* isn't one
* @busy_bit: the index of the busy bit within reg, or -1 if there isn't one
* @stop_bit: the index of the stop bit within reg, or -1 if there isn't one
* isn't one
* @busy_bit: the index of the busy bit within reg, or -1 if there isn't one
* @stop_bit: the index of the stop bit within reg, or -1 if there isn't one