AP_AHRS: rename yaw_initialised access method to dcm_yaw_initialised

This is what it really means.

Also put the relevant state within the DCM object

libraries/AP_AHRS/AP_AHRS.h

@@ -200,6 +200,11 @@ public:
     // true if the AHRS has completed initialisation
     bool initialised() const override;
 
+    // return true if *DCM* yaw has been initialised
+    bool dcm_yaw_initialised(void) const {
+        return AP_AHRS_DCM::yaw_initialised();
+    }
+
     // get_filter_status - returns filter status as a series of flags
     bool get_filter_status(nav_filter_status &status) const;
 

libraries/AP_AHRS/AP_AHRS_Backend.h

@@ -273,11 +273,6 @@ public:
     // return true if we will use compass for yaw
     virtual bool use_compass(void) = 0;
 
-    // return true if yaw has been initialised
-    bool yaw_initialised(void) const {
-        return _flags.have_initial_yaw;
-    }
-
     // helper trig value accessors
     float cos_roll() const  {
         return _cos_roll;
@@ -479,7 +474,6 @@ protected:
 
     // flags structure
     struct ahrs_flags {
-        uint8_t have_initial_yaw        : 1;    // whether the yaw value has been intialised with a reference
         uint8_t wind_estimation         : 1;    // 1 if we should do wind estimation
     } _flags;
 

libraries/AP_AHRS/AP_AHRS_DCM.cpp

@@ -493,11 +493,11 @@ AP_AHRS_DCM::drift_correction_yaw(void)
             // we force an additional compass read()
             // here. This has the effect of throwing away
             // the first compass value, which can be bad
-            if (!_flags.have_initial_yaw && compass.read()) {
+            if (!have_initial_yaw && compass.read()) {
                 const float heading = compass.calculate_heading(_dcm_matrix);
                 _dcm_matrix.from_euler(roll, pitch, heading);
                 _omega_yaw_P.zero();
-                _flags.have_initial_yaw = true;
+                have_initial_yaw = true;
             }
             new_value = true;
             yaw_error = yaw_error_compass(compass);
@@ -536,13 +536,13 @@ AP_AHRS_DCM::drift_correction_yaw(void)
                operator pulls back the plane rapidly enough then on
                release the GPS heading changes very rapidly
             */
-            if (!_flags.have_initial_yaw ||
+            if (!have_initial_yaw ||
                     yaw_deltat > 20 ||
                     (_gps.ground_speed() >= 3*GPS_SPEED_MIN && fabsf(yaw_error_rad) >= 1.047f)) {
                 // reset DCM matrix based on current yaw
                 _dcm_matrix.from_euler(roll, pitch, gps_course_rad);
                 _omega_yaw_P.zero();
-                _flags.have_initial_yaw = true;
+                have_initial_yaw = true;
                 yaw_error = 0;
             }
         }

libraries/AP_AHRS/AP_AHRS_DCM.h

@@ -62,6 +62,11 @@ public:
     void            update(bool skip_ins_update=false) override;
     void            reset(bool recover_eulers = false) override;
 
+    // return true if yaw has been initialised
+    bool yaw_initialised(void) const {
+        return have_initial_yaw;
+    }
+
     // dead-reckoning support
     virtual bool get_position(struct Location &loc) const override;
 
@@ -146,6 +151,8 @@ private:
     float _omega_I_sum_time;
     Vector3f _omega;                            // Corrected Gyro_Vector data
 
+    bool have_initial_yaw; // true if the yaw value has been initialised with a reference
+
     // variables to cope with delaying the GA sum to match GPS lag
     Vector3f ra_delayed(uint8_t instance, const Vector3f &ra);
     Vector3f _ra_delay_buffer[INS_MAX_INSTANCES];