1# 2 3BTstack implements a set of Bluetooth protocols and profiles. To connect to other Bluetooth devices or to provide a Bluetooth services, BTstack has to be properly configured. 4 5The configuration of BTstack is done both at compile time as well as at run time: 6 7- compile time configuration: 8 - adjust *btstack_config.h* - this file describes the system configuration, used functionality, and also the memory configuration 9 - add necessary source code files to your project 10 11- run time configuration of: 12 - Bluetooth chipset 13 - run loop 14 - HCI transport layer 15 - provided services 16 - packet handlers 17 18In the following, we provide an overview of the configuration 19that is necessary to setup BTstack. From the point when the run loop 20is executed, the application runs as a finite 21state machine, which processes events received from BTstack. BTstack 22groups events logically and provides them via packet handlers. 23We provide their overview here. For the case that there is a need to inspect the data exchanged 24between BTstack and the Bluetooth chipset, we describe how to configure 25packet logging mechanism. Finally, we provide an overview on power management in Bluetooth in general and how to save energy in BTstack. 26 27## Configuration in btstack_config.h {#sec:btstackConfigHowTo} 28The file *btstack_config.h* contains three parts: 29 30- \#define HAVE_* directives [listed here](#sec:haveDirectives). These directives describe available system properties, similar to config.h in a autoconf setup. 31- \#define ENABLE_* directives [listed here](#sec:enableDirectives). These directives list enabled properties, most importantly ENABLE_CLASSIC and ENABLE_BLE. 32- other #define directives for BTstack configuration, most notably static memory, [see next section](#sec:memoryConfigurationHowTo) and [NVM configuration](#sec:nvmConfiguration). 33 34<!-- a name "lst:platformConfiguration"></a--> 35<!-- --> 36 37### HAVE_* directives {#sec:haveDirectives} 38System properties: 39 40| \#define | Description | 41|-----------------------|-----------------------------------------------------------------------| 42| HAVE_AES128 | Use platform AES128 engine | 43| HAVE_BTSTACK_STDIN | STDIN is available for CLI interface | 44| HAVE_LWIP | lwIP is available | 45| HAVE_MALLOC | Use dynamic memory | 46| HAVE_MBEDTLS_ECC_P256 | mbedTLS provides NIST P-256 operations e.g. for LE Secure Connections | 47 48Embedded platform properties: 49 50| \#define | Description | 51|---------------------------------|--------------------------------------| 52| HAVE_EMBEDDED_TIME_MS | System provides time in milliseconds | 53| HAVE_EMBEDDED_TICK | System provides tick interrupt | 54| HAVE_HAL_AUDIO | Audio HAL is available | 55| HAVE_HAL_AUDIO_SINK_STEREO_ONLY | Duplicate samples for mono playback | 56 57FreeRTOS platform properties: 58 59| \#define | Description | 60|------------------------------|------------------------------------------------------------------| 61| HAVE_FREERTOS_INCLUDE_PREFIX | FreeRTOS headers are in 'freertos' folder (e.g. ESP32's esp-idf) | 62 63POSIX platform properties: 64 65| \#define | Description | 66|--------------------|--------------------------------------| 67| HAVE_POSIX_FILE_IO | POSIX File i/o used for hci dump | 68| HAVE_POSIX_TIME | System provides time function | 69| LINK_KEY_PATH | Path to stored link keys | 70| LE_DEVICE_DB_PATH | Path to stored LE device information | 71 72<!