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

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#44 1 comentario 0 reacciones 1 asignado Ver en GitHub

@tarek-bochkati ya está trabajando en esto.

Desde el 6/1/2026.

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Descripción

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.

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