VOGONS


KVM Rollover Issues?

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First post, by mattlacey

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I've got an Aten CS82U KVM, which is a USB & PS/2 + VGA KVM and I use it to switch between a PIII running Windows 2k and a Pentium 100 that runs DOS. It works well, except for when it comes to games. I was trying to play Doom and noticed some weird behaviour, and after playing around in notepad in Win 3.1 worked out what was happening.

If I press and hold a cursor, then press a modifier (shift/ctrl) the key repeat on the cursor stops. It appears as though it stops sending that key code. If I hold a modifier, and then press and hold a cursor everything works as expected, i.e. in notepad I can hold shift and then hold left/right to highlight text. Anyone know if there's a mode switch or similar that might be affecting this? Or is it just a case that it's a KVM and as a rule, they always seem to suck?

Reply 1 of 13, by Tiido

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My 8 port KVM seems to do similar stuff, if cursor keys are used when shift or ctrl are pressed you often get stuck cursor keys problem and only way out is pressing the stuck key again, makes most games unplayable. Rarely in text editing programs I see shift or ctrl getting stuck when cursor keys are used (shift+cursor=selection making). It seems the KVM misses cursor key releases when ctrl or shift is held down and only fix is pretty much getting another KVM that hopefully doesn't have this problem. I have couple other low end KVMs that I should try to see if they have that issue, if yes then there's one more project going into my todo list 🤣.

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Reply 2 of 13, by chinny22

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I'm guessing the hotkey combination is getting in the way where the KVM is always checking if Ctrl is pressed
Chapter 4 in the manual says by default Scroll lock is the hot key, but maybe yours is set to use Ctrl or maybe it always "listens" for that key no matter what?

The manual does have a section on changing the hot key that you could try
https://assets.aten.com/product/manual/cs82u- … _2015-04-16.pdf

Reply 3 of 13, by mattlacey

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It definitely responds to scroll lock, but I'll give that a whirl just on the off chance that it resets something! It's a shame because it's otherwise perfect, and I don't have the desk space for yet another keyboard!

Reply 4 of 13, by mattlacey

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No luck. Reset it's settings, toggle short cut keys and things and still the same issue. Half tempted to see if I can get PS/2 cable splitters or something, I don't often use both machines at the same time and could easily avoid doing so.

Reply 5 of 13, by mattlacey

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I realise that this is a niche topic and only likely to be of interest to me right now, but keeping the thread up to date in case others find it useful in the future. I opened a support case with Aten, expecting them to close it instantly saying it wasn't of interest, but to my surprise they not only responded with some suggestions, but have reproduced the behaviour themselves with several keyboards and have said they're looking into it! Hoping that sometime soon they'll release a new version of the firmware and then I'll be good to go.

Reply 6 of 13, by ElementalChaos

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Apologies for the necro, but I have the same KVM with the same issue and I hope this will be useful to future googlers. Interestingly it doesn't affect USB keyboards, and using that I found a workaround. I used an active PS/2 to USB converter to connect the keyboard via USB, enabled keyboard emulation on the KVM, then plugged the PS/2 keyboard end of the KVM cable into the machine as usual. The KVM converts the USB keyboard commands back to PS/2 and somehow bypasses the issue entirely. It's a MacGyver fix but it works.

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Reply 7 of 13, by mattlacey

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Don't apologise! Just got an email notification for this and this is great to know! I thought I'd tried a USB keyboard but perhaps not. Wi'll have a crack with a converter this weekend and see how I go. Maybe I tried USB but without the emulation enabled. A MacGyver fix is always better than no fix 😁

Reply 8 of 13, by SirNickity

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Interesting. I have to say, after studying the AT / PS2 protocol, I'm surprised most devices work as well as they do. It's not super complicated, but it's not trivial either. There are a lot of corner cases baked-in, and expected behavior is based on the code running on the original IBM implementation of the keyboard controller. You really have to pay attention to the details to reproduce the behavior in a way that seems natural. A KVM has to emulate a keyboard to the computer, and a keyboard controller to the keyboard, so there's plenty of room for error.

