Category : C Source Code
Archive   : ZTIMER20.ZIP
Filename : ULZTIMER.C

/****************************************************************************
*
* Ultra Long Period Timer
*
* Copyright (C) 1993-4 SciTech Software
* All rights reserved.
*
* Filename: $RCSfile: ulztimer.c $
* Version: $Revision: 1.5 $
*
* Language: ANSI C
* Environment: any
*
* Description: Module to interface to the BIOS Timer Tick for timing
* code that takes up to 24 hours (ray tracing etc). There
* is a small overhead in calculating the time, this
* will be negligible for such long periods of time.
*
* $Id: ulztimer.c 1.5 1994/08/22 11:56:13 kjb release $
*
****************************************************************************/

#include "pmode.h"
#include "ztimer.h"

ushort _ZTimerBIOS;
static ulong start,finish;

void ZTimerInit(void)
{ _ZTimerBIOS = PM_getBIOSSelector(); }

void ULZTimerOn(void)
{ start = ULZReadTime(); }

void ULZTimerOff(void)
{ finish = ULZReadTime(); }

ulong ULZTimerLap(void)
{ return ULZElapsedTime(start,ULZReadTime()); }

ulong ULZTimerCount(void)
{ return ULZElapsedTime(start,finish); }

ulong ULZReadTime(void)
/****************************************************************************
*
* Function: ULZReadTime
* Returns: Current timer tick count.
*
* Description: We turn of interrupts while we
* get the value from the BIOS data area since it is stored
* as two bytes and an interrupt COULD stuff up our reading.
*
****************************************************************************/
{
ulong ticks;

_disable(); /* Turn of interrupts */
ticks = PM_getLong(_ZTimerBIOS,0x6C);
_enable(); /* Turn on interrupts again */

return ticks;
}

ulong ULZElapsedTime(ulong start,ulong finish)
/****************************************************************************
*
* Function: ULZElapsedTime
* Parameters: start - Starting timer tick value
* finish - Ending timer tick value
*
* Returns: Elapsed timer between starting time and ending time in
* 1/18 ths of a second.
*
****************************************************************************/
{
/* Check to see whether a midnight boundary has passed, and if so
* adjust the finish time to account for this. We cannot detect if
* more that one midnight boundary has passed, so if this happens
* we will be generating erronous results.
*/

if (finish < start)
finish += 1573040L; /* Number of ticks in 24 hours */

return finish - start;
}