RTC_RCNR
rtc0 = bus_space_read_4(sc->sc_bust, ioh, RTC_RCNR);
while ((rtc1 = bus_space_read_4(sc->sc_bust, ioh, RTC_RCNR)) == rtc0)
while(rtc1 == bus_space_read_4(sc->sc_bust, ioh, RTC_RCNR))
tv->tv_sec = bus_space_read_4(sc->sc_iot, sc->sc_ioh, RTC_RCNR);
bus_space_write_4(sc->sc_iot, sc->sc_ioh, RTC_RCNR, tv->tv_sec);
cntr = bus_space_read_4(sc->sc_iot, sc->sc_ioh, RTC_RCNR);