The RP2040 chip designed by Raspberry Pi has many features including the ability to emulate a SWD interface and act as the debugger for other ARM microcontrollers. Connecting two Picos together creates a mess of wires, so I came up with the idea of designing an RP2040-based board to take the job of the second of the second Pico and get rid of the messy wiring.

With the Pico Debug Carrier, we can solder on the target Pico and use the Picoprobe firmware written by Raspberry Pi to debug the target Pico. All of the circuitry is squeeze onto a PCB the same size as an Arduino Uno and accessed by an USB type C port. Although the target Pico is soldered onto the PCB, the Pico Debug Carrier still provides full access of the pins on the Pico through pin headers.

The Pico Debug Carrier is designed to be a 2-in-1 development kit. Since debugging the Pico only requires 4 GPIO pins, the rest of the GPIOs are broken out, so that this board can also be used as a normal development board. The PCB is designed to match the form factor of the Arduino Uno, and the position of the special pins(I2C, UART) are rearranged to be at same place as the Arduino Uno.

There are a few improvements in terms of development board to the Pi Pico.

1. A reset button is added, we no longer need to short the RUN pin to ground with wires to reset the microcontroller.

2. There is 16MB of flash. Although 2MB is plenty for the Picoprobe firmware, a larger flash chip is used just in case.

3. There is a USB-C connector. No more up-side-down USB connectors!

4. There are 2 user LEDs connected to GPIOs 24 and 25.