Installing a custom firmware: muOS, Knulli, ArkOS, ROCKNIX, Batocera — which one for your console?

The same console can be disappointing with its factory firmware and genuinely enjoyable with a community firmware. Slow menus, unreliable saves, sleep mode that loses your game, cores frozen for two years: on many entry-level and mid-range machines, these flaws come from the software, not the hardware. Switching firmware costs nothing more than a microSD card and an hour of your time. It's the best free upgrade for a retro handheld console. If you're still wondering why you'd do it, first read Alternative firmwares: should you install one?. This article answers which one and how.

What a custom firmware really changes

• The interface. Fast navigation, clean game lists, themes, direct resume of your last game.
• Automatic saves. Most of them save a state when you power off and restore it at startup. On stock firmware, this feature is often missing or unreliable.
• Up-to-date cores. RetroArch and standalone emulators are recompiled regularly, which fixes bugs game by game.
• Extra systems. Native ports via PortMaster, media players, sometimes systems the manufacturer never planned for.
• Sleep mode. Closing the console and finding your game intact: this is often the point factory firmwares handle worst.
• Cover art and metadata. Automatic retrieval of artwork and descriptions.

What a firmware doesn't change: the machine's power. The processor, RAM and GPU stay the same. No firmware will run PlayStation 2 on a €100 Linux console fitted with an Allwinner H700 or a RockChip RK3566. The realistic range goes from 8-bit to PlayStation 1, with Nintendo 64, Dreamcast and PSP giving variable results depending on the title. A firmware can bring a few extra frames per second thanks to better-compiled cores. It won't let you jump a generation.

The risks, stated plainly

• The warranty. As long as you only write to a microSD card, the hardware isn't modified and you lose nothing. As soon as you touch the internal memory (eMMC) or the bootloader, the question becomes debatable depending on the seller.
• The risk of bricking. It almost exclusively concerns installations to internal memory and bootloader tinkering. On the Anbernic RG353P/M/V, installing ROCKNIX internally requires erasing the Android partition: the operation is irreversible without a recovery image.
• Beta versions. Some projects release images marked beta for a given model, even when the project is stable elsewhere. Read the page dedicated to your console, not just the home page.
• Discontinued projects. A firmware can stop being maintained. That's not a disaster if it works, but you won't get any more fixes.

The master table

Two cases from our catalogue fall outside this table. The Miyoo Mini Plus (SigmaStar SSD202D) isn't supported by any of the six firmwares above: its ecosystem is built on Onion OS. The TrimUI Brick and the Smart Pro also have projects of their own, such as NextUI or CrossMix-OS.

The generic procedure in 7 steps

1. Identify your model precisely. It's the step people skip and that costs them an evening. An RG35XX Plus, an RG35XX H and an RG35XX Pro don't take the same image. An RG353V isn't an RG353PS, a TrimUI Brick isn't a Smart Pro. Some models even exist in two circuit board revisions that require a different file.
2. Back up your data. Copy the entire original card to your computer, or at the very least the save and configuration folders. Our guide to saves on retro handheld consoles shows where they live.
3. Download the image from the project's official website. muos.dev, knulli.org, rocknix.org, batocera.org, amberelec.org, or the ArkOS GitHub repository. Don't use a "preinstalled" image bought on a marketplace: you don't know what it contains.
4. Verify the checksum. Projects publish a SHA256 hash next to each image. On Windows, certutil -hashfile image.img SHA256; on macOS or Linux, shasum -a 256 image.img. An incomplete download is a common cause of a console that won't boot.
5. Write the image to a second card. Unzip the archive (7-Zip for .7z files), then write the .img with Rufus, Raspberry Pi Imager, balenaEtcher or dd. ROCKNIX offers its own tool on Windows. Don't format the card beforehand: the image contains its own partition table. Eject it properly, otherwise it may not boot.
6. First boot and setup. With the console off, insert the card into the expected slot, then switch it on. The first boot takes a while: partitioning, folder creation, sometimes an automatic restart. Allow five to ten minutes without touching anything. Then: language, Wi-Fi, buttons, backlight.
7. Restore your saves. Copy your files back into the new firmware's folder structure. .srm and .sav files transfer well. Save states are tied to the core and its version: they don't always survive the switch.

