| RXFIFO_START_ADDR | This is the offset address of the last receiving data as described in nonfifo_rx_thres_register. |
| RXFIFO_END_ADDR | This is the offset address of the first receiving data as described in nonfifo_rx_thres_register. |
| TXFIFO_START_ADDR | This is the offset address of the first sending data as described in nonfifo_tx_thres register. |
| TXFIFO_END_ADDR | This is the offset address of the last sending data as described in nonfifo_tx_thres register. |