Continued the CH554 Atari USB-Quadrature Adapter. Used VSCode and Platformio this time :

It works quite well with the mouse : I still would like to add some configurable options (divide DPI, minimum pulse frequency, maximum pulse frequency etc…).
I also started testing it with HID-Joystick, and it is almost OK with one of the joystick I have here. Got some ideas to make it more ‘universal’, while keeping it simple (The CH554 only has 16kb mem – it is using about 12k at the moment, even if removing debug brings it to less than 10k).