Controller resets when switching clock from 32MHz to 65kHz

[noobmaster69]

I am using STM32L031 for my project and since it is battery operated, I am planning to use Low Power Sleep mode for the same. And for that, I need clock below MSI range 1. So I chose to switch to 65kHz clock. But it gets stuck somewhere during clock configuration and because of watchdog, it resets the controller.

Any idea how to fix this issue?

here is my code to switch clock frequency and enter low power mode followed by clock_config functions:

  while (1)
  {
	  HAL_IWDG_Refresh(&hiwdg);
	  SystemClock_Config_65kHz();
          HAL_SuspendTick();
	  HAL_PWR_EnterSLEEPMode(PWR_LOWPOWERREGULATOR_ON, PWR_SLEEPENTRY_WFI);
	  SystemClock_Config_32MHz();
          HAL_ResumeTick();
  }

32MHz clock configuration function:

void SystemClock_Config_32MHz(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
  RCC_PeriphCLKInitTypeDef PeriphClkInit = {0};
 
  /** Configure the main internal regulator output voltage
  */
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);
 
  /** Configure LSE Drive Capability
  */
  HAL_PWR_EnableBkUpAccess();
  __HAL_RCC_LSEDRIVE_CONFIG(RCC_LSEDRIVE_LOW);
 
  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI|RCC_OSCILLATORTYPE_LSI
                              |RCC_OSCILLATORTYPE_LSE;
  RCC_OscInitStruct.LSEState = RCC_LSE_ON;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
  RCC_OscInitStruct.LSIState = RCC_LSI_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
  RCC_OscInitStruct.PLL.PLLMUL = RCC_PLLMUL_4;
  RCC_OscInitStruct.PLL.PLLDIV = RCC_PLLDIV_2;
  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_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
 
  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_1) != HAL_OK)
  {
    Error_Handler();
  }
  PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_LPUART1|RCC_PERIPHCLK_I2C1;
  PeriphClkInit.Lpuart1ClockSelection = RCC_LPUART1CLKSOURCE_LSE;
  PeriphClkInit.I2c1ClockSelection = RCC_I2C1CLKSOURCE_PCLK1;
  if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)
  {
    Error_Handler();
  }
  __HAL_RCC_PWR_CLK_SLEEP_DISABLE();
}

65kHz clock configuration function:

void SystemClock_Config_65kHz(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_SCALE1);
 
	  /** Configure LSE Drive Capability
	  */
	  HAL_PWR_EnableBkUpAccess();
	  __HAL_RCC_LSEDRIVE_CONFIG(RCC_LSEDRIVE_LOW);
 
	  /** Initializes the RCC Oscillators according to the specified parameters
	  * in the RCC_OscInitTypeDef structure.
	  */
	  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI|RCC_OSCILLATORTYPE_LSI
	                              |RCC_OSCILLATORTYPE_LSE|RCC_OSCILLATORTYPE_MSI;
	  RCC_OscInitStruct.LSEState = RCC_LSE_ON;
	  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
	  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
	  RCC_OscInitStruct.LSIState = RCC_LSI_ON;
	  RCC_OscInitStruct.MSIState = RCC_MSI_ON;
	  RCC_OscInitStruct.MSICalibrationValue = 0;
	  RCC_OscInitStruct.MSIClockRange = RCC_MSIRANGE_0;
	  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_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_MSI;
	  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
	  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
	  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
 
	  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK)
	  {
	    Error_Handler();
	  }
	  __HAL_RCC_MSI_RANGE_CONFIG(RCC_MSIRANGE_0);
	  __HAL_RCC_PWR_CLK_SLEEP_DISABLE();
}

[Bubbles]

hi @Community member​ ,

it looks like you tried to disable the PLL while it was still supplying the system clock. When switching the clock like this, you must make sure that every intermediate step is correct. These default CubeMX SystemClock_config() are sufficient for initial configuration going from the default MSI clock, but they do not take into account every possible previous state.

I suggest to look at HAL_LL examples, their clock configuration functions are more detailed and you can make finer steps, including some intermediate value.

BR,

J

[noobmaster69]

Hi @JHOUD​ ,

What you said makes sense but I tried following example code(attached main.c file) from ST. This also resets the controller.

(I just added IWDG and LED to indicate if controller resets)

It doesnt even use PLL.

Regards,

noobmaster69

[Bubbles]

hi @Community member​ ,

sorry I don't have time to debug your code, but you can also check out the https://www.st.com/resource/en/data_brief/x-cube-ref-pm.pdf

It contains a L0 code which does a lot of clock switching.

BR,

J