Add support for OpenBLT Bootloader.

[matt-alencar]

Support for OpenBLT Bootloader by adding the checksum pattern right after the interrupt vector table, this is required by the bootloader to ensure that a valid firmware is present on the flash memory and be able to jump to the app code.

On the bootloader's code you will have to adjust the BOOT_FLASH_VECTOR_TABLE_CS_OFFSET to match your specific build, use the following command to check where your isr vector table finishes, as it's build dynamically by a script.
arm-none-eabi-objdump -s -j .text out/klipper.elf | grep ee11aa55
80070e0 ee11aa55 4ff0000c 0849094a 8b6810b4 ...UO....I.J.h..

-> 0x08007000 is the app start address (28KB bootloader size, 0x7000 offset)
-> 0x080070e0 is where the checksum are located, right after ISR vector table, so the BOOT_FLASH_VECTOR_TABLE_CS_OFFSET is 0xE0 in this case.

Convert the compiled Klipper firmware to .srec format using:
arm-none-eabi-objcopy -I binary -O srec --change-addresses 0x08007000 out/klipper.bin out/firmware.srec
For the app firmware be accepted by the bootloader, it must be in .srec format, then you can put it to a SD card or upload using serial port, ModBus RTU, CAN or USB HID as the OpenBLT has support for all of this protocols.
Note that the "--change-addresses" parameter must match your bootloader size, for 28KB the app start address are 0x08007000.

[nefelim4ag]

Silly question, why use the OpenBLT bootloader if there is Katapult already available, for, I think, all of the supported platforms?
And it can even fit in the first 4kb in some cases.

Cheers,
-Timofey

[matt-alencar]

Silly question, why use the OpenBLT bootloader if there is Katapult already available, for, I think, all of the supported platforms? And it can even fit in the first 4kb in some cases.

Cheers, -Timofey

Thanks for asking :)
Currently Katapult only supports CAN and Serial communication, I was looking for an alternative that also supports SD cards, using this method is easier (at least for me) and the risk of bricking the device is mitigated because OpenBLT always try to update the device if the correct firmware file are present on the SD card.

[github-actions]

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