KVM/Scroll Lock behavior

[milk]

As far as I know, the KVM switching should be hardware triggered. It should
not be related to X at all because it does not require any software at all.
If it did, then you wouldn't be able to switch inputs when no computers are
attached.

-milki

On Wed, Jan 18, 2012 at 20:07, Todd Pytel <tppytel at sophrosune.org> wrote:

> Hi all,
>
> I'm digging around at a quirk involving Scroll Lock and KVM switching
> that I think X is responsible for and hoping someone here can explain
> it. At this point I can work around it myself. But I'd really like to
> understand it, or perhaps provoke a change to make it work better for
> others less inclined to dig at this than I am.
>
> Like many other KVM's out there, mine triggers switches through double
> Scroll Lock taps. This has often required some fiddling to get working
> properly in the past, usually by adding Scroll_Lock to mod3 using
> xmodmap. But sometime recently, (I think) something changed in X11's key
> handling. A while back, my GNOME desktop stopped switching on Scroll
> Lock (even with the xmodmap) but still switched on Num Lock. Then it
> stopped working entirely in GNOME, XFCE, or Openbox.
>
> What I found after poking around some more tonight is that I can get the
> KVM trigger working by twiddling the LED's with xset...
>
> xset led 3 && sleep 0.2 && xset -led 3
>
> That toggles the LED's and triggers the KVM.
>
> In some sense, this solves my problem. I can put that in a script and
> bind it to a key. But I'd like to actually understand what's going on.
> Also, since Scroll Lock is the most common KVM trigger, it would be nice
> to fix this so that it "just works" for people with less enthusiasm for
> this sort of detective work. It seems like this shouldn't be an
> earth-shaking architectural change, but I admit I don't know jack about
> the internals of X.
>
> Specifically, here's what I see on Debian Sid...
>
> 1) In the console, Scroll Lock and KVM switching work properly with no
> tweaks.
>
> 2) In an untweaked X session, the Num Lock LED works while the Scroll
> Lock one does not. Both keys register in xev output.
>
> 3) After "xmodmap -e 'add mod3 = Scroll_Lock'", the Scroll Lock LED
> works. But it still doesn't trigger the KVM.
>
> 4) Even without the xmodmap line, twiddling the LED's via xset both
> toggles the LED's and triggers the KVM.
>
> What I'd really like to understand is what's different internally
> between toggling the LED via xset and doing it through an xmodmap'd
> Scroll Lock. Clearly the KVM is seeing those events differently and I
> don't know enough about X to understand why.
>
> If it's not too much of an undertaking, I'd also suggest that Scroll
> Lock should work as expected, or at least have an easy xorg.conf option
> to make it work as expected. A little Googling will show a decade's
> worth of posts across the web from KVM users trying to get their boxes
> to switch properly. And since the old xmodmap solution doesn't work
> anymore, it would be helpful to have a solution that doesn't involve
> hacky scripts and keybinding.
>
> Cheers!
> Todd
>
> _______________________________________________
> xorg at lists.x.org: X.Org support
> Archives: http://lists.freedesktop.org/archives/xorg
> Info: http://lists.x.org/mailman/listinfo/xorg
> Your subscription address: niteshadez at gmail.com
>



-- 
Hope is a dimension of the spirit. It is not outside us, but within us.
When you lose it, you must seek it again within yourself and in people
around you -- not in objects or even events.    -
-Vaclav Havel
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.x.org/archives/xorg/attachments/20120118/c4cc38fc/attachment.html>