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Embedded Firmware

The CC uses two different embedded firmware for the bed and the hotend boards with allegedly the same bootloader. The firmwares as of 2025-05-19 are a substitute of Klipper commit 28f60f7e with a lot of changes.

Official update method

To update both the hotend and the bed boards, the main firmware attempts to send a file through YModem protocol when the said boards are power cycled during bootup. The firmware files are not encrypted and are stored on the rootfsA or rootfsB partition (whichever is active) in the /lib/firmware folder. The hotend firmware is called upgrade-hotend.bin and the bed board's is upgrade-bed.bin. On firmware 1.1.29 the hotend/bed firmware got moved into the /app/resources folder.

To replicate this behaviour outside of elegoo's official software, a flasher has been developed that is able to push new firmware.

STM32 flash structure

Start offset End offset Description
0x08000000 0x08007FFF 32Kb Bootloader
0x08008000 0x0800BFFF 16Kb Unknown
0x0800C000 ... Elegoo-Klipper Firmware

The firmware upgrade files include the 16Kb of unknown (mostly 0xFF with some random bytes) data so it must be flashed on address 0x08008000.

Flashing custom firmware (mcu-flasher)

Using mcu-flasher a custom firwmare can be flashed through the official elegoo bootloader. Run the program with -h for more information.

Flashing custom firmware (STM32CubeProgrammer)

No going back

Flashing a new firmware will ERASE THE ELEGOO BOOTLOADER.

Currently the stock mainboard CANNOT boot from custom firmwares nor the stock firmware without the original bootloader. This essentially means you cannot use the stock mainboard anymore after wiping the firmware from the hotend or bed boards!

Ask in the discord for a backup of the original bootloader.

Readout Protection

The hotend and bed boards come with the readout protection enabled by default. As long as you don't remove it, the stock flash is safe. If you instruct the programmer to deactivate the readout protection, the entire flash memory, with the bootloader and the firmware will be wiped.

Hotend

  1. Remove the hotend board (only the main one, the supplementary board is not needed).
  2. On the back side, there is a 2x4 copper pad row. Short the 3.3v and the BOOT with a tweezer
    • img
  3. Connect it to your PC via an USB-C cable (no adapter is needed) while shorting the pins
  4. Keep it shorted for ~2 seconds, then you can let go
  5. Open STM32CubeProgrammer software
  6. On the top right, select the USB mode. If you shorted the pins correctly, it should find the hotend board. if not, you'll get a "No DFU detected".
    • img
  7. Go to the second tab in the left side vertical button column
  8. In the "Download" section, select the firmware file.
  9. Click Start Programming

Bed

  1. Either via an added connector or solder jumper wires directly to the right side serial pins to an USB-TTL transciever as

    • Bed Board USB-TTL
      5v 5v
      RX RX
      TX TX
      GND GND

    • Note: Depending on the USB-TTL board, RX and TX lines might need to be switched.

  2. Short the BOOT pin to 3.3v

    • img

  3. Connect the USB-TTL board to your PC

  4. Short the RESET pins on the bed board (no need to keep it shorted, just touch it)

    • img

  5. In STM32CubeProgrammer, select UART mode and select your USB-TTL device

    • img

  6. Go to the second tab in the left side vertical button column

  7. In the "Download" section, select the firmware file.
  8. Click Start Programming

Firmware Creation

The STM32F402 is an STM32 variant specifically made for the Chinese market. For any configuration, use STM32F401RTC6 (sometimes just STM32F401).

Building for stock bootloader

The following options need to be set in make menuconfig in klipper. See our klipper fork for config examples.

Hotend

Option Value
Micro-controller Architecture STMicroelectronics STM32
Processor model STM32F401
Bootloader offset 48KiB bootloader
Clock reference 24Mhz crystal
Communication interface USB (on PA11/PA12)

Bed

Option Value
Micro-controller Architecture STMicroelectronics STM32
Processor model STM32F401
Bootloader offset 48KiB bootloader
Clock reference 24Mhz crystal
Communication interface Serial (on USART2 PA3/PA2)
Baud rate for serial port 115200

If the serial pins are used on the right side (non stock configuration), UART1 PA9 / PA10 can be used also.