I'm just thinking, if we can find out how the keypads are differentiated, it could be implemented into the common.h for simpler cross-pad compatibility.

For instance, when ndless 2.0 comes out, many people may find the touch-version of the GBC emu to be mapped strangely. With changing key definitions, it could even work with the 84+ keypad flawlessly.

I was thinking something like this for the header.

Keys are defined for all the pads already

If (insert keypad detection function here)=84+ (or a number, maybe)
      {
        #define KEY_GEN_UP KEY_84_UP
        #define KEY_GEN_DOWN KEY_84_DOWN
       }
Repeat the if statement for the touch and clickpad, then when you write a program you use the generic keymap instead of a specific one. Obviously, it won't work for every program, but it should work for many, like the GBC emu and other Games.

Your program can just detect everything on the fly; its unlikely it will use that many keys.
So, for example:
if (keypadType() == 84 && isKeyPressed(KEY_84_UP) || keypadType() == NSPIRE && isKeyPressed(KEY_NSPIRE_UP)) {
  //up code here
}
Unfortunately, I do not know how to implement the function keypadType().

You can already do it using isKeyPressed(), which supports multiple keypresses.

What nonexistent keys?

You could try testing it. Turn on a pixel if the key in question is down, since you can't print things to the screen.

Drat. Well, now that idea's shot.

Brain Flash! What about having the user press the Enter key at the beginning? That way, if it's the 84+ keypad enter will be mapped in a different place than the ClickPad, and probably the TouchPad too. You couldn't use the define command, though, so you'd have to use int.