RSU_RXBUFSZ
if (len > RSU_RXBUFSZ) {
usbd_setup_xfer(xfer, data->pipe, data, data->buf, RSU_RXBUFSZ,
RSU_RXBUFSZ, USBD_SHORT_XFER_OK | USBD_NO_COPY,
data->buf = usbd_alloc_buffer(data->xfer, RSU_RXBUFSZ);