Putting together a board support for a custom board, it is not clear what code or libraries should be used for processor internal peripheral support.
There is a profusion of include files for the AVR processors and it is hard to know which one is best supported. The ASF files are really complicated and cluttered. #include <atmel_start.h> seems incomplete. There are older include files, but they seem to be broken. Since the reorganization of the online files, things have gotten messier, as the links to documentation have been broken.
What support / include files are prefered?