PositionManager/LinkManager: fall back to internal GPS when NMEA disabled

src/Comms/LinkManager.cc

@@ -509,7 +509,8 @@ void LinkManager::_updateAutoConnectLinks()
     _reconnectAutoConnectLinks();
 
     // check to see if nmea gps is configured for UDP input, if so, set it up to connect
-    if (_autoConnectSettings->autoConnectNmeaPort()->cookedValueString() == "UDP Port") {
+    const QString nmeaPortValue = _autoConnectSettings->autoConnectNmeaPort()->cookedValueString();
+    if (nmeaPortValue == "UDP Port") {
         if ((_nmeaSocket->localPort() != _autoConnectSettings->nmeaUdpPort()->rawValue().toUInt()) || (_nmeaSocket->state() != UdpIODevice::BoundState)) {
             qCDebug(LinkManagerLog) << "Changing port for UDP NMEA stream";
             _nmeaSocket->close();
@@ -526,6 +527,22 @@ void LinkManager::_updateAutoConnectLinks()
 #endif
     } else {
         _nmeaSocket->close();
+
+        // Only tear things down when NMEA is switched off entirely ("Disabled"). Any other
+        // value is a serial NMEA port, which is set up by _addSerialAutoConnectLink() below;
+        // touching _nmeaPort / the position source here would break it on every tick.
+        if (nmeaPortValue == "Disabled") {
+#ifndef QGC_NO_SERIAL_LINK
+            if (_nmeaPort) {
+                _nmeaPort->close();
+                delete _nmeaPort;
+                _nmeaPort = nullptr;
+                _nmeaDeviceName = "";
+            }
+#endif
+            // Revert QGCPositionManager to the integrated GPS if it was using an NMEA source
+            QGCPositionManager::instance()->resetNmeaSourceDevice();
+        }
     }
 
 #ifndef QGC_NO_SERIAL_LINK

src/PositionManager/PositionManager.cpp

@@ -101,6 +101,26 @@ void QGCPositionManager::setNmeaSourceDevice(QIODevice *device)
     _setPositionSource(QGCPositionManager::NmeaGPS);
 }
 
+void QGCPositionManager::resetNmeaSourceDevice()
+{
+    if (!_nmeaSource) {
+        return;
+    }
+
+    if (_currentSource == _nmeaSource) {
+        // Switch away while the NMEA source is still valid so _setPositionSource() can run its
+        // usual cleanup (stop updates, disconnect, and reset the stale GCS position/accuracy)
+        // before we delete it. Falls back to the platform's default source (e.g. integrated GPS).
+        _setPositionSource(QGCPositionManager::InternalGPS);
+    } else {
+        _nmeaSource->stopUpdates();
+        (void) disconnect(_nmeaSource);
+    }
+
+    delete _nmeaSource;
+    _nmeaSource = nullptr;
+}
+
 void QGCPositionManager::_positionUpdated(const QGeoPositionInfo &update)
 {
     _geoPositionInfo = update;

src/PositionManager/PositionManager.h

@@ -37,6 +37,9 @@ class QGCPositionManager : public QObject
     int updateInterval() const { return _updateInterval; }
 
     void setNmeaSourceDevice(QIODevice *device);
+    /// Tears down any active NMEA source and falls back to the platform's default
+    /// position source (e.g. the integrated Android GPS).
+    void resetNmeaSourceDevice();
 
 signals:
     void gcsPositionChanged(QGeoCoordinate gcsPosition);