STM32F205RG RTC Problem.

[Nimit Vachhani]

Greetings,

I have connected external crystal of 32.768 KHz to STM32F205RG for RTC time keeping purpose. I have also enabled RTC output on pin PC13. Below is my code for RTC Initialization ...

int main(void)
{
  /* USER CODE BEGIN 1 */

  /* USER CODE END 1 */

  /* MCU Configuration--------------------------------------------------------*/

  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();

  /* USER CODE BEGIN Init */

  /* USER CODE END Init */

  /* Configure the system clock */
  SystemClock_Config();

  /* USER CODE BEGIN SysInit */

  /* USER CODE END SysInit */

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_RTC_Init();
			
  if (HAL_RTCEx_BKUPRead(&hrtc, RTC_BKP_DR1) != 0x32F2)
  {
    /* Configure RTC Calendar */
    RTC_CalendarConfig();
  }
  else
  {
    /* Check if the Power On Reset flag is set */
    if (__HAL_RCC_GET_FLAG(RCC_FLAG_PORRST) != RESET)
    {
    }
    /* Check if Pin Reset flag is set */
    if (__HAL_RCC_GET_FLAG(RCC_FLAG_PINRST) != RESET)
    {
    }
    /* Clear source Reset Flag */
    __HAL_RCC_CLEAR_RESET_FLAGS();
  }

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
		RTC_CalendarShow(aShowTime, aShowDate);
		if(_set)
		{
			RTC_CalendarConfig();
			_set = 0;
		}
  }
  /* USER CODE END 3 */
}

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This is the main code and code for RTC_CalendarShow and RTC_CalendarConfig is as below

static void RTC_CalendarConfig(void)
{  
  if(HAL_RTC_SetDate(&hrtc,&sDate,RTC_FORMAT_BCD) != HAL_OK)
  {
    /* Initialization Error */
    Error_Handler();
  }
	
  if (HAL_RTC_SetTime(&hrtc, &sTime, RTC_FORMAT_BCD) != HAL_OK)
  {
    /* Initialization Error */
    Error_Handler();
  }

  /*##-3- Writes a data in a RTC Backup data Register1 #######################*/
  HAL_RTCEx_BKUPWrite(&hrtc, RTC_BKP_DR1, 0x32F2);
}
static void RTC_CalendarShow(uint8_t *showtime, uint8_t *showdate)
{
  RTC_DateTypeDef sdatestructureget;
  RTC_TimeTypeDef stimestructureget;
	
  /* Get the RTC current Time */
  HAL_RTC_GetTime(&hrtc, &stimestructureget, RTC_FORMAT_BIN);
  /* Get the RTC current Date */
  HAL_RTC_GetDate(&hrtc, &sdatestructureget, RTC_FORMAT_BIN);
  /* Display time Format : hh:mm:ss */
  sprintf((char *)showtime, "%2d:%2d:%2d", stimestructureget.Hours, stimestructureget.Minutes, stimestructureget.Seconds);
  /* Display date Format : mm-dd-yy */
  sprintf((char *)showdate, "%2d-%2d-%2d", sdatestructureget.Date, sdatestructureget.Month, 2000 + sdatestructureget.Year);
}

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The problem is after like 4 hours of run rtc is ahead approx 2 seconds or more. How to solve this problem ? 

The calibration output on pin PC13 gives me perfect 512 Hz wave as i have verified on oscilloscope. The same code is running prefectly fine on NUCLEO-F207ZG board.

[Tesla DeLorean]

Sorry didn't see any initialization code, need to have different prescalers for LSI vs LSE.

Need to use 6-7pF crystals on the F2

[Nimit Vachhani]

Greetings Tesla,

I have used cube for code initialization. I am attaching the screen shots of the cube for better understanding.