1.. _bluetooth_le_audio_arch: 2 3LE Audio Stack 4############## 5 6.. graphviz:: 7 :caption: Bluetooth Audio Architecture 8 9 digraph bluetooth_audio_arch { 10 r [shape=record, width=5, height=3 11 label="{{TMAP | HAP | PBP | GMAP | ...} | 12 GAF | 13 {{{ GATT | GAP } | Low-level protocols (L2CAP, ATT, etc.)} | GAP | ISO} 14 | HCI Driver (USB, UART, SPI, virtual, etc.)}" 15 ]; 16 } 17 18Overall design 19************** 20 21The overall design of the LE Audio stack is that the implementation follows the specifications 22as closely as possible, 23both in terms of structure but also naming. 24Most API functions are prefixed by the specification acronym 25(e.g. ``bt_bap`` for the Basic Audio Profile (BAP) and ``bt_vcp`` for the Volume Control Profile 26(VCP)). The functions are then further prefixed with the specific role from each profile where 27applicable (e.g. :c:func:`bt_bap_unicast_client_discover` and :c:func:`bt_vcp_vol_rend_set_vol`). 28There are usually a function per procedure defined by the profile or service specifications, 29and additional helper or meta functions that do not correspond to procedures. 30 31The structure of the files generally also follow this, 32where BAP related files are prefixed with ``bap`` and VCP related files are prefixed with ``vcp``. 33If the file is specific for a profile role, the role is also embedded in the file name. 34 35Generic Audio Framework (GAF) 36***************************** 37The Generic Audio Framework (GAF) is considered the middleware of the Bluetooth 38LE Audio architecture. The GAF contains the profiles and services that allows 39higher layer applications and profiles to set up streams, change volume, control 40media and telephony and more. The GAF builds on GATT, GAP and isochronous 41channels (ISO). 42 43GAF uses GAP to connect, advertise and synchronize to other devices. 44GAF uses GATT to configure streams, associate streams with content 45(e.g. media or telephony), control volume and more. 46GAF uses ISO for the audio streams themselves, both as unicast (connected) 47audio streams or broadcast (unconnected) audio streams. 48 49GAF mandates the use of the LC3 codec, but also supports other codecs. 50 51.. graphviz:: 52 :caption: Generic Audio Framework (GAF) 53 54 digraph gaf { 55 node [shape=record]; 56 edge [style=invis]; 57 compound=true; 58 nodesep=0.1; 59 60 subgraph hap_layer { 61 cluster=true; 62 label="HAP"; 63 HAS; 64 BAS [style=dashed]; 65 IAS [style=dashed]; 66 } 67 68 subgraph pbp_layer { 69 cluster=true; 70 label="PBP"; 71 PBS[style=invis]; // Make it possible to treat PBP like the others 72 } 73 74 subgraph tmap_layer { 75 cluster=true; 76 label="TMAP"; 77 TMAS; 78 } 79 80 subgraph gmap_layer { 81 cluster=true; 82 label="GMAP"; 83 GMAS; 84 } 85 86 subgraph gaf_layer { 87 cluster=true; 88 label="Generic Audio Framework"; 89 90 subgraph transition_and_coordination_control_layer { 91 cluster=true; 92 label="Transition and Coordination Control"; 93 style=dashed; 94 95 subgraph cap_layer { 96 cluster=true; 97 style=solid; 98 label="CAP"; 99 CAS; 100 } 101 102 subgraph csip_layer { 103 cluster=true; 104 style=solid; 105 label="CSIP"; 106 CSIS; 107 } 108 } 109 110 subgraph stream_control_layer { 111 cluster=true; 112 label="Stream Control"; 113 style=dashed; 114 115 subgraph bap_layer { 116 cluster=true; 117 label="BAP"; 118 style=solid; 119 PACS [style=dashed]; 120 ASCS [style=dashed]; 121 BASS [style=dashed]; 122 } 123 } 124 125 subgraph content_control_layer { 126 cluster=true; 127 label="Content Control"; 128 style=dashed; 129 130 subgraph mcp_layer { 131 cluster=true; 132 label="MCP"; 133 style=solid; 134 MCS; 135 } 136 137 subgraph ccp_layer { 138 cluster=true; 139 label="CCP"; 140 style=solid; 141 TBS; 142 } 143 } 144 145 subgraph rendering_and_capture_control_layer { 146 cluster=true; 147 label="Rendering and Capture Control"; 148 style=dashed; 149 150 subgraph micp_layer { 151 cluster=true; 152 label="MICP"; 153 style=solid; 154 MICS; 155 MICP_AICS [style=dashed]; 156 } 157 158 subgraph vcp_layer { 159 cluster=true; 160 label="VCP"; 161 style=solid; 162 VCS; 163 VOCS [style=dashed]; 164 VCP_AICS [style=dashed]; 165 } 166 } 167 } 168 169 HAS -> CAS; 170 PBS -> CAS; 171 TMAS -> CAS; 172 GMAS -> CAS; 173 174 CAS -> MCS; 175 CAS -> TBS; 176 CAS -> ASCS; 177 CAS -> PACS; 178 CAS -> BASS; 179 CAS -> MICS; 180 CAS -> MICP_AICS; 181 CAS -> VCS; 182 CAS -> VOCS; 183 CAS -> VCP_AICS; 184 185 CSIS -> MCS; 186 CSIS -> TBS; 187 CSIS -> ASCS; 188 CSIS -> PACS; 189 CSIS -> BASS; 190 CSIS -> MICS; 191 CSIS -> MICP_AICS; 192 CSIS -> VCS; 193 CSIS -> VOCS; 194 CSIS -> VCP_AICS; 195 } 196 197The top-level profiles TMAP and HAP are not part of the GAF, but rather provide 198top-level requirements for how to use the GAF. 199 200GAF and the top layer profiles gave been implemented in Zephyr with the following structure. 201 202.. graphviz:: 203 :caption: Zephyr Generic Audio Framework 204 205 digraph gaf { 206 node [shape=record]; 207 edge [style=invis]; 208 compound=true; 209 nodesep=0.1; 210 211 subgraph hap_layer { 212 cluster=true; 213 label="HAP"; 214 HAS_H [label="has.h"]; 215 BAS_H [label="bas.h"]; 216 IAS_H [label="ias.h"]; 217 } 218 219 subgraph pbp_layer { 220 cluster=true; 221 label="PBP"; 222 PBP_H [label="pbp.h"]; // Make it possible to treat PBP like the others 223 } 224 225 subgraph tmap_layer { 226 cluster=true; 227 label="TMAP"; 228 TMAP_H [label="tmap.h"]; 229 } 230 231 subgraph gmap_layer { 232 cluster=true; 233 label="GMAP"; 234 GMAP_H [label="gmap.h"]; 235 GMAP_PRESET_H [label="gmap_lc3_preset.h"]; 236 } 237 238 subgraph gaf_layer { 239 cluster=true; 240 label="Generic Audio Framework"; 241 AUDIO_H [label="audio.h"]; 242 LC3_H [label="lc3.h"]; 243 244 subgraph transition_and_coordination_control_layer { 245 cluster=true; 246 label="Transition and Coordination Control"; 247 style=dashed; 248 249 subgraph cap_layer { 250 cluster=true; 251 style=solid; 252 label="CAP"; 253 CAP_H [label="cap.h"]; 254 } 255 256 subgraph csip_layer { 257 cluster=true; 258 style=solid; 259 label="CSIP"; 260 CSIP_H [label="csip.h"]; 261 } 262 } 263 264 subgraph stream_control_layer { 265 cluster=true; 266 label="Stream Control"; 267 style=dashed; 268 269 subgraph bap_layer { 270 cluster=true; 271 label="BAP"; 272 style=solid; 273 PACS_H [label="pacs.h"]; 274 BAP_H [label="bap.h"]; 275 BAP_PRESET_H [label="bap_lc3_preset.h"]; 276 } 277 } 278 279 subgraph content_control_layer { 280 cluster=true; 281 label="Content Control"; 282 style=dashed; 283 284 subgraph mcp_layer { 285 cluster=true; 286 label="MCP"; 287 style=solid; 288 MCS_H [label="mcs.h"]; 289 MCC_H [label="mcc.h"]; 290 MP_H [label="media_proxy.h"]; 291 } 292 293 subgraph ccp_layer { 294 cluster=true; 295 label="CCP"; 296 style=solid; 297 TBS_H [label="tbs.h"]; 298 } 299 } 300 301 subgraph rendering_and_capture_control_layer { 302 cluster=true; 303 label="Rendering and Capture Control"; 304 style=dashed; 305 306 subgraph micp_layer { 307 cluster=true; 308 label="MICP"; 309 style=solid; 310 MICP_H [label="micp.h"]; 311 AICS_H [label="aics.h"]; 312 } 313 314 subgraph vcp_layer { 315 cluster=true; 316 label="VCP"; 317 style=solid; 318 VCP_H [label="vcp.h"]; 319 VOCS_H [label="vocs.h"]; 320 AICS_H [label="aics.h"]; 321 } 322 } 323 } 324 325 HAS_H -> CAP_H; 326 PBP_H -> CAP_H; 327 TMAP_H -> CAP_H; 328 GMAP_H -> CAP_H; 329 GMAP_PRESET_H -> CAP_H; 330 331 CAP_H -> MCS_H; 332 CAP_H -> MCC_H; 333 CAP_H -> MP_H; 334 CAP_H -> TBS_H; 335 CAP_H -> BAP_H; 336 CAP_H -> BAP_PRESET_H; 337 CAP_H -> PACS_H; 338 CAP_H -> MICP_H; 339 CAP_H -> VCP_H; 340 341 CSIP_H -> MCS_H; 342 CSIP_H -> MCC_H; 343 CSIP_H -> MP_H; 344 CSIP_H -> TBS_H; 345 CSIP_H -> BAP_H; 346 CSIP_H -> BAP_PRESET_H; 347 CSIP_H -> PACS_H; 348 CSIP_H -> MICP_H; 349 CSIP_H -> VCP_H; 350 } 351 352Profile Dependencies 353==================== 354 355The LE Audio profiles depend on other profiles and services, as outlined in the following tables. 