[Arm-netbook] EOMA-68 laptop Keyboard support improvement pushed

[Albert ARIBAUD]

Le Sun, 31 Jul 2016 21:56:13 +0100
Luke Kenneth Casson Leighton <lkcl at lkcl.net> a écrit:

> > Hmm... Not getting what you're hinting at. Can you develop?  
> 
>  it's related to mis-detection of keys.  if you press certain
> combinations in certain ways, you get "ghost" keys that you can't tell
> if they were actually pressed or not.  by reducing the number of keys
> that are "live" (16 fan-in only activates up to 8 maximum where as 8
> fan-in could activate up to 16 maximum) you reduce the possibility of
> "ghosting".
>
>  there was an article online about it... ah!  found it:
> http://pcbheaven.com/wikipages/How_Key_Matrices_Works/

Ok, got your point now.

Too late today to do probabilities (heck, even in the morning right
after my coffee shot I would not trust my skills in probabilities).
Still, I intuitively (yeah, I know) think there is no reduction in the
risk of ghosting when transposing the matrix, because there is no
asymmetry in the ghosting problem; ghosting occurs as soon as three of
the four connections between two rows and two columns are closed: at
that point, there is no way to tell whether the fourth connection is
open or closed, and this, regardless of any notion of "row", "column",
or "activity".

IOW, whether or not a given state of the keyboard matrix will exhibit
ghosting is only defined by the distribution of the depressed keys on
the matrix, not by the rotation with which we look at that matrix or
whether it currently has an active column.

Amicalement,
-- 
Albert.