While it’s definitely possible to buy a new handheld, load up some games, and start playing, you might run into a few issues here and there. Some companies seem to be committed to introduce new features and updates for the custom firmware, but there are still dragons to be wary of.

This is where the community gets to flex its muscles, as we have custom firmware solutions for many of the best retro handhelds. If you own an Anbernic handheld, such as the RG35XX SP, you’ll definitely want to give muOS a spin. This is easily one of the best custom firmware solutions we’ve seen to date, and it’s continuing to get even better.

muOS Supported Devices

Anbernic RG28XX Angled view

Before getting started, muOS isn’t available for every retro handheld out there. Instead, it’s been specifically created with Anbernic devices in mind. In fact, you can even install and set up muOS on the original RG35XX 2023, despite it being the only one on the list that isn’t powered by the Allwinner H700 chip.

  • Anbernic RG35XX SP
  • RG35XX Plus
  • RG35XX H
  • RG35XX 2024
  • RG28XX
  • RG35XX 2023

How to Install muOS

So you’ve decided to install muOS on your RG-X handheld, and want to go through the steps to set everything up. Before you do that, the first recommendation we have to make is to not use the microSD card that came with your handheld. The only exception to this rule is if you happen to get a “KIOXIA” branded card. Those are actually pretty good, and you shouldn’t find yourself waking up one day to a dead microSD card.

microSD Card Recommendations

Steps to Install muOS

With your microSD card and handheld at the ready, here’s the muOS setup guide for your Anbernic devices:

  1. From your computer, head over to the muOS website.
  2. In the sidebar on the left, under Release, select your handheld.
  3. Under Current Release, click the Download hyperlink.
  4. Click the top Download link again.
  5. Download the muOS ZIP file listed.
  6. Once downloaded, extract the ZIP file.
  7. Plug your microSD card into your PC.
  8. Open your USB formatting utility of choice. Here are a few recommendations:
  9. Flash your microSD card by selecting the muOS Disc Image that just extracted.
  10. After the card is finished being flashed, remove it from your PC.
  11. Insert the card into your handheld.
  12. Wait for it to finish booting.

After muOS is finished booting for the first time, you’ll be greeted with a “Device Type” screen. Select your device from the list. Then, pick your Time Zone and manually enter the Time and Date. Once this is finished, turn off your handheld and plug the microSD card back into your PC.

Set Up Your muOS microSD Card

When you plug your microSD card back into your computer, you’ll probably run into a slight speed bump. For one reason or another, Windows doesn’t recognize the ROMs partition. Instead, File Explorer makes it appear as though there are two partitions with not much space. Fear not, as there’s a quick and easy fix.

  1. With your microSD card inserted into your PC, open Disk Management.
  2. Locate and highlight the microSD card from the list.
  3. In the bottom panel of Disk Management, right-click the ROMS partition.
  4. Select Change Drive Letter and Paths…
  5. Click the Add… button.
  6. Make sure that Assign the following drive letter is selected.
  7. Click the drop-down box to the right.
  8. Select the drive letter that you want to use.
  9. Click the OK button.

The ROMS partition is now accessible, and you can start transferring your games to the microSD card.

Add Games and BIOS Files to muOS

Unlike a lot of the other custom firmware options out there, muOS doesn’t force you to follow strict guidelines. Really, all you need to do is have folders for each system and have your ROMs placed accordingly. Here’s an example of how you can lay things out:

  • ROMs
    • NES
      • <game file>
    • SNES
      • <game file>
    • SEGA
      • Master System
        • <game file>
      • Mega Drive
        • <game file>

When it comes to systems like the PS1 or Dreamcast with games that have multiple discs, things get a tiny bit trickier. The basic idea is still the same, but you’ll need to first make sure the disc names are formatted as either .m3u or .chd. The easiest way to do this is to convert any necessary files using CHDMAN.

Additionally, the muOS devs note that in order to “prevent the individual discs appearing in the content list simply move them to a hidden subfolder. Folders can be hidden by prefixing the name with a . or _.” With that in mind, here’s how the file structure looks for multi-disc games.

  • roms
    • Sony Playstation
      • .hidden
        • <game discs here>
      • GAME.m3u (folder)
        • GAME (DISC 1).chd
        • GAME (DISC 2).chd

Provided that you have your ROMs organized accordingly, just drag and drop your folders onto the microSD card. Just be prepared to wait a bit, depending on the size of your personal retro gaming library.

On the bright side, things are pretty easy in terms of adding BIOS files. Head over to the Libretro Docs landing page to figure out what BIOS files you need. Then, drag and drop them into the following folder:

  • SD1/MUOS/bios

Cheats, Configs, and Themes

Before you take the microSD card out of your PC, there are a few more things you might want to have with muOS. These include things such as themes, cheats, and config files.


