-23 13:16:18 +01:00
parent 6c7544dffb
commit 67093196ea
3 changed files with 102 additions and 12 deletions

View file

@ -1,22 +1,34 @@
open Bytes
open Printf
(** http://bgb.bircd.org/pandocs.htm#memorymap
http://imrannazar.com/GameBoy-Emulation-in-JavaScript:-Memory *)
(** @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 *)
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 *)
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;
@ -25,7 +37,19 @@ let init (cartridge: Cartridge.t) =
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
@ -50,3 +74,28 @@ let get mem addr =
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