Planet Bob - Even more problems...

RSS Bot · September 24, 2006

Hi there!

Ah, the challenge!

I ran into some more things making my port more and more complicated:

1. The game uses raster interrupts. Since I decided to make my port a 32K no-mapper game, this is something I have to analyse carefully. Of course there's workarounds for this. For example one can approximate the amount of cycles until a certain scannline is met. Or one can have an invisible sprite hitting an invisible background block at a certain scanline, I think the NES has an interrupt for this. Of course, once I find out what the C64 version uses them IRQs for, maybe the NES can solve that particular task without tricks anyway

2. The game creates some 4K worth of lookup tables, which I have to stuff into the ROM somewhere. It's also using 1K of the C64s internal charset ROM. I already dumped those 5K from a VICE savegame, but I really hope the rest of the ROM doesn't continue to get used up at this pace...

3. Selfmodifying code... ugh... there is a snippet within the initialization code of the game that overwrites stuff of the code that ran before it. I *think* it shall prevent some reset delay by disabling uneccessary copying jobs. Anyway, I have found me a good 6502 simulator by now, were I can execute this code and have a close look on what it'll do exactly :ponder: