Sending DMX messages to an ENTTEC Pro USB controller over WebUSB

lighting.js

async function setUpLights() {
  const lightingDevice = await navigator.usb.requestDevice({ filters: [] });
  await lightingDevice.open();
  await lightingDevice.claimInterface(0);

  // This comes from https://github.com/NERDDISCO/webusb-dmx512-controller 
  lightingDevice.controlTransferOut({
    // It's a USB class request
    requestType: "class",
    // The destination of this request is the interface
    recipient: "interface",
    // CDC: Communication Device Class
    // 0x22: SET_CONTROL_LINE_STATE
    // RS-232 signal used to tell the USB device that the computer is now present.
    request: 0x22,
    // Yes
    value: 0x01,
    // Interface #2
    index: 0x00
  });

  // This comes from https://github.com/node-dmx/dmx
  const universe = new Array(512).fill(0);

  const ENTTEC_PRO_DMX_STARTCODE = 0x00;
  const ENTTEC_PRO_START_OF_MSG = 0x7e;
  const ENTTEC_PRO_END_OF_MSG = 0xe7;
  const ENTTEC_PRO_SEND_DMX_RQ = 0x06;

  const hdr = Uint8Array.from([
    ENTTEC_PRO_START_OF_MSG,
    ENTTEC_PRO_SEND_DMX_RQ,
    universe.length & 0xff,
    (universe.length >> 8) & 0xff,
    ENTTEC_PRO_DMX_STARTCODE
  ]);

  // Send a message with a blank DMX universe. This turns off all the lights.
  lightingDevice.transferOut(
    2,
    Uint8Array.from([...hdr, ...universe, ENTTEC_PRO_END_OF_MSG])
  );
  
  
  let count = 0;
  // This does a sine pulse.
  const loop = delta => {
    count = delta / 1000;
    universe[2] = Math.round(Math.sin(count) * 127 + 128);
    lightingDevice
      .transferOut(
        2,
        Uint8Array.from([...hdr, ...universe, ENTTEC_PRO_END_OF_MSG])
      )
      .then(() => {
        window.frame = requestAnimationFrame(loop);
      });
  };
  loop(0);
}