AP_InertialSensor: added get_temperature() interface

this will allow logging of individual temperature sensors

libraries/AP_InertialSensor/AP_InertialSensor.h

@@ -160,6 +160,10 @@ public:
     const Vector3f &get_accel_scale(uint8_t i) const { return _accel_scale[i]; }
     const Vector3f &get_accel_scale(void) const { return get_accel_scale(_primary_accel); }
 
+    // return the temperature if supported. Zero is returned if no
+    // temperature is available
+    float get_temperature(uint8_t instance) const { return _temperature[instance]; }
+
     /* get_delta_time returns the time period in seconds
      * overwhich the sensor data was collected
      */
@@ -261,6 +265,9 @@ private:
     AP_Vector3f _accel_offset[INS_MAX_INSTANCES];
     AP_Vector3f _gyro_offset[INS_MAX_INSTANCES];
 
+    // temperatures for an instance if available
+    float _temperature[INS_MAX_INSTANCES];
+
     // filtering frequency (0 means default)
     AP_Int8     _accel_filter_cutoff;
     AP_Int8     _gyro_filter_cutoff;

libraries/AP_InertialSensor/AP_InertialSensor_Backend.cpp

@@ -95,3 +95,11 @@ uint16_t AP_InertialSensor_Backend::get_sample_rate_hz(void) const
     // enum can be directly cast to Hz
     return (uint16_t)_imu._sample_rate;
 }
+
+/*
+  publish a temperature value for an instance
+ */
+void AP_InertialSensor_Backend::_publish_temperature(uint8_t instance, float temperature)
+{
+    _imu._temperature[instance] = temperature;
+}

libraries/AP_InertialSensor/AP_InertialSensor_Backend.h

@@ -73,6 +73,9 @@ protected:
     // rotate accel vector, scale, offset and publish
     void _publish_accel(uint8_t instance, const Vector3f &accel, bool rotate_and_correct = true);
 
+    // publish a temperature value
+    void _publish_temperature(uint8_t instance, float temperature);
+
     // set accelerometer error_count
     void _set_accel_error_count(uint8_t instance, uint32_t error_count);
 

libraries/AP_InertialSensor/AP_InertialSensor_PX4.cpp

@@ -270,6 +270,9 @@ void AP_InertialSensor_PX4::_new_accel_sample(uint8_t i, accel_report &accel_rep
     // report error count
     _set_accel_error_count(frontend_instance, accel_report.error_count);
 
+    // publish a temperature (for logging purposed only)
+    _publish_temperature(frontend_instance, accel_report.temperature);
+
 #ifdef AP_INERTIALSENSOR_PX4_DEBUG
     _accel_dt_max[i] = max(_accel_dt_max[i],dt);
 
@@ -377,12 +380,26 @@ void AP_InertialSensor_PX4::_get_sample()
     _last_get_sample_timestamp = hal.scheduler->micros64();
 }
 
-bool AP_InertialSensor_PX4::_get_accel_sample(uint8_t i, struct accel_report &accel_report) {
-    return i<_num_accel_instances && _accel_fd[i] != -1 && ::read(_accel_fd[i], &accel_report, sizeof(accel_report)) == sizeof(accel_report) && accel_report.timestamp != _last_accel_timestamp[i];
+bool AP_InertialSensor_PX4::_get_accel_sample(uint8_t i, struct accel_report &accel_report) 
+{
+    if (i<_num_accel_instances && 
+        _accel_fd[i] != -1 && 
+        ::read(_accel_fd[i], &accel_report, sizeof(accel_report)) == sizeof(accel_report) && 
+        accel_report.timestamp != _last_accel_timestamp[i]) {
+        return true;
+    }
+    return false;
 }
 
-bool AP_InertialSensor_PX4::_get_gyro_sample(uint8_t i, struct gyro_report &gyro_report) {
-    return i<_num_gyro_instances && _gyro_fd[i] != -1 && ::read(_gyro_fd[i], &gyro_report, sizeof(gyro_report)) == sizeof(gyro_report) && gyro_report.timestamp != _last_gyro_timestamp[i];
+bool AP_InertialSensor_PX4::_get_gyro_sample(uint8_t i, struct gyro_report &gyro_report) 
+{
+    if (i<_num_gyro_instances && 
+        _gyro_fd[i] != -1 && 
+        ::read(_gyro_fd[i], &gyro_report, sizeof(gyro_report)) == sizeof(gyro_report) && 
+        gyro_report.timestamp != _last_gyro_timestamp[i]) {
+        return true;
+    }
+    return false;
 }
 
 bool AP_InertialSensor_PX4::gyro_sample_available(void)