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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"STM32N647: OpenOCD halt/debug fails with UNDEFINED while CubeIDE works","articleBody":"Dear ST Support Team,\n\nI am reporting a debug issue on STM32N647 where debugging works correctly in STM32CubeIDE, but fails when using OpenOCD (ST fork) with ST-LINK.\n\nSummary\nOn 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.\n\n# Hardware\n- MCU: STM32N647X0HxQ\n- Debug probe: ST-LINK (V2J46S7)\n- Target voltage: ~3.3 V\n\n# Software / Tools\n- STM32CubeIDE: Debug works normally (halt/step/breakpoints OK)\n- ST-LINK Server: API v3, FW 2.1.1\n- OpenOCD: 0.12.0+dev-00623-g0ba753ca7 (STMicroelectronics fork)\n- VS Code + cortex-debug 1.12.1\n\n# Project / Boot Mode\n- Boot mode: Internal SRAM boot\n- Program under debug: FSBL\n- Debug mode: load and run\n- Debug Authentication: OPEN (confirmed, since CubeIDE debugging works)\n\n# OpenOCD Behavior\n\nOpenOCD connects successfully:\n- SWD/DAP connection OK\n- Cortex-M55 detected\n- Registers and memory can be read\n\n## However, when GDB connects or when “Pause” is issued:\n\n\u003e halted due to undefined\n\u003e undefined debug reason 8 (UNDEFINED)\n\n## VS Code / cortex-debug then reports:\n\n\u003e Received readMemory request while busy (SCB fault registers)\n\u003e Returning dummy thread-id / stack frame to workaround pause button not working\n\nHalt, step, and breakpoints never work. Changing reset configuration, SWD speed, or OpenOCD options does not change the behavior.\n\n# Questions\n- Is OpenOCD (ST fork) officially expected to support full halt/step debugging on STM32N647?\n- Is there a known limitation or missing Secure Debug / TrustZone handling in OpenOCD for STM32N6?\n- Is there a recommended OpenOCD configuration, patch, or restriction note for STM32N647?\n\nI can provide full OpenOCD logs, CubeIDE screenshots, and configuration files if needed.","author":{"url":"https://github.com/songshuaisong","@type":"Person","name":"songshuaisong"},"datePublished":"2025-12-25T06:42:45.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/44/OpenOCD/issues/44"}