how to designate wakeup msec by HAL_RTCEx_SetWakeUpTimer()

[curiae]

Hello,

Now I mean to generate periodic wake-up by HAL_RTCEx_SetWakeUpTimer().

But I'm not sure about arguments WakeUpCounter and WakeUpClock.

For realize 50msec wake-up what value should be set to  WakeUpCounter and which RTCCLK_DIV should be selected.

Thanks

[Saket_Om · Accepted solution]

Hello @curiae 

To generate a periodic wake-up using HAL_RTCEx_SetWakeUpTimer() for a 50ms interval, you need to set the WakeUpCounter and WakeUpClock arguments appropriately.

WakeUpClock: This parameter determines the clock source for the wake-up timer. The available options are typically:

• RTC_WAKEUPCLOCK_RTCCLK_DIV16
• RTC_WAKEUPCLOCK_RTCCLK_DIV8
• RTC_WAKEUPCLOCK_RTCCLK_DIV4
• RTC_WAKEUPCLOCK_RTCCLK_DIV2
• RTC_WAKEUPCLOCK_CK_SPRE_16BITS
• RTC_WAKEUPCLOCK_CK_SPRE_17BITS

WakeUpCounter: This parameter sets the counter value for the wake-up timer. The counter value is calculated based on the desired wake-up interval and the selected clock source.

To achieve a 50ms wake-up interval, you need to calculate the appropriate counter value based on the selected clock source. For example, if you choose RTC_WAKEUPCLOCK_RTCCLK_DIV16, the calculation would be as follows:

Assume the RTCCLK is 32.768 kHz (LSE clock).

• The clock source after division by 16 would be 32.768 kHz / 16 = 2.048 kHz.
• The period of this clock source is 1 / 2.048 kHz = 0.48828125 ms.
• To achieve a 50ms interval, the counter value should be 50ms / 0.48828125ms ≈ 102.4.

Since the counter value must be an integer, you can round it to 102.