ITStatus USART_GetITStatus(USART_TypeDef* USARTx, uint16_t USART_IT)
{
  uint32_t bitpos = 0x00, itmask = 0x00, usartreg = 0x00;
  ITStatus bitstatus = RESET;
  /* Check the parameters */
  assert_param(IS_USART_ALL_PERIPH(USARTx));
  assert_param(IS_USART_GET_IT(USART_IT));
  /* The CTS interrupt is not available for UART4 and UART5 */
  if (USART_IT == USART_IT_CTS)
  {
    assert_param(IS_USART_123_PERIPH(USARTx));
  }   

  /* Get the USART register index */
  usartreg = (((uint8_t)USART_IT) >> 0x05);
  /* Get the interrupt position */
  itmask = USART_IT & IT_Mask;//请问这是干嘛的啊
  itmask = (uint32_t)0x01 << itmask;

  if (usartreg == 0x01) /* The IT  is in CR1 register */
  {
    itmask &= USARTx->CR1;
  }
  else if (usartreg == 0x02) /* The IT  is in CR2 register */
  {
    itmask &= USARTx->CR2;
  }
  else /* The IT  is in CR3 register */
  {
    itmask &= USARTx->CR3;
  }

  bitpos = USART_IT >> 0x08;
  bitpos = (uint32_t)0x01 << bitpos;
  bitpos &= USARTx->SR;
  if ((itmask != (uint16_t)RESET)&&(bitpos != (uint16_t)RESET))
  {
    bitstatus = SET;
  }
  else
  {
    bitstatus = RESET;
  }

  return bitstatus;