Connectivity:Bluetooth LE Audio - STM32WBA Telephony & Media Audio Profile

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1. Telephony & Media Audio Profile

1.1. Introduction

The Telephony and Media Audio Profile is a BLE Audio profile specified by the Bluetooth SIG. It's categorized as a "use-case profile", meaning that it's a high-layer profile designed for a specific use case. The complete specification can be found on the Bluetooth SIG website. Location of PBP inside BLE Audio Profiles architecture

The TMAP addresses the use-cases of Telephony and Media over BLE Audio. This covers Broadcast audio, where audio data is “broadcasted” from a Broadcast Source to an unlimited number of Broadcast Sinks, using Broadcast Isochronous Streams. It also covers the Unicast audio, where audio is streamed between two connected devices, allowing bidirectional streams and more efficient acknowledgement. For more details about Unicast and Broadcast features, see the wiki page "Introduction to Bluetooth LE Audio".

1.2. Roles

The TMAP introduces 6 different roles:

• Call Gateway: Based on the BAP Unicast Client, it concerns devices connected to networks used for telephony or VoIP applications. Example of devices implementing this role are smartphones, laptops, tablets, and PCs.
• Call Terminal: Based on the BAP Unicast Server, it concerns devices rendering audio for telephony and VoIP applications. Examples of devices implementing this role are earbuds, headphones, headsets, and speakers.
• Unicast Media Sender: Based on the BAP Unicast Client, it concerns devices able to send media audio content using Unicast. Example of devices implementing this role are smartphones, laptops, media players, TV, tablets, and PCs.
• Unicast Media Receiver: Based on the BAP Unicast Server, it concerns devices rendering audio for media streams using Unicast. Examples of devices implementing this role are earbuds, headphones, headsets, and speakers.
• Broadcast Media Sender: Based on the BAP Unicast Client, it concerns devices able to send media audio content using Broadcast. Example of devices implementing this role are smartphones, laptops, media players, TV, tablets, and PCs.
• Broadcast Media Receiver: Based on the BAP Unicast Server, it concerns devices rendering audio for media streams using Broadcast. Examples of devices implementing this role are earbuds, headphones, headsets, and speakers.

The requirements for the 6 roles are the following:

TMAP Role	CAP Roles	BAP Roles	GAP Roles	VCP Roles
Call Gateway	Initiator & Commander	Unicast Client	Central	Volume Controller
Call Terminal	Acceptor	Unicast Server	Observer & Peripheral	Volume Renderer
Unicast Media Sender	Initiator & Commander	Unicast Client	Central	Volume Controller
Unicast Media Receiver	Acceptor	Unicast Server	Peripheral	Volume Controller
Broadcast Media Sender	Initiator	Broadcast Source	Broadcaster
Broadcast Media Receiver	Acceptor	Broadcast Sink & Scan Delegator	Observer & Peripheral	Volume Controller

1.3. TMAP Announcement

A device implementing a TMAP role shall put a bitfield of the TMAP roles supported it in the advertising data.

1.4. Telephony And Media Audio Service (TMAS)

A device implementing a TMAP role (except for BMS role) shall implement the GATT Server role with one instance of Telephony and Media Service (TMAS). This service permits a remote TMA Client to retrieve the roles of the device upon connection.

2. Telephony and Media Audio Profile Application APIs

The following section lists and describes APIs typically Used in a TMAP Application.

2.1. TMAP APIs

The following APIs are available for the TMAP:

TMAP_Init	Initialize the Telephony and Media Audio Profile with the selected role(s)
TMAP_Linkup	Link Up the TMAP Client with remote TMAP Server.
TMAP_DB_IsPresent	Indicate if a TMAP Database is saved in NVM
TMAP_BuildAdvPacket	Build Advertising Packet for TMAP Peripheral
TMAP_ReadRemoteTMAPRole	Read the remote TMAP Role Value

2.1.1. TMAP Initialization

'1. First initialize the Use-case Device Management module:

USECASE_DEV_MGMT_Init();

2. Then, initialize the TMAP with a TMAP_Config_t structure containing the desired role(s), the maximum number of links and a pointer to a RAM section that will contain the TMAP data:

static uint32_t aTMAPMemBuffer[DIVC(TMAP_DYN_ALLOC_SIZE,4)];
TMAP_Config_t tmap_config;

tmap_config.Role = Role;
tmap_config.MaxNumBleLinks = CFG_BLE_NUM_LINK;
tmap_config.pStartRamAddr = (uint8_t *)&aTMAPMemBuffer;
tmap_config.RamSize = TMAP_DYN_ALLOC_SIZE;
  
TMAP_Init(&tmap_config);

3. When implementing the CT or the UMR roles, mandatory Published Audio Capabilities (PAC) must be registered using the following APIs:

CAP_RegisterSnkPACRecord(&aSnkPACRecord,&aSnkPACRecordHandle);
CAP_RegisterSrcPACRecord(&aSrcPACRecord,&aSrcPACRecordHandle);

2.1.2. Linkup remote TMAP Server

To perform Linkup on a remote TMAP Server, use the dedicated API. If a database is already present, use the Restore mode.

/* Check if TMAP link is present in NVM from a previous connection*/
if (TMAP_DB_IsPresent(p_conn->Peer_Address_Type,p_conn->Peer_Address) == 0)
          {
TMAP_Linkup(ConnHandle, TMAP_LINKUP_MODE_COMPLETE);
          }
else
{
   TMAP_Linkup(pNotification->ConnHandle,TMAP_LINKUP_MODE_RESTORE);
}

During the Linkup process, the TMAP_REM_ROLE_VALUE_EVT and TMAP_LINKUP_COMPLETE_EVT events will be generated:

void TMAP_Notification(TMAP_Notification_Evt_t *pNotification)
{
  switch(pNotification->EvtOpcode)
  {
    case TMAP_LINKUP_COMPLETE_EVT:
    {
      break;
    }
    case TMAP_REM_ROLE_VALUE_EVT:
    {
      uint16_t *tmap_role = (uint16_t *) pNotification->pInfo;
      break;
    }
}

3. PBP Demonstrator using STM32WBA

The STM32WBA Cube firmware allows to easily build and deploy Public Broadcast Sources and Public Broadcast Sinks applications.

