Porting iOS 7 JoyStick support to be compatible with Android Gamepad/JoyStick

Hi!

I got a lot of requests from my Android players requesting me to add GamePad android controller support, anyone can point me to the documentation or the exact button codes?

Currently I use all the available buttons on iOS 7 controller, including both right and left stick, right and left triggers (1 only), A, B, X, Y and the arrows.

Also one more thing, is there a universal android controller? Or do I have to code for a few, if yes how can I differentiate between the different ones?

I do not own one, but I suppose mapping the keys is pretty simple and I'm looking to let my android players do the testing and report back, but I need a guideline to start with, for example there's this for iOS:

http://docs.unity3d.com/Manual/iphone-joystick.html

I'm trying to find something similar!

Thank you.