Remote debugging not possible

Trying to attach to a GDB server with no luck. All I want is to connect to the GDB server, run target remote localhost:4444 and start sending some monitor commands.

As soon as I uncomment miDebuggerServerAddress I get

Unable to start debugging. Cannot access a disposed object.

Also, why am I required to specify a process id? I am trying to debug on a embedded target, so my GDB server, that I run through, speaks with it over JTAG. Which process id is referred to?

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "C++ Attach",
            "type": "cppdbg",
            "request": "attach",
            "program": "${workspaceRoot}/Sw/A_XMC/out/use/A_Myriad_A_6_13.elf",
            "processId": "${command.pickProcess}",
            "MIMode": "gdb",
            // "miDebuggerServerAddress": "localhost:4444",
            "miDebuggerPath": "C:/dev/ELF/GDB/gdb.exe"
        }
    ]
}