The same content updated with more explanation and showing how it's done. Twitch stream style.
https://www.youtube.com/playlist?list=PLjwOF_LvxhqTXVUdWZJEVZxEUG5qt8fsA
Controller Input
https://github.com/PeterLemon/N64/tree/master/Input/CPU
Lesson 7 | Lesson 9