Raspberry Pi als Netzwerk- und Bluetooth-Audiogerät (Teil 1)

Installation Hifiberry

Hifiberry stellt eine allgemeine Installationsanleitung zur Verfügung, die auch für Arch Linux ARM gilt. Meine /boot/config.txt sieht danach folgendermaßen aus:

# See /boot/overlays/README for all available options

gpu_mem=64
initramfs initramfs-linux.img followkernel

dtoverlay=hifiberry-dacplus

Je nach Modell des Hifiberry muss natürlich ein anderes Overlay eingefügt werden. Das reicht dann auch bereits schon aus, um dem Hifiberry nach einem Neustart Töne zu entlocken.

Konfiguration Pulseaudio

Als erstes müssen ein paar Pakete installiert werden:

[root@alarmpi ~]# pacman -S pulseaudio pulseaudio-zeroconf pulseaudio-bluetooth

Das Zeroconf-Paket dient dazu, damit Pulseaudio per Avahi im Netzwerk seine Dienste anbieten, das Bluetooth-Paket sorgt dafür, dass Pulseaudio den Audioeingang per Bluetooth via BlueZ erstellen kann.

Entgegen aller Ratschläge im Web wird Pulseaudio als Systemdienst betrieben. Üblicherweise wird der Pulseaudio-Dämon als Benutzer-Dämon betrieben, aber der Audio-Pi soll ja ohne Benutzer-Anmeldung ganz stupide Audio entgegennehmen und auf dem Audioausgang des Hifiberry ausgeben. Auf einem regulären Desktop oder Laptop sollte das tatsächlich nicht so gemacht werden.

Damit Pulseaudio als Systemdienst starten kann, braucht systemd eine Datei namens bspw. /etc/systemd/system/pulseaudio.service:

[Unit]
Description=PulseAudio system server

[Service]
ExecStart=/usr/bin/pulseaudio --system --disallow-exit --log-target=journal
#ExecStart=/usr/bin/pulseaudio --system --disallow-exit --disallow-module-loading --log-target=journal
ExecReload=/bin/kill -HUP $MAINPID

[Install]
WantedBy=multi-user.target

Solange die Konfiguration nicht finalisiert ist, bleibt --disallow-module-loading auskommentiert. Wenn Pulseaudio als Systemdienst betrieben wird, braucht es einen Nutzer namens pulse und zwei Gruppen, pulse und pulse-access:

[root@alarmpi ~]# groupadd --system pulse
[root@alarmpi ~]# groupadd --system pulse-access
[root@alarmpi ~]# useradd --system -g pulse -G audio -d /var/run/pulse -m pulse
[root@alarmpi ~]# usermod -G pulse-access root
[root@alarmpi ~]# usermod -G pulse-access alarm

Ich habe keine Ahnung, ob die beiden letzten Befehle wirklich notwendig sind, schaden tun sie aber auch erstmal nicht. Als nächstes wird verhindert, dass Pulseaudio bei Anmeldung eines Nutzers normal startet:

[root@alarmpi ~]# echo "default-server = /var/run/pulse/native" >> /etc/pulse/client.conf
[root@alarmpi ~]# echo "autospawn = no" >> /etc/pulse/client.conf

Der Dienst kann jetzt enabled und gestartet werden:

[root@alarmpi ~]# systemctl daemon-reload
[root@alarmpi ~]# systemctl enable pulseaudio.service
[root@alarmpi ~]# systemctl start pulseaudio.service

Bevor alles funktioniert, wird Pulseaudio sicher noch ein paar Mal neu gestartet. Für die Konfiguration von Pulseaudio werden die Dateien system.pa und daemon.conf in /etc/pulse benutzt.

/etc/pulse/system.pa:

#!/usr/bin/pulseaudio -nF
#
# This file is part of PulseAudio.
#
# PulseAudio is free software; you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# PulseAudio is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.

