(Maybe an older approach):
When granted a new job, employer 'required' detailed study of the IC, by recommending a book that had both hardware and software intro, for the uP. That meant the memory mapping and I/O ports mapping, with some basic examples in the book.
I think that the mapping of things, and explanation of formats, such as '16 bit word size, transfered all at once' and such as 'Ram uses (up to) 20 bits for addresses', and some details on how to transfer address out from IC to RAM interface.
So, I guess I'm saying that the mapping features are a key aspect, whether interested in hardware design, or in writing software.