diff --git a/packages/core/cyclistworker.js b/packages/core/cyclistworker.js
index 832c8172..b0028698 100644
--- a/packages/core/cyclistworker.js
+++ b/packages/core/cyclistworker.js
@@ -1,17 +1,120 @@
-const ports = [];
+const allPorts = [];
+let cps = 1;
+let num_ticks_since_cps_change = 0;
+let lastTick = 0; // absolute time when last tick (clock callback) happened
+let lastBegin = 0; // query begin of last tick
+let lastEnd = 0; // query end of last tick
+// let getTime = getTime; // get absolute time
+let num_cycles_at_cps_change = 0;
+// let onToggle = onToggle;
+let latency = 0.1; // fixed trigger time offset
+let interval = 0.1;
 
-self.onconnect = function (ev) {
-  let port = ev.ports[0];
-  port.onmessage = (e) => {
-    setTimeout(() => {
-      ports.forEach((p) => p.postMessage([e.data, ev.ports.length]));
-    }, 300);
-  };
-  port.start();
-  ports.push(port);
+//incoming
+//cps message
+// {type: 'cpschange', payload: {cps}}
+
+//toggle
+// {type: toggle, payload?: {started: boolean}}
+
+//sending
+//{type: 'tick', payload: {begin, end, phase, time }}
+//{type: 'log', payload: {type, text}}
+
+const getTime = () => {
+  return performance.now();
 };
-self.onmessage = ({ data: { question } }) => {
-  self.postMessage({
-    answer: 42,
+
+const sendMessage = (message) => {
+  allPorts.forEach((port) => {
+    port.postMessage(message);
   });
 };
+const log = (text, type) => {
+  sendMessage({ type: 'log', payload: { text, type } });
+};
+
+createClock(
+  getTime,
+  // called slightly before each cycle
+  (phase, duration, tick) => {
+    if (num_ticks_since_cps_change === 0) {
+      num_cycles_at_cps_change = lastEnd;
+    }
+    num_ticks_since_cps_change++;
+    try {
+      const time = getTime();
+      const begin = lastEnd;
+      lastBegin = begin;
+      //convert ticks to cycles, so you can query the pattern for events
+      const eventLength = duration * cps;
+      const num_cycles_since_cps_change = num_ticks_since_cps_change * eventLength;
+      const end = num_cycles_at_cps_change + num_cycles_since_cps_change;
+      lastEnd = end;
+      const tickdeadline = phase - time; // time left until the phase is a whole number
+      lastTick = time + tickdeadline;
+      sendMessage({ type: 'tick', payload: { begin, end, phase, time } });
+    } catch (e) {
+      log(`[cyclist] error: ${e.message}`, 'error');
+    }
+  },
+  interval, // duration of each cycle
+);
+
+self.onconnect = function (e) {
+  // the incoming port
+  var port = e.ports[0];
+  allPorts.push(port);
+
+  allPorts.forEach((port) => {
+    port.postMessage('yoooo');
+  });
+
+  port.start(); // Required when using addEventListener. Otherwise called implicitly by onmessage setter.
+};
+
+function createClock(
+  getTime,
+  callback, // called slightly before each cycle
+  duration = 0.05, // duration of each cycle
+  interval = 0.1, // interval between callbacks
+  overlap = 0.1, // overlap between callbacks
+) {
+  let tick = 0; // counts callbacks
+  let phase = 0; // next callback time
+  let precision = 10 ** 4; // used to round phase
+  let minLatency = 0.01;
+  const setDuration = (setter) => (duration = setter(duration));
+  overlap = overlap || interval / 2;
+  const onTick = () => {
+    const t = getTime();
+    const lookahead = t + interval + overlap; // the time window for this tick
+    if (phase === 0) {
+      phase = t + minLatency;
+    }
+    // callback as long as we're inside the lookahead
+    while (phase < lookahead) {
+      phase = Math.round(phase * precision) / precision;
+      phase >= t && callback(phase, duration, tick);
+      phase < t && console.log('TOO LATE', phase); // what if latency is added from outside?
+      phase += duration; // increment phase by duration
+      tick++;
+    }
+  };
+  let intervalID;
+  const start = () => {
+    clear(); // just in case start was called more than once
+    onTick();
+    intervalID = setInterval(onTick, interval * 1000);
+  };
+  const clear = () => intervalID !== undefined && clearInterval(intervalID);
+  const pause = () => clear();
+  const stop = () => {
+    tick = 0;
+    phase = 0;
+    clear();
+  };
+  const getPhase = () => phase;
+  // setCallback
+  return { setDuration, start, stop, pause, duration, interval, getPhase, minLatency };
+}
diff --git a/packages/core/repl.mjs b/packages/core/repl.mjs
index 609fbb42..245b651f 100644
--- a/packages/core/repl.mjs
+++ b/packages/core/repl.mjs
@@ -37,6 +37,14 @@ export function repl({
   worker.onmessage = ({ data: { answer } }) => {
     console.log(answer);
   };
+
+  const sharedworker = new SharedWorker(new URL('./cyclistworker.js', import.meta.url));
+
+  sharedworker.port.start();
+  sharedworker.port.addEventListener('message', (message) => {
+    console.log(message);
+  });
+
   const updateState = (update) => {
     Object.assign(state, update);
     state.isDirty = state.code !== state.activeCode;