ti-RTOS例程，串口例程，无法打印串口，求指教

你好，这是我写的一段UART的代码，

/*串口声明*/
char input;
UART_Handle uart;
UART_Params uartParams;

static PIN_State ledPinState;
const char echoPrompt[]="\fEchoing characters:\r\n";

PIN_Config ledPinTable[] = {
Board_LED1 | PIN_GPIO_OUTPUT_EN | PIN_GPIO_LOW | PIN_PUSHPULL | PIN_DRVSTR_MAX,
Board_LED2 | PIN_GPIO_OUTPUT_EN | PIN_GPIO_LOW | PIN_PUSHPULL | PIN_DRVSTR_MAX,
PIN_TERMINATE
};
void echoFxn(UArg a0,UArg a1)
{

while(1)
{
UART_read(uart, &input, 1);
UART_write(uart, &input, 1);
}
}
int main(void)
{

/**************************GPIO灯********************************************/
PIN_Handle ledPinHandle;
Board_initGeneral();
ledPinHandle = PIN_open(&ledPinState, ledPinTable);
PIN_setOutputValue(ledPinHandle, Board_LED1, 1);

/******************************任务初始化*************************************/
Task_Params_init(&taskParams);
taskParams.stackSize=sizeof(task0Stack);
taskParams.stack=&task0Stack;
Task_construct(&task0Struct,(Task_FuncPtr)echoFxn,&taskParams,NULL);

/*************************串口***********************************************/

UART_init(); //USart ini
UART_Params_init(&uartParams); //串口配置
uartParams.writeDataMode = UART_DATA_BINARY; //写数据模式
uartParams.readDataMode = UART_DATA_BINARY; //读数据模式
uartParams.readReturnMode = UART_RETURN_FULL; //返回模式
uartParams.readEcho = UART_ECHO_OFF;
uartParams.baudRate = 9600; //波特率
uartParams.stopBits=UART_STOP_ONE;
uartParams.parityType=UART_PAR_NONE;
uart = UART_open(Board_UART0, &uartParams); //打开串口

UART_write(uart, echoPrompt, sizeof(echoPrompt));
UART_read(uart, &input, 1);
UART_write(uart, &input, 1);
// System_flush();

// /* This example has logging and many other debug capabilities enabled */
// System_printf("This example does not attempt to minimize code or data "
// "footprint\n");
// System_flush();
//
// System_printf("Starting the UART Echo example\nSystem provider is set to "
// "SysMin. Halt the target to view any SysMin contents in "
// "ROV.\n");
// /* SysMin will only print to the console when you call flush or exit */
// System_flush();

/* Start BIOS */
BIOS_start();

return (0);
}

在TI-RTOS例程基础上改了一点，编译没有报错，单步调试时，可以执行UART_write(uart, echoPrompt, sizeof(echoPrompt));但是却无法执行UART_write(uart, &input, 1); 请问是什么问题啊，无法打印出来，求指教！

求指教啊

求指教