STM32U585 communication error DEV_TARGET_CMD_ERROR

[PJose.4]

Hi All,

Greetings

We are using STM32U585 on custom board with Trust zone enabled and now facing a connection issue with stm cube programmer in hotplug mode, now unable to connect to the microcontroller and getting ST-LINK error  as : DEV_TARGET_CMD_ERROR.

When NRST is low continuously(pressing the Reset Switch) the connection to the controller through Cube Programmer is happening, but we are unable to change any option bytes, to revert back to Non Trust Zone Code. Once the reset switch(NRST) is high, it is going back to the same error. 

Any suggestions for this issue and how can we resolve this?

Thanks and Regards
Philip

[Aziz BRIGUI]

Hi @PJose.4,

Have you changed the RDP (Readout protection) option byte?

Try connecting BOOT0 to 1 and re-connect (Also please refer to section 9 of Introduction to Arm® TrustZone® features on STM32L5, STM32U5, and STM32U3 MCUs - Application note).

Aziz

[PJose.4]

Hi @Aziz BRIGUI 

Thanks for the quick reply, 

RDP was in AA. We checked the Boot 0 pin from high and checked still the same issue.

Thanks

Philip

[Aziz BRIGUI]

Hi @PJose.4,

I assume you were able to connect previously; can you describe if you changed any setting?

PS: Forgot to mention on my previous comment that to apply the new boot configuration you need to reset or better power off/on your device. So the steps are:

1- Boot0 high

2- Power off/on

3- Try to connect

Aziz

[PJose.4]

Hi Aziz,

Thanks for the clarification regarding the boot configuration.
We are running the scripts regression.sh and SBSFU_Update.sh for running the SBSFU code from ST official Relase code. Couple of times we were able to run the source code successfully and after a particular time this behaviour is observed as described above.
Here is the current behavior we are observing on our board:
Initially, the board was configured with BOOT0 = Low. In this condition, we were able to connect to the controller via ST-LINK and successfully program the device multiple times without any issue.
However, all of a sudden the board entered a locked state, and we are now unable to access the controller through ST-LINK.
We then changed BOOT0 to High and performed a power cycle as recommended, but the controller still does not respond to ST-LINK.
Interestingly, we observe that when the NRST line is held low, the device becomes detectable and accessible through ST-LINK. But as soon as NRST is released, the board immediately returns to a locked/unresponsive state.
This behavior is consistent across multiple connection attempts.
Hope the picture is clear
Thank you for your support.
Philip