This is called whenever the application selects an input device which has already been selected. The relevant input device number is passed to this function as an argument. Some input devices may require re-initialisation after receiving input; for example it is common practice to disable a bar code reader after each bar code has been read and only to re-enable it when the application is ready for another bar code: this is done to avoid reading bar codes which the application will reject as invalid input. Such re-initialisation may be done in this function.