Correct way to set NONAUDIO flag

Correct way to set NONAUDIO flag

[Arun Raghavan]

Hello,
I'm trying to figure out the right way to set the NONAUDIO flag on an
iec958 device. The idea is that when we get a new stream in PulseAudio
that signals a non-PCM format, we'd like to set the NONAUDIO flag to let
receivers know that this isn't PCM data. I tried doing what iecset does
in the PA alsa-sink code but this fails.

As far as I can tell, this happens because: (a) if I set the flag before
snd_pcm_open(), the AES0 value from iec958.conf gets used, and (b) if I
set the flag after snd_pcm_open(), changing the value is no longer
permitted.

Any help/pointers would be appreciated.

Thanks,
Arun

Re: Correct way to set NONAUDIO flag

[Clemens Ladisch]

Arun Raghavan wrote:
> I'm trying to figure out the right way to set the NONAUDIO flag on an
> iec958 device.

Use the device name "iec958:AES0=6".


Regards,
Clemens

Re: Correct way to set NONAUDIO flag

[Arun Raghavan]

Hi Clemens,

On Wed, 2011-08-17 at 14:42 +0200, Clemens Ladisch wrote:
> Arun Raghavan wrote:
> > I'm trying to figure out the right way to set the NONAUDIO flag on an
> > iec958 device.
> 
> Use the device name "iec958:AES0=6".

Thanks. As I understand it, this forces us to set all the flags instead
of just the one that we're interested in. Is this the only way?

Regards,
Arun

Re: Correct way to set NONAUDIO flag

[Clemens Ladisch]

Arun Raghavan wrote:
> On Wed, 2011-08-17 at 14:42 +0200, Clemens Ladisch wrote:
> > Arun Raghavan wrote:
> > > I'm trying to figure out the right way to set the NONAUDIO flag on an
> > > iec958 device.
> > 
> > Use the device name "iec958:AES0=6".
> 
> Thanks. As I understand it, this forces us to set all the flags instead
> of just the one that we're interested in.

Yes.  However, using 'default' values for these other flags would not
make much sense because your application is the only one that knows the
correct values.

> Is this the only way?

It's the only portable way.


Regards,
Clemens

Re: Correct way to set NONAUDIO flag

[Arun Raghavan]

On Wed, 2011-08-17 at 16:55 +0200, Clemens Ladisch wrote:
> Arun Raghavan wrote:
> > On Wed, 2011-08-17 at 14:42 +0200, Clemens Ladisch wrote:
> > > Arun Raghavan wrote:
> > > > I'm trying to figure out the right way to set the NONAUDIO flag on an
> > > > iec958 device.
> > > 
> > > Use the device name "iec958:AES0=6".
> > 
> > Thanks. As I understand it, this forces us to set all the flags instead
> > of just the one that we're interested in.
> 
> Yes.  However, using 'default' values for these other flags would not
> make much sense because your application is the only one that knows the
> correct values.
> 
> > Is this the only way?
> 
> It's the only portable way.
> 

Got it -- thanks for the help!

-- Arun

Re: Correct way to set NONAUDIO flag

[Pierre-Louis Bossart]

> > > I'm trying to figure out the right way to set the NONAUDIO flag on
> an
> > > iec958 device.
> >
> > Use the device name "iec958:AES0=6".
> 
> Thanks. As I understand it, this forces us to set all the flags instead
> of just the one that we're interested in. Is this the only way?

I banged my head against the wall on this one for eAC3 support. For some
strange reason my receiver works fine with AC3 without touching the C bits,
but for eAC3 setting the NONAUDIO bit is required.
If you try to set the bits with ALSA controls in PulseAudio, somehow the
settings are overwritten when the iec958 device is opened and initialized
with default values. Clemens is right, setting the AES0=6 in the hdmi
profile proved to be the only solution. It'd be nice to find a solution in
which the iec958 device preserves the AES values set beforehand. That way we
could set the NONAUDIO bit only in passthrough mode.
-Pierre

Re: Correct way to set NONAUDIO flag

[Arun Raghavan]

On Wed, 2011-08-17 at 10:31 -0500, Pierre-Louis Bossart wrote:
> > > > I'm trying to figure out the right way to set the NONAUDIO flag on
> > an
> > > > iec958 device.
> > >
> > > Use the device name "iec958:AES0=6".
> > 
> > Thanks. As I understand it, this forces us to set all the flags instead
> > of just the one that we're interested in. Is this the only way?
> 
> I banged my head against the wall on this one for eAC3 support. For some
> strange reason my receiver works fine with AC3 without touching the C bits,
> but for eAC3 setting the NONAUDIO bit is required.
> If you try to set the bits with ALSA controls in PulseAudio, somehow the
> settings are overwritten when the iec958 device is opened and initialized
> with default values. Clemens is right, setting the AES0=6 in the hdmi
> profile proved to be the only solution. It'd be nice to find a solution in
> which the iec958 device preserves the AES values set beforehand. That way we
> could set the NONAUDIO bit only in passthrough mode.

Well, given this is the best way to do it, my plan is to just close
(suspend) and reopen (unsuspend) and tack on the the right flags to the
device name when we're in passthrough mode.

-- Arun

Re: Correct way to set NONAUDIO flag

[Clemens Ladisch]

Pierre-Louis Bossart wrote:
> If you try to set the bits with ALSA controls in PulseAudio, somehow the
> settings are overwritten when the iec958 device is opened and initialized
> with default values.

That's how the iec958 device is intended to work.

The AES0..3 parameters of the iec958 device are the _only_ way to set
these flags.  If you don't set them, they get a static default value;
see <http://git.alsa-project.org/?p=alsa-lib.git;a=blob;hb=HEAD;f=src/conf/pcm/iec958.conf>.

If PA wants to set these flags, it must do so when opening the device;
any other mechanism will not work.


Regards,
Clemens