Size does matter: QPI/Vtt!

[jdvoracek]

No matter the memory timings, if you are running 1600Mhz speeds you will for sure need more than 1.1 QPI/Vtt.

Newbies, hear hear to the above! Overclocking ANYTHING, including just MEMORY on an i7, can be an adventure for the i7 newcomer (me). I've learned a lot, but the most important thing I've learned is the importance of QPI/Vtt when running memory at any speed over 1066. QPT/Vtt is so important because it powers the onboard memory controller (among other things). If all you want to do is speed up your memory to its capabilites, it's easy to overlook QPI/Vtt, especially if you don't read any overclocking guides, and why would you since we often don't think of speeding memory as requiring anything but a little multiplier adjustment and maybe a little more DIMM voltage?

I manually adjusted multipliers and found my Muskin Redline would run all the way up to 1900+ on just 1.5 v - most of the time. 1600 ran pretty well with only occasional BSOD's, perhaps every second or third day, but I could not get Windows 7 to resume from sleep no matter what I tried with memory and core voltages. I had not really researched XMP much, so I had never enabled it, but once I did, the BSOD's went away and Windows 7 would now resume from sleep.

I did try to figure out what was different about running memory at 1600 using XMP versus using my various settings, especially voltages. Finally I noticed that when XMP is enabled, QPI/Vtt is increased from 1.1 to 1.35 - see image below. I think the BIOS must just do this. I looked at Intel's specification for XMP, and there is no memory map slot for QPI voltage, only for DIMM voltage. The XMP QPI/Vtt setting appears to over-ride the AUTO setting in the main voltage adjustment page.

[wazza300]

Re: Size does matter: QPI/Vtt!

xmp is a stored profile stored either in the bios or on the memory module itself,you can manually set qpi/vtt to 1.35 or maybe slightly less than what xmp sets it too and still be 100% stable

always manually setup memory timings and voltages inc,dram,qpi/vtt and cpu voltage as auto will more than likely overvolt and xmp wont be as accurate as trial and error testing and manually adjusting voltages untill stable

[sin0822]

Re: Size does matter: QPI/Vtt!

shouldn't qpi/vtt set to auto automatically move up qpi/vtt voltage when setting ram at higher speeds? I didnt know there was a need for voltage increase for 1600mhz?

[wazza300]

Re: Size does matter: QPI/Vtt!

it should do but its not reliable and always uses too much or sometimes not enough,amount depends on speed/timings amount of ram installed and whether its running in dual or tri channel mode ect,generally the more/faster and tighter the ram/timings the more you will need

[sin0822]

Re: Size does matter: QPI/Vtt!

troll dont click his link.

[NуроFеn]

Re: Size does matter: QPI/Vtt!

GA-X58A-UD5 rev 2.0 why I do not have the BIOS ?

[wazza300]

Re: Size does matter: QPI/Vtt!

not all memory has xmp,my ram doesnt have it

[Acebmxer]

Re: Size does matter: QPI/Vtt!

With my ram when i choose xmp profile it will set my bclk and timings but will show the default qpi/vtt voltage where in your pic it shows 1.35v. I think at default speeds and xmp profile enabled it sets 143 blck 14x ram multi and 28 uncore and 9-9-9-20 timings. With qpi/vtt voltage set to auto it is something like 1.4-1.5v something like that.

[jdvoracek]

Re: Size does matter: QPI/Vtt!

With my ram when i choose xmp profile it will set my bclk and timings but will show the default qpi/vtt voltage where in your pic it shows 1.35v. I think at default speeds and xmp profile enabled it sets 143 blck 14x ram multi and 28 uncore and 9-9-9-20 timings. With qpi/vtt voltage set to auto it is something like 1.4-1.5v something like that.

The is no XMP parameter for qpi/vtt, so this is being selected by the BIOS. Since your mobo is different, the BIOS probably has a different way of handling XMP. This emphasizes what I am slowly learning the hard way - take control of your voltages and timings as much as possible when overclocking. I read that about a 100 times before I understood it -:)

I have subsequently learned in the hours since my original post that my memory will run fine at 1600 with qpi/vtt at the default 1.175! The XMP profile timings are more important in the case of my Mushkin Redline memory. Everyone pays a lot of attention to tCL (CAS latency), tRCD, tRP, and tRAS. However XMP has settings for tRRD, tWTP, tRFC, and tCMD. You can get at these with a program that reads the XMP extension, or you can just look at advanced BIOS settings after you select the XMP profile - see image below. The yellow box is around these settings. Once I copied these along with the big four into the advanced memory timing control, I could turn off XMP, set qpi/vtt at 1.175 and my memory worked just liked when XMP was enabled. I'm trying to learn more about memory timings, but they appear hugely critical to overclocking memory.

[Lsdmeasap]

Re: Size does matter: QPI/Vtt!

Jdvoracek, maybe these rules will help you a little further, if you want to tinker that is :)

tRC ........................................ (Should be = tRAS + tRP or above for stability)
tRRD .......................................
tWTR ...................................... (Must be Write to Read Delay/Same Rank - (tWL + 4)
tWR ........................................ 5-12 (Odd # values likely will fail)
tWTP ....................................... (tWTP Must = tWR + tWL + 4)
tWL ........................................ (tWL Must be CAS Latency -1)

[Chike]

Re: Size does matter: QPI/Vtt!

The is no XMP parameter for qpi/vtt

I used to think the same, but apperantly there is a 1.2 revision to XMP which I cannot find it's datasheet, which define QPI voltage.
It seems a bit odd since no one knows which machine they are goin to be installed in.
Maybe someone that own a G.Skill Ripjaws-X can share their SPD.
Here is a report of Thaiphoon which supports XMP rev. 1.2.

[Lsdmeasap]

Re: Size does matter: QPI/Vtt!

Some have a QPI Voltage parameter on XMP settings, some do not, I guess it's up to the company to decide?

I've seen XMP QPI/Vtt 1.5-1.7 even!

The set I am using now is 1.2 and doesn't have it, but others I have do.

[Chike]

Re: Size does matter: QPI/Vtt!

I don't know if they are XMP certified, but absolute max QPI/VTT in the i7-900 datasheet is 1.35v, so this is very weird.

[Lsdmeasap]

Re: Size does matter: QPI/Vtt!

I've seen Corsair and some Team (I think) have above 1.5-1.6 XMP setting for QPI/Vtt.

Actually here, you can follow a link in my previous post a year ago about QPI/Vtt, there is a link here to Corsair's site where they show what some sets have XMP Programed and tested to use
QPI/Vtt Voltage post (High is OK)