LCR_SBREAK
lcr = ISSET(sc->sc_lcr, LCR_SBREAK) | cflag2lcr(t->c_cflag);
CLR(sc->sc_lcr, LCR_SBREAK);
SET(sc->sc_lcr, LCR_SBREAK);
lcr = ISSET(sc->sc_lcr, LCR_SBREAK);