各位大神看看，为啥程序用usart4一发数据就死掉，显示HardFault_Handler\

lubo0505

  void UART4_Configuration(void)    
 {
  /* USART1 configuration ------------------------------------------------------*/
  /* USART1 configured as follow:
        - BaudRate = 9600 baud
        - Word Length = 8 Bits
        - One Stop Bit
        - No parity
        - Hardware flow control disabled (RTS and CTS signals)
        - Receive and transmit enabled
        - USART Clock disabled
        - USART CPOL: Clock is active low
        - USART CPHA: Data is captured on the second edge
        - USART LastBit: The clock pulse of the last data bit is not output to
                         the SCLK pin
  */
  USART_ClockInitTypeDef USART_ClockInitStructure;
  USART_InitStructure.USART_BaudRate = 9600;   ///////////////波特率设置
  USART_InitStructure.USART_WordLength = USART_WordLength_8b;
  USART_InitStructure.USART_StopBits = USART_StopBits_1;
  USART_InitStructure.USART_Parity = USART_Parity_No;
  USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
  USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
  /* Configure the USART4 */
  USART_Init(UART4, &USART_InitStructure);

 USART_ClockInitStructure.USART_Clock = USART_Clock_Disable;
 USART_ClockInitStructure.USART_CPOL = USART_CPOL_Low;
 USART_ClockInitStructure.USART_CPHA = USART_CPHA_2Edge;
 USART_ClockInitStructure.USART_LastBit = USART_LastBit_Enable;
 USART_ClockInit(UART4, &USART_ClockInitStructure);

  USART_ITConfig(UART4, USART_IT_RXNE, ENABLE);
    /* Enable USART4 */
     USART_Cmd(UART4, ENABLE);
   MY_NVIC_Init(2,2,UART4_IRQChannel,1);//组2，最低优先级
  }

正点原子

中断服务函数在哪里？