Can I configure STM32L0 to wake up from Standy Mode Every 15 minutes with RTC?

[Bruno Sena]

I'm using LSI clock, I just have ALRMA for:

1second

1 minute

1 hour.

I woul like to configure it for every 15 second, every 15 minutes.

Thanks

[waclawek.jan · Accepted solution]

You'd need to reconfigure the alarm at each wakeup. For example, to wake up every 15 seconds, you'd have unmasked the seconds (and masked the minutes etc. fields); and then upon each wakeup write to the seconds fields the next time of wakeup, in the 00-15-30-45 sequence.

If you need regular wakeup, maybe it's more efficient to use the wakeup timer (RTC_WUTR).

JW

[Bruno Sena]

Sorry about the time to answer.

I used the wakeup timer, and this works fine for my application.

Bruno Sena

[IEEE]

@Bruno Sena​ 

How did you configure the wakeup timer?

I am trying it with CUBEMX. -> In the STM32F44_en.DM00135183.pdf under section 22.3.4 "Periodic auto-wakeup"

I found:

The wakeup timer clock input can be:

• RTC clock (RTCCLK) divided by 2, 4, 8, or 16.

When RTCCLK is LSE(32.768 kHz), this allows to configure the wakeup interrupt

period from 122 μs to 32 s, with a resolution down to 61μs.

• ck_spre (usually 1 Hz internal clock)

When ck_spre frequency is 1Hz, this allows to achieve a wakeup time from 1 s to

around 36 hours with one-second resolution. This large programmable time range is

divided in 2 parts:

– from 1s to 18 hours when WUCKSEL [2:1] = 10

– and from around 18h to 36h when WUCKSEL[2:1] = 11. In this last case 216 is

added to the 16-bit counter current value.When the initialization sequence is complete (see Programming the wakeup timer), the timer starts counting

down.When the wakeup function is enabled, the down-counting remains active in

low power modes. In addition, when it reaches 0, the WUTF flag is set in the

RTC_ISR register, and the wakeup counter is automatically reloaded with its

reload value (RTC_WUTR register value).

-> programming the wakeup timer:

The following sequence is required to configure or change the wakeup timer auto-reload

value (WUT[15:0] in RTC_WUTR):

1. Clear WUTE in RTC_CR to disable the wakeup timer.

2. Poll WUTWF until it is set in RTC_ISR to make sure the access to wakeup auto-reload

counter and to WUCKSEL[2:0] bits is allowed. It takes 1 to 2 RTCCLK clock cycles

(due to clock synchronization).

3. Program the wakeup auto-reload value WUT[15:0] and the wakeup clock selection

(WUCKSEL[2:0] bits in RTC_CR).Set WUTE in RTC_CR to enable the timer again.

The wakeup timer restarts down-counting. Due to clock synchronization, the WUTWF

bit is cleared up to 2 RTCCLK clocks cycles after WUTE is cleared.

Lets say for every 15 min?

Beste Regards

Ibrahim Evren

[IEEE]

(respond before)

• ck_spre (usually 1 Hz internal clock)

When ck_spre frequency is 1Hz, this allows to achieve a wakeup time from 1 s to

around 36 hours with one-second resolution.

I have configured the wakeup Timer with CubeMx:

For 3 Seconds:

In the main.c File I added and using the Wakeup-Callback function: