Could not connect to the target

[dtiziano]

Version/Branch:

1.2.6

Operating system:

MacOS 26.1

Debug probe:

ST-Link V"

Microcontroller:

STM32H562V

Details:

I can successfully select the STLINK in the configuration tab, but when trying to connect to it, it always fails (see pictures).
When doing so, no other debugging software is currently connected to the debugging probe. Connecting with STM32 Cube IDE debugger works without any issue - so no cabling problem. Problem persists on my Mac Machine. Connecting to the same setup from another Windows machine works also in MCU Viewer - so I would think the problem is rather Mac side than MCU/Debugger side. Is there a way to dig deeper into the problem - the current error message does not tell much.

Screenshots/Video:

[klonyyy]

Hey, thanks for reporting it. Could you check the logs that you can find in Settings -> General and open log directory?

[dtiziano]

Here is a log.

Testing another file, with STM32F401RE (NUCLEO) works, but here with STM32H562 and stlink-v3 (actually it is v3 and v2 as previously stated) I get:

[2026-03-17 18:37:16.518] [logger] [info] GDB executable working!
[2026-03-17 18:37:16.670] [logger] [info] Is C2000 *.efl file: false
[2026-03-17 18:37:25.105] [logger] [info] STLink serial number 003A001B3331510E34333834
[2026-03-17 18:37:27.383] [logger] [info] GDB executable working!
[2026-03-17 18:37:27.498] [logger] [info] Is C2000 *.efl file: false
[2026-03-17 18:37:58.244] [logger] [info] Explorer command executed successfully: open "/Users/tiziano/Library/Logs/MCUViewer"
[2026-03-17 18:38:19.171] [logger] [info] Start clicked!
[2026-03-17 18:38:19.206] [logger] [error] Sample list is empty!
[2026-03-17 18:38:21.762] [logger] [info] GDB executable working!
[2026-03-17 18:38:34.090] [logger] [info] GDB executable working!
[2026-03-17 18:38:34.203] [logger] [info] Is C2000 *.efl file: false
[2026-03-17 18:38:36.044] [logger] [info] Start clicked!
[2026-03-17 18:38:36.079] [logger] [error] Sample list is empty!
[2026-03-17 18:38:39.846] [logger] [info] Start clicked!
[2026-03-17 18:38:39.854] [logger] [info] Connecting to STLink (003A001B3331510E34333834)...
[2026-03-17 18:38:39.876] [logger] [error] Could not connect to the target! Please make sure the target is connected and powered and a proper SWD speed is selected.
[2026-03-17 18:38:44.380] [logger] [info] Explorer command executed successfully: open "/Users/tiziano/Library/Logs/MCUViewer"
[2026-03-17 18:39:51.452] [logger] [info] Disconnected from STLink
[2026-03-17 18:39:52.773] [logger] [info] STLink serial number 003A001B3331510E34333834
[2026-03-17 18:39:55.511] [logger] [info] Disconnected from STLink
[2026-03-17 18:39:55.657] [logger] [info] GDB executable working!
[2026-03-17 18:39:55.785] [logger] [info] Is C2000 *.efl file: false
[2026-03-17 18:40:30.236] [logger] [warning] It seems the path was already absolute: /Users/tiziano/Downloads/STM32H562VGT6_config.elf
[2026-03-17 18:40:30.373] [logger] [info] GDB executable working!
[2026-03-17 18:40:30.503] [logger] [info] Is C2000 *.efl file: false
[2026-03-17 18:40:32.790] [logger] [info] GDB executable working!
[2026-03-17 18:40:32.907] [logger] [info] Is C2000 *.efl file: false
[2026-03-17 18:40:34.375] [logger] [info] Start clicked!
[2026-03-17 18:40:34.389] [logger] [info] Connecting to STLink (003A001B3331510E34333834)...
[2026-03-17 18:40:34.406] [logger] [error] Could not connect to the target! Please make sure the target is connected and powered and a proper SWD speed is selected.
[2026-03-17 18:40:39.386] [logger] [info] Explorer command executed successfully: open "/Users/tiziano/Library/Logs/MCUViewer"
[2026-03-17 18:40:45.268] [logger] [info] Explorer command executed successfully: open "/Users/tiziano/Library/Logs/MCUViewer"
[2026-03-17 18:41:52.317] [logger] [info] Start clicked!
[2026-03-17 18:41:52.323] [logger] [info] Connecting to STLink (003A001B3331510E34333834)...
[2026-03-17 18:41:52.344] [logger] [error] Could not connect to the target! Please make sure the target is connected and powered and a proper SWD speed is selected.

[dtiziano]

And also, I just realised, that after the error occurs, I cannot close the app anymore although it is still responsive - needs force quit to exit

[klonyyy]

Generally the H5 connection issues are a known limitation of the stlink library (#74, #39). I will try to obtain a H5 eval, and maybe propose a fix, however until then you have to try to connect in some other way, GDB server being one of them, or the Serial Driver.

You can also switch to JLink.

[dtiziano]

Hi

GDB works fine, thanks for the suggestion

If you want me to test something on H5 feel free to let me know - would be great to support you.

[klonyyy]

Hello, thank you for the update. I'll probably need my own eval anyway, but - I will contact you directly if I have some fix to test. Thanks!

[klonyyy]

The connection with H5 and other new ST's MCUs will be solved in the next release (1.2.7) using CubeProgrammerAPI. Unfortunately it's very slow on Mac - I will look for the rootcause, however it works very well on Windows and Linux.