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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
     
  9. I have a dual monitor displayport KVM setup with absolutely NO intervening devices and I see this problem when I switch monitors. The problem is really bad with Windows 10. Mac OS actually deals with it OK, but it's obvious that this is software doing a better job when it gets the wrong answer from the hardware (all of the windows appear on one monitor at first, but magically disperse to their original location when the second monitor comes on-line).

    Also, it is obvious to me, as a computer engineer, that this can't work unless the KVM switch remembers the EDID data an regurgitates it to the disconnected computers (unless there is something in the protocol that can actually tell the computer that there is a KVM switch and the monitor was switched). Hardware vendors really only have two choices here: Implement it correctly or wait and hope the the vendor of the aforementioned broken operating system will somehow learn how to fix the problem (I wouldn't hold my breath for the second option).

    A company called "Connect Pro" claims to be producing a Displayport KVM switch that does this correctly, but it is backordered....
     
  10. Man

    Man Guest

    Is a DisplayPort to USB-C (alternate mode) adapter supposed to work with the EDID passthrough? I have a DisplayPort KVM and DP/USB-C adapters on each computer and doesn't seem to work.

    Is there a way to debug this issue or learn more about how EDID is handled in DP? Thanks!
     
  11. goetion

    goetion Guest

    I'm in the market for a DP KVM and this conversation is really interesting.
    So bumping this thread hoping Herbie and FePhoenix questions get answers

    In the past I've shied away from DP KVMs particularly because of iffy EDID support. Manufacturers who do claim support always seem to plaster EDID on their listing for click-bait and few have any description in their manuals.

    Adding my own question.
    Could an EDID passthrough (eg. Lindy 32116) help solve the case of FePheonix?
     
  12. KVMGalore Expert

    KVMGalore Expert Staff Member

    We can't attest to Lindy 32113 you referenced, but the DisplayPort EDID emulators we carry can definitely alleviate DisplayPort EDID issues.
     
  13. OK, some answers. I read the specs and FePhoenix is correct. DisplayPort doesn't have a separate pin for the EDID information. It is buried in the DP high-speed datastream, which will make more expensive to intercept and regurgitate.

    I can confirm that a cheap KVM will not work. Well, let me re-phrase that. It will not work with Windows. It works fine with Mac OS (although, slowly enough that it would be unacceptable if you switch monitors frequently). Windows behavior when the monitor is disconnected is to pretty much immediately decide you only have one 800x600 monitor on the port and it will scrunch all of your windows onto the upper left corner of one screen. So any solution has to maintain a connection to windows and keep telling it the monitor is there and what kind of monitor it is (or at least the basic screen configuration). In order to do it, it needs permanent power from someplace or it needs non-volatile storage. The Lindy emulator gets it power from the monitor (which the KVM switch disconnects); so, they will not work and they say that on their web site.

    The new NTI emulator gets it's power from the computer and it does work better. I have two of them in between my Windows PC and a cheap KVM switch. Unfortunately, when Windows sleeps, it removes power from the monitor port(s). And as before, all of you windows end up shrunk into the upper right corner. You can increase the timeout for the sleep, but you can't turn it off (or maybe the corporate owners of my PC have disabled that). You can lock the computer to manually with the Command L key sequence (Command key on Mac keyboards, windows key on Windows keyboards -- not the control key) and it usually doesn't sleep -- if you immediately switch to the other computer -- if you don't, vibrations can move the mouse around and wake it. Using this technique I can usually go half a week or so without my windows getting messed up (I don't switch frequently, one computer is for work and one is personal).

    So, the upshot is for a displayport EDID emulator to work, it either needs its own power supply or the ability to store the monitor parameters in non-volatile memory. If would have to have some sort of "learn" button on it for that.

    Of have one of the ConnectPro KVMs on backorder...
     
  14. Herbie Robinson

    Herbie Robinson New member

    OK, here are some answers. I read the specs instead of just looking at the connector pinouts and KVM Galore is correct. DisplayPort doesn't have a separate pin for the EDID information. It is buried in the DP high-speed datastream, which will make it more expensive to intercept and regurgitate. There is no way around that.

    I can confirm that a cheap displayport KVM will not work. Well, let me re-phrase that. It will not work with Windows. It works fine with Mac OS (although, slowly enough that it would be unacceptable if you switch monitors frequently). Windows behavior when the monitor is disconnected is to pretty much immediately decide you only have one 800x600 monitor on the port and it will scrunch all of your windows onto the upper left corner of one screen. So any solution has to maintain a connection to windows and keep telling it the monitor is there and what kind of monitor it is (or at least the basic screen configuration). In order to do it, it needs permanent power from someplace or it needs non-volatile storage.

    The Lindy emulator gets it power from the monitor (which the KVM switch disconnects); so, the Lindy will not work with KVM switches. If you can find the actual web site, they will confirm this.
     
  15. Herbie Robinson

    Herbie Robinson New member

    The new NTI emulator gets its power from the computer and it does work better. I have two of them in between my Windows PC and a cheap KVM switch. Unfortunately, when Windows sleeps, it removes power from the monitor port(s). And as before, all of your windows end up shrunk into the upper right corner. You can increase the timeout for the sleep, but you can't turn completely disable it (energy regulations or maybe the corporate owners of my PC have disabled that). You can lock the computer manually with the Command L key sequence (Command key on Mac keyboards, windows key on Windows keyboards -- not the control key) and that usually prevents the sleep -- if you immediately switch to the other computer -- if you don't, vibrations can move the mouse around and seem to let it sleep. Using this technique I can usually go half a week or so without my windows getting messed up (I don't switch frequently, one computer is for work and one is personal). I suspect that not sleeping with command L is, in fact, a bug in Windows that might get fixed if they notice it; so, I wouldn’t depend on this working forever.

    I should add that NTI is great company -- They spent a lot of time helping me with the emulators -- They came up with the command L trick that makes them tolerable. Those emulators should be really helpful if you are rapidly switching back and forth often between computers (at shorter intervals than the sleep time) and shut the computer down when you are done. I should also mention that NTI was willing to take them back, but they are worth keeping until the ConnectPro comes in.

    So, the upshot is for a displayport EDID emulator to work in all situations, it either needs its own power supply or the ability to store the monitor parameters in non-volatile memory. It would have to have some sort of "learn" button on it if it has non-volatile memory -- These exist for other video formats, but not displayport.

    I have one of the ConnectPro KVMs on backorder... Supposedly shipping in a couple of days. I ordered July 1; so, the backlog is quite a bit more than 2 weeks…
     
  16. DesertRat

    DesertRat Guest

    I have two desktops, one with a Titan X Pascal and one with an RTX 2080. The monitors are Dell U3014, 2560x1600 @ 60hz. I am also running a Logitech wireless trackball/keyboard dongle. I bought an Iogear GCS1942 and experienced the windows moving when switched. I learned of EDID and the GCS1942 also had a USB port problem so I returned it. I was going to try a Connectpro but their website shows a backorder of 7+ weeks. Is there any other option - I would prefer a USB 3 hub but can live with a USB 2 hub.
     
  17. Customer Service

    Customer Service Staff Member

    Hi DesertRat,

    Your new question appears to be unrelated to this thread - Please post your question as a new thread, and we'll be happy to advise. Thanks!
     

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