Gigabyte HD7950 ROM observations (power draw)

Discussion in 'Mac Pro' started by owbp, Apr 10, 2016.

  1. owbp macrumors 6502a

    owbp

    Joined:
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    Location:
    Belgrade, Serbia
    #1
    I've just bought Gigabyte's HD7950 V2 for a good price to treat my cMP1,1.
    Didn't know that V2 of this card came with 6 pin and 8 pin adapters, so i had to improvise a jumper for the 8 pin, just to test it and to use it until tomorrow when i'll buy proper one (6 to 8 pin).

    The funny thing happened when i was flashing BIOS and doing Lexmark bench test.

    First i did it with stock bios, monitoring PCIe Booster that goes into 8 pin socket.
    It was between 6 and 7 amps most of the time, with fast jumps from 5 to 7,5 amps. Stock clock was 1000Mhz.
    Stock Gigabyte.png

    Then i flashed it with MacVidCards stock Mac 7950 ROM, that is using 800MHz Clock. Result is lower, but the thing that confused me is that iStats was reporting solid 9+ amps on PCIe booster that goes into 8 pin slot on the card?!
    Mac 7950 EFI.png

    Lastly, i combined Gigabyte's BIOS with Mac7950 EFI and got same results and clocks from the first test. but with added boot screens, and model/PCI recognition in About This Mac. Also, power consumption was 7,5 amps at maximum, same with stock PC BIOS.
    Gigabyte+MacEFI.png

    Is anybody familiar with this, why would lower clocked, but same, card draw so much more power?

    Also, OpenGL Extension Viewer is reporting OpenGL 4.1, isn't this supposed to be 4.2 supported card?

    Thanks to averyone who have time to read and participate!

    EDIT: Added ROMs - Gigabyte's, MAC7950 and mine Original+MacEFI that I continued using.
     

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  2. h9826790, Apr 10, 2016
    Last edited: Apr 10, 2016

    h9826790 macrumors 604

    h9826790

    Joined:
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    #2
    Solid 9+? May I know which version of iStat (and OSX)? I think iStat cap the number at 8.99A regardless if the card actually pull more than that.

    I think the MVC ROM may be not for your card. If you flash an incompatible ROM to the card. Of course it can lead to some strange behaviour (or even damage). Especially if you flash a 6+8 card with a 6+6 ROM. I don't know how the firmware told the card to draw power. But if the firmware "think" that's a 6pin and ask it to draw more, may lead to the 8pin draw much more than it normal does with the correct ROM.

    Anyway, you then make your own Mac EFI ROM, IMO, this is the correct way to flash a PC Card (unless you know exactly buy which card to fit the ROM).

    P.S. OpenGL 4.1 is normal
    Screen Shot 2016-04-11 at 08.01.26.jpg
     
  3. owbp thread starter macrumors 6502a

    owbp

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    #3
    @h9826790 , thank you for the reply and clarification.
    iStat is 5.11 (i think that's the current one) and OS X 10.11.4.

    Maybe i should clarify, solid 9+ meant that t was more on 8,9, 9,2 or 9,3 than it was below it.
    With any version of stock bios (pure PC or mixed with Mac EFI) it never went over 7,5.
    If you think it wont damage my card, ill be glad to do it again with screenshots or video.
    Now i'm questioning myself if i really saw that 9 amps, but i'm positive i did.

    MVC's Mac ROM definitely isn't for my card, but i was so frustrated with trying to add EFI to my HD6850 that i thought i wouldn't be able to do it on 7950, but it was easier than anything - just extract BIOS, copy/paste EFI part, flash.
    That's the only reason i tried official Mac7950 first.

    Thanks for the OpenGL tip!
     
  4. h9826790 macrumors 604

    h9826790

    Joined:
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    #4
    No, don't do it. I don't want you to take any more risk. If the ROM is not for that card, don't use it.

    In my own experience, different card (even though they both are 7950), the power draw pattern can be quite different. IMO, use wrong ROM may cause irreversible damage. So, don't do it.

    And iStat 5.11 in 10.11.4 should max at 8.99A, I am quite sure it's the Mac Pro's SMC limit. iStat itself should be no problem for higher number, the scales is up to 18A, but the sensor just won't send any reading higher than 8,99A to iStat. However, a short fluctuation which cause the reading go up to 9.2 may be possible.

    The good news is there is a protection inside the Mac, so if your card really drawing too much power, the Mac will shut itself down. Since your Mac did't do it. So I guess the real power draw may be right at 110W, but still have few watt spare to reach the 120W cut off point. My understanding is that the reading is coming from the sensor's on the Mac Pro, but not the card. So this 9A reading should be correct, regardless if the graphic card has a the right ROM or not. But 110W still much higher than the official 75W limit. So, I won't recommend you to do this test again.

