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.

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Introduction

Introduction

With records being broken left and right with the new Clarkdale CPUs from Intel it was high time to see what the different limits are and how to “break” them to achieve even better results. In a recent finding published at Anandtech they ran into a BCLK “wall” of ~170Mhz when they had the IGP enabled.

In our testing however we were able to push the BCLK to 200+, even reaching 220Mhz. So what is causing this discrepancy in results? Time to find out

The problem

"We've run out of time to explore every angle of IGP performance and QPI ratios in this article, but we will endeavor to cover this angle in a future article if need be. Right now, we'll say it appears that you're going to be BCLK limited south of 170 MHz with the IGP in tow. Subtract another 20MHz off that for 8GB configurations, and bear in mind that you'll need to use low memory speeds, capping you to a maximum of around DDR3-1333MHz with things in their current state."

(~ Anandtech: "Choosing the Best H55/H57 Motherboard - Part 1")


As you can read in the quote, it looks like the BCLK overclocking capabilities are hurt quite badly by enabling the integrated graphics processor. With default configuration the limitations can be found below 170MHz BCLK with 4GB of memory, and even lower using 8GB of memory. In our testing, however, we obtained these results:

Madshrimps (c)
200MHz 8GB on the left, 220MHz 4GB on the right (clickable)


As you can seen in the screenshots, a perfectly 3D stable configuration using the same Core i5 661, 8GB of Corsair memory and a BCLK frequency of 200MHz in combination with DDR3-1600MHz speeds. In addition, we also reached a BCLK frequency of 220MHz in a 4GB memory configuration resulting in an astonishing (or not?) DDR3-1760MHz. On the next page, I will be explaining how we managed to get this result and give you the hypothesis by which we explain this behavior, but first let's have a look at the used test setup.

Test setup

Madshrimps Clarkdale IGP Test Setup
Madshrimps (c)
CPU Intel Core i5 661 (ES)
Cooling Cooler Master V8
MainboardGigabyte GA-H55M-UD2H
VideocardIntel GMA HD (IGP)
Memory 4x2GB Corsair Dominator 1600MHz CL8-8-8-24 1.65V, v3.1
(p/n: CMD8GX3M4A1600C8)
Storage Western Digital 250GB
Chassis Cooler Master Lab Test Bench
PSU Antec TruePower 1KW

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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
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Comment from rickss69 @ 2010/03/14
***

 

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