Alsa configuration for embedded device

[Pieter Cardoen <P.Cardoen@xxxxxxxxxxx>]

Dear

For our new audio platform, we are facing some problems to configure ALSA.

Our operating system will be installed on different devices containing different codecs. By now we are able to detect the codec:

# aplay -l
card 0: onboardcodec1 [onboardcodec1], device 0: 2028000.sai-adau1372 adau1372.0-003c-0 [2028000.sai-adau1372 adau1372.0-003c-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: onboardcodec2 [onboardcodec2], device 0: 202c000.sai-adau1372 adau1372.0-003d-0 [202c000.sai-adau1372 adau1372.0-003d-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: externalaudio [externalaudio], device 0: 2030000.sai-snd-soc-dummy-dai snd-soc-dummy-dai-0 [2030000.sai-snd-soc-dummy-dai snd-soc-dummy-dai-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

I was already able to configure our different audio playback and record branches using /etc/asound.conf. However I noticed that all branches were shown using aplay -L, even these related to codecs of different devices. A snippet of our configuration:
pcm.amp_1 {
    type plug
    slave {
        pcm "dmixer_0"
    }
    ttable {
        0.0 1
        0.1 0
    }
    hint {
         show on
         description "Amplifier branch 1"
    }
}

pcm.dsnoop_0 {
    type dsnoop
    ipc_key 512
    ipc_key_add_uid true
    slave {
        pcm "onboardcodec1"
        period_time 5000
        period_size 0
        buffer_time 15000
        buffer_size 0
        rate 32000
        format S24_LE
        channels 4
    }
}

pcm.dmixer_0 {
    #dmix plugin can be only connected to hw plugin
    type dmix
    ipc_key 2048
    ipc_key_add_uid true
    slave {
        pcm "onboardcodec1"
        period_time 5000
        period_size 0
        buffer_time 15000
        buffer_size 0
        rate 32000
        format S24_LE
        channels 4
    }
}

pcm.onboardcodec1 {
    type hw
    card onboardcodec1
}

As I only want to list the audio branches which are really available on the hardware, I needed a configuration which is selected using the sound card.
I continued configuring using /usr/share/alsa/pcm/ and /usr/share/alsa/cards/ but until now I am not getting a clue on how this has to be done  and I cannot find any documentation on how this must be configured. It's quite complex.

My current state is included below. The default audio branches are shown using aplay -L and contains a dmixer and dsnoop element. I am now trying to create an amplifier branch using the front speaker type but I don't know how to link it to the dmixer element.

TracsAmpliOnboard1.pcm.default {
        @args [ CARD ]
        @args.CARD {
                type string
        }
        type asym
        playback.pcm {
                type plug
                slave.pcm {
                       @func concat
                       strings [ "dmix:" $CARD ",DEV=0"]
                }
        }
        capture.pcm {
                type plug
                slave.pcm {
                        @func concat
                        strings [ "dsnoop:" $CARD ]
                }
                # to avoid possible phase inversions with digital mics
                route_policy copy
        }
        hint.device $DEVICE
}


TracsAmpliOnboard1.pcm.front.0 {
        @args [ CARD ]
        @args.CARD {
                type string
        }
        type asym
        playback.pcm {
                type plug
                slave.pcm {
                        pcm TracsAmpliOnboard1
                        subdevice 0
                }
                ttable {
                        0.0 1
                        0.1 0
                        0.2 0
                        0.3 0
                }
        }
        hint.device $DEVICE
}

Is it possible to advice me how to handle these configurations?

Thanks

Pieter Cardoen
Embedded Linux Development Engineer

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