STM32H5 RTC count through power cycles

[jreina]

What is the expected RTC peripheral behavior through power cycles on VDD? We have a 3.3V system design with the STM32H562VGT6 right now.

Setup:

• VDD = 3.3V from external supply
• VBAT = 220mF supercap attached
• RTC is enabled & counting, system is stable
• LSE oscillation is active on the PC14/15 lines

Action:

1. VDD = 0V for 1-2 sec (unplugged PSU)
2. VDD = 3.3V restored (reconnected PSU)

Expected Behavior Through Power-Cycle:

• RTC count maintains operation & counting (count increases)
• LSE signal is oscillating at PC14/15 lines

Observed:

• RTC count freezes when power is removed & resumes counting when power is restored

Is this expected? Is it possible to keep the RTC counter active & counting through power cycles?

[STOne-32]

Dear @jreina ,

This is not expected and is strange behavior , VBAT mode is used exactly for such use cases where we loose main VDD and keep the RTC counting and LSE Oscillation stable . To debug this case, we need to see schematics of power supplies including VBAT , try to monitor the PC13 output of the LSE/Div and see what happens using an oscilloscope probes while probing the VDD supply and PC13 output. As well as the Firmware sequence.

Hope it helps you .

STOne-32

[Justin1]

Thank you for the quick response STOne-32!

back shortly

[jreina]

Hi STOne-32, here is our problem in further detail. - 

Target:

• RTC for continuous operation & counts through Vdd power cycles

Circuit:

Source:

/**
  * @brief  The application entry point.
  * @retval int
  */
int main(void)
{
	...
	
	HAL_Init();

	...
	
	SystemClock_Config();
	
	...
	
	MX_RTC_Init();

	... 
	
	os/freertos init & start
	
	...
	
	for(;;);
}
	

/**
  * @brief System Clock Configuration
  * @retval None
  */
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /** Configure the main internal regulator output voltage
  */
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE3);

  while(!__HAL_PWR_GET_FLAG(PWR_FLAG_VOSRDY)) {}

  /** Configure LSE Drive Capability
  */
  HAL_PWR_EnableBkUpAccess();
  //__HAL_RCC_LSEDRIVE_CONFIG(RCC_LSEDRIVE_LOW);
  __HAL_RCC_LSEDRIVE_CONFIG(RCC_LSEDRIVE_HIGH);

  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI48|RCC_OSCILLATORTYPE_HSI
									|RCC_OSCILLATORTYPE_LSI|RCC_OSCILLATORTYPE_LSE;
  RCC_OscInitStruct.LSEState = RCC_LSE_ON;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.HSIDiv = RCC_HSI_DIV2;
  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
  RCC_OscInitStruct.LSIState = RCC_LSI_ON;
  RCC_OscInitStruct.HSI48State = RCC_HSI48_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
	Error_Handler();
  }

  /** Initializes the CPU, AHB and APB buses clocks
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
							  |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2
							  |RCC_CLOCKTYPE_PCLK3;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB3CLKDivider = RCC_HCLK_DIV1;

  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_1) != HAL_OK)
  {
	Error_Handler();
  }
}


/**
  * @brief RTC Initialization Function
  *  None
  * @retval None
  */
static void MX_RTC_Init(void)
{
	RTC_PrivilegeStateTypeDef privilegeState = {0};

	/** Initialize RTC Only
	*/
	hrtc.Instance = RTC;
	hrtc.Init.HourFormat = RTC_HOURFORMAT_24;
	hrtc.Init.AsynchPrediv = 127;
	hrtc.Init.SynchPrediv = 255;
	hrtc.Init.OutPut = RTC_OUTPUT_DISABLE;
	hrtc.Init.OutPutRemap = RTC_OUTPUT_REMAP_NONE;
	hrtc.Init.OutPutPolarity = RTC_OUTPUT_POLARITY_HIGH;
	hrtc.Init.OutPutType = RTC_OUTPUT_TYPE_OPENDRAIN;
	hrtc.Init.OutPutPullUp = RTC_OUTPUT_PULLUP_NONE;
	hrtc.Init.BinMode = RTC_BINARY_NONE;

	if (HAL_RTC_Init(&hrtc) != HAL_OK)
	{
		Error_Handler();
	}

	privilegeState.rtcPrivilegeFull = RTC_PRIVILEGE_FULL_NO;
	privilegeState.backupRegisterPrivZone = RTC_PRIVILEGE_BKUP_ZONE_NONE;
	privilegeState.backupRegisterStartZone2 = RTC_BKP_DR0;
	privilegeState.backupRegisterStartZone3 = RTC_BKP_DR0;

	if (HAL_RTCEx_PrivilegeModeSet(&hrtc, &privilegeState) != HAL_OK)
	{
		Error_Handler();
	}

	return;
}

Test:

1. Power is applied (Vdd=3.3V) and the system stabilizes
2. Power is removed (Vdd=0V) for 1 second
3. Power is applied (Vdd=3.3V)

Results:

1. RTC signal is visible for steps #1-3 above
2. RTC count starts at #1, halts unexpectedly for #2 and resumes at #3

Why is the RTC time count halting for #2 for us here? This is not expected

[STOne-32]

Dear @jreina 

thanks for the details . Just wanted to understand what means :

1. RTC signal is visible for steps #1-3 above ?

is it visible for all steps from 1 to 3 including 2?

if possible to activate the output on PC13 and monitor the LSE clock in continuous way ? As PC13 is powered by backup domain and we should see what happens . Is you can try to change and LSE drive level to low as well to debug further .