Firmware by firmware

muOS

A .7z archive containing an image to write directly. The first boot runs a factory reset that creates the folder structure. Current version 2601.1, stable. The trap: choosing the image for a neighbouring model. The download list distinguishes every variant, including the RG34XX H and RG34XX SP.

Knulli

Derived from Batocera, with EmulationStation and lots of per-system settings. The Scarab release changes the partition table: the project recommends a clean install rather than an update. The trap: migrating an old Knulli card by overwriting a few files. Start from a fresh image and re-import your data afterwards.

ArkOS

For a long time the reference on RockChip RK3326 and RK3566 machines. The main repository was archived at the end of 2025: it remains downloadable and functional, but won't evolve any further. Variants maintained by other developers exist. The trap: installing it on a console for which ROCKNIX is active, and missing out on fixes. On an RG353V or a Powkiddy RGB20S, compare the two.

ROCKNIX

The broadest hardware coverage of the six, with monthly releases. On Anbernic Allwinner H700 machines, installation requires a manual step: copy the right file from the device_trees folder to the root of the partition and rename it dtb.img. The documentation specifies that some RG35XX units exist in two revisions that can't be told apart without opening the machine, and that you have to try one and then the other. The trap: an unreadable screen at startup simply means the wrong file was chosen. Power off with a long press, and rewrite with the other one.

Batocera

The same system as on PC, with its separate data partition. Handheld support covers RockChip RK3326 and RK3566/RK3568 and a few Retroid Snapdragon devices. Allwinner H700 devices aren't on the official list: the images in circulation are third-party work. The trap: installing it on a machine whose internal memory is occupied by Android. Since version 42, these configurations are no longer supported.

AmberELEC

Aimed at the Anbernic RG351P/M/V/MP and RG552. The latest published release dates from early 2023: the project is usable but dormant. The trap: considering it for a recent console. Apart from the RG351 and RG552, this firmware isn't for you.

Stock firmware: when to keep it

Keep it if your machine already does what you expect, if no project supports your model, or if you don't want to deal with updates. Some factory firmwares have improved noticeably, particularly at TrimUI and Miyoo. On a console given to a child, its simplicity is a serious argument.

How to roll back

If you followed the second-card rule, rolling back takes thirty seconds: switch off the console, put the original card back in, switch it on again. Nothing in the machine has been modified.

Consoles whose firmware lives in internal memory are a different case. On these RockChip machines with eMMC, an internal installation overwrites the factory system. To roll back, you have to rewrite the original image to the internal memory: that means having kept it or getting it again from the manufacturer, and using a manufacturer flashing tool connected over USB. Some Anbernic devices with eMMC also require erasing the Android partition, an operation with no way back.

The Android case

The Android machines in our catalogue, such as the Retroid Pocket 4 Pro, 5, 6 and Classic, the Anbernic RG557, RG556, RG406V, RG406H, RG476H, RG 477M and RG 477V, or the AYN Odin 2 Portal and Thor, aren't customised in the same way. What the community offers for them isn't a firmware, but launchers and frontends: apps installed on top of Android that replace the home screen with a console-style interface, with game lists, cover art and direct launch into the emulator. ES-DE, Daijishō and Beacon work this way. You install them like any other app, without erasing anything, and you can uninstall them. The difference matters: a frontend doesn't replace the system, doesn't touch the bootloader and carries no risk of bricking. A few Snapdragon machines are the exception and can boot a real Linux firmware, ROCKNIX or Knulli depending on the model, but that goes through fastboot mode. For Android Anbernic devices, no official Linux firmware has been released to date: consider compatibility unverified until it appears in our compatibility table. These machines are in our handheld consoles section.

Frequently asked questions