[alsa-devel] dmix produces garbled sound on ARM
Hi All!
When using the dmix on ARM, the sound comes out garbled, with as if overlapping, increasing-in-number echoes. That happens even with a single aplay instance.
In a forum discussion, it was suggested that ARM lacks optimized dmix implementation. But that implies that the generic dmix code is broken, since it is what is used on ARM/etc, but not on i386/amd64. (The forum discussion about my particular issue: http://unix.stackexchange.com/questions/288451/sound-corruption-echo-when-tr... )
Does anybody has any suggestions how to fix/avoid the dmix issue on ARM?
Thanks.
P.S. Versions: Linux v3.18.24, alsa-lib/-utils v1.0.29. The hardware: FreeScale i.MX35 (ARM1136) with SGTL5000 sound chip (used in 48KHz mode).
P.P.S. The generic code has outdated functions for the "concurrent" implementation with cmpxchg. The code probably could be updated, and revised to use the C11's stdatomic.h when available.
On Thu, 09 Jun 2016 13:38:19 +0200, Ihar Filipau wrote:
Hi All!
When using the dmix on ARM, the sound comes out garbled, with as if overlapping, increasing-in-number echoes. That happens even with a single aplay instance.
In a forum discussion, it was suggested that ARM lacks optimized dmix implementation. But that implies that the generic dmix code is broken, since it is what is used on ARM/etc, but not on i386/amd64. (The forum discussion about my particular issue: http://unix.stackexchange.com/questions/288451/sound-corruption-echo-when-tr... )
Does anybody has any suggestions how to fix/avoid the dmix issue on ARM?
Thanks.
P.S. Versions: Linux v3.18.24, alsa-lib/-utils v1.0.29. The hardware: FreeScale i.MX35 (ARM1136) with SGTL5000 sound chip (used in 48KHz mode).
P.P.S. The generic code has outdated functions for the "concurrent" implementation with cmpxchg. The code probably could be updated, and revised to use the C11's stdatomic.h when available.
This is likely the cache coherency issue. For example, the generic dmix code works fine on x86-64 if I modify the ifdef condition (I tested now).
I suppose the mmap support is broken with your device / driver. Does "aplay -Dhw -M --period-size=1024 somefile.wav" work? This should show a similar problem.
Takashi
On 6/9/16, Takashi Iwai tiwai@suse.de wrote:
On Thu, 09 Jun 2016 13:38:19 +0200, Ihar Filipau wrote:
Hi All!
When using the dmix on ARM, the sound comes out garbled, with as if overlapping, increasing-in-number echoes. That happens even with a single aplay instance.
In a forum discussion, it was suggested that ARM lacks optimized dmix implementation. But that implies that the generic dmix code is broken, since it is what is used on ARM/etc, but not on i386/amd64. (The forum discussion about my particular issue: http://unix.stackexchange.com/questions/288451/sound-corruption-echo-when-tr... )
Does anybody has any suggestions how to fix/avoid the dmix issue on ARM?
This is likely the cache coherency issue. For example, the generic dmix code works fine on x86-64 if I modify the ifdef condition (I tested now).
Thanks for the test!
I suppose the mmap support is broken with your device / driver. Does "aplay -Dhw -M --period-size=1024 somefile.wav" work? This should show a similar problem.
The command plays the audio perfectly well.
The hardware works, and it worked for quite some time now. But apparently it doesn't support the hardware mixing (I'm not even sure how to check that, found no documentation) while now we need the audio playback from two applications. The second applications gets -EBUSY when trying to open the "default" pcm. I have tried the 'dmix' - e.g. "aplay -Dplug:dmix somefile.wav" . With that I can open the pcm multiple times - "for X in 1 2 3 4; do aplay -Dplug:dmix somefile.wav & ; done" - but the sound is garbled, whether it is a single aplay or multiple aplays.
Is there any other way I can debug/trace the alsa to shed light on the problem I'm having?
Thanks.
On Thu, 09 Jun 2016 15:17:53 +0200, Ihar Filipau wrote:
On 6/9/16, Takashi Iwai tiwai@suse.de wrote:
On Thu, 09 Jun 2016 13:38:19 +0200, Ihar Filipau wrote:
Hi All!
When using the dmix on ARM, the sound comes out garbled, with as if overlapping, increasing-in-number echoes. That happens even with a single aplay instance.
In a forum discussion, it was suggested that ARM lacks optimized dmix implementation. But that implies that the generic dmix code is broken, since it is what is used on ARM/etc, but not on i386/amd64. (The forum discussion about my particular issue: http://unix.stackexchange.com/questions/288451/sound-corruption-echo-when-tr... )
Does anybody has any suggestions how to fix/avoid the dmix issue on ARM?
This is likely the cache coherency issue. For example, the generic dmix code works fine on x86-64 if I modify the ifdef condition (I tested now).
Thanks for the test!
I suppose the mmap support is broken with your device / driver. Does "aplay -Dhw -M --period-size=1024 somefile.wav" work? This should show a similar problem.
The command plays the audio perfectly well.
Hm, then try to adjust all parameters as same as dmix slave PCM. As default, dmix slave PCM takes 16 x 1024 frames periods, S16_LE format.
The hardware works, and it worked for quite some time now. But apparently it doesn't support the hardware mixing (I'm not even sure how to check that, found no documentation) while now we need the audio playback from two applications. The second applications gets -EBUSY when trying to open the "default" pcm. I have tried the 'dmix' - e.g. "aplay -Dplug:dmix somefile.wav" . With that I can open the pcm multiple times - "for X in 1 2 3 4; do aplay -Dplug:dmix somefile.wav & ; done" - but the sound is garbled, whether it is a single aplay or multiple aplays.
Is there any other way I can debug/trace the alsa to shed light on the problem I'm having?
If the hw works and dmix doesn't even with the very same parameters for a single stream, it can be in the update timing. But it's doubtful, as basically dmix slave is freewheeling...
Takashi
Thanks.
participants (2)
-
Ihar Filipau -
Takashi Iwai