lkml.org 
[lkml]   [1997]   [Aug]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: Keyboard error
Date
In article <Pine.LNX.3.96.970810224835.25559A-100000@entropy.muc.muohio.edu>,
George <greerga@entropy.muc.muohio.edu> wrote:
>This is probably a dumb question, but I've always wondered: If I hold down
>ENTER and K, and then hit F, I can get a 'keyboard error' for every single
>letter. Holding down ENTER and K and hitting D does not. Kernel is 2.1.36
>but I've seen it all the way back in 1.2.8. It's just a standard 101 key
>keyboard, doesn't even have a brand name on it. On an old 286-era Suntouch
>model keyboard on another machine with Linux 2.1.42 kernel I have to hold
>SHIFT, ENTER, K, and then hit F to do it. Both machines are Pentium class.
>
>Does the keyboard signal error or should the driver cope with that or
>should I just not do that?

The keyboard signals the error, and there is nothing the driver can do
about it. So yes, the answer is "don't do that, then".

The deeper reason for the error can be found in how the keyboard
physcially scans which keys are pressed. For reasons of economy, most
keyboards have a simple "scanning array" where a keypress shorts one
array corner (*). Depending on how the array is set up, pressing
multiple keys will not always work - and the exact keys that result in
breakage depend on the topology of the scanning array.

Many multi-key-presses will create a "shadow key press" (so when you
press three keys, the keyboard controller will actually think that
you're pressing four keys, and I suspect that the keyboard controller
just notices that two keys changed simulataneously and will consider
this an error.

The keyboard array is usually set up in such a way that the "normal"
keys that are often pressed together (alt, shift, cursor keys etc)
create as few of these shadows as possible, but you've obviously found
one of them. I suspect that you'll easily find more by just pressing
lots of keys at the same time..

You can probably fix this a few different ways:
- get a new, expensive keyboard. I can't guarantee it, but I suspect
the better keyboards will have much fewer of the shadow keys (maybe
they'll even have separate lines for each key instead of using an
array, who knows?)
- uncomment the kernel message. You probably don't really care, anyway.
- "don't do that, then". It's only likely to be a problem if you have
a game that requires the keys in question and you really want to
press them together.

(*) NOTE! It's been a _long_ time since I did any keyboard work, and I
can not guarantee that this is actually how the keyboard you have is
done. I suspect it is, but maybe PC keyboards of today are different
from what I remember. Who knows? On a PC, all the keyboard scanning
details are hidden by the keyboard controller, so what I remember from
doing the scanning by hand isn't necessarily true any more.

Linus

\
 
 \ /
  Last update: 2005-03-22 13:40    [W:0.042 / U:0.776 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site