This is far more exciting, since it adds functionality to they system. Maybe I'll dust off my old hacked up NES and do this at some point. If only I had the free time these days.
Thx for sharing :)
The game only has a limited amount of time to do all of its logic before the VSYNC interrupt forces it to draw to the screen. Game have different ways of handling this, e.g. by rolling back and abandoning the changes, drawing whatever they have, etc.
A faster clock should make it s/t games that don't always get done in time should at least have a better chance.
Is this a case of "you ain't gonna need it" overengineering; or was the PPU used in other products. (And thus these pins were used elsewhere?)
I don't know if there were any actual machines that used dual PPUs, but the functionality was likely intended for creating an arcade machine with dual-layer background graphics.
If they had extra pins that they had no use for, I'm sure this would have seemed like a very easy and cheap addition. You take 4 unused pins and add 4 pulldown resistors. Then when you go to draw the background, instead of using index 0, you take the value for the index from those pins.
Maybe they planned to use this in arcade hardware, where you'd have a bigger budget than a home console and could afford two PPUs. Then you'd get more colors, and you could scroll the background layer independently from the foreground layer. I believe they later added support for independent layers on the SNES hardware so this type of thing was probably already in demand from game designers.
I found this video that shows a Playstation running in the background of Super Mario Bros: https://youtu.be/TCsle-J9YzY?si=oyj_zZCKGionnzLu&t=423
EvanAnderson•1d ago
It would have been neat if Nintendo had set this up so the stock unit could have been expanded like this.