From: Dmitry Torokhov <dtor_core@ameritech.net>
To: Andries Brouwer <aebr@win.tue.nl>
Subject: Re: [PATCH 24/44] Workaround i8042 chips with broken MUX mode
Date: Sat, 27 Mar 2004 22:11:09 -0500
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Cc: Vojtech Pavlik <vojtech@suze.cz>, torvalds@osdl.org, vojtech@ucw.cz,
       linux-kernel@vger.kernel.org
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On Saturday 27 March 2004 08:25 pm, Andries Brouwer wrote:
> On Sat, Mar 27, 2004 at 07:40:39PM -0500, Dmitry Torokhov wrote:
> 
> > > The Synaptics multiplexing proposal uses 0xf0, 0x56, 0xa4
> > > to activate and 0xf0, 0x56, 0xa5 to deactivate.
> > > In both cases the replies must be 0xf0, 0x56, version.
> > > 
> > > Thus, I suppose one might get a more robust detection
> > > by checking that both the activation and deactivation
> > > sequences yield the same version.
> > >
> > 
> > Unfortunately in this particular case it looks like something flips
> > 4th bit on some (but not all, like every 3rd) bytes, so it may very
> > well respond with 0xAC to both queries.
> 
> If one flips that bit on 0xa5 the result is 0xad, not 0xac.

Yes, you are right.

> 
> That the bit is set is not strange.
> The standard PS/2 protocol requires bit 3 in the first word of
> every 3-byte packet to be 1.

If it did it in every 3rd byte and not in response to loopback requiest
but to real data stream coming from a device I would agree...

-- 
Dmitry
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