I have two laptops connected to an L1 KVM which is connected to a single display. The connections between the KVM and laptops are USBC-to-DP1.4. The connection between the KVM and the display is DP-to-DP 1.4. The operating systems are MacOS 11+ and Windows 10 and it happens on both.
Swapping between inputs on the KVM causes one laptop to disconnect from the external display and the other to reconnect. This makes swapping take several seconds as the resolutions need to readjust and the laptop needs to send the video feed to the KVM.
Is there a way to persist this connection? I want the KVM to act as a sink and just drop the signal instead of disconnecting from the display on swaps. Is this a consequence of the USBC-to-DP connection? Is this a laptop setting? If I use DP-to-DP on the laptops, will I achieve the expected behavior?
So this is due to a few different things, Windows, EDID, and hybrid graphics.
Windows is setup to detect displays being added and removed particularly on a laptop so you can quickly connect to external displays or projectors. To assist in this Microsoft will redraw and re-align all the windows that are open. You can fix that part with Power Tools.
Second is EDID, EDID is the automatic protocal that tells computers what kind of display is attached. The L1 KVM does not include EDID emulation because of the high bandwidth high performance of the design (at least as far as I understand it). You can use a passthrough EDID minder or dummy plug which will “trick” the laptop into thinking a display is still attached.
Something like this ( i have not tested this product) should help as it will allow a connection through the EDID emulator.
Lastly is the way Laptops are wired, where the primary and generally electrically connected GPU is the IGP. The Discrete GPU is generally just copping its rendered frame into the IGP so that no expensive switching is required. There are higher end laptops that have these dedicated switches and even have directly wired connections but they are not as common outside of boutique brands.
If you have an Nvidia dGPU that is a Quadro or A series you can actually tell it to force a connection and that will hold the display info on the adapter rather than detecting the EDID at least until the next windows update (thanks MS). Otherwise the EDID pass-through is the best option.
I would add that persistent windows is a software solution for this on windows 10 and windows 11 has this functionality built in, but it is not on by default (no hardware needed)
“ideally” doing this does not require hardware, and it won’t in the future
Thank you for the input! I updated the original post to include operating systems, both MacOS 11+ and Windows 10. I’ll look into the EDID emulators. Appreciate it!
Would like to add to this. The one posted will not work with the KVM. I still don’t get why a plug like this exists. I bought two from Lindy that say not for headless operation also and when the KVM switches to the other inputs it kills the connection. So they are pretty pointless in my opinion. The only think I can think of is the repeater and EDID cloner that @wendell sells. I’m hoping they come in stock soon.