Intermittent Debug Connectivity Failures on STM32H745BIT6 Custom Boards

Kavya · ‎2026-03-29

Hi Team,

We are observing persistent and repeatable debug connectivity issues on multiple custom boards based on the STM32H745BIT6 MCU. These boards were initially functioning as expected; however, after repeated debug sessions, they started exhibiting failures. We request your support in identifying the potential root causes and guidance on recovery. We have performed Full Chip erase also whenever it was possible.

Below are our consolidated observations captured across multiple boards.

Observed Issues

Debug Interface Failures After Multiple Sessions
After several debug sessions, the following errors are observed intermittently:
- TARGET_HELD_UNDER_RESET
- TARGET_NOT_HALTED
- TARGET_NO_DEVICE
- Error: Unable to get core ID
Inconsistent Connectivity Between Tools
- The device intermittently connects using STM32CubeProgrammer.
- The same device frequently fails to connect in Debug mode using STM32CubeIDE.
Loss of Debug Connection During Runtime
- During debugging, the controller runs for a few seconds.
- The STM32CubeIDE console repeatedly reports:
```
Target is not responding, retrying...
```
- Eventually, the session terminates with a GDB server error.
Temporary Recovery After Power Cycle
- After a power cycle, the device connects for a short duration.
- Once the connection is lost, subsequent attempts fail with:
  - Error: No STM32 target found
  - Error: ST-LINK error (DEV_TARGET_NOT_HALTED)
  - Error: Unable to get core ID
- In some cases, the tool suggests Debug Authentication discovery, even though authentication is not intentionally enabled.

Detailed Logs – STM32CubeIDE

After Power Cycle

STMicroelectronics ST-LINK GDB server. Version 7.11.0

Starting server with the following options:

Persistent Mode : Disabled

Logging Level : 1

Listen Port Number : 61234

Status Refresh Delay : 15s

Verbose Mode : Disabled

SWD Debug : Enabled

InitWhile : Enabled

Waiting for debugger connection...

Target is not responding, retrying...

Debugger connected

Target is not responding, retrying...

Session manager. Fail starting session.

GDB server. Fail create session.

Waiting for debugger connection...

Shutting down...

Exit.

Without Power Cycle

STMicroelectronics ST-LINK GDB server. Version 7.11.0

Starting server with the following options:

Persistent Mode : Disabled

Logging Level : 1

Listen Port Number : 61234

Status Refresh Delay : 15s

Verbose Mode : Disabled

SWD Debug : Enabled

InitWhile : Enabled

Target no device found

Error in initializing ST-LINK device.

Reason: No device found on target.

STM32CubeProgrammer Logs

Log 1 – Partial Connection Followed by Failure

Device ID detected: 0x450 (STM32H745, Rev V)
Option bytes and flash memory read initially succeed.
After some time

10:21:00 : UR connection mode is defined with the HWrst reset mode
10:21:00 : ST-LINK SN : 004A00303234510537333934
10:21:00 : ST-LINK FW : V3J16M9B5S1
10:21:00 : Board : STLINK-V3SET
10:21:00 : Voltage : 3.30V
10:21:00 : Error: No STM32 target found! If your product embeds Debug Authentication, please perform a discovery using Debug Authentication
10:21:10 : UR connection mode is defined with the HWrst reset mode
10:21:10 : ST-LINK SN : 004A00303234510537333934
10:21:10 : ST-LINK FW : V3J16M9B5S1
10:21:10 : Board : STLINK-V3SET
10:21:10 : Voltage : 3.29V
10:21:10 : SWD freq : 8000 KHz
10:21:10 : Connect mode: Normal
10:21:10 : Reset mode : Core reset
10:21:10 : Device ID : 0x450
10:21:10 : Revision ID : Rev V
10:21:10 : Debug in Low Power mode is not supported for this device.
10:21:11 : UPLOADING OPTION BYTES DATA ...
10:21:11 : Bank : 0x00
10:21:11 : Address : 0x5200201c
10:21:11 : Size : 308 Bytes
10:21:11 : UPLOADING ...
10:21:11 : Size : 1024 Bytes
10:21:11 : Address : 0x8000000
10:21:11 : Read progress:
10:21:11 : Data read successfully
10:21:11 : Time elapsed during the read operation is: 00:00:00.004
10:21:18 : UPLOADING ...
10:21:18 : Size : 1024 Bytes
10:21:18 : Address : 0x8100000
10:21:18 : Read progress:
10:21:18 : Data read successfully
10:21:18 : Time elapsed during the read operation is: 00:00:00.003
10:21:47 : Error: Unable to get core ID
10:21:47 : Error: Unable to get core ID
10:21:47 : Error: Unable to get core ID
10:21:47 : Warning: Connection to device 0x450 is lost
10:21:48 : Disconnected from device.

