Re: some keys not seen in xev(1) when pressed in combination with both Alt_L and Alt_R

["Jonathan A. Kollasch" <jakllsch%kollasch.net@localhost>]

On Thu, Dec 26, 2013 at 01:35:12PM +0100, Michai Ramakers wrote:
> Hello,
> 
> first of all, I am not well versed in xmodmap(1) or general key
> handling whatsoever.
> 
> I would like to use specific key combinations in the window manager I
> use ('herbstluftwm' - but I think this is irrelevant in this post),
> but failed. One of those key combinations is 'left Alt + right Alt +
> h'.
> 
> After starting X11 without window manager but only an xterm instead,
> and running xev(1), I noticed that
>   1) either Alt-key shows a pressed/released events,
>   2) the 'h' key in combination with either Alt-key shows events,
>   3) the 'h' key in combination with both Alt-keys at once does not show 
> events
> 
> Pressing more letter-keys while both Alt-keys were pressed, showed
> that on this particular system (Dell Latitude C840), keys 'g', 'h',
> 'b' and 'n' out of 'a'-'z' did not generate events with both Alt_L and
> Alt-R pressed.
> 
> Repeating this test with an external USB keyboard showed the same
> results. Repeating this test on another system (VIA Epia something)
> showed that about 50% of the letter-keys would not generate events in
> combination with both Alt-keys pressed.
> 
> As far as I could tell, all letter-keys generate events when used with
> any combination of left-hand Ctrl, Alt and Shift. So that's what I'll
> use for now, then.
> 
> Does anyone know an explanation for this behaviour? The reason I would
> like to use both Alt-keys simultaneously, is that I can assign those
> particular combinations to the window manager, leaving Alt+letterkey
> combinations available for applications.

The "Multiple Key Operation Requirements" section of the "Keyboard Scan
Code Specification" (from Microsoft) does not require that 3-key
combinations involving LALT and RALT work.

        Jonathan Kollasch