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Multi-screen EDID passthrough emulation required

Discussion in 'KVM' started by FePhoenix, Feb 16, 2021.

  1. FePhoenix

    FePhoenix Member

    Looking for a 2-port dual-monitor DisplayPort KVM. The key thing is EDID passthrough emulation. I want both screens of each computer to be as I left it when I come back to it, so NO EDID disconnects!
    Got anything that can handle that? (and preferably not break the budget, either...)
    (USB doesn't need to be fancy. Just need kb & mouse)

    (why is this concept NOT standard on every kvm out there???)
     
  2. KVMGalore Expert

    KVMGalore Expert Staff Member

    Hello FePhoenix,

    Thank you for reaching out on our HelpCenter.

    It is! Except for KVM switches supporting DisplayPort input and output, being that the DisplayPort protocol itself is supposed to perform the EDID, hence requiring that the switch does not.

    2-port DisplayPort dual-monitor KVM switches are typically offered in two flavors:
    a) DisplayPort input and output
    b) DisplayPort input and HDMI output

    a) KVM switches with DisplayPort input and output do not support EDID emulation - the DisplayPort protocol itself is supposed to handle the keep-alive on its own. This, though, requires all of the DisplayPort components (video sources and monitors) to also behave properly. If there are any docks, adapters, port replicators, etc. involved, it's more likely to fail and result in the monitors acting like they've been disconnected.

    b) KVM switches with DisplayPort input and HDMI output do support video emulation by converting the video output to HDMI. As a result, the screens will not "disconnect" and both screens of each computer will be as you left them when you switch between the two computers. The biggest consequence of this video conversion is the elimination of any support for MST.

    Hope this helps!
    We welcome your questions - please come back and ask us anything, anytime. You may also give us a call at 1-800-636-3434 for further clarifications on this thread.

    Important note: To continue this discussion - please respond via KVMGalore HelpCenter thread, NOT via e-mail.
     
  3. FePhoenix

    FePhoenix Member

    I guess I worded my question/complaint poorly. Why is it not standard to have the *hardware* in the KVM to eliminate the issues you describe. Obviously, the path is broken between a video port and a monitor when the KVM is on the other computer. The protocol itself can't handle this when the connection doesn't exist; it's equivalent to unplugging the monitor. It should be standard in the KVMs to deal with this.

    Anyway... My current setup is 2x docked laptops (Dell 7520 and HP ProBook 640 G3), dual DP each (at the docks), to a StarTech SV231DPDDUA2. From the KVM's DP output, a pair of DP to HDMI converting cables to the monitors.

    If I just get monitors that are native DP, this issue goes away? Or a KVM that takes DP inputs and has HDMI outputs (point at some)?
     
  4. KVMGalore Expert

    KVMGalore Expert Staff Member

    Hello again, FePhoenix,

    It is a standard feature in most KVM switches, except those dealing with pure DisplayPort.
    DisplayPort encapsulates all the data in packets rather than directly over the lines. It also does not have a native EDID pin like VGA/DVI/HDMI do. So in order to get to the EDID data, the KVM switch would have to intercept the packet, open it, add the EDID data, and repackage it. 'Standard' DisplayPort KVM switches do not do this, but rather send the DisplayPort packets along, uninterrupted.
    DisplayPort KVM switches described as 'flavor b' above do intercept the packet, open it, add the EDID data, and repackage it, but to accomplish this they must send the video out as HDMI, not DisplayPort.

    If all your components are natively DisplayPort (with no adapters, converters, docking stations or anything in between the DisplayPort inputs form the computers' video cards to the KVM switch and from the KVM switch to the monitors) then a 'standard' DisplayPort KVM switch should work fine.

    SM-MST-4D
    CS1964
    D2H-4P-Duo

    Hope this helps!
    We welcome your questions - please come back and ask us anything, anytime. You may also give us a call at 1-800-636-3434 for further clarifications on this thread.

    Important note: To continue this discussion - please respond via KVMGalore HelpCenter thread, NOT via e-mail.
     
  5. FePhoenix

    FePhoenix Member

    Huh? Not even docks? I ask because these computers have 1x DP on chassis. It takes the docks to get 2x DP each. Guess I'll just borrow a couple DP monitors and find out, and buy them if it works.

    I'm stuck with the former option, as all the KVMs pointed at above are out of my price range.
     
  6. FePhoenix

    FePhoenix Member

    Bought a couple native DP monitors (HP Compaq LA2405x) and put them in, replacing the HDMI monitors that were there, and replacing the DP->HDMI cables with native DP. So, it's now native DP all the way from the computers to the monitors. No change. I even tried without the docking stations, as a single monitor setup (unacceptable, but tested). No. it still loses the window sizing - they all go to the top-left, abt 1/4 the screen size, on return.

    The explanations given about how the EDID is software in DP vs hardware elsewhere, and this is why it's so hard with emulators and conversions and why it works with a native path, makes absolutely no sense to me. Oh, I get the format differences, but I see no reason why it would matter what format the data is in: if the path is broken, the path is BROKEN, and the switch needs to emulate the monitor for the offline computer, regardless of encoding method.
     
  7. KVMGalore Expert

    KVMGalore Expert Staff Member

    Which KVM switch (model number) are you using?

    A docking station will interfere (as mentioned above) with a DisplayPort KVM switch to perform the needed EDIT using the DisplayPort protocol.
     
  8. FePhoenix

    FePhoenix Member

    StarTech SV231DPDDUA2

    And, as I said, I tried it both with and without the dock. Without the dock, I get one monitor (unacceptable, but tried it to test). Same behavior.

    HOWEVER...

    In the meantime, I've discovered something odd. If not odd, unexpected...? I find that if I don't touch the kybd/mouse when switching (no "wakeup" mouse movement), it actually works. If the mouse is moved *before* the monitor comes back, it does not work. Is this expected?

    With that in mind (keeping paws off the mouse/keyboard when switching until *after* the monitors light up), dual monitors via docking stations does work properly. At least with these docks
     

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