USART RX and TX issue

[Mani1]

I am using STM32F746G discovery board.

~~~

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart) {

   HAL_UART_Receive_IT (&huart6, Rx_buff, USART_RX_BUFFER_SIZE);

   HAL_Delay(500);

   HAL_UART_Transmit(&huart6, &Rx_buff, USART_RX_BUFFER_SIZE, 1000);

}

~~~

This is the way i am using USART6, TX and RX.

here my doubt is, i fixed my USART_RX_BUFFER_SIZE =10.

I send 10 bytes data via serial terminal(hercules), in this case my usart transmit also works with same 10 bytes data.

But i send 9 bytes data means, the uart transmit is not transmit the 9 bytes data.

my requirement is,

how much amount of bytes received via UART_Receive(); , that amount of bytes, send via UART_Transmit();

Thanks

Manikandan D

[Imen GH]

Hello,

I recommend you to have a look to the following articles:

https://community.st.com/s/article/STM32-UART-DMA-RX-TX

https://community.st.com/s/article/faq-stm32-hal-driver-api-and-callbacks

Imen 

[Tesla DeLorean]

You'd need to count the bytes. Perhaps there is an index in the uart instance structure, or you need to accumulate your own buffer one byte at a time.

You should not delay or call blocking functions in the call-back.

If you ask the function to receive 10 bytes before entering the call-back, 9 will not be sufficient.

Watch the definition of Rx_buff

[Mani1]

thanks @Community member​  this is very helpful

[TDK]

Use HAL_UARTEx_ReceiveToIdle or HAL_UARTEx_ReceiveToIdle_IT.

/**
 * @brief Receive an amount of data in blocking mode till either the expected number of data
 * is received or an IDLE event occurs.
 * @note HAL_OK is returned if reception is completed (expected number of data has been received)
 * or if reception is stopped after IDLE event (less than the expected number of data has been received)
 * In this case, RxLen output parameter indicates number of data available in reception buffer.
 * @note When UART parity is not enabled (PCE = 0), and Word Length is configured to 9 bits (M1-M0 = 01),
 * the received data is handled as a set of uint16_t. In this case, Size must indicate the number
 * of uint16_t available through pData.
 * @note When FIFO mode is enabled, the RXFNE flag is set as long as the RXFIFO
 * is not empty. Read operations from the RDR register are performed when
 * RXFNE flag is set. From hardware perspective, RXFNE flag and
 * RXNE are mapped on the same bit-field.
 * @param huart UART handle.
 * @param pData Pointer to data buffer (uint8_t or uint16_t data elements).
 * @param Size Amount of data elements (uint8_t or uint16_t) to be received.
 * @param RxLen Number of data elements finally received
 * (could be lower than Size, in case reception ends on IDLE event)
 * @param Timeout Timeout duration expressed in ms (covers the whole reception sequence).
 * @retval HAL status
 */
HAL_StatusTypeDef HAL_UARTEx_ReceiveToIdle(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size, uint16_t *RxLen,
 uint32_t Timeout)
{

[Mani1]

thanks @TDK​ 

[Mani1]

Hello,

I am facing another issue in UART_Receive_DMA();

USART_RX_BUFFER_SIZE = 10

void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart) {

  Rx_ok_flag=1;

  HAL_UART_Receive_DMA (&huart6, Rx_buff, USART_RX_BUFFER_SIZE);

}

I send 10 bytes of String "HIHELLOLCS" via Serial terminal(Hercules).

After sending this string , i read my Rx_buff. But my Rx_buff does not have 10 bytes of data. It's have only Three bytes.

After sending the data i am getting like this, i don't know what's happening.

Rx_buff [0] = 'H' Rx_buff [1] ='\000' Rx_buff [2] ='\000' Rx_buff [3] ='\000' Rx_buff [4] ='I' Rx_buff [5] ='\000' Rx_buff [6] ='\000' Rx_buff [7] ='\000' Rx_buff [8] ='H' Rx_buff [9] ='\000'

Thanks

Manikandan D

[Tesla DeLorean]

It might be helpful to provide a more complete perspective, these code snippets lack a lot in context.

For example you'd want this flag as a volatile variable, and you'd want to copy the data to a staging buffer because the DMA can overwrite the content of the active buffer at any time.

[TDK]

Are your DMA memory size and peripheral size both 1 byte?

[Mani1]

Hai,

how to know the DMA memory size.

This issue not only for DMA method. I tried with Interrupt method also. But i am getting same issue.

Thanks

Manikandan D

[Mani1]

Now my doubt is clear. Inside ISR function they are typecasting the Rx_buff.

like,

HAL_DMA_Start_IT(huart->hdmarx, (uint32_t)&huart->Instance->RDR, (uint32_t)huart->pRxBuffPtr, Size)

Because Function declaration of HAL_DMA_Start_IT is,

HAL_StatusTypeDef HAL_DMA_Start_IT(DMA_HandleTypeDef *hdma, uint32_t SrcAddress, uint32_t DstAddress, uint32_t DataLength);

Thanks for your replies :smiling_face_with_smiling_eyes: