/*----------------------------------------------------------------------

	File:        fir.c

	Description: Perform 128-tap fir filtering on codec input.

		     Input: Right channel of line-in

		     Output: Right channel = original signal

			     Left channel  = filtered signal

	

 -----------------------------------------------------------------------*/



#include <stdio.h>

#include <string.h>

#include <common.h>

#include <codec.h>

#include <mcbspdrv.h>

#include <board.h>

#include <stdlib.h>

#include <timer.h>

#include <intr.h>

#include <regs.h>



#define SAMPLING_RATE 44100



extern int inicodec (int sampling_rate);



short R_in[128]; // Input samples R_in[0] most recent, R_in[127] oldest.

short h[]=       // Impulse response of FIR filter.

{

	   -2,    10,    14,     7,    -7,   -17,   -13 ,    3,

     19,    21,     4,   -21,   -32,   -16,    18 ,   43,

	   34,    -8,   -51,   -56,   -11,    53,    81 ,   41,

		-44,  -104,   -81,    19,   119,   129,    24 , -119,

   -178,   -88,    95,   222,   171,   -41,  -248 , -266,

		-50,   244,   366,   181,  -195,  -457,  -353 ,   85,

		522,   568,   109,  -540,  -831,  -424,   474 , 1163,

		953,  -245, -1661, -2042,  -463,  2940,  6859 , 9469,

	 9469,  6859,  2940,  -463, -2042, -1661,  -245 ,  953,

	 1163,   474,  -424,  -831,  -540,   109,   568 ,  522,

	   85,  -353,  -457,  -195,   181,   366,   244 ,  -50,

   -266,  -248,   -41,   171,   222,    95,   -88 , -178,

   -119,    24,   129,   119,    19,   -81,  -104 ,  -44,

     41,    81,    53,   -11,   -56,   -51,    -8 ,   34,

     43,    18,   -16,   -32,   -21,     4,    21 ,   19,

	    3,   -13,   -17,    -7,     7,    14,    10 ,   -2

};



#pragma CODE_SECTION (fir_filter, ".iprog") // Put routine in internal memory.

short fir_filter (short input)

{

	int i;

	short output;

	int acc=0;

	int prod;



	R_in[0] = input;              // Update most recent sample.



	acc = 0;                      // Zero accumulator.

	for (i=0; i<128; i++)         // 128 taps

	{   

		prod = (h[i]*R_in[i]);  // perform Q.15 multiplication

		acc = acc + prod;           // Update 32-bit accumulator, catering

	}                             // for temporary overflow. 

	output = (short) (acc>>15);       // Cast output to 16-bits.



	for (i=127; i>0; i--)         // Shift delay samples.

		R_in[i]=R_in[i-1];



	return output;

}



#pragma CODE_SECTION (isr_rint0, ".iprog") // Put routine in internal memory.

interrupt void isr_rint0 (void)

{

	int sample;

	short output;



	sample = MCBSP0_DRR;

	sample &= 0xffff;



	output = fir_filter ((short) sample);



	sample |= (((int)output)<<16);

       MCBSP0_DXR = sample;

   

	return;

}



void Init_Interrupts ()

{

	intr_reset();                     // Reset the interrupt system,

					  // disable all interrupts.

	INTR_CLR_FLAG (CPU_INT15);        // Clear previous interrupt request

	INTR_ENABLE (CPU_INT15);          // Enable cpu interrupt line 15

	intr_map(CPU_INT15,ISN_RINT0);    // Link receive interrupt of serial

					  // port 0 to interrupt line 15.

	intr_hook (isr_rint0,CPU_INT15);  // Assign the interrupt service routine

}



void main(void)

{

	evm_init();                        // Initialise EVM board.

	inicodec (SAMPLING_RATE);         // Initialise codec, adjust sampling rate.

	Init_Interrupts ();               // Initialise interrupts and hook isr.

	INTR_GLOBAL_ENABLE();             // Enable global interrupt.



	for (;;);                         // Main loop, does nothing.

}