[alsa-devel] Pinpoint audio audio corruption (Layla3G)
Mark Hills
mark at xwax.org
Sun Sep 23 15:24:31 CEST 2018
I have a bug in ALSA somewhere; playback is corrupted. Nothing is
pro-actively telling me of a problem (eg. underrun)
I could use some assistance getting to the bottom of this.
Listen to [1] for what it sounds like -- analogue recording from the
output.
Look at the waveform [2] in Baudlien and it seems both L+R channels geting
zero'd for some buffer period of 2.5 or 5 milliseconds.
This is Layla3G, snd-echo3g.
This problem has been rare, but persisted for many years. I've finally got
something reproducable to investigate.
It began ~10 years ago where very occasionally recordings or playback
would do this. This was a simple self-contained application in production
use; written by me, using plughw:Layla3G,0,0 (no desktops, browsers, dmix
etc.)
Problems were frequent enough to be annoying, but infrequent enough that I
just had to put it down to 'cosmic rays', with no useful bug report.
These days I am on a desktop using dmix; and more recently with Google
Chrome and found I can reliably 'trigger' it.
To reset, I must close all applications using /dev/snd, and re-open.
It seems to be:
* whether or not Google Chrome is first to open the device
* about 10-60 minutes after Chrome has opened the device
* more prone to happening if other applications are using the dmix
* not related to buffer sizes; I use larger sizes in the asoundrc it
doesn't affect the likelihood, or the 'sound' when it does happen
* I've seen two Layla's affected
* I've had many kernels and PCs over the years
There's a bug somewhere, and with nothing printed to dmesg, console etc.,
I'm at a loss here, imagining my problem could be anywhere between dmix,
alsa-lib, snd-echo3g or even the firmware itself.
Whatever the case, I've finally got some combination I can do in userland
as a trigger.
Below is:
- .asoundrc describing today's setup (previously I used stereo with no
route, still with problems)
- output of the 'aplay' that produced the recording above; and
- some other stats.
[1] http://www.pogo.org.uk/~mark/tmp/layla-glitch.flac
[2] http://www.pogo.org.uk/~mark/tmp/layla-glitch.png
Many thanks
--
Mark
pcm.!default {
type plug
slave.pcm layla_multi
}
pcm.layla_multi {
type route
slave.pcm {
type dmix
ipc_key 1742
slave {
pcm "hw:Layla3G,0,0"
period_size 992
buffer_size 10912
channels 5
rate 48000
format S16_LE
}
}
ttable {
# Headphones
0.0 1
1.1 1
# Speakers
0.2 1
1.3 1
# Subwoofer; mono mix
0.4 0.5
1.4 0.5
}
}
$ uname -a
Linux stax 4.18.5 #113 SMP PREEMPT Mon Sep 3 23:14:59 BST 2018 x86_64 Intel(R) Core(TM) i5-6500 CPU @ 3.20GHz GenuineIntel GNU/Linux
$ head -99l /proc/asound/Layla3G/pcm0p/sub0/*
==> /proc/asound/Layla3G/pcm0p/sub0/hw_params <==
access: MMAP_INTERLEAVED
format: S16_LE
subformat: STD
channels: 6
rate: 48000 (48000/1)
period_size: 992
buffer_size: 10912
==> /proc/asound/Layla3G/pcm0p/sub0/info <==
card: 0
device: 0
subdevice: 0
stream: PLAYBACK
id: Analog PCM
name: Layla3G
subname: subdevice #0
class: 0
subclass: 0
subdevices_count: 8
subdevices_avail: 7
==> /proc/asound/Layla3G/pcm0p/sub0/prealloc <==
128
==> /proc/asound/Layla3G/pcm0p/sub0/prealloc_max <==
256
==> /proc/asound/Layla3G/pcm0p/sub0/status <==
