Using driver service from another driver

Using driver service from another driver

[Himanshu Chauhan]

Dear all,

I am writing a virtual audio driver (similar to dummy.c in alsa tree).
But I need to
access the driver services of the soundcard installed on the system. How
can this
be done? Can I directly call the functions or I need to specifically
open the
device?

This is for the first time I am doing ALSA drivers so I seek your help.

Thanks

Regards
--Himanshu

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Re: Using driver service from another driver

[Takashi Iwai]

At Tue, 07 Nov 2006 22:47:46 +0530,
Himanshu Chauhan wrote:
> 
> Dear all,
> 
> I am writing a virtual audio driver (similar to dummy.c in alsa tree).
> But I need to
> access the driver services of the soundcard installed on the system. How
> can this
> be done? Can I directly call the functions or I need to specifically
> open the
> device?

The question is too ambiguous to answer.  Could you elaborate what you
want to achieve?  Something like output <-> input loopback?


Takashi

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Re: Using driver service from another driver

[Himanshu Chauhan]

Takashi Iwai wrote:
> At Tue, 07 Nov 2006 22:47:46 +0530,
> Himanshu Chauhan wrote:
>   
>> Dear all,
>>
>> I am writing a virtual audio driver (similar to dummy.c in alsa tree).
>> But I need to
>> access the driver services of the soundcard installed on the system. How
>> can this
>> be done? Can I directly call the functions or I need to specifically
>> open the
>> device?
>>     
>
> The question is too ambiguous to answer.  Could you elaborate what you
> want to achieve?  Something like output <-> input loopback?
>
>
> Takashi
>
>   
Okay. I am writing a dummy driver from which the application play and
record.
Suppose, mplayer is playing some movie and the audio is going to this dummy
driver and Audacity is running which is recording from this dummy driver
 (the stream coming from mplayer). But as no actual device is there, user
can't listen to what is being played or recorded. I want a playthru like
thing
so that whatever data audacity is getting for recording can also be
directed to an actual sound card driver from within the kernel.
So that user can listen to whatever is being played by mplayer and
is being recorded by audacity.

Same thing can be achieved by enabling playthru in audacity but I
wish to do it in kernel mode using services of a driver for which
actual hardware is present in the system.


--Himanshu

-- 
=============================
     Himanshu Chauhan
	System Software Engineer
	inDSP Audio Technologies
	341 Nila
	Technopark
	Trivandram, Kerala

	M:(+91)-(999)-(518)-(5989)
=============================


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Re: Using driver service from another driver

[Sampo Savolainen]

On Wed, 2006-11-08 at 21:56 +0530, Himanshu Chauhan wrote:
> Okay. I am writing a dummy driver from which the application play and
> record.
> Suppose, mplayer is playing some movie and the audio is going to this dummy
> driver and Audacity is running which is recording from this dummy driver
>  (the stream coming from mplayer). But as no actual device is there, user
> can't listen to what is being played or recorded. I want a playthru like
> thing
> so that whatever data audacity is getting for recording can also be
> directed to an actual sound card driver from within the kernel.
> So that user can listen to whatever is being played by mplayer and
> is being recorded by audacity.

For inter-application audio plumbing, jackd (http://www.jackaudio.org)
is the way to go.

And for exporting audio out of mplayer:

 mplayer -ao pcm:file=out.wav -vo null [inputfile]


I'd say writing a device driver to do this task is like trying to squash
a fly with an expensive vase.


  Sampo



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Re: Using driver service from another driver

[Lee Revell]

On Tue, 2006-11-07 at 22:47 +0530, Himanshu Chauhan wrote:
> Dear all,
> 
> I am writing a virtual audio driver (similar to dummy.c in alsa tree).
> But I need to
> access the driver services of the soundcard installed on the system. How
> can this
> be done? Can I directly call the functions or I need to specifically
> open the
> device?
> 
> This is for the first time I am doing ALSA drivers so I seek your help.

EXPORT_SYMBOL() the driver functions you wish to call from the other
driver.  "grep -r EXPORT_SYMBOL sound/drivers/" for examples.

Lee


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Re: Using driver service from another driver

[Himanshu Chauhan]

Lee Revell wrote:
> On Tue, 2006-11-07 at 22:47 +0530, Himanshu Chauhan wrote:
>   
>> Dear all,
>>
>> I am writing a virtual audio driver (similar to dummy.c in alsa tree).
>> But I need to
>> access the driver services of the soundcard installed on the system. How
>> can this
>> be done? Can I directly call the functions or I need to specifically
>> open the
>> device?
>>
>> This is for the first time I am doing ALSA drivers so I seek your help.
>>     
>
> EXPORT_SYMBOL() the driver functions you wish to call from the other
> driver.  "grep -r EXPORT_SYMBOL sound/drivers/" for examples.
>
> Lee
>
>
>   
But then that would require changes to the other driver. So
it won't work on all systems. Different systems have different
sound cards. Is there any "universally applicable" way?

Regards
--Himanshu


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Using driver service from another driver

[Himanshu Chauhan]

Dear all,

I am writing a virtual audio driver (similar to dummy.c in alsa tree).
But I need to access the driver services of the soundcard installed
on the system. How can this be done? Can I directly call the
functions or I need to specifically open the device?

This is for the first time I am doing ALSA drivers
so I seek your help.

Thanks

Regards
--Himanshu


-------------------------------------------------------------------------
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