main.c

基于DSP 6711 的数字滤波器

//IIR 19阶butterworth低通滤波器
//采样频率fs=40k,截止频率fc=10k
//吴臻志作于2006/12/8

#include <c6x.h>
#include "math.h"
#define N 20
#define Length 128
float input[Length],output[Length];

const float b[N] = {
1.532234455e-005,0.0002911245683, 0.002620120998,  0.01484735217,  0.05938940868,
     0.1781682223,    0.415725857,   0.7720623016,    1.158093452,    1.415447593,
      1.415447593,    1.158093452,   0.7720623016,    0.415725857,   0.1781682223,
    0.05938940868,  0.01484735217, 0.002620120998,0.0002911245683, 1.532234455e-005
  };
const float a[N] = {
   1,-1.341377151e-015,    2.582051277,-3.020413399e-015,    2.629014969,
  -2.643519736e-015,    1.364365935,-1.157850946e-015,   0.3901539147,-2.727497971e-016,
    0.06217307225,-3.461429587e-017, 0.005333174486,-2.247626948e-018,0.0002255303698,
  -6.607450878e-020,3.915039997e-006,-6.698137419e-022,1.784284365e-008,-9.904767921e-025
	};

void filter(){

		int n,j;
		float temp;
		float x[N],y[N];
		//采样频率fs=40k,截止频率fc=10k
		for (j=0;j<N;j++){
			x[j]=y[j]=0;
		}
		for (n=0;n<Length;n++){
					temp=0;
					x[0]=input[n];
					for (j=0;j<N;j++){
						temp=temp+x[j]*b[j];
						}
					for (j=1;j<N;j++){
						temp=temp-y[j]*a[j];
						}
					y[0]=temp;
				//record values
					output[n]=y[0];
				//refresh state
					for (j=N-1;j>0;j--){
						x[j]=x[j-1];
						y[j]=y[j-1];
			}
				
		}
while(1);
}
void test1(){
		int n;
		for (n=0;n<Length;n++){
			input[n]=0;
		}
		input[Length/2]=1e034;	
}
void test2(){
		int n;
		for (n=0;n<Length;n++){
			input[n]=sin(2*3.1415926*n*9000/40000)+sin(2*3.1415926*n*11000/40000);
		}
}

void main(){		
	test2();
	filter();
}