diff -r bc7b6aa5d67a -r 7030706266df rust/hwphysics/src/time.rs
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/hwphysics/src/time.rs	Fri Dec 06 22:20:53 2019 +0100
@@ -0,0 +1,97 @@
+use crate::common::{GearId, Millis};
+use std::{
+    cmp::{Eq, Ord, Ordering, PartialEq, PartialOrd},
+    collections::BinaryHeap,
+};
+
+pub type EventId = u16;
+
+struct TimeEvent {
+    time: Millis,
+    gear_id: GearId,
+    event_id: EventId,
+}
+
+impl PartialOrd for TimeEvent {
+    #[inline]
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        self.time.partial_cmp(&other.time)
+    }
+}
+
+impl PartialEq for TimeEvent {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        self.time.eq(&other.time)
+    }
+}
+
+impl Ord for TimeEvent {
+    #[inline]
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.time.cmp(&other.time)
+    }
+}
+
+impl Eq for TimeEvent {}
+
+pub struct OccurredEvents {
+    events: Vec<(GearId, EventId)>,
+}
+
+impl OccurredEvents {
+    fn new() -> Self {
+        Self { events: vec![] }
+    }
+
+    fn clear(&mut self) {
+        self.events.clear()
+    }
+}
+
+pub struct TimeProcessor {
+    current_event_id: EventId,
+    current_time: Millis,
+    events: BinaryHeap<TimeEvent>,
+    timeouts: OccurredEvents,
+}
+
+impl TimeProcessor {
+    pub fn new() -> Self {
+        Self {
+            current_event_id: 0,
+            current_time: Millis::new(0),
+            events: BinaryHeap::with_capacity(1024),
+            timeouts: OccurredEvents::new(),
+        }
+    }
+
+    pub fn register(&mut self, gear_id: GearId, timeout: Millis) -> EventId {
+        let event_id = self.current_event_id;
+        self.current_event_id.wrapping_add(1);
+        let event = TimeEvent {
+            time: self.current_time + timeout,
+            gear_id,
+            event_id,
+        };
+        self.events.push(event);
+        event_id
+    }
+
+    pub fn cancel(&mut self, gear_id: GearId) {}
+
+    pub fn process(&mut self, time_step: Millis) -> &OccurredEvents {
+        self.timeouts.clear();
+        self.current_time = self.current_time + time_step;
+        while self
+            .events
+            .peek()
+            .filter(|e| e.time <= self.current_time)
+            .is_some()
+        {
+            let event = self.events.pop().unwrap();
+            self.timeouts.events.push((event.gear_id, event.event_id))
+        }
+        &self.timeouts
+    }
+}