Writing a Game Boy emulator
I've been developing a Game Boy emulator with a friend as well, and struggling a lot with the poor documentation. There's a very thorough PDF with lots of information online but when it comes to Opcodes (and cpu flags) it's quite inaccurate.  Most often than not I have to skim through several github projects to check that the implementations match. (which sometimes don't)<p>Perhaps we'll start doing a Nintendo64 emulator instead which is more complex but from what I've heard/read has much better documentation.