/*    Program IIR.C                                                       */
/*      This is an all C implementation of a 6-th order bandpass IIR      */
/*      filter based on an elliptic prototype with a passband of 500 to   */
/*      1250 Hz and stop bands of 0-200 and 1750-2000 Hz. The passband    */
/*      ripple was chosen to be 0.3 dB and stopband attenuation to be     */
/*      40 dB.  A 4 kHz sampling rate is used.  C:\DIGFIL\IIR\IIR.EXE was */
/*      used to generate the filter coefficients.  The filter is          */
/*      implemented as the cascade of three biquad sections.              */

/* Provided by Professor Gansman at the University of Maryland            */
/*========================================================================*/
/*  These header files can be found in C:\UTIL.DSP                        */
/*========================================================================*/
#include "bus.h"
#include "serial.h"
#include "timers.h"
/*#include "aic.h"                /* MACROS and  STRUCTURES for AIC         */
/*========================================================================*/

/*========================================================================*/
/*   Standard header files used for various tasks in the program          */
/*========================================================================*/

#include <math.h>
#include <stdlib.h>
#include <limits.h>
#include <string.h>


/*========================================================================*/
/*  Defines to setup global constants                                     */
/*========================================================================*/

#define PI 3.14159
#define SAMPLING_FREQUENCY 8000.0
#define SCALING_FACTOR 10.0
#define NFIR 10 						/* FIR filter size				*/   

/*========================================================================*/
/*  Proto-types of Procedures                                             */
/*========================================================================*/
void init_c30bus(void);
void init_aic(void);

/*========================================================================*/
/* This is the main function.										      */
/*========================================================================*/

void main(void)
{
	
/*  State variables for the 3 biquad sections.  s[k][0] used for         */
/*  intermediate calculations.                                           */

    float s[3][3] = { {0.0, 0.0, 0.0},
		      {0.0, 0.0, 0.0},
		      {0.0, 0.0, 0.0} };                                 

/*  Denominator coefficients for the 3 biquad sections.  The first       */
/*  column of 1.0's is included to make indexing correspond to block     */
/*  diagrams of type 1 direct form sections.                             */

    float a[3][3] = { {1.0, -.312065, -1.298487},
		      {1.0, .730459, .706656},
		      {1.0, -1.298487, .770969} };

/*  Numerator coefficients for the 3 biquad sections.  The first column  */
/*  of 1.0's is included to make indexing easy.                          */

    float b[3][3] = { {1.0, .000000,  -1.000000},
		      {1.0, -1.923943,  1.000000},
		      {1.0, 1.807937,  1.000000} };

/*  Overall scale factor for unity gain                                   */

    float scale = .10739946612456;

    float y;
    int   iy = 0, k;

    gie_clear();               /* In C:\UTIL.DSP\BUS.LIB.  Disable        */
			       /* interrupts by clearing GIE bit.         */
    clear_ints();              /* In C:\UTIL.DSP\BUS.LIB.  Clear all flags*/
			       /* in interrupt flag (IF) register.        */
    init_c30bus();             /* Set 0 bus wait states and enable cache. */

    init_aic();                /* Set up Timer 0, initialize Serial Port  */
			       /* 0, start AIC and set its parameters     */

    for(;;){

	p0_xmit(iy);           /* Send out filtered sample on XRDY true   */
	y = p0_receive()<<16>>18; /* Get input sample and adjust it       */

/*  Now do the three biquad filter sections.                              */

	for(k=0; k<3; k++){
	    s[k][0] = y - a[k][1]*s[k][1] - a[k][2]*s[k][2];

	/* Compute section output         */
	    y = s[k][0] + b[k][1]*s[k][1] + b[k][2]*s[k][2];

	/* Update section state variables */
	    s[k][2] = s[k][1];
	    s[k][1] = s[k][0];
	}

	iy = y*scale; /* Scale output and convert to int                 */
	iy <<=2;      /* Shift up to make 2 lsb's zero for AIC           */
	
    }

}