The steps to build it are: Take a final sonic 2 rom from somewhere, name it s2.bin, stick it in the directory with split.bat and run that, then run build.bat. You don't have to download AS (that's included this time). The main file to edit is called s2.asm.
- Unmodified, it assembles to be perfectly identical to Sonic 2 final, even with the unchanged (source) version of AS like the one I included, and it assembles fairly fast (1-5 seconds depending on the computer).
- The Z80 sound driver is disassembled and integrated into the build process such that it gets assembled and compressed into the rom when you build. It uses labels from the 68k code to choose the correct pointers to use and banks to switch to, so you don't have to worry about breaking the sound by adding unrelated stuff anymore.
- I identified more objects and addresses, split more things to file like the sprite mappings, added lots of comments, named some labels, added more equates, fixed disassembly mistakes here and there, etc. etc. just look at it already.
Extra downloads (the above download is needed first in any case):
Linux build tools
Mac build tools
s2.asm split into many little included asm files
Thanks to shobiz for reviewing my changes and providing invaluable feedback and numerous suggestions, Puto for compiling the build tools for Linux and Mac and giving some suggestions, Tweaker for recommending I use Hivebrain's terminology and answering some questions that helped a little, Varion Icaria for answering some questions and showing me some labels, Hivebrain for his 2005 S1 disassembly, everyone behind the Sonic 2 articles on SCHG, everyone that contributed to Kens, and Nemesis and Aurochs and everyone who made the previous S2 disassembly possible.