ADK Audio Sink Application Peer Device User Guide

ADK Audio Sink Application Peer Device User Guide
ADK
Audio Sink Application Peer Device
User Guide
Issue 5
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Document History
Revision
Date
History
1
05 MAY 15
Original publication of this document
2
15 JUN 14
Minor corrections
3
25 JUN 14
Minor editorial corrections
4
7 APR 15
Updated for ADK 4
5
05 MAY 15
Minor editorial corrections
General information
Information on this product
Customer support for this product
More detail on compliance and standards
Help with this document
www.csr.com
[email protected]
www.csrsupport.com
[email protected]
[email protected]
Trademarks, Patents and Licences
Unless otherwise stated, words and logos marked with ™ or ® are trademarks registered or owned by CSR plc
and/or its affiliates.
Bluetooth® and the Bluetooth logos are trademarks owned by Bluetooth SIG, Inc. and licensed to CSR.
Other products, services and names used in this document may have been trademarked by their respective owners.
The publication of this information does not imply that any licence is granted under any patent or other rights owned
by CSR plc or its affiliates.
CSR reserves the right to make technical changes to its products as part of its development programme.
While every care has been taken to ensure the accuracy of the contents of this document, CSR cannot accept
responsibility for any errors.
Life Support Policy and Use in Safety-critical Compliance
CSR’s products are not authorised for use in life-support or safety-critical applications. Use in such applications is
done at the sole discretion of the customer. CSR will not warrant the use of its devices in such applications.
Performance and Conformance
Refer to www.csrsupport.com for compliance and conformance to standards information.
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ADK Audio Sink Application Peer Device User Guide
Contacts
Contents
Tables, Figures and Equations
Table 3.1: Configuring Peer Device Roles .................................................................................................................... 7
Table 3.2: Peer Device States ...................................................................................................................................... 7
Table 3.3: Audio Sink Application Events for Peer Device Mode .................................................................................. 8
Table 3.4: Vendor Specific AVRCP Commands for Peer Device Mode ........................................................................ 9
Table 3.5: GAIA Commands Supported by Peer Device Mode .................................................................................. 10
Table 3.6: Peer Device Mode Supported A2DP Codecs............................................................................................. 10
Table 3.7: Peer Device Pairing Methods..................................................................................................................... 11
Table 3.8: Peer Device Pairing Procedure .................................................................................................................. 12
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Document History ......................................................................................................................................................... 2
Contacts........................................................................................................................................................................ 2
Trademarks, Patents and Licences .............................................................................................................................. 2
Life Support Policy and Use in Safety-critical Compliance............................................................................................ 2
Performance and Conformance .................................................................................................................................... 2
Contents ....................................................................................................................................................................... 3
Tables, Figures and Equations ..................................................................................................................................... 3
1.
Introduction ........................................................................................................................................................ 5
2.
Overview ............................................................................................................................................................ 6
2.1. Peer Sessions ................................................................................................................................................ 6
3.
Peer Device Mode.............................................................................................................................................. 7
3.1. Multipoint ........................................................................................................................................................ 7
3.2. Peer Device Roles .......................................................................................................................................... 7
3.3. Peer Device States ......................................................................................................................................... 7
3.4. Peer Device Events ........................................................................................................................................ 8
3.5. Supporting Multiple AV Sources ..................................................................................................................... 9
3.6. Vendor Specific Peer Device AVRCP Commands ......................................................................................... 9
3.7. GAIA with Peer Devices ............................................................................................................................... 10
3.8. Supported A2DP Codecs ............................................................................................................................. 10
3.9. Voice Prompts .............................................................................................................................................. 11
3.10.
Peer Device Pairing .................................................................................................................................. 11
3.11.
Ending a Peer Session ............................................................................................................................. 12
3.12.
Peer Device Link Loss .............................................................................................................................. 12
4.
TrueWireless Stereo ........................................................................................................................................ 13
4.1. Supported Bluetooth Transports ................................................................................................................... 13
4.2. TWS Audio Sources ..................................................................................................................................... 13
4.3. TWS Audio Routing ...................................................................................................................................... 13
4.4. TWS Volume Control .................................................................................................................................... 16
4.5. TWS Device Trim ......................................................................................................................................... 16
4.6. TWS Single Device Mode ............................................................................................................................. 17
4.7. TWS Separate Device Mode ........................................................................................................................ 17
5.
ShareMe .......................................................................................................................................................... 19
5.1. ShareMe Audio Routing ............................................................................................................................... 19
5.2. ShareMe Volume Control ............................................................................................................................. 19
5.3. Remote Peer Controls AV Source ................................................................................................................ 19
Document References ................................................................................................................................................ 21
Terms and Definitions ................................................................................................................................................. 22
Table 4.1: TWS Audio Sources ................................................................................................................................... 13
Table 4.2: Priority List for Audio Sources in TWS Automatic Mode ............................................................................ 14
Table 4.3: Events Used to Control Audio Routing for TWS Mode ............................................................................... 14
Table 4.4: TWS Default Routed Source ...................................................................................................................... 15
Table 4.5: TWS Rendering Options ............................................................................................................................ 15
Table 4.6: User Events to Control TWS Device Trim .................................................................................................. 16
Table 5.1: Default Audio Priority List for ShareMe ...................................................................................................... 19
Table 5.2: AVRCP Commands used to control ShareMe relay streams ..................................................................... 20
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Figure 4.1: Example TWS Audio Rendering Use Case............................................................................................... 15
Figure 4.2: Peer Device Single Device Mode ............................................................................................................. 17
Figure 4.3: Peer Device Separate Device Mode ......................................................................................................... 17
Figure 5.1: ShareMe AVRCP Control ......................................................................................................................... 20
1.
Introduction
This document describes the Peer Device features of the Audio Sink application software that is included with the
standard installation of the CSR Audio Development Kit.
Note:
This document is an extension to the Audio Sink Application User Guide.
ADK Audio Sink Application Peer Device User Guide
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2.
Overview
In Peer Device mode, two Audio Sink application devices can connect and relay audio between each another.
2.1.
Peer Sessions
When connected, the devices are in a Peer session for the duration of the connection. There are two types of Peer
sessions:
1.
TrueWireless Stereo
2.
ShareMe
2.1.1.
TrueWireless Stereo
2.1.2.
ShareMe
ShareMe Peer sessions allow two ShareMe enabled devices to connect to one another. Audio received at one
device is relayed to the second, rendering is not synchronised. See section 5.
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ADK Audio Sink Application Peer Device User Guide
TrueWireless Stereo (TWS) Peer sessions allow two TWS enabled devices to connect to one another. Audio
received at one device is relayed to the other Peer Device and rendering is synchronised. See section 4.
3.
Peer Device Mode
This section describes the generic features of Peer Device mode that are adopted by TrueWireless Stereo and
ShareMe.
3.1.
Multipoint
Multipoint must be enabled for Peer Device Functionality to work correctly. A Peer Device relies on using one of the
available Multipoint connections to link to another Peer Device.
3.2.
Peer Device Roles

