/*********************************************************************************************************
 *  ------------------------------------------------------------------------------------------------------
 *  file description
 *  ------------------------------------------------------------------------------------------------------
 *         \file  pid.c
 *         \unit  pid
 *        \brief  This is a general-purpose C language pid module
 *       \author  Lamdonn
 *      \version  v1.0.0
 *      \license  GPL-2.0
 *    \copyright  Copyright (C) 2023 Lamdonn.
 ********************************************************************************************************/
#include "pid.h"


void pid_init(PIDC *pid) 
{
    /* Initialize pid structure members */
    pid->point      = 0.0;
    pid->process    = 0.0;
    pid->kp         = 0.0;
    pid->ki         = 0.0;
    pid->kd         = 0.0;
    pid->integral   = 0.0;
    pid->error      = 0.0;
    pid->output     = 0.0;
}

double pid_compute(PIDC *pid) 
{
    double error;                           /* Record current error */
    double delta;                           /* Record delta error */
    double derivative;                      /* Record derivative item */

    /* Calculate current error */
    error = pid->point - pid->process;

    /* Calculate the change in error */
    delta = error - pid->error;

    /* Accumulation of integral terms */
    pid->integral += error * pid->ki;

    /* Calculate differential terms */
    derivative = delta * pid->kd;

    /* Calculate PID output */
    pid->output = pid->kp * error + pid->integral + derivative;

    /* Update previous error */
    pid->error = error;

    return pid->output; /* Return controller output */
}