XMOS xCORE-200 Multi-channel Audio board Design Manual page 76

USB Audio Design Guide 76/110
hidData [0] = ( a << H I D _ C O N T R O L _ V O L U P _ S H I F T ) | ( b << H I D _ C O N T R O L _ V O L D N _ S H I F T
) ;
If the switch input is high (i.e. low when inverted) then the buttons states are
used to either indicate play/pause or next/previous. Based on counter and a small
state-machine a single click on either button provides a play/pause command. A
double tap on button A or B provides a previous or next command respectively.
The full code listing is shown below:
XM0088546.1