Edit Bootlader (MEGA2560) for programming, regardless of one of the 3 serial.

[sergioxdev]

Hi Guys
I have a mega2560, I would like to enable programming on the 3 UART0, UART1 or UART2

so that we can load our program, regardless of one of the 3.

I have read a lot of documentation, I have tried but I cannot.
maybe it will be me, or maybe it's not feasible, someone has already faced this problem.

[WestfW]

Currently, optiboot has to be compiled for a specific single UART; it doesn't have the ability to scan multiple ports to see which one might be active.
It would probably fit in the 1k minimum space of a 2560 bootloader, though.