Peer Master: The Peer Master is the Peer Device whose audio source is relayed.

Peer Slave: The Peer Slave is the Peer Device that receives relayed audio from a Peer Master.
3.2.1.
Role Configuration
Each Peer Device can be configured to support a particular Peer Device role, Table 3.1 outlines the configuration
roles for a Peer Device.
Role
Description
Audio Sink
When enabled, the Peer Device will be able to adopt the Peer Slave role
Audio Source
When enabled, the Peer Device will be able to adopt the Peer Master role
Table 3.1: Configuring Peer Device Roles
Note:
By default the Peer Device is configured to support all roles. This can be re-configured, see Audio Sink
Application Configuration User Guide.
3.3.
Peer Device States
Table 3.2 describes Peer Device states.
State
Description
Peer Inquiry Mode
Peer Device is searching for another Peer Device in Discoverable mode
Peer Discoverable Mode
Peer Device is discoverable to other Peer Devices performing inquiry
Peer Device Connectable
The Peer Device is waiting to be connected to another Peer Device
Peer Device Connected
Two Peer Devices are connected in a Peer Session
Table 3.2: Peer Device States
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ADK Audio Sink Application Peer Device User Guide
Peer Devices that are connected in an active Peer Session adopt fluid roles dictated by the active state. These roles
are.
3.4.
Peer Device Events
Table 3.3 describes the Audio Sink application events explicitly handled when Peer Device mode is active.
Audio Sink Application Event
Description
EventUsrPeerSessionInquire
Start Peer Inquiry mode
EventUsrPeerSessionConnDisc
Start Peer Discoverable mode
EventUsrPeerSessionEnd
Disconnect the peer devices ending the Peer Session
EventUsrEstablishPeerConnection
Make a connection request to the paired Peer Device
ADK Audio Sink Application Peer Device User Guide
Table 3.3: Audio Sink Application Events for Peer Device Mode
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3.5.
Supporting Multiple AV Sources
Peer Devices can only support connections with up to two AV Source devices, therefore:

