ardupilot/libraries/PID/PID.h

// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: t -*-

/// @file	PID.h
/// @brief	Generic PID algorithm, with EEPROM-backed storage of constants.

#ifndef PID_h
#define PID_h

#include <AP_Common.h>
#include <math.h>		// for fabs()

/// @class	PID
/// @brief	Object managing one PID control
class PID {
public:

    PID(const float &initial_p = 0.0,
        const float &initial_i = 0.0,
        const float &initial_d = 0.0,
        const int16_t &initial_imax = 0) :
		_kp  (initial_p),
		_ki  (initial_i),
		_kd  (initial_d),
		_imax(initial_imax)
    {
	}

	/// Iterate the PID, return the new control value
	///
	/// Positive error produces positive output.
	///
	/// @param error	The measured error value
	/// @param dt		The time delta in milliseconds (note
	///					that update interval cannot be more
	///					than 65.535 seconds due to limited range
	///					of the data type).
	/// @param scaler	An arbitrary scale factor
	///
	/// @returns		The updated control output.
	///
	int32_t	get_pid(int32_t error, float scaler = 1.0);

	/// Reset the PID integrator
	///
	void	reset_I();

	/// Load gain properties
	///
	void 	load_gains();

	/// Save gain properties
	///
	void 	save_gains();

	/// @name	parameter accessors
	//@{

	/// Overload the function call operator to permit relatively easy initialisation
	void operator() (const float p,
	                 const float i,
	                 const float d,
	                 const int16_t imaxval) {
		_kp = p; _ki = i; _kd = d; _imax = imaxval;
	}

	float	kP() const				{ return _kp.get(); }
	float	kI() const 				{ return _ki.get(); }
	float	kD() const 				{ return _kd.get(); }
	int16_t	imax() const			{ return _imax.get(); }

	void	kP(const float v)		{ _kp.set(v); }
	void	kI(const float v)		{ _ki.set(v); }
	void	kD(const float v)		{ _kd.set(v); }
	void	imax(const int16_t v)	{ _imax.set(abs(v)); }

	float	get_integrator() const	{ return _integrator; }

    static const struct AP_Param::GroupInfo var_info[];

private:
	AP_Float			_kp;
	AP_Float			_ki;
	AP_Float			_kd;
	AP_Int16			_imax;

	float				_integrator;		///< integrator value
	int32_t				_last_error;		///< last error for derivative
	float				_last_derivative; 	///< last derivative for low-pass filter
	uint32_t			_last_t;

	int32_t	_get_pid(int32_t error, uint16_t dt, float scaler);

	/// Low pass filter cut frequency for derivative calculation.
	///
	/// 20 Hz becasue anything over that is probably noise, see
	/// http://en.wikipedia.org/wiki/Low-pass_filter.
	///
	static const uint8_t _fCut = 20;
};

#endif