(**
 * Copyright (c) 2016, 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.
 *)

let frequence = 4194304

type t = {
  clock_rate          : int;
  period              : int;
  mutable enabled     : bool;
  mutable cycles_left : int;
}

let create clock_rate enabled =
  let period = frequence / clock_rate in
  {
    clock_rate;
    period;
    enabled;
    cycles_left = period;
  }

(** TIMA - Timer counter *)
let create_tima tac =
  let enabled = Bit.is_set tac 2 in 
  let clock_select = tac land 0b00000011 in
  let clock_rate = match clock_select with
    | 0 -> 4096
    | 1 -> 262144
    | 2 -> 65536
    | 3 -> 16384
    | _ -> failwith "Unreachable clock rate code."
  in
  create clock_rate enabled

let update timer cycles =
  let remain = timer.cycles_left - cycles in
  let should_inc = remain <= 0 in
  if should_inc then
    timer.cycles_left <- remain + timer.period;
  should_inc