Intel Clarkdale CPU Overclocking With IGP Enabled - Reaching High BCLK

Overclocking/OC-Team.be by massman @ 2010-02-02

Since the launch of the new CPUs from Intel, nicknamed Clarkdale, we have seen a fair share of overclocking attempts; some people even breaking world records, pushing the a Clarkdale over 7Ghz. We have read reports from overclockers who had issues with pushing the BCLK higher when the IGP was enabled. In this article we will explore possible solutions to help circumvent this limit, so you can enjoy high BCLK while using the IGP.

  • prev
  • Go to mainpage

The solution and some additional thoughts

The solution ...

... is pretty straight-forward: if you intend to overclock the BCLK with the IGP enabled, you'll have to change the IGP offset frequency in the bios if you don't want to run into stability issues. That's the positive news. Sadly enough, there's a lot more involved, it seems, when overclocking the IGP than this article might tell you.

We have noticed, for instance, that changing the QPI frequency can have a negative affect on the stability of the overclock, both when increasing and decreasing. From my notes, for example, I see that the 36x QPI multiplier gave me the most stable results whereas 32x and 40x decreased the stability of the system. In addition, it seems that certain BCLK/IGPclk combinations produce a bit better results in 3DMark, mainly in GT1 which is the most system bound subtest. We suspect that the memory performance is somehow affected by the IGPclk and/or the BCLK. It's possibly not the smartest move to throw in the word "strap", but that's how it comes across when looking at the performance numbers at the bottom of last page. Maybe it's for the best that there's still some oddities ... it's no fun when technology is easy to understand.

Truth be told, I was actually preparing for a much larger article regarding the Clarkdale IGP, mainly focussing on the overclocking part of the story. But, I was triggered to release this smaller article because I wanted to set a few mistakes straight and possibly also because I have a hard time convincing some manufacturers that BCLK is indeed affecting the IGPclk. I think the numbers on the bottom of the previous page speak for themselves: the combination of BCLK and IGP frequency set in the bios are determining the performance of the IGP ... not the IGP option alone!

Madshrimps (c)


I'd like to thank the people from Gigabyte and Corsair for sending me the hardware needed to test this platform, as well as the folks over at Intel Belgium who allow me to do a lot of research using this one CPU. To end with, thanks goes out to Manu from TONES who's always there to support Madshrimps with the latest hardware!

Also, please visit HWBOT.org, the worlds largest OC database.

Madshrimps (c)
  • prev
  • Go to mainpage
Comment from Massman @ 2010/02/02
Attaching the screenshots of the "721MHz frequency testing". Warning ... a lot!
Comment from Massman @ 2010/02/02
As far as I can understand how the IGP frequency is made, the IGPbase frequency is not function of BCLK, but of BCLK/4.

So:

IGPbase = 133*multiplier/4

or

IGPbase = 33*multiplier.

The multiplier itself is one value ... officially.
Comment from Massman @ 2010/02/02
Straight from Intel datasheet:

//edit: added second one.
Comment from geoffrey @ 2010/02/02
011000binary makes 24decimal, 24x33 gives 800
Comment from Massman @ 2010/02/03
It seems that the clock frequency of the Intel GMA can vary between 166MHz and 900MHz. For desktop CPU's, that's 733 and 900 only, for mobile the igp frequency is automatically decreased when turbo mode is enabled and you're running high load CPU applications. So:

166 = 33 x 5 = 000101b
200 = 33 x 6 = 000110b
233 = 33 x 7 = 000111b
266 = 33 x 8 = 001000b
300 = 33 x 9 = 001001b
333 = 33 x 10 = 001010b
366 = 33 x 11 = 001011b
400 = 33 x 12 = 001100b
433 = 33 x 13 = 001101b
466 = 33 x 14 = 001110b
500 = 33 x 15 = 001111b
533 = 33 x 16 = 010000b
566 = 33 x 17 = 010001b
600 = 33 x 18 = 010010b
633 = 33 x 19 = 010011b
666 = 33 x 20 = 010100b
700 = 33 x 21 = 010101b
733 = 33 x 22 = 010110b - DESKTOP
766 = 33 x 23 = 010111b
800 = 33 x 24 = 011000b
833 = 33 x 25 = 011001b
866 = 33 x 26 = 011010b
900 = 33 x 27 = 011011b - DESKTOP
Comment from Massman @ 2010/02/03
IGPclk = IGPbase x (BCLKset / 133) MHz

Now: IGPbase = (BCLKset / 4) x IGPmp

Thus: IGPclk = (BCLKset / 4) x IGPmp x (BCLKset / 133) MHz

Or: IGPclk = (BCLKset² x IGPmp) / 533 MHz

That looks weird
Comment from Massman @ 2010/02/03
When looking a the desktop datasheets, I'm a bit confused, though.
Comment from Massman @ 2010/02/05
A bit more testing: 100MHz and 200MHz BCLK:

1200 * (100/133) = 902MHz
600 * (200/133) = 902MHz

Performance: 5525 vs 5435
Comment from geoffrey @ 2010/02/05
Don't make clock dividers over-complicated
PS home tomorrow?
Comment from Massman @ 2010/02/05
Yes.
Comment from thorgal @ 2010/02/22
Comment from rickss69 @ 2010/03/14
***
Comment from rickss69 @ 2010/03/14
***

 

reply