No Debug Access to STM32 Nucleo U575ZI-Q after enabling TrustZone and RDP Level 0.5

[jho]

Hi everyone,

I'm working with a Nucleo U575ZI-Q running a blinky example with secure and non-secure mode. After flashing, I enabled TrustZone and set the RDP level from 0 to 0.5. Since then, I have been unable to access via debug with the onboard and external ST-Links.

Here are the errors:

Connection in "Normal" or "Under Reset" Mode:

14:20:21 : UR connection mode is defined with the HWrst reset mode
14:20:23 : ST-LINK SN : 002B0007544B500420343637
14:20:23 : ST-LINK FW : V3J15M7
14:20:23 : Board : NUCLEO-U575ZI-Q
14:20:23 : Voltage : 3.30V
14:20:23 : Error: ST-LINK error (DEV_TARGET_NOT_HALTED)

Connection in "Hot Plug" Mode:

14:22:02 : UR connection mode is defined with the HWrst reset mode
14:22:04 : ST-LINK SN  : 002B0007544B500420343637
14:22:04 : ST-LINK FW  : V3J15M7
14:22:04 : Board       : NUCLEO-U575ZI-Q
14:22:04 : Voltage     : 3.30V
14:22:04 : SWD freq    : 8000 KHz
14:22:04 : Connect mode: Hot Plug
14:22:04 : Reset mode  : Hardware reset
14:22:04 : Device ID   : 0x482
14:22:04 : Revision ID : Rev X
14:22:04 : Debug in Low Power mode enabled.
14:22:04 : UPLOADING OPTION BYTES DATA ...
14:22:04 :   Bank          : 0x00
14:22:04 :   Address       : 0x40022040
14:22:04 :   Size          : 48 Bytes
14:22:04 : Error: Uploading Option Bytes bank: 0 failed
14:22:04 : Error: Initializing the Option Bytes failed
14:22:04 : Disconnected from device.
14:22:04 : Disconnected from device.

I was previously able to connect over USB DFU, read out the Option Bytes (confirming TrustZone was enabled and RDP was 0.5), and attempt to revert to TrustZone disabled and RDP level 0, but those attempts failed. Additionally, pulling BOOT0 high no longer brings up the system bootloader (LD3 steady blue).

Question:
Is there a way to reset the MCU or restore the Option Bytes to their factory defaults? I presume I first need to gain access to the debug interface—how can I do that?

Thank you!

[Imen.D]

Hello @jho and welcome to the Community,

Perform a mass erase to reset RDP level using "Full Chip Erase" option with STM32CubeProgrammer.

Verify also the protection status.

[jho]

Unfortunately, I’m unable to perform a full chip erase because I first need to establish a connection.

When I managed to connect via USB‑DFU, I executed a full chip erase - but my code still appears to be running, as the LED continued blinking.

I still encounter the following issue when connecting in “Normal” mode with either Software Reset or Hardware Reset:

20:29:23 : UR connection mode is defined with the HWrst reset mode
20:29:25 : ST-LINK SN  : 002B0007544B500420343637
20:29:25 : ST-LINK FW  : V3J15M7
20:29:25 : Board       : NUCLEO-U575ZI-Q
20:29:25 : Voltage     : 3.30V
20:29:25 : Error: ST-LINK error (DEV_TARGET_NOT_HALTED)

I’ve also tried numerous other combinations of connection modes and reset methods without any success.