What is /dev/snd/hwC0D0 used for ?

What is /dev/snd/hwC0D0 used for ?

[Carlos Munoz]

Hi all,

Does any anyone know what /dev/snd/hwCxDx and /dev/snd/timer are used for?

Is there a document explaining what all the devices are used for ? I 
searched but didn't find anything.

Thanks,


Carlos Munoz


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Re: What is /dev/snd/hwC0D0 used for ?

[Lee Revell]

On Thu, 2006-03-30 at 11:09 -0800, Carlos Munoz wrote:
> Hi all,
> 
> Does any anyone know what /dev/snd/hwCxDx and /dev/snd/timer are used for?
> 

Yes, these provide the ioctl() interface (specifically the hwdep and
timer ioctls, respectively) that alsa-lib uses to communicate with the
kernel.  They are only intended for use by alsa-lib.

> Is there a document explaining what all the devices are used for ? I 
> searched but didn't find anything.
> 

No because these interfaces are intended to be private to alsa-lib.  The
source code is authoritative.

Lee





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Re: What is /dev/snd/hwC0D0 used for ?

[Paul Davis]

On Thu, 2006-03-30 at 16:37 -0500, Lee Revell wrote:
> On Thu, 2006-03-30 at 11:09 -0800, Carlos Munoz wrote:
> > Hi all,
> > 
> > Does any anyone know what /dev/snd/hwCxDx and /dev/snd/timer are used for?
> > 
> 
> Yes, these provide the ioctl() interface (specifically the hwdep and
> timer ioctls, respectively) that alsa-lib uses to communicate with the
> kernel.  They are only intended for use by alsa-lib.
> 
> > Is there a document explaining what all the devices are used for ? I 
> > searched but didn't find anything.
> > 
> 
> No because these interfaces are intended to be private to alsa-lib.  The
> source code is authoritative.

is this confirmed policy?

what happens about support for devices that have classes of control that
do not fit into the existing ALSA schema and have traditionally been
handled via device-specific ioctl's on /dev/snd/hwFOO ?

--p




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Re: What is /dev/snd/hwC0D0 used for ?

[Lee Revell]

On Thu, 2006-03-30 at 20:45 -0500, Paul Davis wrote:
> On Thu, 2006-03-30 at 16:37 -0500, Lee Revell wrote:
> > > Is there a document explaining what all the devices are used for ? I 
> > > searched but didn't find anything.
> > > 
> > 
> > No because these interfaces are intended to be private to alsa-lib.  The
> > source code is authoritative.
> 
> is this confirmed policy?
> 

Nope, just my understanding of the situation.  Corrections are welcome.

> what happens about support for devices that have classes of control
> that do not fit into the existing ALSA schema and have traditionally
> been handled via device-specific ioctl's on /dev/snd/hwFOO ?
> 

Good question.  I know the upstream kernel policy is "no new ioctls,
period"...

Lee



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Re: What is /dev/snd/hwC0D0 used for ?

[Takashi Iwai]

At Thu, 30 Mar 2006 21:47:10 -0500,
Lee Revell wrote:
> 
> On Thu, 2006-03-30 at 20:45 -0500, Paul Davis wrote:
> > On Thu, 2006-03-30 at 16:37 -0500, Lee Revell wrote:
> > > > Is there a document explaining what all the devices are used for ? I 
> > > > searched but didn't find anything.
> > > > 
> > > 
> > > No because these interfaces are intended to be private to alsa-lib.  The
> > > source code is authoritative.
> > 
> > is this confirmed policy?
> > 
> 
> Nope, just my understanding of the situation.  Corrections are welcome.

It's right about the access to the "device file".  They can be all
accessed gracefully via alsa-lib, and that's preferred.

But it's not intentional that there are no documents about that.  Just
no time and interest for such a thing :)

> > what happens about support for devices that have classes of control
> > that do not fit into the existing ALSA schema and have traditionally
> > been handled via device-specific ioctl's on /dev/snd/hwFOO ?
> > 
> 
> Good question.  I know the upstream kernel policy is "no new ioctls,
> period"...

The hwdep can have its own reads, writes, ioctls, whatever.  Iit's the
very reason of this device.

The hwdep-specific methods can be issued from alsa-lib such as
snd_hwdep_read(), snd_hwdep_write(), snd_hwdep_ioctl().  The mmap is
not implmented as alsa-lib's method, so you'd need to do it manually
using snd_hwdep_poll_descriptor().  Maybe this should be properly
implemented, too.


Takashi


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