HAL_RTCEx_DeactivateWakeUpTimer returns HAL_RTC_STATE_TIMEOUT

[markH]

I am using STM32L0 with LSE rtc xtal, CubeMX/HAL. I have a 20 second wakup using

if (HAL_RTCEx_SetWakeUpTimer_IT(&hrtc, 40960, RTC_WAKEUPCLOCK_RTCCLK_DIV16) != HAL_OK)
{
  Error_Handler();
}

AND

HAL_SuspendTick();
HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
HAL_ResumeTick();

this works ok as long as I don't use //HAL_PWR_DisableBkUpAccess(); or it never enters stop mode

now I use HAL_PWR_EnterSTANDBYMode(); to shutdown the device but it wakes 20 seconds later.

so I tried adding

if (HAL_RTCEx_DeactivateWakeUpTimer(&hrtc) != HAL_OK)
{									
 ErrorHandler(ERR_ALARM_DEACT);
}

 but the call returns HAL_RTC_STATE_TIMEOUT

Any ideas?

[markH · Accepted solution]

OK as none has commented here I will fill in the solution, it looks like I was calling

HAL_PWR_DisableBkUpAccess();

in another place I did not realise and this was stopping

(HAL_RTCEx_DeactivateWakeUpTimer(&hrtc) != HAL_OK)

from completing without error.

I find it strange that wakeup timer is dependant on backup register access being disabled, I would not expect this behavior and no note in the function header to inform users this is so.

"@note  Ensure HAL_PWR_EnableBkUpAccess is called before this function" would be helpful.