CHNCTL_RS_CONTROL
CZTTY_CHAN_WRITE(sc, CHNCTL_RS_CONTROL, sc->sc_chanctl_rs_control);
CZTTY_CHAN_WRITE(sc, CHNCTL_RS_CONTROL, sc->sc_chanctl_rs_control);
CZTTY_CHAN_WRITE(sc, CHNCTL_RS_CONTROL, sc->sc_chanctl_rs_control);
CZTTY_CHAN_WRITE(sc, CHNCTL_RS_CONTROL, 0);