You choose the worst file in the whole tree to start. You are not supposed understand it unless you are Eric Biederman ;-)
I disagree with the above. When I was produceing the base files for the 440bx I looked at a lot of the different files in the tree and IMO the amd source code was some of the cleanist and well designed of all the files I looked at. I found those files easyiest to follow and the most consistent in naming and in methodoloy.
I think they are an excellent place to start. The only thing the user should recognize is that those devices are somewhat complicated and that all the layers are a result of that.