UATH_MAX_RXCMDSZ
usbd_setup_xfer(xfer, sc->cmd_rx_pipe, cmd, cmd->buf, UATH_MAX_RXCMDSZ,
UATH_MAX_RXCMDSZ, USBD_SHORT_XFER_OK | USBD_NO_COPY,
cmd->buf = usbd_alloc_buffer(cmd->xfer, UATH_MAX_RXCMDSZ);