[TM4C1294NCPDT] UART interupt code example doesn't work with Tivaware???

Hi everyone, i'm a newbie here. I'm now learning about ARM on EK-TM4C1294XL kit with CCS ver 6.1 and TivaWare_C_Series-2.1.0.12573.

I have tried build code example about using UART with interupt, but it doesn't work. The trouble is some of warnnings show up, though i can still debug the code. So, when i send some character through uart, the kit cant echo it back. Can someone help me fix it. Thank you.

// This is the example code for uart using interupt. I haven't modified it.
#include <stdint.h>
#include <stdbool.h>
#include "inc/hw_memmap.h"
#include "inc/hw_types.h"
#include "driverlib/gpio.h"
#include "driverlib/pin_map.h"
#include "driverlib/sysctl.h"
#include "driverlib/uart.h"
#include "inc/hw_ints.h"
#include "driverlib/interrupt.h"

uint32_t ui32SysClkFreq;

void UARTIntHandler(void)
{
	uint32_t ui32Status;

	ui32Status = UARTIntStatus(UART0_BASE, true); //get interrupt status

	UARTIntClear(UART0_BASE, ui32Status); //clear the asserted interrupts

	while(UARTCharsAvail(UART0_BASE)) //loop while there are chars
	{
		UARTCharPutNonBlocking(UART0_BASE, UARTCharGetNonBlocking(UART0_BASE)); //echo character
		GPIOPinWrite(GPIO_PORTN_BASE, GPIO_PIN_0|GPIO_PIN_1, 0xFF); 			// LEDs on
		SysCtlDelay(ui32SysClkFreq / (3 * 10)); 							    // delay .1 sec
		GPIOPinWrite(GPIO_PORTN_BASE, GPIO_PIN_0|GPIO_PIN_1, 0); 				// LEDs off
	}
}

int main(void)
{
	ui32SysClkFreq = SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
			SYSCTL_OSC_MAIN | SYSCTL_USE_PLL |
			SYSCTL_CFG_VCO_480), 120000000);

	SysCtlPeripheralEnable(SYSCTL_PERIPH_UART0);
	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);

	GPIOPinConfigure(GPIO_PA0_U0RX);
	GPIOPinConfigure(GPIO_PA1_U0TX);
	GPIOPinTypeUART(GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1);

	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPION);
	GPIOPinTypeGPIOOutput(GPIO_PORTN_BASE, GPIO_PIN_0|GPIO_PIN_1);

	UARTConfigSetExpClk(UART0_BASE, ui32SysClkFreq, 115200,
			(UART_CONFIG_WLEN_8 | UART_CONFIG_STOP_ONE | UART_CONFIG_PAR_NONE));

	IntMasterEnable();
	IntEnable(INT_UART0);
	UARTIntEnable(UART0_BASE, UART_INT_RX | UART_INT_RT);

	UARTCharPut(UART0_BASE, 'E');
	UARTCharPut(UART0_BASE, 'n');
	UARTCharPut(UART0_BASE, 't');
	UARTCharPut(UART0_BASE, 'e');
	UARTCharPut(UART0_BASE, 'r');
	UARTCharPut(UART0_BASE, ' ');
	UARTCharPut(UART0_BASE, 'T');
	UARTCharPut(UART0_BASE, 'e');
	UARTCharPut(UART0_BASE, 'x');
	UARTCharPut(UART0_BASE, 't');
	UARTCharPut(UART0_BASE, ':');
	UARTCharPut(UART0_BASE, ' ');

	while (1)
	{
		//		if (UARTCharsAvail(UART0_BASE)) UARTCharPut(UART0_BASE, UARTCharGet(UART0_BASE));
	}
}