/**
 * Protocol (main -> worker):
 *   { type: 'start', bpm, ppqn, lookahead, interval }
 *   { type: 'stop' }
 *   { type: 'setBpm', bpm }
 *   { type: 'setPpqn', ppqn }
 *   { type: 'setLookahead', lookahead }
 *
 * Protocol (worker -> main):
 *   { type: 'started', startPerf }
 *   { type: 'tick', tick, timeMs }
 */
declare let bpm: number;
declare let ppqn: number;
declare let lookahead: number;
declare let interval: number;
declare let running: boolean;
declare let tickCount: number;
declare let nextTickPerf: number;
declare let lastEmittedTick: number;
declare function tickIntervalMs(): number;
declare function schedule(): void;