OC BIOS Config for FSB:250 MEM:2000 - VREF Requirements

[RangerXP]

So I have been working with my new GSkill 2133 ram, and they are awesome. I am able to hit 2000Mhz no problem with my AMD 1090T - which is a feat in and of itself. Though in order to get the system to boot properly, I have to set the VREF in BIOS to something => .525. Anything uneder .575 generates instability and I don't really get stable results in prime95 until around .59 or .60.

I am just curious if I am missing something here, as I also am not able to set the HT > 2250 at FSB250 else no boot. I don't know if it is neccessary either, but trying to keep everything running as fast as possible.

Why would I need to set such a high vref? Why does a higher HT >2250 result in a no boot?

Cheers,
Ranger

[HiVizMan]

The why is because that is what works best for your system I guess. Not being trite Ranger but there is no real other way of saying it.

FSB at 250 is a king of threshold I noticed when I did the Bulldozer overclocking guide and had to really play with the voltages to make the test system work. Other CPU's of the same model behaved differently so I guess it is pretty much luck of the draw. The good thing with AMD is you can get to the same outcome via a number of different routes.

[Raja]

RangerXP wrote:
So I have been working with my new GSkill 2133 ram, and they are awesome. I am able to hit 2000Mhz no problem with my AMD 1090T - which is a feat in and of itself. Though in order to get the system to boot properly, I have to set the VREF in BIOS to something => .525. Anything uneder .575 generates instability and I don't really get stable results in prime95 until around .59 or .60.

I am just curious if I am missing something here, as I also am not able to set the HT > 2250 at FSB250 else no boot. I don't know if it is neccessary either, but trying to keep everything running as fast as possible.

Why would I need to set such a high vref? Why does a higher HT >2250 result in a no boot?

Cheers,
Ranger

Lower the memory ratio and see if the system POSTs with default VREF (not sure which you are changing as you did not specify). if the system POSTs with lower memory frequency, then you may want to investigate DRAM sub-timings and drive strengths.

Check the memory controller frequency also. You may need to adjust CPU/NB voltage somewhat depending upon the frequency. Not to be confused with Northbridge voltage mind, that rail is for the external Northbridge and is not responsible for memory controller stability directly at all. See too many people making that mistake over and over.


-Raja

[RangerXP]

Thanks Raja - I went back through Dolk's guide on FSB/DRAM ratios and for the life of me couldn't figure out how to set an optimal AMD ratio for the DRAM. My goal is to OC my DRAM to FSB:240-250 (1920/2000) - that is a 24:6 ratio. On your advice I tried getting the DRAM frequency set lower at FSB:229 (1833) but was never able to get it to boot. Assuming there is a strange ratio at play, I just upped it to 240 and started solving for a 17.5x mulitplier at 4.2Ghz. While it would not boot on default VREFs, a slight bumpt to .525 solved it.

As I had to set the VREF again, I don't think I did what you asked correctly. Are you saying that if I have the timings set correctly it would boot with a higher FSB at default VREF's? Given that I can effectively test under prime95 for several iterations and memtest - I am inclined to think that they are set correctly - according to GSKill anyways.

I am now pretty darn stable at 4.2Ghz, though I have a couple of issues still impacting my ability to run prime for more than 15+ mins.:


1. I had the PWM Phase set to ultra-high and VRM: 500 at the frequency/VCore I was running, stressing under Prime95 when the system powered off under temp monitoring protection - it had hit the 90c threshold I had set on the temp probe I stuck in between the (horiz/vert) two banks of chokes.

- The issue is that when I bring it back down to fast/400 the system will fault in a system service exception BSOD after 10-12 iteration of Prime95. I am presuming that I should find a happy medium - is this the correct approach to preventing service exceptions thrown under load testing that fault after several iterations?

2. I understand that AMDs should have the HT set higher than for Intels. I keep mine relatively low - currently NB:2890/HT:2167. What is the best profile for NB/HT on a 1090t - Thuban? Are there optimal ratios I should be shooting for?


Thanks again,
Ranger

[Raja]

TBH if the system needs VREF set to 0.525X to even POST, you are not going to get it 100% stable with your settings. If Vref is not near stable around the center-point of voltage swing, it hints at an issue with DQ being misaligned with DQS.

I think you are trying to hit the ball out of the park without looking at all of the variables. Bring the memory controller frequency down to around 2500 MHz (even lower). Relax some of the DRAM timings. Get the system stable like that at default Vref. Even use a lower FSB frequency so that you get a feel for how the CPU reacts to various settings. Then increase FSB slowly upwards looking at what you need to change on the way.