I’m assuming the problem is that the version of the game or neogeo are not matched to the version of MAME. The thing is, the trial and error is taking forever and I think I’m even redownloading some ROMs from sites I’ve already been to. Is there a smarter way to go about this?
Add the bios to your library (neogeo.zip)
I have two zip files added: neogeo.zip and the game itself. I still get the error for the Metal Slug games.
Should work. Are you using merged, split, non merged? I’m not really familiar with openemu and just looked at a basic guide really fast. Does version match matter with openemu? I assume so. It def can with mame and you want to ensure your rom and bios came from the proper version set (typically most recent which iirc is 0.274) though tbf this probably doesn’t impact a game like metal slug unless your rom is ancient, which is possible if you got it from a rom site
Note that if you do get them to run they run poorly. Mame emulates them accurately but they ran poorly on the original hardware. The frame rate counter will read 100% but it will be choppy. This is accurate behavior. You can overclock the emulated cpu which sometimes fixes this but also sometimes breaks the game
In case it’s still needed, or if someone needs it, a suggestion that could work in OpenEmu (can’t test as I don’t have a Mac), try putting neogeo.zip of the correct region in the same folder as the ROM. Usually emulators can find the Neo Geo BIOS that way.
And a tip, most modern PC releases, including iirc the Amazon Prime bonus, come with both the ROM and a matching BIOS. At worst, you’ll have to extract the ROM from the Linux build with 7-Zip or similar (points at GOG). And those PC releases, they’re dirt cheap too, specially when discounted. Metal Slug specifically, 1 to 3 and X all are emulated, and further titles already on PC, I have yet to confirm.



