Added a transmitOnly flag to UDP config. When enabled, the socket receive buffer is set to zero such that no data is ever received. Also updated the MavlinkSettings page such that new config settings respect the setting visibility.

src/comm/LinkManager.cc

@@ -512,6 +512,7 @@ void LinkManager::_updateAutoConnectLinks(void)
 
         UDPConfiguration* udpConfig = new UDPConfiguration(_mavlinkForwardingLinkName);
         udpConfig->setDynamic(true);
+        udpConfig->setTransmitOnly(true);
 
         QString hostName = _toolbox->settingsManager()->appSettings()->forwardMavlinkHostName()->rawValue().toString();
         udpConfig->addHost(hostName);

src/comm/UDPLink.cc

@@ -293,10 +293,18 @@ bool UDPLink::_hardwareConnect()
         //-- Make sure we have a large enough IO buffers
 #ifdef __mobile__
         _socket->setSocketOption(QAbstractSocket::SendBufferSizeSocketOption,     64 * 1024);
-        _socket->setSocketOption(QAbstractSocket::ReceiveBufferSizeSocketOption, 128 * 1024);
+        if (_udpConfig->isTransmitOnly()) {
+            _socket->setSocketOption(QAbstractSocket::ReceiveBufferSizeSocketOption, 0);
+        } else {
+            _socket->setSocketOption(QAbstractSocket::ReceiveBufferSizeSocketOption, 128 * 1024);
+        }
 #else
         _socket->setSocketOption(QAbstractSocket::SendBufferSizeSocketOption,    256 * 1024);
-        _socket->setSocketOption(QAbstractSocket::ReceiveBufferSizeSocketOption, 512 * 1024);
+        if (_udpConfig->isTransmitOnly()) {
+            _socket->setSocketOption(QAbstractSocket::ReceiveBufferSizeSocketOption, 0);;
+        } else {
+            _socket->setSocketOption(QAbstractSocket::ReceiveBufferSizeSocketOption, 512 * 1024);;
+        }
 #endif
         _registerZeroconf(_udpConfig->localPort(), kZeroconfRegistration);
         QObject::connect(_socket, &QUdpSocket::readyRead, this, &UDPLink::readBytes);
@@ -369,7 +377,9 @@ void UDPLink::_deregisterZeroconf()
 //--------------------------------------------------------------------------
 //-- UDPConfiguration
 
-UDPConfiguration::UDPConfiguration(const QString& name) : LinkConfiguration(name)
+UDPConfiguration::UDPConfiguration(const QString& name)
+    : LinkConfiguration(name)
+    , _transmitOnly(false)
 {
     AutoConnectSettings* settings = qgcApp()->toolbox()->settingsManager()->autoConnectSettings();
     _localPort = settings->udpListenPort()->rawValue().toInt();
@@ -379,7 +389,9 @@ UDPConfiguration::UDPConfiguration(const QString& name) : LinkConfiguration(name
     }
 }
 
-UDPConfiguration::UDPConfiguration(UDPConfiguration* source) : LinkConfiguration(source)
+UDPConfiguration::UDPConfiguration(UDPConfiguration* source)
+    : LinkConfiguration(source)
+    , _transmitOnly(false)
 {
     _copyFrom(source);
 }

src/comm/UDPLink.h

@@ -112,6 +112,14 @@ public:
     void setLocalPort   (quint16 port);
 
     /*!
+     * @brief Set the UDP port to be transmit only. Receive buffer is set to zero.
+     *
+     */
+    void setTransmitOnly (bool state) { _transmitOnly = state; }
+
+    bool isTransmitOnly () { return _transmitOnly; }
+
+    /*!
      * @brief QML Interface
      */
     QStringList hostList    () { return _hostList; }
@@ -142,6 +150,7 @@ private:
     QList<UDPCLient*>   _targetHosts;
     QStringList         _hostList;      ///< Exposed to QML
     quint16             _localPort;
+    bool                _transmitOnly;
 };
 
 class UDPLink : public LinkInterface

src/ui/preferences/MavlinkSettings.qml

@@ -158,6 +158,7 @@ Rectangle {
                         id:         mavlinkForwardingChecked
                         text:       qsTr("Enable MAVLink forwarding")
                         fact:       QGroundControl.settingsManager.appSettings.forwardMavlink
+                        visible:    QGroundControl.settingsManager.appSettings.forwardMavlink.visible
                     }
 
                     Row {
@@ -165,21 +166,24 @@ Rectangle {
                         QGCLabel {
                             width:              _labelWidth
                             anchors.baseline:   mavlinkForwardingHostNameField.baseline
-                            visible:            QGroundControl.settingsManager.appSettings.forwardMavlink.rawValue
+                            visible:            QGroundControl.settingsManager.appSettings.forwardMavlink.rawValue &&
+                                                QGroundControl.settingsManager.appSettings.forwardMavlink.visible
                             text:               qsTr("Host name:")
                         }
                         FactTextField {
                             id:                     mavlinkForwardingHostNameField
                             fact:                   QGroundControl.settingsManager.appSettings.forwardMavlinkHostName
                             width:                  _valueWidth
-                            visible:                QGroundControl.settingsManager.appSettings.forwardMavlink.rawValue
+                            visible:                QGroundControl.settingsManager.appSettings.forwardMavlink.rawValue &&
+                                                    QGroundControl.settingsManager.appSettings.forwardMavlink.visible
                             anchors.verticalCenter: parent.verticalCenter
                         }
 
                     }
                    QGCLabel {
                         text:       qsTr("<i> Changing the host name requires restart of application. </i>")
-                        visible:    QGroundControl.settingsManager.appSettings.forwardMavlink.rawValue
+                        visible:    QGroundControl.settingsManager.appSettings.forwardMavlink.rawValue &&
+                                    QGroundControl.settingsManager.appSettings.forwardMavlink.visible
                     }
                 }
             }