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STM32F7 bootloader usart comm

Question asked by Barta.Hank on Jan 31, 2017
Latest reply on Jan 31, 2017 by Barta.Hank

Hi All,

I'm working with a board with two STM32F7 processors and trying to connector to the built in bootloader on one from the other via USART. The TX/RX lines are connected to the target on USART3 and on the master on USART4. I'm using the following code to configure the  USART4 on the master (8E1, no handshaking.)


/* UART4 init function */
static void MX_UART4_Init(void)

  huart4.Instance = UART4;
  huart4.Init.BaudRate = 19200;
  huart4.Init.WordLength = UART_WORDLENGTH_8B;
  huart4.Init.StopBits = UART_STOPBITS_1;
  huart4.Init.Parity = UART_PARITY_EVEN;
  huart4.Init.Mode = UART_MODE_TX_RX;
  huart4.Init.HwFlowCtl = UART_HWCONTROL_NONE;
  huart4.Init.OverSampling = UART_OVERSAMPLING_16;
  huart4.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
  huart4.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
  if (HAL_UART_Init(&huart4) != HAL_OK)



The code to establish communication between boards is:

// First set the BOOTA pin high and then drive the RST pin
vTaskDelay(pdMS_TO_TICKS(10)); // hold for 10 ms
vTaskDelay(1); // hold for shortest FreeRTOS delay

// Proc A should be in built in bootloader mode.
// establish contact by sending 0x7F until the device responds.
uartBuf[0] = 0x7F;
do {
  if(loopCount >= BUFFER_LEN)
  st = HAL_UART_Transmit(&PROC_A_UART, uartBuf, 1, 1);
  if(st == HAL_TIMEOUT)
  if(st != HAL_OK)
  vTaskDelay(pdMS_TO_TICKS(1)); // delay 1 ms
  st = HAL_UART_Receive(&PROC_A_UART, uartBuf+loopCount, 1, 1);
  if(!(st == HAL_OK || st == HAL_TIMEOUT))
  vTaskDelay(pdMS_TO_TICKS(1)); // delay 1 ms
  if(uartBuf[loopCount] != 0)
// } while(uartBuf[loopCount] != 0x79);
  } while(uartBuf[loopCount] != 0x7F);

// Get command
uartBuf[0] = 0x00;
uartBuf[1] = 0xFF; // checksum
st = HAL_UART_Transmit(&PROC_A_UART, uartBuf, 2, 1);
if(st != HAL_OK)


Depending on baud rates I seem to be able to read something back from time to time but I have yet to see an ACK (0x79). With the present setup I do see 0x73 on the 17th read and 0xF7 on the 18th read. If I exit the loop when a 0xF7 is received and try to send the Get command, I get a HAL timeout.


I have add some delay between send and receive to allow the target time to configure the UART once the baud rate is determined and also time to send out the reply. Two questions I have include:

  1. What should I try differently to get proper baud rate detection? 
  2. How can I get a HAL_TIMEOUT return status when a UART is configured with no handshaking?


Apologies if the code is not correctly formatted above. I can't seem to get the "Source Code" button to work as expected and I can't find a way to preview the post.