IER_EUART
sc->sc_ier |= IER_EUART;
ier |= IER_EUART;
com_write_reg(sc, com_ier, IER_EUART);
sc->sc_ier |= IER_EUART | IER_ERXTOUT;
ier |= IER_EUART;
com_write_reg(sc, com_ier, IER_EUART);