tm4c123gxl的串口通信为什么可以发但不能收？

效仿uart_echo的uart0通信，采用uart3，请问为什么发可以，但是收不可以

//*****************************************************************************
//
// The UART interrupt handler.
//
//*****************************************************************************
void
UARtintHandler(void)
[
uint32_t ui32Status;
//
// Get the interrrupt status.
//
ui32Status = ROM_UARTIntStatus(UART3_BASE, true);
//
// Clear the asserted interrupts.
//
ROM_UARTIntClear(UART3_BASE, ui32Status);
//
// Loop while there are characters in the receive FIFO.
//
while(ROM_UARTCharsAvail(UART3_BASE))
[
//
// Read the next character from the UART and write it back to the UART.
//
ROM_UARTCharPutNonBlocking(UART3_BASE,
ROM_UARTCharGetNonBlocking(UART3_BASE));
//
// Blink the LED to show a character transfer is occuring.
//
GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_2, GPIO_PIN_2);
//
// Delay for 1 millisecond. Each SysCtlDelay is about 3 clocks.
//
SysCtlDelay(SysCtlClockGet() / (1000 * 3));
//
// Turn off the LED
//
GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_2, 0);
]
]
//*****************************************************************************
//
// Send a string to the UART.
//
//*****************************************************************************
void
UARTSend(const uint8_t *pui8Buffer, uint32_t ui32Count)
[
//
// Loop while there are more characters to send.
//
while(ui32Count--)
[
//
// Write the next character to the UART.
//
ROM_UARTCharPutNonBlocking(UART3_BASE, *pui8Buffer++);
]
]
//*****************************************************************************
//
// This example demonstrates how to send a string of data to the UART.
//
//*****************************************************************************
int
main(void)
[
//ʹÄÜFPU
ROM_FPUEnable();
ROM_FPULazyStackingEnable();
//ÉèÖÃʱÖÓÖ±½ÓʹÓÃÍⲿ¾§ÕñÔ´
ROM_SysCtlClockSet(SYSCTL_SYSDIV_1 | SYSCTL_USE_OSC | SYSCTL_OSC_MAIN |
SYSCTL_XTAL_16MHZ);
//ʹÄÜLEDËùÓö˿Ú
ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
//ʹÄÜÒý½Å
ROM_GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, GPIO_PIN_2);
//ʹÄÜÍâÉè
ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_UART3);
ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOC);
//ʹÄÜÖÕ¶Ë
ROM_IntMasterEnable();
//ÅäÖô®¿Úuart3µÄÒý½Å
GPIOPinConfigure(GPIO_PC6_U3RX);
GPIOPinConfigure(GPIO_PC7_U3TX);
ROM_GPIOPinTypeUART(GPIO_PORTC_BASE, GPIO_PIN_6 | GPIO_PIN_7);
//115,200, 8-N-1 operation.
ROM_UARTConfigSetExpClk(UART3_BASE, ROM_SysCtlClockGet(), 115200,
(UART_CONFIG_WLEN_8 | UART_CONFIG_STOP_ONE |
UART_CONFIG_PAR_NONE));
//ʹÄÜUART
ROM_IntEnable(INT_UART3);
ROM_UARTIntEnable(UART3_BASE, UART_INT_RX | UART_INT_RT);
//
// Prompt for text to be entered.
//
UARTSend((uint8_t *)"TEST ", 55);
//
// Loop forever echoing data through the UART.
//
while(1)
[
]
]