BOARD_OPTIONS files are created and used by dno(1), or dno_menu(1) to define selected build options for an Arduino board.
The default options are determined from BOARD_INFO(5). Running dno menu or dno_menu allows the user to interactively select desired options from the options available via a terminal-based menu interface. If the selected options are all left as default, then no BOARD_OPTIONS file will be created, and any existing one will be deleted. If non-default options are selected, the selected options will be recorded in the BOARD_OPTIONS file.
Note that the available options recorded in BOARD_INFO are determined from the boards.txt file for the selected Arduino board.
FILES boards.txt