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PCI-E drops from x16 to x8 (AMD = PCI-E 2.0) when rig overclocked.

post #1 of 11
Thread Starter 
Hi, I can't figure this out for my life. When I leave my computer at stock (3.4)ghz my GPU uses pci-e 2 x16, but when I overclock to 3.9 the lane drops to x8. AMD don't do 3.0 and my 7970 needs the throughput. What could cause this?

When rig is overclocked:

The GPU at rest (idle) reads as: Bus Interface "PCI-E 3.0 x16 @ x8 1.1" and the clocks are at core 300mhz and mem 150mhz.

When I put it to work The Bus Interface jumps to "PCI-E 3.0 x16 @ x8 2.0" and the clocks go back up to 1000mhz and 1500mhz.

So it's not a card at rest issue.

When I'm not overclocked, at rest/idle the Bus Interface read "PCI-E 3.0 x16 @ x16 1.1"

and in use "PCI-E 3.0 x16 @ x16 2.0" as it should be.

(thanks AMD! why would a mobo advertise PCI-E 3.0 when it's AMD and can only use 2.0? anyways) and the clocks go back up to 1000mhz and 1500mhz. Not a power saving or slot issue. Something in the BIOS might be choking the lane? The obvious stuff I ruled out. That I don't know how voltages and speeds mix and affect things is where I'm lost and think the problem is.

I can switch from regular to overclock with one simple BIOS selection. Regular x16, OC'd x8, never fails, it's like switch lol.

I can't seem to add pics or I would show my BIOS settings, someone might see something...sigh
post #2 of 11
Thread Starter 
Here's some pics!

post #3 of 11
Thread Starter 
PS I remember hearing look into the PCI-E Voltage but was told not to mess with it without indepth knowledge and the ability to physically check voltages with a multi-meter.
post #4 of 11
Does it do the same thing when using the multiplier to overclock rather than the ht link (FSB)?


EDIT: just noticed the oc genie lite was enabled, I'd disable that and manually overclock things in the bios probably clear things up in a hurry.
Edited by cssorkinman - 5/15/14 at 11:01am
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post #5 of 11
Thread Starter 
When you say "in a hurry" i hear more like hours of learning to overclock and incremental testing lol.

If I switch to the multiplier and lower the fsb, would I need to change any voltages? I'm hoping to use OC genie as a springboard to move forward from - unless that's stupid rolleyes.gif
So far my attempts at doing that to get my ram timings right haven't been encouraging but that's a whole other can of worms... which I also have a post up here for!
post #6 of 11
Thread Starter 
SUCCESSish

So I got x16 with the cpu overclocked to 3.9 by multiplier not ht link (fsb). AND the RAM at cl7 XMP timings. It's a bush league overclock, but it narrows the field. The numbers may be there but I'm not feeling the speed.

Ok so the FSB speed is choking my PCI-E lane. FOR WHY? maybe when it increased it's voltage or something?
post #7 of 11
Quote:
Originally Posted by Darkhaze View Post

SUCCESSish

So I got x16 with the cpu overclocked to 3.9 by multiplier not ht link (fsb). AND the RAM at cl7 XMP timings. It's a bush league overclock, but it narrows the field. The numbers may be there but I'm not feeling the speed.

Ok so the FSB speed is choking my PCI-E lane. FOR WHY? maybe when it increased it's voltage or something?

Not choking, just stressing something to the point that it set the pci express to 8X rather than 16. Weird things happen like that when you use auto overclocking features.

I'd manually set your ram timings , speed and voltage in bios to their rated specs and use the 19.5 multiplier that seems to be stable for you. You won't notice a difference between 8x and 16x in this instance at all, from what I've seen.

Watch your temps, but C3 965's are usually good for 4ghz plus with the right cooling.
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post #8 of 11
...per some comments above, could be the OC (FSB / BCLK). I ran into that w/ some AMD GPUs when I oc'ed the FSB and this PCIe bus 'too far'
post #9 of 11
Thread Starter 
Quote:
Originally Posted by cssorkinman View Post

Not choking, just stressing something to the point that it set the pci express to 8X rather than 16. Weird things happen like that when you use auto overclocking features.

I'd manually set your ram timings , speed and voltage in bios to their rated specs and use the 19.5 multiplier that seems to be stable for you. You won't notice a difference between 8x and 16x in this instance at all, from what I've seen.

Watch your temps, but C3 965's are usually good for 4ghz plus with the right cooling.
Ya i did set everything manually, and even as I've been messing around with under this "OC" my CPU temp never hit 42c (Sycthe Mugen ftw). That HWmon Temp 2 issue is sitting pretty at 32c, much more relaxing than 56... - The stability has not been tested tho, I just did it lol. There are some kinks that need to be smoothed even if it is stable, I'll have to investigate, any ideas what could use a tad more voltage or mhz?
post #10 of 11
Thread Starter 
Quote:
Originally Posted by Joa3d43 View Post

...per some comments above, could be the OC (FSB / BCLK). I ran into that w/ some AMD GPUs when I oc'ed the FSB and this PCIe bus 'too far'
Please elaborate, FSB/BCLK? Run into this b4? Tells me! biggrin.gif
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