ret = usb_set_altinterface(usb_devhandle, usi->dwAlternateSetting);
if (ret)
fprintf(stderr, "usb_set_altinterface: %d\n", ret);
ret = usb_set_altinterface(usb_devhandle, usi->dwAlternateSetting);
if (ret)
fprintf(stderr, "usb_set_altinterface: %d\n", ret);