L1 KVM triggers DP Alt Mode without plugged in DP Cable

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Hello,

First time poster. I did all I could to research the issue to no avail. Nothing plugged into the KVM gets recognized.

Setup:

  • L1 KVM (CAAB-P3112 / USB-C Gen 2 KVM)
  • AsRock X670e Steel Legend Motherboard
  • AMD 7900X

KVM connections:

  • HID Keyboard and Mouse
  • Non-HID Camera and Microphone
  • No video output (bought with video output to future-proof)

Plugging the KVM into my Win10 work laptop, everything works fine.

On the desktop, whenever I plug the KVM in, I get the following symptoms:

  1. connection sound,
  2. disconnection sound two seconds later
  3. followed by the warning that “display connection might be limited”.

Windows 11 and Driver are on the latest version.

What I have tried:

  • Using both USB-C ports of the motherboard
  • Using both USB-A port types (chipset and CPU ports, rated for 10Gbps)
  • Switching cables (Thunderbold 4 certified cable for USB-C and 2 10Gbps certified cables for USB-A)

My best theory is that for some reason, Windows is trying to activate USB DP Alt Mode and failing. I couldn’t find any other person with the same issue, so it’s probably something specific to my setup.

If someone has any idea what I could try next I would be very thankful.

2

theres a displayport chipset inside the kvm? so that’s probably what the usbc interface sees on the computer side.

it’s just like you plugged in a usbc to displayport cable when you’ve got the kvm plugged in?

3

That could be it. It’s probably an issue with my motherboard then… I looked if there is a way to disable USB Alt Modes but it seems the only thing I can do is disable XHCI handoff, which according to a short search limits me to USB 2.0 speeds.

I tried adding a DP connection to the KVM, but it also doesn’t get detected.

I have a Thunderbold-4 Add-in card, I’ll try installing it (goodbye 10GbE :frowning: ) and see if it works from that. I’ll update once done.

Thank you for the help!

4

We have a USBC signal combiner on the store if that helps

1 Like
5

Oh I didn’t see it the first time. I’ve signed up for notification for when it gets back in stock. Thank you!

This restores my hope to get a working setup :slight_smile:

6

Confirmed. It was the motherboard not managing the displayport chipset correctly. Using the Thunderbolt 4 Add-In Card (and after enabling TB in the UEFI) I was able to use the KVM perfectly.

Thank you for your help ! :slight_smile:

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