LXR linux/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 ***********************************************************************/
  44struct pid_params p_param;
  45/* cached data from previous loop */
  46static 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 */
  55int 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
  71void 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)
  87void 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}
 121