1/*
  2 * pid.c PID controller for testing cooling devices
  3 *
  4 *
  5 *
  6 * Copyright (C) 2012 Intel Corporation. All rights reserved.
  7 *
  8 * This program is free software; you can redistribute it and/or
  9 * modify it under the terms of the GNU General Public License version
 10 * 2 or later as published by the Free Software Foundation.
 11 *
 12 * This program is distributed in the hope that it will be useful,
 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 15 * GNU General Public License for more details.
 16 *
 17 * Author Name Jacob Pan <jacob.jun.pan@linux.intel.com>
 18 *
 19 */
 20
 21#include <unistd.h>
 22#include <stdio.h>
 23#include <stdlib.h>
 24#include <string.h>
 25#include <stdint.h>
 26#include <sys/types.h>
 27#include <dirent.h>
 28#include <libintl.h>
 29#include <ctype.h>
 30#include <assert.h>
 31#include <time.h>
 32#include <limits.h>
 33#include <math.h>
 34#include <sys/stat.h>
 35#include <syslog.h>
 36
 37#include "tmon.h"
 38
 39/**************************************************************************
 40 * PID (Proportional-Integral-Derivative) controller is commonly used in
 41 * linear control system, consider the the process.
 42 * G(s) = U(s)/E(s)
 43 * kp = proportional gain
 44 * ki = integral gain
 45 * kd = derivative gain
 46 * Ts
 47 * We use type C Alan Bradley equation which takes set point off the
 48 * output dependency in P and D term.
 49 *
 50 *   y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
 51 *          - 2*x[k-1]+x[k-2])/Ts
 52 *
 53 *
 54 ***********************************************************************/
 55struct pid_params p_param;
 56/* cached data from previous loop */
 57static double xk_1, xk_2; /* input temperature x[k-#] */
 58
 59/*
 60 * TODO: make PID parameters tuned automatically,
 61 * 1. use CPU burn to produce open loop unit step response
 62 * 2. calculate PID based on Ziegler-Nichols rule
 63 *
 64 * add a flag for tuning PID
 65 */
 66int init_thermal_controller(void)
 67{
 68	int ret = 0;
 69
 70	/* init pid params */
 71	p_param.ts = ticktime;
 72	/* TODO: get it from TUI tuning tab */
 73	p_param.kp = .36;
 74	p_param.ki = 5.0;
 75	p_param.kd = 0.19;
 76
 77	p_param.t_target = target_temp_user;
 78
 79	return ret;
 80}
 81
 82void controller_reset(void)
 83{
 84	/* TODO: relax control data when not over thermal limit */
 85	syslog(LOG_DEBUG, "TC inactive, relax p-state\n");
 86	p_param.y_k = 0.0;
 87	xk_1 = 0.0;
 88	xk_2 = 0.0;
 89	set_ctrl_state(0);
 90}
 91
 92/* To be called at time interval Ts. Type C PID controller.
 93 *    y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
 94 *          - 2*x[k-1]+x[k-2])/Ts
 95 * TODO: add low pass filter for D term
 96 */
 97#define GUARD_BAND (2)
 98void controller_handler(const double xk, double *yk)
 99{
100	double ek;
101	double p_term, i_term, d_term;
102
103	ek = p_param.t_target - xk; /* error */
104	if (ek >= 3.0) {
105		syslog(LOG_DEBUG, "PID: %3.1f Below set point %3.1f, stop\n",
106			xk, p_param.t_target);
107		controller_reset();
108		*yk = 0.0;
109		return;
110	}
111	/* compute intermediate PID terms */
112	p_term = -p_param.kp * (xk - xk_1);
113	i_term = p_param.kp * p_param.ki * p_param.ts * ek;
114	d_term = -p_param.kp * p_param.kd * (xk - 2 * xk_1 + xk_2) / p_param.ts;
115	/* compute output */
116	*yk += p_term + i_term + d_term;
117	/* update sample data */
118	xk_1 = xk;
119	xk_2 = xk_1;
120
121	/* clamp output adjustment range */
122	if (*yk < -LIMIT_HIGH)
123		*yk = -LIMIT_HIGH;
124	else if (*yk > -LIMIT_LOW)
125		*yk = -LIMIT_LOW;
126
127	p_param.y_k = *yk;
128
129	set_ctrl_state(lround(fabs(p_param.y_k)));
130
131}