Hutterer: Understanding HID report descriptors

For those who would like a deeper understanding of how the human interface
device (HID) protocol works, Peter Hutterer has posted a
detailed overview. 'Originally HID was designed to work over
USB. But just like Shrek the technology world is obsessed with layers so
these days HID works over different transport layers. HID over USB is what
your mouse uses, HID over i2c may be what your touchpad uses. HID works
over Bluetooth and it's celebrity-diet version BLE. Somewhere, someone out
there is very slowly moving a mouse pointer by sending HID over carrier
pigeons just to prove a point. Because there's always that one guy.'