356In these tables 'Server' refers to acting in the GATT server role, and 'Client' refers to acting in the GATT client role for the specific 357service. 358If a profile role depends on another profile that depends on a service, then that dependency is implicitly also applied to that profile. 359For example, if the CAP Acceptor uses the BAP Unicast Server role, then the requirements on the ASCS Server and PACS Server also apply to the CAP Acceptor. 360 361The dependencies for Stream Control (BAP) are in the following table. 362 363.. table:: BAP dependencies 364 :widths: auto 365 :align: center 366 367 +--------------------+----------------+----------------+------------------+----------------+----------------+---------------------+ 368 | | Unicast Server | Unicast Client | Broadcast Source | Broadcast Sink | Scan Delegator | Broadcast Assistant | 369 +====================+================+================+==================+================+================+=====================+ 370 | BAP Scan Delegator | | | | M | | | 371 +--------------------+----------------+----------------+------------------+----------------+----------------+---------------------+ 372 | ASCS Client | | M | | | | | 373 +--------------------+----------------+----------------+------------------+----------------+----------------+---------------------+ 374 | ASCS Server | M | | | | | | 375 +--------------------+----------------+----------------+------------------+----------------+----------------+---------------------+ 376 | PACS Client | | M | | | | O | 377 +--------------------+----------------+----------------+------------------+----------------+----------------+---------------------+ 378 | PACS Server | M | | | M | | | 379 +--------------------+----------------+----------------+------------------+----------------+----------------+---------------------+ 380 | BASS Client | | | | | | M | 381 +--------------------+----------------+----------------+------------------+----------------+----------------+---------------------+ 382 | BASS Server | | | | | M | | 383 +--------------------+----------------+----------------+------------------+----------------+----------------+---------------------+ 384 385Note: 386 387* As the table shows, the Broadcast Source role has no dependencies on other LE Audio profiles or services 388 389The dependencies for Content Control (MCP and CCP) are in the following tables. 390 391.. table:: MCP dependencies 392 :widths: auto 393 :align: center 394 395 +-------------+----------------------+----------------------+ 396 | | Media Control Server | Media Control Client | 397 +=============+======================+======================+ 398 | GMCS Server | M | | 399 +-------------+----------------------+----------------------+ 400 | GMCS Client | | M | 401 +-------------+----------------------+----------------------+ 402 | MCS Server | O | | 403 +-------------+----------------------+----------------------+ 404 | MCS Client | | O | 405 +-------------+----------------------+----------------------+ 406 | OTS Server | O | | 407 +-------------+----------------------+----------------------+ 408 | OTS Client | | O | 409 +-------------+----------------------+----------------------+ 410 411.. table:: CCP dependencies 412 :widths: auto 413 :align: center 414 415 +--------------+---------------------+---------------------+ 416 | | Call Control Server | Call Control Client | 417 +==============+=====================+=====================+ 418 | GTBS Server | M | | 419 +--------------+---------------------+---------------------+ 420 | GTBS Client | | M | 421 +--------------+---------------------+---------------------+ 422 | TBS Server | M | | 423 +--------------+---------------------+---------------------+ 424 | TBS Client | | M | 425 +--------------+---------------------+---------------------+ 426 427 428The dependencies for Rendering Control (MICP and VCP) are in the following tables. 429 430.. table:: MICP dependencies 431 :widths: auto 432 :align: center 433 434 +-------------+-----------------------+-------------------+ 435 | | Microphone Controller | Microphone Device | 436 +=============+=======================+===================+ 437 | MICS Server | M | | 438 +-------------+-----------------------+-------------------+ 439 | MICS Client | | M | 440 +-------------+-----------------------+-------------------+ 441 | AICS Server | O | | 442 +-------------+-----------------------+-------------------+ 443 | AICS Client | | O | 444 +-------------+-----------------------+-------------------+ 445 446.. table:: VCP dependencies 447 :widths: auto 448 :align: center 449 450 +-------------+------------------+-------------------+ 451 | | Volume Renderer | Volume Controller | 452 +=============+==================+===================+ 453 | VCS Server | M | | 454 +-------------+------------------+-------------------+ 455 | VCS Client | | M | 456 +-------------+------------------+-------------------+ 457 | VOCS Server | O | | 458 +-------------+------------------+-------------------+ 459 | VOCS Client | | O | 460 +-------------+------------------+-------------------+ 461 | AICS Server | O | | 462 +-------------+------------------+-------------------+ 463 | AICS Client | | O | 464 +-------------+------------------+-------------------+ 465 466The last element in GAF is Transition and Coordination Control (CAP and CSIP) with the dependencies from the following tables. 