Secondary UART bootloader example

I'm looking for some example code to write a secondary UART based bootloader, my design has an external supervisor/watchdog IC on the board, this means that for the initial programming I need to disable this with a jumper.

Currently the unit is programmed by opening up the unit, fitting a jumper to disable the watchdog and another to pull the ISP pin low, power on the unit and then load the firmware using flash magic.

What i'd like to be able to do is send the application code a command to enter my secondary bootloader, and have that take care of kicking the watchdog.

However when i look for examples everything I find is for things like USB, Ethernet or CAN/I2C, and I don't think are using the same command set as the ROM bootloader.

are there any examples of a UART based bootloaders?

I'd really like to avoid having to write my own flash applications to go with the bootloader, hence wanting to basically replicate the ROM bootloader.

Thanks

More questions in this forum