1. FIR and IIR Filters with on and off Functionality
By: Nitin Jalan
For: Dr. V. Kepuska
Subject: Microcomputer System 1

2. IIR Filter: High And Low Pass
//Low pass filter IIR function
void lowpassfilter_IIR(void) {
float x = (float)(iChannel0LeftIn<<8); //shifts bits of the float x 8 bits to the left
int s;
for(s = 0; s <= 2; s++) //increments s from 0 to 2
lpd0[s] = x - (lpA1[s]*lpd1[s]) - (lpA2[s]*lpd2[s]); //delay equation
x = (lpB2[s] * lpd2[s]) + (lpB1[s] * lpd1[s]) + (lpB0[s] * lpd0[s]); //output equation
lpd2[s] = lpd1[s]; //shifts the delays each sampling
lpd1[s] = lpd0[s]; }
iChannel0LeftOut = ((int)x) >> 8; //shifts the output back 8 bits to the right

3. FIR FIltters: High Pass and Low PAss
void highpassfilter_FIR(void) {
x[n] = (fract16) (iChannel0RightIn>>8); //shifts the x[n] 8 bits to the right
if (variables<1024)
buffer[variables++]= x[n]; //Buffer }
output = 0; //sets the output to 0
for(p=0; p<101; p++)
output = add_fr1x16(output, mult_fr1x16(x[(n-p+101) %101],yhp[p])); //filter delay equation including circular buffer
//uses fract16 funcions
n++; //increment pointer
n = n % 101; //keeps the pointer positive
iChannel0RightOut=((int)(output))<<8; //Output is shifted back 8 bits to the left

4. References my.fit.edu/~vkepuska/ece3551
Christian Stumf and Ryan Boleman Lab