Test ROM Request: Details of Accessing VRAM During Rendering

[alyosha-tas]

Hello,

As the title says, I'm requesting a test ROM that can give the details for what is returned from reads from VRAM by the CPU during rendering. The reason for this request is that recently there was an attempt to play back a Tool Assisted Speedrun of Wario Land II on console, but there was a de-sync. I tracked the de-sync down to a VRAM access that happens at the very end of rendering on scanline 22.

Up until now, this case had been dealt with by returning 0xFF. However this is not what console showed. Also, the actual value at the address being read is already 0xFF. So, it has to be returning something else. I think it's returning the last value read by the PPU, and when I put this behaviour in my emulator I get the correct result (the same de-sync displayed on console.) But, this is just speculation.

So, it would be very helpful to have a test that evaluates what is being returned for individual cycles during scanline rendering, especially near the end of a scnaline when the PPU stops accessing VRAM.

(Also thanks for your current tests, they are very helpful and easy to understand.)