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FLY-MMU Bootloader (Katapult) Recovery

For use only in brick repair

FLY-MMU comes pre-installed with Katapult. Do not re-flash this firmware during normal use or when updating the Klipper firmware; it is intended solely for repairing a broken bootloader.

Firmware Overview​

Name Explanation

Katapult was formerly known as CanBoot, and both names may appear simultaneously in older tutorials or firmware names.

Katapult is a bootloader used to boot and update Klipper:

  • Katapult itself cannot be used as a Klipper MCU; after flashing, you still need to write Klipper firmware that matches the hardware and communication method.
  • Supported tool boards can enter Katapult by quickly double-pressing the RESET button; after entering, there is usually a status light blinking.
  • CAN, RS232, and USB use independent Katapult firmware; you cannot simply modify file names or mix them directly.
  • For CAN firmware, you must also select the correct bus speed, with common speeds being 500K and 1M.
  • FLY-MMU supports communication via CAN, RS232, and USB.
  • The repository provides USB firmware, as well as CAN firmware at speeds of 500K and 1M.
Select only one firmware

USB and CAN firmware cannot be used simultaneously. When choosing CAN firmware, its speed must match that of the host computer and all other CAN devices on the same bus.

Entering Flashing Mode​

Power-off required

Before starting, make sure the printer is completely turned off and disconnected from power. Do not plug or unplug cables, rearrange interface connections, or touch terminals while it is powered on.

The RESET button is located at the top, and the BOOT button is at the bottom in the diagram:

  1. Keep the control board completely unplugged from power.
  2. Press and hold the BOOT button.
  3. Connect the control board to a computer or host using a Type-C cable with data transfer capabilities.
  4. Once the device is recognized, release the BOOT button.
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Flashing the Firmware​

Download the FLY-MMU Katapult firmware:

The firmware is located in the following directory in the repository:

FLY-Firmware/ToolBoard/MMU
Power Off Operation

Before connecting or re-plugging the USB cable, completely shut down the printer and disconnect other power sources. Do not allow the tool board to be powered simultaneously via the printer's power supply and the USB interface.

USB Connection Compatibility

Some computer USB ports may cause unstable flashing due to driver or signal compatibility issues. If connection fails, try switching to a different USB port on the computer or use a reliable USB hub. If the error shown below appears, check the USB connection and drivers first.

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  1. Download and install SetupSTM32CubeProgrammer and the STM32 DFU driver from the Auxiliary Software Download Page.
  2. Save the firmware downloaded from this page to a location on your computer that is easy to find.
Windows File Extension Display

Windows may hide file extensions. Please check "File name extensions" in File Explorer to confirm the firmware is still in .bin or .hex format. Do not modify the file extension.

  1. Confirm the device has entered DFU flashing mode according to the product tutorial, then connect it to the computer using a USB cable that supports data transfer.
  2. Open STM32CubeProgrammer, select USB mode, refresh the device list, and connect.
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  1. If no error popup appears, the connection is successful.
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  1. Click the download icon on the left side, and check the flashing options as shown in the image below.
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  1. Click Browse and select the firmware to be flashed.
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  1. When flashing .bin firmware, set Start address to 0x08000000. When using .hex firmware, keep the address embedded in the file.
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  1. Click Start automatic mode to begin flashing.
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  1. When the success message appears, the firmware flashing is complete.
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Completing the Flashing Process​

Power-off required

After flashing is complete, first disconnect the USB cable and external power from the control board, then reconnect everything as usual. Do not plug or unplug cables while it is powered on.

After powering on again, the status light will blink when Katapult starts up properly:

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