// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * pid.c PID controller for testing cooling devices
 *
 * Copyright (C) 2012 Intel Corporation. All rights reserved.
 *
 * Author Name Jacob Pan <jacob.jun.pan@linux.intel.com>
 */

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <sys/types.h>
#include <dirent.h>
#include <libintl.h>
#include <ctype.h>
#include <assert.h>
#include <time.h>
#include <limits.h>
#include <math.h>
#include <sys/stat.h>
#include <syslog.h>

#include "tmon.h"

/**************************************************************************
 * PID (Proportional-Integral-Derivative) controller is commonly used in
 * linear control system, consider the process.
 * G(s) = U(s)/E(s)
 * kp = proportional gain
 * ki = integral gain
 * kd = derivative gain
 * Ts
 * We use type C Alan Bradley equation which takes set point off the
 * output dependency in P and D term.
 *
 *   y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
 *          - 2*x[k-1]+x[k-2])/Ts
 *
 *
 ***********************************************************************/
struct pid_params p_param;
/* cached data from previous loop */
static double xk_1, xk_2; /* input temperature x[k-#] */

/*
 * TODO: make PID parameters tuned automatically,
 * 1. use CPU burn to produce open loop unit step response
 * 2. calculate PID based on Ziegler-Nichols rule
 *
 * add a flag for tuning PID
 */
int init_thermal_controller(void)
{

        /* init pid params */
        p_param.ts = ticktime;
        /* TODO: get it from TUI tuning tab */
        p_param.kp = .36;
        p_param.ki = 5.0;
        p_param.kd = 0.19;

        p_param.t_target = target_temp_user;

        return 0;
}

void controller_reset(void)
{
        /* TODO: relax control data when not over thermal limit */
        syslog(LOG_DEBUG, "TC inactive, relax p-state\n");
        p_param.y_k = 0.0;
        xk_1 = 0.0;
        xk_2 = 0.0;
        set_ctrl_state(0);
}

/* To be called at time interval Ts. Type C PID controller.
 *    y[k] = y[k-1] - kp*(x[k] - x[k-1]) + Ki*Ts*e[k] - Kd*(x[k]
 *          - 2*x[k-1]+x[k-2])/Ts
 * TODO: add low pass filter for D term
 */
#define GUARD_BAND (2)
void controller_handler(const double xk, double *yk)
{
        double ek;
        double p_term, i_term, d_term;

        ek = p_param.t_target - xk; /* error */
        if (ek >= 3.0) {
                syslog(LOG_DEBUG, "PID: %3.1f Below set point %3.1f, stop\n",
                        xk, p_param.t_target);
                controller_reset();
                *yk = 0.0;
                return;
        }
        /* compute intermediate PID terms */
        p_term = -p_param.kp * (xk - xk_1);
        i_term = p_param.kp * p_param.ki * p_param.ts * ek;
        d_term = -p_param.kp * p_param.kd * (xk - 2 * xk_1 + xk_2) / p_param.ts;
        /* compute output */
        *yk += p_term + i_term + d_term;
        /* update sample data */
        xk_1 = xk;
        xk_2 = xk_1;

        /* clamp output adjustment range */
        if (*yk < -LIMIT_HIGH)
                *yk = -LIMIT_HIGH;
        else if (*yk > -LIMIT_LOW)
                *yk = -LIMIT_LOW;

        p_param.y_k = *yk;

        set_ctrl_state(lround(fabs(p_param.y_k)));

}