Debug from VS Code to a remotely located J-Link

[longh]

Hey All,

I've been debugging a Cortex M4 micrcocontroller using a J-Link probe connected over USB and the cortex debug plugin for VS Code. I like it a lot, but the launch.json file still confuses me. As does the interaction between all the J-Link command line utilities and VS Code.

For the J-Link connected locally over USB, I can use this in my launch.json
        {
            "name"                   : "JLink: debug over usb",
            "cwd"                    : "${workspaceFolder}",
            "request"                : "launch",
            "type"                   : "cortex-debug",
            "servertype"             : "jlink",
            "executable"             : "${workspaceFolder}/build/app.elf",
            "interface"              : "swd",
            "device"                 : "Cortex-M4",
            "runToEntryPoint"        : "main",
            "svdFile"                : "scripts/my.svd",
        },

And it looks like this is causing the command
JLinkGDBServer -singlerun -nogui -if swd -port 50000 -swoport 50001 -telnetport 50002 -device Cortex-M4 to be run behind the scenes, and I guess VS Code connects to this GDB server?

It would be great if I could debug something in my home network, while out and about. Looks like it is possible: https://wiki.segger.com/J-Link_Remote_Server

I've started by connecting the J-Link over USB to a Raspberry pi, then making a tunnel with
 JLinkRemoteServerCLExe -UseTunnel -TunnelByName <name_of_tunnel> -TunnelPW <password>

And I can even connect to it with the JLinkGDBServer command line on my laptop
 JLinkGDBServer -singlerun -nogui -if swd -port 50000 -swoport 50001 -telnetport 50002 -device Cortex-M4 -select "ip=tunnel:<name_of_tunnel>:<password>"

But the launch.json I've tried doesn't work, it says failed to launch GDB server: Timeout. But it seems close to working!

       
            {
                "name"                   : "REMOTE: JLink",
                "cwd"                    : "${workspaceFolder}",
                "request"                : "launch",
                "type"                   : "cortex-debug",
                "servertype"             : "jlink",
                "executable"             : "${workspaceFolder}/build/app.elf",
                "device"                 : "Cortex-M4",
                "runToEntryPoint"        : "main",
                "ipAddress"              : "tunnel:<name_of_tunnel>:<password>",
                "svdFile"                : "scripts/my.svd",
            },

Kind of a weird obscure question, but maybe someone understands how J-Link software works better than I do.

Thanks!
-Hunter

[longh]

I think I got it working! For posterity's sake I'll post what I did here:

First on the Pi where the J-Link is connected over USB I run:

$ JLinkRemoteServerCLExe -UseTunnel -TunnelByName <tunnel_name> -TunnelPW <tunnel_password>

Then on my laptop at a coffee shop I run the command:

$ JLinkGDBServer -singlerun -nogui -if swd -port 50000 -swoport 50001 -telnetport 50002 -device Cortex-M4 -select "ip=tunnel:<tunnel_name>:<tunnel_password>"

Then I add this to my vs code launch.json:
{
            "name": "tunnel to j-link",
            "type": "cortex-debug",
            "request": "launch",
            "executable": "${workspaceFolder}/build/app.elf",
            "cwd": "${workspaceFolder}",
            "servertype": "external",
            "interface": "swd",
            "gdbTarget": "localhost:50000",
            "showDevDebugOutput": "raw",
            "runToEntryPoint"        : "main",
},

And then when I click debug, it works! Like magic.

I still don't understand why I have to start GDB from the command line first, I think it is because it takes longer and VS Code times out or something.

-Hunter

[longh]

Maybe I spoke too soon, this doesn't seem to work reliably.

[__george__]

The J-Link server has a no-timeout option:
https://wiki.segger.com/J-Link_GDB_Server#-notimeout

It seems that by default it timeouts after 5 seconds so what you see probably makes sense.