RNG_STATUS
bus_space_write_4(sc->sc_iot, sc->sc_ioh, RNG_STATUS, 0x40000);
status = bus_space_read_4(sc->sc_iot, sc->sc_ioh, RNG_STATUS);
size_t nwords = __SHIFTOUT(bcmrng_read_4(sc, RNG_STATUS), RNG_VAL);