RTC_RTCCON
reg = bus_space_read_1(sc->sc_iot, sc->sc_ioh, RTC_RTCCON);
bus_space_write_1(sc->sc_iot, sc->sc_ioh, RTC_RTCCON, reg | RTCCON_RTCEN);
reg = bus_space_read_1(sc->sc_iot, sc->sc_ioh, RTC_RTCCON);
bus_space_write_1(sc->sc_iot, sc->sc_ioh, RTC_RTCCON, reg & ~RTCCON_RTCEN);