[alsa-devel] Arecord issue

[Daniel Mack]

On 11.10.2012 14:54, kartik natarajan wrote:
>     I am working on a 2.6.37 kernel and on a DM365 davinci board with a
> tlv320aic3254 audio codec (i2c control lines, i2s data transfer)
> I wanted to get the audio up on my board so got the alsa-lib and alsa-utils
> 1.0.25 compiled them and got the aplay to work fine.
> When I got to working on the arecord things haven't worked fine. I have
> traced all the calls and have reached so far;
> codec gets set properly
> davinci_pcm_trigger executes with success
> snd_pcm_sw_params() executes successfully.
> aplay calls begin_wave()
> aplay calls pcm_read() that invokes  snd_pcm_readi()
> Finally my app seems to not go beyond the snd_pcm_start()

I've been working on a custom AM33xx boards lately which features the
same digital audio interface than the Davincis do.

I've been running into similar issues when I tested the recording
channels, and hooking up a logic analyzer showed that the clocks were
not driven by the CPU. That causes the DMA engine not receive any
samples (as the frame and bit clocks are missing), which will eventually
lead to a timeout.

This issue was worked around for now by starting the playback first and
then the record. Unfortunately though, a simply "arecord | aplay" does
not suffice, as aplay won't start before it received any samples from
its input side, so you have a deadlock here.

So I wrote a very simple test tool in order to prove that the overall
system is working and published it here:

  https://github.com/zonque/simple-alsa-loop

For the application of this board I'm working on, there's no case where
we would record anything but not use the output, so this workaround will
do for me. If you have other requirements, you might need to dig deeper.
Note that the driver has seem quite some refactorization in 3.7.


Daniel