Re: [BUG & PATCH] media/rc/ir-nec-decode : phantom keypress

["David Härdeman" <david@hardeman.nu>]

On 2014-06-12 13:22, Niels Laukens wrote:
> On 2014-06-12 12:42, David Härdeman wrote:
>> Hi,
> 
> Hi, thanks for the response
> 
> 
>> the problem with triggering a keypress as soon as 32 bits have been
>> received (i.e. before the trailing silence is detected)
> 
> Just for clarity: this patch does wait for the trailing silence. It 
> does
> NOT wait for the trailing silence to have (at least) a specific length.
> (The pulse event is only fired after the pulse has ended, because the
> length of the pulse needs to be known)

True.

Interpret "trailing silence" above as "silence long enough to indicate 
end of message" :)

>> is that it would
>> cause phantom keypresses on some other protocols (I'm thinking of 
>> NEC48,
>> which does exist in the wild).
> 
> I don't think the current code is able to decode NEC48.

No, but it would still be nice not to interpret a NEC48 signal as NEC32.

> Is NEC48 recognizable in some other way than just being longer?

IIRC, no.

> In that case, the alternative would be to start a timer when the
> TRAILING_SPACE is entered, and trigger the key-event after, say 2 
> bit-times.

Another alternative is fix the driver to implement a timeout so that 
"unreasonable" values are not generated (I saw a 240550us space in your 
log).

That's basically what the filtering version of the raw interface does 
(cf. the use of dev->timeout in ir_raw_event_store_with_filter()).

And it's what most of the popular hardware does. For instance, the 
mceusb hardware will send a USB packet with timings including that 
trailing silence. And the decoder can only do their work once a packet 
has arrived (which will contain a number of samples). That also 
demonstrates a potential problem with your suggested approach (i.e. 
timings can be buffered so calls to the decoders are not necessarily 
"real-time").

>> Now, the question is why the trailing silence isn't generated within a
>> reasonable time. Which hardware decoder do you use?
> 
> I use the IR receiver built in to the TBS6281 DVB-T tuner card. I also
> have a TBS6982 DVB-S card, but I guess it's the same hardware.

Which driver?

> It also depends on what "reasonable" means. I've found 300+ms, which is
> unusable long.

Agreed...

//David