In a Peer Session:
It is only possible to connect a single AG to each device.

When not in a Peer Session:
A Peer Device can connect to two AV Sources.
Note:
If no Peer Session is in place and the Peer Device is connected with two AV Sources, it is not possible to initiate
a TWS session.
Vendor Specific Peer Device AVRCP Commands
Along with the standard set of AVRCP commands, additional vendor specific AVRCP commands have been
implemented to support Peer Sessions, see Table 3.4.
OPID
Command
Description
0x0
AVRCP_PEER_CMD_NOP
No Operation
0x1
AVRCP_PEER_CMD_PEER_STATUS_CHANGE
Relay availability status change
from a Peer
0x2
AVRCP_PEER_CMD_TWS_AUDIO_ROUTING
Set which audio channels a peer
will render
0x3
AVRCP_PEER_CMD_TWS_VOLUME
Not used (reserved for future use)
0x4
AVRCP_PEER_CMD_AUDIO_CONNECTION_STATUS
Update the connection status of the
audio source to the peer
0x5
AVRCP_PEER_CMD_UPDATE_AUDIO_ENHANCEMENT_SETTINGS
Update the audio enhancement
settings to the peer
0x6
AVRCP_PEER_CMD_UPDATE_USER_EQ_SETTINGS
Update the audio EQ settings to the
Peer device
0x7
AVRCP_PEER_CMD_UPDATE_TRIM_VOLUME
Set the trim volume a peer should
use
0x8
AVRCP_PEER_CMD_REQUEST_USER_EQ_SETTINGS
A TWS Peer Slave can request the
TWS Peer Master sends the EQ
settings that should be active at
both devices
Table 3.4: Vendor Specific AVRCP Commands for Peer Device Mode
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ADK Audio Sink Application Peer Device User Guide
3.6.
3.7.
GAIA with Peer Devices
For Peer Devices that support GAIA and are participating in a Peer Session as the Peer Master, certain GAIA
commands can be used to control both devices in the Peer Session. These commands are received at the Peer
Master and relayed to the Peer Slave using a custom AVRCP command. Table 3.5 lists GAIA commands actioned in
this way:
Description
GAIA_COMMAND_TOGGLE_BASS_BOOST_CONTROL
Toggle Bass Boost On/Off
GAIA_COMMAND_SET_BASS_BOOST_CONTROL
Explicitly turn Bass Boost On/Off
GAIA_COMMAND_SET_USER_EQ_PARAMETER
Set a single Multi-Band User EQ Parameters
GAIA_COMMAND_SET_USER_EQ_GROUP_PARAMETER
Set a group of Multi-Band User EQ Parameters
GAIA_COMMAND_TOGGLE_USER_EQ_CONTROL
Toggle Multi-Band User EQ On/Off
GAIA_COMMAND_SET_USER_EQ_CONTROL
Explicitly use Multi-Band User EQ On/Off
GAIA_COMMAND_TOGGLE_3D_ENHANCEMENT_CONTROL
Toggle 3D Enhancement On/Off
GAIA_COMMAND_SET_3D_ENHANCEMENT_CONTROL
Explicitly turn 3D Enhancement On/Off
Table 3.5: GAIA Commands Supported by Peer Device Mode
Note:
Other GAIA commands such as volume control and device trim control are handled by the Peer but are not
relayed to the Peer Slave.
3.8.
Supported A2DP Codecs
During an active Peer Session, support of A2DP codecs is limited, see Table 3.6.
Codec
TrueWireless Relay Support
ShareMe Relay Support
SBC
Yes
Yes
aptX
Yes
Yes
MP3
Yes
Yes
AAC
Yes
No*
aptX Low Latency
No
No
Faststream
No
No
* If an AV Source opens an AAC media channel with a ShareMe Peer Device, the
ShareMe Peer Device closes the media channel and requests the AV Source to
use one of the supported codecs.
Table 3.6: Peer Device Mode Supported A2DP Codecs
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ADK Audio Sink Application Peer Device User Guide
GAIA Command
Notes:
(1)
A Peer Device that is not participating in a Peer Session is capable of supporting the standard list of A2DP
codecs.
(2)
Peer Devices participating in a Peer Session must support the same set of A2DP codecs for Peer Device
functionality to work reliably.
3.9.
Voice Prompts
If configured, voice prompts are played on the local device and are not relayed during a Peer Session.
Voice prompts are configured as for normal Audio Sink applications. See the Audio Sink Application User Guide.
3.10. Peer Device Pairing
3.10.1. Pairing Modes
Table 3.7 describes the pairing modes supported in Peer Device mode.
Pairing Mode
Supports
Description
Temporary
TWS and
ShareMe
No pairing information is retained when the Peer session ends.
However, attempts to recover from a link loss situation are made.
Standard
TWS and
ShareMe
Pairing information is stored in the normal way. An entry is used within
the device’s PDL. This entry can drop of the end of the list if too many
pairings with other devices are made.
Permanent
TWS Only.
Pairing information is protected and permanent. Performing the “clear
paired device list procedure” does not remove the pairing information.
The pairing information can only be overwritten by pairing another
TWS device.
Table 3.7: Peer Device Pairing Methods
Notes:
(1)
The default pairing mode used by ShareMe mode is temporary.
(2)
The default pairing method used by the TWS mode is permanent.
(3)
The active pairing mode can be can be modified through configuration. See the Audio Sink Application
Configuration User Guide.
3.10.2. Peer Discoverable Mode
Peer Discoverable mode makes the Peer Device discoverable to other Peer Devices. Peer Discoverable mode can
be started by triggering the EventUsrPeerSessionConnDisc user event.
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ADK Audio Sink Application Peer Device User Guide
Before two Peer Devices can connect and begin a Peer Session, they must complete Peer Device pairing. See
sections 3.10.1 to 3.10.4.
3.10.3. Peer Inquiry Mode
Peer Inquiry mode allows a Peer Device to discover and pair with Peer Devices. Peer Inquiry mode can be started
by triggering the EventUsrPeerSessionInquire user event.
Notes:
(1)
Peer Inquiry mode provides a configurable way to limit which discovered devices are paired, see section
3.10.3.1.
(2)
Both Limited Discoverable mode and General Discoverable mode are supported for Peer Device inquiries.
This is configurable, see the Audio Sink Application Configuration User Guide.
3.10.3.1. Limiting Discovered Devices
A two stage filtering process can be used to determine if a discovered Peer Device is suitable to be paired with:
Device ID:
If selected as a device filter, the first three records of a remote Peer’s Device ID i.e. the Vendor ID
Source, Vendor ID and Product ID are matched against the local Peer’s Device ID.
If a match is found then a connection is allowed.

