[dragontamer]

Writing a bootloader in one file is easy enough and will avoid the need of a linker.

The issue is when you have two, three or four .c files that are compiled as separate units that then need to be combined together.

Today, AVR chips and assembly works perfectly fine with .elf objects. But you will likely need to mess with linker scripts to get your bootloader working across different setups.

Especially if you have an element of dynamic boot loading (ex: bootloader program that later continues to load more Application code off of a MicroSD card or UART or over I2C comms.

I'm really not sure how far you can get with this toy project without running into immediate linker issues (or linker scripts).