GTL Ref is important for ultra high fsb dual core oc/450FS+ Quad Core OC so i decide to start a discussion thread on this subject.
This is in my opinion,that most of the lyn ocer ignore this and only a few ocer realize the importance of gtl ref(cstkl1,bryanyeo87.vignesh and a few).+

Let us start by the definition of gtl ref:
Introduction to A/GTL+ Signaling Conventions

Most Intel processor Front Side Bus (FSB) signals use [Advanced] Gunning Transceiver Logic (A/GTL+) signaling technology. GTL is a standard for electrical signals in CMOS circuits used to provide higher data transfer speeds with smaller voltage swings. (The GTL signal swings between 0.4v and 1.2v with a reference voltage of about 0.8v.) Only a small deviation of 0.4 volts (or thereabouts) from the reference voltage is required to switch between on and off states. Therefore, a GTL signal is said to be a low voltage swing logic signal. This technology provides improved noise margins and reduced ringing through low voltage swings and controlled edge rates.

Gunning Transceiver Logic has several advantages. The resistive termination of a GTL signal provides a clean signaling environment. Moreover, the low terminating voltage of 1.2 volts results in reduced voltage drops across the resistive elements. GTL has low power dissipation and can operate at high frequency and causes less electromagnetic interference (EMI) and signal line crosstalk than previous solutions.

Intel platforms implement a termination voltage level for GTL+ signals defined as VTT. Because these platforms implement separate power planes for each processor (and chipset), separate VCC and VTT supplies are necessary. This configuration allows for improved noise tolerance as processor frequency increases as the voltage supplies are not coupled. Speed enhancements to data (4x) and address (2x) busses have caused signal integrity considerations and platform design methods to become even more critical than with previous processor families.

The A/GTL+ inputs require a reference voltage (GTLREF) which is used by the receivers to determine if a signal is a logical 0 (low) or a logical 1 (high). GTLREF must be generated on the motherboard (usually derived from VTT by a passive voltage divider network). Termination resistors (RTT) for A/GTL+ signals are provided on the processor silicon and are terminated to VTT. Intel chipsets will also provide on-die termination, thus eliminating the need to terminate the bus on the motherboard for most A/GTL+ signals.

Guide to adjusting/fine tuning gtl ref:
http://www.thetechrepository.com/showthread.php?t=87
http://ocxtreme.org/main/?q=node/1&page=0%2C0
http://edgeofstability.com/articles/dfi_p35/gtl/gtl3.html
http://forum.xcpus.com/overclocking/12932-...king-guide.html

Here is my noob guide,just sharing what i know from what i had read about gtl ref so far
From what i can understand,GTL Ref is derive from VTT voltage.As our FSB bus is higher,the gtl input will run beyond what intel spec so what gtl ref essentially is adjusting the input voltage back to intel spec,therefore some stability can be make up,am i correct??

This post has been edited by OC4/3: Nov 10 2008, 01:37 AM

This guide mostly apply to quad core but will work on dual core as well
Summary of practical guide to gtl ref tweaking:
Thing needed:
A good cooling
A motherboard with a lot of gtl ref tweaking option
A good processor
A lot of patience
A lot of time(Few Days-Week)
Your own self
Common sense

Starting by:
Setting the right PL
Disable unneeded cpu option(spread spectrum,C1E,EIST......)

Part 2:
Set the ram to right divider,strap and advance sub timing

Part 3:
Kentsfield:
vFSB/VTT=1.3-1.7V (start with 1.3V)
GTL Ref=Manual
GTL 0/1(GTLREF1)=67%
GTL 2/3(GTLREF2)=67%

Yorkfield:
vFSB/VTT=1.2-1.55V
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

Part 4:
Target your target FSB

Part 5,tweaking:
Stability testing:
1.Once booted into Windows environment open Task Manager
2.Fire up Prime95 and set to 'Small FFT'
3.Set Prime95 affinity to core 0
4.Make sure this core pass 30min for starting
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
7.Once you manage to stabilise Core0, move onto Core1 and repeat step 1-6
8.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
9.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...)
10.When you're happy with all four cores passing at least 1hr of Prime95, go outside and breath some fresh air
11.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.
12.Uh, congrats?
PS:When switching to testing Core2 and Core3 you'll need to change GTLREF2(3/4) instead
PS2:Tip: Some form of table for crossing-off used GTL Ref settings and stability for each core will help you minimize repeating yourself

