STM32U575 PWR_S3WU IRQ

[r-drage]

I am developing an application for the STM32U575, and am currently testing on the Nucleo-U575ZI-Q. As per the reference manual (Rev. 4) Section 10.9 PWR Interrupts, Table 110 Note 1: "The PWR_S3WU interrupt is generated only when the device is in Stop 3 mode (not applicable in Run, Sleep, Stop 0, Stop 1, and Stop 2 modes)."

However this is not the behaviour I am observing. I have found that the PWR_S3WU interrupt is generated whenever the Stop 3 mode is configured as the Deep Sleep Mode (i.e. PWR_CR1 LPMS[2:0] = 0b011), even if the stop mode is never entered.

Can I please get confirmation what behaviour I can expect, for the nucleo and my target hardware (STM32U575VIT6Q)

[Imen.D]

Hello @r-drage and welcome to the Community 🙂

This can be caused by the limitation detailed in the STM32U575 errata sheet.

2.2.14 The PWR_S3WU interrupt is generated for internal wakeup sources (WUSELx = 11)

[r-drage]

Hi Imen, thanks for your response and the welcome 😀

I had read that note in the errata and did not think it applied to my case - I should have specified but the WU selections I have made are external pins. (WUSELx != b11)

[Imen.D]

Hi @r-drage and Happy new year 🙂

We tried to reproduce your behavior, but we have found that the PWR_S3WU interrupt is generated only when the system is in STOP3 mode.

Can you please share your code to reproduce the observed behavior?

[r-drage]

Happy new year @Imen.D 😀

I have attached a basic example. It is a basic blinky app for the Nucleo u575 board that goes to Stop3 mode every 5 green LED blinks (10 seconds), and then can be woken up using the blue user button. The blue LED is set up to toggle with the PWR_S3WU interrupt.

After the first wake up, I see the blue LED toggle every time I press the button, but I am expecting it to only toggle waking up from Stop 3.

[Imen.D · Accepted solution]

Hi @r-drage,

It seems that the note below in the RefMan RM0456 is wrong:
1. The PWR_S3WU interrupt is generated only when the device is in Stop 3 mode (not applicable in Run, Sleep, Stop 0, Stop 1, and Stop 2 modes).

We are updating the note as below:
1. The PWR_S3WU interrupt is generated only when STOP3 mode is selected (LPMS=011 in PWR_CR1 register, not applicable in Run, Sleep, Stop 0, Stop 1, and Stop 2 modes)

As a SW workaround, you can push this activation only just before entering STOP3 mode.
Can you please try this change to your application and please keep me updated on this.

[r-drage]

Thanks Imen, this works. I'm glad to here the Ref Manual note will be updated 🙂

Thanks again