Mainboard Firmware

Mainboard firmware

What this page will help you do

Understand the small piece of firmware on the printer's mainboard, why it changes by itself when you switch systems, and how to install a different one if you need to.

What you need

Nothing for the normal case - NebulaOS manages this on its own. For installing a specific firmware file: a .bin file, and either a USB stick or Mainsail.

The short version

The mainboard has its own firmware, separate from the system NebulaOS replaces. Each system needs its own version, and each system puts its own version back automatically:

• Creality's system installs its firmware when it starts from cold.
• NebulaOS checks the board at every boot and reinstalls its own if it finds a known Creality version there.

So switching between systems is safe and self-correcting. You do not need to do anything, and you cannot get stuck by using the power switch.

Firmware you installed yourself is left alone. NebulaOS only replaces what it recognises as a known Creality version. If you deliberately installed something else, it stays.

The one real caution

Do not switch the printer off while firmware is being installed. The screen tells you when that is happening - it says not to switch off, and that Klipper is stopped. It takes a short time. Wait for it.

That is the only moment in normal use when cutting power can leave the board needing a computer to recover.

Where the controls are

Settings → Printer → MCU firmware.

Option	What it does
Built-in MCU firmware	Reinstalls the version that came with your NebulaOS image
Install MCU firmware	Installs a .bin file you provide

To provide a file, put it either on a USB stick, or upload it in Mainsail to Machine → config → uploads → mainboard-firmware. The screen lists what it finds.

No screenshot yet: the MCU firmware page is not reached by the simulator's capture tour. This one needs a photograph of a real printer.

Step-by-step: reinstalling the built-in firmware

Worth doing if the screen reports it cannot reach the board, or after you have been running another system.

1. Settings → Printer → MCU firmware.
2. Tap Built-in MCU firmware.
3. Confirm.
4. Wait. Klipper stops, the board is reflashed, and Klipper restarts. The screen says not to switch off while this runs.
5. The screen reports the firmware it now finds on the board.

Step-by-step: installing your own firmware file

1. Put the .bin on a FAT32 USB stick, or upload it in Mainsail to Machine → config → uploads → mainboard-firmware.
2. Settings → Printer → MCU firmware → Install MCU firmware.
3. Pick your file from the list.
4. Confirm, and wait as above.

Once you have installed your own firmware, NebulaOS will not replace it at boot - it only reinstalls over a version it recognises as Creality's.

Expected result

The screen reports the board running the firmware you installed, and Klipper connects.

Troubleshooting

What happens	What to do
"Klipper can't reach the board"	Reinstall the built-in firmware, as above.
No files are listed	Check the USB stick is FAT32, or that the upload went to uploads → mainboard-firmware.
You switched off during a flash	The board may need recovery from a computer. See Recovery.
The firmware changed by itself after switching systems	Expected - each system reinstalls its own. See the short version above.

Recovery and reversal

Built-in MCU firmware is the way back from any firmware you installed. It is always available and does not need a file.

Related

• Safety first
• Going back to your old firmware
• Recovery