ardupilot/libraries/PID/PID.cpp

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

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

#include <math.h>
#include <avr/eeprom.h>

#include "PID.h"

// make the gain array members a little easier to identify
#define	_kp		_gain_array[0]
#define	_ki		_gain_array[1]
#define	_kd		_gain_array[2]
#define	_imax	_gain_array[3]

long
PID::get_pid(int32_t error, uint16_t dt, float scaler)
{
	float output		= 0;
 	float delta_time	= (float)dt / 1000.0;

	// Compute proportional component
	output += error * _kp;

	// Compute derivative component if time has elapsed
	if (_kd && (dt > 0)) {
		float derivative = (error - _last_error) / delta_time;

		// discrete low pass filter, cuts out the 
		// high frequency noise that can drive the controller crazy
		float RC = 1/(2*M_PI*_fCut);
		derivative = _last_derivative + 
			(delta_time / (RC + delta_time)) * (derivative - _last_derivative);

		// update state
		_last_error 		= error;
		_last_derivative    = derivative;

		// add in derivative component
		output 				+= _kd * derivative;
	}

	// scale the P and D components
	output *= scaler;
	
	// Compute integral component if time has elapsed
	if (_ki && (dt > 0)) {
		_integrator 		+= (error * _ki) * scaler * delta_time; 
		if (_integrator < -_imax) {
			_integrator = -_imax;
		} else if (_integrator > _imax) {
			_integrator = _imax;
		}
		output 				+= _integrator;
	}
	
	return output;
}

void
PID::imax(float v)
{
	_imax = fabs(v); 
}

void
PID::load_gains()
{
	switch(_storage)
	{
		case STORE_OFF:
			// load is a NOP if the gain array is managed externally
			break;
		case STORE_EEPROM_UINT16:
		//	_kp 	= (float)(eeprom_read_word((uint16_t *)	 _address))      / 1000.0;
		//	_ki 	= (float)(eeprom_read_word((uint16_t *)	(_address + 2))) / 1000.0;
			//_kd 	= (float)(eeprom_read_word((uint16_t *)	(_address + 4))) / 1000.0;
			//_imax 	= eeprom_read_word((uint16_t *)	(_address + 6)) * 100;
			
			_kp 	= (float)_ee.read_int(_address) / 1000.0;
			_ki 	= (float)_ee.read_int(_address + 2) / 1000.0;
			_kd 	= (float)_ee.read_int(_address + 4) / 1000.0;
			_imax 	= (float)_ee.read_int(_address + 6) * 100;

			break;
			
		case STORE_EEPROM_FLOAT:
			//eeprom_read_block((void*)&_kp,(const void*)(_address),sizeof(_kp));
			//eeprom_read_block((void*)&_ki,(const void*)(_address+4),sizeof(_ki));
			//eeprom_read_block((void*)&_kd,(const void*)(_address+8),sizeof(_kd));
			//eeprom_read_block((void*)&_imax,(const void*)(_address+12),sizeof(_imax));
			break;
	}
}

void
PID::save_gains()
{
	switch(_storage)
	{
		case STORE_OFF:
			// save is a NOP if the gain array is managed externally
			break;
		case STORE_EEPROM_UINT16:
			/*
			eeprom_write_word((uint16_t *)	 _address, 		(int)(_kp * 1000));
			eeprom_write_word((uint16_t *)	(_address + 2), (int)(_ki * 1000));
			eeprom_write_word((uint16_t *)	(_address + 4), (int)(_kd * 1000));
			eeprom_write_word((uint16_t *)	(_address + 6), (int)_imax/100);
			*/
			_ee.write_int(_address, 	(int)(_kp * 1000));
			_ee.write_int(_address + 2, (int)(_ki * 1000));
			_ee.write_int(_address + 4, (int)(_kd * 1000));
			_ee.write_int(_address + 6, (int)(_imax /100));
			break;
		case STORE_EEPROM_FLOAT:
			//eeprom_write_block((const void *)&_kp,(void *)(_address),sizeof(_kp));
			//eeprom_write_block((const void *)&_ki,(void *)(_address+4),sizeof(_ki));
			//eeprom_write_block((const void *)&_kd,(void *)(_address+8),sizeof(_kd));
			//eeprom_write_block((const void *)&_imax,(void *)(_address+12),sizeof(_imax));
			break;
	}
}