interrupt.rs

// ...
static G_LED: Mutex<RefCell<Option<LedPin>>> = Mutex::new(RefCell::new(None));


#[entry]
fn main() -> ! {
    // ...
    let mut led = setup.gpioa.pa5.into_push_pull_output();
    cortex_m::interrupt::free(|cs| {
        *G_LED.borrow(cs).borrow_mut() = Some(led);
    });
    unsafe {
        cortex_m::peripheral::NVIC::unmask(pac::Interrupt::EXTI15_10);
    }    

    loop {
        wfi(); // do nothing
    }
}

#[interrupt]
fn EXTI15_10() {
    cortex_m::interrupt::free(|cs| {
        G_LED
            .borrow(cs)
            .borrow_mut()
            .as_mut()
            .unwrap()
            .toggle();
    });  
}