tools/thermal/tmon/pid.c

   1 /*
   2  * pid.c PID controller for testing cooling devices
   3  *
   4  *
   5  *
   6  * Copyright (C) 2012 Intel Corporation. All rights reserved.
   7  *
   8  * This program is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU General Public License version
  10  * 2 or later as published by the Free Software Foundation.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * Author Name Jacob Pan <jacob.jun.pan@linux.intel.com>
  18  *
  19  */
  20
  21 #include <unistd.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <stdint.h>
  26 #include <sys/types.h>
  27 #include <dirent.h>
  28 #include <libintl.h>
  29 #include <ctype.h>
  30 #include <assert.h>
  31 #include <time.h>
  32 #include <limits.h>
  33 #include <math.h>
  34 #include <sys/stat.h>
  35 #include <syslog.h>
  36
  37 #include "tmon.h"
  38
  39 /**************************************************************************
  40  * PID (Proportional-Integral-Derivative) controller is commonly used in
  41  * linear control system, consider the the process.
  42  * G(s) = U(s)/E(s)
  43  * kp = proportional gain
  44  * ki = integral gain
  45  * kd = derivative gain
  46  * Ts
  47  * We use type C Alan Bradley equation which takes set point off the
  48  * output dependency in P and D term.
  49  *
  50  *   y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
  51  *          - 2*x[k-1]+x[k-2])/Ts
  52  *
  53  *
  54  ***********************************************************************/
  55 struct pid_params p_param;
  56 /* cached data from previous loop */
  57 static double xk_1, xk_2; /* input temperature x[k-#] */
  58
  59 /*
  60  * TODO: make PID parameters tuned automatically,
  61  * 1. use CPU burn to produce open loop unit step response
  62  * 2. calculate PID based on Ziegler-Nichols rule
  63  *
  64  * add a flag for tuning PID
  65  */
  66 int init_thermal_controller(void)
  67 {
  68         int ret = 0;
  69
  70         /* init pid params */
  71         p_param.ts = ticktime;
  72         /* TODO: get it from TUI tuning tab */
  73         p_param.kp = .36;
  74         p_param.ki = 5.0;
  75         p_param.kd = 0.19;
  76
  77         p_param.t_target = target_temp_user;
  78
  79         return ret;
  80 }
  81
  82 void controller_reset(void)
  83 {
  84         /* TODO: relax control data when not over thermal limit */
  85         syslog(LOG_DEBUG, "TC inactive, relax p-state\n");
  86         p_param.y_k = 0.0;
  87         xk_1 = 0.0;
  88         xk_2 = 0.0;
  89         set_ctrl_state(0);
  90 }
  91
  92 /* To be called at time interval Ts. Type C PID controller.
  93  *    y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
  94  *          - 2*x[k-1]+x[k-2])/Ts
  95  * TODO: add low pass filter for D term
  96  */
  97 #define GUARD_BAND (2)
  98 void controller_handler(const double xk, double *yk)
  99 {
 100         double ek;
 101         double p_term, i_term, d_term;
 102
 103         ek = p_param.t_target - xk; /* error */
 104         if (ek >= 3.0) {
 105                 syslog(LOG_DEBUG, "PID: %3.1f Below set point %3.1f, stop\n",
 106                         xk, p_param.t_target);
 107                 controller_reset();
 108                 *yk = 0.0;
 109                 return;
 110         }
 111         /* compute intermediate PID terms */
 112         p_term = -p_param.kp * (xk - xk_1);
 113         i_term = p_param.kp * p_param.ki * p_param.ts * ek;
 114         d_term = -p_param.kp * p_param.kd * (xk - 2 * xk_1 + xk_2) / p_param.ts;
 115         /* compute output */
 116         *yk += p_term + i_term + d_term;
 117         /* update sample data */
 118         xk_1 = xk;
 119         xk_2 = xk_1;
 120
 121         /* clamp output adjustment range */
 122         if (*yk < -LIMIT_HIGH)
 123                 *yk = -LIMIT_HIGH;
 124         else if (*yk > -LIMIT_LOW)
 125                 *yk = -LIMIT_LOW;
 126
 127         p_param.y_k = *yk;
 128
 129         set_ctrl_state(lround(fabs(p_param.y_k)));
 130
 131 }