The code for the Advanced Microcontroller Topics Workshop #4: Bootloaders.
This project is split into two parts, both built with ninja: the bootloader, and the target program. The bootloader code is in the project root. The target program code is under program/. To build either, navigate to their directory, and run ./configure.py, followed by ninja.
There are two linker scripts in this project. The one for the bootloader specifies a 4096-byte region at the bottom of the flash for the bootloader code, and all .text sections are placed there. For the target program, the linker script specifies the bottom 4096-byte region of the flash as being part of the bootloader, and the rest of the flash as being part of the target program. The target program's .text sections are placed into the latter.
To bootload the device, first burn the bootloader with ./program.sh -p from the bootloader root. Then, to bootload the device, run program/bootload.py <serial port> <baud rate> <firmware image>. The ninja build script for the target program specifies that the .elf file is objcopy'd to a .bin file, which can be specified as the <firmware image> argument to bootload.py. Finally, once bootload.py has opened the serial port to the target, press the reset button on the target to reboot back into the bootloader and start the upload process. You should see bootload.py spit out a series of messages about each of the flash regions programmed, followed by Done! on success.
The presentation slides that accompany this code can be viewed here.