Date: Wed, 6 May 92 13:11 +1000
From: Bill Metzenthen <APM233M AT vaxc DOT cc DOT monash DOT edu DOT au>
Subject: Re: delay()
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Status: O


Ted Cox (jtcox AT gumby DOT syr DOT edu) writes:

>Has anyone implemented a version of Borland's delay() for djgpp?  I
>would like to use such a function, and have the source for Borland's
>routine, but am not eager (or competent) to convert the ASM from tasm
>style to as style.

I had a need for this and wrote a kludge to perform the function.
I can't say that I am proud of it, but it works for me  ;-)
The file "delay.c" is attached...


--Bill


--------------- snip,snip ----  file "delay.c"  ---- snip,snip -----------
/*
     A delay() function for DJGPP
 */


#define	DJGPP_BASE	0xe0000000
#define	TICK_COUNT	( /* (volatile unsigned short) */ \
			 *((volatile unsigned short *)(DJGPP_BASE + 0x46c)) \
			)
#define	DIDDLE		( /* (volatile unsigned short) */ \
			 *((volatile unsigned short *)(DJGPP_BASE + 0x00)) \
			)

static initialize_delay(void);


static	unsigned short	calibration = 0;


void delay(unsigned int milliseconds)
{
unsigned short	j;
unsigned short	diddle;
int		i;

if ( calibration == 0 )
	{
	unsigned short first = TICK_COUNT;
	unsigned int	taken;

	initialize_delay();
	if ( (taken = (TICK_COUNT - first)*55) >= milliseconds )
		return;
	milliseconds -= taken;
	}


diddle = DIDDLE;
for ( i = 0; i < milliseconds; i++ )
	{
	for ( j = 0; j < calibration; j++ )
		if ( DIDDLE != diddle )
			/* diddle = DIDDLE */ ;
	}

}


static initialize_delay(void)
{
unsigned short	first;
unsigned short	count;

count = 0;

/* wait for a change of tick count */
first = TICK_COUNT;
while ( first == TICK_COUNT ) ;

first = TICK_COUNT;
while ( first == TICK_COUNT ) count++;

#ifdef DEBUG
printf("count = %d\n", count);
#endif /* DEBUG */

/* This should over-estimate the required value of calibration */
calibration = count/55;

/* determine FUDGE by experiments with the compiler */
#define	FUDGE	42
calibration -= (calibration/100)*FUDGE;

#ifdef DEBUG
count = 0;
#endif /* DEBUG */
while ( 1 )
	{
	first = TICK_COUNT;
	while ( first == TICK_COUNT ) ;
	first = TICK_COUNT;

	delay(55);

	if ( first == TICK_COUNT )
		{
#ifdef DEBUG
printf("Repeated %d times\n", count);
#endif /* DEBUG */
		return;
		}

	/* adjust in 2% steps */
	calibration -= calibration/50;
#ifdef DEBUG
count++;
#endif /* DEBUG */
	}

}
------------------------------- snip,snip -----------------------------------