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Bluetooth: Common Audio Profile Shell

This document describes how to run the Common Audio Profile functionality.

CAP Acceptor

The Acceptor will typically be a resource-constrained device, such as a headset, earbud or hearing aid. The Acceptor can initialize a Coordinated Set Identification Service instance, if it is in a pair with one or more other CAP Acceptors.

Using the CAP Acceptor

When the Bluetooth stack has been initialized (bt init), the Acceptor can be registered by calling cap_acceptor init, which will register the CAS and CSIS services, as well as register callbacks.

cap_acceptor --help
cap_acceptor - Bluetooth CAP acceptor shell commands
Subcommands:
  init          :Initialize the service and register callbacks [size <int>]
                 [rank <int>] [not-lockable] [sirk <data>]
  lock          :Lock the set
  release       :Release the set [force]
  sirk          :Set the currently used SIRK <sirk>
  get_sirk      :Get the currently used SIRK
  sirk_rsp      :Set the response used in SIRK requests <accept, accept_enc,
                 reject, oob>

Besides initializing the CAS and the CSIS, there are also commands to lock and release the CSIS instance, as well as printing and modifying access to the SIRK of the CSIS.

Setting a new SIRK

This command can modify the currently used SIRK. To get the new RSI to advertise on air, bt adv-data or bt advertise must be called again to set the new advertising data. If CONFIG_BT_CSIP_SET_MEMBER_NOTIFIABLE is enabled, this will also notify connected clients.

uart:~$ cap_acceptor sirk 00112233445566778899aabbccddeeff
SIRK updated

Getting the current SIRK

This command can get the currently used SIRK.

uart:~$ cap_acceptor get_sirk
SIRK
36 04 9a dc 66 3a a1 a1 |6...f:..
1d 9a 2f 41 01 73 3e 01 |../A.s>.

CAP Initiator

The Initiator will typically be a resource-rich device, such as a phone or PC. The Initiator can discover CAP Acceptors’s CAS and optional CSIS services. The CSIS service can be read to provide information about other CAP Acceptors in the same Coordinated Set. The Initiator can execute stream control procedures on sets of devices, either ad-hoc or Coordinated, and thus provides an easy way to setup multiple streams on multiple devices at once.

Using the CAP Initiator

When the Bluetooth stack has been initialized (bt init), the Initiator can discover CAS and the optionally included CSIS instance by calling (cap_initiator discover). The CAP initiator also supports broadcast audio as a source.

uart:~$ cap_initiator --help
cap_initiator - Bluetooth CAP initiator shell commands
Subcommands:
  discover          : Discover CAS
  unicast_start     : Unicast Start [csip] [sinks <cnt> (default 1)] [sources
                     <cnt> (default 1)] [conns (<cnt> | all) (default 1)]
  unicast_list      : Unicast list streams
  unicast_update    : Unicast Update <all | stream [stream [stream...]]>
  unicast_stop      : Unicast stop streams [stream [stream [stream...]]] (all by default)
  unicast_cancel    : Unicast cancel current procedure
  ac_1              : Unicast audio configuration 1
  ac_2              : Unicast audio configuration 2
  ac_3              : Unicast audio configuration 3
  ac_4              : Unicast audio configuration 4
  ac_5              : Unicast audio configuration 5
  ac_6_i            : Unicast audio configuration 6(i)
  ac_6_ii           : Unicast audio configuration 6(ii)
  ac_7_i            : Unicast audio configuration 7(i)
  ac_7_ii           : Unicast audio configuration 7(ii)
  ac_8_i            : Unicast audio configuration 8(i)
  ac_8_ii           : Unicast audio configuration 8(ii)
  ac_9_i            : Unicast audio configuration 9(i)
  ac_9_ii           : Unicast audio configuration 9(ii)
  ac_10             : Unicast audio configuration 10
  ac_11_i           : Unicast audio configuration 11(i)
  ac_11_ii          : Unicast audio configuration 11(ii)
  broadcast_start   :
  broadcast_update  : <meta>
  broadcast_stop    :
  broadcast_delete  :
  ac_12             : Broadcast audio configuration 12
  ac_13             : Broadcast audio configuration 13
  ac_14             : Broadcast audio configuration 14

Before being able to perform any stream operation, the device must also perform the bap discover operation to discover the ASEs and PAC records. The bap init command also needs to be called.

