LuneOS Communication Infrastructure

Overview

Audio

Audio within LuneOS will be handled by PulseAudio (http://www.freedesktop.org/wiki/Software/PulseAudio). It offers a great integration in into the Linux system and with the software we're using for communication purpose (ofono, bluez). Handling audio on an embedded device is different than on a desktop system. [...]

ALSA Use Case Manager

 The ALSA Use Case Manager (UCM) is a LGPL library designed to allow high
 level control of audio use cases in sound device hardware. It is intended
 to be used by applications to quickly and easily change the hardware audio
 use case of a device in a generic and portable manner.

http://www.slimlogic.co.uk/2009/02/alsa-use-case-manager/
alsaucm command line utility is available in version 1.0.25 of alsa-utilities which is already available in oe-core

UCM support in PulseAudio

Basic UCM support is in Pulseaudio HEAD available but not released. Latest version is 2.0.

Links:

Linaro Blueprint: https://blueprints.launchpad.net/linaro-ubuntu/+spec/enable-update-alsa-pulseaudio-ucm
Linaro Multimedia UCM integration: https://launchpad.net/linaro-multimedia-ucm/2011.11/2011.11
PulseAudio UCM mapping: https://wiki.linaro.org/WorkingGroups/Middleware/Multimedia/Specs/1111/AudioIntegration/UCMPulseAudio/Analyzation
https://wiki.linaro.org/WorkingGroups/Middleware/Multimedia/Specs/1111/AudioIntegration/UCMPulseAudio

Using PulseAudio with UCM

Setting card profile (HiFi or Voice Call):

pactl set-card-profile 0 HiFi
pactl set-card-profile 0 "Voice Call"

Communication Daemon

The communication daemon will offer interfaces for the different communication interfaces like

bluetooth
network
telephony
NFC

The UI can access the different interfaces via various service interfaces

org.webosports.Bluetooth
org.webosports.Network
org.webosports.Telephony
org.webosports.NFC

The communication daemon is just a thin wrapper for different service daemons providing the real functionality:

bluetooth: BlueZ
network: ConnMan
telephony: oFono, mmsd
NFC: neard

Design

Communications between native services and userland applications is generally handled through dbus. This is great, until your userland applications exist in a JavaScript VM. The easiest way to get data in and out of JavaScript applications right now appears to be WebSockets, so let's use that.

Applications speak WebSockets
Services speak DBus

NodeJS can do both of these nicely, and lets our frontend guys have a bit of say in how they expect their data, since it's the same language they speak. After evaluating a handful of DBus libraries for NodeJS, dbus-native seems to be our best bet: It's actively developed, pure javascript and has a nice clean API:

  var dbus = require('dbus-native');

  var bus = dbus.systemBus();
  var nm = bus.getInterface('org.freedesktop.NetworkManager', '/org/freedesktop/NetworkManager', 'org.freedesktop.NetworkManager');
  nm.Enable(true, function(err, res) {
      console.log(err, res);
  });

There will be a basic router daemon which will require in the actual models which speak DBus; this lets us keep a single endpoint and also do service-name-based routing (ie: org.webosports.NFC, rather than ws://localhost:12345).

Caveats

Node has to be run with --harmony_proxies to support the ECMAScript 6 Proxy objects which dbus-native relies on.