+/* On some devices, there is a factory set internal serial number which can be automatically sent to the host as\r
+ * the device's serial number when the Device Descriptor's .SerialNumStrIndex entry is set to USE_INTERNAL_SERIAL.\r
+ * This allows the host to track a device across insertions on different ports, allowing them to retain allocated\r
+ * resources like COM port numbers and drivers. On demos using this feature, give a warning on unsupported devices\r
+ * so that the user can supply their own serial number descriptor instead or remove the USE_INTERNAL_SERIAL value\r
+ * from the Device Descriptor (forcing the host to generate a serial number for each device from the VID, PID and\r
+ * port location).\r
+ */\r
+#if (USE_INTERNAL_SERIAL == NO_DESCRIPTOR)\r
+ #warning USE_INTERNAL_SERIAL is not available on this AVR - please manually construct a device serial descriptor.\r
+#endif\r
+\r