Sempron 64 s754 -- any way to undervolt?

[KansaKilla]

After enduring a Celeron with a 60mm fan and a 10 gb Quantum Fireball in our bedroom for 5 years, I managed to convince my wife to let me upgrade her computer. So, after some research, I decided on a 2500+ Sempron 64 and a NF4 6100 based board, the ASRock K8NF4G-SATAII. I even read the manual for the mobo prior to purchase, which showed it to be undervoltable to 0.8 V. I put everything together yesterday, and no voltage adjustment in the BIOS. Update BIOS, still no adjustment. Do some looking, try CrystalCPUID, CLockgen, and RMClock. Still no dice. According to a recent forum I read at 4 am or so, and can't remember where, an ASRock representative says there is no voltage adjustment available if the CPU doesn't support CnQ.

I stuck a Nexus 3.5" fanbus in the system that makes the stock HSF very quiet (especially considering what we came from), and the only other fan in the system is a 120mm on the PSU (also very quiet). In truth, it's probably not necessary to drop the Vcore any lower from an auditory standpoint, but I'm a little miffed that I can't decrease the voltage to reduce the power requirements.

Does anybody have any suggestions on how I might drop the Vcore, or further reduce power, in light of the limitations listed above? Any help would be appreciated.

Thanks,
--KansaKilla

[niels007]

The <3000+ models don't support cool and quiet and you apparantly can't change the voltage on them because of that.. I think that is the issue..

[KansaKilla]

If that is the case, would a modded BIOS be of any use? There was some talk in other forums of working on a modded BIOS for this purpose.

[dukla2000]

According to a recent forum I read at 4 am or so, and can't remember where, an ASRock representative says there is no voltage adjustment available if the CPU doesn't support CnQ.

Could have been OCWorkbench? But that is (as per niels007) 100% the bottom line for Asrock & ASUS and most other mobos. There are apparently exceptions (DFI?) where the CPU VCore circuitry is more independent of the CPU desires (I also recall reading somewhere that this requires an extra chip).

You could try drop the HTT, but even at stock settings that has to be a doddle to cool: my overclocked 3000+ system, folding 24/7, is comfortably cooled by 2 inaudible (to me) fans.

[KansaKilla]

That was the forum I read early this morning (the baby was cranky).

Not to sound like a newb, but what do you mean by HTT? I'm more used to the Phoenix BIOS rather than the AMI that this board has, and I don't recall seeing a setting for that.

Thanks,
--KansaKilla

[frostedflakes]

You should be able to adjust voltage via Windows software. Programs like CrystalCPUID even have options for software CnQ.

[Hifriday]

You should be able to adjust VID/FID via software only if both your mb and CPU support CnQ. Unfortunately 2800+ and lower Semprons do not support CnQ. For BIOS VID adjustments, it seems most budget matx 754 mb don't have this; the DFI K8M800-MLVF is an exception (but it has no temp/voltage sensors!!). A modded BIOS sounds like it could work, if you can find one.
Also it seems that it's not possible to drop voltages below 1.1v for these Semprons (and Venice cores?), either via software or BIOS. Even if the setting is at 0.8v, the vcore remains at 1.1v. Some discussion in
this thread.

With a Sempron3000+, the system AC wattage draw difference between 1.1v and 1.4v running stock 1.8ghz is approx 4w at idle and 14w under Prime95. For a Sempron2500+ at only 1.4ghz the difference should be even less, and these few extra watts probably would not make a significant difference unless maybe in a fanless system.

[dukla2000]

... what do you mean by HTT?

HTT is the clock used to drive the CPU frequency and HyperTransport bus (HT). Typically it is 200MHz, and in your case a 2500+ Sempron has a fixed 7* multiplier resulting in a CPU speed of 1400MHz. Overclocking is accomplished by raising the HTT to 210 (or 250 or 300 or ...) but there may be an option in your BIOS to drop it, with a direct effect on the overall CPU MHz.

(In simple terms it is equivalent to the FSB - Front Side Bus - used in socket A and P4 systems, but technically the HyperTransport technology is different to FSB and so it is incorrect to use FSB terminology in an A64 system.)

[KansaKilla]

dukla2000 wrote:

HTT is the clock used to drive the CPU frequency and HyperTransport bus (HT). Typically it is 200MHz, and in your case a 2500+ Sempron has a fixed 7* multiplier resulting in a CPU speed of 1400MHz. Overclocking is accomplished by raising the HTT to 210 (or 250 or 300 or ...) but there may be an option in your BIOS to drop it, with a direct effect on the overall CPU MHz.

Thanks for the explanation. This is the first AMD system I have ever built, so HTT was a new term to me.

I cycled the BIOS HTT settings last night, and it seems 200 is the lowest I can go. I ran Prime95 with the stock HSF at 7 volts, and found it stable for 8 hours without errors.

Since I couldn't undervolt the system, I decided that I might as well try to make the most of the current Vcore and the current acoustic signature. Upped the HTT to 250, backed the memory off to DDR333 speeds, kept the stock HSF at 7volts, and Prime95 was stable for 8 hours. I need to let it run for 24 hours or so to make sure, but it seems good for the moment.

Since I have now gone the other way from what I had originally intended and increased the HTT and therefore the overall frequency of the processor, how much extra power will it be drawing versus stock? I haven't done power calcs since sophomore physics in undergrad, but I remember that the vcore has a bigger influence (?non-linear association?) on the overall power draw of the system versus a frequency change (?linear association?).

Thanks,
--KansaKilla

[dukla2000]

... how much extra power will it be drawing versus stock?

My 3000+ is about 62W Folding @ 1272MHz, 82W Folding @ 2286MHz (total gross AC power draw for entire system). So you are probably somewhere in the region of 10W extra. (Power is proportional to the square of voltage, BTW.)

I think overclocking these E6 Semprons is a hoot: the power usage/cooling issues are trivial compared to socket-A, and there are easy performance gains to be had. They tend to get up to 2.2/2.4GHz on stock VCore so your 250*7 should definately be stable (but do carry on checking). That Asrock mobo may start running into limits around 270/280 HTT, but your CPU should be good for 300 or more.

ps - I should clarify that my 3000+ power numbers above are 1.1 VCore at 1272MHz (with CnQ kicked in) and 1.4 VCore @ 2286MHz. So my 20W increase is a factor of both higher frequency & VCore.

[KansaKilla]

Hey, thanks for the info. If the setup is 24 hours Prime95 stable at 7v with the stock HSF, I'll increase the HTT a little more, maybe to 1800GHz total or so. It's so fast now compared to the old system, it would be hard to justify the instability risk (especially since it's my wife's computer).

Thanks for all the info and help. Always appreciate the community here at SPQR.

--KansaKilla

[KansaKilla]

Err, SPCR. (Latin flashback)