Android in Wonderland

Modern software development is a complex task, and having an IDE that guides the developer can make this a bit more directed.  I imported the ardmix github java code into Android Studio 3.2 and converted it to kotlin, just to make life interesting.  The syntax is similar to java, but cleaner, and has a more modern feel.  Android Studio considers this a first class language and I was able to compile and run the app after a bit of tweaking.  I will not miss Java, and suspect Google feels the same.

The source is posted on gitlab ardosc, under the GPL3+ license.  It uses an OSC Library called NetUtil to handle the UDP communication to Ardour.  The java sources for de.sciss.net NetUtil were developed by Hanns Holger Rutz and licensed under LGPL 2.1 or later.  The original sources can be found at https://github.com/Sciss/NetUtil/.

I plan to release this as a free Google Play store app with no strings once I am finished testing, and will be using the app with the RPi3 in the field as part of the tests.  There is more conversion to do from Java idioms to Kotlin, as I begin to be comfortable with the syntax and best practices.  The mechanical conversion compiled and ran but lint finds lots of fluff and I know it can be much cleaner.

Controlling Ardour with OSC and Android

Now that I have a stable RPi3 running alpine linux 4.14.52-0-rpi2, jackd2 1.9.10, and ardour 5.12.0, and have the recording and playback operational; it is time to work on the remote control.  The use case I am working on is to have the RPi3 with a battery and a stereo mic in a small bag that can be placed unobtrusively in the center of a jam circle and record the session.  I want to have a small android tablet controlling the mix and transport in hand.  That will operate ardour using the OSC protocol.  

It is easy to enable OSC in Ardour, see the Ardour Manual section here. 
The more complicated part is to acquire a suitable Android app that can deal with Ardour.
Candidates include TouchOSC for Android and iPad, which looks full featured and not very expensive, and a number of other apps in various states of development or abandonment. 

As I prefer free and open source software,  I settled on ardmix, by Detlef Urban, which is a working Android app.  The app has to be built from source so my Android Studio adventure begins.

I installed and built oscchief, a very useful command line osc tool from Sebastian Ruml.  This allows me to emulate both sides of the full system, either ardour or the ardmix app.  I can see the OSC messages being sent, and send appropriate canned messages for testing and debugging.

Android development is a complex and dynamic effort.  I feel like Alice in Wonderland, 

"Now, here, you see, it takes all the running you can do to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!"

So my implicit task list has just enlarged while I refresh my Android development skill.
I also want to add the led blinking lights to my list, as the RPi3 has a red and a green LED and I think they should indicate running (green) and recording (red).  That looks like a fun diversion when the android complexities get overwhelming.

Jack configuration: running with low latency

I have been using the jack audio connection kit  on linux since I can recall and ardour since 1999, and trust them to run well together.  I tried both jack1 and jack2 on the RPi3 and both run fine, so I went with jack2 as it can use more than one cpu.  I wrote an OpenRC start/stop/status script that handles the desired ulimit settings, as I could not get pam limits.conf to work in Alpine.   I built my own jackd from jack2 git source so I could do without the dbus configuration, trying to keep this simple.

#!/sbin/openrc-run

#

# Copyright (C) 2018, Samuel S Chessman

# SPDX-License-Identifier: GPL-3.0-or-later

# Start the jackd audio daemon as root for rt/memlock

# the settings below are in /etc/conf.d/jackd

#name=jackd

#pidfile=/var/run/jackd.pid

#command_user="sam:realtime"

#command="/usr/local/bin/jackd"

#command_args="-t 200 -p 2048 -R -n default -d alsa -s -n2 -r96000 -p 512 -dhw:RPiCirrus"

#command_background=true

# set the jackd ulimit

ulimit -r 99

ulimit -l 131072

ulimit -e unlimited

# set the users ulimit on ssh login

PID=$(cat /var/run/sshd.pid)

prlimit  -p $PID  --rtprio=99

prlimit  -p $PID  --memlock=134217728

prlimit  -p $PID  --nice=-20

depend() {

        after alsa

        after sshd

}

status() {

        if [ -e ${pidfile} ] ; then

                su $user -c "jack_lsp -A"

                eend $? "jackd is not running"

        else

                eerror "jackd is not running"

        fi

}

To have this run at boot:
rc-update add jackd default

There is a status command:
/etc/init.d/jackd status
system:capture_1
   alsa_pcm:hw:RPiCirrus:out1
system:capture_2
   alsa_pcm:hw:RPiCirrus:out2
system:playback_1
   alsa_pcm:hw:RPiCirrus:in1
system:playback_2
   alsa_pcm:hw:RPiCirrus:in2    

This corresponds to what ALSA and jack_lsp are reporting.
aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: vc4hdmi [vc4-hdmi], device 0: MAI PCM vc4-hdmi-hifi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: RPiCirrus [RPi-Cirrus], device 0: WM5102 AiFi wm5102-aif1-0 []
  Subdevices: 0/1
  Subdevice #0: subdevice #0
oscar:/opt/audiopi$ jack_lsp
system:capture_1
system:capture_2
system:playback_1
system:playback_2