--- 工业控制中常用算法 ---

/    这是从网上找来的，在使用单片机作为控制cpu时，请稍作简化，具体的PID
参数必须由具体对象通过实验确定。由于单片机的处理速度和ram资源的限制，一般不采用浮点数运算，
而将所有参数全部用整数，运算到最后再除以一个2的N次方数据（相当于移位），作类似定点数运算，可
大大提高运算速度，根据控制精度的不同要求，当精度要求很高时，注意保留移位引起的“余数”，做好余
数补偿。这个程序只是一般常用pid算法的基本架构，没有包含输入输出处理部分。
=========================================*/
#include <string.h>
#include <stdio.h>
/    PID Function
   
    The PID (比例、积分、微分) function is used in mainly
    control applications. PIDCalc performs one iteration of the PID
    algorithm.

    While the PID function works, main is just a dummy program showing
    a typical usage.
======================================*/

typedef struct PID {

        double  SetPoint;           //  设定目标 Desired Value

        double  Proportion;         //  比例常数 Proportional Const
        double  Integral;           //  积分常数 Integral Const
        double  Derivative;         //  微分常数 Derivative Const

        double  LastError;          //  Error[-1]
        double  PrevError;          //  Error[-2]
        double  SumError;           //  Sums of Errors

} PID;

/*==============================================  

 PID计算部分
===============================================

double PIDCalc( PID *pp, double NextPoint )
{
    double  dError,
            Error;

        Error = pp->SetPoint -  NextPoint;          // 偏差
        pp->SumError += Error;                      // 积分
        dError = pp->LastError - pp->PrevError;     // 当前微分
        pp->PrevError = pp->LastError;
        pp->LastError = Error;
        return (pp->Proportion * Error              // 比例项
            +   pp->Integral * pp->SumError         // 积分项
            +   pp->Derivative * dError             // 微分项
        );
}

/*=======================================

   Initialize PID Structure
========================================*/

void PIDInit (PID *pp)
{
    memset ( pp,0,sizeof(PID));
}

/*====================================

    Main Program
=====================================*/

double sensor (void)                    //  Dummy Sensor Function
{
    return 100.0;
}

void actuator(double rDelta)            //  Dummy Actuator Function
{}

void main(void)
{
    PID         sPID;                   //  PID Control Structure
    double      rOut;                   //  PID Response (Output)
    double      rIn;                    //  PID Feedback (Input)

    PIDInit ( &sPID );                  //  Initialize Structure
    sPID.Proportion = 0.5;              //  Set PID Coefficients
    sPID.Integral   = 0.5;
    sPID.Derivative = 0.0;
    sPID.SetPoint   = 100.0;            //  Set PID Setpoint

    for (;;) {                          //  Mock Up of PID Processing

        rIn = sensor ();                //  Read Input
        rOut = PIDCalc ( &sPID,rIn );   //  Perform PID Interation
        actuator ( rOut );              //  Effect Needed Changes