A list of open problems in how the SNES works:

  1. What exactly happens in the DMA crash bug on the v1 CPU?

  1. What is the exact timing for the garbage that appears on the screen when switching modes mid-frame?

  1. How is the sprite data cached for each scanline and is there a way to abuse the timing to inject data into OAM midframe?

  1. Are there any unexpected interactions with ExtBG that haven't been tested? For example I am not sure if anybody tried Direct color mode with ExtBG yet (probably won't work, but who knows)

rainwarror wrote a test ROM for direct color mode+EXTBG in 2022: https://forums.nesdev.org/viewtopic.php?t=24081


  1. What are the exact decay rates for the MDR?

  1. Emulating Coprocessor bus conflicts

  1. What about unused pins on the PPU, CPU, and APU -- Even though a game can't use them they are worth exploring IMO

https://sneslab.net/wiki/List_of_unconnected_pins


  1. can we predict the APU crosstalk 16 bit bug?

https://forums.nesdev.org/viewtopic.php?p=279491&hilit=APU+crosstalk#p279491


  1. What happens to the very first pixel on the scanline in Hi-res Math?

  1. Various PPU registers still need to know when writing to them is effective.

TODO: put list of PPU registers here


Most of these problems require access to a logic analyzer.

Discorded but not wiki'd by p4plus2