Miyoo Mini Plus Onion OS setup — ROMs, BIOS files, and common fixes

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Install Onion OS from the official GitHub releases and transfer your ROMs to the correct folders on the SD card. This is the recommended first step for any new Miyoo Mini Plus.

1. Download the latest Onion OS release from github.com/OnionUI/Onion — look for the file named Onion-v4.x.x.zip (the full release, not just a patch).
2. Insert your Miyoo Mini Plus's microSD card into your PC. If the card has stock firmware on it, you can update in-place — Onion installs alongside stock and does not erase your ROMs.
3. Extract the Onion zip to the root of the SD card. Overwrite any existing files when prompted.
4. Safely eject the SD card, insert it back into the Miyoo Mini Plus, and power on. The device will reboot once or twice during installation — this is normal. Wait for the setup wizard to complete (about 60–90 seconds).
5. After Onion OS boots, copy your ROM files back into the SD card at the correct paths. ROMs go in Roms/[SYSTEM]/:

• Roms/FC/ — NES (.nes)
• Roms/SFC/ — SNES (.sfc .smc)
• Roms/GB/ — Game Boy (.gb)
• Roms/GBC/ — Game Boy Color (.gbc)
• Roms/GBA/ — Game Boy Advance (.gba)
• Roms/MD/ — Sega Genesis / Mega Drive (.md .bin .smd)
• Roms/PS/ — PlayStation (.chd recommended; .bin+.cue also works)
• Roms/PCE/ — PC Engine / TurboGrafx-16
• Roms/NEOGEO/ — Neo Geo arcade games (.zip ROM set)

6. After copying, go to Apps → Onion → GameSwitcher → Refresh ROMs, or simply navigate to a system on the main screen — Onion scans automatically on first access.

Scraping game art: Onion includes a Scraper app (requires Wi-Fi). Open it from the Apps section, sign in with a ScreenScraper account (screenscraper.fr — free), and scrape by system or full library. Art downloads take a few minutes per system.

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PS1, Neo Geo, and Sega CD require BIOS or firmware files that Onion OS does not include. Without them, games exit immediately after launch.

All BIOS files go in the BIOS/ folder at the root of the SD card.

• PS1 (required) — place scph1001.bin in BIOS/. This is the most universally compatible PS1 BIOS. Dump it from your own PlayStation 1 console. Without it, PS1 games will not launch on Onion OS. Some cores also accept scph5500.bin (Japan), scph5501.bin (USA), or scph5502.bin (Europe) — but the scph1001.bin covers most games.
• Neo Geo (required for most games) — place the neogeo.zip ROM file (the Neo Geo system BIOS) in Roms/NEOGEO/ alongside your game ROM zips. Without it, most Neo Geo games will not boot.
• Sega CD (required) — place bios_CD_U.bin (USA), bios_CD_E.bin (Europe), and/or bios_CD_J.bin (Japan) in BIOS/. The region file must match the region of your Sega CD game.
• GBA (optional) — gba_bios.bin in BIOS/. Not required; the mGBA core handles most GBA games without it.

After placing BIOS files, retry launching the game. If PS1 still fails, open RetroArch → Settings → Directory → System/BIOS and confirm it points to /mnt/SDCARD/BIOS.

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If games appear in the list but will not launch (or do not appear at all), these are the most common causes and fixes.

• Wrong ROM folder: Onion's folder names are short system codes (GBA, SFC, PS). A folder named PlayStation or PSX is not scanned. The complete folder name list is at onionui.github.io/Onion/docs/systems.
• PS1 CHD vs BIN format: CHD is the recommended PS1 format on Onion — smaller files, faster loading. If you have .bin + .cue files, both must be present and the .cue file must reference the correct .bin filename. A .bin file without its .cue sheet will not launch.
• Multi-disc PS1 games: each disc is a separate .chd or .bin+.cue set. In Onion, use the disc swap option inside RetroArch (open the RetroArch menu mid-game with Select + R2 → Disc Control → Eject / Load New Image) to switch discs.
• Core mismatch: if a game launches but looks wrong or crashes, try switching the RetroArch core. In Onion, long-press on a game → Core → select an alternate core. For PS1, Beetle PSX has better compatibility than PCSX ReARMed on demanding titles (but PCSX ReARMed is faster on the Miyoo's limited hardware).
• Storage corruption: the Miyoo Mini Plus ships with cheap SD cards. If games worked then stopped, the bundled card may be failing. Re-flash Onion to a reliable card (SanDisk Ultra or Samsung PRO Endurance at 64–128 GB).

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Quick settings and Onion features that improve the experience after the initial setup.

• GameSwitcher (Select held): hold Select from anywhere to open GameSwitcher — resume the last game instantly or switch between recently played titles without navigating menus.
• Save states: in RetroArch, Select + R1 saves a state; Select + L1 loads the last state. RetroArch auto-saves on exit if Save State on Exit is enabled (Settings → Saving).
• Wi-Fi apps (Miyoo Mini Plus has Wi-Fi; V1/V2 do not): connect to your network under Apps → Onion → Wi-Fi, then use the SSH server, FTP file transfer, or browser-based ROM manager to transfer files wirelessly instead of swapping the SD card.
• Display settings: Onion lets you choose between pixel-perfect integer scaling and aspect-ratio-correct display per system. Set under RetroArch → Settings → Video → Scaling. For SNES and GBA, integer scale (4:3 on the Plus's screen) preserves pixel sharpness.
• Brightness and battery: the Plus screen at full brightness drains the 3000 mAh battery in about 5–6 hours. Set brightness to ~70% for 7–8 hours. Onion displays the battery percentage in the status bar.
• Onion update: go to Apps → Package Manager to update Onion or add optional packages (themes, ports, apps) without re-flashing the full image.

Community and support: the Miyoo Mini Plus community is active on the r/MiyooMini Reddit and the Retro Handhelds Discord (discord.gg/retrohandhelds). Both have pinned setup guides for Onion OS and troubleshooting megathreads.