MEMAC_IEVENT
while ((bus_read_4(regs, MEMAC_IEVENT) & IEVENT_RX_EMPTY) == 0)
while ((bus_read_4(regs, MEMAC_IEVENT) & IEVENT_TX_EMPTY) == 0)
bus_write_4(sc->sc_base.sc_mem, MEMAC_IEVENT, 0);