BIOS Setting "Throttle Slow Clock Ratio"

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BIOS Setting "Throttle Slow Clock Ratio"

Post by postul8or » Fri Apr 22, 2005 10:41 am

I have an ASUS P4C800-E Deluxe motherboard and I noticed in the power section of the BIOS that there is a Throttle Slow Clock Ratio setting (by default 50%). The booklet for the motherboard explains it very briefly/ambiguously as "Allows you to select the duty cycle in throttle mode 87.5%".....down to 12.5% I find it fairly ambiguous, does a higher number mean more idle cycles, or does it mean higher active cycles. Their description could be more clear and more detailed. Hopefully other people with similar motherboards can give me some of their experience with these features.

What I think this means is that when the computer is "idle" that it will skip more/less cycles. I am thinking that being aggressive at skipping more cycles will keep CPU temps down but when you stop idling the computer might hesitate for a moment in turning on the active cpu cycles again. If you choose to skip fewer CPU cycles your CPU runs hotter (and cools more slowly after being pushed) but is more responsive.

The reason I want to know more about this setting is obvious, if less heat is created quieter solutions can be used in my PC in terms of fans. I have a 2.8C processor whichs stands to gain a lot of potential seeing as it starts off quite hot! This motherboard also has a feature called Q-fan (if I recall correctly) which will throttle down the CPU fan speed by about 1/3 if it detects that the CPU is cool. Unfortunately I don't think they specify the temperature that needs to be reached in order to achieve slowdown.

I'm looking for additional information, thoughts and discussion about the features I have mentioned.

Here's a link to the motherboard booklet if you want to take a look. What I am talking about is page 4-28 of the manual (page 96 of PDF file). ... deluxe.pdf

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Post by mr pink » Fri Apr 22, 2005 4:40 pm

I know the feeling. I've got a 'thermal throttling' setting in my abit nf7-s bios and I dont really know what it's for.

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Post by postul8or » Sun Apr 24, 2005 9:42 am

I spent a little bit of time playing with the ASUS AI program (software that allows you to overclock in the OS instead of doing it in the BIOS before loading Windows). I found it interesting that the throttle back setting wasn't one of the things that could be altered by this program.

One would think that you could overclock like crazy if you were doing small sporadic tasks where heat buildup wouldn't be a problem. A way to push the limits of this would be to have a more aggressive cooldown cycle via high throttle back percentages.

...all assuming that I have guessed what this throttling really means.

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Post by Tibors » Sun Apr 24, 2005 10:09 am

The way you explain this throttling, it is a kind of Cool'n'Quiet for P4's. If that was true, then I think Asus would make a lot more fuss about it, as that would be a big selling point.

The only time I know P4's use throttling, is when they (almost) reach their max temp. Then they start to skip cycles. To me it sounds like this setting determines how aggressive this is done.

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Post by postul8or » Sun Apr 24, 2005 5:07 pm

Actually that is a good point, the setting may not matter until sh1t hits the fan and it needs to protect the machine.

I guess if you overclock you should also be more aggressive at protecting the processor. Thing is, if you do something that stresses the CPU (eg. a game) you could be too conservative and put yourself in a situation where you skip cycles and experience a lot of slowdown instead of running the CPU at a pretty high temp but is still safe.

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Post by jeffleyda » Tue Apr 26, 2005 1:28 pm

This is the same throttling mechanism that my software uses:

I'm actually surprised to see BIOS vendors starting to incorporate this feature. (it's been around since about 1996 or so) and I'm curious if this is a permanent setting, or if it has some kind of real time monitoring to adjust this throttle amount?
[edit: Ah, I see now that this throttle is only enabled during a power management event. Yeah, that manual doesn't tell you much!]

Anyway, there are 2 throttle methods built into all ACPI compliant southbridges. Here's some text from intel's ICH4 manual:
Throttling Using STPCLK#

Throttling is used to lower power consumption or reduce heat. The ICH4 asserts STPCLK# to throttle the processor clock and the processor appears to temporarily enter a C2 state. After a programmable time, the ICH4 deasserts STPCLK# and the processor appears to return to the C0 state. This allows the processor to operate at reduced average power, with a corresponding decrease in performance.

Two methods are included to start throttling:

1. Software enables a timer with a programmable duty cycle. The duty cycle is set by the THTL_DTY field and the throttling is enabled using the THTL_EN field. This is known as Manual Throttling. The period is fixed to be in the non-audible range, due to the nature of switching power supplies.

2. A Thermal Override condition (THRM# signal active for >2 seconds) occurs that unconditionally forces throttling, independent of the THTL_EN bit. The throttling due to Thermal Override has a separate duty cycle (THRM_DTY) which may vary by field and system. The Thermal Override condition will end when THRM# goes inactive.
Throttling due to the THRM# signal has higher priority than the software-initiated throttling.
Throttling does not occur when the system is in a C2, C3, or C4, even if Thermal override occurs.
My software (and your BIOS) use method #1. Method #2 is done entirely by hardware and causes all sorts of alarms and events to trigger.

You can probably give my software a shot to verify how the BIOS is doing its job-the percentages should be the same in both, and my program can give you a real-time look at how slow your machine is at various levels.


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