lingpio
sysfs based linux gpio "library"
A "library" comprised from bits collected all over the web, structured to my liking and made to work together
The "upstream" documentation: https://www.kernel.org/doc/Documentation/gpio/
when compiling you can select the board with CFLAGS+=-D'GPIO_BOARD()=BOARD_XXXXX' if board_XXXXX.h is provided and integrated in board.h. See board_chip.h for example.