pid.h

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 * @details
 * This file defines the @ref control_system::pid::PID class, which
 * implements a discrete-time PID controller.
 *
 * The controller combines proportional, integral, and derivative
 * components to generate a control output based on the error between
 * a reference value and the measured value.
 *
 * The controller maintains previous error and output values as internal
 * state variables and applies a configurable maximum output limit.
 *
 * The class is templated to support different numeric types such as
 * @c float and @c double.
 *
 * @tparam T Numeric data type used for the controller calculations.
 *
 * @author Abhinay Kumar
 * @version 1.0.0
 * @date 2026-08-11
 *
 * @copyright
 * Copyright (c) 2026 Abhinay Kumar
 */
 
#ifndef CONTROL_SYSTEM_PID_PID_H
#define CONTROL_SYSTEM_PID_PID_H
 
#include <cstdint>
#include "../utility/utility.h"
 
namespace control_system
{
 
    namespace pid
    {

         * The controller uses the sampling time to calculate the
         * discrete-time integral and derivative contributions.
         *
         * The previous control output and previous error values are
         * maintained internally as controller state.
         *
         * @tparam T Numeric data type used for the controller.
         *
         * @par Example
         * @code{.cpp}
         * control_system::pid::PID<double> controller;
         *
         * controller.init(
         *     0.001,
         *     Kp,
         *     Ki,
         *     Kd,
         *     0.0,
         *     100.0
         * );
         *
         * double output = controller.update(reference, measurement);
         * @endcode
         */
        template <typename T>
        class PID
        {
        public:

             * state initialized to their default values.
             */
            PID();


             *
             * @param[in] dt_ Controller sampling time in seconds.
             * @param[in] Kp_ Proportional gain.
             * @param[in] Ki_ Integral gain.
             * @param[in] Kd_ Derivative gain.
             * @param[in] u_k_1 Previous controller output.
             * @param[in] u_max_ Maximum allowed controller output.
             *
             * @details
             * Initializes the controller parameters and previous output
             * state.
             */
            void init(T dt_, T Kp_, T Ki_, T Kd_, T u_k_1_, T u_max_);


             * @param[in] Kp_ Proportional gain.
             * @param[in] Ki_ Integral gain.
             * @param[in] Kd_ Derivative gain.
             * @param[in] u_k_1 Previous controller output.
             * @param[in] u_max_ Maximum allowed controller output.
             *
             * @details
             * Updates the controller gains, sampling time, previous
             * output, and output limit.
             */
            void set_param(T dt_, T Kp_, T Ki_, T Kd_, T u_k_1_, T u_max_);

            /**
             * @brief Computes the PID control output.
             *
             * @param[in] x_0 Reference or desired value.
             * @param[in] x Current or measured value.
             *
             * @return PID controller output limited by the configured
             * maximum output.
             *
             * @details
             * Calculates the control output from the proportional,
             * integral, and derivative contributions using the current
             * control error and the stored controller state.
             */
            T update(T x_0, T x);


             *
             * @details
             * Resets the stored previous errors, previous output, and
             * startup state of the controller.
             */
            void reset();


            void merge(T u_k_1_);

            void set_dt(T dt_);

            void set_Kp(T Kp_);

            void set_Ki(T Ki_);

            void set_Kd(T Kd_);

            void set_u_0(T u_k_1_);

            void set_u_max(T u_max_);

            T get_dt();

            T get_Kp();

            T get_Ki();

            T get_Kd();

            T get_u_k_1();

            T get_e_k_1();

            T get_e_k_2();

            T get_u_max();
 
        private:
            T dt = 0.0;

            T u_k_1 = 0.0;

            T e_k_1 = 0.0;

            T e_k_2 = 0.0;

            T Kp = 0.0;

            T Ki = 0.0;

            T Kd = 0.0;

            T u_max = 9999999999;

            uint8_t start = 0;
        };
 
#include "../../src/pid/pid.tpp"
    }
}
 
#endif