Practical GTL Reference Tweaking Guide

[wuzy]

Practical GTL Reference Tweaking Guide

This guide is aimed at the practical approach to GTL Ref tweaking rather than theoretical explaining.
If you're interested in the theoretical aspect of GTL Ref and its origin then read here and here

A few basic 'ideas' when it comes to GTL Ref tweaking and those are:
-GTL Ref voltage is a percentage of CPU VTT/vFSB i.e. Changing vFSB would shift all GTL Ref voltages (the default is 67%)
-Every different CPU has a different GTL Ref preference and then every FSB in generally also has a different GTL Ref preference. So there's no right or wrong value.

Requirement:
-A motherboard with GTL Ref tweaking options in the BIOS. Preferably ones with more than one GTL Ref setting. e.g. ASUS P5E3 Premium and GA-X38-DQ6 has two GTL Ref and all 780i/790i has 4.
Almost all P35 motherboard has only one GTL Ref setting (except a few DFI) so are not ideal for tweaking Kentsfield/Yorkfield.
-Time. A least 7 whole days so it may take you over 3 weeks if you work on GTL Ref tweaking 2days/week on weekends.
-A multiplier limited Core2 processor especially quads with multi of 8.5x and below which is what this guide will focus on mainly.
-Top end cooling. One of the 'byproduct' of this guide is making your processor performing at its highest capable potential without being limited by FSB due to lowish multiplier. e.g. For a Kentsfield going beyond 3.8Ghz watercooling is almost a must. The same goes for a Yorkfield running over 4Ghz. Make your life easier

LETS GET STARTED!

Part1. Tidying Up Your BIOS ((not all BIOS may have those options or may be named differently)
*You must update your BIOS to the latest version before proceeding*

1.Disable any 'automatic overclocking' feature you see in the BIOS
2.Set PCI Express (PCIe) frequency @100-102Mhz
3.Set PCI frequency @33Mhz
4.Set Performance Level(PL)/tRP to 8 for P35/X48/X38/P45
5.Disable any ‘spread spectrum’
6.Disable ‘Limit CPUID Max to 3’
7.Disable ‘C1E’
8.Disable ‘EIST’
9.Disable Virtualization Technology
10.Disable No-Execute Memory Protect
11.Disable any other features you don’t use e.g. Firewire, sound, WiFi...etc.
12.Do not enable any speed enhancements you see

Part2. Memory Adjustments
**Expand options for Gigabyte BIOS under ‘M.I.T.’ by pressing CTRL+F1**

We're aiming for a range of 480-500Mhz FSB so set a comfortable range for your RAM to work with.
Set a matching strap to your FSB:RAM dividers need also.
That includes setting your subtimings too!

Part3. Voltages (again not all BIOS will have the options or uses a different name)

Kentsfield:
vFSB=1.3-1.7V (start with 1.3V)
vCore=1.6V and vdroop under load no less than 1.58V (see, you need watercooling!)
GTL Ref=Manual
GTL 0/1(GTLREF1)=67%
GTL 2/3(GTLREF2)=67%

Yorkfield:
vFSB=1.2-1.55V (start with 1.2V, going above 1.4V is for less than 2hr testing only)
vCore=1.475V
GTL Ref=Manual
GTL 0/1(GTLREF1)=67%
GTL 2/3(GTLREF2)=67%

For DFI users, you'll need your calculator to work out vFSB x GTL% = GTL Ref voltage

P35 vMCH=1.7V
X38/X48 vMCH=1.60V
P45 vMCH=1.5V (?)

Part4. Frequency Control
-Kentfield has a limit of just under 4Ghz on ambient [~23C] cooling (that includes water)
-Yorkfields limit is ~4.4Ghz on watercooling
-Both quads has a limit of usually between 480-500Mhz FSB

Due to the time consuming nature of GTL Ref tweaking, we start off high. Or a clock you're willing to settle with when finished
Recommended first attempt for 8x multiplier (Kent/York):
475x8=3800Mhz

Part5. Stability Testing
You will need the following programs:
- CPU-Z
- Prime95
- OCCT

1.Once booted into Windows environment open Task Manager
2.Fire up Prime95 and set to 'Small FFT' then run just one instance
3.Use Task Manager to set this instance to Core0
4.The target here is at least 30minutes stable per core on the first round
5.If Prime95 errors then go back into GTL Ref section of the BIOS and change the value of GTLREF1(0/1) to another value
6.Repeat step 1-5 (Yeah, it's going to take a few hours just for one core)
7.Once you manage to stabilise Core0, move onto Core1 and repeat step 1-6 (hang in there...)
8.When switching to testing Core2 and Core3 you'll need to change GTLREF2(3/4) instead.
9.Sometimes one setting for GTLREF on Intel motherboards might not be the most ideal value for the two cores it controls. So just pick one with the best compromise (lasting longest in Prime95) between the Core0&Core1 or Core2&Core3
Tip: Some form of table for crossing-off used GTL Ref settings and stability for each core will help you minimize repeating yourself
10.Once you've roughly dailed in the GTLREF voltage required for the 4 cores, set vFSB to the next higher notch and start repeating steps 1-9 again (oh dear...)
11.When you're happy with all four cores passing at least 1hr of Prime95, go outside and breath some fresh air
12.Fire Up Prime95 and run 4 instances simultaneously this time. Remember to assign each instances to each core individually through Task Manager. If any of the 4 cores errors within 1hr, then go back to the GTL Ref settings in BIOS and sort that core out.
13.For final stability testing fire up OCCT and set it to RAM mode. Passing the 45min mark is considered as extremely stable
14.Uh, congrats?