state: RUNNING
owner_pid : 9250
trigger_time: 663739.627559736
tstamp : 680208.555428028
delay : -790500256
avail : 790511168
avail_max : 790511168
-----
hw_ptr : 790500256
appl_ptr : 0
==> /proc/asound/Layla3G/pcm0p/sub0/sw_params <==
tstamp_mode: ENABLE
period_step: 1
avail_min: 1
start_threshold: 1
stop_threshold: 6142909891733356544
silence_threshold: 0
silence_size: 6142909891733356544
boundary: 6142909891733356544
$ aplay -vv all48000.wav
Playing WAVE 'all48000.wav' : Float 32 bit Little Endian, Rate 48000 Hz,
Stereo
Plug PCM: Linear Integer <-> Linear Float conversion PCM (S16_LE)
Its setup is:
stream : PLAYBACK
access : RW_INTERLEAVED
format : FLOAT_LE
subformat : STD
channels : 2
rate : 48000
exact rate : 48000 (48000/1)
msbits : 32
buffer_size : 10912
period_size : 992
period_time : 20666
tstamp_mode : NONE
tstamp_type : MONOTONIC
period_step : 1
avail_min : 992
period_event : 0
start_threshold : 10912
stop_threshold : 10912
silence_threshold: 0
silence_size : 0
boundary : 6142909891733356544
Slave: Route conversion PCM (sformat=S16_LE)
Transformation table:
0 <- 0
1 <- 1
2 <- none
3 <- none
4 <- none
5 <- none
Its setup is:
stream : PLAYBACK
access : MMAP_INTERLEAVED
format : S16_LE
subformat : STD
channels : 2
rate : 48000
exact rate : 48000 (48000/1)
msbits : 16
buffer_size : 10912
period_size : 992
period_time : 20666
tstamp_mode : NONE
tstamp_type : MONOTONIC
period_step : 1
avail_min : 992
period_event : 0
start_threshold : 10912
stop_threshold : 10912
silence_threshold: 0
silence_size : 0
boundary : 6142909891733356544
Slave: Route conversion PCM
Transformation table:
0 <- 0
1 <- 1
2 <- 0
3 <- 1
4 <- 0*0.5 + 1*0.5
Its setup is:
stream : PLAYBACK
access : MMAP_INTERLEAVED
format : S16_LE
subformat : STD
channels : 6
rate : 48000
exact rate : 48000 (48000/1)
msbits : 16
buffer_size : 10912
period_size : 992
period_time : 20666
tstamp_mode : NONE
tstamp_type : MONOTONIC
period_step : 1
avail_min : 992
period_event : 0
start_threshold : 10912
stop_threshold : 10912
silence_threshold: 0
silence_size : 0
boundary : 6142909891733356544
Slave: Direct Stream Mixing PCM
Its setup is:
stream : PLAYBACK
access : MMAP_INTERLEAVED
format : S16_LE
subformat : STD
channels : 6
rate : 48000
exact rate : 48000 (48000/1)
msbits : 16
buffer_size : 10912
period_size : 992
period_time : 20666
tstamp_mode : NONE
tstamp_type : MONOTONIC
period_step : 1
avail_min : 992
period_event : 0
start_threshold : 10912
stop_threshold : 10912
silence_threshold: 0
silence_size : 0
boundary : 6142909891733356544
Hardware PCM card 0 'Layla3G' device 0 subdevice 0
Its setup is:
stream : PLAYBACK
access : MMAP_INTERLEAVED
format : S16_LE
subformat : STD
channels : 6
rate : 48000
exact rate : 48000 (48000/1)
msbits : 16
buffer_size : 10912
period_size : 992
period_time : 20666
tstamp_mode : ENABLE
tstamp_type : MONOTONIC
period_step : 1
avail_min : 992
period_event : 0
start_threshold : 1
stop_threshold : 0
silence_threshold: 0
silence_size : 0
boundary : 6142909891733356544
appl_ptr : 0
hw_ptr : 807111136
############################ + | 56%^C
Aborted by signal Interrupt...
aplay: pcm_write:2004: write error: Interrupted system call
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