AP_Baro: changed HIL driver to use floats and better handle starup

libraries/AP_Baro/AP_Baro.cpp

@@ -136,6 +136,11 @@ float AP_Baro::get_altitude(void)
 {
     float scaling, temp;
 
+    if (_ground_pressure == 0) {
+        // called before initialisation
+        return 0;
+    }
+
     if (_last_altitude_t == _last_update) {
         // no new information
         return _altitude + _alt_offset;

libraries/AP_Baro/AP_Baro_HIL.cpp

@@ -3,6 +3,7 @@
 #include <AP_Baro.h>
 #include "AP_Baro_HIL.h"
 #include <AP_HAL.h>
+
 extern const AP_HAL::HAL& hal;
 
 // Public Methods //////////////////////////////////////////////////////////////
@@ -21,8 +22,8 @@ uint8_t AP_Baro_HIL::read()
     if (_count != 0) {
         hal.scheduler->suspend_timer_procs();
         result = 1;
-        Press = ((float)_pressure_sum) / _count;
-        Temp = ((float)_temperature_sum) / _count;
+        Press = _pressure_sum / _count;
+        Temp = _temperature_sum / _count;
         _pressure_samples = _count;
         _count = 0;
         _pressure_sum = 0;

libraries/AP_Baro/AP_Baro_HIL.h

@@ -11,8 +11,8 @@ private:
     uint8_t BMP085_State;
     float Temp;
     float Press;
-    int32_t _pressure_sum;
-    int32_t _temperature_sum;
+    float _pressure_sum;
+    float _temperature_sum;
     volatile uint8_t _count;
 
 public: