AP_InertialSensor: pass backend instead of pointer to function

Different detect() function might need different arguments and passing a
pointer to function here is cumbersome. For example, it forces to have a
method like "detect_i2c2" rather than allowing hal.i2c2 to be passed as
parameter.

libraries/AP_InertialSensor/AP_InertialSensor.cpp

@@ -379,21 +379,15 @@ AP_InertialSensor::init( Start_style style,
     _have_sample = false;
 }
 
-/*
+void AP_InertialSensor::_add_backend(AP_InertialSensor_Backend *backend)
-  try to load a backend
- */
-void AP_InertialSensor::_add_backend(AP_InertialSensor_Backend *(detect)(AP_InertialSensor &))
 {
-    if (_backend_count == INS_MAX_BACKENDS) {
+    if (!backend)
+        return;
+    if (_backend_count == INS_MAX_BACKENDS)
         hal.scheduler->panic(PSTR("Too many INS backends"));
-    }
+    _backends[_backend_count++] = backend;
-    _backends[_backend_count] = detect(*this);
-    if (_backends[_backend_count] != NULL) {
-        _backend_count++;
-    }
 }
 
-
 /*
   detect available backends for this board
  */
@@ -401,27 +395,27 @@ void
 AP_InertialSensor::_detect_backends(void)
 {
     if (_hil_mode) {
-        _add_backend(AP_InertialSensor_HIL::detect);
+        _add_backend(AP_InertialSensor_HIL::detect(*this));
         return;
     }
 #if HAL_INS_DEFAULT == HAL_INS_HIL
-    _add_backend(AP_InertialSensor_HIL::detect);
+    _add_backend(AP_InertialSensor_HIL::detect(*this));
 #elif HAL_INS_DEFAULT == HAL_INS_MPU60XX_SPI
-    _add_backend(AP_InertialSensor_MPU6000::detect_spi);
+    _add_backend(AP_InertialSensor_MPU6000::detect_spi(*this));
 #elif HAL_INS_DEFAULT == HAL_INS_MPU60XX_I2C && HAL_INS_MPU60XX_I2C_BUS == 2
-    _add_backend(AP_InertialSensor_MPU6000::detect_i2c2);
+    _add_backend(AP_InertialSensor_MPU6000::detect_i2c2(*this));
 #elif HAL_INS_DEFAULT == HAL_INS_PX4 || HAL_INS_DEFAULT == HAL_INS_VRBRAIN
-    _add_backend(AP_InertialSensor_PX4::detect);
+    _add_backend(AP_InertialSensor_PX4::detect(*this));
 #elif HAL_INS_DEFAULT == HAL_INS_OILPAN
-    _add_backend(AP_InertialSensor_Oilpan::detect);
+    _add_backend(AP_InertialSensor_Oilpan::detect(*this));
 #elif HAL_INS_DEFAULT == HAL_INS_MPU9250
-    _add_backend(AP_InertialSensor_MPU9250::detect);
+    _add_backend(AP_InertialSensor_MPU9250::detect(*this));
 #elif HAL_INS_DEFAULT == HAL_INS_FLYMAPLE
-    _add_backend(AP_InertialSensor_Flymaple::detect);
+    _add_backend(AP_InertialSensor_Flymaple::detect(*this));
 #elif HAL_INS_DEFAULT == HAL_INS_LSM9DS0
-    _add_backend(AP_InertialSensor_LSM9DS0::detect);
+    _add_backend(AP_InertialSensor_LSM9DS0::detect(*this));
 #elif HAL_INS_DEFAULT == HAL_INS_L3G4200D
-    _add_backend(AP_InertialSensor_L3G4200D::detect);
+    _add_backend(AP_InertialSensor_L3G4200D::detect(*this));
 #else
     #error Unrecognised HAL_INS_TYPE setting
 #endif

libraries/AP_InertialSensor/AP_InertialSensor.h

@@ -236,7 +236,7 @@ public:
 private:
 
     // load backend drivers
-    void _add_backend(AP_InertialSensor_Backend *(detect)(AP_InertialSensor &));
+    void _add_backend(AP_InertialSensor_Backend *backend);
     void _detect_backends(void);
 
     // gyro initialisation