Support for JLink Remote Server IP Tunnel

[kwalker-plxs]

Hello,

I am attempting to use cortex-debug to connect to a JLink Remote Server instance via an IP tunnel. I have this launch configuration:

{
            "name": "(remote) L476RG - J-Link",
            "type": "cortex-debug",
            "request": "launch",
            "cwd": "${workspaceFolder}",
            "executable": "${command:cmake.launchTargetPath}",
            "ipAddress": "tunnel:my_probe_id:*****:jlink-america.segger.com",
            "servertype": "jlink",
            "serverpath": "/usr/bin/JLinkGDBServerCLExe",
            "device": "STM32L476RG",
            "interface": "swd",
            "runToEntryPoint": "main",
            "svdPath": "/tools/stm32-debug/svd/STM32L476.svd",
            "showDevDebugOutput": "raw",
        },

I see JLink Remote Server report that a client does connect, but then the GDB server reports a timeout. Based on the gdb-server output, it looks to timeout while connecting to the target

Connecting to J-Link...
J-Link is connected.
Firmware: J-Link WiFi-V2 compiled Apr  1 2025 10:05:40
Hardware: V2.00
S/N: 12345
Feature(s): RDI, FlashBP, FlashDL, JFlash, GDB
Checking target voltage...
Target voltage: 3.35 V
Listening on TCP/IP port 50000
Connecting to target...
[2025-07-03T17:17:30.828Z] SERVER CONSOLE DEBUG: onBackendConnect: gdb-server session closed
GDB server session ended. This terminal will be reused, waiting for next session to start...

I see that cortex-debug is invoking the GDB server using this command: /usr/bin/JLinkGDBServerCLExe -singlerun -nogui -if swd -port 50000 -swoport 50001 -telnetport 50002 -device STM32L476RG -select "ip=tunnel:my_probe_id:*****:jlink-america.segger.com". If I use this command in a terminal, then the server successfully connects.

Does anyone see issues in my configuration that could be causing my issue?

Furthermore, has anyone gotten cortex-debug to successfully connect to a JLink Remote Server using an IP tunnel? If so, I would be curious to see your configuration.

[frelwx]

I just use the SSH local Port forwarding to my remote server where my J-Link is connected. This allows me to use J-Link as if it was a local device.
In my case， setting "ipAddress": "localhost" works

[frelwx]

can you post the timeout/error log message after "Connecting to target..."?

[kwalker-plxs]

I just use the SSH local Port forwarding to my remote server where my J-Link is connected. This allows me to use J-Link as if it was a local device. In my case， setting "ipAddress": "localhost" works

So you are configuring JLink Remote Server to "Use LAN"? Then your PC running VSCode is configured to forward the "listening port" to the PC running Remote Sever?

can you post the timeout/error log message after "Connecting to target..."?

There is no additional output after the "Connecting to target..." message. I did not see any further settings I could use to get more verbose output there.

[J-Rios]

Hello, your configuration seems correct @kwalker-plxs, problem is that indeed there is a timeout issue caused due cortex-debug only waits for 10s to make the gdb server completely stablish a connection with the target MCU (the timeout it is not only expecting connection between remote gdb server and client, it also includes that all the hardware debugger connect and setup the tgarget MCU). At high latency networks due usage of VPN or intermediate servers (like the JLink Remote Server) sometimes this timeout value seems to not be enough.

This issue was already reported:
#1130

And a simple fix (already tested) is to increase that timeout value. A merge request for it was already provided but it was not reviewed or merged, so it is not available in released versions of the extension:
#1129

Regards :)