SM502_INTR_MASK
bus_space_write_4(sc->sc_memt, sc->sc_regh, SM502_INTR_MASK, 0);
mask = bus_space_read_4(sc->sc_memt, sc->sc_regh, SM502_INTR_MASK);
reg = bus_space_read_4(sc->sc_memt, sc->sc_regh, SM502_INTR_MASK);
bus_space_write_4(sc->sc_memt, sc->sc_regh, SM502_INTR_MASK, reg);