Bios files typically just go in the retroarch system folder most times. There are a few exceptions that require their own sub-folder in the systems folder, but this isn't one of them. Many emulators are very picky when it comes to needing certain bios dumps.
For example, the atari800 bios core in question here is looking for several bios files with certain MD5SUM checksums. Make sure you check the files you have to make sure they match what's listed on the core info page for libretro to make sure you don't have issues due to having the wrong bios files. From the libretro forums:. Load any atari800 or 5200 with Atari800 3.1.0 core. Does not matter if your game does not work, we just need to be able to enter the menu. when game is loaded, press F1 (this is quick-menu, just cancel or press F1 again or whichever is your quickmenu hotkey) - this will show you Atari800 menu(use joystick/gamepad to navigate. On Xbox 360 controller.
Button B is OK while Y is back. If nothing is working, go to quick menu-Controls and choose ATARI Joystick for User 1 Device Type. While im Menu, goto Emulator Configuration - System ROM Settings then Find ROM images in a directory. Locate your atari5200 and atari800 bios roms. These roms have to be uncompressed.Atari400/800 - atariosb.rom -XL/XE - atarixl.rom -Basic - ataribas.rom -5200 - 5200.rom Once rom folders are set, press SPACEBAR to save location.
In both emulators, the atari.cfg file is shared between Atari computers and the 5200. In lr-atari800, the core options likewise apply to both by default. However, for either emulator, if you have a core options file in your atari5200 directory, it will let you have separate settings for just the 5200 system. Adjust your Hyperspin “Atari 5200.ini” to match the same rompath set in the “a5200.ini” Set your extensions to zip, 7z; Set your exe; Set your parameters; MY SETTINGS FILE Atari 5200.ini If you don’t have a settings file for Atari 5200 I have attached mine above or a full set can be found HERE.
5.go back to Emulator Settings and then choose Save Configuration file. goto quick menu and close content. By this time, you can now play games. Do note that the games has to be extracted and uncompressed too.
You can use Load Content method in Retroarch. If you load a compressed rom, your game will not play and you are stuck in Self Test mode. When you do load a game, and see only black screen, just press Enter or OK on your gamepad. I'm not a big fan of the Atari 5200 core in retroarch, as I always seem to have one issue or another with it. Although those issues can be overcome, I generally just use a stand-alone emulator for Atari 5200 games now as it's just easier.
I'm not sure how many of them are out there for the Atari 5200, but here are a couple that I know of that work well:Kat5200 -Altirra -They're both relatively easy to setup (the controller bindings can be a little odd to setup at first).I know it doesn't directly help with your issue, but if you're willing to try a stand-alone emulator, then this might help.Edited January 13 by CDBlue.