467 468.. table:: CAP dependencies 469 :widths: auto 470 :align: center 471 472 +----------------------------+----------+-----------+-----------+ 473 | | Acceptor | Initiator | Commander | 474 +============================+==========+===========+===========+ 475 | CAS Server | M | | C.8 | 476 +----------------------------+----------+-----------+-----------+ 477 | CAS Client | | M | M | 478 +----------------------------+----------+-----------+-----------+ 479 | BAP Unicast Client | | C.1 | | 480 +----------------------------+----------+-----------+-----------+ 481 | BAP Unicast Server | C.2 | | | 482 +----------------------------+----------+-----------+-----------+ 483 | BAP Broadcast Source | | C.1 | | 484 +----------------------------+----------+-----------+-----------+ 485 | BAP Broadcast Sink | C.2 | | | 486 +----------------------------+----------+-----------+-----------+ 487 | BAP Broadcast Assistant | | | C.4, C.6 | 488 +----------------------------+----------+-----------+-----------+ 489 | BAP Scan Delegator | C.3 | | C.6 | 490 +----------------------------+----------+-----------+-----------+ 491 | VCP Volume Controller | | | C.6 | 492 +----------------------------+----------+-----------+-----------+ 493 | VCP Volume Renderer | O | | | 494 +----------------------------+----------+-----------+-----------+ 495 | MICP Microphone Controller | | | C.6 | 496 +----------------------------+----------+-----------+-----------+ 497 | MICP Microphone Device | O | | | 498 +----------------------------+----------+-----------+-----------+ 499 | CCP Call Control Server | | O | | 500 +----------------------------+----------+-----------+-----------+ 501 | CCP Call Control Client | O | | C.6 | 502 +----------------------------+----------+-----------+-----------+ 503 | MCP Media Control Server | | O | | 504 +----------------------------+----------+-----------+-----------+ 505 | MCP Media Control Client | O | | C.6 | 506 +----------------------------+----------+-----------+-----------+ 507 | CSIP Set Coordinator | | C.5 | M | 508 +----------------------------+----------+-----------+-----------+ 509 | CSIP Set Member | C.7 | | | 510 +----------------------------+----------+-----------+-----------+ 511 512Notes: 513 514* C.1: Support at least one of BAP Unicast Client or BAP Broadcast Source 515* C.2: Support at least one of BAP Unicast Server or BAP Broadcast Sink 516* C.3: Mandatory if BAP Broadcast Sink 517* C.4: Mandatory if BAP Scan Delegator 518* C.5: Mandatory if BAP Unicast Client 519* C.6: Support at least one 520* C.7: Mandatory if part of a coordinated set 521* C.8: Mandatory if the Commander transmits CAP announcements 522 523 524.. table:: CSIP dependencies 525 :widths: auto 526 :align: center 527 528 +------------+------------+-----------------+ 529 | | Set Member | Set Coordinator | 530 +============+============+=================+ 531 | CSIS Server| M | | 532 +------------+------------+-----------------+ 533 | CSIS Client| | M | 534 +------------+------------+-----------------+ 535 536 537The dependencies of the higher level profiles (GMAP, HAP, PBP and TMAP) are listed in the following tables. 538 539.. table:: GMAP dependencies 540 :widths: auto 541 :align: center 542 543 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 544 | | Unicast Game Gateway | Unicast Game Terminal | Broadcast Game Sender | Broadcast Game Receiver | 545 +============================+======================+=======================+=======================+=========================+ 546 | GMAS Server | M | M | O | M | 547 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 548 | GMAS Client | M | O | O | O | 549 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 550 | CAP Initiator | M | | M | | 551 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 552 | CAP Acceptor | | M | | M | 553 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 554 | CAP Commander | M | | M | | 555 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 556 | BAP Broadcast Source | | | M | | 557 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 558 | BAP Broadcast Sink | | | | M | 559 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 560 | BAP Unicast Client | M | | | | 561 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 562 | BAP Unicast Server | | M | | | 563 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 564 | VCP Volume Controller | M | | | | 565 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 566 | VCP Volume Renderer | | C.1 | | M | 567 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 568 | MICP Microphone Controller | O | | | | 569 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 570 | MICP Microphone Device | | C.2 | | | 571 +----------------------------+----------------------+-----------------------+-----------------------+-------------------------+ 572 573Notes: 574 575* C.1 Mandatory if the UGT supports the UGT Sink feature 576* C.2 Optional if the UGT supports the UGT Source feature 577 578.. table:: HAP dependencies 579 :widths: auto 580 :align: center 581 582 +----------------------------+-------------+----------------------------+-------------------------------+ 583 | | Hearing Aid | Hearing Aid Unicast Client | Hearing Aid Remote Controller | 584 +============================+=============+============================+===============================+ 585 | HAS Client | | | M | 586 +----------------------------+-------------+----------------------------+-------------------------------+ 587 | HAS Server | M | | | 588 +----------------------------+-------------+----------------------------+-------------------------------+ 589 | CAP Initiator | | M | | 590 +----------------------------+-------------+----------------------------+-------------------------------+ 591 | CAP Acceptor | M | | | 592 +----------------------------+-------------+----------------------------+-------------------------------+ 593 | CAP Commander | | | M | 594 +----------------------------+-------------+----------------------------+-------------------------------+ 595 | BAP Unicast Client | | M | | 596 +----------------------------+-------------+----------------------------+-------------------------------+ 597 | BAP Unicast Server | M | | | 598 +----------------------------+-------------+----------------------------+-------------------------------+ 599 | VCP Volume Controller | | | M | 600 +----------------------------+-------------+----------------------------+-------------------------------+ 601 | VCP Volume Renderer | M | | | 602 +----------------------------+-------------+----------------------------+-------------------------------+ 603 | VOCS Server | C.1 | | | 604 +----------------------------+-------------+----------------------------+-------------------------------+ 605 | AICS Server | O | | | 606 +----------------------------+-------------+----------------------------+-------------------------------+ 607 | MICP Microphone Controller | | | O | 608 +----------------------------+-------------+----------------------------+-------------------------------+ 609 | MICP Microphone Device | C.2 | | | 610 +----------------------------+-------------+----------------------------+-------------------------------+ 611 | CCP Call Control Client | O | | | 612 +----------------------------+-------------+----------------------------+-------------------------------+ 613 | CCP Call Control Server | | O | | 614 +----------------------------+-------------+----------------------------+-------------------------------+ 615 | CSIP Set Coordinator | | M | M | 616 +----------------------------+-------------+----------------------------+-------------------------------+ 617 | CSIP Set Member | C.3 | | | 618 +----------------------------+-------------+----------------------------+-------------------------------+ 619 | BAS Server | C.4 | | | 620 +----------------------------+-------------+----------------------------+-------------------------------+ 621 | IAS Server | O | | | 622 +----------------------------+-------------+----------------------------+-------------------------------+ 623 624Notes: 625 626* C.1 Mandatory if the HA supports the Volume Baslance feature and is part of a Binaural Hearing Aid Set 627* C.2 Mandatory if the HA supports the BAP Audio Source Role 628* C.3 Mandatory if the HA is capable of being part of a Binaural Hearing Aid set 629* C.4 If equipped with batteries 630* C.5 If CCP Call Control Server is supported 631 632.. table:: PBP dependencies 633 :widths: auto 634 :align: center 635 636 +-------------------------+-------------------------+-----------------------+----------------------------+ 637 | | Public Broadcast Source | Public Broadcast sink | Public Broadcast Assistant | 638 +=========================+=========================+=======================+============================+ 639 | CAP Initiator | M | | | 640 +-------------------------+-------------------------+-----------------------+----------------------------+ 641 | CAP Acceptor | | M | | 642 +-------------------------+-------------------------+-----------------------+----------------------------+ 643 | CAP Commander | | | M | 644 +-------------------------+-------------------------+-----------------------+----------------------------+ 645 | BAP Broadcast Assistant | | | M | 646 +-------------------------+-------------------------+-----------------------+----------------------------+ 647 648.. table:: TMAP dependencies 649 :widths: auto 650 :align: center 651 652 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 653 | | Call Gateway | Call Terminal | Unicast Media Sender | Unicast Media Receiver | Broadcast Media Sender | Broadcast Media Receiver | 654 +===================================+==============+===============+======================+========================+========================+==========================+ 655 | TMAS Server | M | M | M | M | O | M | 656 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 657 | TMAS Client | O | O | O | O | O | O | 658 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 659 | CAP Initiator | M | | M | | M | | 660 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 661 | CAP Acceptor | | M | | M | | M | 662 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 663 | CAP Commander | M | O | M | O | O | O | 664 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 665 | BAP Broadcast Source | | | | | M | | 666 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 667 | BAP Broadcast Sink | | | | | | M | 668 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 669 | BAP Unicast Client | M | | M | | | | 670 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 671 | BAP Unicast Server | | M | | M | | | 672 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 673 | VCP Volume Controller | M | | M | | | | 674 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 675 | VCP Volume Renderer | | C.1 | | M | | M | 676 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 677 | MCP Media Control Server | | | M | | | | 678 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 679 | CCP Call Control Server | M | | | | | | 680 +-----------------------------------+--------------+---------------+----------------------+------------------------+------------------------+--------------------------+ 681 682Notes: 683 684* C.1 Mandatory to support if the BAP Unicast Server is acting as an Audio Sink 685 686Bluetooth Audio Stack Status 687============================ 688 689The following table shows the current status and support of the profiles in the 690Bluetooth Audio Stack. 691 692.. table:: Bluetooth Audio Profile status 693 :widths: auto 694 695 +--------+-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 696 | Module | Role | Version | Added in Release | Status | Remaining | 697 +========+===============================+=========+==================+=======================+==================================================+ 698 | VCP | Volume Renderer | 1.0 | 2.6 | - Feature complete | - Sample Application | 699 | | | | | - Shell Module | | 700 | | | | | - BSIM test | | 701 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 702 | | Volume Controller | 1.0 | 2.6 | - Feature complete | - Sample Application | 703 | | | | | - Shell Module | | 704 | | | | | - BSIM test | | 705 +--------+-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 706 | MICP | Microphone Device | 1.0 | 2.7 | - Feature complete | - Sample Application | 707 | | | | | - Shell Module | | 708 | | | | | - BSIM test | | 709 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 710 | | Microphone Controller | 1.0 | 2.7 | - Feature complete | - Sample Application | 711 | | | | | - Shell Module | | 712 | | | | | - BSIM test | | 713 +--------+-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 714 | CSIP | Set Member | 1.0.1 | 3.0 | - Feature complete | - Sample Application | 715 | | | | | - Shell Module | | 716 | | | | | - BSIM test | | 717 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 718 | | Set Coordinator | 1.0.1 | 3.0 | - Feature complete | - Sample Application | 719 | | | | | - Shell Module | | 720 | | | | | - BSIM test | | 721 +--------+-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 722 | CCP | Call Control Server | 1.0 | 3.0 | - Feature complete | - API refactor | 723 | | | | | - Shell Module | - Sample Application | 724 | | | | | - BSIM test | | 725 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 726 | | Call Control Client | 1.0 | 3.0 | - Feature complete | - API refactor | 727 | | | | | - Shell Module | - Sample Application | 728 | | | | | - BSIM test | | 729 +--------+-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 730 | MCP | Media Control Server | 1.0 | 3.0 | - Feature complete | - API refactor | 731 | | | | | - Shell Module | - Support for multiple instances and connections | 732 | | | | | - BSIM test | - Sample Application | 733 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 734 | | Media Control Client | 1.0 | 3.0 | - Feature complete | - API refactor | 735 | | | | | - Shell Module | - Sample Application | 736 | | | | | - BSIM test | | 737 +--------+-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 738 | BAP | Unicast Server | 1.0.1 | 3.0 | - Feature complete | | 739 | | | | | - Shell Module | | 740 | | | | | - BSIM test | | 741 | | | | | - Sample Application | | 742 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 743 | | Unicast Client | 1.0.1 | 3.0 | - Feature complete | | 744 | | | | | - Shell Module | | 745 | | | | | - BSIM test | | 746 | | | | | - Sample Application | | 747 