benierc/4a-softmixer

Softmixer controller for 4A (AGL Advance Audio Architecture).

Object: Simulate a hardware mixer through and snd-aloop driver and a user space mixer
Status: In Progress
Author: Fulup Ar Foll fulup@iot.bzh
Author: Thierry Bultel thierry.bultel@iot.bzh
Date : July-2018

Features

Definition of multiple audio zones, and multiple audio cards
Usage of streams to access audio zones
Direct read from HW capture devices (eg radio chips & microphones)

Compile

    mkdir build
    cd build
    cmake ..
    make

Install Alsa Loopback Driver

    sudo modprobe snd-aloop

Assert LUA config file match your config

    vim $PROJECT_ROOT/conf.d/project/lua.d/softmixer-01.lua

    # make sure both your loopback and targeted sound card path are valid

Run from shell

    afb-daemon --name 4a-softmixer-afbd --port=1234 --workdir=/home/fulup/Workspace/Audio-4a/4a-softmixer/build \
               --binding=package/lib/softmixer-binding.so --roothttp=package/htdocs --token= --tracereq=common --verbose

    # lua test script should return a response looking like
    response= {
      [1] = { ["uid"] = navigation,["runid"] = 101,["alsa"] = hw:5,0,6,["volid"] = 103,}
            , ["params"] = { ["channels"] = 2,["format"] = 2,["rate"] = 48000,["access"] = 3,} 
     ,[2] = {  ....
    }

    # runid: pause/resume alsa control you may change it with 'amixer -D hw:Loopback cset numid=101 on|off
    # volid: volume alsa control you may change it from 'alsamixer -Dhw:Loppback' or with 'amixer -D hw:Loopback cset numid=103 NN (o-100%)

Retrieve audio-stream alsa endpoint from response to 'L2C:snd_streams' command. Depending on your config 'hw:XXX' will change. Alsa snd-aloop impose '0' as playback device. Soft mixer will start from last subdevice and allocates one subdev for each audio-stream.

Play some music

snd-aloop only supports these audio formats:

S16_LE S16_BE S32_LE S32_BE FLOAT_LE FLOAT_BE

Using gstreamer is a simple way to perform the conversion, if your audio file is not of one of these.

    gst-launch-1.0 filesrc location=insane.wav ! wavparse ! audioconvert ! audioresample ! alsasink device=hw:Loopback,0,2

Warning

Alsa tries to automatically store current state into /var/lib/alsa/asound.state when developing/testing this may create impossible situation. In order to clean up your Alsa snd-aloop config, a simple "rmmod" might not be enough in some case you may have to delete /var/lib/alsa/asound.state before applying "modprobe".

In case of doubt check with folling command that you start from a clear green field

rmmod snd-aloop && modprobe --first-time  snd-aloop && amixer -D hw:Loopback controls | grep vol

Work in Progress

Support capture from bluez

Known issues

From times to times, playing an audio file make the sound output with higher pitch
The playback loop could be improved, using direct access to the ring buffer instead of copies to stack (could save some CPU time)

benierc / 4a-softmixer