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 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]
  print_sirk    :Print the currently used SIRK
  set_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.

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).

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 all streams

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
Unicast stopped for group 0x81e41c0 completed