I've been coding and testing all night in Lua, and I've come up with something that's somewhat useful, well, I guess not useful, but this is my first PSP app .
Basically this will output whichever button you press to the PSP screen, except for Home, Vol +/-, Display Brightness, and the Musical Note buttons. It isn't too hard, but if you put too much power into it, you can turn the PSP off instead of turning Hold off (if you press it to show the output on the screen).
You can go into and out of USB mode while still in this program. Read the readme to see the controls for clearing the screen, starting USB mode, and exiting USB mode.
I think that covers it...hopefully I'll release a more advanced game soon .
Looks like there's an attachment limit...
[Download - Click Here]