systemlib: added library for hysteresis

There have been two cases where a hysteresis function wasn't working
correctly. It is therefore a good idea to abstract the hysteresis
functionality into a library.

src/modules/systemlib/hysteresis/hysteresis.cpp

@@ -0,0 +1,73 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2016 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @file hysteresis.cpp
+ *
+ * @author Julian Oes <julian@oes.ch>
+ */
+
+#include <px4_log.h>
+#include "systemlib/hysteresis/hysteresis.h"
+
+
+namespace systemlib {
+
+
+void
+Hysteresis::set_state_and_update(const bool new_state)
+{
+	if (new_state != _state) {
+		if (new_state != _requested_state) {
+			_requested_state = new_state;
+			_last_time_to_change_state = hrt_absolute_time();
+		}
+	} else {
+		_requested_state = _state;
+	}
+	update();
+}
+
+void
+Hysteresis::update()
+{
+
+
+	if (_requested_state != _state &&
+	    hrt_elapsed_time(&_last_time_to_change_state) >= _hysteresis_time_us) {
+
+		_state = _requested_state;
+	}
+}
+
+} // namespace systemlib

src/modules/systemlib/hysteresis/hysteresis.h

@@ -0,0 +1,78 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2016 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @file hysteresis.h
+ *
+ * Hysteresis of a boolean value.
+ *
+ * @author Julian Oes <julian@oes.ch>
+ */
+
+#pragma once
+
+#include <drivers/drv_hrt.h>
+
+namespace systemlib {
+
+class Hysteresis
+{
+public:
+	Hysteresis(unsigned hysteresis_time_us, bool init_state) :
+		_hysteresis_time_us(hysteresis_time_us),
+		_state(init_state),
+		_requested_state(init_state),
+		_last_time_to_change_state(0)
+	{}
+
+	~Hysteresis()
+	{}
+
+	bool get_state() const {
+		return _state;
+	}
+
+	void set_state_and_update(const bool new_state);
+
+	void update();
+
+private:
+
+	unsigned _hysteresis_time_us;
+	bool _state;
+
+	bool _requested_state;
+	hrt_abstime _last_time_to_change_state;
+};
+
+} // namespace systemlib