X370 Taichi - PCIe slot for capture card

Hello AsRock community,

Got a bit of and odd setup and issue here.

I'm currently running on an X370 Taichi (BIOS v2.40). I'm having some issues getting a capture card to function correctly, the Datapath VisionRGB E1S:
https://www.datapath.co.uk/datapath-products/video-capture-cards/vision-range/visionrgb-e1s

It's my understanding that the PCIe slots are setup for the X370 Taichi as follows (by slot, from top to bottom):

PCIE1 2.0 x1
PCIE2 (w/ M2_1) 3.0 x16
PCIE3 3.0 x8
PCIE4 2.0 x1
PCIE5 (w/ M2_2) 2.0 x16 (Physically x16, but x4 in operation)

At the moment, PCIE2 is occupied by a Nvidia 1080ti graphics card and the M2_1 slot is occupied by a Crucial MX300 SSD (SATA only) for storage. I don't believe this is causing any issues, as it's operating via SATA -- not NVME. I'm not claiming to be an expert on how this motherboard operates by any means, so please correct me if I'm wrong on this.

I'm trying to use the PCIE5 slot for my E1S capture card, but when in the PCIE5 slot the E1S does not seem to function correctly. The card's specs say it requires PCIe x4, so I figured the PCIE5 slot should have the correct amount of lanes\bandwidth available. However, after inserting the card in PCIE5, installing the latest drivers for the capture card and subsequently utilizing the supplied video capture software, the operating system locks up and often automatically reboots the computer when detecting an incoming video signal.

I suspect that perhaps I'm trying to use too many PCIe lanes or that the PCIe x4 bandwidth from PCIE5 (which I believe connects to the chipset, not the CPU) isn't enough.

When inserting the capture card into PCIE3, the capture card seems to function normally and I can visualize and capture incoming video. However, this reduces my video card utilization in PCIE2 to x8 -- which I'd like to avoid, if possible.

Am I missing something obvious? Shouldn't I technically be able to use the bottom slot (PCIE5) for my capture card?

Thanks for the reply jdilipl. I emailed Datapath support and recently received a reply. While they did not really provide any specifics for required bandwidth, they mentioned it's a "rather low bandwidth card" relative to the other capture cards they offer. Support did say their products are primarily designed to work with PCIe 3.0 and it may be possible to get the card working in a 2.0 slot -- but functionality would not be guaranteed.

Not sure if that's a "canned" response or not (not their fault, the E1S probably doesn't get much attention these days), as the E1S does seem to be a relatively old card. Therefore, I wouldn't be surprised if it's compatible with PCIe 2.0. They also recommended to ensure that I'm running the latest drivers for the capture card (which I am), etc.

However, while I was waiting for a reply I decided to test whether something else was taking up motherboard resources and creating problems, e.g., USB 3.0 connections. To start the testing, I started with my initial configuration (SSD in M2_1, GPU in PCIE2 and the Datapath card in PCIE5) while unplugging anything unnecessary from the motherboard and case USB ports.

Much to my surprise, the card seems to work just as well as in the PCIE3 slot! Unfortunately I'm not sure if a BIOS setting got switched (I tried Gen1 and Gen2 settings previously, to no success), the firmware was automatically updated via the OS due to switching slots, or that clearing up some resources by unplugging USB devices did the trick...but the card seems to be operating normally in PCIE5. I think I'll be pleased with this configuration, as I don't have to worry about the GPU potentially being bottlenecked by available PCIe lanes.

Anyways, I just wanted to update this post in the off chance anyone else has similar issues with similar AsRock motherboards and PCIe expansion cards. I'll try to update this post in the days to come if something else seems off.

My take away thus far: Try switching PCIe slots, even switching back and forth, multiple times or unplugging unnecessary USB devices.