thermal/tmon/pid.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /*
0003  * pid.c PID controller for testing cooling devices
0004  *
0005  * Copyright (C) 2012 Intel Corporation. All rights reserved.
0006  *
0007  * Author Name Jacob Pan <jacob.jun.pan@linux.intel.com>
0008  */
0009
0010 #include <unistd.h>
0011 #include <stdio.h>
0012 #include <stdlib.h>
0013 #include <string.h>
0014 #include <stdint.h>
0015 #include <sys/types.h>
0016 #include <dirent.h>
0017 #include <libintl.h>
0018 #include <ctype.h>
0019 #include <assert.h>
0020 #include <time.h>
0021 #include <limits.h>
0022 #include <math.h>
0023 #include <sys/stat.h>
0024 #include <syslog.h>
0025
0026 #include "tmon.h"
0027
0028 /**************************************************************************
0029  * PID (Proportional-Integral-Derivative) controller is commonly used in
0030  * linear control system, consider the process.
0031  * G(s) = U(s)/E(s)
0032  * kp = proportional gain
0033  * ki = integral gain
0034  * kd = derivative gain
0035  * Ts
0036  * We use type C Alan Bradley equation which takes set point off the
0037  * output dependency in P and D term.
0038  *
0039  *   y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
0040  *          - 2*x[k-1]+x[k-2])/Ts
0041  *
0042  *
0043  ***********************************************************************/
0044 struct pid_params p_param;
0045 /* cached data from previous loop */
0046 static double xk_1, xk_2; /* input temperature x[k-#] */
0047
0048 /*
0049  * TODO: make PID parameters tuned automatically,
0050  * 1. use CPU burn to produce open loop unit step response
0051  * 2. calculate PID based on Ziegler-Nichols rule
0052  *
0053  * add a flag for tuning PID
0054  */
0055 int init_thermal_controller(void)
0056 {
0057
0058     /* init pid params */
0059     p_param.ts = ticktime;
0060     /* TODO: get it from TUI tuning tab */
0061     p_param.kp = .36;
0062     p_param.ki = 5.0;
0063     p_param.kd = 0.19;
0064
0065     p_param.t_target = target_temp_user;
0066
0067     return 0;
0068 }
0069
0070 void controller_reset(void)
0071 {
0072     /* TODO: relax control data when not over thermal limit */
0073     syslog(LOG_DEBUG, "TC inactive, relax p-state\n");
0074     p_param.y_k = 0.0;
0075     xk_1 = 0.0;
0076     xk_2 = 0.0;
0077     set_ctrl_state(0);
0078 }
0079
0080 /* To be called at time interval Ts. Type C PID controller.
0081  *    y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
0082  *          - 2*x[k-1]+x[k-2])/Ts
0083  * TODO: add low pass filter for D term
0084  */
0085 #define GUARD_BAND (2)
0086 void controller_handler(const double xk, double *yk)
0087 {
0088     double ek;
0089     double p_term, i_term, d_term;
0090
0091     ek = p_param.t_target - xk; /* error */
0092     if (ek >= 3.0) {
0093         syslog(LOG_DEBUG, "PID: %3.1f Below set point %3.1f, stop\n",
0094             xk, p_param.t_target);
0095         controller_reset();
0096         *yk = 0.0;
0097         return;
0098     }
0099     /* compute intermediate PID terms */
0100     p_term = -p_param.kp * (xk - xk_1);
0101     i_term = p_param.kp * p_param.ki * p_param.ts * ek;
0102     d_term = -p_param.kp * p_param.kd * (xk - 2 * xk_1 + xk_2) / p_param.ts;
0103     /* compute output */
0104     *yk += p_term + i_term + d_term;
0105     /* update sample data */
0106     xk_1 = xk;
0107     xk_2 = xk_1;
0108
0109     /* clamp output adjustment range */
0110     if (*yk < -LIMIT_HIGH)
0111         *yk = -LIMIT_HIGH;
0112     else if (*yk > -LIMIT_LOW)
0113         *yk = -LIMIT_LOW;
0114
0115     p_param.y_k = *yk;
0116
0117     set_ctrl_state(lround(fabs(p_param.y_k)));
0118
0119 }