AP_InertialSensor: BMI160: add backend

The reason of defining BMI160_MAX_FIFO_SAMPLES as 8 can be found on the
following histogram of the number of samples in the FIFO on each read while
performing the accelerometer calibration process:

Samples Count   Freq Acc. Freq
------------------------------
      1  3842 0.1201  0.120111
      2 13172 0.4118  0.531904
      3  9065 0.2834  0.815300
      4  2710 0.0847  0.900022
      5  2231 0.0697  0.969769
      6   816 0.0255  0.995279
      7   137 0.0043  0.999562
      8    13 0.0004  0.999969
     13     1 0.0000  1.000000

libraries/AP_InertialSensor/AP_InertialSensor.cpp

@@ -11,6 +11,7 @@
 #include <AP_Vehicle/AP_Vehicle.h>
 
 #include "AP_InertialSensor.h"
+#include "AP_InertialSensor_BMI160.h"
 #include "AP_InertialSensor_Backend.h"
 #include "AP_InertialSensor_HIL.h"
 #include "AP_InertialSensor_L3G4200D.h"

libraries/AP_InertialSensor/AP_InertialSensor_BMI160.h

@@ -0,0 +1,119 @@
+/*
+ * Copyright (C) 2016  Intel Corporation. All rights reserved.
+ *
+ * This file is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+
+#include <AP_HAL/AP_HAL.h>
+
+#if CONFIG_HAL_BOARD == HAL_BOARD_LINUX
+
+#include "AP_InertialSensor.h"
+#include "AP_InertialSensor_Backend.h"
+
+class AP_InertialSensor_BMI160 : public AP_InertialSensor_Backend {
+public:
+    static AP_InertialSensor_Backend *probe(AP_InertialSensor &imu,
+                                            AP_HAL::OwnPtr<AP_HAL::SPIDevice> dev);
+
+    /**
+     * Configure the sensors and start reading routine.
+     */
+    void start() override;
+
+    bool update() override;
+
+private:
+    AP_InertialSensor_BMI160(AP_InertialSensor &imu,
+                             AP_HAL::OwnPtr<AP_HAL::Device> dev);
+
+    /**
+     * If the macro BMI160_DEBUG is defined, check if there are errors reported
+     * on the device's error register and panic if so. The implementation is
+     * empty if the BMI160_DEBUG isn't defined.
+     */
+    void _check_err_reg();
+
+    /**
+     * Try to perform initialization of the BMI160 device.
+     *
+     * The device semaphore must be taken and released by the caller.
+     *
+     * @return true on success, false otherwise.
+     */
+    bool _hardware_init();
+
+    /**
+     * Try to initialize this driver.
+     *
+     * Do sensor and other required initializations.
+     *
+     * @return true on success, false otherwise.
+     */
+    bool _init();
+
+    /**
+     * Configure accelerometer sensor. The device semaphore must already be
+     * taken before calling this function.
+     *
+     * @return true on success, false otherwise.
+     */
+    bool _configure_accel();
+
+    /**
+     * Configure gyroscope sensor. The device semaphore must already be
+     * taken before calling this function.
+     *
+     * @return true on success, false otherwise.
+     */
+    bool _configure_gyro();
+
+    /**
+     * Configure INT1 pin as watermark interrupt pin at the level of one sample
+     * if using fifo or data-ready pin otherwise.
+     *
+     * @return true on success, false otherwise.
+     */
+    bool _configure_int1_pin();
+
+    /**
+     * Configure FIFO.
+     *
+     * @return true on success, false otherwise.
+     */
+    bool _configure_fifo();
+
+    /**
+     * Timer routine to read data from the sensors.
+     */
+    void _poll_data();
+
+    /**
+     * Read samples from fifo.
+     */
+    void _read_fifo();
+
+    AP_HAL::OwnPtr<AP_HAL::Device> _dev;
+
+    uint8_t _accel_instance;
+    float _accel_scale;
+
+    uint8_t _gyro_instance;
+    float _gyro_scale;
+
+    AP_HAL::DigitalSource *_int1_pin;
+};
+
+#endif