ETH_MAC_RX
err = lan78xx_read_reg(sc, ETH_MAC_RX, &buf);
err = lan78xx_write_reg(sc, ETH_MAC_RX, buf);
lan78xx_read_reg(sc, ETH_MAC_RX, &buf);
lan78xx_write_reg(sc, ETH_MAC_RX, buf);
lan78xx_write_reg(sc, ETH_MAC_RX, buf);
lan78xx_write_reg(sc, ETH_MAC_RX, buf);