ardupilot/libraries/AC_PID/AC_PID.h

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

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

#ifndef AC_PID_h
#define AC_PID_h

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

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

	/// Constructor for PID that saves its settings to EEPROM
	///
	/// @note	PIDs must be named to avoid either multiple parameters with the
	///			same name, or an overly complex constructor.
	///
	/// @param  initial_p       Initial value for the P term.
    /// @param  initial_i       Initial value for the I term.
    /// @param  initial_d       Initial value for the D term.
    /// @param  initial_imax    Initial value for the imax term.4
	///
	AC_PID(
	    const float &initial_p = 0.0,
	    const float &initial_i = 0.0,
	    const float &initial_d = 0.0,
	    const int16_t &initial_imax = 0.0) :

		_kp  (initial_p),
		_ki  (initial_i),
		_kd  (initial_d),
		_imax(initial_imax)
	{
		// no need for explicit load, assuming that the main code uses AP_Param::load_all.
	}

	/// 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 dt);
	int32_t get_pi(int32_t error, float dt);
	int32_t get_p(int32_t error);
	int32_t get_i(int32_t error, float dt);
	int32_t get_d(int32_t error, float dt);


	/// 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_input;		///< last input for derivative
	float				_last_derivative; 	///< last derivative for low-pass filter
	float				_output;
	float				_derivative;

	/// Low pass filter cut frequency for derivative calculation.
	///
	static const float _filter = 7.9577e-3; // Set to  "1 / ( 2 * PI * f_cut )";
	// Examples for _filter:
	// f_cut = 10 Hz -> _filter = 15.9155e-3
	// f_cut = 15 Hz -> _filter = 10.6103e-3
	// f_cut = 20 Hz -> _filter =  7.9577e-3
	// f_cut = 25 Hz -> _filter =  6.3662e-3
	// f_cut = 30 Hz -> _filter =  5.3052e-3
};

#endif