Attribute Macro entry 

#[entry]

Mark the program entry point.

Exports the function as the Game Boy entry symbol and forces the gb-rt startup (rrt0) into the link. The signature must be fn() -> !, since rrt0 jumps to it and never expects it back. Use it once per program:

#[gb_rt::entry]
fn main() -> ! {
    loop { /* ... */ }
}