When connected

Discovering CAS and CSIS on a device:

uart:~$ cap_initiator discover
discovery completed with CSIS

Discovering ASEs and PAC records on a device:

uart:~$ bap discover
conn 0x81cc260: #0: codec 0x81d5b28 dir 0x01
codec 0x06 cid 0x0000 vid 0x0000 count 5
data #0: type 0x01 len 2
00000000: f5                                               |.                |
data #1: type 0x02 len 1
data #2: type 0x03 len 1
data #3: type 0x04 len 4
00000000: 1e 00 f0                                         |...              |
data #4: type 0x05 len 1
meta #0: type 0x01 len 2
00000000: 06                                               |.                |
dir 1 loc 1
snk ctx 6 src ctx 6
Conn: 0x81cc260, Sink #0: ep 0x81e4248
Conn: 0x81cc260, Sink #1: ep 0x81e46a8
conn 0x81cc260: #0: codec 0x81d5f00 dir 0x02
codec 0x06 cid 0x0000 vid 0x0000 count 5
data #0: type 0x01 len 2
00000000: f5                                               |.                |
data #1: type 0x02 len 1
data #2: type 0x03 len 1
data #3: type 0x04 len 4
00000000: 1e 00 f0                                         |...              |
data #4: type 0x05 len 1
meta #0: type 0x01 len 2
00000000: 06                                               |.                |
dir 2 loc 1
snk ctx 6 src ctx 6
Conn: 0x81cc260, Source #0: ep 0x81e5c88
Conn: 0x81cc260, Source #1: ep 0x81e60e8
Discover complete: err 0

Both of the above commands should be done for each device that you want to use in the set. To use multiple devices, simply connect to more and then use bt select the device to execute the commands on.

Once all devices have been connected and the respective discovery commands have been called, the cap_initiator unicast_start command can be used to put one or more streams into the streaming state.

uart:~$ cap_initiator unicast_start sinks 1 sources 0 conns all
Setting up 1 sinks and 0 sources on each (2) conn
Starting 1 streams
Unicast start completed

To stop all the streams that has been started, the cap_initiator unicast_stop command can be used.

uart:~$ cap_initiator unicast_stop all
Unicast stop completed

When doing broadcast

To start a broadcast as the CAP initiator there are a few steps to be done:

  1. Create and configure an extended advertising set with periodic advertising

  2. Create and configure a broadcast source

  3. Setup extended and periodic advertising data

The following commands will setup a CAP broadcast source using the 16_2_1 preset (defined by BAP):

bt init
bap init
bt adv-create nconn-nscan ext-adv name
bt per-adv-param
bap preset broadcast 16_2_1
cap_initiator ac_12
bt adv-data discov
bt per-adv-data
cap_initiator broadcast_start

The broadcast source is created by the cap_initiator ac_12, cap_initiator ac_13, and cap_initiator ac_14 commands, configuring the broadcast source for the defined audio configurations from BAP. The broadcast source can then be stopped with cap_initiator broadcast_stop or deleted with cap_initiator broadcast_delete.

The metadata of the broadcast source can be updated at any time, including when it is already streaming. To update the metadata the cap_initiator broadcast_update command can be used. The command takes an array of data, and the only requirement (besides having valid data) is that the streaming context shall be set. For example to set the streaming context to media, the command can be used as

cap_initiator broadcast_update 03020400
CAP Broadcast source updated with new metadata. Update the advertised base via `bt per-adv-data`
bt per-adv-data

The bt per-adv-data command should be used afterwards to update the data is the advertised BASE. The data must be little-endian, so in the above example the metadata 03020400 is setting the metadata entry with 03 as the length, 02 as the type (streaming context) and 0400 as the value BT_AUDIO_CONTEXT_TYPE_MEDIA (which has the numeric value of 0x).

CAP Commander

The Commander will typically be a either co-located with a CAP Initiator or be on a separate resource-rich mobile device, such as a phone or smartwatch. The Commander can discover CAP Acceptors’s CAS and optional CSIS services. The CSIS service can be read to provide information about other CAP Acceptors in the same Coordinated Set. The Commander can provide information about broadcast sources to CAP Acceptors or coordinate capture and rendering information such as mute or volume states.

Using the CAP Commander

When the Bluetooth stack has been initialized (bt init), the Commander can discover CAS and the optionally included CSIS instance by calling (cap_commander discover).

cap_commander --help
cap_commander - Bluetooth CAP commander shell commands
Subcommands:
  discover                :Discover CAS
  cancel                  :CAP commander cancel current procedure
  change_volume           :Change volume on all connections <volume>
  change_volume_mute      :Change volume mute state on all connections <mute>
  change_volume_offset    :Change volume offset per connection <volume_offset
                           [volume_offset [...]]>
  change_microphone_mute  :Change microphone mute state on all connections <mute>
  change_microphone_gain  :Change microphone gain per connection <gain
                           [gain [...]]>

Before being able to perform any stream operation, the device must also perform the bap discover operation to discover the ASEs and PAC records. The bap init command also needs to be called.

