dm9051_read_mem
ret = dm9051_read_mem(db, DM_SPI_MRCMDX, &rxbyte, 2);
ret = dm9051_read_mem(db, DM_SPI_MRCMD, &db->rxhdr, DM_RXHDR_SIZE);
ret = dm9051_read_mem(db, DM_SPI_MRCMD, rdptr, rxlen);