This allows a modern USB mouse to be used by a PC-FX machine. The PC-FX did have a mouse which could be used on various games, or even on the startup screen. It was a mouse with a rotating ball and a cord (anybody familiar with this type of mouse would be familiar with the desire to use a modern cordless optical mouse).
The RP2040 board is used as the USB Host for the mouse, and PIOs are used for signalling to the PC-FX console.
Other Projects are coming... the PIOs on the RPi Pico are very interesting and flexible, so will be well-suited to retrocomputing/retrogaming projects.
As soon as the Adafruit KB2040 board was released, I started using it for my projects, since it made the USB lines available externally. These are crucial for mounting alternate USB connectors (such as USB-A sockets for plugging in mouse devices).
In future, I hope to design a more purpose-specific board with just the necessary parts and the RP2040 directly.