# This startup script is used only if PulseAudio is started in system
# mode.

### Automatically load driver modules depending on the hardware available
.ifexists module-udev-detect.so
load-module module-udev-detect tsched=0
.else
### Use the static hardware detection module (for systems that lack udev/hal support)
load-module module-detect
.endif

### Load several protocols
.ifexists module-esound-protocol-unix.so
load-module module-esound-protocol-unix
.endif
load-module module-native-protocol-unix

### Automatically restore the volume of streams and devices
load-module module-stream-restore
load-module module-device-restore

### Automatically restore the default sink/source when changed by the user
### during runtime
### NOTE: This should be loaded as early as possible so that subsequent modules
### that look up the default sink/source get the right value
load-module module-default-device-restore

### Automatically move streams to the default sink if the sink they are
### connected to dies, similar for sources
load-module module-rescue-streams

### Make sure we always have a sink around, even if it is a null sink.
load-module module-always-sink

### Automatically suspend sinks/sources that become idle for too long
load-module module-suspend-on-idle

### Enable positioned event sounds
load-module module-position-event-sounds

### Customizations
#load-module module-native-protocol-unix auth-anonymous=1
load-module module-zeroconf-publish
load-module module-native-protocol-tcp auth-ip-acl=127.0.0.1;192.168.1.0/24 auth-anonymous=1

set-default-sink 0
#set-card-profile 0 stereo-fallback

### Automatically load driver modules for Bluetooth hardware
.ifexists module-bluetooth-policy.so
load-module module-bluetooth-policy
.endif

.ifexists module-bluetooth-discover.so
load-module module-bluetooth-discover
.endif

/etc/pulse/daemon.conf:

# This file is part of PulseAudio.
#
# PulseAudio is free software; you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# PulseAudio is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.

## Configuration file for the PulseAudio daemon. See pulse-daemon.conf(5) for
## more information. Default values are commented out.  Use either ; or # for
## commenting.

; daemonize = no
; fail = yes
; allow-module-loading = yes
; allow-exit = yes
; use-pid-file = yes
; system-instance = no
; local-server-type = user
; enable-shm = yes
; enable-memfd = yes
; shm-size-bytes = 0 # setting this 0 will use the system-default, usually 64 MiB
; lock-memory = no
; cpu-limit = no

; high-priority = yes
; nice-level = -11

; realtime-scheduling = yes
; realtime-priority = 5

; exit-idle-time = 20
; scache-idle-time = 20

; dl-search-path = (depends on architecture)

; load-default-script-file = yes
; default-script-file = /etc/pulse/default.pa

; log-target = auto
; log-level = notice
; log-meta = no
; log-time = no
; log-backtrace = 0

; resample-method = speex-float-1
resample-method = trivial
; avoid-resampling = false
; enable-remixing = yes
; remixing-use-all-sink-channels = yes
; enable-lfe-remixing = no
; lfe-crossover-freq = 0

flat-volumes = no
; flat-volumes = yes

; rlimit-fsize = -1
; rlimit-data = -1
; rlimit-stack = -1
; rlimit-core = -1
; rlimit-as = -1
; rlimit-rss = -1
; rlimit-nproc = -1
; rlimit-nofile = 256
; rlimit-memlock = -1
; rlimit-locks = -1
; rlimit-sigpending = -1
; rlimit-msgqueue = -1
; rlimit-nice = 31
; rlimit-rtprio = 9
; rlimit-rttime = 200000

; default-sample-format = s16le
; default-sample-rate = 44100
; alternate-sample-rate = 48000
; default-sample-channels = 2
; default-channel-map = front-left,front-right

; default-fragments = 4
; default-fragment-size-msec = 25

; enable-deferred-volume = yes
; deferred-volume-safety-margin-usec = 8000
; deferred-volume-extra-delay-usec = 0<

Nach einem Neustart von Pulseaudio

[root@alarmpi ~]# systemctl restart pulseaudio.service

finden andere Pulseaudio-Dämonen im Netz dann auch schon den Pi. Vielleicht müssen noch entsprechende Zeroconf-Pulseaudio-Pakete auf den jeweiligen Rechnern installiert werden, sollte der Pi nicht in der Liste der Audioausgabegeräte auftauchen.

Konfiguration Bluetooth

Bluetooth unter Linux kann einen in den Wahnsinn treiben. Als Lektüre dazu empfehle ich Bluez must be one of the best kept secrets in Linux und Bluez – greatest Linux mystery. Ohne ordentliche Dokumentation sehe ich leider auch kaum eine Möglichkeit, die letzten Bluetooth-Baustellen zu beseitigen.

