/*---------------------------------------------------------------------------
* filename - delay.cas
*
* function(s)
* delay - wait for specified period.
*--------------------------------------------------------------------------*/
/*
* C/C++ Run Time Library - Version 5.0
*
* Copyright (c) 1987, 1992 by Borland International
* All Rights Reserved.
*
*/
#pragma inline
#include <asmrules.h>
#include <dos.h>
static unsigned long multiplier = 1193*2L;
static void near dummy (void) {}
/*--------------------------------------------------------------------------*
Name readtimer - read the complemented value of timer 0
Usage unsigned readtimer (void);
Prototype in local
Description Obtain the complement of the value in timer 0. The
complement is used so that the timer will appear to
count up rather than down. The value returned will
range from 0 to 0xffff.
Return value The complement of the value in timer 0.
*---------------------------------------------------------------------------*/
static unsigned near readtimer (void)
{
asm pushf /* Save interrupt flag */
asm cli /* Disable interrupts */
asm mov al,0h /* Latch timer 0 */
asm out 43h,al
dummy(); /* Waste some time */
asm in al,40h /* Counter --> bx */
asm mov bl,al /* LSB in BL */
dummy(); /* Waste some time */
asm in al,40h
asm mov bh,al /* MSB in BH */
asm not bx /* Need ascending counter */
asm popf /* Restore interrupt flag */
return( _BX );
}
/*--------------------------------------------------------------------------*
Name timer_init - initialize multiplier for delay function
Usage void timer_init (void);
Prototype in local
Description Determine the multiplier required to convert milliseconds
to an equivalent interval timer value. Interval timer 0
is normally programmed in mode 3 (square wave), where
the timer is decremented by two every 840 nanoseconds;
in this case the multiplier is 2386. However, some
programs and device drivers reprogram the timer in mode 2,
where the timer is decremented by one every 840 ns; in this
case the multiplier is halved, i.e. 1193.
When the timer is in mode 3, it will never have an odd value.
In mode 2, the timer can have both odd and even values.
Therefore, if we read the timer 100 times and never
see an odd value, it's a pretty safe assumption that
it's in mode 3. This is the method used in timer_init.
Return value None
*---------------------------------------------------------------------------*/
static void timer_init(void)
{
int i;
for (i = 0; i < 100; i++)
if ((readtimer() & 1) == 0) /* readtimer() returns complement */
{
multiplier = 1193L;
return;
}
}
#pragma startup timer_init 16
/*--------------------------------------------------------------------------*
Name delay - wait for specified period.
Usage void delay(unsigned milliseconds);
Prototype in dos.h
Description The current thread of execution is suspended for the specified
number of milliseconds.
Return value None
*---------------------------------------------------------------------------*/
void _CType delay( unsigned milliseconds )
{
unsigned long stop;
unsigned cur, prev;
stop = (prev = readtimer()) + (milliseconds * multiplier);
while ((cur = readtimer()) < stop)
{
if (cur < prev) /* Check for timer wraparound */
{
if (stop < 0x10000L)
break;
stop -= 0x10000L;
}
prev = cur;
}
}
