tools/thermal/tmon/pid.c

   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 }