HIL: changes to fix HIL for ArduCopter after recent timing changes.

Changes include using AP_PeriodicProcess and calling imu.init even in HIL mode

ArduCopter/ArduCopter.pde

@@ -274,7 +274,6 @@ AP_AHRS_MPU6000  ahrs(&imu, g_gps, &ins);               // only works with APM2
 AP_AHRS_DCM ahrs(&imu, g_gps);
  #endif
 
-AP_TimerProcess timer_scheduler;
 #elif HIL_MODE == HIL_MODE_SENSORS
 // sensor emulators
 AP_ADC_HIL adc;
@@ -283,20 +282,18 @@ AP_Compass_HIL compass;
 AP_GPS_HIL              g_gps_driver(NULL);
 AP_IMU_Shim imu;
 AP_AHRS_DCM                         ahrs(&imu, g_gps);
-AP_PeriodicProcessStub timer_scheduler;
 AP_InertialSensor_Stub ins;
 
 static int32_t gps_base_alt;
 
 #elif HIL_MODE == HIL_MODE_ATTITUDE
 AP_ADC_HIL adc;
-AP_IMU_Shim imu;                     // never used
+AP_IMU_Shim imu;
 AP_AHRS_HIL             ahrs(&imu, g_gps);
 AP_GPS_HIL              g_gps_driver(NULL);
 AP_Compass_HIL compass;                  // never used
 AP_Baro_BMP085_HIL barometer;
 AP_InertialSensor_Stub ins;
-AP_PeriodicProcessStub timer_scheduler;
  #ifdef OPTFLOW_ENABLED
 AP_OpticalFlow_ADNS3080 optflow(OPTFLOW_CS_PIN);
  #endif
@@ -309,7 +306,8 @@ static int32_t gps_base_alt;
  #error Unrecognised HIL_MODE setting.
 #endif // HIL MODE
 
-
+// we always have a timer scheduler
+AP_TimerProcess timer_scheduler;
 
 ////////////////////////////////////////////////////////////////////////////////
 // GCS selection

ArduCopter/system.pde

@@ -381,14 +381,12 @@ static void startup_ground(void)
 {
     gcs_send_text_P(SEVERITY_LOW,PSTR("GROUND START"));
 
-#if HIL_MODE != HIL_MODE_ATTITUDE
     // Warm up and read Gyro offsets
     // -----------------------------
     imu.init(IMU::COLD_START, mavlink_delay, flash_leds, &timer_scheduler);
  #if CLI_ENABLED == ENABLED
     report_imu();
  #endif
-#endif
 
     // initialise ahrs (may push imu calibration into the mpu6000 if using that device).
     ahrs.init();

libraries/AP_IMU/AP_IMU_Shim.h

@@ -26,7 +26,9 @@ public:
                              void                   (*callback)(unsigned long t) = delay,
                              void                   (*flash_leds_cb)(bool on) = NULL,
                              AP_PeriodicProcess *   scheduler = NULL) {
-                                scheduler->register_process( AP_IMU_Shim::read );
+        if( scheduler != NULL ) {
+            scheduler->register_process( AP_IMU_Shim::read );
+        }
     };
     virtual void        init_accel(void (*callback)(unsigned long t) = delay,
                                    void (*flash_leds_cb)(bool on) = NULL) {