Refresh Period (tREF)

Big.Wayne · 25 Jun 2009 at 17:35

Hello,

I am looking for help understanding this tREF thing, I don't know much about it and can see the board is automatically changing it depending on the overclock and how the memory is set to run. I gather this can be tweaked for extra performance or increased stability but I'm not sure where to start? :confused:

If anyone has been here before and can share a few insights that would be great!

Greebo · 25 Jun 2009 at 18:00

This has always made the most sense to me. As to whether you gain much performance I am not sure but it certainly affacts stability.

TREF is the # of clock cycles between RAM refreshes. (Information in RAM is stored in capacitors and decays/disipates over time.. requiring periodic refresh of information before it disappears)

Lower # of clock cycles is less stringent and should be more easily handled... but the more often you refresh, the more of your time you take up doing it instead getting down to business of getting and changing data. So, for optimal performance, the TREF should be as large as your memory can handle. (it typically accounts for 2-4% of memory time)

So, whats the deal with "200Mhz 7.8us" vs "166Mhz 7.8us"?
Suppose that the absolute latest that you can deley RAM refresh is 5.0us. Well, that will translate to different number of clock cycles dependent on the frequency of the chips. It has nothing to do with multipliers, fsb, htt, command rate or anything else. In its infinite wisdom the memory controller periodically cycles through all the memory banks and refreshes their data contents.

Your ram spec should say a refresh interval time, eg 7.8uS or 15.6uS. And 200Mhz = 5nano-seconds, 250Mhz = 4nano-seconds, 300Mhz = 3.3nano-seconds, nano-seconds x clock cycles = Refresh rate.

Now, Clock cycles = Refresh rate / nano-seconds, sooooo! Clock cycles = Your refresh rate (7.8 or 15.6) / (1/memory speed)

Example:
Clock cycles = 7.8 / (1/300)
Clock cycles = 2340
Then check for the closest value to 2340 in the BIOS

all indications I've seen point to that TREF has negligible impact on performance, and unless incorrectly set to begin with, would not improve overclockability.

Here's a chart: (Assumes a 1:1 divider. With diferent divider, use memory frequency as FSB in the chart.

Tref VALUES FOR FSB:
TREF 15.6 TREF 7.8 TREF 3.9 TREF 1.95
FSB SET FSB SET FSB SET FSB SET
66.0,1032,132.0,1032,265.0,1032,796,1552
75.0,1168,150.0,1168,299.5,1168,1058,2064
83.0,1296,166.0,1296,332.0,1296,1329,2592
98.5,1536,197.0,1536,394.0,1536,1600,3120
99.5,1552,199.0,1552,398.0,1552,1863,3632
100.0,1560,200.0,1560,400.0,1560,-,-
116.0,1816,233.0,1816,466.0,1816,-,-
131.0,2048,263.0,2048,525.0,2048,-,-
132.0,2064,265.0,2064,529.0,2064,-,-
150.0,2336,299.5,2336,599.0,2336,-,-
164.0,2560,328.0,2560,656.0,2560,-,-
166.0,2592,332.0,2592,665.0,2592,-,-
197.0,3072,394.0,3072,800.0,3120,-,-
200.0,3120,400.0,3120,931.0,3632,-,-
233.0,3632,466.0,3632,1058.0,4128,-,-
236.0,3684,472.0,3684,-,-,-,-
265.0,4128,529.0,4128,-,-,-,-
269.0,4196,538.0,4196,-,-,-,-
299.5,4672,599.0,4672,-,-,-,-
302.0,4708,-,-,-,-,-,-

(Use the Tref 7.8 column for the ASUS A8N32-SLI Deluxe.)

Tref VALUES FOR FSB:
TREF 15.6 TREF 7.8 TREF 3.9 TREF 1.95 <Memory's spec.
FSB SET FSB SET FSB SET FSB SET < Set tREF to this for this FSB
66 1032 132 1032 265 1032 796 1552
75 1168 150 1168 299.5 1168 1058 2064
83 1296 166 1296 332 1296 1329 2592
98.5 1536 197 1536 394 1536 1600 3120
99.5 1552 199 1552 398 1552 1863 3632
100 1560 200 1560 400 1560 - -
116 1816 233 1816 466 1816 - -
131 2048 263 2048 525 2048 - -
132 2064 265 2064 529 2064 - -
150 2336 299.5 2336 599 2336 - -
164 2560 328 2560 656 2560 - -
166 2592 332 2592 665 2592 - -
197 3072 394 3072 800 3120 - -
200 3120 400 3120 931 3632 - -
233 3632 466 3632 1058 4128 - -
236 3684 472 3684 - - - -
265 4128 529 4128 - - - -
269 4196 538 4196 - - - -
299.5 4672 599 4672 - - - -
302 4708 - - - - - -

Greebo · 26 Jun 2009 at 09:01

While I have your attention Wayne, can you answer me a question please?

I have read all your postings with gtl ref and I think I understand the theory now.

But in summary, am I correct in saying there is no way of calculating the required gtl and it's just trial and error to find the ones which work with your rig?

Big.Wayne · 26 Jun 2009 at 17:10

Hi Greebo,

thanks for the info, I'm gonna have to read that a dozen times as it quite complicated!

Regarding the GTL thing, I did start with them all on [Auto] and just changed the master VTT voltage. Once I understood how the GTL values were derived (0.63x - 63% etc) I did actually make a calculation and *lucked* out.

I suppose with enough understanding of the subject it would be possible to perform calculations for the whole shebang but until that point is reached you can just go down the trial and error route!

Anyway I should stop talking GTL there as this thread was hopefully gonna net some tREF info!

Although I have a feeling tREF is one of those fuzzy areas (like GTL) where there isn't a lot of public info going round, I suppose I'll put some time aside for some Trial And error testing!

kitfit1 · 28 Jun 2009 at 16:07

For all intents and purposes BW, tREF, when using a P35/P45/X48 is pretty much irrelevant. It can't be changed in the bios anyway because you have no setting for it. If you use Memset, like all windows based bios setting software, it's dubious at best. Plus of course, it isn't a permanent solution to any percieved problem, because you can only use it in windows.

Greebo · 30 Jun 2009 at 17:54

My feeling on it is like this.

Hopefully your bios will set the correct amount for stability but may be shorter than needed just to be on the safe side.

Let's say worse case scenario your bios sets your memory to refresh twice as often as it's needed. Typically this is only 2-4% of the memories time so even if you can set it to be twice as slow and still stable, you will only gain 1-2% in memory performance and hence even less in real life total system speed.

I'm going to check tonight and see if my bios sets it to the "correct" tREF just out of interest.

As my original quote says, it can do very, very little for performance and only affect stability if it has being set for too slow of a time for your ram. So once checked I reckon it doesn't need tweaking at all IMO.

Big.Wayne · 1 Jul 2009 at 03:49

Thanks for the replies Greebo & kitfit1!

It's all above my head atm but will hopefully get some time soon to get some testing sorted out. I didn't actually see tREF in the BIOS, is it really not an available option then? :confused:

Greebo · 1 Jul 2009 at 09:12

No, no tref setting in bios. And kitfit may be right about memtest. On one boot up last night it was showing 3600 for tref, the next time it was above 10,000.