[kouteiheika]

> Are there any specs about the hardware that you used, or that anyone else can share?

Everything you need is either on http://wiki.nesdev.com or on their forums. I know because that's what I did with my NES emulator - I explicitly didn't want to look at any source code and instead wanted to implement everything only based on the docs.

Granted, what's on the NESdev isn't always easy to grok, up to the point of being really confusing sometimes. What I've found really helped is gradually setting up a test suite based on various test ROMs I could find, which even allows you to implement some parts of the emulator TDD-style once you get the basics up and running.