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post #11 of 27 (permalink) Old 10-11-2016, 03:55 AM
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There is very little info out there, but what I dug out was
>>
GPC = "General Purpose Core" - This is the primary core of your GPU
L2C = "L2 Cache" - This is the on core memory that your GPU core has access to. Running it at the same clockspeed as the core itself nets a large gain.
XBAR = "Memory Controler Crossbar" - This is the bus speed of the memory controller that talks to the core.
SYS = "System" - This is the rest of the card that isn't tied to another clock domain.
>>

In my case, I discovered that core clock (no matter what voltage) above 1392 gives me blackscreens in The Witcher 3, so I currently limited all my clocks to 1392.5 and also set all those max values to it. Which interestingly is also what's in the reference BIOS of the GTX 970.

I think it is definitely the case that dropping the values there might yield you higher GPU clocks, since this is exactly what all those vendors who make factory OCed cards do! On my EVGA, some values there are as low as 1344, but then a higher GPC. So or so, I have all of them at 1392.5 now since currently I am not chasing after overclocks but want highest stability. (Amazingly my EVGA which craps out at 1418 in The Witcher needs only 1.125V at 1392 and is then stable....)

Bios modding and flashing until the EEPROM smokes!! Yay!!
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post #12 of 27 (permalink) Old 10-11-2016, 05:28 AM
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8051, forget about changing those values. I wrote above that I set them all to 1392.5, way too instable. I set the XBAR, SYS etc. values back to what they were before. I guess there is a reason that they set them to what they were before. Otherwise you're just opening a can of worms messing with those values... (I just did some testing)

PS: You got your name from the microcontrollers? I used to program 8051 micro controllers back in the day smile.gif

Bios modding and flashing until the EEPROM smokes!! Yay!!
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post #13 of 27 (permalink) Old 10-11-2016, 10:37 AM
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Quote:
Originally Posted by flexy123 View Post

8051, forget about changing those values. I wrote above that I set them all to 1392.5, way too instable. I set the XBAR, SYS etc. values back to what they were before. I guess there is a reason that they set them to what they were before. Otherwise you're just opening a can of worms messing with those values... (I just did some testing)

PS: You got your name from the microcontrollers? I used to program 8051 micro controllers back in the day smile.gif

Yep the old 8051, a Harvard architected MCU. We used the 80251 though, because it was much faster.
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post #14 of 27 (permalink) Old 10-11-2016, 10:49 AM
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Quote:
Originally Posted by flexy123 View Post

There is very little info out there, but what I dug out was
>>
GPC = "General Purpose Core" - This is the primary core of your GPU
L2C = "L2 Cache" - This is the on core memory that your GPU core has access to. Running it at the same clockspeed as the core itself nets a large gain.
XBAR = "Memory Controler Crossbar" - This is the bus speed of the memory controller that talks to the core.
SYS = "System" - This is the rest of the card that isn't tied to another clock domain.
>>

In my case, I discovered that core clock (no matter what voltage) above 1392 gives me blackscreens in The Witcher 3, so I currently limited all my clocks to 1392.5 and also set all those max values to it. Which interestingly is also what's in the reference BIOS of the GTX 970.

I think it is definitely the case that dropping the values there might yield you higher GPU clocks, since this is exactly what all those vendors who make factory OCed cards do! On my EVGA, some values there are as low as 1344, but then a higher GPC. So or so, I have all of them at 1392.5 now since currently I am not chasing after overclocks but want highest stability. (Amazingly my EVGA which craps out at 1418 in The Witcher needs only 1.125V at 1392 and is then stable....)

I wonder if the XBAR is more or less just cross-coupled multiplexers that connect the memory controller(s) to the core/L2C?

Maybe the SYS (system) corresponds to the part of the GPU that communicates w/the PCIe bus?

I'm running 1.281V through my 980Ti to get 1468 MHz. stable, I've run all the way up to 1.3V in BIOS at which point I think the VRM's were having thermal issues, but it could've been the overclocked XBAR as well. I currently have my XBAR/SYS/L2C @ 1447/1479/1479.

I wonder how the memory controllers are configured in modern video cards? Do they read/write in quad-word quantities?
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post #15 of 27 (permalink) Old 10-11-2016, 08:42 PM
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Quote:
Originally Posted by 8051 View Post

I wonder if the XBAR is more or less just cross-coupled multiplexers that connect the memory controller(s) to the core/L2C?

Maybe the SYS (system) corresponds to the part of the GPU that communicates w/the PCIe bus?

