[stm32u585] wakeup failed from standby mode, "Wait till LSI is disabled" timeout in HAL_RCC_OscConfig()

[lll]

hello,

I encountered a problem while developing for stm32u585. When the stm32 wakes up from standby mode, the HAL_RCC_OscConfig() function occasionally fails, "Wait till LSI is disabled" timeout in HAL_RCC_OscConfig() (this project uses IWDG)
The specific process is as follows:

1. start boot
    HAL_Init();
    SystemClock_Config();
    MX_GPIO_Init();
    MX_ICACHE_Init();
    MX_UART4_Init();
    boot to other address(app)
2. app init
    HAL_Init();
    SystemClock_Config();
          RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI48|RCC_OSCILLATORTYPE_LSI
                              |RCC_OSCILLATORTYPE_HSE|RCC_OSCILLATORTYPE_LSE;
          RCC_OscInitStruct.HSEState = RCC_HSE_ON;
          RCC_OscInitStruct.LSEState = RCC_LSE_ON_RTC_ONLY;
          RCC_OscInitStruct.HSI48State = RCC_HSI48_ON;
          RCC_OscInitStruct.LSIState = RCC_LSI_ON;
          RCC_OscInitStruct.LSIDiv = RCC_LSI_DIV128;
          RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
          RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
          RCC_OscInitStruct.PLL.PLLMBOOST = RCC_PLLMBOOST_DIV1;
          RCC_OscInitStruct.PLL.PLLM = 1;
          RCC_OscInitStruct.PLL.PLLN = 40;
          RCC_OscInitStruct.PLL.PLLP = 2;
          RCC_OscInitStruct.PLL.PLLQ = 2;
          RCC_OscInitStruct.PLL.PLLR = 2;
          RCC_OscInitStruct.PLL.PLLRGE = RCC_PLLVCIRANGE_1;
          RCC_OscInitStruct.PLL.PLLFRACN = 0;
          if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
          {
            Error_Handler();
          }
3. timeout in HAL_RCC_OscConfig()
        /* Turn off LSI before changing RCC_BDCR_LSIPREDIV */
        if ((bdcr_temp & RCC_BDCR_LSION) == RCC_BDCR_LSION)
        {
          __HAL_RCC_LSI_DISABLE();

          tickstart = HAL_GetTick();

          /* Wait till LSI is disabled */
          while (READ_BIT(RCC->BDCR, RCC_BDCR_LSIRDY) != 0U)
          {
            if ((HAL_GetTick() - tickstart) > LSI_TIMEOUT_VALUE)
            {
              return HAL_TIMEOUT;
            }
          }
        }

How to solve this problem

[Saket_Om · Accepted solution]

Hello @lll 

The LSI should only be initialized once at power-on reset (POR). Re-initializing or reconfiguring the LSI after each wake-up from standby can cause issues, as the oscillator may already be in use by IWDG, and the LSIRDY flag may not behave as expected.

[lll]

Does this mean I have to modify HAL_RCC_OscConfig() ?

I have added this condition in HAL_RCC_OscConfig():

__HAL_PWR_GET_FLAG(PWR_FLAG_SBF)

Can it ensure that this startup is from standby wake-up

/*------------------------------ LSI Configuration -------------------------*/
  if ((((pRCC_OscInitStruct->OscillatorType) & RCC_OSCILLATORTYPE_LSI) == RCC_OSCILLATORTYPE_LSI)
      && __HAL_PWR_GET_FLAG(PWR_FLAG_SBF))

[lll]

or modify SystemClock_Config()

  if (__HAL_PWR_GET_FLAG(PWR_FLAG_SBF))
    RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI48
                                |RCC_OSCILLATORTYPE_HSE|RCC_OSCILLATORTYPE_LSE;
  else
    RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI48|RCC_OSCILLATORTYPE_LSI
                                |RCC_OSCILLATORTYPE_HSE|RCC_OSCILLATORTYPE_LSE;

[Saket_Om]

Hello @lll 

In your own SystemClock_Config(), do not request LSI/LSIDiv changes when IWDG might already be running.
That way, HAL_RCC_OscConfig() never enters the “disable LSI” branch, so no timeout.