GD_CLK11.ZIP

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v1.1	05/95
FOR:	CIRRUS LOGIC GD-542X/543X USERS

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INCORRECT USAGE OF THIS UTILITY MAY RESULT IN DAMAGE TO THE USER'S MONITOR.

PLEASE READ ALL THE DOCUMENTATION CAREFULLY, BEFORE USING THESE PROGRAMS.
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WHAT IS "MCLK", AND WHAT DOES IT DO?

	It lets you re-program one of the Cirrus Logic's clock generators,
mainly the memory clock (MCLK.)  The "memory clock" controls the DRAM refresh
frequency on your video card, which indirectly affects the video card's
performance under accelerated environments (Windows, OS/2, etc.)  The GD-542x
and GD-543x families possess a common clock register interface, making
this program possible.
	Programming a higher value into the MCLK register increases the
DRAM bandwidth, and conversely a lower MCLK value means less bandwidth.
In short, you can potentially boost your video card's throughput by cranking
up the MCLK.

HOW DOES "DRAM BANDWIDTH" AFFECT MY SYSTEM'S PERFORMANCE?

	With respect to your video card, several "requesters" compete for
DRAM access:  the host CPU, the CRTC (screen re-drawer), and the 
video accelerator.  The CRTC receives highest priority;  whatever bandwidth 
the CRTC doesn't use becomes available for the video accelerator and host CPU.
	Video modes with high resolutions (1024x768) or high #colors (65k, 16M)
leave little surplus bandwidth for the accelerator & CPU.  If you run Windows
with the high-color driver, you may notice substantially slower screen-redraws.

	If you are running a graphical application with accelerated video 
drivers (like Windows), your computer will use the video accelerator.  The
accelerator will grab all surplus bandwidth.  So by increasing the surplus
video DRAM bandwidth, we also boost video performance.
	Suffice it to say, a higher MCLK value will make more DRAM available
to the accelerator and host CPU.  We'll perceive the most improvement under
these conditions:

	1)	high-color video modes with high refresh rates
		(examples: 800x600x65k 60Hz on Cirrus GD-542x
		 	   1024x768x65k 75Hz on Cirrus GD-543x) 

	2)	true-color video modes
		( 640x480x16M on Cirrus GD-542x )
		( 800x600x16M on Cirrus GD-543x )

	(Actually, all video modes will be sped-up, but some more noticeably
than others.)  The following modes probably won't look any faster:

	1)	640x480x256, 800x600 and other low-color/low-resolution modes

Your mileage may vary...

I have omitted the technical discussion from the original (v1.0) docs, since
it merely confused most users.

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Notes...

1)	If your Cirrus video BIOS is v1.4 or newer, be aware that the
	"power-down" (VESA/DPMS) modes re-program the MCLK to its original
	value.

2)	If you program your MCLK too fast, several things may happen:

	a) Computer locks-up / hangs

	b) Random dots left behind whenever something is drawn on-screen,
		like when you scroll/drag documents in Windows.

	c) smoke rises from your computer... ( <-- just kidding! :)