Well, the answer is - partially. What I found out:
- both lock and unlock bits currently are deprecated, so the warning only goes away if I modify both.
- Too keep the same behavior as specified in the boards.txt, I have to have a look in the datasheet and boards.txt
Original from boards.txt:
nano.bootloader.unlock_bits=0x3F
nano.bootloader.lock_bits=0x0F
Error message says that unused bytes have to be written to 1.
According to datasheet, unused bits are (the same for lock and unlock bit mask):
So, I add 12 to the first nibble and yield:
board_bootloader.unlock_bits = 0xEF
board_bootloader.lock_bits = 0xCF
Result:
Warning gone. All fine. Will raise an issue.