KVM Rollover Issues?

Discussion about old PC hardware.

KVM Rollover Issues?

Postby mattlacey » 2018-8-15 @ 02:15

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?
User avatar
mattlacey
Newbie
 
Posts: 8
Joined: 2016-7-23 @ 00:39
Location: Australia

Re: KVM Rollover Issues?

Postby Tiido » 2018-8-15 @ 10:40

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 lol.
User avatar
Tiido
Oldbie
 
Posts: 1004
Joined: 2018-1-14 @ 04:40
Location: Estonia

Re: KVM Rollover Issues?

Postby chinny22 » 2018-8-15 @ 14:48

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/ ... -04-16.pdf
User avatar
chinny22
l33t
 
Posts: 2403
Joined: 2011-8-26 @ 12:02
Location: Australian but living in the UK for now

Re: KVM Rollover Issues?

Postby mattlacey » 2018-8-16 @ 00:16

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!
User avatar
mattlacey
Newbie
 
Posts: 8
Joined: 2016-7-23 @ 00:39
Location: Australia

Re: KVM Rollover Issues?

Postby mattlacey » 2018-8-20 @ 05:16

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.
User avatar
mattlacey
Newbie
 
Posts: 8
Joined: 2016-7-23 @ 00:39
Location: Australia

Re: KVM Rollover Issues?

Postby mattlacey » 2018-9-10 @ 23:32

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.
User avatar
mattlacey
Newbie
 
Posts: 8
Joined: 2016-7-23 @ 00:39
Location: Australia

Re: KVM Rollover Issues?

Postby ElementalChaos » 2019-7-12 @ 01:03

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.
Pluto, the maxed out Dell Dimension 4100: Pentium III 1400S | 256MB | GeForce4 Ti4200 + Voodoo4 4500 | SB Live! 5.1
Charon, the DOS and early Windows time machine: K6-III+ 600 | 256MB | TNT2 Ultra + Voodoo3 2000 | Audician 32 Plus
User avatar
ElementalChaos
Member
 
Posts: 154
Joined: 2015-6-05 @ 01:36
Location: Illinois, USA

Re: KVM Rollover Issues?

Postby mattlacey » 2019-7-12 @ 01:41

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 :D
User avatar
mattlacey
Newbie
 
Posts: 8
Joined: 2016-7-23 @ 00:39
Location: Australia

Re: KVM Rollover Issues?

Postby SirNickity » 2019-7-12 @ 18:57

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.
SirNickity
Oldbie
 
Posts: 739
Joined: 2018-11-08 @ 04:51


Return to General Old Hardware

Who is online

Users browsing this forum: canthearu, Majestic-12 [Bot], Old PC Hunter, Qwantify [Bot] and 17 guests