[alsa-devel] MCP7A HDMI passthrough audio Linux/ALSA

Takashi Iwai tiwai at suse.de
Wed Jul 1 08:18:22 CEST 2009

At Tue, 30 Jun 2009 22:51:03 +0200,
Stephane BERTHELOT wrote:
> Takashi Iwai a écrit :
>     At Tue, 30 Jun 2009 15:04:05 +0200,
>     Stéphane BERTHELOT wrote:
>         Hi Takashi,
>         Thanks for you answer.
>         I have the exact same problem and configuration than reported here 
>         https://bugtrack.alsa-project.org/alsa-bug/view.php?id=4406
>         apart :
>         - I'm using a ION platform (Acer Revo R3600 but still MCP7A : 0x10de0007)
>         - I never get the Dolby Digital or DTS indicator illuminated on my Amp.
>         - My TV is a Sharp LC-52X20E
>         I thought this was a known problem and than someone at Nvidia could 
>         provide the missing HDA Verbs, if you prefer I can post to the 
>         alsa-devel mailing list to investigate further.
>         I can get a alsa-info output tonight, though it's very very similar to 
>         the one in the bug report. (and Raymond was saying that we should get 
>         "PCM AC3" on digital outputs)
>     Try ac3dec for a primary testing instead of mplayer.  It's included in
>     alsa-tools.
>             % ac3dec -C -H foo.ac3
>     Use the latest one so that it accespt -H option.
>     Takashi
> Thank you Takashi for taking time to review my problem. I cc'ed alsa-devel
> since I have more info now and maybe some other people have the same problem
> or already a workaround.
> I'm attaching the output of alsa-info.sh with my mixer settings and after
> having run ac3dec -H -C file.ac3
> It works with -R instead of -C but does not work with -C or with -P (consumer
> or pro)
> I also tried modifying settings using iecset (audio off / audio on and
> consumer/pro) and no combination seems to work.
> When I play stereo LPCM my TV set plays sound and so does my Amp in PCM mode.
> When I try to play in AC3 mode (-C) my TV set says "incompatible format
> received" and both the TV and Amp stay silent.

Hm, so apparently your TV doesn't accept non-audio format?
But TV accepted the ac3dec output with -R option, right?
(Make sure this -- otherwise ac3dec might have decoded by itself.)

Basically, -R means to send the encoded an AC3 stream (packed in the
SPDIF format) without setting non-audio bit.  Whether non-audio bit is
1 or 0 is the only difference between -C and -R.  So, if -R really
works but not -C, it means that the non-audio bit must be off no
matter what you send.  Weird.

> I may try again on XP/Vista tomorrow to be really sure it works on them.
> When changing play mode AES0 changes from 0x00 to 0x02 and AES1 to AES3 stay
> the same (0x82,0x00,0x02 if I remember well)

Note that the setup you made before ac3dec will be overridden anyway.
And during ac3dec playback, the status bits are locked and can't be
changed by others.


More information about the Alsa-devel mailing list