Part6,Finalization:
-Lower vCore by one notch at a time until lowest possible while maintaining the same stability
-Do the same for vMCH after the above step is completed
-Record the BIOS settings which works

Credit:http://forum.xcpus.com/overclocking/12932-practical-gtl-reference-tweaking-guide.html
http://www.anandtech.com/mb/showdoc.aspx?i=3283&p=18



This post has been edited by OC4/3: Nov 10 2008, 01:49 AM

Reserved thread slot for future posting
All the experience member,please share on this matter.

Never had a reason to play with this as my hardware is only E21XX series, but i'm wondering, would GTL ref be any useful in getting me above the 424mhz FSB wall im encountering?

This is mostly apply to dual core above 500fsb and quad core over 400fsb or so
But you can try to play,who know you can lower the vcore a notch and gain some knowledge?

Nice guide

Unfortunately for me, no matter how many times I read about GTL ref, I still cannot fully grasp it.

For myself I keep it to 63%/63%

mind to ellaborate more on X38/X48 GTLREF1/2 part and relate them to what u have first posted? coz all i see from the bios is for these 2 options are +3% -3% -6% normal auto thingy. unlike those 67% that u mentioned

thanks in advance bro

Mind to share some ss of your bios dube???
I am still not expert on it as i am still not at that level to tweak gtl ref yet
See what can i help from my rough understanding so far

GTL Ref. , quite a hot topic for Penryn family (Yorky+Wolfie) for a better OC tweaking.

what about kentsfield? /conroe?
does it applies to them as well?
i've heard p965 handles gtl much better.

p965 got gtl setting?? i cant find any on my p965-ds3

another misguided person
TS start posting results if u understand....

if not its just blind leading the blind...
well makes good laughs though.

i already told u guys.. theres no fix gtl reasoning...
only with a vmm u can be sure..
and it has to do with nb crossovers..
nothing to do with fsb...

Thumbs up for a very simple guide.... Got one question.... If my mobo's GTL settings are in mV, then how to determine the start point???

I already say i am noob in this
cstkl1,what should be the vref?From what i can understand,vref is important to prevent overshoot.
That why i start this thread,to promote ocing/gtl ref tweaking
Anyway,i hope you can lead us into the right direction as you are the expert on this matter

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Added on November 10, 2008, 3:41 pmTry this:
http://67.90.82.13/forums/showthread.php?t=202292

This post has been edited by OC4/3: Nov 10 2008, 03:41 PM

ok so ure board has enough settings??
even in the asus category
only this boards has full control
asus x48's ddr3's all of them
asus p45 maximus 2 formula some.
the rampage formula , maximus formula, blitz.. all dont..
dfi all the Ut's and Lt's only. and require a serious amount of vmm time.
gaygay hardly anything except their ddr3 boards...

so again no point.

theres no fix thing..
different proc's different vids.. different rams all require different drives
some rams i used need ddr1200 at 1.12vnb
some needs 1.2vnb
so this topic is pointless when most mobos in lyn i would say 99 percent dont have enough features to benefit...from understanding gtl's , vdimm refs, ram clk,cmd,ctl skews,

myths of gtl tweaking
u get less vcore..
rubbish...

most of gtl tweaking is nb and ram related.. so is the skews etc...

look at the whole xs threads on dfi, maximus 2, RE..
only a few can clock well... cause they spend serious amount of time

i spend nearly a week to a month already on different dimms to see the skews...
thats tweaking atleast 6 hours a day to understand the board..

mobo's like biostar dk... u just clock much as u can with the hope that the bios mem tables take care of the rest..until u hit a wall.


This post has been edited by cstkl1: Nov 10 2008, 05:08 PM

Very well said, seriously Very well said. bravo. No wonder until now, I just can't seem to relate all these explanations from many forums to my freakin gigabyte X38. but at least, cstkl1 has given me a new insight on the skews. maybe i should read up on that instead




Moderators Note: Edited post due to Profanity. Don't Repeat.

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Added on November 11, 2008, 7:08 amoh sorry mod... won't do that again

This post has been edited by metsatsu: Nov 11 2008, 07:08 AM