Recent Level1 KVM Issues

So since starting work from home, my desk configuration has become a bit more complex and I’m seeing some weird behavior with my dual dp1.2 L1KVM.

The main issue is that my mouse cuts out completely time to time after switching inputs. After lots of unplugging the mouse, pulling power to the KVM and switching inputs, it eventually comes back. In Windows, I can hear the device attach/detach sound repeating every second or 2.

It works reliably if I use the non-HID port, but it needs to be physically replugged when switching inputs.

The mouse is a 3DConnexion Cadmouse. I would say that it’s probably the mouse, except that this issue only started recently after having the KVM for over a year. That said, I am switching inputs much more often recently, so maybe it’s a pre-existing issue…

Additionally, I currently have a 2013 Mac Pro attached to the KVM, which I’ve heard has some problems, but I don’t remember the nature of them. Is it possible this is causing the mouse to behave erratically between all computers? It mostly works fine otherwise. Occasionally the displays get confused, but nbd.

One last thing, double-tapping numlock doesn’t seem to have any effect at all. I’m not sure if this is something I should notice when it works, but nothing indicates that the usb hub is resetting.

Shameless bump @wendell

ctrl+ctrl f7 will turn on/off follow mode for usb3 (two beep on, one beeps off).

So some USB devices use different size packets depending on if they have their driver loaded or not. So it will be critical the same driver/version is loaded on all PCs you are switching between. Logitech mice have that special handler for this reason. They use 20 byte USB packets when you have the MX master software loaded, otherwise it is like 12 bytes. If you have a machines with mixed driver/not then it confuses the crap out of the mouse receiver and needs the soft reset.

You can actually use wireshark to capture the usb packets of your mouse and confirm if this is the case. Does that cad mouse have roughly comparable drivers on the two platforms?


This might be it. The cad mouse only partially works in macos without the driver installed (no left click, inexplicably), but was plug and play in linux. Windows automatically installs a driver for it.

Currently, I am seeing switching between Windows and Linux working fine, but mac doesn’t like it.

Related, is there a usb hub that is confirmed working with the kvm? I have a startech one that does not. I know it’s hit or miss with them.

ALSO, work just sent me a workstation upgrade, so I have the new Mac Pro now with a Vega II in it. Not sure if this has ever been tested with the kvm, but if you ever want to test a configuration with it, I’d be happy to do that for you.

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I don’t remember seeing this documented anywhere. Is this part of your customizations?

It might be beneficial to create a list of these features. Even if it doesn’t have a verbose explanation, it will be incredibly helpful so we don’t have to refer to you on a regular basis for keymaps.


Yes, please.

Best case, ship it with a cheat sheet sticker that end user can stick to it or wherever makes sense.

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Hehe. I learned bad habits from Scotty from star trek.

Also trial by fire on obscure product features that then people depend on that might disappear in future firmware. I tried to bake in a lot of oh shit just in case to avoid returns/recalls.


Time to make a gist.

Or send me a brain dump and I’ll wiki-ify it.

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If there’s a way to power cycle the usb hub with a keystroke, I think that would help me out.

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There’s an emacs command for that.

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Hey @wendell, I am having quite a bit of trouble with the kvm now. The mouse will only work in the front usb3 port. In the HID ports, it no longer functions at all in any OS, despite power cycling the kvm. It had been plugged into the same HID port in the back for 2 years before this issue arose.

Also, it appears that Apple’s dp over usb c/thunderbolt implementation continues to be out of spec (I’m assuming), even using the usb c ports that are physically on the gpu in the new mac pro. I can boot into it, but if I switch to another input and then back to the mac pro, the displays never come back up. I suspect I need active usb c to dp cables? Any recommendations? I see monoprice makes one…

Currently, dp cable-wise, all my cables are either from the l1 cable kit, or are club3d dp1.4 cables. No adapters are being used. All cables are tested working when bypassing the kvm.

In the kvm store, it mentions to email you for support. I assumed doing it here was preferable, but happy to switch to email if that gets me into a ticket system or something.

The monoprice stuff is usually good. I can’t speak to my personal experience, but it might be worth trying.

Make sure the whole string is the L1 kit from your mac to the display, I’ve found that otherwise solid cables have issues, and the only cables that truly work on the more finicky GPUs are the Dell cables that are sold with the L1 kit.

Come to think of it, I’m experiencing the same issue with my KVM. Are you on the dual port quad system KVM? I guess I just tossed it up to user error.