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 748 | | Broadcast Source | 1.0.1 | 3.0 | - Feature complete | | 749 | | | | | - Shell Module | | 750 | | | | | - BSIM test | | 751 | | | | | - Sample Application | | 752 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 753 | | Broadcast Sink | 1.0.1 | 3.0 | - Feature complete | | 754 | | | | | - Shell Module | | 755 | | | | | - BSIM test | | 756 | | | | | - Sample Application | | 757 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 758 | | Scan Delegator | 1.0.1 | 3.3 | - Feature complete | | 759 | | | | | - Shell Module | | 760 | | | | | - BSIM test | | 761 | | | | | - Sample Application | | 762 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 763 | | Broadcast Assistant | 1.0.1 | 3.3 | - Feature complete | | 764 | | | | | - Shell Module | | 765 | | | | | - BSIM test | | 766 | | | | | - Sample Application | | 767 +--------+-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 768 | CAP | Acceptor | 1.0 | 3.2 | - Feature complete | | 769 | | | | | - Shell Module | | 770 | | | | | - BSIM test | | 771 | | | | | - Sample Application | | 772 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 773 | | Initiator | 1.0 | 3.3 | - Feature complete | | 774 | | | | | - Shell Module | | 775 | | | | | - BSIM test | | 776 | | | | | - Sample Application | | 777 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 778 | | Commander | | | - WIP | - Feature complete | 779 | | | | | | - Shell Module | 780 | | | | | | - BSIM test | 781 | | | | | | - Sample Application | 782 +--------+-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 783 | HAP | Hearing Aid | 1.0 | 3.1 | - Feature complete | | 784 | | | | | - Shell Module | | 785 | | | | | - BSIM test | | 786 | | | | | - Sample Application | | 787 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 788 | | Hearing Aid Unicast Client | 1.0 | 3.1 | - Feature complete | | 789 | | | | | - Shell Module | | 790 | | | | | - BSIM test | | 791 | | | | | - Sample Application | | 792 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 793 | | Hearing Aid Remote Controller | | | - WIP | - Feature complete | 794 | | | | | | - Shell Module | 795 | | | | | | - BSIM test | 796 | | | | | | - Sample Application | 797 +--------+-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 798 | TMAP | Call Gateway | 1.0 | 3.4 | - Feature complete | | 799 | | | | | - Shell Module | | 800 | | | | | - BSIM test | | 801 | | | | | - Sample Application | | 802 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 803 | | Call Terminal | 1.0 | 3.4 | - Feature complete | | 804 | | | | | - Shell Module | | 805 | | | | | - BSIM test | | 806 | | | | | - Sample Application | | 807 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 808 | | Unicast Media Sender | 1.0 | 3.4 | - Feature complete | | 809 | | | | | - Shell Module | | 810 | | | | | - BSIM test | | 811 | | | | | - Sample Application | | 812 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 813 | | Unicast Media Receiver | 1.0 | 3.4 | - Feature complete | | 814 | | | | | - Shell Module | | 815 | | | | | - BSIM test | | 816 | | | | | - Sample Application | | 817 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 818 | | Broadcast Media Sender | 1.0 | 3.4 | - Feature complete | | 819 | | | | | - Shell Module | | 820 | | | | | - BSIM test | | 821 | | | | | - Sample Application | | 822 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 823 | | Broadcast Media Receiver | 1.0 | 3.4 | - Feature complete | | 824 | | | | | - Shell Module | | 825 | | | | | - BSIM test | | 826 | | | | | - Sample Application | | 827 +--------+-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 828 | PBP | Public Broadcast Source | | 3.5 | - Feature complete | | 829 | | | | | - Shell Module | | 830 | | | | | - BSIM test | | 831 | | | | | - Sample Application | | 832 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 833 | | Public Broadcast Sink | | 3.5 | - Feature complete | | 834 | | | | | - Shell Module | | 835 | | | | | - BSIM test | | 836 | | | | | - Sample Application | | 837 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 838 | | Public Broadcast Assistant | | | | - Feature complete | 839 | | | | | | - Shell Module | 840 | | | | | | - BSIM test | 841 | | | | | | - Sample Application | 842 +--------+-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 843 | GMAP | Unicast Game Gateway | | 3.5 | - Feature complete | - Sample Application | 844 | | | | | - Shell Module | | 845 | | | | | - BSIM test | | 846 | | | | | | | 847 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 848 | | Unicast Game Terminal | | 3.5 | - Feature complete | - Sample Application | 849 | | | | | - Shell Module | | 850 | | | | | - BSIM test | | 851 | | | | | | | 852 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 853 | | Broadcast Game Sender | | 3.5 | - Feature complete | - Sample Application | 854 | | | | | - Shell Module | | 855 | | | | | - BSIM test | | 856 | | | | | | | 857 | +-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 858 | | Broadcast Game Receiver | | 3.5 | - Feature complete | - Sample Application | 859 | | | | | - Shell Module | | 860 | | | | | - BSIM test | | 861 | | | | | | | 862 +--------+-------------------------------+---------+------------------+-----------------------+--------------------------------------------------+ 863 864Using the Bluetooth Audio Stack 865=============================== 866 867To use any of the profiles in the Bluetooth Audio Stack, including the top-level 868profiles outside of GAF, :kconfig:option:`CONFIG_BT_AUDIO` shall be enabled. 869This Kconfig option allows the enabling of the individual profiles inside of the 870Bluetooth Audio Stack. Each profile can generally be enabled on its own, but 871enabling higher-layer profiles (such as CAP, TMAP and HAP) will typically 872require enabling some of the lower layer profiles. 873 874It is, however, possible to create a device that uses e.g. only Stream Control 875(with just the BAP), without using any of the content control or 876rendering/capture control profiles, or vice versa. Using the higher layer 877profiles will however typically provide a better user experience and better 878interoperability with other devices. 879 880Common Audio Profile (CAP) 881-------------------------- 882 883The Common Audio Profile introduces restrictions and requirements on the lower layer profiles. 884The procedures in CAP works on one or more streams for one or more devices. Is it thus possible via 885CAP to do a single function call to setup multiple streams across multiple devices. 886 887The figure below shows a complete structure of the procedures in CAP and 888how they correspond to procedures from the other profiles. The circles with I, A and C show whether 889the procedure has active involvement or requirements from the CAP Initiator, CAP Accept and CAP 890Commander roles respectively. 