Tue Jun 04 2019 00:39:39 EDT from IGnatius T FoobarWell that was a bit of a failure.
So the switch is indeed completely passive -- there is no spoofing of EDID and no other simulation of the presence of KVM on the non-selected computer.
As far as the computers are concerned, you're just hotplugging the monitor and keyboard and mouse.
This wasn't a problem; both Linux and Windows seem to handle that with little difficulty.
But what I discovered was that my personal rig (an older Intel NUC) and my big monitor (native resolution 1920x1200) simply don't get along. I tried it on Linux and Windows, I tried it without the KVM in between, it just wouldn't display at any resolution higher than 800x600. Sooooooo the smaller monitor is back on the desk, and I'm only using the switch for the keyboard and monitor.
Try this one. I've got a Pi, a Surface 3, a G4 Quicksilver and an old Dell GX260 P4 hooked up to it... with a Westinghouse 22" and a Samsung 27"
It all works, all the time.
So I ended up just using it as a keyboard/mouse switch. Maybe when I have some time I can play with custom ModeLines on Linux like it's the early 1990's again. Windows is a lost cause; it starts up in 800x600, then downloads the "correct" driver at which point the screen goes completely dark.
So you get no video from the NUC on your monitor, or it just can't drive it at the native resolution so it is blurry? Is it a matter of the native resolution being too high for the NUC GPU?
I'm assuming built in Intel HD video?
When I first hooked it up to the big monitor without rebooting, it kept the resolution of the little monitor (Xorg doesn't hot-switch by default) which is 1600x900. It was blurry enough that it wasn't worth looking at. But when it boots under the big monitor, it doesn't find any working modes at all.
I'd be willing to bet that there's a way to program a custom mode if I worked at it long enough. Right now I don't have the time and I'm just happy to get the extra keyboard and mouse off the desk. I also installed Synergy on both machines so I don't even have to use the button except during startup.
I was able to force the video mode to 1900x1200 at 60 Hz using the "xrandr" tool. I got the command ready on the little monitor, then ran it while plugged into the big monitor, and it is displaying perfectly.
Now I know the hardware is at least *capable* of displaying this resolution.
I just have to figure out how to force it to use this mode at every startup.
It's going to be tricky, but at least it's not the dead end of "use one of the built-in modes or GFY" that I got with Windows.
Apparently "xrandr" has some sort of persistence across reboots. When I created a custom video mode, it seems to have "learned" it and is capable of using it again. So I re-enabled my display manager and it's working at the native resolution of the monitor.
But! It only starts up properly when the monitor is plugged directly into the computer. It won't start properly when attached through the switch. So it's a nuisance, but I can live with it since I want to leave this computer on all the time anyway, it's very low power, and my electric service is very reliable.
My other computer seems to have no problem passing EDID through the switch, under either operating system.
So I guess I'll just live with it for now. The one computer doesn't get rebooted much anyway, and when it does, I just have to bypass the switch to do it. As a slow-burn project I'll work on finding a way to get it to ignore EDID and force-feed it the video mode I want to use. The problem starts pre-boot, though, and it won't even proceed through the hardware boot screens with the switch attached.