In this case, $10 says the behavior that's FUBAR is not of rollover, exactly, but how key repeats are handled. The last key held down should be repeated by sending its scan code continuously at the interval set by the typematic rate parameter (or the default of 10/sec.) Obviously, it doesn't make sense to behave this way with modifier keys, so pressing shift after an arrow key ought to continue sending the arrow key's scan code, but I would bet the KVM is not paying any attention to which key was pressed since it doesn't have any reason to interpret the codes, so it's just repeating the shift key code like it was any ordinary key.

The funny thing is, the KB is probably doing the right thing here and sending the arrow key code. But, either the KVM discards repetitive scan codes if they're already registered as "pressed" in its own buffer, or it disables key repeat entirely on the keyboard end. Either would make sense, since the KVM would need to emulate whatever key repeat interval the selected host asked for, and that might be different between hosts on different channels. So rather than reset the KB every time the input is switched from one host to another, it could just disable the feature on the device end and track key up / down state alone.

Reply 9 of 13, by dumpsterac1d

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Necro-ing this thread simply to update, I have the same series of switch just the 4-port version, and after upgrading to the most recent firmware it looks like there hasn't been any improvement. I'm getting repeated/stuck buttons when using a USB keyboard on a PS/2 machine, and getting "rollover-style" issues using a PS/2 keyboard with a PS/2 machine. At my wits end with this, makes games completely unplayable. Hoping some combination of PS/2 to USB, and/or straight PS/2 or straight USB works because it's super frustrating.

Reply 10 of 13, by mattlacey

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I never found a working combination with it unfortunately, and swapped it for an older unit a friend was throwing away that worked perfectly well. I even hit up support for them but they just said it was "as designed" and wasn't going to be changed. Very frustrating 🙁

Reply 11 of 13, by dumpsterac1d

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mattlacey wrote on 2022-02-19, 16:47:

I never found a working combination with it unfortunately, and swapped it for an older unit a friend was throwing away that worked perfectly well. I even hit up support for them but they just said it was "as designed" and wasn't going to be changed. Very frustrating 🙁

That's extremely unfortunate.

What model is the replacement you use, if you don't mind me asking? I might have to go a similar route, I have my own open ticket with Aten at the moment but I don't anticipate any different responses than you got.

Reply 12 of 13, by mattlacey

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dumpsterac1d wrote on 2022-02-19, 19:50:

What model is the replacement you use, if you don't mind me asking? I might have to go a similar route, I have my own open ticket with Aten at the moment but I don't anticipate any different responses than you got.

I'm not 100% sure as I've just moved a little over 10,000 miles and all of my gear is in storage right now, but doing some searches on Google Images I think this DLink model is the most likely candidate: https://www.amazon.co.uk/D-Link-DKVM-4K-KVM-S … h/dp/B0001FC5B6

I should have my hands on it again by the end of March or early April, will try and remember to report back once I do!

Reply 13 of 13, by dumpsterac1d

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mattlacey wrote on 2022-02-21, 09:49:
dumpsterac1d wrote on 2022-02-19, 19:50:

What model is the replacement you use, if you don't mind me asking? I might have to go a similar route, I have my own open ticket with Aten at the moment but I don't anticipate any different responses than you got.

I'm not 100% sure as I've just moved a little over 10,000 miles and all of my gear is in storage right now, but doing some searches on Google Images I think this DLink model is the most likely candidate: https://www.amazon.co.uk/D-Link-DKVM-4K-KVM-S … h/dp/B0001FC5B6

I should have my hands on it again by the end of March or early April, will try and remember to report back once I do!

Absolutely wild. After reading a lot of manuals and narrowing down, I now have an older D-Link on my desk! Just waiting for the cabling to come in from Monoprice!

Great news, if it does indeed do what it's supposed to.