eg.rs

static mut USB_SERIAL: Option<usbd_serial::SerialPort<UsbBusType>> = None;
static mut USB_DEVICE: Option<UsbDevice<UsbBusType>> = None;

#[entry]
fn main() -> ! {
    if let (Some(dp), Some(mut cp)) = (pac::Peripherals::take(), Peripherals::take()) {
    // ...
        unsafe {
            let bus = UsbBus::new(usb);
            USB_BUS = Some(bus);
            USB_SERIAL = Some(SerialPort::new(USB_BUS.as_ref().unwrap()));
            USB_DEVICE = Some( /* ... */ );
    // ...
    }
}


#[interrupt]
fn USB_HP_CAN_TX() {
    usb_interrupt();
}

#[interrupt]
fn USB_LP_CAN_RX0() {
    usb_interrupt();
}

fn usb_interrupt() {
    let usb_dev = unsafe { USB_DEVICE.as_mut().unwrap() };
    cortex_m::interrupt::free(|_| unsafe {
        // ... use it