Debug from VS Code to a remotely located J-Link

• Debug from VS Code to a remotely located J-Link
  Posted by longh on 28 Mar, 2024 17:57
• 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
  
• #1 Reply
  Posted by longh on 28 Mar, 2024 18:18
• 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
• #2 Reply
  Posted by longh on 28 Mar, 2024 18:33
• Maybe I spoke too soon, this doesn't seem to work reliably.
• #3 Reply
  Posted by __george__ on 01 Apr, 2024 20:30
• 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.