Fix SI1K radio RSSI calculation to correctly represent received power

src/comm/MAVLinkProtocol.cc

@@ -291,8 +291,25 @@ void MAVLinkProtocol::receiveBytes(LinkInterface* link, QByteArray b)
                 // process telemetry status message
                 mavlink_radio_status_t rstatus;
                 mavlink_msg_radio_status_decode(&message, &rstatus);
+                int rssi = rstatus.rssi,
+                    remrssi = rstatus.remrssi;
+                // 3DR Si1k radio needs rssi fields to be converted to dBm
+                if (message.sysid == '3' && message.compid == 'D') {
+                    /* Per the Si1K datasheet figure 23.25 and SI AN474 code
+                     * samples the relationship between the RSSI register
+                     * and received power is as follows:
+                     *
+                     *                       10
+                     * inputPower = rssi * ------ 127
+                     *                       19
+                     *
+                     * Additionally limit to the only realistic range [-120,0] dBm
+                     */
+                    rssi    = qMin(qMax(qRound(static_cast<qreal>(rssi)    / 1.9 - 127.0), - 120), 0);
+                    remrssi = qMin(qMax(qRound(static_cast<qreal>(remrssi) / 1.9 - 127.0), - 120), 0);
+                }
 
-                emit radioStatusChanged(link, rstatus.rxerrors, rstatus.fixed, rstatus.rssi, rstatus.remrssi,
+                emit radioStatusChanged(link, rstatus.rxerrors, rstatus.fixed, rssi, remrssi,
                     rstatus.txbuf, rstatus.noise, rstatus.remnoise);
             }
 

src/comm/MAVLinkProtocol.h

@@ -269,8 +269,8 @@ signals:
      *
      * @param rxerrors receive errors
      * @param fixed count of error corrected packets
-     * @param rssi local signal strength
-     * @param remrssi remote signal strength
+     * @param rssi local signal strength in dBm
+     * @param remrssi remote signal strength in dBm
      * @param txbuf how full the tx buffer is as a percentage
      * @param noise background noise level
      * @param remnoise remote background noise level

src/ui/toolbar/MainToolBarController.cc

@@ -98,14 +98,12 @@ void MainToolBarController::_activeVehicleChanged(Vehicle* vehicle)
 
 void MainToolBarController::_telemetryChanged(LinkInterface*, unsigned, unsigned, int rssi, int remrssi, unsigned, unsigned, unsigned)
 {
-    if((unsigned)_telemetryLRSSI != rssi) {
-        // According to the Silabs data sheet, the RSSI value is 0.5db per bit
-        _telemetryLRSSI = rssi >> 1;
+    if(_telemetryLRSSI != rssi) {
+        _telemetryLRSSI = rssi;
         emit telemetryLRSSIChanged(_telemetryLRSSI);
     }
-    if((unsigned)_telemetryRRSSI != remrssi) {
-        // According to the Silabs data sheet, the RSSI value is 0.5db per bit
-        _telemetryRRSSI = remrssi >> 1;
+    if(_telemetryRRSSI != remrssi) {
+        _telemetryRRSSI = remrssi;
         emit telemetryRRSSIChanged(_telemetryRRSSI);
     }
 }

src/ui/toolbar/MainToolBarIndicators.qml

@@ -536,7 +536,7 @@ Row {
                     color: colorWhite
                 }
                 QGCLabel {
-                    text: _controller.telemetryRRSSI + 'dB'
+                    text: _controller.telemetryRRSSI + 'dBm'
                     width: getProportionalDimmension(30)
                     horizontalAlignment: Text.AlignRight
                     font.pixelSize: ScreenTools.smallFontPixelSize
@@ -553,7 +553,7 @@ Row {
                     color: colorWhite
                 }
                 QGCLabel {
-                    text: _controller.telemetryLRSSI + 'dB'
+                    text: _controller.telemetryLRSSI + 'dBm'
                     width: getProportionalDimmension(30)
                     horizontalAlignment: Text.AlignRight
                     font.pixelSize: ScreenTools.smallFontPixelSize