891 892.. figure:: img/cap_proc.svg 893 :align: center 894 :alt: Common Audio Profile Procedures 895 896 Common Audio Profile Procedures 897 898The API reference for CAP can be found in :ref:`Common Audio Profile <bluetooth_cap>`. 899 900Stream Control (BAP) 901-------------------- 902 903Stream control is implemented by the Basic Audio Profile. This profile 904defines multiple roles: 905 906* Unicast Client 907* Unicast Server 908* Broadcast Source 909* Broadcast Sink 910* Scan Delegator 911* Broadcast Assistant 912 913Each role can be enabled individually, and it is possible to support more than 914one role. 915 916Notes about the stream control services 917~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 918 919There are 3 services primarily used by stream control using the Basic Audio Profile. 920 921Audio Stream Control Service (ASCS) 922^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 923 924ASCS is a service used exclusively for setting up unicast streams, 925and is located on the BAP Unicast Server device. 926The service exposes one or more endpoints that can either be a sink or source endpoint, 927from the perspective of the Unicast Server. 928That means a sink endpoint is always audio from the Unicast Client to the Unicast Server, 929and a source endpoint is always from the Unicast Server to the Unicast Client. 930 931Unlike most other GATT services, 932ASCS require that each characteristic in the service has unique data per client. 933This means that if a Unicast Server is connected to multiple Unicast Clients, 934the Unicast Clients are not able to see or control the endpoints configured by the other clients. 935For example if a person's smartphone is streaming audio to a headset, 936then the same person will not be able to see or control that stream from their smartwatch. 937 938Broadcast Audio Scan Service (BASS) 939^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 940 941BASS is a service that is exclusively used by the Scan Delegator and Broadcast Assistant. 942The main purpose of the service is to offload scanning from low power peripherals to e.g. phones 943and PCs. 944Unlike ASCS where the data is required to be unique per client, 945the data in BASS (called receive states) are (usually) shared among all connected clients. 946That means it is possible for a person to tell their headphones to synchronize to a 947Broadcast Source using their phone, 948and then later tell their headphones to stop synchronizing using their smartwatch. 949 950A Broadcast Assistant can be any device, 951and may only support this one role without any audio capabilities. 952This allows legacy devices that do not support periodic advertisements or isochronous channels to 953still provide an interface and scan offloading for peripherals. 954The Bluetooth SIG have provided a guide on how to develop such legacy Broadcast Assistants that can 955be found at 956https://www.bluetooth.com/bluetooth-resources/developing-auracast-receivers-with-an-assistant-application-for-legacy-smartphones/. 957An important note about this guide is that many operating systems (especially on phones), 958do not allow generic usage of the BASS UUID, 959effectively making it impossible to implement your own Broadcast Assistant, 960because you cannot access the BASS. 961 962Published Audio Capabilities Service (PACS) 963^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 964 965PACS is used to expose a device's audio capabilities in Published Audio Capabilities (PAC) records. 966PACS is used by nearly all roles, 967where the Unicast Client and Broadcast Assistant will act as PACS clients, 968and Unicast Server and Broadcast Sink will act as PACS servers. 969These records contain information about the codec, and which values are supported by each codec. 970The values for the LC3 codec are defined by the Bluetooth Assigned numbers 971(https://www.bluetooth.com/specifications/assigned-numbers/), and the values for other codecs such 972as SBC are left undefined/implementation specific for BAP. 973 974PACS also usually share the same data between each connected client, 975but by using functions such as :c:func:`bt_pacs_conn_set_available_contexts_for_conn`, 976it is possible to set specific values for specific clients. 977 978The API reference for stream control can be found in 979:ref:`Bluetooth Audio <bluetooth_audio>`. 980 981 982Rendering and Capture Control 983----------------------------- 984 985Rendering and capture control is implemented by the Volume Control Profile 986(VCP) and Microphone Control Profile (MICP). 987 988The VCP implementation supports the following roles 989 990* Volume Control Service (VCS) Server 991* Volume Control Service (VCS) Client 992 993The MICP implementation supports the following roles 994 995* Microphone Control Profile (MICP) Microphone Device (server) 996* Microphone Control Profile (MICP) Microphone Controller (client) 997 998The API reference for volume control can be found in 999:ref:`Bluetooth Volume Control <bluetooth_volume>`. 1000 1001The API reference for Microphone Control can be found in 1002:ref:`Bluetooth Microphone Control <bluetooth_microphone>`. 1003 1004 1005Content Control 1006--------------- 1007 1008Content control is implemented by the Call Control Profile (CCP) and 1009Media Control Profile (MCP). 1010 1011The CCP implementation is not yet implemented in Zephyr. 1012 1013The MCP implementation supports the following roles 1014 1015* Media Control Service (MCS) Server via the Media Proxy module 1016* Media Control Client (MCC) 1017 1018The API reference for media control can be found in 1019:ref:`Bluetooth Media Control <bluetooth_media>`. 1020 1021Generic TBS and Generic MCS 1022~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1023 1024Both the Telephone Bearer Service (TBS) used by CCP and the Media Control Service (MCS) used by MCP 1025have the concept of generic instances of the services called Generic TBS (GTBS) and 1026Generic MCS (GMCS). 1027 1028While these share a common name prefix, the behavior of these two may be significantly different. 1029 1030Generic TBS 1031^^^^^^^^^^^ 1032 1033The TBS spec defines GTBS as 1034 1035 GTBS provides a single point of access and exposes a representation of its internal telephone 1036 bearers into a single telephone bearer. 1037 This service provides telephone status and control of the device as a single unit with a 1038 single set of characteristics. 1039 It is left up to the implementation to determine what telephone bearer a characteristic of 1040 GTBS represents at any time. 1041 There is no specified manner of representing a characteristic from each individual TBS that 1042 resides on the device to the same characteristic of the GTBS. 1043 1044 For example, if there is more than one TBS on a device and each has a unique telephone bearer 1045 name (e.g., Name1 and Name2), 1046 the way the GTBS represents the telephone bearer name is left up to the implementation. 1047 GTBS is suited for clients that do not need to access or control all the 1048 information available on specific telephone bearers. 