Open question in NESdev: measure the worst-case setup and hold time for the NES PPU, so we can have a proper timing diagram. Apparently it has never been done, even after we have transistor-level emulators. You need many hard-to-obtain samples across revisions and date codes, and the question only matters if your cartridge ROM is slow enough to walk on the edge of stability. This is irrelevant to emulators and 99.99% of homebrew developers with <= 150 ns chips (unless you're a stubborn developer like me who wants to bitbang the NES bus), which is why nobody has done it.
#NES #NESdev