PicoDualProbe 🟡🟢🔵

One probe. Two protocols. Five dollars.

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Your Segger J-Link just bricked itself mid-session. A new one costs $60. You've got an RP2040-Zero in your parts bin that cost $4.37.

This is the firmware that turns it into a better debug probe.

PicoDualProbe does SWD for ARM Cortex-M and JTAG for RISC-V — from the same board, with a color-coded LED that tells you what mode it's in before you even open a terminal. It's a fork of the Raspberry Pi Debug Probe firmware, hardened for dual-protocol use with real RISC-V targets.

     ┌──────────────────────┐
     │   🔵🔵  Ready         │
     │   🟢🟢  SWD (ARM)     │
     │   🟡🟡  JTAG (RISC-V) │
     │   🔴🔴  Error         │
     └──────────────────────┘
     RP2040-Zero · $4.37 · USB-C

What It Debugs

Target	Protocol	Status
NeoRV32 RISC-V (Alchitry Pt V2, XC7A100T)	JTAG	✅ Halt, reg read, GDB, flash
RP2040 (Pico)	SWD	✅ DPIDR 0x0bc12477, both cores
SAMD21	SWD	✅ Config provided
Any ARM Cortex-M	SWD	✅ Standard CMSIS-DAP
Any RISC-V with JTAG DTM	JTAG	✅ OpenOCD riscv target

30-Second Start

# 1. Flash the firmware (drag .uf2 onto RPI-RP2 drive)
# 2. Wire it up:
#    GP2→TCK/SWCLK  GP1→TMS/SWDIO  GP0→TDI  GP3→TDO  GND→GND
# 3. The LED pulses blue. You're ready.

# SWD — ARM target:
openocd -f scripts/openocd/picodualprobe-swd.cfg -f target/rp2040.cfg

# JTAG — RISC-V target:
openocd -f scripts/openocd/picodualprobe-jtag.cfg -f scripts/openocd/neorv32.cfg

Pinout

All debug signals on one edge. Clean wiring, no spaghetti.

GP0  = TDI          GP12 = UART TX →
GP1  = TMS / SWDIO  GP13 = UART RX ←
GP2  = TCK / SWCLK  GP16 = WS2812 LED
GP3  = TDO          GND  = Ground
GP4  = nRESET

Why Not Just Buy a J-Link?

Because when a J-Link bricks (and it will), you're dead in the water waiting for shipping. A PicoDualProbe is:

• $5 vs $60 for a J-Link EDU Mini
• Dual protocol — SWD for ARM, JTAG for RISC-V. One board, both protocols.
• Repairable — brick it? Re-flash the .uf2 in 3 seconds. Try that with a Segger.
• Visible state — the LED tells you what's happening. J-Link gives you a blinking green dot
• Open source — you can read the firmware, fix bugs, add features

Pre-built Firmware

Board	File
RP2040-Zero	releases/debugprobe_on_zero.uf2
Standard Pico	releases/debugprobe_on_pico.uf2

Build From Source

git clone https://github.com/greg676/PicoDualProbe.git
cd PicoDualProbe
git submodule update --init --recursive

# For RP2040-Zero:
mkdir build-zero && cd build-zero
cmake -DPICO_BOARD=waveshare_rp2040_zero ..
make

Known Issue

CMSIS-DAP USB endpoint doesn't cleanly reset between OpenOCD sessions. First connection works. Second fails. Workaround: unplug/replug, or use scripts/jtag.sh which does a USB reset. See BUG-CMSIS-DAP-RECONNECT.md.

Companion Projects

Project	What
NeoRV32 on Alchitry Pt V2	The RISC-V platform this probe was built to debug
NeoRV32 MCP Server	AI agent bridge — 15 tools for hardware control

Credits

Built on the Raspberry Pi Debug Probe firmware. Added JTAG, LED signaling, Zero pinout, pre-built firmware, and OpenOCD configs for RISC-V.

BSD-3-Clause © 2026 Greg Jackson