1049 1050This means that a GTBS instance represents one or more telephone bearers. 1051A telephone bearer could be any application on a device that can handle (telephone) calls, 1052such as the default Call application on a smartphone, 1053but also other applications such as Signal, Discord, Teams, Slack, etc. 1054 1055GTBS may be standalone (i.e.the device only has a GTBS instance without any TBS instances), 1056and the behavior of the GTBS is mostly left up to the implementation. 1057In Zephyr the implementation of GBTS is that it contains some generic information, 1058such as the provider name which is defined to simply be "Generic TBS", 1059but the majority of the information in the GTBS instance in Zephyr has been implemented to be a 1060union of the data of the other bearers. 1061For example if you have a bearer for regular phone calls and 1062Teams and have an active call in both bearers, 1063then each of those bearers will report a single call, 1064but the GTBS instance will report 2 calls, 1065making it possible for a simple Call Control Client to control all calls from a single bearer. 1066Similarly the supported URIs for each bearer are also made into a union in GTBS, and when placing 1067a call using the GTBS the server will pick the most suited bearer depending on the URI. 1068For example calls with URI ``tel`` would go to the regular phone application, 1069and calls with the URI ``skype`` would go to the Teams application. 1070 1071In conclusion the GTBS implementation in Zephyr is a union of the non-generic telephone bearers. 1072 1073Generic MCS 1074^^^^^^^^^^^ 1075 1076The MCS spec defines GMCS as 1077 1078 The GMCS provides status and control of media playback for the device as a single unit. 1079 An MCS instance describes and controls the media playback for a 1080 specific media player within the device. 1081 A device implements MCS instances to allow clients to access the 1082 separate internal media player entities. 1083 1084and where the behavior of GMCS is defined as 1085 1086 ... the behavior of MCS and GMCS is identical, 1087 and all the characteristics and the characteristics' behaviors are the same. 1088 The term “MCS” is used throughout the document. 1089 Unless otherwise specifically stated in this specification, 1090 the same meaning applies to GMCS as well. 1091 1092This means that a GMCS instance works the same way as an MCS instance, 1093and it follows that GMCS 1094 1095 controls the media playback for a specific media player within the device 1096 1097A media player on a device could be anything that plays media, 1098such as a Spotify or Youtube application on a smartphone. 1099Thus if a device has multiple MCS instances, 1100then each of these control media for that specific application, 1101but the GMCS also controls media playback for a specific media player. 1102GMCS can thus be considered a pointer to a specific MCS instance, 1103and control either e.g. Spotify or Youtube, but not both. 1104 1105The MCS spec does however provide an example of GMCS where a device can 1106 1107 Implement a GMCS that provides status and control of media playback for the device as a whole. 1108 1109Which may indicate that an implementation may use GMCS to represent all media players with GMCS and 1110not a specific media player as stated above. In the case where a device does not have any MCS 1111instances and only GMCS, then GMCS will point to a generic instance. 1112 1113The Zephyr implementation of MCS and GMCS is incomplete, 1114and currently only supports instantiating a single instance that can either be an MCS or GMCS. 1115This means that the implementation is neither complete nor spec-compliant. 1116 1117Difference between GTBS and GMCS 1118^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 1119 1120The definitions and implementations of GTBS and GMCS as stated above are notably different. 1121GTBS works as a union between the other TBS instances (if any), 1122and GMCS works as a pointer to a specific MCS instance (if any). 1123This effectively means that a simple Call Control Client can control all calls just using GTBS, 1124but a Media Control Client may only be able to control a single player using GMCS. 1125 1126Coordinated Sets 1127---------------- 1128 1129Coordinated Sets is implemented by the Coordinated Sets Identification Profile 1130(CSIP). 1131 1132The CSIP implementation supports the following roles 1133 1134* Coordinated Set Identification Service (CSIP) Set Member 1135* Coordinated Set Identification Service (CSIP) Set Coordinator 1136 1137The API reference for media control can be found in 1138:ref:`Bluetooth Coordinated Sets <bluetooth_coordinated_sets>`. 1139 1140Specification correctness and data location 1141------------------------------------------- 1142 1143The implementations are designed to ensure specification compliance as much as possible. 1144When a specification introduces a requirement with e.g. a **shall** then the implementation should 1145attempt to ensure that this requirement is always followed. 1146Depending on the context of this, 1147the implementation ensures this by rejecting invalid parameters from the application, 1148or from the remote devices. 1149 1150Some requirements from the specifications are not or can not be handled by the stack itself for 1151various reasons. 1152One reason when the stack cannot handle a requirement is if the data related to the requirement is 1153exclusively controlled by the application. 1154An example of this is the advertising data, 1155where multiple service have requirements for what to advertise and when, 1156but where both the advertising state and data is exclusively controlled by the application. 1157 1158Oppositely there are also requirements from the specification, 1159where the data related to the requirement is exclusively controlled by the stack. 1160An example of this is the Volume Control Service (VCS) state, 1161where the specifications mandata that the VCP Volume Renderer (VCS server) modify the values 1162without a choice, 1163e.g. when setting the absolutely volume. 1164In cases like this the application is only notified about the change with a callback, 1165but cannot reject the request (the stack will reject any invalid requests). 1166 1167Generally when the data is simple (like the VCS state which only take up a few bytes), 1168the data is kept in and controlled by the stack, 1169as this can ensure that the requirements can be handled by the stack, 1170making it easier to use a profile role correctly. 1171When the data is more complex (e.g. the PAC records), 1172the data may be kept by the application and the stack only contains a reference to it. 1173When the data is very application specific (e.g. advertising data), 1174the data is kept in and controlled by the application. 1175 1176As a rule of thumb, the return types of the callbacks for each profile implementation indicate 1177whether the data is controlled by the stack or the application. 