AP_RPM: changed get_rpm() API to be scripting compatible

return a bool and use a reference for the value

libraries/AP_RPM/AP_RPM.cpp

@@ -188,6 +188,18 @@ bool AP_RPM::enabled(uint8_t instance) const
     return true;
 }
 
+/*
+  get RPM value, return true on success
+ */
+bool AP_RPM::get_rpm(uint8_t instance, float &rpm_value) const
+{
+    if (!healthy(instance)) {
+        return false;
+    }
+    rpm_value = state[instance].rate_rpm;
+    return true;
+}
+
 // singleton instance
 AP_RPM *AP_RPM::_singleton;
 

libraries/AP_RPM/AP_RPM.h

@@ -75,12 +75,7 @@ public:
     /*
       return RPM for a sensor. Return -1 if not healthy
      */
-    float get_rpm(uint8_t instance) const {
-        if (!healthy(instance)) {
-            return -1;
-        }
-        return state[instance].rate_rpm;
-    }
+    bool get_rpm(uint8_t instance, float &rpm_value) const;
 
     /*
       return signal quality for a sensor.

libraries/AP_RPM/examples/RPM_generic/RPM_generic.cpp

@@ -56,9 +56,11 @@ void loop(void)
             sensor_state = '-';
         }
 
+        float rpm = -1;
+        RPM.get_rpm(ii, rpm);
         hal.console->printf("%u - (%c) RPM: %8.2f  Quality: %.2f  ",
                             ii, sensor_state,
-                            (double)RPM.get_rpm(ii),
+                            (double)rpm,
                             (double)RPM.get_signal_quality(ii));
 
         if (ii+1 < RPM.num_sensors()) {