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  */
init_thermal_controller(void)55 int 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 
controller_reset(void)70 void 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)
controller_handler(const double xk,double * yk)86 void 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