I poked around a little bit with the Atari 800 emulation. I found the core (atari800.so) and the info. According to what I could find, this core does indeed need a BIOS. It looks like a combination core that encorporates both computers and the Atari 5200 console. I found reference materials for this core over in the RetroPie wiki: Atari 800 and 5200 · RetroPie/RetroPie-Setup Wiki · GitHub. I've gotten close, but nowhere. I can get the core to load, but nothing displays. If I press (on my Xbox360 controller) the B button, it will eventually bring up an in-emulator menu for controlling various aspects of it. If I go in and tell it to load a program, then point to the ROM, it will come up to a screen that says I need a real OS to make it run. This is noted in the wiki reference above, but that is all the farther I got. Apparently I need to do so more work as far as configuring where it finds the BIOS files, as the core doesn't associate directly with RetroArch's default settings (and the preset path for BIOS). I'll keep messing with this when I can.
did you get any advance on this?
hey guys
Been trying to get IARL working via GS... Didnt think it should be that hard with a fresh build of LE 7.0.2. 
All I did was install the latest fresh LE 7.0.2 on rpi3, installed gamestarter 2.5, then tried IARL and its not installing. Complains of missing dependencies which prob should be part of the build. Am I missing something obvious here? Didn't think I was doing anything out the ordinary? Seems to be talk of LE8 now maybe I should try that?
Have also posted on Zach m's git see if he can help..
thanks
Just install LE, install Gamestarter and go to addon settings -> "download iarl & repo". It will download 2 zip files into /storage folder (addon and creators repo). Install both and update addon if an update is available. Until here, it can not be any problem, if something is wrong in this point, please check your internet connection and try to install iarl addon from zip again. Note that iarl addon installs a lot of dependencies and needed addons, so you must let it install everything until you see the "addon installed" notification.
After iarl is installed, these are the steps I follow to get it working with gamestarter:
addon settings:
-external launcher -> My system type: openelec RPi (Gamestarter addon)
-> RetroArch System folder (leave blank)
System list - context menu:
- update launcher: external
- update EXternal Launch command : select system -> YES
Enter system then launch game.
Gamestarter v2.5 does not start RetroArch Frontend on Libreelec v7.9.
Do I have to install something else?
EmulaterStation was started.However, ROM does not work
what raspberry model do you have? are you downloading/installing correct addon version for your OS? what is the output in gamestarter.log?
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By the way, some days ago I released latest v2.5 with some structural changes and some new features, you can take a look:
Release Gamestarter v2.5 · bite-your-idols/Gamestarter-Pi · GitHub