| XON_THRESHOLD | when the data amount in receiver’s fifo is more than this register value. it will send a xoff char with uart_sw_flow_con_en set to 1. |
| XOFF_THRESHOLD | When the data amount in receiver’s fifo is less than this register value. it will send a xon char with uart_sw_flow_con_en set to 1. |
| XON_CHAR | This register stores the xon flow control char. |
| XOFF_CHAR | This register stores the xoff flow control char. |