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}