RTC system doesn't work with LSI clock source

[george-metasphere]

When "Activating clock source" is ticked in RTC module, my MCU doesn't start up if I reset it from RST button. But as soon as I switch the RCC clock source to LSE external 32.768khz crystal and change RTC Clock Mux to LSE, it works without a hitch. Is this by design or there may be a bug?

[KDJEM.1]

Hello @george-metasphere ;

Could you please give more details about your configuration and project?

Are you testing a STM32CubeU3 firmware example? 

I tested the RTC_ALARM example in the STM32CubeU3 firmware. In this example the RTC work with LSI.

After I click on RESET button, I can see that LD2 is turned ON. So, the RTC Alarm is generated correctly.

Thank you.

Kaouthar

[george-metasphere]

OK, i found the problem. Apparently this has to be launched early on in the init phase for the system to work properly with reset:

HAL_PWR_EnableBkUpAccess();

There should be a disclaimer or CubeMX should automatically add this in.

[KDJEM.1]

Hello @george-metasphere ,

Thank you for bringing this issue to our attention. I reported it internally for checking.

Internal ticket number: 214838 (This is an internal tracking number and is not accessible or usable by customers).

Thank you.

Kaouthar

[george-metasphere]

Also, the following needs to be added at the RTC_Init phase:

  /* Enable Wakeup Pin */
  HAL_PWR_EnableWakeUpLine(PWR_WAKEUP_LINE7,PWR_WAKEUP_SELECT_3,PWR_WAKEUP_POLARITY_HIGH);

  /* Set Calendar Ultra-Low power mode */
  if (HAL_RTCEx_SetLowPowerCalib(&hrtc, RTC_LPCAL_SET) != HAL_OK)
  {
    Error_Handler();
  }