Peer Device SDP Record:
This SDP record contains a 128-bit UUID which is used to identify Peer Device support.
If selected as a device filter, the remote Peer’s UUID is matched against the local Peer’s UUIID. If a
match is found then a connection is allowed.
Both filters are optional, see the Audio Sink Application Configuration User Guide.
3.10.4. Peer Device Pairing Procedure
Table 3.8 describes the procedure required to pair two Peer Devices.
Step
Procedure
1
Place one Peer Device into Peer Discoverable mode, see section 3.10.2
2
Place the other Peer Device into Peer Inquiry mode, see Section 3.10.3
3
The Peer Device in Peer Inquiry Mode will discover and pair with the Peer Device in Peer
Discoverable mode
4
When paired, the Peer Devices are connected and the Peer Session begins
Table 3.8: Peer Device Pairing Procedure
3.11. Ending a Peer Session
At any time during a Peer Session the session can be ended using the EventUsrPeerSessionEnd user event.
Note:
Ending Peer Sessions does not affect connections between the Peer Devices and their connected AV Sources.
3.12. Peer Device Link Loss
When link loss is detected during an active Peer Session the default behaviour is for the Peer Master to become
connectable and the Peer Slave starts link loss recovery.
The default link loss recovery method can be switched so the Peer Master starts link loss recovery.
Note:
CSR recommend using the Peer Slave to start link loss recovery to prevent audio glitches at the Peer Master.
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ADK Audio Sink Application Peer Device User Guide

