Shanti777, really good job on the emulator so far, thank you. Sound, controls and emulation is good. After alot more testing, the main issue that needs fixing so far is the virtual keyboard not working after loading up some of the atari 5200 games. (testing version 1.2 in the first post) This makes it not able to start many atari 5200 games after the game has loaded since some of the games require keys not currently mappable to buttons to start up the game. I cant press those keys since I cant move the cursor at all on the virtual keyboard right now which needs fixing or many atari 5200 games will remain unplayable on your emulator. Some of the games such as ms pacman, berzerk, hero, frogger therefore I could not actually start the game after loading at the moment. Again this only happens in an atari 5200 game so far (keyboard worked fine on atari 800 game montezumas revenge and castle wolfenstein). One specific game Bounty Bob Strikes Back which is a atari 5200 40kb cartridge the keyboard did work.
It would be good if possible to also add the ability to map keys to other buttons and even the second analog stick (if present) and save the keyboard layouts, so that certain important keys can be mapped in game to buttons, otherwise some may rely on the keyboard during play to access other needed/important keys which makes it hard to play. Try playing castle wolfenstein without mapping buttons
A bit related, I just tested a wireless Logitech K360 keyboard works on the RG350 but it did not work unfortunately on the playgo (a black version of the pocketgo2). Another wired keyboard, Foldable Bluetooth Keyboard, Jelly Comb Dual Mode Bluetooth & USB Wired also worked on RG350 both using a JSAUX USB-C to USB A 3.0 Adapter (2-Pack). Perhaps you can support the external keyboard.
Dingux-Atari seems to have some of the keyboard mapping to buttons code you might be able to use. Your new emulator is based on 4.1.0 with better sound etc while this one is based on the older 2.0.2 OPK: https://github.com/retrogamehandheld/OpenDingux/raw/master/Emulators/DinguxAtari_2014-04-28.opk
Source Code: https://github.com/kerheol/dingux-atari
I put the 5200.rom, ataribas.rom, atariosb.rom and atarixl.rom and put those files in /media/data/local/home/.atari/roms to make it work after installing the OPK for dingux-atari. Original version thread which discusses keyboard: https://boards.dingoonity.org/dingux-releases/dingux-atari-atari-8001305200-emulator-for-dingux-v1-1-0/
I still have it installed since some of the games I cant yet run on your emulator until the virtual keyboard works in all the atari 5200 games and because it has keyboard mapping to buttons. Most 5200 games you still have to use the cartridge management/insert catridge/warm reboot from main menu, it crashes some when trying load atari 5200 from the main load screen instead. By the way zx81 mentioned he bought a RG350 so may start redeveloping his emulators.
A few may need some tweaking, pitfall 1 doesnt seem to start for me after the game loads fine even when I also tried on the other emulator as well which I could even access the virtual keyboard.
There is also Atari 5200 only emulator by AlekMaul (a5200) which doesnt require selecting the cartridge type, but lacks keyboard mapping or a virtual keyboard. It doesnt run 100% of the games. The opk is at: https://github.com/retrogamehandheld/OpenDingux
Put the 5200.rom (the bios) into /media/home (not in the /media/home/.a5200 - the emulator wont work) Games can be anywhere unzipped. Games did not load for me when they were zipped one file per zip on that one.