Part6. Finalising
-Lower vCore by one notch at a time until lowest possible while maintaining the same stableness
-Do the same for vMCH after the above step is completed
-Record the BIOS settings which works
-(Optional) Pull off a PCMark and/or SuperPi32M score and compare to stock to gauge performance increase

Written by Wuzy
V1.0 18/07/08 (for quads only)

Reference:
AnandTech: ASUS Striker II Extreme: Mucho Bang, Mucho Bucks

[MagicLess]

Imma read the **** outta this when I get home in the morning.

Thanks Wu!

[Holy_COW]

nice walk-thru! :thumbsup:

If I get crazy for some more OC will make sure to use it, (right now im happy at 3.4)... maybe crysis2 or some new game will make it necessary lol :P

[YMAA]

Nice work!

[DaSickNinja]

Stickied. Unfortunately, my hand got stuck when I sticked the thread...

[tool_462]

Thank you sir. When/if I get a Q9300 or other quad for my HTPC, I will be forced to play with GTL REF much more than I currently have to with my dual core

[huddy]

Thanks for posting this Wuzy. I'm going to get good use out of it very shortly.

[Eurasianman]

Wuzy, note that using more than 1.40V on the FSB will kill a Yorkfield if used 24/7.

AnandTech

[monst0r]

Does anyone know if Gigabyte disables this feature on their P35 motherboards? I can't seem to find any quality options... dammit Gigabyte

[sirheck]

Does anyone know if Gigabyte disables this feature on their P35 motherboards? I can't seem to find any quality options... dammit Gigabyte

Have you tried (ctrl+f1)?
It enables extra memory settings.

I cant remember about gtl volt settings

[monst0r]

Have you tried (ctrl+f1)?
It enables extra memory settings.

I cant remember about gtl volt settings

Haha, yeah of course I've tried that. Gigabyte might call it something else. I can't find one that makes sense, though. All the options are "Normal, +.1,+.2,+.3". Probably easier to explain with a picture..I'll get one ASAP. Right now, I'm going to bed.

[wuzy]

Wuzy, note that using more than 1.40V on the FSB will kill a Yorkfield if used 24/7.

AnandTech

I was kinda aware of that, but I figured if anyone is crazy enough to test all the way over 1.4V (those modern X38/48 mobo have very fine vFSB increases) then they might as well go for it and venture into the extreme side with better than air cooling.

And we all know about Intel's wonderful warranty.

I'll add a note about it. But I still don't believe people should be warned/prevented from using more.
If anything, the mobo should be held accountable for giving killer voltages. Then there are people like me who vmod and want even MORE!

[wuzy]

Like almost all other P35 that has GTL ref setting, like your P35-DS3R, they only have one. I think they control only the data bus side of things and leave the address bus at default ratio, if you're bothered reading through the theory.

With Gigabyte BIOS and it's -.3 to Normal to +.3 refers to deviation from 0.67 (67%).

Having one any GTL ref adjustment is better than nothing. When I had my X3210 I carried out testing extensively on a P5K-E which had only one GTL ref. Default ratio got me to less than 420Mhz FSB (unstable, didn't test much) while a tweaked GTL+vFSB combination gave me 480Mhz+ (stable enough for long hr gaming/benching)

[monst0r]

Like almost all other P35 that has GTL ref setting, like your P35-DS3R, they only have one. I think they control only the data bus side of things and leave the address bus at default ratio, if you're bothered reading through the theory.

With Gigabyte BIOS and it's -.3 to Normal to +.3 refers to deviation from 0.67 (67%).

Having one any GTL ref adjustment is better than nothing. When I had my X3210 I carried out testing extensively on a P5K-E which had only one GTL ref. Default ratio got me to less than 420Mhz FSB (unstable, didn't test much) while a tweaked GTL+vFSB combination gave me 480Mhz+ (stable enough for long hr gaming/benching)

I didn't read through the theory, yet. I still don't see which option affects the GTL ref. Here's a good picture of my options. There aren't any negative values available.:


Hope you can help me understand my options better.

[wuzy]

Oh that's right, P35-DS3R didn't have any GTL ref option even with the latest BIOS. That was the reason why I didn't pick the DS3R back then with P35 when I got the X3210 first as I knew I was heading into trouble.

[NoahLDiamond]

Thank you for your information. I am going for 4 hours straight stable with OCCT. If I can get 4 hours straight with no errors with OCCT at Large Data Set and High Priority, can I deem the machine stable? I am trying to overclock my Q9550 E0 to 4GHz with a 470 FSB on a MSI P45 Platinum. I hope it works out. What do you all think?

[wuzy]

Welcome to XCPUS!

I find 1hr+ of running infinite loop to be enough. OCCT catches error a lot faster than Prime95. But you won't know which core is causing the trouble. If you've only got one GTL ref option in BIOS then it doesn't matter anyway.
What GTL Reference options are available in the MSI P45 Plat?

btw, what pointed you to search for GTL ref? Because to find this guide you'd obviously have to know it existed first.