The USB Gecko is a Wii/Gamecube development and hacking tool which connects to the USB port of the computer, and to the GameCube memory slot of the Wii. It can be used to upload homebrew, to use your computer as a remote terminal under Wii Linux and as a remote debugging tool. For more information see the USB Gecko homepage. It has recently been discontinued and the schematics released on Google code.
See Gecko OS for the Hombrew application to launch a game and be able to debug it remotely using this device.
Windows Side Application Programming
Linux Side Application Programming
The USB Gecko will usually be recognized as a USB to serial port converter and a device file of the form /dev/ttyUSB0 will appear. Simply writing to and reading from this device file will send data across the USBGecko link.
Failing that, userspace tools could use the libusb library and usb_bulk_write and usb_bulk_read functions. The USBGecko will appear as 0403:6001 in the lsusb output.
The USB Gecko is a two step converter to convert EXI<->serial<->usb. It is a fancy serial port. All the fun is provided by software. No, the EXI interrupt is not possible to trigger from the PC.