6800 XT, PCI-E 4.0, and the Strix B550-E -- [SOLVED -- it's the mobo]

Long story short, I picked up an XFX 6800 XT Merc319 -- slotted it in a ASUS Strix B550-E motherboard {latest bios, also tried beta bioses}, installed drivers, then immediately noticed I was running at PCI-E 3.0. Admittedly my mobo has never been verified capable of 4.0, being that I did not own a single 4.0 capable device until now..

Unfortunately, no matter what I do -- the 6800 XT runs in PCI-E 3.0 mode. On auto, forced 4.0, etc, bios settings. Re-seated card numerous times, blew compressed air in the slot, tried an ASROCK B550 board -- no dice.




-- Post times are also abnormally long on auto detection, or 4.0. It seems the motherboard attempts initialization repeatedly, fails, and falls back to 3.0.


Working, not working? Wondering if anyone has tested similar combinations {such as a Strix B550-E with a 5700, or a 6800}. Will be reaching out to ASUS, XFX, and AMD support tomorrow, yet figure I'd ask here first.


Update: On a hunch, I tried using Google's Image Search for GPU-Z pics of the 6800 XT. Low and behold, I didn't come across a single one of them showing the card in PCI-E 4.0 mode.

-- This might mean that people are simply setting their bioses manually to 3.0 due to issues though. Still would appreciate if anyone owning one could let me know if they're capable of running on 4.0.


Update: Looks like TechPowerUp did some 4.0 testing, and included a GPU-Z screenshot showing that indeed does work. Albeit this was on an MSI X570 Godlike.

I'm more interested if anyone on B550 got this working.

 

remove the pcie riser, replace the cpu.

 

No riser present, two motherboards exhibiting the symptom with different processors slotted in each {5900x on the Strix, 3900x on the Phantom}. Though both boards are B550 / I have no X570's to try at the moment.

Post loop wise, the initial boot will end with 94, then reboot. Each subsequent ends with 15, until the bios gives up and apparently drops to 3.0. It's probably worth mentioning that both systems seem completely stable and post reliably with the XFX card inserted, long as they're not running PCI-E 4.0.

 

Cards gotta be bad then

 

Could it be you saturated all pcie4 lanes and gpu has to run gen3. Remove the drives if you have more than one nvme.

 

It is the case that both machines have NVMe present, though according to the manuals there should be no sharing with the first PCI-E slot's lanes. I'll give it a shot.


Edit: You're onto something here. If I remove the NVMe, the system boots snappy on cold boot with PCI-E 4.0 manually set for PCI-E slot 1... {meaning no post loop / retries} Albeit I can't boot into the OS then for verification that it's actually working, since that's also on the drive.

Will move the OS over to a SATA tomorrow for testing if it's actually in 4.0.

Yep, that's something that's crossed my mind if it ain't something B550 specific. I guess we'll see if XFX is going to propose that I RMA with the current stock conditions when I contact support.

I'm almost inclined to buy an X570 for the sake of testing before giving up the card, since I doubt I'll get it back for months.

 

Stupid question: Do you have a CPU that is actually PCI-e 4.0 ( ie. Zen 2, Zen 3 ) ?

Because Ryzen 2000 series or the 3000G series do not support PCI-e 4.0

 

Yes, I'm testing on a 3900x {old system with my Vega in it} and 5900x -- the new workstation built for Big Navi. Though I probably made a bad choice going B550 in hindsight.

-- Updated profile page accordingly. Been a long time since I've been active.

 

It's stuff like this is why I tell people to invest in X570. I have 2 NVMe drives installed and I run my GPU @ 4.0.

 

Yep, that's basically how my chats with ASUS right now are going -- that it's a chipset problem / stay away from B550. The rep told me that TimmyJoeTech and a few other YT reviewers ran into this issue on B550, so it's apparently known. Most consumers aren't running PCI-E 4.0 capable cards, and it's not deemed that much a problem, yet that if you want PCI-E 4.0, go X570.


They don't know if / when there'll be a BIOS update though... Their recommendation was to replace the board with an X570, which they said they'd be willing to do a discounted swap with my current board for. (refund / only charge the difference if I move up to a Crosshair VIII)

 

I can confirm that as long as there are zero NVMe's installed {both slots empty}, the Strix posts reliably, and 4.0 works within Windows. The Phantom, no matter what I do, I can't get it working.

Looks like I'm going to upgrade to X570.


Oh, one more thing to add for my fellow hardware enthusiasts here. If you buy a 6800 XT, and it's the Merc319, SERIOUSLY, read up on the card length. It's legit 340mm long, if you own a case like the HAF XB, you will have to take a saw to the case to make it fit.

