How to raise the limit of 32 pcm.softvol interfaces?

Barry Scott <barry.scott@xxxxxxxxxxxx> · Wed, 03 Sep 2014 18:23:49 +0100

It seems that there is a limit of 32 pcm softvol interfaces.

In my test script I loop running speaker-test with a new softvol
on each run and finally see this after creating 32 pcm softvol.

speaker-test 1.0.27.2

Playback device is default
Stream parameters are 48000Hz, S16_LE, 1 channels
Using 16 octaves of pink noise
ALSA lib pcm_softvol.c:747:(softvol_load_control) Cannot add a control
Playback open error: -12,Cannot allocate memory

This is the code we use in asound.conf to create the softvol:

pcm.softvol
{
    type softvol
    slave
    {
        pcm "playback"
        format "S16_LE"
    }
    control
    {
        name
        {
            @func concat
            strings [ "NTB_"
                      {
                        @func getenv
                        vars [ ONELAN_MIXER_SUFFIX ]
                        default "Unknown"
                      }
                    ]
        }
        card "PCH"
    }
}

pcm.!default
{
    type plug
    slave.pcm "softvol"
}

I have been reading alsa code and Googling but have not yet found where this limit is coming from.

Could you point in the right direction please?

Barry

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