As for cheats, you’ll first need to head over to the Libretro GitHub and download the libretro-database. Once downloaded, extract the contents and navigate to libretro-database > cht. Then, copy all of the folders and paste them into the following location on your microSD card:

  • muOS > retroarch > cheats

NOTE: Do not try to update the cores through the RetroArch app on your Anbernic device as it will cause problems when trying to play games.

Config Files

As Zu points out in his video, there are still a wonky things to deal with regarding muOS. For example, DraStic does not actually work as you’d expect as it’s “not an open source app.” However, the developers made “some special configs” so that we can still play DS games on devices running muOS.

At the time of this writing, the muOS devs are working on implementing the fix directly. But until that happens, follow these steps:

  1. Join the muOS Discord.
  2. Under Discussions, open the Issues channel.
  3. Search for Drastic.
  4. Locate and open the thread titled “DraStic keybinds got COMPLETELY F’d up…”
  5. Download the most recent config.zip file that is provided.
  6. Extract the contents.
  7. Drag and drop the downloaded config files into the following location on your muOS microSD card:
    • MUOS emulator drastic > config
  8. When prompted, select Replace the files in the destination.


Anbernic RG35XX 2024 on muOS Main Screen

Anbernic RG35XX 2024 on muOS Main Screen

muOS has a lot of really cool things built into it, including the ability to install different themes. There’s an entire channel dedicated to just themes on the muOS Discord. You could go through the options, downloading the ones that you like.

However, there’s also an entire Theme Repository available for download on GitHub. If you go this route, download the latest ZIP file under the Releases tag. Then, extract the contents of the folder.

Whether you downloaded a single theme or the entire muOS Theme Repository, make sure that the theme itself remains as a .ZIP file. Then, move the ZIP file to the ARCHIVE folder. And that’s it, for now.

To actually install the downloaded theme, follow these steps:

  1. Turn on your handheld.
  2. Once it’s booted up, open Applications.
  3. Select Archive Manager from the list.
  4. Highlight and select one of the themes that you transferred.
  5. Click the A button to extract and install it.
  6. From there, you’ll want to go back to the main muOS screen.
  7. Then, select Configuration.
  8. Highlight and select Theme Picker.
  9. Choose the theme that you want to use.
  10. Enjoy!

Set Up Portmaster

Anbernic RG35XX 2024 next to RG35XX Plus running muOS

It’s great being able to emulate a bunch of retro consoles on your retro handhelds. But with PortMaster, you can even play PC games on your handheld. That’s just one of the great reasons to switch over to muOS, as it offers support for PortMaster, something that can’t be said for all of the custom firmware options.

Install PortMaster

If you want to see what all of the hubbub is about, here’s how you can get PortMaster set up on muOS:

  1. Make sure your handheld is connected to Wi-Fi.
  2. Open Applications.
  3. Highlight and select PortMaster.
  4. Wait for PortMaster to load. You might be prompted to install an update, just follow the on-screen steps.
  5. Go through the different sections to find a Port that you want to install.
  6. Open the Port listing and click the button to install it.
  7. Power off your handheld.
  8. Insert your microSD card into your computer.

Unless you installed one of the “Ready to Run” PortMaster games, you’ll need to actually transfer some files in order to get games up and running.

Put the Files in the Right Folders

The instructions for doing so vary from game to game, so you’ll need to refer to the PortMaster website and the listing for the game you want to play. With the necessary files acquired, here’s the structure so you know where to place the game files for PortMaster:

  • ports
    • <game>
      • <game files>
    • <roms>
      • <ports>
        • <file used to launch game>

Once the files have been successfully transferred, just safely remove the SD card from your computer and put it in your handheld. Then, turn your handheld back on and follow these steps:

  1. From the main screen, open the Explore section.
  2. Highlight and select Ports.
  3. Locate and open the PortMaster game that you want to play.

If your files are installed correctly, the game should start within just a minute or two. However, there are some instances, such as TMNT: Shredder’s Revenge, where the initial startup process takes at least 10-15 minutes, if not longer. Patience is key, and if it takes any longer than 30 minutes, turn off your handheld, power it back up, and try again.

God of War Chains of Olympus on the Anbernic RG35XX 2024

God of War Chains of Olympus on the Anbernic RG35XX 2024

Now’s the perfect time to pick up a new retro handheld for yourself, especially with muOS on Anbernic devices. Hit one of the links below to grab one for yourself, or if you want to get one for a friend who enjoys retro gaming.

What did you think of this article? Let us know in the comments below, and chat with us in our Discord!

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