Add ADXRS450_Gyro.

This is a digital gyro interfaced via SPI.  Uses the HAL SPI accumulator.

Basic code function successfully tested on a ADXRS453.

Change-Id: Ibc0c7db9964c041fb1e04af4db17e3310ea83c04

wpilibc/Athena/include/ADXRS450_Gyro.h

@@ -0,0 +1,44 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2015. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+#pragma once
+
+#include "GyroBase.h"
+#include "Notifier.h"
+#include "SPI.h"
+#include "HAL/cpp/priority_mutex.h"
+
+#include <memory>
+
+/**
+ * Use a rate gyro to return the robots heading relative to a starting position.
+ * The Gyro class tracks the robots heading based on the starting position. As
+ * the robot rotates the new heading is computed by integrating the rate of
+ * rotation returned by the sensor. When the class is instantiated, it does a
+ * short calibration routine where it samples the gyro while at rest to
+ * determine the default offset. This is subtracted from each sample to
+ * determine the heading.
+ *
+ * This class is for the digital ADXRS450 gyro sensor that connects via SPI.
+ */
+class ADXRS450_Gyro : public GyroBase {
+ public:
+  ADXRS450_Gyro();
+  explicit ADXRS450_Gyro(SPI::Port port);
+  virtual ~ADXRS450_Gyro() = default;
+
+  float GetAngle() const override;
+  double GetRate() const override;
+  void Reset() override;
+  void Calibrate() override;
+
+  std::string GetSmartDashboardType() const override;
+
+ private:
+  SPI m_spi;
+
+  uint16_t ReadRegister(uint8_t reg);
+};

wpilibc/Athena/include/WPILib.h

@@ -14,6 +14,7 @@
 #include "ADXL345_I2C.h"
 #include "ADXL345_SPI.h"
 #include "ADXL362.h"
+#include "ADXRS450_Gyro.h"
 #include "AnalogAccelerometer.h"
 #include "AnalogGyro.h"
 #include "AnalogInput.h"