usb_dev_handle *open_dev(void){
    struct usb_bus *bus;
    struct usb_device *dev;

    for (bus = usb_get_busses(); bus; bus = bus->next){
        for (dev = bus->devices; dev; dev = dev->next){
            if (dev->descriptor.idVendor == MY_VID
                    && dev->descriptor.idProduct == MY_PID){
                return usb_open(dev);
            }
        }
    }
    return NULL;
}