ref:

  1. https://geekhack.org/index.php?topic=55960.msg1291412#msg1291412
  2. https://deskthority.net/workshop-f7/t400-keyboard-trackpoint-pinout-t7678.html
  3. https://deskthority.net/workshop-f7/tmk-chibios-stm32-with-ps-2-mouse-trackpoint-t12666.html
  4. https://github.com/rampadc/arduino-trackpoint-extended
  5. https://www.facebook.com/notes/wez-furlong/building-a-keyboard-ii/10154296367151787