Log 2 – Subsequent Attempts

Initial device identification succeeds.
Flash read succeeds briefly.
Connection is later lost with repeated

10:53:37 : UR connection mode is defined with the HWrst reset mode
10:53:37 : ST-LINK SN : 004A00303234510537333934
10:53:37 : ST-LINK FW : V3J16M9B5S1
10:53:37 : Board : STLINK-V3SET
10:53:37 : Voltage : 3.30V
10:53:37 : SWD freq : 8000 KHz
10:53:37 : Connect mode: Normal
10:53:37 : Reset mode : Core reset
10:53:37 : Device ID : 0x450
10:53:37 : Revision ID : Rev V
10:53:37 : Debug in Low Power mode is not supported for this device.
10:53:38 : UPLOADING OPTION BYTES DATA ...
10:53:38 : Bank : 0x00
10:53:38 : Address : 0x5200201c
10:53:38 : Size : 308 Bytes
10:53:38 : UPLOADING ...
10:53:38 : Size : 1024 Bytes
10:53:38 : Address : 0x8100000
10:53:38 : Read progress:
10:53:38 : Data read successfully
10:53:38 : Time elapsed during the read operation is: 00:00:00.003
10:54:14 : Error: Unable to get core ID
10:54:14 : Error: Unable to get core ID
10:54:14 : Error: Unable to get core ID
10:54:14 : Warning: Connection to device 0x450 is lost
10:54:15 : Disconnected from device.
10:55:02 : UR connection mode is defined with the HWrst reset mode
10:55:04 : ST-LINK SN : 004A00303234510537333934
10:55:04 : ST-LINK FW : V3J16M9B5S1
10:55:04 : Board : STLINK-V3SET
10:55:04 : Voltage : 3.30V
10:55:04 : Error: ST-LINK error (DEV_TARGET_NOT_HALTED)
10:56:03 : UR connection mode is defined with the HWrst reset mode
10:56:03 : ST-LINK SN : 004A00303234510537333934
10:56:03 : ST-LINK FW : V3J16M9B5S1
10:56:03 : Board : STLINK-V3SET
10:56:03 : Voltage : 3.30V
10:56:03 : Error: No STM32 target found! If your product embeds Debug Authentication, please perform a discovery using Debug Authentication

Subsequent attempts result in:

DEV_TARGET_NOT_HALTED
No STM32 target found

Request for Support

Based on the above behavior, we would appreciate your help with:

Identifying possible root causes.
Guidance on device recovery

Looking forward to your guidance on restoring the affected devices to a stable and debuggable state.

Best regards,
M S Kavya

mƎALLEm · ‎2026-03-30

Hello,

It could be a hardware issue.

Please review your schematics based on the AN4938 "Getting started with STM32H74xI/G and STM32H75xI/G MCU hardware development", especially VCAP capacitors, the decoupling capacitors.

It could be also a soldering joint issue.

To give better visibility on the answered topics, please click on "Accept as Solution" on the reply which solved your issue or answered your question.