For systematic debugging, an engineer needs a debug probe. For the Raspberry Pi Pico (RP2040) device there are plenty of debug options with VS Code.

In this article I show different options, from professional tools to DIY solutions and the settings in VS Code I’m using.

VS Code Extension

I’m using Cortex-Debug extension from marus25 which is versatile and supports many embedded features including FreeRTOS, SEGGER RTT and multi-core debug. It works with many debug probes, including J-Link and CMSIS-DAP based ones.

Debug Adapter

Unfortunately, the Raspberry Pi foundation decided not to use the standard 10pin SWD/JTAG connector, but a simple header with 3 wires (GND, clock and data). I put the standard 10pin connector on my boards, but if you have only the 3 pins available, you can use an adapter like the one from Adafruit:

J-Link Debug Probes

The SEGGER J-Link comes with many utilities and excellent support for the RP2040. Students love the J-Link EDU Mini (only for hobby or educational use) because it tiny and they can carry it easily with the board.

I prefer the J-Link because it is a professional tool and it works for many vendors out of the box, imho opinion worth the price.

Note that you can turn your J-Link into a debug probe for OpenOCD, see https://wiki.segger.com/OpenOCD#Restoring_the_USB_driver.

RP2040-based Debug Probes

With OpenOCD one can use a RP2040 as a debug probe, there are plenty of options for this. This is usually the least-expensive option: all you need is a RP2040 pico board and some wires, so around $5.

The Raspberry Pi Foundation provides its own probe and firmware: https://github.com/raspberrypi/picoprobe

I recommend the ‘yet-another-pico-probe’ firmware which I’m using: https://github.com/rgrr/yapicoprobe

You can use a breadboard with some wires, see Picoprobe: Using the Raspberry Pi Pico as Debug Probe.

Or you can build your own circuit: Open Source picoLink: Raspberry Pi RP2040 CMSIS-DAP Debug Probe

On some of my classroom boards I have added the circuit so the board can debug another RP2040, both with the standard 10pin cable and the non-standard 3pin connection:

MCU-Link

If you don’t own a J-Link and you don’t want to build a DIY probe with wires, then I can recommend using the NXP MCU-Link. Because the debug probe is enumerating as CMSIS-DAP debug probe, it can be used for the RP2040 too, and costs around $13 (e.g. Mouser)

From NXP there is the MCU-Link Pro (around $50) which includes power measurement and can be turned into a J-Link debug probe (for NXP devices) too.

VS Code Launch.json

Below is my current version of the launch.json for RP204 and J-Link and OpenOCD, both with semihosting enabled:

{
    "version": "0.2.0",
    "configurations": [
        { // see https://github.com/Marus/cortex-debug/blob/master/debug_attributes.md
            "name": "TSM_PicoW_Blinky J-Link Cortex-Debug",
            "type": "cortex-debug",
            "request": "launch",
            "servertype": "jlink",
            "serverpath": "${env:PICO_SEGGER_PATH}/JLinkGDBServerCL.exe", // or: set in global json: cortex-debug.JLinkGDBServerPath
            "cwd": "${workspaceRoot}",
            "executable": "${command:cmake.launchTargetPath}",
            "armToolchainPath": "${env:PICO_TOOLCHAIN_PATH}",  // needed for the gdb
            "device": "RP2040_M0_0",
            "interface": "swd",
            "serialNumber": "", // add J-Link serial number if having multiple attached the same time.
            "runToEntryPoint": "main", // "_reset_handler" or for example "main"
            "postLaunchCommands": [
                "monitor semihosting enable",
                "monitor semihosting ioclient 3", // 1: telnet (port 2333); 2: gdb; 3: both telnet and gdbclient output
            ],
            "postRestartCommands": [],
            "postResetCommands": [],
             "rtos": "FreeRTOS",
            "svdFile": "${env:PICO_SDK_PATH}/src/rp2040/hardware_regs/rp2040.svd",
            "rttConfig": {
                "enabled": false,
                "address": "auto",
                "decoders": [
                    {
                        "label": "",
                        "port": 0,
                        "type": "console"
                    }
                ]
            },
            "showDevDebugOutput": "none",
        },

        { // see https://github.com/Marus/cortex-debug/blob/master/debug_attributes.md
            "name": "AEMBS_pico_Game CMSIS-DAP Cortex-Debug",
            "type": "cortex-debug",
            "request": "launch",
            "servertype": "openocd",
            "serverpath": "openocd.exe", // or: set in global json: cortex-debug.JLinkGDBServerPath
            "serverArgs": [
                "-c adapter speed 5000",
                "-c set USE_CORE 0", // TIMER stops, see https://github.com/raspberrypi/picoprobe/issues/45
            ],
            "cwd": "${workspaceRoot}",
            "executable": "${command:cmake.launchTargetPath}",
            "armToolchainPath": "${env:PICO_TOOLCHAIN_PATH}",  // needed for the gdb
            "device": "RP2040",
            "configFiles": [
                "interface\\cmsis-dap.cfg",
                "target\\rp2040.cfg"
            ],
            "runToEntryPoint": "main", // "_reset_handler" or for example "main"
            "postLaunchCommands": [
                "monitor arm semihosting enable",
            ],
            "postRestartCommands": [],
            "postResetCommands": [],
            "rtos": "FreeRTOS",
            "svdFile": "${env:PICO_SDK_PATH}/src/rp2040/hardware_regs/rp2040.svd",
            "rttConfig": {
                "enabled": false,
                "address": "auto",
                "decoders": [
                    {
                        "label": "",
                        "port": 0,
                        "type": "console"
                    }
                ]
            },
            "showDevDebugOutput": "none",
        },
    ]
}

With this, I can debug with a J-Link or a CMSIS-DAP based debug probe in VS Code:

Summary

For the RP2040, I have plenty of choices and options to debug the device. I prefer to have different options and probes at hand, because sometimes one probe cannot do everything.

This is just a selection of debug probes which I use for the RP2040, and of course there are many other choices.

Happy probing 🙂

Links

• Cortex-Debug by marus25: https://marketplace.visualstudio.com/items?itemName=marus25.cortex-debug
• OpenOCD: https://openocd.org/
• SEGGER: https://www.segger.com
• MCU-Link: OpenOCD with MCU-Link
• Adafruit Adapter: https://www.adafruit.com/product/2094
• PicoProbe firmware: https://github.com/raspberrypi/picoprobe