rtc.isTimeSet() returns true if RTC backup registers are used even if time was not set

[ndoo]

Describe the bug
rtc.isTimeSet() returns true if RTC backup registers are used even if time was not set.

I suspect the re-entrant/reinit check needs to be tightened up.

To Reproduce

1. HAL_PWR_EnableBkUpAccess();
2. HAL_RTCEx_BKUPWrite(rtc.getHandle(), 0, 0xFFFF);
3. rtc.isTimeSet() returns true after this

Expected behavior
rtc.isTimeSet() should return false

Screenshots

Desktop (please complete the following information):

• STM32 core version: 2.12.0
• Library version: 1.8.0
• Tools menu settings if not the default: -
• Upload method: USB DFU

Hardware (please complete the following information):

• Board Name: Custom STM32U073CC
• Hardware Revision: -
• Extra hardware used if any: -

Additional context
Add any other context about the problem here.

We are using RTC backup registers to store stateful information.

[fpistm]

Hi @ndoo
I have no issue with a Nucleo U083RC

void setup()
{
  Serial.begin(9600);
  //rtc.begin(); // initialize RTC 24H format

  HAL_PWR_EnableBkUpAccess();
  HAL_RTCEx_BKUPWrite(rtc.getHandle(), 0, 0xFFFF);

  if (rtc.isTimeSet()) {
    Serial.println("Time is set");
  } else {
    Serial.println("Time is NOT set");
  }
}

When rtc begin is not call time is not set. Else time is set and it is correct.
I suspect your custom board have a battery on vbat so when rtc is initialised it is kept initialised?

[ndoo]

On my board, all voltage pins are tied together. Perhaps the stray capacitance buffering various pins is enough to keep the RTC running. Let me check tomorrow whether grounding VDD clears this condition.

[fpistm]

OK. Thanks for the feedback. As I'm unable to reproduce and looking how _timeset is managed I don't see any issue.