SSCOM_UMCON
bus_space_write_2(iot, ioh, SSCOM_UMCON, UMCON_RTS);
int umcon = bus_space_read_1(sc->sc_iot, sc->sc_iot, SSCOM_UMCON);
SSCOM_UMCON, sc->sc_umcon & UMCON_HW_MASK);
OUTW(SSCOM_UMCON, UMCON_RTS);