1178For example all the callbacks for the VCP Volume Renderer have the return type of ``void``, 1179but the return type of the BAP Unicast Server callbacks are ``int``, 1180indicating that the application not only controls a lot of the Unicast Server data, 1181but can also reject the requests. 1182The choice of what the return type of the callbacks often depend on the specifications, 1183and how much control the role has in a given context. 1184 1185Things worth knowing or considering when using LE Audio 1186======================================================= 1187 1188This section describes a few tings to consider when contributing to or using LE Audio in Zephyr. 1189The things described by this section are not unique to Zephyr as they are defined by the 1190specifications. 1191 1192Security requirements 1193--------------------- 1194 1195All LE Audio services require Security Level 2 but where the key must be 128-bit and derived via an 1196OOB method or via LE Secure connections. 1197There is no Core-spec defined way of reporting this in GATT, 1198as ATT does not have a specific error code for missing OOB method or LE Secure Connections 1199(although there is a way to report wrong key size). 1200 1201In Zephyr we do not force the device to always use these, as a device that uses LE Audio may also 1202use other profiles and services that do not require such security. 1203We guard all access to services using a custom security check implemented in 1204:zephyr_file:`subsys/bluetooth/audio/audio.c`, where all LE Audio services must use the 1205internal :c:macro:`BT_AUDIO_CHRC` macro for proper security verification. 1206 1207Access to the LTK for encrypted SIRKs in CSIS 1208--------------------------------------------- 1209 1210The Coordinated Set Identification Service (CSIS) may encrypt the SIRK (set identity resolving key). 1211The process of encrypting the SIRK requires the LTK as the encryption key, 1212which is typically not exposed to higher layer implementations such as CSIS. 1213This does not have any effect on the security though. 1214 1215MTU requirements 1216---------------- 1217 1218The Basic Audio Profile (BAP) has a requirement that both sides shall support a minimum ATT_MTU of 1219at least 64 on the unenhanced ATT bearer or at least one enhanced ATT bearer. 1220The requirement comes from the preferred (or sometimes mandatory) use of GATT Write Without 1221Response, and where support for Write Long Characteristic Value is optional in most cases. 1222 1223If a ASCS device supports values larger than the minimum ATT_MTU of 64 octets, then it shall support 1224Read long Characteristic Value by setting :kconfig:option:`CONFIG_BT_ATT_PREPARE_COUNT` to a 1225non-zero value. 1226 1227LE Audio resources 1228################## 1229 1230This section contains some links and reference to resources that are useful for either contributors 1231to the LE Audio Stack in Zephyr, LE Audio application developers or both. 1232 1233The LE audio channel on Discord 1234******************************* 1235 1236Zephyr has a specific Discord channel for LE Audio development, which is open to all. 1237Find it here at https://discordapp.com/channels/720317445772017664/1207326649591271434 or simply 1238search for "ble-audio" from within Discord. 1239Since the ``#ble-audio`` channel is open for all, 1240we cannot discuss any specifications that are in development in that channel. 1241For discussions that require a Bluetooth SIG membership we refer to the ``#bluetooth-sig`` 1242Discord channel found at https://discordapp.com/channels/720317445772017664/869172014018097162. 1243 1244Zephyr weekly meetings 1245********************** 1246 1247Anyone who is a Bluetooth SIG member and a Zephyr member can join the weekly meetings where we 1248discuss and plan the development of LE Audio in Zephyr. You can find the time of the meetings by 1249joining the Bluetooth-sig group at https://lists.zephyrproject.org/g/Bluetooth-sig. 1250 1251Github project 1252************** 1253 1254LE Audio in Zephyr has its own Github project available at 1255https://github.com/orgs/zephyrproject-rtos/projects/26. 1256The project is mostly automated, 1257and the LE Audio contributors almost only rely on the automated workflows 1258to present the state of development. 1259Anyone is able to pick any of the open issues and work on it. 1260If you cannot assign the issue to yourself, 1261please leave a comment in the issue itself or ping the Discord channel for help. 1262 1263Bluetooth SIG errata for LE Audio 1264********************************* 1265 1266There are many specifications for LE Audio, 1267and several of them are still being updated and developed. 1268To get an overview of the errata for the LE Audio specifications you can visit 1269 1270* Generic Audio (GA) errata https://bluetooth.atlassian.net/wiki/spaces/GA/pages/1634402349/GAWG+Errata+Lists 1271* Hearing Aid (HA) errata https://bluetooth.atlassian.net/wiki/spaces/HA/pages/1634140216/HA+WG+Errata+List 1272* Audio, Telephony and Automotive (ATA) errata https://bluetooth.atlassian.net/wiki/spaces/ATA/pages/1668481034/ATA+Errata+Lists 1273 1274Access to errata requires a Bluetooth SIG membership. 1275 1276Bluetooth SIG working groups for LE Audio 1277***************************************** 1278 1279There are 3 working groups in the Bluetooth SIG related to LE Audio: 1280 1281* Generic Audio (GA) https://www.bluetooth.org/groups/group.aspx?gId=665 1282* Hearing Aid (HA) https://www.bluetooth.org/groups/group.aspx?gId=605 1283* Audio, Telephony, and Automotive (ATA) https://www.bluetooth.org/groups/group.aspx?gId=659 1284 1285By joining these groups you will also get emails from their respective mailing lists, 1286where multiple questions and discussions are handled. 1287The working groups also have scheduled weekly meetings, 1288where issues and the development of the specifications are handled. 1289 1290Access to the Bluetooth SIG working groups requires a Bluetooth SIG membership. 1291 1292The LE Audio Book 1293***************** 1294 1295There is a free ebook on LE Audio at https://www.bluetooth.com/bluetooth-resources/le-audio-book/. 1296The book was released in January 2022, 1297and thus before some of the specifications were finalized, 1298but also before some of the released updates to the specifications. 1299Nevertheless the book still provides a good explanation for many of the concepts and ideas, 1300but please refer to the individual specifications for technical information. 1301 1302Bluetooth SIG informational papers, reports and guides 1303****************************************************** 1304 1305The Bluetooth SIG occasionally release new informational papers, report and guides. 1306These can be found at https://www.bluetooth.com/bluetooth-resources/?tags=le-audio&keyword. 1307Here you will also find the aforementioned LE Audio book, among many other good resources. 1308
