No wake up possibility after a discontinuity power supplies

[srain]

Hi,

Someone could help me, please?

When I remove battery on my system (NO VDD and NO Vbat on the MCU), and I connect it back, the system do not start!!!!

The only way to start the system is a NRST signal.

OR

Switch OFF and ON only the VDD power supply (VBAT still 1.8V).

What should be investigated ?

Thank's for any reply.

Stef

[Piranha]

Hardware problem. Look for respective "Getting started with STM32xx Series MCU hardware development" application note.

P.S. My crystal ball is at a repair shop, so I can't guess the MCU part number...

[srain]

Thanks for your answer.

The hardware used is quiet the same as Nucleo demo board (STM32l476RG).

The system goes in shutdown mode and restart properly on wakeup pin (PC13).

But if the system lost power (Batt too low) when power goes back, the wake up pin doesn't work !

In that case I need to do Hard reset by NRST signal or just turn OFF and ON VDD on the MCU.

Does the MCU need to follow an order power sequence (Vbat first and then VDD, VDDA ...) ?

Thx

Stef

[Piranha]

AN4555 section 2.3.2:

Note: VBAT is an independent supply and has no constraint versus VDD.

> But if the system lost power (Batt too low) when power goes back, the wake up pin doesn't work !

Maybe in that situation the system actually starts and goes into shutdown mode without configuring the wake-up pin?

[srain]

Thanks,

How can I check that? Or how can I fix that?

BR

Stef

[Piranha]

Exactly as almost everything - by reading documentation and debugging.

No schematics, no code, no detailed description of what and how You've tested. How do You imagine someone to be able to help You?

[Ozone]

> When I remove battery on my system (NO VDD and NO Vbat on the MCU), and I connect it back, the system do not start!!!!

This is no "wake up", but a restart.

Perhaps you have the BOOT pins floating.

[srain]

Hi Ozone(O3), thanks for your reply.

I checked the BOOT0 and it's pulled down (Res10k).

Here the screenshot after a battery deconnection. The wake up should work properly but it is stuck in SysTick_Handler!

Tel me if you can see the picture!!!

Any ideas ?

Thx

[Ozone]

You should have told that an OS (presumably FreeRTOS) is involved.

First, the terminology is not clear.

If you disconnect both VDD and Vbat, the MCU is basically power supply. Reconnecting it constitutes a POR, not a wakup.

No system states (variables, values) are defined then, and need initialisation (done in the startup code before calling _main).

Caps on the board might keep some RAM cells and register values alive for a short period, but better not rely on it.

If the system hangs in the systick handler, you could possible check what goes wrong. Better switch to assembly mode, and check addresses and register contents.

Since (as I understand it) the code works after a hard reset (NRST), I assume skipped parts of the initialization (or reliance on unitialized values) is the culprit.

[srain]

Sorry for that it is the first time for me !

Thank you very much for explanation.

I will try to have a look in that direction.

BR

Stef