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federico.massimi
federico.massimi
Associate III
March 16, 2017
Question

UART variable length message

Posted on March 16, 2017 at 10:48

Good morning, I'm making a program that should receive from the UART a variable length message. The message ends with '\n'

I tried it with this

uint8_t rxChar=0;

int main() {

      HAL_UART_Receive_IT(&huart2, &rxChar, 1);

}

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart) {

      / /appendCharToBuffer 

rxChar

      HAL_UART_Receive_IT(&huart2, &rxChar, 1);

}

but after receiving two bytes I have a 'overrun error'.

using

HAL_UART_Receive_IT(&huart2, serial_command_buffer, COMMAND_BUFFER); 

works, but the message must be at least 

COMMAND_BUFFER char length.

Is possile to generate an interrupt when UART receives an '\n' although have not yet been received

COMMAND_BUFFER

 characters? Or can I use an approach like the previous one without causing an overrun error?

or what is the proper way to handle the need to receive a variable length message?

Thanks in advance

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    1 reply

    federico.massimi
    federico.massimiAuthor
    Associate III
    March 24, 2017
    Posted on March 24, 2017 at 13:07

    After several attempts I found a solution.

    In the main I simply add this line

    HAL_UART_Receive_IT(&huart2, rxBuffer, RX_BUFFER_SIZE) 

    then in the 'STM32L4xx_it.c' file I modified the

    function

     'USART2_IRQHandler' in this way:

    /* USER CODE BEGIN USART2_IRQn 0 */

    if(((READ_REG(huart2.Instance->ISR) & USART_ISR_RXNE) != RESET) && ((READ_REG(huart2.Instance->CR1) & USART_CR1_RXNEIE) != RESET)) {

       static uint8_t buffer_index = 0;

       uint8_t tmp = (uint8_t)((uint16_t) READ_REG(huart2.Instance->RDR) & (uint8_t)huart2.Mask);

       if(tmp != '\n'&& buffer_index < huart2.RxXferSize) {

          huart2.pRxBuffPtr[buffer_index++] = tmp;

       } else{

          MyCallback(huart2.pRxBuffPtr, buffer_index);

          buffer_index = 0;

          memset(huart2.pRxBuffPtr, '\0', huart2.RxXferSize); // clear buffer

       }

       CLEAR_BIT(READ_REG(huart2.Instance->ISR), USART_ISR_RXNE);

    } else {

    /* USER CODE END USART2_IRQn 0 */

    HAL_UART_IRQHandler(&huart2);

    /* USER CODE BEGIN USART2_IRQn 1 */

    }

    /* USER CODE END USART2_IRQn 1 */

    I do not know if this is the best way, but it works.

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