I'm running 1.281V through my 980Ti to get 1468 MHz. stable, I've run all the way up to 1.3V in BIOS at which point I think the VRM's were having thermal issues, but it could've been the overclocked XBAR as well. I currently have my XBAR/SYS/L2C @ 1447/1479/1479.

I wonder how the memory controllers are configured in modern video cards? Do they read/write in quad-word quantities?

I am not familiar at all with those internals, besides the basics. Ever since I have this card I am suspecting VRM related issues as well.
I know that one of these clocks, possibly SYS also refers to the CUDA processing clock.

My normal testing routine is with Heaven benchmark, where I can otherwise easily OC to 1481, but right now I am focusing on this particular scene in The Witcher 3 which seems to cause many people problems.

Bios modding and flashing until the EEPROM smokes!! Yay!!
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post #16 of 27 (permalink) Old 10-12-2016, 01:35 AM
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I've looked over the VBIOS for several different models of 980TI's (the factory o'clocked models). It's interesting they all seem to have different values for XBAR/L2C/SYS. Could it be that these values are customized for each individual 980Ti? Or at least for each model of 980Ti?

I'm going to revert back to stock XBAR/SYS/L2C and see if it resolves my boot problems and FPS stutters.
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post #17 of 27 (permalink) Old 10-12-2016, 01:59 AM
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To me it seems that all factory OC cards take their factory OCs at cost of those clocks, they're all lower values than stock/reference. So I'd definitely set them back to what you had them before. I mean I tested yesterday, set them all to 1392 and Heaven benchmark crapped out after 10 mins. Then I set it back to what it were before and run it without problems, at the same (main) clock speed. That's why I said "can of worms" touching these values smile.gif

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post #18 of 27 (permalink) Old 10-19-2016, 04:11 PM
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Quote:
Originally Posted by flexy123 View Post

To me it seems that all factory OC cards take their factory OCs at cost of those clocks, they're all lower values than stock/reference. So I'd definitely set them back to what you had them before. I mean I tested yesterday, set them all to 1392 and Heaven benchmark crapped out after 10 mins. Then I set it back to what it were before and run it without problems, at the same (main) clock speed. That's why I said "can of worms" touching these values smile.gif

Actually, in my research I found some of the factory overclocked VBIOS for the 980Ti's had higher XBAR/L2C/SYS values:

a. EVGA classified XBAR=L2C=SYS = 1455.5

b. Zotac AMP! Extreme XBAR=1431 L2C=1447 SYS=1479 (what I've got)

Two different ASUS models:

d. ASUS XBAR=1459.5 L2C=1492 SYS=1525

e. ASUS XBAR=1393 L2C=1424 SYS=1456

I believe the stock, reference 980Ti has the L2C/XBAR/SYS set to 1392 as you pointed out.

It turns out my problems had nothing to do w/o'clocking the L2C/SYS/XBAR on my 980Ti and everything to do w/an unstable o'clock on my CPU. I managed to crank the
XBAR/L2C/SYS to 1479 @ 1.87V Vcore and it seems like games run smoother w/those values than the stock ones.
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post #19 of 27 (permalink) Old 10-25-2016, 12:37 AM
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wow neat. i guess now we know a little more of what each of the things were in the bios editor.

if anyone was curious what my 980 ti looks like without wanting to open up a bios file here are some pictures for ya





EDIT: this is how you beat a 1070 ^_^

8700k
(10 items)
CPU
Intel Core i7 8700k
Motherboard
Gigabyte Z370 AORUS Gaming 7
GPU
EVGA GeForce GTX 1080 Ti 11GB FTW3 GAMING iCX
RAM
Corsair Vengeance LPX 32GB CMK32GX4M4A2666C15
Hard Drive
SanDisk Ultra II 480GB 2.5"
Hard Drive
PNY CS1311 960GB 2.5"
Power Supply
SeaSonic PRIME Titanium 850W 80+ Titanium Certified Fully-Modular ATX Power Supply
Cooling
Noctua NH-D15
Case
Fractal Design Define S ATX Mid Tower Case
Operating System
Windows 10 Pro
▲ hide details ▲


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post #20 of 27 (permalink) Old 02-04-2017, 01:32 AM
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I've been experimenting w/the L2C/SYS/XBAR values in my 980Ti. I was hoping by lowering them I could increase my core overclock. The strange thing is that lowering them resulted in less ability to overclock the core.

@ L2C/SYS/XBAR setting of 1394 MHz, I couldn't even get 1443MHz core clock stable, but at 1494 MHz L2C/SYS/XBAR I can overclock to a 1493 Mhz. core. But this doesn't make any sense does it?
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