trivia: dumping USB HID report descriptors

[Werner Almesberger]

The USB HID protocol has a descriptor that defines the layout of
the reports the HID device sends. If you're ever in a situation
where you need this sort of information, here's how you can decode
it:

Download:

  get usbhid-dump-1.2.tar.gz from
  http://sourceforge.net/projects/digimend/files/usbhid-dump/

  get hidrd-0.2.tar.gz from
  http://sourceforge.net/projects/digimend/files/hidrd/0.2/

Build and install:

  tar xfz usbhid-dump-1.2.tar.gz
  cd usbhid-dump-1.2
  ./configure
  make
  make install

  cd ..
  tar xfz hidrd-0.2.tar.gz
  cd hidrd-0.2
  ./configure
  make
  make install

  ldconfig

Find the VID:PID of your device with lsusb or whatever you prefer.

usbhid-dump -d VID:PID | grep -v : | tr -d ' \n' | xxd -r -p |
  hidrd-convert -o spec

And all the pesky little details will be revealed before your very
eyes.

If you forget to specify the VID:HID, it seems that this will grab
your USB keyboard, etc. Just waiting for one minute supposedly
returns it to you. I didn't test this :-)

Further reading:

http://kerneltrap.org/mailarchive/linux-usb/2010/2/27/6258315
http://digimend.sourceforge.net/

- Werner