I want to build one myself as well, but I don't want to use existing code as a guide, rather challenge myself to implement from raw specs.
The problem is I haven't really found any yet that helped me (admittedly, I have so far devoted just one Saturday morning to it.) Are there any specs about the hardware that you used, or that anyone else can share?
> 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.
Shoutout to TASVideos here, who maintain a fairly up to date list of test ROMs for various hardware features. Once you have the emulator basics down (working well enough, say, to run Super Mario Bros, which is surprisingly demanding) you can throw blargg's tests at your emulator and start chasing the accuracy rabbit down the most marvelous of rabbit holes.
The problem is I haven't really found any yet that helped me (admittedly, I have so far devoted just one Saturday morning to it.) Are there any specs about the hardware that you used, or that anyone else can share?