stm32F4 RTC wake up from standby with ALARM_A and ALARM_B

[David Lichterov]

Posted on July 26, 2017 at 17:00

Hello all, 

I am trying to set 2 ALARMS that will wake up my MCU. I want to set ALARM A to wake up the MCU at time X and set ALARM B to wake up the MCU at time X+Y. When i set both of the ALARMS only the first ALARM works. I am able to get 2 alarms working if i set the first one and then after the MCU wakes up from standby i set the second one (in this case it works only if i set both of the ALARMS as ALARM A/ALARM B - doesnt work if i set it with ALARM A and after the wakeup as ALARM B). 

My question is is it possible to set ALARM A for time X and then set ALARM B for time X+Y and then wake up the MCU 2 times from standby mode, one time with the first ALARM and another time with the second ALARM ??

[Vangelis Fortounas]

Posted on July 26, 2017 at 22:01

Hello David!

What is your Hardware?

Provide us more details ..to try to help you.

[David Lichterov]

Posted on July 27, 2017 at 08:22

Hey , I am using STM32F446RE, what other details you would like ?. my question is it possible to do what i am trying to do ? and if so is there a good example for that ? 

Thanks !!

[Vangelis Fortounas]

Posted on July 27, 2017 at 11:58

Hello again!!

Look at this

https://my.st.com/content/ccc/resource/technical/document/errata_sheet/c3/6b/f8/32/fc/01/48/6e/DM00155929.pdf/files/DM00155929.pdf/jcr:content/translations/en.DM00155929.pdf

(Errata sheet) page 11

[David Lichterov]

Posted on July 27, 2017 at 15:23

Thanks for you answer it really helps me , but i am not sure how to preform the required steps.

The needed steps are : 

• 

Disable all used wakeup sources

• Clear all related wakeup flags

• Re-enable all used wakeup sources

• Enter Standby mode

I have couple of questions about the steps above : 

• I can disable all my wake-up sources(ALARM A and B), but how do i Re-enable them ? 
• What wakeup flags i should clear ?

Thank again !!