    If you want to prove that iSTAT can show higher number, running Furmark with your current ROM may still able to achieve that.
     
  5. owbp, Apr 11, 2016
    Last edited: Apr 11, 2016

    owbp thread starter macrumors 6502a

    owbp

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    #5
    I didn't run Furmark, but i have tried GFXBench GL and CompuBnech CL. Two that wouldn't run on unlfashed HD6850.
    It ran across the Compubench CL like it was nothing aka very low power draw, but in GFXBench GL it peaked to 12A during one scene and went over 9A on few others. The Mac itself was stable (no shutdowns) during tests, only GPU's fans were ramping up.

    Screen Shot 2016-04-11 at 12.51.05.png Screen Shot 2016-04-11 at 12.50.08.png

    So at its highest draw GPU was still under 220W overall but i really don't like how is that draw arranged.
    I don't plan on using this Mac for Benchmarks :) but i think ill do the jumper trick to arrange symmetric power draw from both pins.
    And speaking of that, should jumping two pins marked on picture below do the trick of me using only two 6 pin cables in a long run or is there a better way to it with out using two different cables (yeah i know, OCD :D )? (at the moment i have external jumper for marked pins and it works fine)
    IMG_2096.jpg
     
  6. h9826790, Apr 11, 2016
    Last edited: Apr 11, 2016

    h9826790 macrumors 604

    h9826790

    Joined:
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    #6
    Arr.... I miss the point that your Mac Pro is the 1,1, not the 5,1.

    Anyway, may I know what's the number on that 12.02A PCIe boost line during idle?

    Is your 6850 a 2x 6pin card? That power draw looks like a 6+8pin config. And the card heavily rely on the 8pin regardless the 6pin and the slot still has plenty of buffer.

    The 6850 should not draw that much power. TBH, the numbers looks very wrong to me.

    Anyway, I personally don't like this kind of power draw arrangement as well (if the numbers are correct). I love to balance the loading between different source.

    Even my dual 7950 cannot draw that much on a Lexmark 3.1 stress test.
    Screen Shot 2016-04-12 at 01.38.34.jpg
     
  7. owbp thread starter macrumors 6502a

    owbp

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    #7
    Of course, its about 1,3-1,4A, here's the picture
    Screen Shot 2016-04-11 at 20.11.40.png
    Sorry for mentioning HD6850, its replaced by this HD7950 and i used it just to say that those benchmarks wouldn't work with unflashed GPU, so i tried them with flashed 7950 and then i saw those results. 6850 drew 4A max from PCI booster and it was one 6 pin card.

    I choose HD7950 for MP1,1 for two reasons
    - the price difference from it and R9 280(X) is enough to upgrade Xeons or WiFi+BT4.0
    - it has two 6 pin connectors and i already have those cables.

    The problem is that Gigabyte HD7950 has 2x6 pin only in V1, and i bought V2 (6 pin + 8 pin) not knowing that...:mad:

    So you're right, you're looking at 8 pin readings.

    As i see it, my options are to
    - soldier pins on the PCB to divide the load and be able to use only 2x6 pin cables
    - order 6pin to 8pin cable and then soldier that one wire from the other topic to divide the load (ill have to order cable from abroad...)
    - order custom adapter that goes from my 2x6pin connections to GPU's 6 and 8 pin and in adapter itself divides load before it reaches the gpu.

    Don't know what is the safest/smartest way to go...:(
     
  8. h9826790 macrumors 604

    h9826790

    Joined:
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    Location:
    Hong Kong
    #8
    Get a "dual mini 6pin -> 8pin" cable + a "8pin -> 6 + 8 "cable

    So, you will have something like

    dual mini 6pin (power course) -> single 8pin (bridge) -> 6+ 8 (GPU)

    use that 8pin as the bridge. So that you don't have to modify the card, and the load will be shared by the 2 mini 6pins.

    This may be easier than order a custom cable. But custom cable is a cleaner solution.
     
  9. owbp thread starter macrumors 6502a

    owbp

    Joined:
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    #9
    @h9826790 Thank you one more time!
    I've ordered a custom cable, but only X extension for two cables i already had - a bit messy but works.
    IMG_1305.jpg IMG_1306.jpg IMG_1308.jpg IMG_1309.jpg

    Both PCI Booster Slot sensors are showing the same power draw, as expected.
    13035676_10153563749627957_2090685363_o.png.jpeg 13016728_10153563751722957_1947605479_o.png.jpeg
     
  10. tripsyou macrumors newbie

    tripsyou

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    Apr 20, 2016
    #10
  11. owbp thread starter macrumors 6502a

    owbp

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    Belgrade, Serbia
    #11
    Hi, i made custom ordered from this guy (makes great power cables for PCs).
     

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