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Hello fellow miners!

I just wanted to share my optimization for these cards.

As you probably know new Gigabyte cards come with locked voltage at 1.25V and stock clocks at 1000Mhz GPU, 1250Mhz memory. This makes cards run hot and power consumption is high.
I have 3x 7950 setup and system took over ¨950W and it was really hard to keep them under 75C at stock clocks with 85% fan speed. Hashes were (avg) 610kh/s per card.

Later I found out that there is an older official BIOS (F43), which has lower voltage lock and lower clocks. So I tried it and flashed the cards.
Here is how I did it:

UPDATE 1:
HDMI port will stop working with F43 BIOS! So you will have to use DP or DVI to connect your monitor.

UPDATE 2:
There are new cards with FT0 BIOS which won't let you flash official F43 BIOS over it.
Please check this thread for further info: http://www.overclock.net/t/1313813/new-bios-update-for-gigabyte-hd7950/790
So check your current BIOS version before you proceed any further!
Thanks Mattzees for this update! (https://forum.litecoin.net/index.php/topic,4317.0.html)

1. Download F43 Bios: http://www.gigabyte.com/products/product-page.aspx?pid=4121&dl=1#bios
2. Download atiflash: http://www.techpowerup.com/downloads/2230/ATIFlash%204.07.html
3. you need DOS bootable USB drive. I used this tutorial: http://www.sevenforums.com/tutorials/46707-ms-dos-bootable-flash-drive-create.html
4. put F43 Bios and ati flash to USB drive
5. Turn off the computer
6. Put BIOS Switch on the GPU to number 1 http://www.jagatreview.com/wp-content/uploads/2012/02/gigabyte-amd-hd-7950-dualbios-switch.jpg
    If anything goes wrong you can just put switch back to number 2 and you have factory default BIOS.
7. Boot with USB drive to DOS
8. Flash to F43 BIOS version (change xxxxxx.F43 to he name of the BIOS file)
9. Reboot

Now my cards are at 900/1250 @ 1.090V stock.

I use this cgminer config:

1155/1420 core/memory clock speed
Thread Concurrency 24000
Workload 256
Threads per gpu 1
lookup gap 2
Intensity 19
Power Limit 20%

My cgminer.bat looks like this:

I am getting (avg) 2005 kh/s with all three cards, so around 668 kh/s per card without HW errors and low stales on stratum pool.
Temperatures are around 65C with 65% fan speed and power consumption dropped for ¨50W per card.
You will still need an open rig with extra fan(s) to get decent temperatures!
Here is pic of my rig:
http://shrani.si/f/Y/sP/2rk1ed85/photo-1-small.jpg

F43 BIOS was total winner in all aspects - power, performance and temperatures.
So if you have the same card, I strongly recommend you to do the same.

Here is my latest screenshot of cgminer:
http://shrani.si/f/45/20/4P3DSqbP/capture.png

If you appreciate this tutorial and it is saving you money you can donate some coins ;)
LTC: LVs3WjD3KfZQ2xniqqqkG2j4Fwetzybpxb
BTC: 1DpLqw6dB2bo5zX9YRYC4AjyMhuPADn8he

Have a great day!

P4xil

P.S.: you can try with TC 16384. It works even better for some. I got 60 kh/s more but I also got around 5 HW errors/day, so it seems 24000 is optimal for my setup.

Disclaimer: I am taking no responsibility for any damage you might have by following these instructions. There is always some risk involved when flashing the BIOS, so you must know what you are doing.

How old are your 7950s? I think the new models are voltage locked by the hardware.

I followed the instructions above and downgraded to the F43 bios, and noticed no differences in temperature. I still need to check and see if the cards are using less power at the outlet...

Also, I thought the --gpu-powertune option added voltage, so I'm confused as to why you downgraded to the F43 bios, and then added 20% using the gpu-powertune option?

I'm glad this worked out well for you, but am very confused as to why I'm not seeing the same results. I think it's because the new gigabyte 7950s contain a hardware voltage lock.

As I wrote in my initial post I have new gigabytes (3 weeks old) voltage locked cards at 1.25V
--gpu-powertune does not increase voltage of the cards but just creates bigger power bandwidth between cards and the motherboard. I used this setting with original and F43 bios, because otherwise one of my cards didn't work properly (CPU usage jumped from 60 to 100).

Use GPU-Z (http://www.techpowerup.com/downloads/SysInfo/GPU-Z/) program to check your current card voltage and clocks then check again when you change the BIOS.

which exact Gigabyte Model are you using?

Great guide btw...i want to buy 10 cards and will try more then one ... if your guide works, i`ll donate for sure!

the exact model is GV-R795WF3-3GD

i`ll buy one, test it and get back to you

Wait, you only have 2005 kilohash?

yeah at mining scrypt coins

I just downgraded the firmware as described and using the alpha GuiScrptyminer was able to set both GPUs running (2x7950) at high workloads and no issues with heat/stability.

Will try with cgminer tonight and see how it goes.
Cheers!

The voltage on mine certainly isn't locked it's about 3 weeks old. The only app that will change the voltage is Gigabyte OC GURU II that comes with it. cgminer wont change or display the changed voltage, but the power meter confirms it works.

It came to my attention (thank you Mattzees) that there are new cards out with FT0 BIOS which won't let you flash F43 BIOS over it.
There seems to be some modded BIOS out there with lower clocks which will let you flash over FT0 but use it with extreme caution!
Please check this thread for further info: http://www.overclock.net/t/1313813/new-bios-update-for-gigabyte-hd7950/790

I've updated the initial post.

p4xil, do you use pci-e riseres? If yes, unpowered or powered?

regards

I use unpowered risers for 3x 7950

I got new 7970 oc giga
although it is rev 2.1 card but it can't run 730khs @ 1044 1500 at another in my rig
i try flashing bios f43 but computer won't boot
other card in my rig work with f43 and clock @ 1040 1250

some one please help me :(

i tried edited bios by robnitro but it can't work, speed cant get higher than 500

This tread and bios is for 7950 not 7970.
Didn`t see that.

did you see that my 797 work with 795 bios?
The main ideal of this topic is speed anh bios relate to it not just only 795
and instead of asking in this topic. Y want me to make another topic with same issue? Some new card dont let me flash over it.
Sr, i dont want to be agg but, afer almost 24h w.o sleeping, i'm in very bad mod

Cool thanks for the tips :)

OP, so now your rig is pulling 800 W out the wall, correct?

yes around that.... my kill-a-watt jumps from 780W - 830W

ovb, your vcore is too high, try to downclocking them i bet you won't get more than 650-700