STM32N647: OpenOCD halt/debug fails with UNDEFINED while CubeIDE works

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#44 opened on Dec 25, 2025 1 comment 0 reactions 1 assignee View on GitHub

@tarek-bochkati is already working on this.

Since Jan 6, 2026.

Assessment

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Description

bug

Dear ST Support Team,

I am reporting a debug issue on STM32N647 where debugging works correctly in STM32CubeIDE, but fails when using OpenOCD (ST fork) with ST-LINK.

Summary
On STM32N647 (Cortex-M55, TrustZone), OpenOCD is able to connect to the target and enumerate the core, but any attempt to halt/pause/step the CPU results in an UNDEFINED debug reason. The same hardware, firmware, and debug authentication state work correctly when debugging with STM32CubeIDE using ST-LINK.

Hardware

MCU: STM32N647X0HxQ
Debug probe: ST-LINK (V2J46S7)
Target voltage: ~3.3 V

Software / Tools

STM32CubeIDE: Debug works normally (halt/step/breakpoints OK)
ST-LINK Server: API v3, FW 2.1.1
OpenOCD: 0.12.0+dev-00623-g0ba753ca7 (STMicroelectronics fork)
VS Code + cortex-debug 1.12.1

Project / Boot Mode

Boot mode: Internal SRAM boot
Program under debug: FSBL
Debug mode: load and run
Debug Authentication: OPEN (confirmed, since CubeIDE debugging works)

OpenOCD Behavior

OpenOCD connects successfully:

SWD/DAP connection OK
Cortex-M55 detected
Registers and memory can be read

However, when GDB connects or when “Pause” is issued:

halted due to undefined
undefined debug reason 8 (UNDEFINED)

VS Code / cortex-debug then reports:

Received readMemory request while busy (SCB fault registers)
Returning dummy thread-id / stack frame to workaround pause button not working

Halt, step, and breakpoints never work. Changing reset configuration, SWD speed, or OpenOCD options does not change the behavior.

Questions

Is OpenOCD (ST fork) officially expected to support full halt/step debugging on STM32N647?
Is there a known limitation or missing Secure Debug / TrustZone handling in OpenOCD for STM32N6?
Is there a recommended OpenOCD configuration, patch, or restriction note for STM32N647?

I can provide full OpenOCD logs, CubeIDE screenshots, and configuration files if needed.

Dominant language: C
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