[alsa-devel] Playback issue while recording simultaneously

[Pierre-Louis Bossart]

On 12/5/19 11:22 PM, Mohan Prasath Ramamoorthy wrote:
> Dear All,
> 
> We are working on external modules of microphone and speaker and we
> are using the kernel version 3.10.96

wow, that is one ancient kernel EOL'ed in 2017...

> 
> We are recording with commands like arecord and aplay for recording
> and playback respectively.
> 
> While doing the below experiments we could able to observe an issue as below,
> 
> 1. With only recording and not playback we haven't faced any issues.
> 2. With only playback and not recording we haven't faced any issues.
> 
> 3. By starting an infinite recording in the background and by doing a
> playback of the audio file(30seconds, the sampling rate of 22050, the
> channel is stereo), after some iterations, we are facing a below error
> and we could not able to listen to the audio.
> 
> Error: aplay: pcm_write:1940: write error: Input/output error
> 
> Below are the respective commands for recording and playback,
> 
> 1. arecord -D hw:0,0 -c 2 -f s16_le -r 8000 /home/ubuntu/mic_testing.wav &
> 2. aplay -D hw:0,3 audio_22k_c2.wav
> 
> But when the issues come, we just stopped recording and restarted the
> recording in the background. After this, the playback is working fine.
> 
> Also, during the issue came, we have checked for the below properties,
> 
> 1. I2S has been enabled. Checked under the file:
> /sys/kernel/debug/clock/clock_tree
> 2. Driver callbacks have been called. (Checked with the kernel logs[dmesg])
> 
> We would like to know the reason behind this error.?

Sounds typical of an interference between the playback and record 
programming flows, e.g. when changing a shared register. Not all I2S 
tolerate dynamic changes from RX or TX only to full-duplex.