ALSA unable to use dmix with route

Question

I have an alsa config file which I use to map stereo speakers on to my 5.0 speaker setup.

The file looks like this:

pcm.all8 {
    type plug
    slave {
        pcm "hw:0,0"
        channels 8
    }
    hint.description "8 channel analog"
}

pcm.music4 {
    type route
    slave {
        pcm all8
        channels 8
    }

    ttable {
      0.0 1
      1.1 1
      0.2 1    # Copy Front Left to Rear Left
      1.3 1    # Copy Front Right to Rear Right
      0.4 0.8  # Copy Front Left to Front Centre
      1.4 0.8  # Copy Front Right to Front Centre
    }

    hint.description "2 channels duplicated on front and rear"
}

I currently use the "music4" device to play music from one program but I now need a second program to have access to the device too. I need to use dmix as, currently, the device is locked.

I tried adding this to the config (which I shamelessly copied from https://www.alsa-project.org/main/index.php/Asoundrc#dmix):

pcm.dmixer  {
        type dmix
        ipc_key 1024
        slave {
                pcm music4
                period_time 0
                period_size 1024
                buffer_size 4096
                rate 44100
        }
        bindings {
                0 0
                1 1
        }

        hint.description "Dmixed - 4 speakers"
}

When I try to use this device I get an error message saying "dmix plugin can be only connected to hw plugin" but how can I do that while preserving my mappings?

Answer 1

Managed to work this one out. Solution looks like this:

pcm.dmixer  {
        type dmix
        ipc_key 1024
        ipc_key_add_uid true
        slave {
                pcm "hw:0,0"
                period_time 0
                period_size 1024
                buffer_size 4096
                rate 44100
                channels 8
        }

        bindings {
          0 0
          1 1
          2 2
          3 3
          4 4
          5 5
          6 6
          7 7
        }


        hint.description "Raw dmixer - 8 channels"
}

pcm.dmix4 {
    type plug
    slave.pcm dmixer
    slave.channels 8

    ttable {
      0.0 1
      1.1 1
      0.2 1    # Copy Front Left to Rear Left
      1.3 1    # Copy Front Right to Rear Right
      0.4 0.8  # Copy Front Left to Front Centre
      1.4 0.8  # Copy Front Right to Front Centre
    }

    hint.description "Dmixed - 2 channels to 5.0"

}