EXUART_S5L_UCON_TXTHRESH
CLR(sc->sc_ucon, EXUART_S5L_UCON_TXTHRESH);
if (!ISSET(sc->sc_ucon, EXUART_S5L_UCON_TXTHRESH)) {
SET(sc->sc_ucon, EXUART_S5L_UCON_TXTHRESH);
if (ISSET(sc->sc_ucon, EXUART_S5L_UCON_TXTHRESH)) {
CLR(sc->sc_ucon, EXUART_S5L_UCON_TXTHRESH);