- Nov 2, 2006
*** This is all done at your own risk. I, any user on this forum, this forum, or MSI will NOT be held responsible for your actions! ***
I'm sure you've heard about GTL reference voltages.
I've decided to write a
A quick breakdown of exactly what A/GTL+ [Advanced Gunning Transceiver Logic] does:
[quote author=Intel Q9000 Datasheet]
Most processor Front Side Bus signals use Gunning Transceiver Logic (GTL+) signaling technology. This technology provides improved noise margins and reduced ringing through low voltage swings and controlled edge rates. Platforms implement a termination voltage level for GTL+ signals defined as VTT. Because 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. Speed enhancements to data and address busses have caused signal integrity considerations and platform design methods to become even more critical than with previous processor families.
Rather optional: read this article on how the values work: http://www.thetechrepository.com/showthread.php?t=87 | It's a great explanation and shouldn't require you to do any more research into the matter. However, if you still don't understand how GTLREF works, and how VTT effects it: Google is your friend.
You can tweak the GTLREF and VTT (AKA FSB VTT voltage/FSB Terminator voltage) via the Cell Menu in the CMOS setup.
There are many different GTLREF voltages. There are GTLREF values all over mainboards. The ones we want however, are for each CPU die (only P45 boards have the settings to signal each die (so far?)) or both CPU dies (every board excluding P45), and the ICH/NB. You could guess the names. They are pretty obvious, and sometimes named differently on each board, but they all do the same thing, generally speaking.
The P45 boards have quite an edge. You can sometimes get a flaky core that needs more voltage than the rest. You can fix that problem with the individual die settings.
NOTE: You will NOT find these options present on a budget/low-end board. Do not ask if it will have the options in a future BIOS release - it won't.
According to Intel's datasheets: the nominal voltages for GTLREF are 2/3 of the VTT voltage. However, I've found better results from setting ~63% on the CPU [Yorkfield and Kentsfield] and ~67% on the NB [780i, P35 and X48].
You use a simple formula to calculate what each value will be:
a * b = c a = FSB VTT voltage b = percentage c = GTLREF setting
1.37v * 67% = 0.9179v - Note how precise my result is. The more precise you are, the better chance you will have of getting in the correct margin. Vnoise must also be taken into account. It's +/-10%. However, I doubt noise is this high on high end boards. Call it +/-3-5% if you have a high end board with a good power phase.
NOTE: If upon tweaking, nothing is improved, you may need to go up/down a few notches.
After further investigation to Intel's datasheets. There is a maximum the GTLREF should be set to both in an above and below manner. The minimum and maximum should be:
0.550 * VTT = min
0.725 * VTT = max
These GTLREF voltages are terminated on-die, going TOO HIGH will most likely mean the death of your CPU! Going TOO LOW is guaranteed instability!
Do not hesitate to tweak these values, but do not go beyond the limits! They can sometimes give you great results. On the other hand, they can also make your results worse (yes, worse). That means you need to tweak the values more. Please keep that in mind.
Post your results in here - I'd like to see them.
Good luck with your tweaking!
If you have anything to add or change here, don't hesitate to contact me!
A sidenote for P45 users:
james1701 contacted me via PM and shared this info with me. It appears MSI refuses to put the GTLREF voltage over the limit of 63%.MSI Tech. 11/03/2008 This is decision of our engineers which work directly with Intel.
End User 11/03/2008 They also recommend you don't go about 1.5 volts on the CPU, but this mobo will do it. Is there a technical reason why the GTL Ref voltage will not to 67%. All technical documents from Intel suggest 72% is the limit.
MSI Tech. 11/03/2008 No, since this is recommended by Intel.
End User 11/03/2008 I can not set the GTL Ref voltage to 67%, the highest it will go is 63%. This may be limiting my overclocking on my quad core. It there anyway to change this? Thanks