Help with dummy.c (where/how to write?)

Help with dummy.c (where/how to write?)

[Smilen Dimitrov]

Hi all,

I am trying to work on dummy.c:

http://lxr.linux.no/#linux+v2.6.32/sound/drivers/dummy.c

as an exercise, and I'd like to modify it so it behaves as an 
'oscillator'; that is, when I choose 'dummy' as an input in say 
Audacity, and press Record - I'd like to be able to write something to 
the audio (pcm) buffer of the driver directly from the driver itself 
(say a single sample), and be able to observe those samples recorded in 
Audacity.

So far, by adding some debug statements, the only thing I can figure, is 
that when 'Record' in Audacity is pressed, 'dummy_hrtimer_callback' is 
called continuously - but I cannot tell what functions to use to modify 
/ write to output buffers (not even sure what the output buffers there 
are, I guess dpcm->substream->private_data).

Could anyone point to me if there is a similar example existing already, 
or if not. provide me with some pointers on how to do this?

Thanks in advance,
Cheers!

Re: Help with dummy.c (where/how to write?)

[Smilen Dimitrov]

Hi Eliot,

Thanks so much for your response:

>>
>> I am trying to work on dummy.c:
>>
>> http://lxr.linux.no/#linux+v2.6.32/sound/drivers/dummy.c
>>
>> as an exercise, and I'd like to modify it so it behaves as an
>> 'oscillator'; [snip]
>>
>
> You are better to look at the loopback driver in alsa-driver repo:
>
> http://git.alsa-project.org/?p=alsa-driver.git;a=blob_plain;f=drivers/aloop-kernel.c;hb=HEAD
>
> You would put your generation code in clear_capture_buf()
>


Fantastic info - that is exactly what I needed :)

(Don't know why your response hasn't shown in the alsa-devel archives 
yet, hopefully my reply will bump it up there)

Cheers!