4.
TrueWireless Stereo
TrueWireless Stereo (TWS) allows two TWS devices connected in a peer session to render the same audio source
at the same time using:

Embedded timestamps in the relayed audio data

Synchronisation delays

Rate matching
In addition TWS provides synchronised volume control, taking advantage of the digital volume control framework in
the Music Manager application to allow greater control of volume timing changes.
4.1.
Supported Bluetooth Transports
The vendor specific Peer Device AVRCP commands supported for TWS Peer Sessions are listed in section 3.6.
4.2.
TWS Audio Sources
TWS Devices support the Audio Sources listed in Table 4.1. Audio sources that can be relayed to the TWS Peer
Device are explicitly listed.
Audio Source
Audio Relayed to TWS Peer
Bluetooth SCO (call audio)
No
A2DP Audio
Yes
USB Audio
Yes
2
Wired Audio (analogue or I S)
Yes*
SPDIF Audio
No
FM Receive
No
Bluetooth SCO (audio)
No
No Active Source
No
2
* Analogue audio sources can be relayed to the TWS Peer. I S
cannot be relayed to the TWS Peer.
Table 4.1: TWS Audio Sources
Note:
Table 3.6 lists the supported A2DP codecs for TWS and lists which are relayed to the TWS Peer.
4.3.
TWS Audio Routing
TWS Devices support automatic and manual audio routing modes described in sections 0 to 4.3.5.
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ADK Audio Sink Application Peer Device User Guide
For TWS devices to achieve synchronised rendering of an audio source, an A2DP connection is used to distribute
the audio data while an AVRCP connection is used to send and receive control commands.
4.3.1.
TWS Automatic Routing Mode
TWS automatic mode routes audio sources based on a priority system. The highest priority source is always routed
whenever available. Sources are routed as soon as they become available and when their priority is higher than the
currently routed source. The priority of each audio source is listed in Table 4.2.
Audio Source
1
Bluetooth SCO (call audio)
2
A2DP Audio
3
USB Audio
4
Wired Audio (analogue or I S)
5
SPDIF Audio
7
FM Receive
8
Bluetooth SCO (audio)
9
No Active Source
2
Table 4.2: Priority List for Audio Sources in TWS Automatic Mode
Note:
When TWS automatic routing is active, the user can switch to TWS Manual Mode using any of the Audio Sink
application events listed in Table 4.3.
4.3.2.
TWS Manual Audio Routing Mode
TWS manual audio routing mode is a manual audio routing process. The user must explicitly select the audio source
to route. Audio sources can be routed by generating the Audio Sink application events listed in Table 4.3.
Audio Sink Application Event
Audio Source Routed
EventUsrSelectAudioSourceNext
The next audio source is routed (based on priority list, i.e. if A2DP
audio source was active, USB audio source becomes active)
EventUsrSelectAudioSourceAnalog
Wired Audio (Analogue or I2S) is routed
EventUsrSelectAudioSourceUSB
USB Audio Source is routed
EventUsrSelectFMAudioSource
FM Receive Audio Source is routed
EventUsrSelectAudioSourceSpdif
SPDIF Audio Source is routed
EventUsrSelectAudioSourceAG1
A2DP Audio Source is routed
EventUsrSelectAudioSourceAG2
A2DP Audio Source is routed
Table 4.3: Events Used to Control Audio Routing for TWS Mode
Note:
When TWS manual routing is active the user can switch to TWS automatic routing by generating the Audio Sink
application event EventUsrSelectAudioSourceNone.
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ADK Audio Sink Application Peer Device User Guide
Priority (1 is Highest)
4.3.3.
Default TWS Audio Routing Mode
The default TWS audio routing mode is used to set which audio routing mode shall be used by the TWS device after
a power cycle. The default TWS audio routing mode is configurable, see the Audio Sink Application Configuration
User Guide.
4.3.4.
TWS Default Routed Source
Once the TWS device has been powered on, the TWS Default Routed Source shall be selected. Table 4.4 lists the
available selections for setting the TWS Default Routed Source
Description
Automatic
Automatically detects the active audio source, see section 0
Analogue
Selects the Analogue audio source
USB
Selects the USB audio source
A2DP
Selects the A2DP audio source
Table 4.4: TWS Default Routed Source
The TWS Default Routed Source is configurable, see Audio Sink Application Configuration User Guide.
4.3.5.
TWS Audio Rendering
When a TWS Peer Session has been established, the TWS Audio Rendering configuration allows the Peer Master to
dictate the audio that is rendered by both the Peer Master and Peer Slave devices. Table 4.5 lists the available
rendering options for TWS Devices.
Render
Description
Stereo
Both Left and Right channels are rendered
Left Only
Only the Left channel is rendered
Right Only
Only the right channel is rendered
Downmix
The Left and Right channels are mixed together then rendered
Table 4.5: TWS Rendering Options
Figure 4.1 outlines an example TWS audio rendering use case where the Peer Master renders the left audio channel
and the Peer Slave renders the right audio channel. The stereo audio stream received at the Peer Master is relayed
to the Peer Slave without modification and the Peer Slave only renders the right audio channel.
Peer Device
(Master)
Stereo Audio (L&R)
Left Only
Rendering audio from
AV Source 1 & relaying
to slave
Peer Device
(Slave)
Right Only
Rendering audio relayed
Stereo Audio (L&R)
from Master
Figure 4.1: Example TWS Audio Rendering Use Case
Notes:
(1)
The rendering options are configurable, see Audio Sink Application Configuration User Guide.
(2)
TWS Audio Rendering configuration is explicitly used only while Peer Sessions are active.
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ADK Audio Sink Application Peer Device User Guide
TWS Default Routed Source
4.4.
TWS Volume Control
TWS Volume is synchronised between the Peer Master and the Peer Slave, i.e:

