The RP2040 microcontroller on the Pi Pico development board has its Serial Wire Debug(SWD) interface exposed to enable interactive debugging. We can interface SWD with another RP2040 using the Picoprobe firmware provided by Raspberry Pi. Basically, we can interactively debug an Pico with another Pico.

However, connecting 2 Picos together creates a mess of wires and takes up a lot of space. To address this problem, I decide to put everything on an Arduino-sized PCB, which I called Pico Debug Carrier(PDC). I created an RP2040-based Arduino board on which a Pico can be soldered. The SWD and UART interfaces of the Pico is connected to the RP2040 on the PDC, the rest of the GPIOs are accessible by the pin headers. After loading the Picoprobe firmware, we can connect the PDC to the computer(with USB type-C!) and run&debug code on the Pico.