Function hifive1::serial::tx_rx

pub fn tx_rx<X, Y>(
    tx: Pin17<X>, 
    rx: Pin16<Y>, 
    out_xor: &mut OUT_XOR, 
    iof_sel: &mut IOF_SEL, 
    iof_en: &mut IOF_EN
) -> (TxPin, RxPin)

Return TX, RX pins.