EP0_SHUTDOWN
udc->ep0state = EP0_SHUTDOWN;
case EP0_SHUTDOWN:
if (is_on && udc->ep0state == EP0_SHUTDOWN) {
} else if (!is_on && udc->ep0state != EP0_SHUTDOWN) {
if (udc->ep0state == EP0_SHUTDOWN)
udc->ep0state = EP0_SHUTDOWN;