When connected

Discovering CAS and CSIS on a device
uart:~$ cap_commander discover
discovery completed with CSIS
Setting the volume on all connected devices
uart:~$ vcp_vol_ctlr discover
VCP discover done with 1 VOCS and 1 AICS
uart:~$ cap_commander change_volume 15
uart:~$ cap_commander change_volume 15
Setting volume to 15 on 2 connections
VCP volume 15, mute 0
VCP vol_set done
VCP volume 15, mute 0
VCP flags 0x01
VCP vol_set done
Volume change completed
Setting the volume offset on one or more devices

The offsets are set by connection index, so connection index 0 gets the first offset, and index 1 gets the second offset, etc.:

uart:~$ bt connect <device A>
Connected: <device A>
uart:~$ cap_commander discover
discovery completed with CSIS
uart:~$ vcp_vol_ctlr discover
VCP discover done with 1 VOCS and 1 AICS
uart:~$
uart:~$ bt connect <device B>
Connected: <device B>
uart:~$ cap_commander discover
discovery completed with CSIS
uart:~$ vcp_vol_ctlr discover
VCP discover done with 1 VOCS and 1 AICS
uart:~$
uart:~$ cap_commander change_volume_offset 10
Setting volume offset on 1 connections
VOCS inst 0x200140a4 offset 10
Offset set for inst 0x200140a4
Volume offset change completed
uart:~$
uart:~$ cap_commander change_volume_offset 10 15
Setting volume offset on 2 connections
Offset set for inst 0x200140a4
VOCS inst 0x20014188 offset 15
Offset set for inst 0x20014188
Volume offset change completed
Setting the volume mute on all connected devices
uart:~$ bt connect <device A>
Connected: <device A>
uart:~$ cap_commander discover
discovery completed with CSIS
uart:~$ vcp_vol_ctlr discover
VCP discover done with 1 VOCS and 1 AICS
uart:~$
uart:~$ bt connect <device B>
Connected: <device B>
uart:~$ cap_commander discover
discovery completed with CSIS
uart:~$ vcp_vol_ctlr discover
VCP discover done with 1 VOCS and 1 AICS
uart:~$
uart:~$ cap_commander change_volume_mute 1
Setting volume mute to 1 on 2 connections
VCP volume 100, mute 1
VCP mute done
VCP volume 100, mute 1
VCP mute done
Volume mute change completed
uart:~$ cap_commander change_volume_mute 0
Setting volume mute to 0 on 2 connections
VCP volume 100, mute 0
VCP unmute done
VCP volume 100, mute 0
VCP unmute done
Volume mute change completed
Setting the microphone mute on all connected devices
uart:~$ bt connect <device A>
Connected: <device A>
uart:~$ cap_commander discover
discovery completed with CSIS
uart:~$ micp_mic_ctlr discover
MICP discover done with 1 VOCS and 1 AICS
uart:~$
uart:~$ bt connect <device B>
Connected: <device B>
uart:~$ cap_commander discover
discovery completed with CSIS
uart:~$ micp_mic_ctlr discover
MICP discover done with 1 VOCS and 1 AICS
uart:~$
uart:~$ cap_commander change_microphone_mute 1
Setting microphone mute to 1 on 2 connections
MICP microphone 100, mute 1
MICP mute done
MICP microphone 100, mute 1
MICP mute done
Microphone mute change completed
uart:~$ cap_commander change_microphone_mute 0
Setting microphone mute to 0 on 2 connections
MICP microphone 100, mute 0
MICP unmute done
MICP microphone 100, mute 0
MICP unmute done
Microphone mute change completed
Setting the microphone gain on one or more devices

The gains are set by connection index, so connection index 0 gets the first offset, and index 1 gets the second offset, etc.:

uart:~$ bt connect <device A>
Connected: <device A>
uart:~$ cap_commander discover
discovery completed with CSIS
uart:~$ micp_mic_ctlr discover
MICP discover done with 1 AICS
uart:~$
uart:~$ bt connect <device B>
Connected: <device B>
uart:~$ cap_commander discover
discovery completed with CSIS
uart:~$ micp_mic_ctlr discover
MICP discover done with 1 AICS
uart:~$
uart:~$ cap_commander change_microphone_gain 10
Setting microphone gain on 1 connections
AICS inst 0x200140a4 state gain 10, mute 0, mode 0
Gain set for inst 0x200140a4
Microphone gain change completed
uart:~$
uart:~$ cap_commander change_microphone_gain 10 15
Setting microphone gain on 2 connections
Gain set for inst 0x200140a4
AICS inst 0x20014188 state gain 15, mute 0, mode 0
Gain set for inst 0x20014188
Microphone gain change completed
Starting a broadcast reception
uart:~$ bt connect <device A>
Connected: <device A>
uart:~$ bap_init
uart:~$ cap_commander discover
discovery completed with CSIS
uart:~$ bap_broadcast_assistant discover
BASS discover done with 1 recv states
uart:~$ cap_commander broadcast_reception_start <device B> 0 4
Starting broadcast reception on 1 connection(s)