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 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 ***********************************************************************/
44 struct pid_params p_param;
45 /* cached data from previous loop */
46 static 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 */
55 int init_thermal_controller(void)
56 {
57 int ret = 0;
58
59 /* init pid params */
60 p_param.ts = ticktime;
61 /* TODO: get it from TUI tuning tab */
62 p_param.kp = .36;
63 p_param.ki = 5.0;
64 p_param.kd = 0.19;
65
66 p_param.t_target = target_temp_user;
67
68 return ret;
69 }
70
71 void controller_reset(void)
72 {
73 /* TODO: relax control data when not over thermal limit */
74 syslog(LOG_DEBUG, "TC inactive, relax p-state\n");
75 p_param.y_k = 0.0;
76 xk_1 = 0.0;
77 xk_2 = 0.0;
78 set_ctrl_state(0);
79 }
80
81 /* To be called at time interval Ts. Type C PID controller.
82 * y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
83 * - 2*x[k-1]+x[k-2])/Ts
84 * TODO: add low pass filter for D term
85 */
86 #define GUARD_BAND (2)
87 void controller_handler(const double xk, double *yk)
88 {
89 double ek;
90 double p_term, i_term, d_term;
91
92 ek = p_param.t_target - xk; /* error */
93 if (ek >= 3.0) {
94 syslog(LOG_DEBUG, "PID: %3.1f Below set point %3.1f, stop\n",
95 xk, p_param.t_target);
96 controller_reset();
97 *yk = 0.0;
98 return;
99 }
100 /* compute intermediate PID terms */
101 p_term = -p_param.kp * (xk - xk_1);
102 i_term = p_param.kp * p_param.ki * p_param.ts * ek;
103 d_term = -p_param.kp * p_param.kd * (xk - 2 * xk_1 + xk_2) / p_param.ts;
104 /* compute output */
105 *yk += p_term + i_term + d_term;
106 /* update sample data */
107 xk_1 = xk;
108 xk_2 = xk_1;
109
110 /* clamp output adjustment range */
111 if (*yk < -LIMIT_HIGH)
112 *yk = -LIMIT_HIGH;
113 else if (*yk > -LIMIT_LOW)
114 *yk = -LIMIT_LOW;
115
116 p_param.y_k = *yk;
117
118 set_ctrl_state(lround(fabs(p_param.y_k)));
119
120 }