STM32U585 hangs after Power-On Reset, works normally after pressing NRST

[HA2375-]

Hi,

I am using an STM32U585 MCU in a Iot Application . I am facing an issue during power-up.

Problem description:

• When the main supply is turned ON, the MCU appears to hang or gets stuck somewhere during startup.

• If I press the reset pushbutton connected to NRST, the MCU starts working normally.

• After that, the system runs without any issues.

• Every time I turn the main supply OFF and ON again, the same problem occurs. A manual reset is required for proper operation.

• This behavior is observed with different power supplies as well.

Hardware details:

• MCU: STM32U585

• NRST pin: 10k  pull-up or 100nf capacitor connected

• Pushbutton reset available on NRST
  
   

Any suggestions or recommended checks would be greatly appreciated.

Thank you.

[KDJEM.1]

Hello ​@HA2375- ;

 

Could you please refer to Getting started with STM32U5 MCU hardware development - Application note and check your hardware.

 

Thank you.

Kaouthar

[Andrew Neil]

Welcome to the forum

Please see How to write your question to maximize your chances to find a solution for best results.

In particular, please give details of your hardware.

 

The symptoms you describe sound sound like your reset circuit is not working properly - as ​@KDJEM.1 said, check your design against AN5373; see also the power rise specs in the datasheet.

Could also be a problem with oscillator startup.

Maybe there is (also) something else in your system which your code is waiting for?

 

the MCU appears to hang or gets stuck somewhere during startup

So you need to find out where, exactly, it is getting stuck.

You can connect the debugger to a “running” (including “stuck”) system without doing a reset or download.

 

• NRST pin: 10k  pull-up or (sic?) 100nf capacitor connected

So which one is it ?

This is a great example of why a schematic is so much better that trying to describe an electronic circuit in words!

Again, see AN5373 and the datasheet.

 

PS:

 

[Ozone]

> - NRST pin: 10k  pull-up or (sic?) 100nf capacitor connected

> So which one is it ?

You are probably aware of it, but the OP not, as it seems.
An RC element on NRST is a simple way to keep the the MCU in reset while Vcc is rising, usually with a time constant in the low millisecond range.

The schematic would be very helpful, at least the power supply section.

[HA2375-]

Hi ​@Ozone ​@Andrew Neil ​@KDJEM.1 

Thanks for the Replay 

I have attached the schematic related to the power supply and reset section for reference. However, I am still unable to identify the root cause.

What I do not understand is why the MCU does not start properly after a power OFF/ON cycle, but starts and operates normally when I press the NRST pushbutton. Once the pushbutton reset is applied, the application runs without any issues until the next power cycle.

Could anyone please suggest what could cause this behavior? Is there anything specific I should check 

Any suggestions would be greatly appreciated.


 

 

 

[Ozone]

> Could anyone please suggest what could cause this behavior? Is there anything specific I should check 
> Any suggestions would be greatly appreciated.

I would highly recommend to check the links Andrew Neil provided. Others had a similiar (or same) problem, thus the cause might be the same.

Check the datasheet for power-up requirements (rise times, sequence of different supplies like VDD / VDDA).
I would recommend to measure this on your board with a scope.
And include the NRST pin if you have a scope with asufficent number of channels.

[HA2375-]

While investigating this issue, I discovered a schematic mistake related to the PSRAM power switch (AP2280-1WG-7).

The PSRAM power rail is controlled by an AP2280 load switch. However, I mistakenly connected the STM32 3.3-V rail (VCC_3V3_STM32) to the DIS pin of the PSRAM switch instead of connecting the PSRAM output rail (VCC_3V3_PSRAM).

Interestingly, when this incorrect connection is left as-is, the board powers up and operates normally. If I disconnect the PSRAM switch or remove this connection, the STM32 does not start properly after a power cycle and only starts after pressing the NRST pushbutton.

Could this incorrect connection be causing back-powering or affecting the startup sequence? Has anyone encountered a similar issue with AP2280-1WG-7 or STM32U585?

I have attached the schematics of both the STM32 and PSRAM power switches for reference. Any suggestions would be greatly appreciated.

 

 

[Andrew Neil]

​@HA2375- 

Could this incorrect connection be causing back-powering or affecting the startup sequence?

It certainly could!

Again, have you used the debugger to find where, exactly, your code is hanging?

It it’s hanging at the first point where the external memory is required - this may well be your answer!

Maybe try code that doesn’t rely on external memory ...

 

In my 1st reply:

Maybe there is (also) something else in your system which your code is waiting for?