diff --git a/bin/read_clock.ml b/bin/read_clock.ml
new file mode 100644
index 0000000..af628d7
--- /dev/null
+++ b/bin/read_clock.ml
@@ -0,0 +1,51 @@
+type clock_source =
+| Internal of int
+| External of int
+
+let milestone : (char option * int) Atomic.t = Atomic.make (None, 96)
+let clock_iterator = ref 0
+
+let process_event queue device (ev : Portmidi.Portmidi_event.t) =
+  let tick () =
+    incr clock_iterator;
+    let note, note_length = Atomic.get milestone in 
+    if !clock_iterator >= note_length then begin
+        (match note with
+        | Some note -> Midi.(
+          write_output device
+            [ message_off ~note ~timestamp:0l ~volume:'\090' ~channel:6 () ]);
+            print_endline "milestone ended: turn off note"
+        | None -> ());
+      match Queue.take_opt queue with
+      | None -> Atomic.set milestone (None, 96)
+      | Some (note, cycles) -> 
+        print_endline "milestone started: turn on note";
+        Midi.(
+          write_output device
+            [ message_on ~note ~timestamp:0l ~volume:'\090' ~channel:6 () ]);
+        Atomic.set milestone (Some note, cycles);
+      clock_iterator := 0
+    end
+  in
+  match ev.message with
+  | 0xF8l -> tick ()
+  | 0xFCl -> clock_iterator := 0
+  | _ -> ()
+
+
+let external_main input_device_id output_device note_queue =
+  let device = Midi.Device.create_input input_device_id in
+  let rec aux () =
+      if Atomic.get Watchdog.terminate then
+        ()
+      else
+      match Portmidi.read_input ~length:1 device with
+      | Ok l -> List.iter (process_event note_queue output_device ) l; aux ()
+      | Error _ -> print_endline "oh no"
+  in
+  aux ()
+
+let clock_domain_main clock_source output_device note_queue () =
+  match clock_source with
+  | External input_device_id -> external_main input_device_id output_device note_queue
+  | Internal _bpm -> assert false
\ No newline at end of file