cli - fix gpspassthrouh when GPS port is not open (#13878)

- return status from gpsPassthrough
- test gpsPort

src/main/cli/cli.c

@@ -3603,7 +3603,9 @@ static void cliGpsPassthrough(const char *cmdName, char *cmdline)
     UNUSED(cmdName);
     UNUSED(cmdline);
 
-    gpsEnablePassthrough(cliPort);
+    if (!gpsPassthrough(cliPort)) {
+        cliPrintErrorLinef(cmdName, "GPS forwarding failed");
+    }
 }
 #endif
 

src/main/io/gps.c

@@ -2486,13 +2486,22 @@ static void gpsHandlePassthrough(uint8_t data)
 #endif
 }
 
-void gpsEnablePassthrough(serialPort_t *gpsPassthroughPort)
+// forward GPS data to specified port (used by CLI)
+// return false if forwarding failed
+// curently only way to stop forwarding is to reset the board
+bool gpsPassthrough(serialPort_t *gpsPassthroughPort)
 {
+    if (!gpsPort) {
+        // GPS port is not open for some reason - no GPS, MSP GPS, ..
+        return false;
+    }
     waitForSerialPortToFinishTransmitting(gpsPort);
     waitForSerialPortToFinishTransmitting(gpsPassthroughPort);
 
-    if (!(gpsPort->mode & MODE_TX))
+    if (!(gpsPort->mode & MODE_TX)) {
+        // try to switch TX mode on
         serialSetMode(gpsPort, gpsPort->mode | MODE_TX);
+    }
 
 #ifdef USE_DASHBOARD
     if (featureIsEnabled(FEATURE_DASHBOARD)) {
@@ -2502,6 +2511,8 @@ void gpsEnablePassthrough(serialPort_t *gpsPassthroughPort)
 #endif
 
     serialPassthrough(gpsPort, gpsPassthroughPort, &gpsHandlePassthrough, NULL);
+    // allow exitting passthrough mode in future
+    return true;
 }
 
 float GPS_cosLat = 1.0f;  // this is used to offset the shrinking longitude as we go towards the poles

src/main/io/gps.h

@@ -386,7 +386,7 @@ void gpsUpdate(timeUs_t currentTimeUs);
 bool gpsNewFrame(uint8_t c);
 bool gpsIsHealthy(void); // Returns true when the gps state is RECEIVING_DATA
 struct serialPort_s;
-void gpsEnablePassthrough(struct serialPort_s *gpsPassthroughPort);
+bool gpsPassthrough(struct serialPort_s *gpsPassthroughPort);
 void onGpsNewData(void);
 void GPS_reset_home_position(void);
 void GPS_calc_longitude_scaling(int32_t lat);