STM32U575 immediate wake from STOP2

[ficklesheep]

Hi everyone, 

I am relatively new to the U575 chips however I have had this working fine on an L4R9. I am trying to enter and exit STOP2 mode on the U575 Nucleo board, but I am experiencing immediate wake-up events. There are no pending interrupts in the NVIC_ISPR registers and nothing in the SCB_ICSR registers upon STOP2 entry however the system immediately wakes and shows SCB_ICSR = 0xf000.

I have Trustzone enabled and I am using Azure RTOS. I am calling... 

HAL_PWREx_EnterSTOP2Mode(PWR_STOPENTRY_WFI);

...from the secure side. I do not single step over this function as that is a known wakeup source, I have breakpoints sometime before and after.

Initial debugging had led me to the tick timers causing the wakeup events (TIM6 and TIM7 - moved due to Trustzone and RTOS), but again there appears to be no pending interrupts to be the obvious cause. Clearly, I am looking in the wrong spot.

Which registers are the go-to to sourcing low power mode wakeup causes? Could this be a Trustzone specific issue? I have been able to debug low power modes before with the L4R9, could this be a U5 debugger interaction issue?

I am struggling to find the issue let alone the solution so apologies if this is vague.

Any help would be appreciated!

[Andrew Neil]

HAL_SuspendTick() ?

[MM..1]

CubeIDE? 
1. Is debug in low power mode settings disabled or enabled ?

2. Best method to testing STOP is complete SWD disconnect power off and on. Place som led blink after stop or scope pin...

3. RTOS require suspend before stop...

[Gyessine]

Hello @ficklesheep 
I'm pretty sure that the issue is due to part of the project preventing the MCU from entering Stop mode correctly, especially because you are using an RTOS and, apparently, timers or other functions in interrupt mode.

The idea is to ensure that you disable everything that can generate an interrupt.

I recommend starting with what was suggested from the other users. Then, ensure that you use 

__disable_irq();

before entering Stop mode. Also, you can check LPMS register to ensure that MCU is really entering the correct low power mode.

Also, I recommend that you start with a simple example like this one to ensure that the issue is not hardware related, especially because you are using a custom PCB design.
BR
Gyessine