/***************************************************/
/* Single-Wire Sensors Interface Directly To A PC  */
/* By: Darvinder Singh Oberoi and Harinder Dhingra */
/***************************************************/
#include <stdio.h>
#include <conio.h>
#include <dos.h>
#include <math.h>
#pragma inline

#define TIMER_FREQUENCY	1193181.7			/* Counter2's operating frequency */
#define PRINTER_PORT	0x378				/* Base Address of Printer Port     */
#define READ_PORT		PRINTER_PORT + 1	/* Input Pulse Port 			    */
#define Resolution		7					/* ~54.9 ms limit Check Resolution Counts */
#define Delay_Count		4					/* Counting Delays due to iteration and checks*/
/* Resolution and Delay_Count values can be changed to get the most precise reading */
/* Resolution variable is required for checking the new and old reading boundary conditions */
/* Delay variable takes care of delays due to iteration cycles, useful for error correction at small pulse width signal */
/* Both these values should be set to minimum */
/* Minimum input pulse width is approx. 0.023 ms */

float averagedata( unsigned data[20], unsigned data_size );  /* Average of data samples */
void screen_display( );			   /* Initial Set Up Screen			   */

main( ) /*  Program Starts Here  */
{
	char ch;
	unsigned count[20],i,prev_count,elapsed_count ;
	float pulse_width, overflow;
	screen_display();
	asm mov al, 0b4h			/* Set  Counter2 mode to 2               */
	asm out 043h,al				/* 8254's control Port address i.e. 43h  */

/*----  Start the read Cycle Here ----*/
  for( ;ch != 'q'; ) /* Endless Loop until 'Q' is  pressed */
  {
	i=0;
	for (;;)
	{
		asm mov dx, READ_PORT   /* Set the input signal port */
		asm mov al, 0ffh
		asm out 042h, al		/* Load the initial count in two cycles  */
		asm out 042h, al        /* Counter2 Port address i.e. 42h 		 */
		prev_count = 65535;		/* Initialization 						 */
		overflow = 0.0;
  /*   Check for the first rising edge - i.e. first transition from 0 to 1 */
  /*   Input Signal  is at pin no:13 */
		reading_1:
		  asm in ax, dx
		  asm and ax, 10h
		  asm jnz  reading_1
		reading_0:
		   asm in ax, dx
		   asm and ax, 10h
		   asm jz  reading_0

  /* Enable Counter2         									*/
		asm mov al, 01h			/* Set enable bit				*/
		asm out 061h, al

  /* Check for High level input signal */
	 still_reading_1:
		asm in al, 042h	   		/* Read the contents of counter2*/
		asm mov bl, al
		asm in al, 042h
		asm mov bh, al
		asm mov elapsed_count, bx
  /* Check if pulse width is greater than multiples of ~54.9 mS */
  /* If pulse is greater, then increment the overflow flag      */
		if( ( prev_count <= Resolution) && (elapsed_count >= (65536 - Resolution) ) )
		  ++overflow;
		prev_count = elapsed_count;
		asm in ax, dx
		asm and ax, 10h
		asm jnz still_reading_1
		count[ i ] = elapsed_count;		/*  Store data in array  */

   /* Disable the counter as soon as 1-to-0 transistion is detected */
		asm mov al, 0h    	/* Reset the enable bit to 0 		*/
		asm out 061h, al	/* Disable counter     				*/

  /* If pulse width is less than 1 mS  */
		if ( elapsed_count >= 64343 && overflow == 0 )
		{
			++i;
			if ( i > 19 ) break;
		}
		else 				/* Pulse width greater than 1mS */
		{
			i = 1;
			break;
		}
	}
/*  Start Calculations, get the average data */
	 pulse_width = (overflow * 65536.0+(float)(0xffff - averagedata(count,i-1)+Delay_Count)) * 1000 /TIMER_FREQUENCY ;
	 gotoxy( 35,11 ); printf("%3.5f ", pulse_width);
	 gotoxy( 35,11 );
	 delay( 20 );				/* Dummy Delay            */
	 if( kbhit( ) )        	/* Check for Quit keys  */
		  ch = getch( );
		if( ch == 'q' || ch == 'Q' ) ch ='q';

  }
	textcolor( LIGHTGRAY );		/*  Restore screen attributes  */
	clrscr( );
}			/*---  End of the MAIN Program 	---*/

/* Arrange the data in ascending order and select 10 middle entries */
float averagedata( unsigned data[ ], unsigned data_size )
{
	float total_sum = 0;
	unsigned temp;
	int ii,j;

/* Arrange data in ascending order */
  if ( data_size > 1 )
  {
	for( ii=0; ii <= data_size; ii++ )
	{
		for( j=0; j <= data_size - 1; j++ )
		{
			if( data[ j ] <= data[ j + 1 ] )
			{
				temp = data[ j ];
				data[ j ]= data[ j + 1 ];
				data[ j + 1 ] = temp;
			}
		}
	 }
  	 /* Get 10 middle values and find the average */
	 for( ii=5; ii <= 14; ii++ )
		total_sum = total_sum + (float) data[ ii ];
	 total_sum /= 10.0;
	 return total_sum;
  }
  else
	return data[ 0 ];
}

/*	Initial screen  setup   */
void screen_display( )
{
	clrscr( );
	textcolor( YELLOW );
	gotoxy( 25, 2 ); cprintf("Pulse  Width Measurement");
	gotoxy( 5, 11 );
	textcolor( YELLOW );
	gotoxy( 30, 10 );
	cprintf( "Pulse Width (ms)" );
	gotoxy( 20, 22 ); cprintf( "< Press Q/q key to Quit the Program > " );
}