function execute() {
  if (context.start === undefined) {
    context.start = parseInt(inPorts[1].value, 10) || 0;
  }
  if (context.end === undefined) {
    context.end = parseInt(inPorts[2].value, 10) || 20;
  }
  if (context.step === undefined) {
    context.step = parseInt(inPorts[3].value, 10) || 1;
  }
  if (context.current === undefined) {
    context.current = context.start;
  }
  switch (trigger) {
    case TRIGGERS.SYSTEM_OUT_DONE:
      if (context.run && context.current < context.end) {
        context.current += context.step;
        sendSync([null, context.current, new Date()]);
      } else {
        context.run = false;
        context.current = context.start;
        unblock();
      }
      break;
    case 0:
      // Trigger
      if (context.run) {
        // Already Running - Start one step before because in loop it will be added again.
        context.current = (context.start - context.step);
      } else {
        context.run = true;
        sendSync([new Date(), context.current, new Date()]);
      }
      break;
    case 1:
      // Start
      if (inPorts[1].value !== undefined) {
        context.start = parseInt(inPorts[1].value, 10);
      }
      break;
    case 2:
      // End
      if (inPorts[2].value !== undefined) {
        context.end = parseInt(inPorts[2].value, 10);
      }
      break;
    case 3:
      // Step
      if (inPorts[3].value !== undefined) {
        context.step = parseInt(inPorts[3].value, 10);
      }
      break;
    case 4:
      context.current = context.start;
      context.run = false;
      unblock();
      break;
    default: break;
  }
}