CanBoot

Bootloader for ARM Cortex-M MCUs

This bootloader was initially designed for CAN nodes to be used with Klipper. The bootloader itself makes use of Klipper's hardware abstraction layer, stripped down to keep the footprint minimal. In addition to CAN, CanBoot now supports USB and UART interfaces.

Currently lpc176x, stm32 and rp2040 MCUs are supported. CAN support is currently limited to stm32 F-series and rp2040 devices.

CanBoot is licensed under the GNU GPL v3.

Building

CanBoot also uses Klipper's build system. The build is configured with menuconfig. The steps to fetch and build are as follows:

git clone https://github.com/Arksine/CanBoot
cd CanBoot
make menuconfig
make

The menuconfig will present the following options:

• Microcontroller Architecture: Choose between lpc176x, stm32 and rp2040
• Processor model: Options depend on the chosen architecture
• Build CanBoot deployment application: See the deployer section below
• Disable SWD at startup: This is an option for GigaDevice STM32F103 clones. Note that this is untested for the bootloader, GigaDevice clones may not work as expected.
• Clock Reference: Choose the appropriate setting for your board's crystal
• Communication interface: Choose between CAN, USB, and UART. Be sure to choose the interface with the appropriate pins for your hardware.
• For CAN Interfaces:
  • CAN bus speed: Select the appropriate speed for your canbus.
• For Serial (USART) Interfaces:
  • Baud rate for serial port: Select the appropriate baud rate for your serial device.
• For USB Interfaces:
  • USB ids: Allows the user to define the USB Vendor ID, Product ID, and/or Serial Number.
• Support bootloader entry on rapid double click of reset button: When enabled it is possible to enter the bootloader by pressing the reset button twice within a 500ms window.
• Enable bootloader entry on button (or gpio) state: Enable to use a gpio to enter the booloader.
  • Button GPIO Pin: The Pin Name of te
• Enable Status Led: Enables the option to select a status LED gpio.
  • Status LED GPIO Pin: The pin name for your LED. The Pin can be inverted if the LED is on when the pin is low. For example, the status LED Pin for a "blue pill" is !PC13.

Once configured and built flash with a programmer such as an ST-Link. If you don't have a programmer available, it should be possible to flash STM32F103 devices via UART and STM32F042/72 devices over DFU. ST's STM32CubeProgrammer software can facilitate all of these methods, however there are also other tools such as stm32flash (UART) and dfu-util (USB DFU).

NOTE: Prior to flashing CanBoot it is recommended to do a full chip erase. Doing so allows CanBoot to detect that no application is present and enter the bootloader. This is required to enter the bootloader if you have not configured an alternative method of entry.

NOTE RP2040: To flash rp2040 targets mcu should be rebooted in system boot mode (usually with BOOT button pressed). After that make flash command could be used. You could also use rp2040 specific mass storage device drag-and-drop method to flash canboot.uf2 from out folder. Flashing canboot will erase main application (i.e. klipper), so it should be uploaded with canboot again.

Uploading Klipper

1. Make sure the klipper service stopped.

2. Build Klipper with CAN support and with the a bootloader offset matching that of the "application offset" in CanBoot.

3. Enter the bootloader. This will occur automatically if no program is detected. If you built CanBoot with an alternative method of entry you may use that. If upgrading from a currently flashed version of Klipper the flash_can.py script will command the device to enter the bootloader (currently for CAN devices only).

4. Run the flash script: For CAN Devices:

   cd ~/CanBoot/scripts
   python3 flash_can.py -i can0 -f ~/klipper/out/klipper.bin -u <uuid>
   

   Replace with the appropriate uuid for your can device. If the device has not been previouisly flashed with Klipper, it is possible to query the bootloader for the UUID:

   flash_can.py -i can0 -q
   

   For USB/UART devices: Before flashing, make sure pyserial is installed. This step only needs to be performed once:

   pip3 install pyserial
   

   python3 flash_can.py -d <serial device> -b <baud_rate>
   

   Replace <serial_device> the the path to the USB/UART device you wish to flash. The <baud_rate> is only necessary for UART devices, and defaults to 250000 baud if omitted.

FlashCan usage

Running flash_can.py -h to display help:

usage: flash_can.py [-h] [-d <serial device>] [-b <baud rate>]
                    [-i <can interface>] [-f <klipper.bin>] [-u <uuid>] [-q]
                    [-v]

Can Bootloader Flash Utility

optional arguments:
  -h, --help            show this help message and exit
  -d <serial device>, --device <serial device>
                        Serial Device
  -b <baud rate>, --baud <baud rate>
                        Serial baud rate
  -i <can interface>, --interface <can interface>
                        Can Interface
  -f <klipper.bin>, --firmware <klipper.bin>
                        Path to Klipper firmware file
  -u <uuid>, --uuid <uuid>
                        Can device uuid
  -q, --query           Query Bootloader Device IDs
  -v, --verbose         Enable verbose responses
  -r, --request-bootloader
                        Requests the bootloader and exits (CAN only)

The interface option defaults to can0 if omitted. The firmware option defaults to ~/klipper/out/klipper.bin. The uuid must be specified unless the user is running a query with -q.

When the -r option is supplied in addition to -u (and optionally -i) the script will request that the node enter the bootloader. The script will then immediately exit, no attempt will be made to upload a new binary over the canbus. This is particularly useful for Klipper devices running "USB to CAN bridge mode". These devices upload firmware using DFU and/or CanBoot-USB. This option allows the user to enter the bootloader without physical access to the board, then use the appropriate tool (dfu-util or flash_can.py -d) to upload the new binary.

CanBoot Deployer

The CanBoot deployer allows a user to overwrite their existing bootloader with CanBoot, allowing modification and updates without a programmer. It is strongly recommended that an alternate recovery (programmer, DFU, etc) method is available in the event that something goes wrong during deployment. If coming from a stock bootloader it is also recommended that the user create a backup before proceeding.

To build the deployer set the Build CanBoot deployment application option in the menuconfig to your existing bootloader offset. The additional settings apply to the CanBoot binary, configure them just as you would without the deployer. Save your settings and build with make.

This will result in an additional binary in the out folder, deployer.bin. Flash deployer.bin with your existing bootloader (SD Card, HID, an older version of CanBoot, etc). Once complete, the deployer should reset the device and enter CanBoot. Now you are ready to use CanBoot to flash an application, such as Klipper.

Contributing

CanBoot is effectively a fork of Klipper's MCU source. As such, it is appropriate to retain similar contributing guidelines as Klipper. Commits should be formatted as follows:

filename: brief description of commit

More detailed explanation of the change if required.

Signed-off-by: Your Name <your email address>

All commits must be signed off with a real name and email address indicating acceptance of the developer certificate of origin.

Notes

• It is recommended to use a USB-CAN device flashed with candlelight, such as a Canable. Alternatively, a device that supports Klipper's USB-CAN bridge mode works well.
• The BTT U2C v2.1 CAN device requires the latest firmware. The binary can be found in the U2C repo and the source can be found at BTT's candlelight fork.
• If using a MCP2515 CAN device (ie: Waveshare RS485 CAN HAT) it is possible that packets will be dropped when reading flash back from the node during the verification process. That said, I have successfully tested the 12 MHz Crystal variant with the recommended settings.
• Details on the protocol used to communicate with the bootloader may be found in protocol.md.