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

[Albert ARIBAUD]

Le Mon, 1 Aug 2016 01:15:43 +0100
Luke Kenneth Casson Leighton <lkcl at lkcl.net> a écrit:

>  my point is: if you've activated 2x the amount of keys because you're
> firing on "rows" (16 activated) instead of "columns (only 8
> activated), there's now 2x the chance of having a "ghosting" problem.

*At a given time*, yes, you may think that one active column crossing 16
rows runs twice more chances of ghosting than if it only crosses 8 rows;
but then, *over the course of a whole scan*, 16 columns run twice more
chances of ghosting than 8 columns do; it cancels out.

Or you can consider this exercize:

Consider our QWERTY laptop keyboard's columns 8 and 9 and rows 2 and 3.
Here they are represented with the keys at their intersections :


                8           9
                |           |
                |           |
          KEY_E |           | KEY_O
----------------X-----------X------------ 2
                |           |
                |           |
                |           |
          KEY_3 |         D | KEY_9
---------------- -----------X------------ 3
                |           |
                |           |
                |           |

The "X" marks at intersections denote a depressed key, which connects
its row and column; so in the example above, the three keys E, O and 9
are depressed.

First exercize: let's "activate" column 8 and read rows 2 and 3,
"Activating" column 8 means pulling it down hard, which drags row 2
down, which drags column 9 down, which drags row 3 down, so we read
both rows 2 and 3 down and conclude that keys E and 3 are down: key
3 is ghosted.

Second exercize: same keyboard with same depressed keys, but instead of
activating column 8 and reading rows, we activate row 3 and read
columns. Pulling row 3 down hard drags column 9 down, which drags row 2
down, which drags column 8 down, so we read both columns 8 and 9 down
and conclude that keys 3 and 9 are down: key 3 is ghosted.

You can try this exhaustively if you like: for every keyboard state
defined by which of its keys are down, you will end up with exactly the
same set of ghosted keys whether you activate columns and read rows
or activate rows and read columns.

>  i think.
>
>  too much for my brain to cope with....

:)

Amicalement,
-- 
Albert.