How to Config Alsa Mixer Controls for a DFSDM Sound Card

[Farid Azhar]

We’ve successfuly configured a digital Microphone on our custom board (based on OSD32MP1-RED) as a “STM32MP15DK” dfsdm sound card and able to record audio using “arecord” command. The recorded audio volume is very low and we find no way to increase it.

We added the /etc/asound.conf file

The contents of amixer utility are empty.

The /var/lib/alsa/asound.state configuration file is also empty.

There is no STM32MP15DK card specific alsa-lib configuration file “STM32MP15DK.conf” in /usr/share/alsa/cards/ directory as stated in Soundcard_configuration wiki

How do we assign the “amixer” contents for the STM32MP15DK dfsdm sound card to modify the audio recording volume.

Here are some of the audio commands output:

debian@device-1293a743:~$ sudo arecord -v -r 16000 -f S16_LE -d 20 sound_S16_16khz.wav
Recording WAVE 'sound_S16_16khz.wav' : Signed 16 bit Little Endian, Rate 16000 Hz, Mono
Plug PCM: Hardware PCM card 0 'STM32MP15-DK' device 0 subdevice 0
Its setup is:
  stream       : CAPTURE
  access       : RW_INTERLEAVED
  format       : S16_LE
  subformat    : STD
  channels     : 1
  rate         : 16000
  exact rate   : 16000 (16000/1)
  msbits       : 16
  buffer_size  : 6144
  period_size  : 1024
  period_time  : 64000
  tstamp_mode  : NONE
  tstamp_type  : MONOTONIC
  period_step  : 1
  avail_min    : 1024
  period_event : 0
  start_threshold  : 1
  stop_threshold   : 6144
  silence_threshold: 0
  silence_size : 0
  boundary     : 1610612736
  appl_ptr     : 0
  hw_ptr       : 0
debian@device-1293a743:~$ 

debian@device-1293a743:~$ ls -al *.wav
-rw-r--r-- 1 root root 640044 Mar 20 20:55 sound_S16_16khz.wav
debian@device-1293a743:~$ 
		=> Volume is very low in this audio

debian@device-1293a743:~$ sudo arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: STM32MP15DK [STM32MP15-DK], device 0: 4400d000.dfsdm:filter@0:dfsdm-dai-dmic-hifi dmic-hifi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
debian@device-1293a743:~$ 

debian@device-1293a743:~$ sudo arecord -L
null
    Discard all samples (playback) or generate zero samples (capture)
default
mic
hw:CARD=STM32MP15DK,DEV=0
    STM32MP15-DK, 
    Direct hardware device without any conversions
plughw:CARD=STM32MP15DK,DEV=0
    STM32MP15-DK, 
    Hardware device with all software conversions
sysdefault:CARD=STM32MP15DK
    STM32MP15-DK, 
    Default Audio Device
dsnoop:CARD=STM32MP15DK,DEV=0
    STM32MP15-DK, 
    Direct sample snooping device
debian@device-1293a743:~$ 

debian@device-1293a743:~$ sudo amixer -v
amixer version 1.2.4
debian@device-1293a743:~$ 

debian@device-1293a743:~$ sudo amixer
debian@device-1293a743:~$ 

debian@device-1293a743:~$ sudo amixer scontrols
debian@device-1293a743:~$ 

debian@device-1293a743:~$ sudo amixer scontrols
debian@device-1293a743:~$ 

debian@device-1293a743:~$ sudo amixer scontents
debian@device-1293a743:~$ 

debian@device-1293a743:~$ sudo amixer controls
debian@device-1293a743:~$ 

debian@device-1293a743:~$ sudo amixer contents
debian@device-1293a743:~$ 

debian@device-1293a743:~$ cat /var/lib/alsa/asound.state
state.STM32MP15DK {
	control {
	}
}
debian@device-1293a743:~$ 

debian@device-1293a743:~$ cat /etc/asound.conf
pcm.!default {
	type asym
	capture.pcm "mic"
}
pcm.mic {
	type plug
	slave {
		pcm "hw:0,0"
	}
}
debian@device-1293a743:~$

debian@device-1293a743:~$ sudo alsactl -v
alsactl version 1.2.4
debian@device-1293a743:~$ 

debian@device-1293a743:~$ cat /sys/bus/iio/devices/iio:device9/name
dfsdm-pdm0
debian@device-1293a743:~$ 

debian@device-1293a743:~$ ls -al /usr/share/alsa/cards/STM32*.conf
ls: cannot access '/usr/share/alsa/cards/STM32*.conf': No such file or directory
debian@device-1293a743:~$

Any help is much appreciated.

/Farid.

[Neeraj Dantu]

Hey Farid,

My apologies for the delayed response. Did you take a  look at the sound card configuration files from meta-st-stm32mp here: https://github.com/STMicroelectronics/meta-st-stm32mp/tree/kirkstone/recipes-bsp/alsa?

Since you are using the DFSDM interface same as STM32MP157C-EV1, I would look at what the STM32MP157C-EV1 is using for the configuration files that are missing in your system.

Best,

Neeraj

[Author]

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