IER_ERXRDY
sc->sc_ier = IER_ETXRDY | IER_ERXRDY;
sc->sc_ier = IER_ERXRDY;
sc->sc_ier = IER_ERXRDY | IER_ERLS | IER_EMSC;
if (com->regs.ier & IER_ERXRDY) {