STM32H755ZQ Debug Issue: ST-LINK Timeout and Target Held Under Reset

venkatakrishnan · ‎2026-01-22

I am using an STM32H755ZQ device and unable to start a debug session using STM32CubeIDE + ST-LINK (SWD).
The system uses two STM32 controllers, where firmware is flashed to one controller and data is shared/communicated to the second controller.
Debug fails with errors like DEV_TARGET_HELD_UNDER_RESET and GDB connection timeout (localhost:61234).
Even with Connect under reset, low SWD frequency, and full chip erase via STM32CubeProgrammer, the issue persists.
Looking for guidance on whether inter-controller communication, reset interaction, or H755-specific debug/security settings could block debugging.

mƎALLEm · ‎2026-01-23

Hello @venkatakrishnan and welcome to the ST community.

You need to provide more details about the hardware you are using and what power configuration is set by hardware SMPS, LDO etc..?

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