STM32 HAL USART receive by interrupt

Question

I have some trouble to receive data over the USART. What I actually want to achieve ist, that I can receive a command over USART with no specific length (only a maximum possible length). So I use the interrupt routine to check each character received, but I somehow still cannot achieve what I want. The routine is called each time I receive a new character, but somehow HAL_UART_Receive_IT(&huart1,rx_data,buff_size_rx) does not upgrade in realtime, then I don't see the received character when I check rx_data[pointer], but a few time later it is in the rx_data buffer.

What I have so far:

int pointer =0;

...

void USART1_IRQHandler(void)
{
  /* USER CODE BEGIN USART1_IRQn 0 */
    if ( USART1->ISR & UART_IT_TXE) {

    }

    if ( USART1->ISR & UART_IT_RXNE) {
        HAL_UART_Receive_IT(&huart1,rx_data,buff_size_rx);
        if(rx_data[pointer]=='\0') {
              pointer=0;
              readCommand(rx_data);
              clearBuffer(rx_data,buff_size_rx);
        } else {
          pointer++;
          if(pointer>=buff_size_rx) {
              pointer=0;
          }
        }
    }
    /* USER CODE END USART1_IRQn 0 */
    HAL_UART_IRQHandler(&huart1);
    /* USER CODE BEGIN USART1_IRQn 1 */



  /* USER CODE END USART1_IRQn 1 */
}

what is the point of duplicating the buffer implementation? BTW you cant call HAL_UART_Receive_IT from here and then call HAL irq handler which calls it again. Do it bare registers or HAL not both. Anyway HAL for the simple peripheral like uart? — 0___________
What do you mean by dublicating the buffer implementation? I would like to achieve this in HAL, but I really found no solution yet. DMA would be nice, but there I need a fixed length for each command or use a timeout, which is not supported by HAL for an STM32F303K8T6. — HansPeterLoft
Hal does it. You should not do anything with the buffet if you use hal. I would implement it bare resister myself but it is your code, without this silly library. How long your messages are? If short there is no point of DMA. — 0___________
Well the messages are only around 16 characters. If I use just HAL_UART_Receive_IT, it will write the characters to the rx_data buffer, but I then never see if I received a null character and it acts like a ring buffer, which only works for a fixed length. — HansPeterLoft
Have a look at the code I use to receive arbitrary GPS data here. It uses HAL but shortcuts the interrupt. If I were to do it again I would dump HAL and go with plain CMSIS. — Paulo Soares

followed Monica to Codidact followed Monica to Codidact · Accepted Answer · 2017-09-13T14:29:33

HAL_UART_Receive_IT() is not meant to be called from an interrupt handler that way, but to initiate receiving a fixed number of bytes via interrupt.

A possible workaround is to check your input buffer after HAL_UART_IRQHandler() completes, i.e. in the /* USER CODE BEGIN USART1_IRQn 1 */ section. When a command is processed, you can reset pRxBuffPtr and RxXferCount in the handle structure to their original values to start from the start of the buffer again.

Another ~~horrible~~ possible workaround would be to call HAL_UART_Receive_IT() with a buffer size of 1, and set up a HAL_UART_RxCpltCallback() handler that checks the received byte each time, and calls HAL_UART_Receive_IT() again when necessary.

Of course you could do it without HAL, as PeterJ and others (always) suggest.

You've already implemented pin and interrupt setup, leave them unchanged at first.
Calculate the UART->BRR value according to the reference manual, or copy the relevant code from hal.
set UART->CR1=USART_CR1_RE|USART_CR1_TE|USART_CR1_UE|USART_CR1_RXNEIE; Now, you are getting interrupts.
In the interrupt function, read UART->SR into a temporary variable, and examine it.
Read UART->DR when there is a received byte waiting, do the error handling otherwise (later).
Get rid of the rest of the HAL calls when the above is working.

Interrupt response and processing time is often critical in embedded applications, and the HAL just wastes a lot of that.

STM32 HAL USART receive by interrupt

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