Last updated: September 2026
muOS is what I put on every Allwinner H700 handheld the day it arrives. Stock Anbernic firmware works, in the sense that games launch; muOS is the version of the device the hardware deserved. Faster menus, every RetroArch core current, PortMaster built in, Wi-Fi that stays connected, and a settings layer that lets you fix per-system behaviour without editing config files.
The install takes fifteen minutes. The part that takes thought is the card layout, so I cover that properly rather than telling you to pick one.
Supported Devices
The current release, named Pixie, supports:
| Brand | Devices |
|---|---|
| Anbernic | RG35XX 2024, RG35XX Plus, RG35XX H, RG35XX SP, RG35XX Pro, RG28XX, RG34XX, RG34XX SP, RG40XX H, RG40XX V, RG CubeXX |
| TrimUI | Smart Pro, Brick |
The original 2022 RG35XX uses a different chip and does not run muOS; that device gets GarlicOS. Check the model on the box or the sticker inside the battery cover before you flash anything.
What You Need
| Item | Notes |
|---|---|
| A microSD card for the OS | 32 GB minimum. A2-rated cards from Samsung or SanDisk make the menus feel faster. |
| Optionally, a second card for games | Any size. This is the two-card layout below. |
| The muOS image for your device | From muos.dev. Open the download page and pick your device under the current release. It downloads as .img.gz. |
| A flashing tool | Rufus or Win32 Disk Imager on Windows, balenaEtcher on any OS. |
| A PC with a card reader |
Do not extract the .img.gz. Rufus and Etcher both read the compressed image directly.
Card Layout: One Card or Two
muOS supports both, and each has a real trade-off.
One card. The OS and your games share the card in slot 1. Simplest install, one card to manage, and a reflash means backing up your ROMs first.
Two cards. Card 1 in slot 1 holds only muOS. Card 2 in slot 2 holds ROMs, saves and BIOS. Reflashing or updating the OS never touches your library, and you can move card 2 between devices. This is what I run.
The RG28XX has one slot and gets one card. Everything else has two.
Flashing
- Insert the OS card in the PC.
- Open Rufus. Select the card under Device, click Select and pick the
.img.gz. Leave everything else default and click Start. Etcher is the same three steps: image, target, flash. - Wait for it to finish, then eject the card. Windows will complain it cannot read the card’s Linux partitions; ignore it.
- Put the card in slot 1 (TF1) and power on.
First boot asks three things: your device model from a list, your time zone, and the time and date. Get the device model right; picking the wrong one gives you a garbled screen and a reflash.
After that it reboots into the main menu. Power off, pull the card, and put it back in the PC: first boot has created the folder structure you need for the next step.
Folders: Where ROMs, BIOS and Saves Go
After first boot, the OS card shows four folders on the partition Windows can read:
| Folder | Purpose |
|---|---|
ROMS | Your games, one subfolder per system |
MUOS | Settings, BIOS, saves, the update archive |
ARCHIVE | Where you drop update and app packages |
BACKUP | Where muOS writes its own backups |
One-card layout
ROMs go in ROMS/<system>/. The system folder names are yours to choose; muOS assigns a core per folder rather than guessing from the name, so ROMS/SNES and ROMS/Super Nintendo both work. Keep them short and obvious.
Two-card layout
Format card 2 as exFAT. Create a ROMS folder at its root with the same per-system structure. Put card 2 in slot 2, boot, and go to Configuration > Storage. Set the ROM, save and BIOS locations to SD2 and choose the migrate option if you already had content on SD1.
BIOS
BIOS files go in MUOS/bios/ on whichever card holds your storage, with the exact filenames RetroArch expects. My BIOS reference has every name and hash, and the PS1 BIOS guide covers the three files most people need first.
Saves
Saves and states live under MUOS/save/. Back this folder up before any update, even though updates preserve it, because SD cards fail on their own schedule.
Assigning Cores
Open Explore Content from the main menu and browse to a system folder. The first time you open a folder, muOS asks which core to use for it. Press the assign button (the on-screen hint shows it, usually Select or Y) and pick from the list. Pick per system, not per game, and it remembers.
My assignments on the RG35XX H and RG40XX:
| System | Core |
|---|---|
| NES | Mesen or Nestopia |
| SNES | Snes9x |
| Game Boy, GBC | Gambatte |
| GBA | mGBA |
| Genesis, Sega CD | Genesis Plus GX |
| PS1 | PCSX ReARMed |
| N64 | Mupen64Plus-Next (the H and 40XX; skip on the Plus) |
| PSP | PPSSPP (standalone, not the core) |
| Arcade | FinalBurn Neo |
The RetroArch cores guide explains the choices in each row.
Wi-Fi, Bluetooth and Settings
Configuration > Wi-Fi on the H, SP, 40XX, CubeXX and Smart Pro. Enter the password with the on-screen keyboard once and it reconnects on its own. Wi-Fi enables PortMaster downloads, RetroArch’s online updater, and scraping box art.
Configuration > General has the settings I change on every install: screen brightness curve, the low-battery warning level, and the button that opens RetroArch’s menu in-game. I bind that to Menu so the shoulder combos stay free for save states.
Configuration > Power controls sleep. Set the idle sleep to five minutes and suspend on power button; the H700 devices resume from suspend instantly and lose almost nothing overnight.
PortMaster
PortMaster brings native ports (Stardew Valley, Half-Life, Celeste, and hundreds more, each needing the game’s own data files) to the device. It ships with muOS.
With Wi-Fi: Applications > PortMaster. It updates its own list and installs ports on demand.
Without Wi-Fi: download muos.portmaster.zip from the PortMaster GitHub releases, put it in MUOS/ARCHIVE/ without unzipping, and install it from Applications > Archive Manager. Ports then go in ROMS/PORTS/ with their data files under ports/<game>/ on the same card.
Updating muOS
Point releases come as patch files rather than full images.
- Download the update from muos.dev.
- Copy it to
MUOS/ARCHIVE/on the OS card. - On the device, open Applications > Archive Manager, select the file, and let it install.
- Reboot.
Major versions with a new name (Pixie replaced its predecessor this way) sometimes require a fresh flash. The release notes say which. With the two-card layout a fresh flash is a five-minute job that leaves your games alone.
Common Problems
Garbled or blank screen on first boot. Wrong device selected at setup. Reflash and pick the right model.
ROMs folder empty in Explore Content. The card is formatted FAT32 with a partition Windows created oddly, or the games are one folder deeper than you think. Reformat card 2 as exFAT and check the path.
No BIOS found for PS1. Files are in ROMS/bios or the root instead of MUOS/bios, or the filenames are wrong. Case matters on the Linux side.
Wi-Fi drops after sleep. Turn off Configuration > Power > Wi-Fi off on sleep.
PortMaster ports fail to launch. The game’s data files are missing from ports/<game>/. Each port’s page on the PortMaster site lists exactly what to copy.
Battery drains in sleep. Suspend is not enabled; the screen is off but the CPU is awake. Check Configuration > Power.
FAQ
Is muOS free?
Yes. Open source, no pledge required.
Does muOS replace the stock firmware?
It runs from its own card. Pull the muOS card and put the stock card back and the device is stock again. Nothing on the device itself is modified.
One card or two?
Two, if the device has two slots. It makes updates and reflashes risk-free.
Does muOS run on the RG35XX 2022?
No. That model uses a different chip. Use GarlicOS.
Can I use my saves from stock firmware or GarlicOS?
Yes. Copy the .srm files into MUOS/save/file/<core name>/. State files go under MUOS/save/state/.
muOS | muOS on GitHub | PortMaster
Last verified: September 2026