 

Curious, thought the deal with the B550's was that the chipset is PCI Express 3.0 but the CPU can be 4.0 so the top x16 lanes to the PCI-E x16 slot should be the CPU's and thus 4.0
Wiring and how it divides this up between CPU and chipset can be a bit complex though my own X570 Master can be split into a variety of modes and the SATA parts get disabled as the remaining M.2 slots are populated as these are otherwise shared.

Interesting, wonder how the PCI-E and initial M.2 are rigged up then, guessing it's more complicated than I was expecting.

24x from the CPU so I was thinking 16x PCI-E 1 and then 4x M.2 and 4x Chipset which then provides the remainder for the rest of the motherboard.
(Perhaps the full 8x goes for the chipset then.)


AMD leaves a lot of that up to the manufacturers too how they wish to divide these, more lanes would be nice but the motherboard prices are already quite high though if they're already doing expensive models for the upper tier ones with some minor extras going for 32x or more with AM5 wouldn't be bad.

Dividing it properly to the x690, x670 and B650 perhaps instead of the X590's becoming the X570's and then the B550's later on followed by A520's I think is how that went.

Wonder if quad channel would work then, might be a bit of a premium feature though and if PCI Express 5.0 and DDR5 both come around with this next chipset that could already make it a premium price product just from being early with adapting this.
(With the X700 inevitably fixing up what went wrong the first time though drivers and bios updates will also do it's part as per usual.)

EDIT: Well thinking about the future besides this was a interesting read, learned something here as I was expecting the CPU to provide the full 4.0 compatibility without problem even if the B550's chipset is a 3.0 one for the rest of what it's routed through with these lanes.

 

mmm ill see what my strix b550-e does when i get the 3080/6800xt. Got both nvme installed.

Anyway, the mb should be able to drive at 4.0 both the gpu and the top nvme.

edit:

 

Honestly I'm hoping ASUS can address this with a bios update as well.. I really quite like my Strix, it's been rock solid stable and never had other issues.


Definitely it should be possible though, you're right on that per the manual's documentation. I don't quite know what the problem is, maybe it's even a defective board or card. I need more hardware to really test. I don't think I'm going to be upgrading away from the Strix {per their offer}. I'll just acquire another board, so that I can test future patches ASUS puts out. I'm not keen on the active cooling of X570, since I don't need most of its feature set as-is.

 

Another dumb questions, did you install the GPU into the TOP most, or EAST most PCIE x16 full length slot, the one closest to the CPU? That is the only PCIE4 x16 slot in most B550 motherboards.

X570 allows for 2 PCIE4 x16 (one in 16x, one in 4x = PCIE 3.0 x8) or both in 8x for SLI certified mother boards.

Plus a bunch of useless x1 slots. I rather pull those and put it to USB or NVME use.

 

Yep, top slot closest to the CPU in all testing. I didn't bother trying the second slot, though according to the Strix manual {and bios} it's capable of 4.0 x8.

I just received and assembled {again} with a Gigabyte B550 Elite, arrived early AM (sometime after midnight) from Amazon. Low and behold, 4.0 works! {including with NVMe installed} So this is isolated to some B550 boards, not all. Hard to say if it's a problem with the Strix, or if it and the Phantom are defective.


--- Will re-test if and when there's a bios from ASUS claiming a fix.

 

Yeah, Gigabyte boards are the best right now. It just works.

 

I didn't have to do anything with my BIOS setting, I simply took out my PC VEGA64 Red Devil, after uninstalling driver with AMDCleanUpUtility, popped in my Sapphire RX6800 Nitro+ and Hey Presto! PCIe 4.0

 

Nice! Though it seems you're on an X570 Aorus Xtreme (according to the info on here). That's on X570 and not a Strix B550-E, right?

When I saw that post I was thinking it's time to call up ASUS and ask for an RMA, heh.



But yeah, on the B550 Gigabyte board that I tested, it was pretty much -- plug it in, done. "It just works"

 

I'm going to call it right now and say that this is the preferred function of the device, its better for it to take a bit and go to Gen 3 automatically than try and brute force a Gen 4 link.

When an nvme is installed on the cpu, most of the b550 boards have unstable/noisy PCIE busses that manifest USB device issues.

In Latencymon and DPC traces, the forced Gen 4 link results in high values (10's of thousands)

Some (if not all) Gigabyte b550's crap themselves with Gen 4 cards, USB dpc latency is nuts, somethings wrong with the amount if REIN/Impulse noise the pcie routing is picking up on these boards.