3.1. Hardware required

The PBP demonstrator requires the following hardware:

• 3x STM32WBA55G-DK1 Boards
• 2x Music Source with a 3.5mm jack output (Laptop or Smartphone with a jack output). If a laptop is used as a source, use a Ground Loop isolator device or run the laptop on battery to avoid Ground issue
• 1x Music renderer with 3.5mm jack input (Headphones or Speakers)

3.2. Setup

The setup is as following:

PBP Demonstrator Setup
File:PBP Setup.png

3.3. Project architecture

The figure below represents the Firmware Architecture of the Public Broadcast Profile example projects inside STM32CubeWBA MCU Package.

STM32WBA PBP Firmware Architecture
File:PBP Project Architecture.png

3.4. PBP Source configuration

Following is a summary of the main changes possible on the PBP_Source project

PBP_Source project configuration
File:PBP Source Config.png

Setting	File	Description
BROADCAST_SOURCE_BAP_CONFIG	pbp_app.c	Configuration index in BroadcastQoSConf array. 0 corresponds to 8_2_1 configuration, 1 to 8_2_2, … Commonly used values are 3 (16_2_1 config), 5 (24_2_1 config), and 13 (48_4_1 config). For more details about the configurations, refer to the Introduction to Bluetooth LE Audio wiki page.
BROADCAST_SOURCE_FRAME_BLOCK_PER_SDU	pbp_app.c	Number of concatenated codec frames sent at the same time. May be 1 or 2. Setting it to 2 reduces the number of events needed to send the packets which can improve reliability but increase the latency.
BROADCAST_SOURCE_NUM_BIS	pbp_app.c	Number of BIS used for the Broadcast Source. May be 1 or 2. Setting it to 1 reduces the number of events needed to send the packets which can improve reliability but a value of 2 reduces the strain on Sink devices synchronizing to mono audio.
BROADCAST_SOURCE_CHANNEL_ALLOC_1	pbp_app.c	Audio Channel Allocation of BIS #1. Bitfield of Audio Location values. Commonly used values are 0x01 for "Front Left" location or 0x03 for "Front Left + Front Right" location.
BROADCAST_SOURCE_CHANNEL_ALLOC_2	pbp_app.c	Audio Channel Allocation of BIS #2. Bitfield of Audio Location values. Commonly used value is 0x02 for "Front Right". Ignored if "BROADCAST_SOURCE_NUM_BIS" is 1.
BROADCAST_CONTROLLER_DELAY	pbp_app.c	Controller delay value. Refer to "STM32WBA LC3 codec and audio data path" wiki page
BAP_BROADCAST_MAX_TRANSPORT_LATENCY	pbp_app.c	Maximum Transport Latency value. Refer to "STM32WBA LC3 codec and audio data path" wiki page
BAP_BROADCAST_ENCRYPTION	pbp_app.c	1 to enable broadcast encryption, 0 to disable it
BIG_HANDLE	pbp_app.c	Handle of the BIG used for the Broadcast
STREAMING_AUDIO_CONTEXT	pbp_app.c	Audio Context Type of the Broadcast Source. Common values are AUDIO_CONTEXT_MEDIA (0x0004) and AUDIO_CONTEXT_CONVERSATIONAL (0x0002). Refer to Assigned Numbers section 6.12.3 for more details
APPEARANCE	pbp_app.c	Appearance value of the Broadcast. Describe the physical appearance of the device. Refer to Assigned Number section 2.6 for more details
BROADCAST_NAME_LENGTH	pbp_app.c	Length of the Broadcast Name
aPBPAPP_BroadcastCode	pbp_app.c	Broadcast Code used when BAP_BROADCAST_ENCRYPTION is set to 1. Broadcast Sinks will have to know the Broadcast Code in order to decrypt the stream
aPBPAPP_BroadcastName	pbp_app.c	Broadcast Name as described in 1.3
BAP_BROADCAST_SOURCE_ID	pbp_app.h	ID of the Broadcast Source. This value is ST specific and permits the PBP Sink to identify the PBP Source with a custom static identifier. Not to be confused with the Broadcast ID which is generated randomly by the BAP layer at Broadcast Source creation.

3.5. PBP Sink configuration

Following is a summary of the main modification possible on the PBP_Sink project

PBP_Sink project configuration
File:PBP Sink Config.png

Setting	File	Description
BROADCAST_CONTROLLER_DELAY	pbp_app.c	Controller delay value. Refer to "STM32WBA LC3 codec and audio data path" wiki page
BAP_BROADCAST_ENCRYPTION	pbp_app.c	1 to enable broadcast decryption, 0 to disable it
BIG_HANDLE	pbp_app.c	Handle of the BIG used for the Broadcast
aPBPAPP_BroadcastCode	pbp_app.c	Broadcast Code used when BAP_BROADCAST_ENCRYPTION is set to 1. Broadcast Code must match the one set on the PBP Source
aSourceIdList	pbp_app.c	List of Source IDs to cycle through using the joystick

3.6. PBP Source Advertising details

The following schematic details the content of a Public Broadcast Source advertising Data.

Detail of PBP Source Advertising Data
File:PBP Source Advertising.png