I have commercial product with Mega128 which requires boot loader.
I made one ( the ones I found were not for Mega128 with its 128kB nor for industrial use).
My boot loader:
- works in binary mode ( for fast sending)
- supports full 128kb ( minus boot area)
- uses 65ms during startup to enter boot mode or execute the application ( just serial communication is needed to enter the lader)
- uses one flash page to store information about application suitability to run
The PC part of the loader is WIN32 console application.