This shows how to setup multiple USB controllers to work with RetroPie and RetroArch emulation. This demo is using an iBuffalo and Retrolink USB controller.
Remember the yellow status text at the bottom of the screen when you start a rom is useful to see which controllers are auto detected.
Retrolink controller:
http://www.amazon.co.uk/gp/product/B002824SNS/
iBuffalo controller
http://www.ebay.co.uk/itm/Buffalo-Super-Nintendo-Turbo-SNES-Retro-Classic-USB-Gamepad-PC-Windows-Gray-/141136848154?pt=UK_Controllers_Attachments&hash=item20dc69651a
Reference to auto configuration in RetroArch:
https://github.com/libretro/RetroArch/wiki/RGUI#joypad-autoconfiguration
List of USB device codes:
http://www.linux-usb.org/usb.ids
Windows tool to ID USB devices:
http://www.softpedia.com/get/System/System-Info/USBView.shtml
