/*將兩個(gè)不同頻率疊加的正弦余弦信號(hào)進(jìn)行FIR濾波，得到頻率較低的正弦信號(hào)*/
 /*濾波器系數(shù)用matlab計(jì)算 */
 
#include "stdio.h"
#include "math.h" 

static void dataIO(); /*提供軟件中斷*/
void FIR(float input[],float output[],int SIZE);/*濾波核心函數(shù)*/

float coffi[21]={
                 0.000478595791017,0.000726931684122,-0.003065643310532,
                 -0.005972516207952,0.009162581410507,0.024305842109567,
                 -0.018305853075952,-0.076072756598977,0.026970528950393,
                 0.306965272918299,0.469427460783227,0.306965272918299,
                 0.026970528950393,-0.076072756598977,-0.018305853075952,
                 0.024305842109567,0.009162581410507,-0.005972516207952,
                 -0.0030656643310532,0.000726931864122,0.000478595791017
                 };/*濾波器系數(shù)*/

float input[256];/*輸入數(shù)據(jù)，使用庫(kù)函數(shù)計(jì)算正余弦疊加信號(hào)*/
float output[256];/*經(jīng)過(guò)fir濾波的輸出數(shù)據(jù)*/

main() 
{ 
   int i; 
   /*計(jì)算輸入信號(hào)*/
   /*正弦頻率1000，余弦頻率2500*/
   for(i = 0;i <= 255;i ++)  
     {
     input[i]=(sin(2*3.14159235*i*1000/8000)+cos(2*3.14159265*i*2500/8000))/4; 
     output[i]=0;
     }
   
   FIR(input,output,256);   /*濾波*/
 while(1)
 {
  dataIO(); /*此處加入軟件中斷，用以觀察圖形*/
 }
}

/*函數(shù)：FIR
  作用：將輸入濾波寫入到輸出信號(hào)中
  輸入：輸入信號(hào)，輸出信號(hào)，變量維數(shù)
  返回：無(wú)*/
/*濾波公式：y(n)=coff[0]*x(n-0)+coff[1]*x(n-1)+.....+coff[N]*x(n-N)*/
/*此時(shí)N為20，n為255*/
void FIR(float input[],float output[],int SIZE)
{
  int i,j;
  for(i=0;i<SIZE;i++)
    for(j=0;j<21;j++)
   output[i]+=coffi[j]*input[i-j];
   
   puts("FIR end!\n");
}

static void  dataIO()
{
  return ; 
}