Natürlich werden erstmal ein paar Pakete benötigt:

[root@alarmpi ~]# pacman -S bluez bluez-utils

Dann wird die /etc/bluetooth/main.conf bearbeitet:

[General]

# Default adapter name
# Defaults to 'BlueZ X.YZ'
Name = wohn

# Default device class. Only the major and minor device class bits are
# considered. Defaults to '0x000000'.
#Class = 0x000100
Class = 0x200420

# How long to stay in discoverable mode before going back to non-discoverable
# The value is in seconds. Default is 180, i.e. 3 minutes.
# 0 = disable timer, i.e. stay discoverable forever
DiscoverableTimeout = 0

# How long to stay in pairable mode before going back to non-discoverable
# The value is in seconds. Default is 0.
# 0 = disable timer, i.e. stay pairable forever
PairableTimeout = 0

# Automatic connection for bonded devices driven by platform/user events.
# If a platform plugin uses this mechanism, automatic connections will be
# enabled during the interval defined below. Initially, this feature
# intends to be used to establish connections to ATT channels. Default is 60.
#AutoConnectTimeout = 60

# Use vendor id source (assigner), vendor, product and version information for
# DID profile support. The values are separated by ":" and assigner, VID, PID
# and version.
# Possible vendor id source values: bluetooth, usb (defaults to usb)
#DeviceID = bluetooth:1234:5678:abcd

# Do reverse service discovery for previously unknown devices that connect to
# us. This option is really only needed for qualification since the BITE tester
# doesn't like us doing reverse SDP for some test cases (though there could in
# theory be other useful purposes for this too). Defaults to 'true'.
#ReverseServiceDiscovery = true

# Enable name resolving after inquiry. Set it to 'false' if you don't need
# remote devices name and want shorter discovery cycle. Defaults to 'true'.
#NameResolving = true

# Enable runtime persistency of debug link keys. Default is false which
# makes debug link keys valid only for the duration of the connection
# that they were created for.
#DebugKeys = false

# Restricts all controllers to the specified transport. Default value
# is "dual", i.e. both BR/EDR and LE enabled (when supported by the HW).
# Possible values: "dual", "bredr", "le"
#ControllerMode = dual

# Enables Multi Profile Specification support. This allows to specify if
# system supports only Multiple Profiles Single Device (MPSD) configuration
# or both Multiple Profiles Single Device (MPSD) and Multiple Profiles Multiple
# Devices (MPMD) configurations.
# Possible values: "off", "single", "multiple"
#MultiProfile = off

# Permanently enables the Fast Connectable setting for adapters that
# support it. When enabled other devices can connect faster to us,
# however the tradeoff is increased power consumptions. This feature
# will fully work only on kernel version 4.1 and newer. Defaults to
# 'false'.
#FastConnectable = false

# Default privacy setting.
# Enables use of private address.
# Possible values: "off", "device", "network"
# "network" option not supported currently
# Defaults to "off"
# Privacy = off

Enable=Source,Sink,Media,Socket

[GATT]
# GATT attribute cache.
# Possible values:
# always: Always cache attributes even for devices not paired, this is
# recommended as it is best for interoperability, with more consistent
# reconnection times and enables proper tracking of notifications for all
# devices.
# yes: Only cache attributes of paired devices.
# no: Never cache attributes
# Default: always
#Cache = always

[Policy]
#
# The ReconnectUUIDs defines the set of remote services that should try
# to be reconnected to in case of a link loss (link supervision
# timeout). The policy plugin should contain a sane set of values by
# default, but this list can be overridden here. By setting the list to
# empty the reconnection feature gets disabled.
#ReconnectUUIDs=00001112-0000-1000-8000-00805f9b34fb,0000111f-0000-1000-8000-00805f9b34fb,0000110a-0000-1000-8000-00805f9b34fb

# ReconnectAttempts define the number of attempts to reconnect after a link
# lost. Setting the value to 0 disables reconnecting feature.
#ReconnectAttempts=7

# ReconnectIntervals define the set of intervals in seconds to use in between
# attempts.
# If the number of attempts defined in ReconnectAttempts is bigger than the
# set of intervals the last interval is repeated until the last attempt.
#ReconnectIntervals=1,2,4,8,16,32,64

# AutoEnable defines option to enable all controllers when they are found.
# This includes adapters present on start as well as adapters that are plugged
# in later on. Defaults to 'false'.
AutoEnable=true

Die wichtigen Dinge passieren in "Enable=" und ich habe keine Ahnung, warum "Source, Sink, Media" nicht ausgereicht hat. "Name=" ist frei wählbar – ich würde auf Sonderzeichen verzichten. "Class=0x200420" sagt an, dass der Bluetooth-Adapter sich als Car Audio System ausgeben soll (Quelle). Vermutlich gehen auch andere – hilfreich dabei dürfte der Bluetooth Class of Device (CoD) Generator sein. Auf der linken Seite einfach Audio oben und Audio unten auswählen, dann erscheint rechts eine Liste möglicher Minor Device Classes. Ich habe es erst mit 0x200428 probiert, aber ohne Erfolg, was aber wohl eher an den fehlenden DBus-Konfigurationen lag.

