Hardware: LG38WNC → Win11 PC w/ nvidia card and macbook air connected via cable matters adapter. Secondary HDMI connected monitor, connected directly and permanently to the PC.
In general this works perfectly. However, for various reasons, I want to emulate EDID for the Windows PC.
I have a Lindy displayport 1.4 EDID emulator, which, in theory, supports the res/refresh. If I connect it to the PC, and learn the EDID, I see the correct settings reported by windows, and it appears to work. However, when I switch away and back, the monitor fails to sync. The PC seems to be correctly detecting the emulated monitor, so I suspect this is an issue on the KVM side.
If I connect the Lindy separately, Windows detects it as another monitor with the right settings.
Other Notes:
ddcutil dot com - reports specific notes on this monitor:
Users of all these recent LG displays report similar problems with VCP feature X60 (Input Source). getvcp 60 always returns x00, which is not a valid value. setvcp 60 flashes the screen, sometimes opens the OSD, never sets the value
Okay so I just tried removing the cable from the back of the KVM rather than switching using hte button… and it works. This suggests to me that the EDID emulator is working, and it is related to the KVM.
FWIW I did not buy the level1techs emulator because (AFAICT anyway) it was only available in DisplayPort to HDMI flavour, which wasn’t what I was trying to do.
it sounds like the edid emulator is working, but the computer is trying to retrain with the monitor when it isn’t there, and gives up after a while. you see the same kind of thing if you have a sketchy connection and the gpu tries to negotiate a lower bit rate. Ofc since the monitor isn’t there the renegotiation can’t happen. The only thing in the kvm that could possibly cause a problem is the engine that does the hdcp rekeying. So the edid emulator may prevent the hdcp key renegotiation that’s supposed to happen on screen switch… I suppose it could be another lg firmware specific problem. LG monitors tend to be a bit buggy too. Probably not a problem with the kvm per se, but the specific combination/sequence of things happening.
The kvm is pretty rock dumb stupid, as dumb as it can be, to avoid these kinds of problems in the first place. So about the only thing it could be is something related to hdcp rekey. Do you have an amd gpu? if so disable hdcp in adrenaline (its hdcp on all the time by default to avoid naving to negotiate on demand) and see if that solves the switching. If it does then you have the answer. Some edid emulators that recognize an hdcp rekey is needed will work around it. physically replugging also does this usually.
I have an nvidia GPU, so don’t think there is a mechanism to disable HDCP. I’ll do some investigating on this.
Okay so I just tested it (KVM switched sources back and forth, no working signal, removed and reconnected the emulator/cable)… and it worked. So this suggests HDCP is the issue. Gotta love copy protection /sigh.