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BIOS voltage terminology?

Discussion in 'AMD Overclocking' started by Yousuf Khan, Nov 29, 2011.

  1. Yousuf Khan

    Yousuf Khan Guest

    What are the following terminologies:

    (1) CPU Over Voltage (aka Vcore)?
    (2) VDDNB Over Voltage?
    (3) Loadline Calibration?

    Yousuf Khan
    Yousuf Khan, Nov 29, 2011
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  2. Yousuf Khan

    Paul Guest

    (1) CPU Over Voltage (aka Vcore)?

    "Over Voltage" means being able to offset the VCore voltage,
    so it is higher than the range suggested by the CPU manufacturer.
    Normally, the VID codes coming from the processor, are range
    limited, to suit the CPU manufacturer and the amount of
    "field returns" they can expect for "defective processors".
    Range limiting VID, is supposed to prevent people from
    abusing their processors.

    An enthusiast board, can add an analog offset to the
    regulator voltage, in an attempt to thwart the
    digital (VID value) limitations imposed by the CPU manufacturer.

    VCore = [dig VID low .. dig VID high] + analog_offset

    VID changes "on the fly", to support EIST or Cool N' Quiet.
    So the digital value, doesn't stand still. It changes while
    the computer is running, as a function of P-State desired.
    Disabling EIST or CNQ, should make VID a constant value.

    If your board doesn't support Over Voltage (like my very nice
    $65 Asrock motherboard), you can add a resistor or do a "pencil
    mod", to do the offsetting yourself. I added 0.1V to VCore,
    by adding a resistor to the regulator. The regulator had
    a trim point, making the addition of the resistor easy.
    All you need for hints, for home hacking, is the regulator

    The regulator has an internal check, which will turn off the
    regulator if you go too far. The regulator checks for MOSFET
    failures, by monitoring the output voltage. If a design tries
    to "trim too high", the regulator will assume a MOSFET has
    failed short, and will turn off MOSFET drive signals in response.
    Or, attempt to clamp the voltage, by turning on all the low side
    MOSFETs until something burns or blows. All in the name of
    protecting an expensive CPU from damage.

    (2) VDDNB Over Voltage?

    AMD processors now, have Integrated Memory Controllers
    right on the processor die. A recent change to the CPU
    designs, is the move to split plane powering. When you
    buy a motherboard with "4+1" phases, the four phases are
    for Vcore, while the fifth phase powers VddNB.

    I couldn't find any nice pictures, with all the voltage shown,
    so this will have to do. There are actually many voltages
    in a motherboard design, but I need a nice picture to list
    them all.


    (3) Loadline Calibration?

    There is a picture of the datasheet specification here. This
    shows a loadline graph, and Intel's spec for "acceptable behavior".
    So if your VID was putting out a fixed value, this graph
    shows how the voltage as measured at the silicon die, changes
    as a function of the current drawn by the processor. Processor
    current, goes up in proportion to computing load.


    That's a curve of VCore versus ICore. Core current flow increases,
    when you run Prime95. The operating point shifts to the right.
    The processor draws 100 amps of current.

    If I stop running Prime95, and go back to idle, the processor
    draws 20 amps. Some of that could be DC leakage for example,
    and not contributing to getting anything done.

    If you had a hardware monitor running at the time, and you
    were an enthusiast, you'd look at that and say "oh, my,
    look at that voltage droop". The change from 20 amps to 100 amps
    of draw, could result in an observed 0.15V change in measured VCore

    Loadline calibration, is an attempt to make the enthusiast
    feel better. It "flattens" out the line, so it's no longer
    a diagonal, but instead shows little voltage change with
    load current (a horizontal line). Doing so, likely violates
    the rules shown in that graph. The question I can't answer,
    is whether enabling a feature like that, is actually helping
    matters. In some ways, it's like a VCore shift.

    That load line has always bothered me. With closed loop
    feedback and remote sensing, you can null out a lot of
    that behavior. So when Intel draws that graph and says
    "thou shalt make it this way", I have to wonder why. I've
    never seen an explanation in plain English, why it has to
    be that way. In the usual way, Intel draws that graph,
    without even one stinking comment about "why".

    Paul, Nov 29, 2011
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  3. Yousuf Khan

    Yousuf Khan Guest

    Okay, I have this setting in my BIOS, is the setting a relative number
    (i.e. VID + offset = final voltage), or an absolute setting (i.e.
    replaces the maximum VID value)?

    My processor's VID range is listed as 1.125-1.40V (http://is.gd/FiNKO6).
    But it's maximum power while running at stock frequency is 1.30V. Would
    I need to change the CPU overvoltage if I am not planning to go over its
    highest range (1.40V), but still need to increase the voltage just for
    overclocking (e.g. need to go from 1.30V to 1.325V, or something)?
    Okay, I understand it's the voltage to deliver to the internal memory
    controller on the processor, and it's got nothing to do with the old
    northbridge chipsets. I suppose I wouldn't have to touch this unless I'm
    overclocking the RAM?
    Okay, I assume this is not something that I'd typically need to play
    with when overclocking?

    Yousuf Khan
    Yousuf Khan, Nov 30, 2011
  4. Yousuf Khan

    Paul Guest

    It's easiest to figure that out, by looking at the BIOS screen.

    I don't know your motherboard model number, and AMD no longer
    offers datasheets on the web site, so I can't even play along here.
    On the Newegg site, one person is using more than 1.4V, so chances are
    you're going to need more than stock.


    "Pros: easily overclocks to 4.4ghz at 1.5125vcore and temps are reasonable
    (<60C) with a CM hyper 212 with an extra 120mm fan for push/pull

    Cons: I can't think of any

    Other Thoughts: good for the money but the "turbo" feature is kind of
    useless when you overclock"
    Since I don't have any motherboards with "load line calibration",
    I have no first hand experience with it. A couple comments I looked
    at, it was hard to tell it was making a difference.

    Paul, Nov 30, 2011
  5. Yousuf Khan

    Yousuf Khan Guest

    Well, "rms" on the other thread has his running at over 4GHz too, and he
    seems to be at 1.475V so he has had to go over stock ratings too. I'm
    gonna limit myself to high stock voltages for the moment, while I'm
    still on stock cooling.
    From the discussions about it, it looks like setting this wrong may
    result in machines that are stable during Prime95, but crash while idle!
    So I think I'll leave it alone.

    These were just the settings in my motherboard that I saw.

    Yousuf Khan
    Yousuf Khan, Nov 30, 2011
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