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post #14 of (permalink) Old 09-09-2019, 12:42 PM
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Quote: Originally Posted by Melodist View Post
Is there a tutorial for a baseline?
No, because no one except me has even considered these things before. No one ever actually looked at the Intel document sheets and tried to understand the relationship between max VID and max CURRENT.
It became sort of clear when in the electrical specifications area, Intel lists Max DC_LL (DC Loadline), as 1.6 mOhms and calls it "Loadline slope within the VR Loop capability", meaning this specifically refers to "VRM Loadline". It also doesn't give any minimum, only a maximum. Then under AC_LL, it just says "AC Loadline" and "Same as max DC_LL". The notes below mention however:

13. LL specification values should not be exceeded. If exceeded, power, performance and reliability penalty are expected.
14. Load Line (AC/DC) should be measured by the VRTT tool and programmed accordingly via the BIOS Load Line override setup
options. AC/DC Load Line BIOS programming directly affects operating voltages (AC) and power measurements (DC). A
superior board design with a shallower AC Load Line can improve on power, performance, and thermals compared to boards
designed for POR impedance

The problem is this gets confusing because they say in the note that "DC Loadline" affects power measurements while AC Loadline affects operating voltages. But in the DC_LL chart, it says "loadline slope within the VR Loop", which is clearly NOT the same thing! So it sounds like the "loadline slope" is the default VRM Loadline that is designed to be used for 8 core processors (1.6 mOhms), and DC Loadline has to be set to the same value as VRM Loadline (in mOhms) so that the CPU Package Power remains accurate (VID * Amps), since lowering DC Loadline will cause the VID to droop less (the same way increasing loadline calibration --VRM Loadline--makes the VCCcore drop less).

I got more bored last night and, with auto voltages, (and AC Loadline set to 1.0 mOhms, whatever), I decided to disable 2 cores while Loadline calibration was set on Standard.

Checking the VR VOUT and VID afterwards, I noticed that now VR VOUT was lower than VID again. I had DC Loadline set to 1.6 mOhms. When I set it to 2.1 mOhms, VID and VR VOUT were exactly the same! And in the intel document sheet, DC_LL is 2.1 mOhms for 4 and 6 core processors! So...there we go! LLC=Standard sets the VRM Loadline slope to 1.6 mOhms on 8 cores and 2.1 mOhms on 4 and 6 cores! Note that on 6 cores, max amps is now 138 amps on 95W SKU's (instead of 193) and for 4 cores, it's 100 amps (91 watt SKU's).

It's very easy then to determine the absolute maximum safe voltage (up to 99C) when you know all of these values (VRM Loadline slope mOhms, max VID in millivolts and max amps).

As I said above you can start like this:

Vhigh=Bios target voltage set on manual voltage, or VRM target voltage @ full load on auto voltage (set DC Loadline=1 and look at VID to find this on auto voltage)

vlow=minimum load voltage at most amps (on-die sense or VR VOUT measured only)

Vhigh-vlow=max vdroop (millivolts)

R=loadline slope resistance (mOhms)
(Vhigh-Vlow) / R = Amps
Vdroop / R = Amps.
Vdroop / Amps = R

Then you can calculate whatever your maximum safe voltage should be at a given amps value (if amps is known)
by using the formula (1520mv - ( VRM Loadline slope * Amps))

If you don't know your amps, you can calculate it by vdroop divided by VRM loadline resistance (provided your voltage measurements are accurate).

The nice thing about the above formula is, you can plug in your custom loadline calibration resistance values instead of the 1.6 or 2.1 mOhms Intel default loadlines, and your VRM target voltage, to tell you what the vdroop should be at full load, and then compare that to all of the absolute max baselines at "default" loadline calibration. Then you'll see if your loadline is too aggressive or your bios voltage is too high.

193 amps: 1520 - (1.6 * 193) = 1.213v
150 amps: 1520 - (1.6 * 150) = 1.280v
125 amps: 1520 - (1.6 * 125) = 1.320v
100 amps: 1520 - (1.6 * 100) = 1.360v


Now let's say you're using a fixed bios voltage and loadline calibration High/LLC6 (0.4 mOhms), and 1.35v:
You're pulling 100 amps:

1350 - (0.4 * 100) = 1310mv load voltage. Looking at the above chart for 100 amps, you're good.

150 amps:
1350 - (0.4 * 150) = 1.290v.

Time to be careful huh?

Also remember that the more LLC you use, the larger the transient spikes are and the larger the transient dips are. Dips could crash you at heavier amps if your RMS voltage is too slow to borderline, spikes could cause slow degradation.


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Quote: Originally Posted by sakete View Post
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