linux-kernel - Re: IR raw input is not sutable for input system

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Date:	Wed, 25 Nov 2009 15:28:54 +0200
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	Trent Piepho <xyzzy@...akeasy.org>
Cc:	Jarod Wilson <jarod@...sonet.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Krzysztof Halasa <khc@...waw.pl>,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Jarod Wilson <jarod@...hat.com>, linux-kernel@...r.kernel.org,
	Mario Limonciello <superm1@...ntu.com>,
	linux-input@...r.kernel.org, linux-media@...r.kernel.org,
	Janne Grunau <j@...nau.net>,
	Christoph Bartelmus <lirc@...telmus.de>
Subject: Re: IR raw input is not sutable for input system

On Tue, 2009-11-24 at 19:32 -0800, Trent Piepho wrote: 
> On Wed, 25 Nov 2009, Maxim Levitsky wrote:
> >
> > Its not the case.
> > There are many protocols, I know that by experimenting with my universal
> > remote. There are many receivers, and all have different accuracy.
> > Most remotes aren't designed to be used with PC, thus user has to invent
> > mapping between buttons and actions.
> > Its is not possible to identify remotes accurately, many remotes send
> > just a 8 bit integer that specifies the 'model' thus many remotes can
> > share it.
> 
> The signal recevied by the ir receiver contains glitches.  Depending on the
> receiver there can be quite a few.  It is also not trivial to turn the raw
> signal sent by the remote into a digital value, even if you know what to
> expect.  It takes digital signal processing techniques to turn the messy
> sequence of inaccurate mark and space lengths into a best guess at what
> digital code the remote sent.
Exactly

> 
> It's like turning raw VBI data into decoded ASCII teletext from a simulated
> keyboard device, all in the kernel.
You hit a nail on the head with this one.


> 
> > Kernel job is to take the information from device and present it to
> > userspace using uniform format, that is kernel does 1:1 translating, but
> > doesn't parse the data.

> 
> One thing that could be done, unless it has changed much since I wrote it
> 10+ years ago, is to take the mark/space protocol the ir device uses and sent
> that data to lircd via the input layer.  It would be less efficient, but
> would avoid another kernel interface.  Of course the input layer to lircd
> interface would be somewhat different than other input devices, so
> it's not entirely correct to say another interface is avoided.
I agree with this one, but it is very optional.

I also want to add that lirc can and does behave just like an input
device. 
It sends the parsed events using uinput, so your remote appears just
like a keyboard.
It can even act like a mouse, and btw I use that feature, and it works
just fine.


So lets put lirc into the kernel finally?

Best regards,
Maxim Levitsky


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