Changing volume at the Peer Master updates the volume at both the Peer Master and the Peer Slave.

Changing volume at the Peer Slave updates the volume at both the Peer Master and the Peer Slave.
Notes:
(1)
AV Sources streaming audio to the Peer Master are not informed of the volume updates if they do not
support AVRCP Absolute Volume Control (introduced in AVRCP version 1.4).
(2)
Volume changes at the Peer Slave are sent to the Peer Master and to the streaming AV Source when the
AV Source supports AVRCP Absolute Volume Control.
TWS Device Trim
There is a Device Trim that can be used to fine tune the volume level output of individual speakers to match the
required levels, see Table 4.6.
Event
Audio Source Routed
EventUsrMasterDeviceTrimVolumeUp
Increase the trim level of the Peer Master
EventUsrMasterDeviceTrimVolumeDown
Decrease the trim level of the Peer Master
EventUsrSlaveDeviceTrimVolumeUp
Increase the trim level of the Peer Slave
EventUsrSlaveDeviceTrimVolumeDown
Decrease the trim level of the Peer Slave
Table 4.6: User Events to Control TWS Device Trim
Notes:
(1)
The Device Trim for both the Peer Master and the Peer Slave can only be modified from the Peer Master.
(2)
The default TWS Device trim levels can be pre-configured so a default trim level is used, to configure these
values, see Audio Sink Application Configuration User Guide.
A maximum and minimum trim level setting is provided to prevent the volume of the TWS slave device
being adjusted with too large a rage. To configure these values, see Audio Sink Application Configuration
User Guide.
(3)
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ADK Audio Sink Application Peer Device User Guide
4.5.
4.6.
TWS Single Device Mode
TWS Single Device mode is when two TWS Devices in an active Peer Session can operate as if they were a single
audio device and both devices can control the active AV Source device using AVRCP commands.
Figure 4.2 outlines typical Single Device mode use cases.
Peer Device: Single Device
HFP, A2DP & AVRCP
AV Source 1
Connected & streaming
audio to Peer Device
AVRCP
(Master)
Peer Device 1
(Master)
Rendering audio from
AV Source 1 & relaying
to slave
A2DP & AVRCP
AVRCP
Peer Device 2
(Slave)
HFP, A2DP & AVRCP
AV Source 2
Rendering audio relayed
Connected (not
streaming audio) to
from Master
Peer Device (Slave)
HFP, A2DP & AVRCP
AV Source 1
Peer Device 1
(Slave)
Connected (not
streaming audio) to
Rendering audio relayed
Peer Device (Slave)
from Master
A2DP & AVRCP
AVRCP
Peer Device 2
(Master)
Rendering audio from
AV Source 2 & relaying
to slave
HFP, A2DP & AVRCP
AV Source 2
Connected & streaming
audio to Peer Device
AVRCP
(Master)
Figure 4.2: Peer Device Single Device Mode
For TWS Single Device mode:

