David Härdeman wrote:
> On Tue, Apr 06, 2010 at 11:26:35AM -0300, Mauro Carvalho Chehab wrote:
>> Hi David,
>>
>> Em Tue, 6 Apr 2010 12:48:11 +0200
>> David Härdeman <david@xxxxxxxxxxx> escreveu:
>>
>>> Content-Type: text/plain; charset=us-ascii
>>> Content-Disposition: inline; filename=use-pulse-space-timings-in-ir-raw
>> Thunderbird 2 really don't like this. It considers the entire body as a file, and
>> refuses to quote it.
>
> Never had people complain when I use quilt before but I'll see what I
> can do.
Thanks. I'll also see if I can get some extension to thunderbird to fix it, or consider
moving (again) to another emailer.
>>> drivers/media/IR/ir-raw-event.c is currently written with the assumption that
>>> all "raw" hardware will generate events only on state change (i.e. when
>>> a pulse or space starts).
>>>
>>> However, some hardware (like mceusb, probably the most popular IR receiver
>>> out there) only generates duration data (and that data is buffered so using
>>> any kind of timing on the data is futile).
>> Am I understanding right and this hardware is not capable of indicating if the
>> event is a pulse or a space? It seems hard to auto-detect what is pulse or space,
>> but IMO such code should belong to mceusb driver and not to the decoders.
>
> No, the driver for mceusb sends a usb packet which contains a couple of
> pulse/space durations in the form of signed integers representing pulse
> (positive) and space (negative) durations in microseconds. It's a pretty
> common arrangement. winbond-cir also has a mode (which is the one I'm
> planning on using in the future) where pulse/space durations are
> accumulated in the UART buffer and an IRQ is generated once the buffer
> level reaches a threshold.
Ok.
>> Based on the code changes you did, I suspect that one of the things the hardware
>> provides is a "machine reset" state, right? If you just need to add a code to reset
>> the state machines, this could be done as easily as adding an event at kfifo with
>> IR_STOP_EVENT. A three line addition at the decoders event handler would be enough
>> to use it to reset the state machine:
>>
>> if (ev->type & IR_STOP_EVENT) {
>> data->state = STATE_INACTIVE;
>> return;
>> }
>>
>> This event were not added yet, since no hardware currently ported needs it. Eventually,
>> we may rename it to IR_RESET_STATE, if you think it is clearer.
>
> Not a particular state per se, I just added a function which the
> hardware can use to reset the state machines when necessary (think
> hardware reset, suspend/resume, switching from RX to TX and back again,
> etc).
>
> I think this:
>
> /* Hardware has been reset, notify ir-core */
> ir_raw_event_reset(input_dev);
>
> is a hell lot clearer than this (your current code):
>
> /* Hardware has been reset, notify ir-core */
> rc = ir_raw_event_store(input_dev, IR_STOP_EVENT);
> if (rc) {
> /* Uh oh, what do we do now? */
> ...
Ok. What about:
#define ir_raw_event_reset(input_dev) ir_raw_event_store(input_dev, IR_STOP_EVENT)
This will save some code and avoid one more symbol to be exported.
> }
> rc = ir_raw_event_handle(input_dev);
> if (rc) {
> /* Not again... */
> ...
> }
>
>>> This patch (which is not tested since I haven't yet converted a
>>> driver for
>>> any of my hardware to ir-core yet, will do soon) is a RFC on my proposed
>>> interface change...once I get the green light on the interface change itself
>>> I'll make sure that the decoders actually work :)
>> Yes, better to discuss before changing everything ;)
>>
>>> The rc5 decoder has also gained rc5x support and the use of kfifo's
>>> for
>>> intermediate storage is gone (since there is no need for it).
>> The RC-5X addition is welcome, but the better is to add it as a separate patch.
>
> Using durations (instead of a combination of struct timespec and enum
> raw_event_type) as the argument to the decoder necessitates rewriting
> most of the decoders, so it seemed like a good time to add it. RC5X or
> not will anyway only mean a couple of lines of difference but I can send
> it as a separate patch if that helps you.
Ok, thanks.
>> I won't comment every single bits of the change, since we're more interested on the conceptual
>> aspects.
>>
>>> -int ir_raw_event_store(struct input_dev *input_dev, enum raw_event_type type)
>> Don't remove the raw_event_store. It is needed by the hardware that gets events from
>> IRQ/polling.
>
> See the comments for kfifo below.
>
>> For sure another interface is needed, for the cases where the hardware
>> pass their
>> own time measure, like cx18 (http://linuxtv.org/hg/~awalls/cx23885-ir2/rev/2cfef53b95a2).
>>
>> For those, we need something like:
>>
>> int ir_raw_event_time_store(struct input_dev *input_dev, enum raw_event_type type, u32 nsecs)
>>
>> Where, instead of using ktime_get_ts(), it will use the timing provided by the hardware.
>
> Um, this sounds exactly like ir_raw_event_duration() which was the main
> point of my patch.
The better is to change rename the original function, passing the timestamp
as the original argument, and then add a function or a macro that adds the
get time logic, but see bellow.
>>> -int ir_raw_event_handle(struct input_dev *input_dev)
>>> +/**
>>> + * ir_raw_event_edge() - notify raw ir decoders of the start of a pulse/space
>>> + * @input_dev: the struct input_dev device descriptor
>>> + * @type: the type of the event that has occurred
>>> + *
>>> + * This routine is used to notify the raw ir decoders on the beginning of an
>>> + * ir pulse or space (or the start/end of ir reception). This is used by
>>> + * hardware which does not provide durations directly but only interrupts
>>> + * (or similar events) on state change.
>>> + */
>>> +void ir_raw_event_edge(struct input_dev *input_dev, enum raw_event_type type)
>>> {
>>> - struct ir_input_dev *ir = input_get_drvdata(input_dev);
>>> - int rc;
>>> - struct ir_raw_event ev;
>>> - int len, i;
>>> -
>>> - /*
>>> - * Store the events into a temporary buffer. This allows calling more than
>>> - * one decoder to deal with the received data
>>> - */
>>> - len = kfifo_len(&ir->raw->kfifo) / sizeof(ev);
>>> - if (!len)
>>> - return 0;
>> The removal of kfifo is not a good idea. On several drivers, the event is generated during
>> IRQ time, or on a very expensive polling loop. So, buffering is needed to release the
>> IRQ as soon as possible and not adding too much processing during polling.
>
> Have you seen any real case where this is a problem or is this just
> conjecture on your behalf? I've written ir decoders for embedded
> hardware which pass the "event" (duration) through the state machines
> directly and it works great on hardware with a fraction of the computing
> power compared to the machines you're using.
>
> The state machines shouldn't have to do much more than rounding of the
> duration followed by a couple of integer comparisons (and possibly some
> bitops). I fail to see how using a kfifo would provide any real
> improvement.
See the comments at the ML about the noise that the IR handling causes on several
devices. They interfere on applications behavior, cause excess of power consumption,
etc.
There are cases where you need have a timer to get 1ms samples, in order
to get the IR pulses on devices that don't use an IRQ line. There are lots
of reports of misc troubles caused by polling the device with high polling rates.
So, the minimal amount of time used to get the event, the better.
Btw, I think we'll end by needing to have protocol decoders that are capable
to handle just pulses, to avoid adding the extra penalty of doubling the
sampling rate on such devices. Maybe the better would be to have two versions
of the most popular decoders (NEC, RC-5), one pulse only and the other pulse/space,
in order to support those hardware. This would probably be better than adding
a more complex logic to handle both cases at the same state machine.
In the specific case of hardware-driven events like the mceusb, maybe we can
have two different implementations: one for the cases where the sampling needs to
be done in software, via kfifo, and another one where the hardware is passing a
buffer of events, so, there's no need to double buffering.
I've already added a driver_type field to distinguish between pure hardware IR
decoders and pure software IR decoders:
http://git.linuxtv.org/mchehab/ir.git?a=commitdiff;h=5b023d2cd652ef42ab8e836cad8d6f077819b83a
So, we may add another driver_type there for the cases where the hardware generates samples.
>>> -
>>> - for (i = 0; i < len; i++) {
>>> - rc = kfifo_out(&ir->raw->kfifo, &ev, sizeof(ev));
>>> - if (rc != sizeof(ev)) {
>>> - IR_dprintk(1, "overflow error: received %d instead of %zd\n",
>>> - rc, sizeof(ev));
>>> - return -EINVAL;
>>> - }
>>> - IR_dprintk(2, "event type %d, time before event: %07luus\n",
>>> - ev.type, (ev.delta.tv_nsec + 500) / 1000);
>>> - rc = RUN_DECODER(decode, input_dev, &ev);
>>> - }
>>> + struct ir_input_dev *ir = input_get_drvdata(input_dev);
>>> + ktime_t now;
>>> + s64 delta; /* us */
>>> +
>>> + if (!ir->raw)
>>> + return;
>>>
>>> - /*
>>> - * Call all ir decoders. This allows decoding the same event with
>>> - * more than one protocol handler.
>>> - */
>>> + now = ktime_get();
>>> + delta = ktime_us_delta(now, ir->raw->last_event);
>>
>> This won't work, in the cases where the hardware is providing its own
>> timings.
>
> Again, see ir_raw_event_duration()
>
>>>
>>> - return rc;
>>> + /* Check for a long duration since last event or if we're
>>> + being called for the first time */
>>> + if (delta > USEC_PER_SEC || !ir->raw->last_type)
>>> + type |= IR_START_EVENT;
>> The "long duration" concept would be better implemented at the driver, since it may
>> vary with the IR carrier and with the protocol details.
>
> Now you're criticizing your own code...this was one of the few concepts
> I carried over from your original code. Specifically, ir-raw-event.c,
> lines 116 - 129 from your current tree:
>
> ktime_get_ts(&ts);
>
> if (timespec_equal(&ir->raw->last_event, &event.delta))
> event.type |= IR_START_EVENT;
> else
> event.delta = timespec_sub(ts, ir->raw->last_event);
>
> memcpy(&ir->raw->last_event, &ts, sizeof(ts));
>
> if (event.delta.tv_sec) {
> event.type |= IR_START_EVENT;
> event.delta.tv_sec = 0;
> event.delta.tv_nsec = 0;
> }
>
> (Note the check on event.delta.tv_sec)
Ok, you beat me on that ;)
The above code is there just to simplify the decoders logic, as no IR
protocol accept a valid delay of 1 sec. So, basically, the decoders
don't need to use tv_sec. This simplified the decoders logic.
An obvious cleanup would be to just send tv_nsec to the decoders, saving
4 bytes/event at the kfifo, by not sending tv_sec.
>>> +
>>> + if (type & IR_START_EVENT)
>>> + ir_raw_event_reset(input_dev);
>>> + else if (ir->raw->last_type & IR_SPACE)
>>> + ir_raw_event_duration(input_dev, (int)-delta);
>>> + else if (ir->raw->last_type & IR_PULSE)
>>> + ir_raw_event_duration(input_dev, (int)delta);
>> Please, don't use a signal to identify between pulse and space. The IR decoding logic
>> is tricky enough. Just pass the type to the decoder and let it explicitly check if it is
>> pulse or space.
>
> No idea what you mean here. Why would it be clearer to put the
> equivalent code in every single decoder instead of adding it once to the
> place which calls the decoders?
I mean: Just use IR_SPACE/IR_PULSE at the decoders, instead of a signal.
>>> Index: ir/drivers/media/IR/ir-nec-decoder.c
>>> ===================================================================
>>> --- ir.orig/drivers/media/IR/ir-nec-decoder.c 2010-04-06 12:16:27.000000000 +0200
>>> +++ ir/drivers/media/IR/ir-nec-decoder.c 2010-04-06 12:17:08.860846045 +0200
>>> @@ -14,22 +14,25 @@
>>>
>>> #include <media/ir-core.h>
>>>
>>> +/*
>>> + * Regarding NEC_HEADER_MARK: some NEC remotes use 16, some 8,
>>> + * some receivers are also good at missing part of the first pulse.
>>> + */
>> The NEC decoder improvements should be on a separate patch.
>
> They can't since the entire patch is about changing the core raw logic
> over to primarily use durations, which means the existing nec and rc5
> decoders need to change in the same patch or bisectability will be
> broken.
I mean: if you're changing the state machine to support the "missing part of
the first pulse", this specific improvement would be on a separate patch,
as it might cause regressions (the same comments I did for the RC5X applies here).
>>> #define NEC_NBITS 32
>>> -#define NEC_UNIT 559979 /* ns */
>>> -#define NEC_HEADER_MARK (16 * NEC_UNIT)
>>> -#define NEC_HEADER_SPACE (8 * NEC_UNIT)
>>> -#define NEC_REPEAT_SPACE (4 * NEC_UNIT)
>>> -#define NEC_MARK (NEC_UNIT)
>>> -#define NEC_0_SPACE (NEC_UNIT)
>>> -#define NEC_1_SPACE (3 * NEC_UNIT)
>>> +#define NEC_UNIT 562 /* us */
>> Why changing to microseconds? ktime_t also handles time on nanosseconds.
>
> Interesting question but you managed to turn it on its head. Why not use
> femtoseconds? Because it's complete and utter overkill. Not a single IR
> protocol needs that kind of precision. Both LIRC and the Microsoft IR
> API's are based on microseconds. Programmable IR hardware (like the
> Philips Pronto) is based on microseconds. The proper question to ask is
> why you'd use nanoseconds...
Because the high precision timers (ktime_t, timeval) in Linux are currently based
on nanoseconds. The worst case we have are the devices that need to be polled
to generate a sample for every (IR unit) / 2. We need to focus on saving CPU cycles
at the sampling event logic for those. By not converting it to something else,
we save one division at the event collect.
As Andy explained, it happens that cx18 also sends data in nanoseconds, so
whatever decision taken, some of the devices with in-hardware samplers will
need to convert to whatever used in Kernel.
>
>>> +#define NEC_HEADER_MARK 6
>>> +#define NEC_HEADER_SPACE -8
>>> +#define NEC_REPEAT_SPACE -4
>>> +#define NEC_MARK 1
>>> +#define NEC_0_SPACE -1
>>> +#define NEC_1_SPACE -3
>> Those negative values here is really weird... I can't stop thinking on time
>> travels, when I see a negative time ;)
>
> Better get used to it, if you're going to maintain ir-core you're going
> to see it in mailing list discussions once ir-core gains a userbase.
>
>> Seriously, this change obfuscates the logic, as it is using the mantissa of a number
>> to indicate a time duration, and the signal to indicate the presence or absence of
>> a carrier. Encoding two different measures into a number is not a good thing. I used
>> to do such tricks when programming in Z80 assembly, back on eighties, basically
>> due to the absolute lack of enough memory on those machines with a few kilobytes of RAM.
>> After a few weeks, returning back to the same code to fix were really hard. We don't have
>> such memory constraints anymore. So, let's keep the code as clearer as possible.
>
> Describing a received ir signal as a number of signed integers
> describing the duration of pulses (positive) and spaces (negative) in
> microseconds is pretty much standard (to the extent that any standard
> exists) in any discussion of IR protocols.
>
> The decoders Jon Smirl implemented used signed integers, the decoders
> I've implemented use signed integers. Microsoft's IR API uses signed
> integers. LIRC uses signed integers (kinda, 23 bits of microsecond
> duration, one bit for pulse or space - as far as I can remember from
> LIRC_MODE_MODE2). Other projects also use it (e.g. the developers of
> decodeir.dll which is probably one of the most used IR API's on the MS
> platform outside of Microsoft's own API).
>
> Instead you want to go with a model where you pass in total three
> arguments to the decoders (struct timespec with nsec and sec + enum
> type). I do not understand how you would consider this clearer or
> better.
There are two arguments only: time and type. No matter how encoded,
they'll be there. So, it is just a matter of better representing it.
As pulse/mark can be distinguished by just one bit, and negative time is
meaningless, I can understand why hardware developers will use a signal
bit to pass this information from the hardware to the OS: this saves one
register on a limited hardware. It is a pretty common practice of abusing
the signal bits in assembler, on similar cases.
Yet, on some moment, this will need to be splitted into time and type again.
One of the main characteristics of Linux development is that the code should
be easy to be read, in order to allow its maintainable by the community. So,
the less obfuscated the code, the better.
For an IR expert, this might be clear that it represents 8 units of space:
#define NEC_HEADER_SPACE -8
but, for most, this is just a negative magic number.
On the other hand, by looking at:
#define NEC_HEADER_SPACE (8 * NEC_UNIT)
All developers will understand that this represents 8 units of space.
>> I've stripped the decoders code, since they're basically implementing
>> the architectural
>> changes you're proposing Let's first finish the discussions about the changes.
>>
>> Btw, I noticed that you've added some improvements to the decoders, like the
>> changes to support RC-5X. The better is to send it as a separate patch, due to a few reasons:
>>
>> - RC-5X addition has nothing to do with "Teach drivers/media/IR/ir-raw-event.c
>> to use durations" (the subject of this RFC patch);
>>
>> - Bigger patches have more chances of getting nacked, since they touch on more parts
>> of the code. So, you'll need to rework more code;
>>
>> - The addition of RC-5X shouldn't break RC-5. By having it as a separate patch,
>> it is easier to test the changes;
>>
>> - If later discovered a regression, it would be easier to bisect and see if the
>> changes were introduced by RC-5X or by the architectural changes, if the changes are broken
>> into two patches.
>>
>
> I've already addressed RC5X above.
Ok.
>>> -static unsigned int ir_rc5_remote_gap = 888888;
>> The idea of static int is that, on saa7134, this value can be adjustable from userspace.
>> probably, some hardware use a non-standard carrier, so we'll need to export it also
>> via sysfs, to avoid regressions.
>
> The decoders in my patch have a +/-50% tolerance for pulse/space unit
> durations, if it turns out to be insufficient, then it's time to look at
> solutions, doing it now is premature.
Yes, the current ir-r5-decoder already have this tolerance.
The saa7134-input RC-5 decoder has a problem: it counts events durations from the start
event. So, if the frequency is shifted, the probability of having a decoding error
on the last bit is higher than the probability of a decoding error on the first bit.
Maybe that's why this parameter was needed.
Ok, let's convert it into a constant for now.
--
Cheers,
Mauro
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