UART loopback test receives only first character

[AADW]

Hi all,

I have an STM32L071VBT6 and want to test the UART functionality. I configured UART4 RX and TX and physically connected them to do a loopback test. 

I define 2 arrays to start with

/* USER CODE BEGIN PV */

uint8_t Send_buffer[] = "Gateway test";

uint8_t Rec_buffer[13];

/* USER CODE END PV */

I start by clearing the Rec_buffer array.

/* USER CODE BEGIN 2 */

  memset(Rec_buffer, 0, sizeof(Rec_buffer));

  /* USER CODE END 2 */

Then in my while loop I try to send and receive, but I always just receive the first character ('G' in this case in Rec_buffer[0])

 while (1)

  {

    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */

      // UART TRANSMIT/RECEIVE TEST CODE

      HAL_UART_Transmit(&huart4, Send_buffer, strlen((char*)Send_buffer), 100);

      HAL_UART_Receive(&huart4, Rec_buffer, strlen((char*)Send_buffer), 100);

      HAL_Delay(1000);

  }

  /* USER CODE END 3 */

Anyone knows why I manage to receive only a single character each time?

Thanks!!

[TDK · Accepted solution]

There is no automatic buffer. You need to be ready to receive when characters come in, not after.

That means you need to use a non-blocking receive call.

HAL_UART_Receive_IT or HAL_UART_Receive_DMA with appropriate data handling. Called before characters are transmitted.

[AADW]

Yes perfect thanks!

[TDK]

Are interrupts enabled and set up?

There's nothing wrong with the code you presented. Issue is elsewhere.