Re: i8042 problem

["Maciej W. Rozycki" <macro@ds2.pg.gda.pl>]

On Mon, 28 Jul 2003, Andries Brouwer wrote:

> > > > Well, are timeouts needed at all?
> > > 
> > > Yes. We send a command to the keyboard. It may react, or it may not.
> > 
> >  But we need not wait for that actively.  If we are unsure about a result
> > of a command, then we may send a command in question followed with an echo
> > request.  This assures an IRQ will finally arrive and if no command
> > response arrives before an echo response, then the keyboard ignored the
> > command.  I used this approach many years ago to differ between PS/2
> > keyboards (which respond with 0xfa,0xab,0x83 to a request for ID) and
> > genuine PC/AT ones (which respond with lone 0xfa).  It worked. 
> 
> And what did you do for XT? :-)

 Nice joke, but I'll answer seriously.  No support was provided.  Hooking
a PC/XT keyboard to the 8042, if supported, requires a different setup of
the command byte and is possibly done by the system firmware.  You can
read the command byte to see which configuration is used.

 Wrt polling vs IRQ-driven probing and setup: using IRQ is a natural
choice as you have to do keyboard detection in the IRQ handler anyway to
properly support hot plugging of a PC/AT or a PS/2 keyboard. 

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +