patch to make drivers/media/rc/ir-rc5-decoder more responsive
From: Stephane Chauveau
Date: Tue Apr 09 2013 - 19:20:52 EST
Hi,
I recently installed a linux based media-center (using XBMC) and I was
quite disappointed but the IR remote. It feels slugish and not very
reliable (unexpected key repeats, ...).
I studied the whole infrastructure (kernel, xorg, xbmc, ...) and found
issues a bit everywhere but the main culprit seems to be the rc decoder
modules.
I focussed on the RC-5 protocol because it is quite simple. Most of the
information below should also be applicable to other decoders. The RC-6
decoder clearly suffers from the same problems.
Here is a patch for the ir-rc5-decoder module with the following
characteristics:
- The keydown event occurs after decoding the first half of the last
bi-phase bit.
- An explicit keyup event is sent (if possible) by the rc5 decoder
instead of waiting for the 250ms timeout in rc-main.
Compared to the original decoder, the first keydown event occurs 100ms
to 200ms earlier and the final keyup event occurs 200ms to 250ms earlier.
The patch is for linux 3.5.0 (sorry that is my current kernel on ubuntu).
A more complete analysis of the problems is after the patch
======================================
--- drivers/media/rc/ir-rc5-decoder.c.old 2013-04-10
00:34:08.000000000 +0200
+++ drivers/media/rc/ir-rc5-decoder.c 2013-04-10 00:33:00.000000000 +0200
@@ -30,11 +30,16 @@
#define RC5_BIT_START (1 * RC5_UNIT)
#define RC5_BIT_END (1 * RC5_UNIT)
#define RC5X_SPACE (4 * RC5_UNIT)
+#define RC5_UP_DELAY 114000000 /* ns */
+
+#define VERB 0
enum rc5_state {
STATE_INACTIVE,
STATE_BIT_START,
STATE_BIT_END,
+ STATE_LAST_START,
+ STATE_LAST_END,
STATE_CHECK_RC5X,
STATE_FINISHED,
};
@@ -52,8 +57,8 @@ static int ir_rc5_decode(struct rc_dev *
u8 toggle;
u32 scancode;
- if (!(dev->raw->enabled_protocols & RC_TYPE_RC5))
- return 0;
+ if (!(dev->raw->enabled_protocols & RC_TYPE_RC5))
+ return 0;
if (!is_timing_event(ev)) {
if (ev.reset)
@@ -99,8 +104,8 @@ again:
if (!is_transition(&ev, &dev->raw->prev_ev))
break;
- if (data->count == data->wanted_bits)
- data->state = STATE_FINISHED;
+ if (data->count == data->wanted_bits-1)
+ data->state = STATE_LAST_START;
else if (data->count == CHECK_RC5X_NBITS)
data->state = STATE_CHECK_RC5X;
else
@@ -109,22 +114,16 @@ again:
decrease_duration(&ev, RC5_BIT_END);
goto again;
- case STATE_CHECK_RC5X:
- if (!ev.pulse && geq_margin(ev.duration, RC5X_SPACE, RC5_UNIT /
2)) {
- /* RC5X */
- data->wanted_bits = RC5X_NBITS;
- decrease_duration(&ev, RC5X_SPACE);
- } else {
- /* RC5 */
- data->wanted_bits = RC5_NBITS;
- }
- data->state = STATE_BIT_START;
- goto again;
-
- case STATE_FINISHED:
- if (ev.pulse)
+ case STATE_LAST_START:
+ if (!eq_margin(ev.duration, RC5_BIT_START, RC5_UNIT / 2))
break;
+ data->bits <<= 1;
+ if (!ev.pulse)
+ data->bits |= 1;
+ data->count++;
+ data->state = STATE_LAST_END;
+
if (data->wanted_bits == RC5X_NBITS) {
/* RC5X */
u8 xdata, command, system;
@@ -152,6 +151,42 @@ again:
}
rc_keydown(dev, scancode, toggle);
+
+ return 0;
+
+ case STATE_LAST_END:
+ if (!is_transition(&ev, &dev->raw->prev_ev))
+ break;
+
+ data->state = STATE_FINISHED;
+
+ decrease_duration(&ev, RC5_BIT_END);
+ goto again;
+
+ case STATE_CHECK_RC5X:
+ if (!ev.pulse
+ && geq_margin(ev.duration, RC5X_SPACE, RC5_UNIT/2)) {
+ /* RC5X */
+ data->wanted_bits = RC5X_NBITS;
+ decrease_duration(&ev, RC5X_SPACE);
+ } else {
+ /* RC5 */
+ data->wanted_bits = RC5_NBITS;
+ }
+ data->state = STATE_BIT_START;
+ goto again;
+
+ case STATE_FINISHED:
+ if (ev.pulse)
+ break;
+
+ /* The message is repeated RC5_UP_DELAY ns after the 1st pulse
+ * so a blank of RC5_UP_DELAY ns after the last pulse shall be
+ * enough to assume that the message is not repeated.
+ */
+ if (ev.duration > RC5_UP_DELAY)
+ rc_keyup(dev) ;
+
data->state = STATE_INACTIVE;
return 0;
}
Signed-off-by: Stephane Chauveau <stephane@xxxxxxxxxxxxxxxxxxxx>
========================================
I added a few printk in the module to obtain some detailed timings.
- DECODE is emited once at the begining of each call of
ir_rc5_decode() to describe the associated event
- FINISHED is emited during the last STATE_BIT_END when setting the
state to STATE_FINISHED
- KEYDOWN is emited just before calling rc_keydown()
- KEYUP is emited by ir_do_keyup() in rc-main.c
Here are the timings for a single even RC-5 message (last bit is 0 so a
blank followed by a pulse) using the original module:
[507703.409737] DECODE +20 (1788us)
[507703.412097] DECODE -19 (1762us)
[507703.413282] DECODE +20 (1788us)
[507703.415622] DECODE -19 (1762us)
[507703.416822] DECODE +19 (1762us)
[507703.419159] DECODE -20 (1788us)
[507703.420357] DECODE +20 (1779us)
[507703.421523] DECODE -9 (885us)
[507703.422691] DECODE +10 (894us)
[507703.423869] DECODE -19 (1771us)
[507703.426239] DECODE +20 (1788us)
[507703.427406] DECODE -19 (1762us)
[507703.428639] DECODE +10 (894us)
[507703.429772] DECODE -9 (877us)
[507703.429779] DECODE +10 (894us)
[507703.430946] DECODE -9 (885us)
[507703.432131] DECODE +10 (894us)
[507703.432138] FINISHED
[507703.631331] DECODE -2255 (200317us)
[507703.631338] KEYDOWN
[507703.880020] KEYUP
The last DECODE of 200ms seems to be caused the timeout in the IR driver
(see ITE_IDLE_TIMEOUT in ite_cir.h).
The final STATE_BIT_END is processed before that long event is received
but, because of the test after the 'goto again', the final
STATE_FINISHED is delayed until the 200ms blank is received.
The timings are similar for an odd RC-5 code (last bit is 1 so a pulse
followed by a blank)
[508157.054735] DECODE +19 (1762us)
[508157.055906] DECODE -10 (929us)
[508157.057098] DECODE +9 (868us)
[508157.057107] DECODE -10 (911us)
[508157.058259] DECODE +9 (842us)
[508157.060730] DECODE -20 (1823us)
[508157.061800] DECODE +19 (1762us)
[508157.064167] DECODE -20 (1788us)
[508157.065341] DECODE +19 (1727us)
[508157.066507] DECODE -10 (937us)
[508157.067686] DECODE +9 (868us)
[508157.068932] DECODE -19 (1771us)
[508157.071227] DECODE +20 (1779us)
[508157.072423] DECODE -20 (1797us)
[508157.073588] DECODE +9 (842us)
[508157.074759] DECODE -10 (929us)
[508157.075937] DECODE +19 (1736us)
[508157.275149] DECODE -2252 (200039us)
[508157.275156] FINISHED
[508157.275159] KEYDOWN
[508157.524021] KEYUP
Here, the final STATE_BIT_END is a blank so it is processed as part of
the final timeout.
In any cases, the KEYDOWN in STATE_FINISHED occurs after the 200ms
timeout so about 220ms after the first pulse.
Finally, the KEYUP occurs 250ms after the KEYDOWN because of the timeout
in rc-main.c (see IR_KEYPRESS_TIMEOUT)
The situation is slightly different when the button remains pressed
because the remote repeats the message after 113ms as required by the
RC-5 protocol:
[507866.803970] DECODE +20 (1831us)
[507866.805169] DECODE -9 (825us)
[507866.806330] DECODE +10 (894us)
[507866.806339] DECODE -10 (911us)
[507866.807511] DECODE +10 (955us)
[507866.809874] DECODE -19 (1736us)
[507866.811043] DECODE +19 (1701us)
[507866.813413] DECODE -21 (1875us)
[507866.814893] DECODE +18 (1675us)
[507866.815758] DECODE -10 (937us)
[507866.817038] DECODE +9 (868us)
[507866.818110] DECODE -20 (1823us)
[507866.820479] DECODE +20 (1788us)
[507866.821646] DECODE -19 (1762us)
[507866.822818] DECODE +9 (816us)
[507866.823989] DECODE -10 (937us)
[507866.823994] DECODE +9 (842us)
[507866.825244] DECODE -10 (963us)
[507866.826358] DECODE +9 (868us)
[507866.826364] FINISHED
[507866.915932] DECODE -1009 (89664us)
[507866.915938] KEYDOWN
[507866.917121] DECODE +19 (1753us)
[507866.918286] DECODE -10 (963us)
[507866.919463] DECODE +9 (842us)
[507866.920685] DECODE -10 (911us)
[507866.920696] DECODE +10 (894us)
[507866.922999] DECODE -20 (1797us)
[507866.924181] DECODE +19 (1727us)
[507866.926530] DECODE -20 (1797us)
[507866.927705] DECODE +20 (1840us)
[507866.928912] DECODE -9 (825us)
[507866.930067] DECODE +9 (842us)
[507866.931238] DECODE -20 (1823us)
[507866.933611] DECODE +20 (1788us)
[507866.934778] DECODE -19 (1762us)
[507866.935954] DECODE +9 (868us)
[507866.937150] DECODE -10 (937us)
[507866.938305] DECODE +9 (816us)
[507866.938310] DECODE -10 (963us)
[507866.939484] DECODE +10 (894us)
[507866.939488] FINISHED
[507867.139873] DECODE -2264 (201081us)
[507867.139880] KEYDOWN
[507867.388021] KEYUP
The long 200ms blank is replaced by a 90ms blank so the first DECODE
occurs earlier and repeats itself every 113ms as long as the remote
keeps sending messages.
The last message is processed as a single message and takes about 470ms:
- about 20ms for decoding the message itself.
- 200ms for the ITE_IDLE_TIMEOUT timeout until KEYDOWN.
- 250ms for the IR_KEYPRESS_TIMEOUT timeout until KEYUP.
To summarize, the first KEYDOWN occurs 113ms or 220ms after the first
pulse and the final KEYUP occurs 450ms after the last pulse. This is
qite bad!
The delay between the first KEYDOWN and final KEYUP is about 470ms for a
double message and 580ms for a triple message.
I found that triple messages are quite common and they are likely to
cause at least one key repeat on most systems: the key repeat delay is
hard-coded to 500ms in XBMC which makes the remove almost unusable. This
is also the current key-repeat value on my XFCE desktop.
My patch improves those timings using 2 techniques.
First, the KEYDOWN is sent immediately after receiving the first half of
the last bit.
Second, ITE_IDLE_TIMEOUT=200ms is longer than the required delay for
repeated messages in RC5 (113ms) so it is possible to explicitly send
the KEYUP event as soon as a long blank is received. This is controlled
by the macro RC5_UP_DELAY. An even better approach could be to
accumulate the duration of all pulses and space until 113ms is reached
but in practice waiting for a long blank seems to be good enough.
With my patch, the timings for a single event look like that
[503403.889246] DECODE +19 (1753us)
[503403.890415] DECODE -11 (990us)
[503403.890421] DECODE +8 (790us)
[503403.891603] DECODE -10 (955us)
[503403.893012] DECODE +9 (816us)
[503403.895133] DECODE -20 (1849us)
[503403.896326] DECODE +19 (1701us)
[503403.898669] DECODE -20 (1849us)
[503403.899885] DECODE +19 (1701us)
[503403.901041] DECODE -10 (963us)
[503403.902201] DECODE +9 (807us)
[503403.903375] DECODE -21 (1884us)
[503403.905749] DECODE +18 (1675us)
[503403.906912] DECODE -20 (1849us)
[503403.908099] DECODE +9 (816us)
[503403.909281] DECODE -10 (963us)
[503403.909289] DECODE +9 (816us)
[503403.910440] DECODE -10 (963us)
[503403.910444] KEYDOWN
[503403.911660] DECODE +10 (894us)
[503403.911670] FINISHED
[503404.110830] DECODE -2255 (200256us)
[503404.110842] KEYUP
The KEYDOWN and the KEYUP respectively occur 20ms and 220ms after the
first pulse (versus 220ms and 470ms with the original module)
For a double message the timings are
[503489.269908] DECODE +20 (1788us)
[503489.271076] DECODE -9 (877us)
[503489.271081] DECODE +9 (868us)
[503489.272268] DECODE -10 (911us)
[503489.273443] DECODE +10 (894us)
[503489.275785] DECODE -20 (1797us)
[503489.276990] DECODE +19 (1727us)
[503489.279317] DECODE -19 (1771us)
[503489.280640] DECODE +19 (1753us)
[503489.281686] DECODE -10 (937us)
[503489.282855] DECODE +9 (842us)
[503489.284050] DECODE -20 (1849us)
[503489.286406] DECODE +19 (1701us)
[503489.287569] DECODE -21 (1875us)
[503489.288766] DECODE +9 (816us)
[503489.289929] DECODE -9 (877us)
[503489.289935] DECODE +10 (894us)
[503489.291108] DECODE -10 (911us)
[503489.291112] KEYDOWN
[503489.292308] DECODE +9 (868us)
[503489.292316] FINISHED
[503489.381904] DECODE -1009 (89682us)
[503489.383064] DECODE +20 (1779us)
[503489.384235] DECODE -10 (911us)
[503489.385408] DECODE +9 (868us)
[503489.386574] DECODE -10 (911us)
[503489.386579] DECODE +9 (868us)
[503489.388960] DECODE -20 (1823us)
[503489.390121] DECODE +19 (1701us)
[503489.392594] DECODE -21 (1901us)
[503489.393658] DECODE +18 (1675us)
[503489.394830] DECODE -10 (929us)
[503489.396039] DECODE +9 (816us)
[503489.397205] DECODE -20 (1823us)
[503489.399547] DECODE +19 (1727us)
[503489.400747] DECODE -20 (1849us)
[503489.401909] DECODE +9 (816us)
[503489.403074] DECODE -10 (963us)
[503489.404268] DECODE +9 (816us)
[503489.404278] DECODE -11 (990us)
[503489.404284] KEYDOWN
[503489.405456] DECODE +8 (781us)
[503489.405465] FINISHED
[503489.604647] DECODE -2252 (200031us)
[503489.604659] KEYUP
The 2 KEYDOWNs and the KEYUP event respectively occur 21ms, 134ms and
334ms after the first pulse (versus 111ms, 335ms and 584ms)
The KEYUP occurs 200ms after the last pulse (versus 450ms).
For a double message, the delay between the first KEYDOWN and the final
KEYUP is around 310ms (vs 470ms).
For a triple message, the delay is 420ms (vs 580) which is still below
the key-repeat delay of 500ms used by XBMC and most desktops.
So my patch makes the remote a lot more responsive and greatly reduces
the probably to have a key repeat by mistake.
The timeout in the IR driver could be reduced from 200ms to any value
above 93ms in order to make the IR remote even more responsive.
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