Well, I spent all day hacking on Sunday and managed to get some graphics to display on the NES emulator. As I hoped, I was able to use the same architecture as the C64 Emulator and actually am using the exact same processor implementation. The ADC and SBC instructions have slightly different modifications (the version of the 6502 used in the NES does not make use of the Decimal flag for BCD mode), but that’s *it*.
I had a business trip and hacked on the plane and manged to get Pacman to become playable (but look horrible).
I was having some major palette issues. Using the tried and true bug-fixing technique of…stepping away…I was able to track down why the graphics were totally jacked (had some incorrect handling of the Attribute tables as they relate to the tiles displayed on the screen). So now Pacman looks *almost* correct. At least I thought so until I made the screenshot. There is a lot of work to do to get the sprites to draw correctly. Thankfully the background is at least correct.
My “end goal” is to get it so that my wife can play Super Mario Brothers 3. I’m hoping to implement the mapping for it soon. Currently Super Mario Brothers (1) will play the starting demo (but has all sorts of artifacts on the screen including the fact that I’m not handling transparent pixels).
So, as you can tell, a lot of work left… but I’m pleased with it as a proof of concept and a definite work in progress. I’d like to also implement the audio for this one (which can hopefully be reused for the C64).