Re: [alsa-devel] em8300 and ALSA problems

[Nicolas Boullis <nboullis@debian.org>]

Hi all, and sorry for the late answer,

On Mon, Feb 04, 2008 at 05:02:01PM +0100, Jan Willies wrote:
> Takashi Iwai wrote:
> > At Mon, 04 Feb 2008 16:46:44 +0100,
> > Jan Willies wrote:
> >> Takashi Iwai wrote:
> >>> At Mon, 04 Feb 2008 16:32:29 +0100,
> >>> Jan Willies wrote:
> >>>> [root@server ~]# alsaplayer --verbose -o alsa -d hw:1,0 Strong.mp3 
> >>>> AlsaPlayer 0.99.80
> >>>> (C) 1999-2004 Andy Lo A Foe <andy@alsaplayer.org> and others.
> >>>> Output plugin: ALSA output v1.9.0beta12
> >>>> error on set_format SND_PCM_FORMAT_S16
> >>>> Unavailable hw params:
> >>>> ACCESS:  RW_INTERLEAVED
> >>>> FORMAT:  S16_BE
> >>> The device is supposed to be big-endian only.  Try plughw:1,0
> >>> instead to convert endianness.
> >> Yes, that seems to work! Only for analog output though. When I try with digital I get the same error again.
> >>
> >> [jan@server ~]$ cat /proc/asound/devices 
> >>   0: [ 0]   : control
> >>   1:        : sequencer
> >>  16: [ 0- 0]: digital audio playback
> >>  24: [ 0- 0]: digital audio capture
> >>  25: [ 0- 1]: digital audio capture
> >>  32: [ 1]   : control
> >>  33:        : timer
> >>  48: [ 1- 0]: digital audio playback
> >>  49: [ 1- 1]: digital audio playback
> >>
> >> [root@server ~]# alsaplayer --verbose -o alsa -d plughw:1,1 Strong.mp3 
> >> AlsaPlayer 0.99.80
> >> (C) 1999-2004 Andy Lo A Foe <andy@alsaplayer.org> and others.
> >> Output plugin: ALSA output v1.9.0beta12
> >> error on set_format SND_PCM_FORMAT_S16
> >> Unavailable hw params:
> >> ACCESS:  RW_INTERLEAVED
> >> FORMAT:  IEC958_SUBFRAME_BE
> >> [...]
> > 
> > The plug plugin doesn't handle the automatic conversion of
> > IEC958-subframe formats.  You'll likely need to create a PCM
> > configuration to use iec958 plugin properly (better as a card-specific
> > config stored in /usr/share/alsa/cards).  Some config files there
> > already use iec958 plugin, such as ATIIXP-SPDMA.conf.
> 
> There is already a /usr/share/alsa/cards/EM8300.conf with EM8300.pcm.iec958.0 {...} (http://pastebin.ca/raw/891351) from Ville Skyttä but I don't know how to use it. Neither how to create a PCM configuration for the iec958 plugin. I guess I'll wait for some dxr3 devs to join the party :-)

As Takashi Iwai noticed, the "EM8300 DAC" device only supports 16-bit 
big-endian 2-channel data, but it also has its channels swapped and 
lacks a volume control. Using plughw:1,0 does not unswap the channels or 
add a volume control.

As for the "EM8300 IEC958" device, it only supports big-endian 
IEC958 subframes, and needs specific values for its preambles.

For those reasons, I had to write a specific configuration file for 
EM8300 card (and fix some bugs in alsa-lib's iec958 plugin).

Using this file is pretty trivial:
  - for the "EM8300 DAC" device, use the "default:1" alsa device
  - for the "EM8300 IEC958" device, use the "iec958:1" alsa device

Not that, if I understand ALSA correctly, this is not EM8300-specifica 
at all, the same syntax should work with any card.

If you wish to add volume control and format conversion to your "EM8300 
IEC958" device, create a ~/.asoundrc file with:

pcm.foobar {
        type plug
        slave.pcm {
                type softvol
                slave.pcm iec958:EM8300
                control {
                        name "IEC958 Playback Volume"
                        card EM8300
                }
        }
}

and then use the "foobar" alsa device. (Note that there might be some 
syntax errors, since it is untested.)

Note that there's nothing specific to the EM8300 cards here, the same 
thing should work with any card that supports IEC958, just replace the 
two "EM8300" with the name or number of the card you want to use.


Hope this helps,

Nicolas

PS: any comment or suggestion for improvement is welcome, especially 
from ALSA experts (which I am not).

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