STM32 USART Interrupt

// Handle Interrupts on USART2 (USB connection)

void USART2_IRQHandler()

{

  uint8_t i;

  uint16_t crc;

  // Receive-Interrupt

  if(USART_GetITStatus(USART2, USART_IT_RXNE))

  {

    // Reset the interrupt-flag

    USART_ClearFlag(USART2, USART_FLAG_RXNE);

    TIM4->CNT = 0x00;

    // Enable the status LED "Connection to computer okay"

    GPIOB -> BSRR = GPIO_Pin_0;

    ReceiveByte(USART_ReceiveData(USART2));

  }

  // Transmit-Interrupt

  else if(USART_GetITStatus(USART2, USART_IT_TXE))

  {

    // Reset the interrupt-flag

    USART_ClearFlag(USART2, USART_FLAG_TXE);

    if(getNewMsg)

    {

        // Calculate the CRC for the temporary buffer

        crc = calcCRC(pcSendBuf[posPCsendBufRead].payload, pcSendBuf[posPCsendBufRead].msgLen);

        // Add the CRC to the last two positions in the temporary buffer

        pcSendBuf[posPCsendBufRead].payload[pcSendBuf[posPCsendBufRead].msgLen] = (crc & 0xff00) >> 8;

        pcSendBuf[posPCsendBufRead].payload[pcSendBuf[posPCsendBufRead].msgLen + 1] = (crc & 0xff);

        pcSendBuf[posPCsendBufRead].msgLen = pcSendBuf[posPCsendBufRead].msgLen + 2;

        getNewMsg = 0;

        pcSendBuf[posPCsendBufRead].pos = 0;

    }

    else

    {

      // Send data via USART

      USART_SendData(USART2, pcSendBuf[posPCsendBufRead].payload[pcSendBuf[posPCsendBufRead].pos]);

      pcSendBuf[posPCsendBufRead].pos++;

      // See if the end of the actual sub-buffer is reached

      if(pcSendBuf[posPCsendBufRead].pos >= pcSendBuf[posPCsendBufRead].msgLen)

      {

        for(i = 0; i < MAX_PC_MESSAGE_SIZE; i++)

        {

          pcSendBuf[posPCsendBufRead].payload[i] = '\0';

        }

        pcSendBuf[posPCsendBufRead].msgLen = 0;

        posPCsendBufRead++;

        getNewMsg = 1;

        // Check if the end of the send-buffer is reached

        if(posPCsendBufRead >= PC_SEND_BUFFER_SIZE)

        {

          // Chose the first sub-buffer

          posPCsendBufRead = 0;

          pcSendBuf[posPCsendBufRead].pos = 0;

        }

        // See if the sendBuf is empty

        if(posPCsendBufRead == posPCsendBufWrite)

        {

          pcSendBuf[posPCsendBufRead].pos = 0;

          // Disable the transmit interrupt on USART

          USART_ITConfig(USART2, USART_IT_TXE, DISABLE);

        }

      }

    }

  }

}