ST1

[Justin1]

Interesting! Back tomorrow, thank you

[unsigned_char_array]

I don't see an external charging circuit. Have you enabled internal charging in software?

Reference manual:

VBAT battery charging
When VDD is present, it is possible to charge the external battery on VBAT through an
internal resistance.
The VBAT charging is done either through a 5 or a 1.5 kΩ resistor, depending upon the
VBRS bit value in the PWR_BDCR register.
The battery charging is enabled by setting VBE bit in the PWR_BDCR register. It is
automatically disabled in V BAT mode

If you have enabled charging, what is the voltage on the VBAT pin?
RC-time constant if you use 1500Ohm and 0.22F is 330 seconds. I don't know what voltage the RTC needs so it could be even longer than this. I would use an external charging circuit (a diode with a series resistor should suffice).

[Justin1]

Interesting !! I am helping a teammate, with their solution including PCB & firmware I will check in the morning

Thank you guys. I had response to STOne-32 prepared at my desk, but another conversation carried long over and I did not get it submitted 

Back tomorrow!

[jreina]

I really appreciate your feedback and insight unsigned_char_array, thank you.

With the feedback from you and STOne-32, I was able to gather responses and test again, see attached.

Question Responses:

1. RTC signal is visible for steps #1-3 above
   1. Yes it is visible for #1-#3, on PC14/15
   2. #2?
2. PC13 is not exposed for this board.
   1. I do have a NUCLEO-H563ZI I can test LSE on PC13 with if useful
   2. There are other GPIO pins exposed for debug if useful
3. Firmware VBAT charging
   1. I am not sure what configuration my teammate is using; it will take some time for review to uncover
4. Test VBAT charging
   1. Now I am manually charging VBAT; see Procedure.StepOne of attached
5. VBAT voltage at pin: 3.28V (see Figure 2 of attached)

Code:

/**
  * @brief  The application entry point
  * @retval int
  */
int main(void) {

	///Locals
	//...

	//Init Vars
	//...


	//Init HAL
	HAL_Init();
	SystemClock_Config();

	//Init Periphs
	MX_RTC_Init();
	//...

	//Console Notice
	//...

	//Init OS
	osKernelInitialize();
	MX_FREERTOS_Init();

	//Start OS
	osKernelStart();

	//Loop
	for(;;);
}


/**
  * @brief System Clock Configuration
  * @retval None
  */
void SystemClock_Config(void) {

  //... provided on request

  return;
}


/**
  * @brief RTC Initialization Function
  *  None
  * @retval None
  */
static void MX_RTC_Init(void) {

  RTC_PrivilegeStateTypeDef privilegeState = {0};

  //Initialize RTC Only
  hrtc.Instance            = RTC;
  hrtc.Init.HourFormat     = RTC_HOURFORMAT_24;
  hrtc.Init.AsynchPrediv   = 127;
  hrtc.Init.SynchPrediv    = 255;
  hrtc.Init.OutPut         = RTC_OUTPUT_DISABLE;
  hrtc.Init.OutPutRemap    = RTC_OUTPUT_REMAP_NONE;
  hrtc.Init.OutPutPolarity = RTC_OUTPUT_POLARITY_HIGH;
  hrtc.Init.OutPutType     = RTC_OUTPUT_TYPE_OPENDRAIN;
  hrtc.Init.OutPutPullUp   = RTC_OUTPUT_PULLUP_NONE;
  hrtc.Init.BinMode        = RTC_BINARY_NONE;

  if(HAL_OK != HAL_RTC_Init(&hrtc)) {
    Error_Handler();
  }

  privilegeState.rtcPrivilegeFull         = RTC_PRIVILEGE_FULL_NO;
  privilegeState.backupRegisterPrivZone   = RTC_PRIVILEGE_BKUP_ZONE_NONE;
  privilegeState.backupRegisterStartZone2 = RTC_BKP_DR0;
  privilegeState.backupRegisterStartZone3 = RTC_BKP_DR0;

  if(HAL_OK != HAL_RTCEx_PrivilegeModeSet(&hrtc, &privilegeState)) {
    Error_Handler();
  }

  return;
}

I did some research into RC charging dynamics with our circuit, and appreciated the feedback there thank you unsigned_char_array

I will try to activate the output on PC13 and monitor the LSE clock in continuous way; posting an updated report next. With the current configuration in code above and results below, if you see any feedback let me know! Back soon, thank you guys

[jreina]

How do you output the LSE or RTC clock to PC13? Do you have any recommendations?

RTC.OUT2?

• Is RTC_OR.OUT2_RMP a consideration for RTC clock routing to PB2? I can rework a jumper to the chip pin directly if useful

Question:

• How do you observe one of these clocks exposed to a pin?