nesdev.org

During the powerup sequence, does the ppu run/clock? ^_^;;

I'd say yes. If the CPU is on, then so is the PPU. I am not aware of anyway that the PPU can be paused by a pin or whatever. When you say power-up sequence I assume you mean the reset that the 6502 must do to use the Reset Vector. As for anything before that, then I assume the same. We need Kevin Norton or Brad Taylor to do a check for us (hint, hint).

I remember having one program that wrote tiles to CHR-RAM immediately without doing the LDA $2002 / BPL loop, and the graphics would always be corrupt. I have no idea how and not much interest in timing or figuring out how that'd be emulated though.

On a somewhat related note the PPU has a reset pin, I know on the front-loader reset button it resets with the CPU (screen goes black) while on the top-loader only the CPU resets (graphics stay on screen).

There's garbage because the PPU registers / scroll data are filled up with junk.

To make the things clear: when I emulate the power-up sequence, I follow the exact thing, but fetching or writting bytes imply PPU running too...