By default, AVRCP commands issued on the TWS Slave are sent to the active AV Source by the Peer
Master.
Configuration options allow AVRCP commands to be sent from the Slave to its connected AV Source.

Powering Off the Peer Master also powers Off the Peer Slave.

Powering Off the Peer Slave also powers Off the Peer Master.

When a call is received on either Peer Device:
4.7.

It is only possible to answer a call on the Peer Device that is actually receiving the call.

If audio is streaming, it is stopped on both devices.

The Peer Master has priority when routing the call.
TWS Separate Device Mode
TWS Separate Device mode is when two TWS Devices in an active Peer Session can operate independently, but
audio sharing between the devices is still available. Figure 4.3 outlines a typical use case for Separate Device mode.
AV Source 1
HFP, A2DP & AVRCP
Connected and
streaming audio to Peer
Device (Master).
AVRCP
Peer Device
(Master)
Rendering audio from
AV Source 1 & relaying
to slave
Peer Device
(Slave)
HFP, A2DP & AVRCP
A2DP & AVRCP
Rendering audio relayed
from Master
AV Source 2
Connected (not
streaming audio) to
AVRCP
Peer Device (Slave)
Figure 4.3: Peer Device Separate Device Mode
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ADK Audio Sink Application Peer Device User Guide
Peer Device: Single Device
For Separate Device mode:

AVRCP commands issued on the Peer Slave are never sent to the Peer Master and onto the active AV
Source.

Powering off the Peer Master does not cause the Peer Slave to power off.

Powering off the Peer Slave does not cause the Peer Master to power off.

When a call is received on the Peer Master:


It is only possible to answer the call using the Peer Master.

Upon answering the call, if audio is streaming, the Peer Master stops relaying audio to the
Peer Slave. The call audio then takes priority at the Peer Master.
When a call is received on the Peer Slave:
It is only possible to answer the call using the Peer Slave.

Upon answering the call, if audio is streaming, the Peer Slave requests the Peer Master stop
relaying audio but the Peer Master continues rendering audio from the AV Source. The call
audio takes priority at the Peer Slave.
Note:
Compatible settings need to be maintained on Peer Master and Peer Slave TWS devices.
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ADK Audio Sink Application Peer Device User Guide

5.
ShareMe
ShareMe allows audio received from an A2DP Source to be relayed to another Peer Device that also supports
ShareMe. The audio is rendered by both devices but rendering is not synchronised between the two Peer Devices.
5.1.
ShareMe Audio Routing
ShareMe only supports automatic audio routing mode. When a new audio source becomes available its priority is
checked against the priority of the currently routed audio source and if higher, becomes the active routed source.
The priority given to each audio source when ShareMe is active is listed in Table 5.1
5.1.1.
Audio Source Priority
Priority (1 is Highest)
Audio Source
Relayed to ShareMe Peer
1
Bluetooth SCO (call audio)
No
2
A2DP Audio
Yes
3
USB Audio
No
4
Wired Audio (PCM or I S)
No
5
FM Receive
No
6
SPDIF Audio
No
7
Bluetooth SCO (audio)
No
8
No Active Source
No
2
Table 5.1: Default Audio Priority List for ShareMe
Note:
Table 3.6 lists the supported A2DP codecs for ShareMe and lists which are relayed to the ShareMe Peer.
5.2.
ShareMe Volume Control
The volume level between connected ShareMe devices is not synchronised, i.e:

Changing volume at the Peer Master does not update the volume of the Peer Slave.

