void do_get_buf (struct usb_dev_handle *sc);
void do_get_screen(struct usb_dev_handle *sc);
void do_display_screen(struct usb_dev_handle *sc);
void do_get_buf (struct usb_dev_handle *sc);
void do_get_screen(struct usb_dev_handle *sc);
void do_display_screen(struct usb_dev_handle *sc);