RE: [GD-Windows] Get exact CPU frequency

[Daniel V. <vo...@ep...>]

In theory you should use QueryPerformanceCounter and Frequency but the
following has worked fine for us so far:

// CPU speed.
guard(CheckCpuSpeed);
FLOAT CpuSpeed;
try
{
	timeBeginPeriod( 1 );
	GSecondsPerCycle = 1.f;

	for( INT i=0; i<3; i++ )
	{
		LARGE_INTEGER	StartCycles,
					EndCycles;
		volatile DOUBLE	DoubleDummy	= 0.0;
		volatile INT		IntDummy	= 0;
		__asm
		{
			rdtsc
			mov StartCycles.HighPart, edx
			mov StartCycles.LowPart, eax
		}

		DWORD	StartMsec	= timeGetTime(),
				EndMsec	= StartMsec;
		while( EndMsec-StartMsec < 200 )
		{
			DoubleDummy += appSqrt(DoubleDummy) + 3.14;
			IntDummy	*= ((INT) (DoubleDummy) + 555) / 13;
			EndMsec = timeGetTime();
		}

		__asm
		{
			rdtsc
			mov EndCycles.HighPart, edx
			mov EndCycles.LowPart, eax
		}
		DOUBLE	C1	= (DOUBLE)(SQWORD)(((QWORD)StartCycles.LowPart) +
((QWORD)StartCycles.HighPart<<32)),
				C2	= (DOUBLE)(SQWORD)(((QWORD)EndCycles.LowPart) +
((QWORD)EndCycles.HighPart<<32));

		GSecondsPerCycle = Min( GSecondsPerCycle, 1.0 / (1000.f * ( C2 - C1 ) /
(EndMsec - StartMsec)) );
	}
	timeEndPeriod( 1 );
	debugf( NAME_Init, TEXT("CPU Speed=%f MHz"), 0.000001 / GSecondsPerCycle );

	appStrcat( GMachineCPU, *FString::Printf(TEXT(" @ %d MHz"),
appRound(0.000001 / GSecondsPerCycle) ) ); // gam
}
catch( ... )
{
	debugf( NAME_Init, TEXT("Timestamp not supported (Possibly 486 or Cyrix
processor)") );
	appStrcat( GMachineCPU, TEXT(" Unknown clock") ); // gam
	GSecondsPerCycle = 1;
}

-- Daniel, Epic Games Inc.

> -----Original Message-----
> From: gam...@li...
> [mailto:gam...@li...]On
> Behalf Of Andrew Grant
> Sent: Monday, July 15, 2002 3:13 PM
> To: Gam...@li...
> Subject: RE: [GD-Windows] Get exact CPU frequency
>
>
> a) I think the method you are using is only supported on some
> OSs. A better
> approach is to use RDTSC before and then after a known time period has
> elapsed, taking measures for slight variations and errors. Try searching
> Intels developers site.
>
> b) GetTickCount can be rather inaccurate, use
> QueryPerformanceCounter/Frequency
>
> Andrew Grant-
> Climax Brighton
>
>
>
> > -----Original Message-----
> > From: Grisha Spivak [mailto:_g...@tu...]
> > Sent: 15 July 2002 12:52
> > To: Gam...@li...
> > Subject: [GD-Windows] Get exact CPU frequency
> >
> >
> > How can I get exact CPU frequency? I need it for timer which
> > uses RDTSC
> > instruction. Currently I read '~MHz' value from
> > HKEY_LOCAL_MACHINE\HARDWARE\DESCRIPTION\System\CentralProcesso
> > r\0, but it
> > not exact - after 2 min running difference between my timer
> > and GetTickCount
> > is 15 ms.
> >
> >
> >
> >
> > -------------------------------------------------------
> > This sf.net email is sponsored by:ThinkGeek
> > Welcome to geek heaven.
> > http://thinkgeek.com/sf
> > _______________________________________________
> > Gamedevlists-windows mailing list
> > Gam...@li...
> > https://lists.sourceforge.net/lists/listinfo/gamedevlists-windows
> > Archives:
> > http://sourceforge.net/mailarchive/forum.php?forum_id=555
> >
>
>
> -------------------------------------------------------
> This sf.net email is sponsored by:ThinkGeek
> Welcome to geek heaven.
> http://thinkgeek.com/sf
> _______________________________________________
> Gamedevlists-windows mailing list
> Gam...@li...
> https://lists.sourceforge.net/lists/listinfo/gamedevlists-windows
> Archives:
> http://sourceforge.net/mailarchive/forum.php?forum_id=555
>