Found a club3d one. I’ve had the best experience with their cables so going with that. They’re also dp1.4 which I’m trying to go with as much as possible. I’m hoping to drop in the next gen kvm next year or whenever it comes out, so trying to go with 1.4 for everything.

Would still need a usb-c to displayport adapter. Everything on the mac pro is usb c, except 1 hdmi port on the gpu. Anyway, the club3d cables are working in every other case. They are a spec above, so I’d expect them to…

Yes, purchased in Feb 2018, possibly around the same time as yours if I remember correctly. What’s your mouse?

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Logitech G502.

Encountering the non-functional USB issue (occasionally) with all HID devices though, rather than just mice.

I had issues with my trackpad, keyboards and mouse.

I’ve encountered this before on a R9 Fury. The cables worked on every other GPU, except that damn fury, and only when the fury was in a VM. I know they’re “a spec above” but I’m convinced those Dell cables were crafted by God himself.

can you do a clean UNINSTALL of the mouse/hid drivers from all computer(s)? Logitech software runs with a 20ish byte protocol, but is backward compatible with hid. However the devices themselves are incompatible with switching modes w/o a reset. The usb3 ports reset on every port change but the hid ports do NOT. By default, without the driver, the mouse operates in a 12 byte mode. You can load wireshark and see the difference.

You must have the same driver/version loaded for things to be sane, with the hid ports, when using fancy peripherals. This is why there is separation between hid and not hid. I don’t have an explanation for why some hid ports work but not others UNLESS windows is just loading the wrong driver for that usb port as it does remember devices by usb port.

I feel 85% sure driver squirrlieness is the cause of this. I’ve only recently come to understand this better when working with logitech mx3 mice, and noticing some driver changes in linux for those logitech devices. You should be “fine” on USB3 ports since it always (almost always?) actually does reset the device.

I have never heard of the hid mouse becoming non functional on any machine though, only after that initial “special driver” handshake.

I actually do have a ticket open with apple. The universal fix for this is the Level1techs DP repeaters. But I have purchased not one but two macbook pros and neither do it. I traded one of those macbooks to a corporate kvm customer for one that does have an issue, and it’s been fascinating but I haven’t made it very far yet.

I am currently testing a special “bi directional” usbc to dp cable. 99% of the adapters out there are meant to adapt the wrong way, and they are not reversible.

The “best” option is the level1 usbc kvm fed into the level1 other kvm, since it is usbc in and dp out, but that is perhaps overkill so I am testing these cables. @Eden has my prototype dp to usbc adapter which is amazeballs but there isn’t really a market for, I think, outside fixing edge cases with kvms and similar peripherals. haha.

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Whats the exact issue out of curiosity? I haven’t had any issue with macbooks so far.

Its a thing of beauty. I’ve had a much better chance to use it more with working from home :smiley: I agree theres maybe not a huge market for it. That said lots of laptops are all USB Type-C, not so much PCs.

I do need to check in with you at some point. I’ve noticed an odd issue with waking my sleeping PC through it. e.g. it doesn’t. Need to see if it’s the adapter or unrelated, ive not troubleshooted it much yet.

Yes, I can try that, although in macOS the mouse needs the driver to function, so I’ll have to re-install it. That should be ok though, since it was working that way before without issue between macOS and Linux.

This is strange because in macOS, I still have to physically unplug the mouse and plug it back in for it to work. Switching to Windows or Linux does always work though on usb3.

I don’t mind keeping it on usb3, but I need a hub. I know hubs are problematic. Do you know of one that is proven to work?

For me, this did arise after adding a Windows machine to the mix. It was only macOS and Linux before, but what’s confusing me is that even if I plug the mouse into HID cold in macOS or Linux, it doesn’t work even though that’s how I always had it before. How could the Windows machine be interfering in that case?

I’ll let you know how the club3d active adapters work. Spec-wise they look like they covers all the bases and the direction is correct.

So the DP repeater doesn’t currently fix the issue, is that correct?

WIndows says to reciever “hey, receiver. Only talk in fancy protocol now” and receiver says “okay” and then other OSs never hear from it again because it doesn’t speak the same protocol. I ran into a few unifying receivers that would NOT reset even when asked to do so. If you have a different unifying receiver can you try it? might just be a marginal device.

the dp repeater is the only thing that so far has universally FIXED the issue with macs. This usbc “bidirectional” cable may fix it for usb devices. not sure yet.

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No receiver, it’s the wired version of the 3dconnexion cadmouse.

I get why it could get tripped up when switching between kvm inputs, but it doesn’t work in the HID ports at all anymore, even when plugging in cold.