Re: [RFC3] Teach drivers/media/IR/ir-raw-event.c to use durations

[Mauro Carvalho Chehab <mchehab@infradead.org>]

Andy Walls wrote:
> On Sat, 2010-04-10 at 08:48 +0200, David Härdeman wrote:
>> On Fri, Apr 09, 2010 at 11:00:41AM -0300, Mauro Carvalho Chehab wrote:
>>> struct {
>>> 	unsigned mark : 1;
>>> 	unsigned duration :31;
>>> }
>>>
>>> There's no memory spend at all: it will use just one unsigned int and it is
>>> clearly indicated what's mark and what's duration.
>> If all three of you agree on this approch, I'll write a patch to convert 
>> ir-core to use it instead.
> 
> I'm OK with it.
> 
> I haven't been paying close attention,so I must ask: What will the units
> of duration be?
> 
> a. If we use nanoseconds the max duration is 2.147 seconds.
> 
> If passing pulse measurments out to LIRC, there are cases where irrecord
> and lircd want the duration of the long silence between the
> transmissions from the remote. Do any remotes have silence periods
> longer than 2.1 seconds?
> 
> b. If we use microseconds, the max duration is 214.7 seconds or 3.6
> minutes.  That's too high to be useful.
> 
> c.  Something in between, like 1/8 (or 1/2, 1/4, or 1/10) of a
> microsecond?  1/8 gives a max duration of 26.8 seconds and a little
> extra precision.

(c) is really ugly.

(b) max limit is too high. Currently, the core assumes that everything longer
than one second is enough to re-start the state machine. So, I think (a)
is the better option.

Another way to see it: it is not reasonable for someone to press a key and wait
for 2.1 seconds to see one bit of the key to be recognized.

So, IMHO, let's just use nanoseconds with 31 bits. the sampling event function
should check for ktime value: if bigger than 2^32-1, then assume it is a
long event, resetting the state machine.

Cheers,
Mauro