// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* pid.c PID controller for testing cooling devices
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*
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* Copyright (C) 2012 Intel Corporation. All rights reserved.
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*
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* Author Name Jacob Pan <jacob.jun.pan@linux.intel.com>
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*/
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#include <unistd.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdint.h>
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#include <sys/types.h>
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#include <dirent.h>
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#include <libintl.h>
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#include <ctype.h>
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#include <assert.h>
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#include <time.h>
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#include <limits.h>
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#include <math.h>
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#include <sys/stat.h>
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#include <syslog.h>
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#include "tmon.h"
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/**************************************************************************
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* PID (Proportional-Integral-Derivative) controller is commonly used in
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* linear control system, consider the the process.
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* G(s) = U(s)/E(s)
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* kp = proportional gain
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* ki = integral gain
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* kd = derivative gain
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* Ts
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* We use type C Alan Bradley equation which takes set point off the
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* output dependency in P and D term.
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*
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* y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
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* - 2*x[k-1]+x[k-2])/Ts
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*
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*
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***********************************************************************/
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struct pid_params p_param;
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/* cached data from previous loop */
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static double xk_1, xk_2; /* input temperature x[k-#] */
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/*
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* TODO: make PID parameters tuned automatically,
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* 1. use CPU burn to produce open loop unit step response
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* 2. calculate PID based on Ziegler-Nichols rule
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*
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* add a flag for tuning PID
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*/
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int init_thermal_controller(void)
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{
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int ret = 0;
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/* init pid params */
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p_param.ts = ticktime;
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/* TODO: get it from TUI tuning tab */
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p_param.kp = .36;
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p_param.ki = 5.0;
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p_param.kd = 0.19;
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p_param.t_target = target_temp_user;
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return ret;
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}
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void controller_reset(void)
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{
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/* TODO: relax control data when not over thermal limit */
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syslog(LOG_DEBUG, "TC inactive, relax p-state\n");
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p_param.y_k = 0.0;
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xk_1 = 0.0;
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xk_2 = 0.0;
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set_ctrl_state(0);
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}
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/* To be called at time interval Ts. Type C PID controller.
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* y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
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* - 2*x[k-1]+x[k-2])/Ts
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* TODO: add low pass filter for D term
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*/
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#define GUARD_BAND (2)
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void controller_handler(const double xk, double *yk)
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{
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double ek;
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double p_term, i_term, d_term;
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ek = p_param.t_target - xk; /* error */
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if (ek >= 3.0) {
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syslog(LOG_DEBUG, "PID: %3.1f Below set point %3.1f, stop\n",
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xk, p_param.t_target);
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controller_reset();
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*yk = 0.0;
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return;
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}
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/* compute intermediate PID terms */
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p_term = -p_param.kp * (xk - xk_1);
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i_term = p_param.kp * p_param.ki * p_param.ts * ek;
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d_term = -p_param.kp * p_param.kd * (xk - 2 * xk_1 + xk_2) / p_param.ts;
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/* compute output */
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*yk += p_term + i_term + d_term;
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/* update sample data */
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xk_1 = xk;
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xk_2 = xk_1;
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/* clamp output adjustment range */
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if (*yk < -LIMIT_HIGH)
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*yk = -LIMIT_HIGH;
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else if (*yk > -LIMIT_LOW)
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*yk = -LIMIT_LOW;
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p_param.y_k = *yk;
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set_ctrl_state(lround(fabs(p_param.y_k)));
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}
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