Re: [PATCH 24/44] Workaround i8042 chips with broken MUX mode
From: Dmitry Torokhov
Date: Sat Mar 27 2004 - 22:12:21 EST
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...
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