[blfs-support] problem using BS or DEL key

Ken Moffat zarniwhoop at ntlworld.com
Thu Dec 5 14:01:00 PST 2013

On Thu, Dec 05, 2013 at 05:43:28PM +0100, Alexey Orishko wrote:
> On Thu, Dec 5, 2013 at 4:40 PM, Ken Moffat <zarniwhoop at ntlworld.com> wrote:
> >>
> >  This gets weirder and weirder.  Most of us don't have a stock of
> > different motherboards to play with, and I've no experience in this
> > area.  I think you said that showkey and dumpkeys reported the
> > keyboard was giving the expected values for the BS and DEL keys
> > even though they were giving white squares when you deleted, so in
> > theory the kernel drivers are ok.
> >
> >  Perhaps make a list of the values for _every_ key you use (with
> > showkey) with this drive on a "good" motherboard, and then put it
> > back on the bad motherboard and repeat the exercise just in case one
> > or more _other_ keys are somehow corrupted.
> Well, I only need to type english letter "k" and space to get into problems..
> While changing fonts I've noticed that white square boxes have inverted "y"
> with two dots over it.. Anyway, they appear on empty position of the
> command line (where no text was typed in).
 From memory, you said that k was involved when you specified that
you were NOT using unicode in the setup, so I'm inclined to ignore
that.  I thought your problem was that *deleting* characters on the
commandline caused spurious garbage to appear after it ?  If that is
wrong, ignore the rest of this reply and instead please restate the

 I still think my suggestion of checking every key will identify if
any of the keys are being garbled in the kernel, and therefore if
this is a kernel _input_ problem.

 But here is an alternative train of thought :

 When you trigger the garbage, is it really there, or only in the
screen output ?  Start a command with '#' so that it is treated as a
comment, type, do whatever you need to so that the spurious garbage
appears, then press enter.  And make a written note of exactly what
you typed, and a guide to what appeared and where it was on the
line, so that you can repeat the test.

 Then key enter again : does the garbage scroll up, so that the
current line is empty apart from the prompt ?

 Then key the up-arrow once to see the last line of history - is the
garbage there in the history ?

 If the garbage is only on the screen then I guess it _is_ a kernel
problem, but in the _video_ driver (i915 I suppose, but maybe you
compiled in vga).

 Conversely, if the garbage appears in the history then ignore the
rest of this mail.

 Your LatArCyrHeb font has two, possibly three, characters which
match a "white square".  If you manage to prove that it is a kernel
video problem, can you please "loadkeys LatGrkCyr-8x16" and repeat
the test.  I'm guessing you will get a capital T with a comma below
it (either U+021A or, in that font, U+0162), or a capital U with an
acute accent (U+00DA), or else a capital U with a breve (U+016C).
Knowing what appears might be useful if this is a bug in a video
driver.  I'll attach the text listing of that font - I'm guessing it
is one of character positions 210, 212, or 216.

 I base that paragraph on what 'showconsolefont' shows me.  If you
get a different character, or more than one, please attempt to
identify them against that listing.  You mentioned a different
character appeared when you tried other fonts, but there is no rule
about where any particular character is stored _within_ a console

 If it is a video-driver problem, please attach the relevant part of
your kernel config ("Graphics support", "I2C encoder or helper
chips" (in mine that is actually Direct Rendering Manager, possibly
because the I2C stuff is disabled and DRM doesn't have a heading),
"Frame buffer hardware drivers" and "Console display driver support"
- cut at "CONFIG_SOUND" which is the start of the sound drivers - they
don't have a neat heading comment.

 And, which kernel is this ?  At this point (for a video problem)
you should have a reliable and simple testcase to show if the system
has a problem.  Either I will suggest that you change the .config (it
is unfortunately very easy to create a config which doesn't work
properly) or else to try building older and newer released kernels.

das eine Mal als Tragödie, dieses Mal als Farce

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