Hello. Although I don't know the Z80 instruction set "by memory" myself, I am a Sega Genesis/Megadrive Assembly hacker, and I am looking for a way to port my game to an arcade system...
I spent a lot of time trying to find a way to make it work on its arcade-brother, the "Sega MegaPlay", but there is little to no documentation that is not "guesswork", and reverse-engineering one of these ROMs is quite painful considering my goal, while feeling I'm not going anywhere with a coming ROM that is not even safe to run on true hardware.

Today I came across this post from other forum: http://www.sega-16.com/forum/showthread.php?19726-The-Neo-Geo-was-just-a-glorified-Genesis
And it feels like a much better alternative!, considering processors (and therefore instruction sets) are the same, I guess I can port my engine with some ease, to an arcade system just like originally planned.

I always try to take the hardware's best possible approach, therefore I ask here first because I don't want to work being misguided, while doing the most possible by hand and not sticking to third-party libraries.
Where may I find the ROM header, Neo Geo's address map, and Interruption design?
Is there any security system or condition(s) to satisfy during ROM boot?
Is there any software doc that explains the input, video and audio system?
Is there any known good debugger?


Hey, I've answered some of your questions in the IRC channel before, but I figured I'll answer them here as well so others can benefit. smile
Where may I find the ROM header, Neo Geo's address map, and Interruption design?
I'm assuming the "ROM header" would either be the 68k program header (found at $100; linked below as part of the answer to another question) or the 68k vector table (starting at $0).
The address map is pretty straightforward. Information on interrupts can be found here, with some specifics about the Timer interrupt elsewhere.
Is there any security system or condition(s) to satisfy during ROM boot?
Yes; these are particularly found in the 68k program header
Is there any software doc that explains the input, video and audio system?
If you don't mind reading leaked/confidential documentation, an English version of SNK's docs were leaked some time ago; otherwise, the Neo-Geo Dev Wiki is your best bet.
Is there any known good debugger?
I personally use MAME; remember to start with -debug.


Is there footage of your game available?

General code will be easy to port obviously, gfx related things might be harder depending on what you achieve on the megadrive. Some VDP effects are de facto impossible on neogeo.


Well, it's a fact that I have to write such a sprite mapping converter that also takes into account to split those sprites with 24 and 32px width into two (Sega Genesis max sprite size is 32x32), which will therefore increase the sprite usage.

My real concern is the layer capability. Sega Genesis support two scrollable plane maps (+ 1 "fix" window, attached to first map plane), and a sprites layer that supports a maximum of 80 sprites, 20 or 16 per scanline depending the screen resolution set.
NeoGeo's Fix map seem unscrollable, therefore I think I have to draw the objects, and both foreground and background using sprites, and probably move the HUD to Fix instead.. And, from Genesis side, I am already using a lot of tricks and illusions to display more parallaxes to the background (with sprites over some things, plane address switching and gradient drawing with Horizontal Interrupt, animated background tiles, etc). The backgrounds are quite wide horizontally and vertically as well.
I'm afraid to overload the sprite limit with much ease.


I was thinking more about shadow/highlight tricks, complex priority abuses or CPU generated tiles.

Replicating a scroll layer just takes 32 linked sprites to get a 512*512 map.

Sprite limit should be fine in most scenarios, again that's hard to tell without knowing the scene setup.


why not using a Genesis chip, and make an adapter for the neogeo? I would be the first to buy it (^_^)




Hello I know only one genesis game to neo geo CD, it's Columns by Neobitz
May be you could see something interesting for you

avatarLa Neo Geo CD à son site (en tout cas elle essaye...): http://neogeocdworld.info/
Le forum de la Neo Geo sur Yaronet: forums/264

Un petit site sur l'Atari Falcon avec plein de trucs bon pour votre poussin: http://falcon.ti-fr.com/


Ouais, je sais. Je l'ai déjà essayé, c'est pour ça, ça m'a donné des idées. XD