AP_AHRS: save memory and reduce pointer references

use a refence for ins, and don't save gyro and accel between updates

libraries/AP_AHRS/AP_AHRS.h

@@ -37,7 +37,7 @@ class AP_AHRS
 {
 public:
     // Constructor
-    AP_AHRS(AP_InertialSensor *ins, GPS *&gps) :
+    AP_AHRS(AP_InertialSensor &ins, GPS *&gps) :
         _ins(ins),
         _gps(gps)
     {
@@ -49,7 +49,7 @@ public:
         // prone than the APM1, so we should have a lower ki,
         // which will make us less prone to increasing omegaI
         // incorrectly due to sensor noise
-        _gyro_drift_limit = ins->get_gyro_drift_rate();
+        _gyro_drift_limit = ins.get_gyro_drift_rate();
 
         // enable centrifugal correction by default
         _flags.correct_centrifugal = true;
@@ -78,7 +78,7 @@ public:
     // allow for runtime change of orientation
     // this makes initial config easier
     void set_orientation() {
-        _ins->set_board_orientation((enum Rotation)_board_orientation.get());
+        _ins.set_board_orientation((enum Rotation)_board_orientation.get());
         if (_compass != NULL) {
             _compass->set_board_orientation((enum Rotation)_board_orientation.get());
         }
@@ -88,7 +88,7 @@ public:
         _airspeed = airspeed;
     }
 
-    AP_InertialSensor* get_ins() const {
+    const AP_InertialSensor &get_ins() const {
 	    return _ins;
     }
 
@@ -263,7 +263,7 @@ protected:
 
     // note: we use ref-to-pointer here so that our caller can change the GPS without our noticing
     //       IMU under us without our noticing.
-    AP_InertialSensor   *_ins;
+    AP_InertialSensor   &_ins;
     GPS                 *&_gps;
 
     // a vector to capture the difference between the controller and body frames

libraries/AP_AHRS/AP_AHRS_DCM.cpp

@@ -48,10 +48,10 @@ AP_AHRS_DCM::update(void)
     float delta_t;
 
     // tell the IMU to grab some data
-    _ins->update();
+    _ins.update();
 
     // ask the IMU how much time this sensor reading represents
-    delta_t = _ins->get_delta_time();
+    delta_t = _ins.get_delta_time();
 
     // if the update call took more than 0.2 seconds then discard it,
     // otherwise we may move too far. This happens when arming motors 
@@ -62,10 +62,6 @@ AP_AHRS_DCM::update(void)
         return;
     }
 
-    // Get current values for gyros
-    _gyro_vector  = _ins->get_gyro();
-    _accel_vector = _ins->get_accel();
-
     // Integrate the DCM matrix using gyro inputs
     matrix_update(delta_t);
 
@@ -91,7 +87,7 @@ AP_AHRS_DCM::matrix_update(float _G_Dt)
     // and including the P terms would give positive feedback into
     // the _P_gain() calculation, which can lead to a very large P
     // value
-    _omega = _gyro_vector + _omega_I;
+    _omega = _ins.get_gyro() + _omega_I;
 
     _dcm_matrix.rotate((_omega + _omega_P + _omega_yaw_P) * _G_Dt);
 }
@@ -461,7 +457,7 @@ AP_AHRS_DCM::drift_correction(float deltat)
     temp_dcm.rotateXY(_trim);
 
     // rotate accelerometer values into the earth frame
-    _accel_ef = temp_dcm * _accel_vector;
+    _accel_ef = temp_dcm * _ins.get_accel();
 
     // integrate the accel vector in the earth frame between GPS readings
     _ra_sum += _accel_ef * deltat;
@@ -625,7 +621,7 @@ AP_AHRS_DCM::drift_correction(float deltat)
 
     if (_flags.fly_forward && _gps && _gps->status() >= GPS::GPS_OK_FIX_2D && 
         _gps->ground_speed_cm < GPS_SPEED_MIN && 
-        _accel_vector.x >= 7 &&
+        _ins.get_accel().x >= 7 &&
 	    pitch_sensor > -3000 && pitch_sensor < 3000) {
             // assume we are in a launch acceleration, and reduce the
             // rp gain by 50% to reduce the impact of GPS lag on

libraries/AP_AHRS/AP_AHRS_DCM.h

@@ -25,7 +25,7 @@ class AP_AHRS_DCM : public AP_AHRS
 {
 public:
     // Constructors
-    AP_AHRS_DCM(AP_InertialSensor *ins, GPS *&gps) :
+    AP_AHRS_DCM(AP_InertialSensor &ins, GPS *&gps) :
         AP_AHRS(ins, gps),
         _last_declination(0),
         _mag_earth(1,0)
@@ -92,9 +92,6 @@ private:
     // primary representation of attitude
     Matrix3f _dcm_matrix;
 
-    Vector3f _gyro_vector;                      // Store the gyros turn rate in a vector
-    Vector3f _accel_vector;                     // current accel vector
-
     Vector3f _omega_P;                          // accel Omega proportional correction
     Vector3f _omega_yaw_P;                      // proportional yaw correction
     Vector3f _omega_I;                          // Omega Integrator correction

libraries/AP_AHRS/AP_AHRS_HIL.h

@@ -5,7 +5,7 @@ class AP_AHRS_HIL : public AP_AHRS
 {
 public:
     // Constructors
-    AP_AHRS_HIL(AP_InertialSensor *ins, GPS *&gps) : 
+    AP_AHRS_HIL(AP_InertialSensor &ins, GPS *&gps) : 
 	    AP_AHRS(ins, gps),
 	    _drift()
 		{}
@@ -21,7 +21,7 @@ public:
 
     // Methods
     void update(void) {
-        _ins->update();
+        _ins.update();
     }
     
     void setHil(float roll, float pitch, float yaw,

libraries/AP_AHRS/examples/AHRS_Test/AHRS_Test.pde

@@ -48,7 +48,7 @@ GPS *g_gps;
 AP_GPS_Auto g_gps_driver(&g_gps);
 
 // choose which AHRS system to use
-AP_AHRS_DCM  ahrs(&ins, g_gps);
+AP_AHRS_DCM  ahrs(ins, g_gps);
 
 AP_Baro_HIL barometer;