Changing volume at the Peer Slave does not update the volume of the Peer Master.
Note:
AV Sources that do not support AVRCP Absolute Volume Control are not informed of volume updates made by
the Peer Master.
5.3.
Remote Peer Controls AV Source
By default, during an active ShareMe Peer Session, only AVRCP commands issued by the ShareMe Master can be
sent to the AV Source.
The Remote Peer Controls AV Source feature allows a ShareMe Slave to send AVRCP commands to the AV Source
via the ShareMe Master. Sections 5.3.1 to 5.3.2 describe this feature.
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ADK Audio Sink Application Peer Device User Guide
Table 5.1 shows the default priority list for audio sources when ShareMe is active.
5.3.1.
Remote Peer Controls AV Source Disabled
When the Remote Peer Controls AV Source feature is disabled, a small subset of AVRCP commands can be used
to control the relay stream. The available commands that can be sent from the ShareMe Slave to the ShareMe
Master to control the relay stream are defined in Table 5.2.
Description
Action
0x44
AVRCP Play
Start relaying immediately or as soon as an audio stream becomes
available
0x45
AVRCP Stop
Stop relaying audio and prevent audio from being relayed when an
audio stream becomes available
0x46
AVRCP Pause
Stop relaying audio and prevent audio from being relayed when an
audio stream becomes available
Table 5.2: AVRCP Commands used to control ShareMe relay streams
Note:
Any AVRCP operation IDs (not listed in Table 5.2) sent from the ShareMe Slave to the ShareMe Master whilst
Remote Peer Controls AV Source is disabled are ignored by the ShareMe Master.
5.3.2.
Remote Peer Controls AV Source Enabled
When the Remote Peer Controls feature is enabled, the ShareMe Master will forward AVRCP commands received
from the ShareMe Slave to the AV Source.
Figure 5.1 shows how the ShareMe Slave device is able to send AVRCP commands to the AV Source using the
ShareMe Master when Remote Peer Controls AV Source is enabled.
AV Source
HFP, A2DP & AVRCP
Connected & streaming
audio to Peer Device
(Master).
AVRCP
Peer Device
(Master)
Rendering audio from
AV Source 1 & relaying
to slave
Forward AVRCP from
Slave to AV Source
A2DP
Peer Device
(Slave)
Rendering audio relayed
AVRCP
from Master
Figure 5.1: ShareMe AVRCP Control
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ADK Audio Sink Application Peer Device User Guide
AVRCP Operation ID
Document References
Document
Reference
Audio Sink Application Configuration User Guide
CS-306726-UG
Audio Sink Application User Guide
CS-236868-UG
ADK Audio Sink Application Peer Device User Guide
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Terms and Definitions
Advanced Audio Distribution Profile
AAC
Advanced Audio Coding
ADK
Audio or Application Development Kit
AG
Audio Gateway Device
AVRCP
Audio/Video Remote Control Profile
BlueCore®
Group term for CSR’s range of Bluetooth wireless technology chips
Bluetooth®
Set of technologies providing audio and data transfer over short-range radio connections
CSR
Cambridge Silicon Radio
DSP
Digital Signal Processor
EQ
Equaliser
FM
Frequency Modulation
GAIA
Generic Application Interface Architecture
i.e.
Id est, that is
2
IS
Inter-Integrated Circuit Sound
ID
Identifier
MP3
MPEG-1 or MPEG-2 Audio Layer III Coding
PCM
Pulse Code Modulation
PDL
Paired Device List (same as Trusted Device List)
SBC
Sub-band Coding
SCO
Synchronous Connection-Oriented
SDP
Service Discovery
SPDIF
Sony/Philips Digital InterFace
TWS
TrueWireless Stereo
USB
Universal Serial Bus
UUID
Universally Unique Identifier
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ADK Audio Sink Application Peer Device User Guide
A2DP
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