Re: Can I expect in-kernel decoding to work out of box?

[Maxim Levitsky <maximlevitsky@gmail.com>]

On Wed, 2010-07-28 at 17:24 +0300, Maxim Levitsky wrote: 
> On Wed, 2010-07-28 at 10:13 -0300, Mauro Carvalho Chehab wrote: 
> > Em 28-07-2010 07:40, Jon Smirl escreveu:
> > > On Wed, Jul 28, 2010 at 2:30 AM, Maxim Levitsky <maximlevitsky@gmail.com> wrote:
> > >> On Tue, 2010-07-27 at 22:33 -0400, Jarod Wilson wrote:
> > >>> On Tue, Jul 27, 2010 at 9:29 PM, Jon Smirl <jonsmirl@gmail.com> wrote:
> > 
> > >> No its not, its just extended NEC.
> > > 
> > > http://www.sbprojects.com/knowledge/ir/nec.htm
> > > Says the last two bytes should be the complement of each other.
> > > 
> > > So for extended NEC it would need to be:
> > > 1100 0010 1010 0101 instead of 1100 0010 1010 0100
> > > The last bit is wrong.
> > > 
> > > From the debug output it is decoding as NEC, but then it fails a
> > > consistency check. Maybe we need to add a new protocol that lets NEC
> > > commands through even if they fail the error checks.
> > 
> > Assuming that Maxim's IR receiver is not causing some bad decode at the
> > NEC code, it seems simpler to add a parameter at sysfs to relax the NEC
> > detection. We should add some way, at the userspace table for those RC's
> > that uses a NEC-like code.
> > 
> > There's another alternative: currently, the NEC decoder produces a 16 bits
> > code for NEC and a 24 bits for NEC-extended code. The decoder may return a
> > 32 bits code when none of the checksum's match the NEC or NEC-extended standard.
> > 
> > Such 32 bits code won't match a keycode on a 16-bits or 24-bits table, so
> > there's no risk of generating a wrong keycode, if the wrong consistent check
> > is due to a reception error.
> > 
> > Btw, we still need to port rc core to use the new tables ioctl's, as cleaning
> > all keycodes on a 32 bits table would take forever with the current input
> > events ioctls.
> > 
> > > It may also be
> > > that the NEC machine rejected it because the timing was so far off
> > > that it concluded that it couldn't be a NEC messages. The log didn't
> > > include the exact reason it got rejected. Add some printks at the end
> > > of the NEC machine to determine the exact reason for rejection.
> > 
> > The better is to discard the possibility of a timing issue before changing
> > the decoder to accept NEC-like codes without consistency checks.
> > 
> > > The current state machines enforce protocol compliance so there are
> > > probably a lot of older remotes that won't decode right. We can use
> > > some help in adjusting the state machines to let out of spec codes
> > > through.
> > 
> > Yes, but we should take some care to avoid having another protocol decoder to
> > interpret badly a different protocol. So, I think that the decoders may have
> > some sysfs nodes to tweak the decoders to accept those older remotes.
> > 
> > We'll need a consistent way to add some logic at the remotes keycodes used by
> > ir-keycode, in order to allow it to tweak the decoder when a keycode table for
> > such remote is loaded into the driver.
> > 
> > > User space lirc is much older. Bugs like this have been worked out of
> > > it. It will take some time to get the kernel implementation up to the
> > > same level.
> > 
> > True.
> 
> 
> I more or less got to the bottom of this.
> 
> 
> It turns out that ENE reciever has a non linear measurement error.
> That is the longer sample is, the larger error it contains.
> Substracting around 4% from the samples makes the output look much more
> standard compliant.
> 
> You are right that my remote has  JVC protocol. (at least I am sure now
> it hasn't NEC, because repeat looks differently).
> 
> My remote now actually partially works with JVC decoder, it decodes
> every other keypress.
> 
> Still, no repeat is supported.
> 
> However, all recievers (and transmitters) aren't perfect.
> Thats why I prefer lirc, because it makes no assumptions about protocol,
> so it can be 'trained' to work with any remote, and under very large
> range of error tolerances.
> 
> Best regards,
> Maxim Levitsky
> 

I think I found the reason behind some of incorrect behavior.

I see that in-kernel decoding is unhappy about the way I process gaps.

I do exactly the same I did in lirc driver.

At the end of keypress, the driver receives series of spaces from
hardware.
I accumulate 'em until patience^Wtimeout runs out.
Then I put hardware in 'idle' mode, and remember current time.

As soon as I get new pulse, I send a sum of accumulated same and time
difference to user.

Therefore every keypress ends with a pulse, and starts with space.
But in-kernel decoding isn't happy about it, it seems.. at least NEC
decoder...

How you think to solve that?
Fix in-kernel decoders maybe?

Best regards,
Maxim  Levitsky