enable label=0 as ping/echo

protocol/enttec/dmx-usb-pro/pro.h

@@ -55,6 +55,7 @@ enum FIRMWARE_TYPE {
  * @brief All message labels from API 1.44
  */
 enum MESSAGE_LABEL {
+  OpNoop                = 0,                //!< null message, out-of-spec definition.  Not in API!
   OpReprogramFirmware   = 1,                //!< Reprogram Firmware Request
   OpProgramFlashPage    = 2,                //!< Program Flash Page Request / Reply
   OpGetWidgetParameters = 3,                //!< Get Widget Parameters Request / Reply
@@ -78,8 +79,16 @@ struct MessageData
   /**
    * @brief Initialize MessageData with the appropriate Label
    * @param l Label
+   *
+   * While null messages (label = 0) are not present in the API spec., allow their IO,
+   * perhaps to act as a "ping/echo" to detect emulated devices.
    */
-  MessageData(uint8_t l) : label(l) {};
+  MessageData(uint8_t l = 0) : label(l) {};
+
+  size_t streamSize() const override { return 0; };
+  void iStream(std::shared_ptr<bufferstream>) override {};
+  void oStream(std::shared_ptr<bufferstream>) const override{};
+
   const uint8_t label;                      //!< Message ID label (OpCode)
 };
 

protocol/enttec/dmx-usb-pro/widget.cpp

@@ -296,7 +296,11 @@ bool Widget::writeFirmware(const uint8_t *data, const size_t size)
  */
 void Widget::routeRxMessage(std::shared_ptr<Pro::MessageData> msg)
 {
-  switch (msg->label) {
+  switch (msg->label)
+    {
+    case Pro::OpNoop:
+      rxMsgHello(msg);
+      break;
     case Pro::OpReprogramFirmware:
       {
         auto data = std::static_pointer_cast<Pro::MsgReprogramFirmware>(msg);
@@ -537,6 +541,25 @@ void Widget::sendDmx(bool trimmed) const
 }
 
 
+/**
+ * @brief Widget::rxMsgHello
+ * @param msg
+ */
+void Widget::rxMsgHello(std::shared_ptr<Pro::MessageData> msg)
+{
+  switch (usb_mode_) {
+  case USBdevice:
+    sendMessage(msg);                       // mirror the message back to the host
+    break;
+  case USBhost:
+    reply_hello_.set_value(true);           // device was polite
+    break;
+  default:
+    break;
+  }
+}
+
+
 /**
  * @brief Widget::rxMsgReprogramFirmware
  * @param msg

protocol/enttec/dmx-usb-pro/widget.h

@@ -101,6 +101,7 @@ protected:
   std::vector<uint8_t> user_configuration; //!< User defined configuration data.
 
 private:
+  void rxMsgHello(std::shared_ptr<Pro::MessageData>);
   void rxMsgReprogramFirmware(std::shared_ptr<Pro::MsgReprogramFirmware>);
   void rxMsgProgramFlashPageRequest(std::shared_ptr<Pro::MsgProgramFlashPageRequest>);
   void rxMsgProgramFlashPageReply(std::shared_ptr<Pro::MsgProgramFlashPageReply>);
@@ -125,6 +126,7 @@ private:
 
   mutable std::mutex mtx_metadata_;
   std::shared_ptr<void> token_data_changed_;
+  std::promise<bool> reply_hello_;
   std::promise<bool> reply_firmwarePage_;
   std::promise<bool> reply_parameters_;
   std::promise<bool> reply_serialNumber_;