STM32U5 TrustZone(Application only starts after Hardware Reset or Debug after programming)

[STM32U5]

Hi everyone,

I am working with an STM32U5 device and have enabled TrustZone (TZEN = 1)  using STM32PROGRAMMER

I created both the Secure and Non-Secure projects, and they compile and program successfully.

Problem

After downloading the firmware from STM32CubeIDE:

• Programming completes successfully.
• The application does not start automatically.
• My LED does not blink.

However:

• If I press the hardware RESET button, the LED immediately starts blinking.
• If I start a Debug session, the LED also starts blinking.

So the firmware itself appears to be correct because it works after a reset.

What I have verified

• TrustZone (TZEN) is enabled.
• Secure and Non-Secure projects are generated by CubeMX.
• Secure project jumps to the Non-Secure application.
• Programming finishes without any errors.
• The issue only occurs immediately after programming.
• Without TrustZone, the application starts automatically after programming.

My question

Is this expected behaviour with STM32U5 TrustZone?

Has anyone experienced the same issue where the application only starts after a hardware reset?

Could this be related to:

• Secure boot sequence?
• SECBOOTADD0 / NSBOOTADD0 option bytes?
• Debugger reset mode (Software Reset vs Hardware Reset)?
• STM32CubeIDE download behaviour?
• Something else in the TrustZone boot process?

I would appreciate any suggestions on what to check next.

Thank you.