genesis rom corrupting/hacking issues

polterguy · 11-02-2010, 03:19 AM

Hi all, after several months of utilizing programs and docs from Zophar, I've worked myself into a corner and decided to actually register and see if any of you can help me. My goal, in short, is to successfully corrupt several genesis/MD roms and video capture the graphical glitches to use in a video project. Unfortunately, I've found out that genesis roms are very prone to crashing when any data in the rom is edited. Corrupt and Erosion have been good tools, but I'm kinda shooting in the dark when it comes to parameters to try. I've been assuming that the portion of the code that assembles the background and sprite layers according to the level and character's position is what I'm looking for, and possibly something to do with the VRAM, if that is possible. Could anyone give me some tips on the subject, and let me know whether data location in ROMs changes depending on the game?

kone191 · 11-02-2010, 07:37 PM

Hard to give any tips expect than this: "whether data location in ROMs changes depending on the game?"

All the roms are different & their data is stored in different places in the rom although as played, some may seem a lot the same.

InVerse · 11-02-2010, 08:47 PM

Many Genesis ROMs have routines that verify that data hasn't been corrupted prior to running. To fix this, you'll need to update the checksum to match that of your hacked ROM. You can do that using Fix Checksum.

I'm not sure how relevant it is to what you're wanting to do, but I would recommend only working with .bin format ROMs. If you need to convert your ROMs, you can do so using SBWin.

And yes, data positions are different from game to game. There is no standard format that says "graphics go here, sound goes here, level layout goes here, etc.". It's all a matter of where the programmers felt like putting it.

polterguy · 11-03-2010, 10:43 PM

Fix Checksum is exactly what I was looking for, I knew it was something simple like that. Now comes much more trial & error.... if anyone is interested i'll post the finished product when I'm done. Thanks a bunch InVerse!