UART hal RX interrupt modification

[Manojkumar Subramaniam]

My scenario I have a master controller keep sending 30Bytes of data with every 500ms..

Issue when use to my slave controller is :

HAL_UART_Receive_IT(&huart1, varPtr, 20);

the packet might not be received properly as the slave is hot swapped.. it can be listening while the transmission going... so that HAL function get's crazy as it's using some pointer increment... So i was looking for a way for sync the start, my master always start with sending a char 'H' so in someway i have to keep the counter resetting to start point when first byte is not 'H'..

I did this hack it only works once why ? my hack start from line 34 to 45

static HAL_StatusTypeDef UART_Receive_IT(UART_HandleTypeDef *huart)
{
  uint16_t* tmp;
  
  /* Check that a Rx process is ongoing */
  if(huart->RxState == HAL_UART_STATE_BUSY_RX) 
  {
    if(huart->Init.WordLength == UART_WORDLENGTH_9B)
    {
      tmp = (uint16_t*) huart->pRxBuffPtr;
      if(huart->Init.Parity == UART_PARITY_NONE)
      {
        *tmp = (uint16_t)(huart->Instance->DR & (uint16_t)0x01FF);
        huart->pRxBuffPtr += 2U;
      }
      else
      {
        *tmp = (uint16_t)(huart->Instance->DR & (uint16_t)0x00FF);
        //if the pRx
        if( (huart->pRxBuffPtr == varPtr) && ( (uint8_t)(huart->Instance->DR & 0xFF) != 'H'  ) )
        {
        	huart->pRxBuffPtr = varPtr;
        }
        else
        {
        huart->pRxBuffPtr += 1U;
        }
      }
    }
    else
    {
      if(huart->Init.Parity == UART_PARITY_NONE)
      {
    	 // *tmp = (uint8_t)(huart->Instance->DR & (uint8_t)0x00FF);
    	  if( (huart->pRxBuffPtr == varPtr) && ( (uint8_t)(huart->Instance->DR & 0xFF) != 'H'  ) )
    	          {
 
    	          	huart->pRxBuffPtr = varPtr;
    	          	*huart->pRxBuffPtr = 'F';
    	          }
    	          else
    	          {
    	          //huart->pRxBuffPtr += 1U;
    	          *huart->pRxBuffPtr++ = (uint8_t)(huart->Instance->DR & (uint8_t)0x00FF);
    	          }
 
 
      }
      else
      {
        *huart->pRxBuffPtr++ = (uint8_t)(huart->Instance->DR & (uint8_t)0x007F);
      }
    }
 
    if(--huart->RxXferCount == 0U)
    {
      /* Disable the UART Parity Error Interrupt and RXNE interrupt*/
      CLEAR_BIT(huart->Instance->CR1, (USART_CR1_RXNEIE | USART_CR1_PEIE));
 
      /* Disable the UART Error Interrupt: (Frame error, noise error, overrun error) */
      CLEAR_BIT(huart->Instance->CR3, USART_CR3_EIE);
 
      /* Rx process is completed, restore huart->RxState to Ready */
      huart->RxState = HAL_UART_STATE_READY;
     
      HAL_UART_RxCpltCallback(huart);
 
      return HAL_OK;
    }
    return HAL_OK;
  }
  else
  {
    return HAL_BUSY;
  }
}

[Tesla DeLorean]

uint16_t* tmp;

...

*tmp = (uint16_t)(huart->Instance->DR & (uint16_t)0x00FF);

Should probably make sure the code path that gets you there actually initializes the pointer.

[S.Ma]

Make sure in the code that the pointer never exceed a max value or it may go out of bound. It is also assumed that H won't occur within a valid data stream.

[Manojkumar Subramaniam]

fixed check again... 🙂

[Manojkumar Subramaniam]

see updated edited the code but still not working..

[After Forever]

  if( (huart->pRxBuffPtr == varPtr) && ( (uint8_t)(huart->Instance->DR & 0xFF) != 'H'  ) )
  {
    huart->pRxBuffPtr = varPtr;
    *huart->pRxBuffPtr = 'F';
  }
  else
  {
    *huart->pRxBuffPtr++ = (uint8_t)(huart->Instance->DR & (uint8_t)0x00FF);
  }

I don't get it, if you are checking in the if that "huart->pRxBuffPtr == varPtr" then why are you doing "huart->pRxBuffPtr = varPtr;"? Either the check is unnecessary/mistake, or the assignment.

[Tesla DeLorean]

No, still wrong. Would also recommend not editing the top post as it damages thread integrity and context of answers/responses.

Couldn't you have just initialized the pointer properly?

Reading DR multiple times is not going to result in the correct response.

[Tesla DeLorean]

Reading the DR twice will also be problematic

Does the pointer need to advance in 'F' case?

Unsure of the logic involved here

{
      uint8_t data = (uint8_t)(huart->Instance->DR & 0xFF) ; // Read once
      if( (huart->pRxBuffPtr == varPtr) && (data != 'H'  ) ) // correct comparison?
      {
        huart->pRxBuffPtr = varPtr;
        *huart->pRxBuffPtr = 'F'; // Should pointer advance?
      }
      else
      {
        *huart->pRxBuffPtr++ =data;
      }
}

[Manojkumar Subramaniam]

the reason i did that was because my header frame packet starts with 'H' and varPtr checking to see if it's still at first byte... ideally the first byte should be 'H' if it's not don't allow the pointer to increment and write F to varPtr[0]; to indicate Failed

[S.Ma]

I would recommend to change the message formatting to follow the universally known text terminal mode and searching for "\n" as termination character. When doing something quite well used, it's easier to find others helping in the details or on the web.