Compass: use_for_yaw for each compass

libraries/AP_Compass/Compass.cpp

@@ -45,7 +45,7 @@ const AP_Param::GroupInfo Compass::var_info[] PROGMEM = {
     // @Description: Enable or disable the use of the compass (instead of the GPS) for determining heading
     // @Values: 0:Disabled,1:Enabled
     // @User: Advanced
-    AP_GROUPINFO("USE",    4, Compass, _use_for_yaw, 1), // true if used for DCM yaw
+    AP_GROUPINFO("USE",    4, Compass, _use_for_yaw[0], 1), // true if used for DCM yaw
 
 #if !defined( __AVR_ATmega1280__ )
     // @Param: AUTODEC
@@ -303,6 +303,21 @@ Compass::set_initial_location(int32_t latitude, int32_t longitude)
 #endif
 }
 
+/// return true if the compass should be used for yaw calculations
+bool
+Compass::use_for_yaw(void) const
+{
+    uint8_t prim = get_primary();
+    return healthy(prim) && use_for_yaw(prim);
+}
+
+/// return true if the specified compass can be used for yaw calculations
+bool
+Compass::use_for_yaw(uint8_t i) const
+{
+    return _use_for_yaw[i];
+}
+
 void
 Compass::set_declination(float radians, bool save_to_eeprom)
 {

libraries/AP_Compass/Compass.h

@@ -151,9 +151,8 @@ public:
     void learn_offsets(void);
 
     /// return true if the compass should be used for yaw calculations
-    bool use_for_yaw(void) const {
-        return healthy() && _use_for_yaw;
-    }
+    bool use_for_yaw(uint8_t i) const;
+    bool use_for_yaw(void) const;
 
     /// Sets the local magnetic field declination.
     ///
@@ -253,7 +252,7 @@ protected:
     AP_Int8 _orientation;
     AP_Vector3f _offset[COMPASS_MAX_INSTANCES];
     AP_Float _declination;
-    AP_Int8 _use_for_yaw;                       ///<enable use for yaw calculation
+    AP_Int8 _use_for_yaw[COMPASS_MAX_INSTANCES];///<enable use for yaw calculation
     AP_Int8 _auto_declination;                  ///<enable automatic declination code
     AP_Int8 _external;                          ///<compass is external
 #if COMPASS_MAX_INSTANCES > 1