Implement timers

src/timer.ml

@@ -0,0 +1,38 @@
+
+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