1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * pid.c PID controller for testing cooling devices
4 *
5 * Copyright (C) 2012 Intel Corporation. All rights reserved.
6 *
7 * Author Name Jacob Pan <jacob.jun.pan@linux.intel.com>
8 */
9
10#include <unistd.h>
11#include <stdio.h>
12#include <stdlib.h>
13#include <string.h>
14#include <stdint.h>
15#include <sys/types.h>
16#include <dirent.h>
17#include <libintl.h>
18#include <ctype.h>
19#include <assert.h>
20#include <time.h>
21#include <limits.h>
22#include <math.h>
23#include <sys/stat.h>
24#include <syslog.h>
25
26#include "tmon.h"
27
28/**************************************************************************
29 * PID (Proportional-Integral-Derivative) controller is commonly used in
30 * linear control system, consider the process.
31 * G(s) = U(s)/E(s)
32 * kp = proportional gain
33 * ki = integral gain
34 * kd = derivative gain
35 * Ts
36 * We use type C Alan Bradley equation which takes set point off the
37 * output dependency in P and D term.
38 *
39 *   y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
40 *          - 2*x[k-1]+x[k-2])/Ts
41 *
42 *
43 ***********************************************************************/
44struct pid_params p_param;
45/* cached data from previous loop */
46static double xk_1, xk_2; /* input temperature x[k-#] */
47
48/*
49 * TODO: make PID parameters tuned automatically,
50 * 1. use CPU burn to produce open loop unit step response
51 * 2. calculate PID based on Ziegler-Nichols rule
52 *
53 * add a flag for tuning PID
54 */
55int init_thermal_controller(void)
56{
57
58	/* init pid params */
59	p_param.ts = ticktime;
60	/* TODO: get it from TUI tuning tab */
61	p_param.kp = .36;
62	p_param.ki = 5.0;
63	p_param.kd = 0.19;
64
65	p_param.t_target = target_temp_user;
66
67	return 0;
68}
69
70void controller_reset(void)
71{
72	/* TODO: relax control data when not over thermal limit */
73	syslog(LOG_DEBUG, "TC inactive, relax p-state\n");
74	p_param.y_k = 0.0;
75	xk_1 = 0.0;
76	xk_2 = 0.0;
77	set_ctrl_state(0);
78}
79
80/* To be called at time interval Ts. Type C PID controller.
81 *    y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
82 *          - 2*x[k-1]+x[k-2])/Ts
83 * TODO: add low pass filter for D term
84 */
85#define GUARD_BAND (2)
86void controller_handler(const double xk, double *yk)
87{
88	double ek;
89	double p_term, i_term, d_term;
90
91	ek = p_param.t_target - xk; /* error */
92	if (ek >= 3.0) {
93		syslog(LOG_DEBUG, "PID: %3.1f Below set point %3.1f, stop\n",
94			xk, p_param.t_target);
95		controller_reset();
96		*yk = 0.0;
97		return;
98	}
99	/* compute intermediate PID terms */
100	p_term = -p_param.kp * (xk - xk_1);
101	i_term = p_param.kp * p_param.ki * p_param.ts * ek;
102	d_term = -p_param.kp * p_param.kd * (xk - 2 * xk_1 + xk_2) / p_param.ts;
103	/* compute output */
104	*yk += p_term + i_term + d_term;
105	/* update sample data */
106	xk_1 = xk;
107	xk_2 = xk_1;
108
109	/* clamp output adjustment range */
110	if (*yk < -LIMIT_HIGH)
111		*yk = -LIMIT_HIGH;
112	else if (*yk > -LIMIT_LOW)
113		*yk = -LIMIT_LOW;
114
115	p_param.y_k = *yk;
116
117	set_ctrl_state(lround(fabs(p_param.y_k)));
118
119}
120