/************************************************************************/
/*      Delta.C            2/23/95                                      */
/*                                                                      */
/************************************************************************/
/*                                                                      */
/*      This program uses delta modulation to encode quantized data     */
/*      from a codec.  The bit rate can be effectively changed by       */
/*      changing the value at which the error signal saturates.         */
/*                                                                      */
/*      This program defines the port addressses for the                */
/*      particular input and output channel being used, sets up the     */
/*      IRQ3 to call the delta-modulation routine, and sets up          */
/*      an idle wait loop to conserve power while waiting for the       */
/*      interrupt.                                                      */
/************************************************************************/
#include <21020.h>    /* For the idle() command */
#include <signal.h>   /* For the interrupt command */
#include <macros.h>   /* For the segment function */
#include <stdlib.h>  

#define MAX_DIFF 32

volatile int in_port segment(hip_reg0); /* hip_reg0, hip_reg2, hip_reg3 are */
volatile int out_port segment(hip_reg2);/* used in architecture file  */
volatile int out_port2 segment(hip_reg3);

int current, previous;  /*current and previous samples */
int received;           /* reconstructed signal value */
int first_sample;       /* flag: is this the first sample? */

void process_input(int);

void main(void)
{ 
  first_sample = 1;
  interrupt(SIG_IRQ3, process_input);

  while (1)
  {  
    idle();
  }
}

void process_input(int sig_number)
{
  int diff;

  /* if this is the first sample, set received signal to xmit signal */
  if (first_sample)  
  {
     current = in_port;
     previous = current;
     received = current;
     out_port = current;
     first_sample = 1;
  }
  else
  {
     current = in_port;
     diff = current - previous;
     if (abs(diff) > MAX_DIFF)
	if (diff < 0) 
	   received = received - MAX_DIFF;
	else
	   received = received + MAX_DIFF;
     out_port = received;
     out_port2 = diff;
  }

}