function pollAll(pollFrequency) {
  return async () => {
    if (this.devicesByPollFrequency[pollFrequency]) {
      return Promise.map(this.devicesByPollFrequency[pollFrequency], (device) => this.poll(device), { concurrency: 1 });
    }
    return Promise.resolve();
  };
}
@description Poll all devices of one frequency.
@param {number} pollFrequency - The frequency in milliseconds.
@returns {function()} Return a function.
@example
pollAll(60000);