Konfiguration DBus

Unter Linux kommunizieren Prozesse untereinander auf verschiedenen Wegen, und DBus ist einer davon. Das ganze Setup erfordert, dass verschiedene Dienste unter verschiedenen Benutzerkonten miteinander sprechen dürfen.

/etc/dbus-1/system.d/pulseaudio.conf:

<?xml version="1.0"?> <!--*-nxml-*-->
<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig>
    <policy group="pulse">
        <allow own="org.pulseaudio.Server"/>
    </policy>

    <policy context="default">
        <allow send_destination="org.pulseaudio.Server"/>
        <allow receive_sender="org.pulseaudio.Server"/>
    </policy>
</busconfig>

/etc/dbus-1/system.d/pulseaudio-bluetooth.conf:

<busconfig>
  <policy user="pulse">
    <allow send_destination="org.bluez"/>
  </policy>
</busconfig>

/etc/dbus-1/system.d/bluetooth.conf:

<!-- This configuration file specifies the required security policies
     for Bluetooth core daemon to work. -->

<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig>

  <!-- ../system.conf have denied everything, so we just punch some holes -->

  <policy user="root">
    <allow own="org.bluez"/>
    <allow send_destination="org.bluez"/>
    <allow send_interface="org.bluez.Agent1"/>
    <allow send_interface="org.bluez.MediaEndpoint1"/>
    <allow send_interface="org.bluez.MediaPlayer1"/>
    <allow send_interface="org.bluez.ThermometerWatcher1"/>
    <allow send_interface="org.bluez.AlertAgent1"/>
    <allow send_interface="org.bluez.Profile1"/>
    <allow send_interface="org.bluez.HeartRateWatcher1"/>
    <allow send_interface="org.bluez.CyclingSpeedWatcher1"/>
    <allow send_interface="org.bluez.GattCharacteristic1"/>
    <allow send_interface="org.bluez.GattDescriptor1"/>
    <allow send_interface="org.freedesktop.DBus.ObjectManager"/>
    <allow send_interface="org.freedesktop.DBus.Properties"/>
    <allow send_destination="org.bluez.Manager"/>
    <allow receive_sender="org.bluez.Manager"/>
    <allow send_destination="org.bluez.Adapter"/>
    <allow receive_sender="org.bluez.Adapter"/>
    <allow send_destination="org.bluez.Device"/>
    <allow receive_sender="org.bluez.Device"/>
    <allow send_destination="org.bluez.Service"/>
    <allow receive_sender="org.bluez.Service"/>
    <allow send_destination="org.bluez.Database"/>
    <allow receive_sender="org.bluez.Database"/>
    <allow send_destination="org.bluez.Security"/>
    <allow receive_sender="org.bluez.Security"/>
  </policy>

  <policy at_console="true">
    <allow send_destination="org.bluez"/>
  </policy>

  <!-- allow users of lp group (printing subsystem) to
       communicate with bluetoothd -->
  <policy group="lp">
    <allow send_destination="org.bluez"/>
  </policy>

  <policy context="default">
    <deny send_destination="org.bluez"/>
  </policy>

</busconfig>

Das ist aus verschiedenen Quellen zusammengetragen. Falls jemand versteht, was die einzelnen Zeilen tun: Ich freue mich über Kommentare. Ich vermute, die Zeilen mit Bluetooth-Druckern sind überflüssig, aber es funktioniert so erstmal. In der verwendeten Anleitung fand ich den Hinweis, dass

[root@alarmpi ~]# systemctl restart dbus && systemctl restart polkit && systemctl restart systemd-logind

bereits reichen sollte, ein Neustart aber die sichere Variante sei. Wie jetzt über Bluetooth Audio empfangen kann, erkläre ich im Abschnitt "Baustellen".

Baustellen