TM4C1290NCPDT: RTOS/TM4C1290:When using RTOS UART Driver, how to set UART Interrupt FIFO Level Select

Hello,

I am using TI-RTOS Drivers to UART. (TI-RTOS 2.16)

I want to change Interrupt FIFO Level Select.

I have tried UARTFIFOLevelSet API after UART_open().

my code:

 //RTOS UART Drivers
 UART_Params uart_params;

 UART_Params_init(uart_params);
 up->baudRate  = 500000;    //boudrate 500kbps
 up->readDataMode = UART_DATA_BINARY;
 up->writeDataMode   = UART_DATA_BINARY;
 up->readReturnMode = UART_RETURN_FULL;
 up->readEcho  = UART_ECHO_OFF;
 up->readTimeout = 100;

 uart = UART_open(Board_UART6, &uart_params);

 //Peripheral Driver Library UART API.
 // UARTIFLS register is Interrupt FIFO Level Select.
 // RX FIFO 1/8 to 1/2(UART_FIFO_RX4_8)
 UARTFIFOLevelSet(UART6_BASE, UART_FIFO_TX1_8, UART_FIFO_RX4_8);

The result showed that UARTIFLS(UART6 UARTIFLS:0x40012034) register value changes 0x00000000 to 0x00000010.

Is this the right approach?
Or is there another right way?

Thanks.