-- a name "lst:btstackFeatureConfiguration"></a--> 73<!-- --> 74 75Chipset properties: 76 77| \#define | Description | 78|------------------------|-------------------------------------------------------| 79| HAVE_BCM_PCM2 | PCM2 is used and requires additional configuration | 80| HAVE_BCM_PCM_NBS_16KHZ | NBS is up/downsampled, use 16 kHz sample rate for NBS | 81 82### ENABLE_* directives {#sec:enableDirectives} 83BTstack properties: 84 85| \#define | Description | 86|-----------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------| 87| ENABLE_CLASSIC | Enable Classic related code in HCI and L2CAP | 88| ENABLE_BLE | Enable BLE related code in HCI and L2CAP | 89| ENABLE_EHCILL | Enable eHCILL low power mode on TI CC256x/WL18xx chipsets | 90| ENABLE_H5 | Enable support for SLIP mode in `btstack_uart.h` drivers for HCI H5 ('Three-Wire Mode') | 91| ENABLE_LOG_DEBUG | Enable log_debug messages | 92| ENABLE_LOG_ERROR | Enable log_error messages | 93| ENABLE_LOG_INFO | Enable log_info messages | 94| ENABLE_SCO_OVER_HCI | Enable SCO over HCI for chipsets (if supported) | 95| ENABLE_SCO_OVER_PCM | Enable SCO ofer PCM/I2S for chipsets (if supported) | 96| ENABLE_HFP_WIDE_BAND_SPEECH | Enable support for mSBC codec used in HFP profile for Wide-Band Speech | 97| ENABLE_HFP_AT_MESSAGES | Enable `HFP_SUBEVENT_AT_MESSAGE_SENT` and `HFP_SUBEVENT_AT_MESSAGE_RECEIVED` events | 98| ENABLE_LE_PERIPHERAL | Enable support for LE Peripheral Role in HCI and Security Manager | 99| ENABLE_LE_CENTRAL | Enable support for LE Central Role in HCI and Security Manager | 100| ENABLE_LE_SECURE_CONNECTIONS | Enable LE Secure Connections | 101| ENABLE_LE_PROACTIVE_AUTHENTICATION | Enable automatic encryption for bonded devices on re-connect | 102| ENABLE_GATT_CLIENT_PAIRING | Enable GATT Client to start pairing and retry operation on security error | 103| ENABLE_MICRO_ECC_FOR_LE_SECURE_CONNECTIONS | Use [micro-ecc library](https://github.com/kmackay/micro-ecc) for ECC operations | 104| ENABLE_LE_DATA_LENGTH_EXTENSION | Enable LE Data Length Extension support | 105| ENABLE_LE_EXTENDED_ADVERTISING | Enable extended advertising and scanning | 106| ENABLE_LE_PERIODIC_ADVERTISING | Enable periodic advertising and scanning | 107| ENABLE_LE_SIGNED_WRITE | Enable LE Signed Writes in ATT/GATT | 108| ENABLE_LE_PRIVACY_ADDRESS_RESOLUTION | Enable address resolution for resolvable private addresses in Controller | 109| ENABLE_CROSS_TRANSPORT_KEY_DERIVATION | Enable Cross-Transport Key Derivation (CTKD) for Secure Connections | 110| ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE | Enable Enhanced Retransmission Mode for L2CAP Channels. Mandatory for AVRCP Browsing | 111| ENABLE_L2CAP_LE_CREDIT_BASED_FLOW_CONTROL_MODE | Enable LE credit-based flow-control mode for L2CAP channels | 112| ENABLE_L2CAP_ENHANCED_CREDIT_BASED_FLOW_CONTROL_MODE | Enable Enhanced credit-based flow-control mode for L2CAP Channels | 113| ENABLE_HCI_CONTROLLER_TO_HOST_FLOW_CONTROL | Enable HCI Controller to Host Flow Control, see below | 114| ENABLE_HCI_SERIALIZED_CONTROLLER_OPERATIONS | Serialize Inquiry, Remote Name Request, and Create Connection operations | 115| ENABLE_ATT_DELAYED_RESPONSE | Enable support for delayed ATT operations, see [GATT Server](profiles/#sec:GATTServerProfile) | 116| ENABLE_BCM_PCM_WBS | Enable support for Wide-Band Speech codec in BCM controller, requires ENABLE_SCO_OVER_PCM | 117| ENABLE_CC256X_ASSISTED_HFP | Enable support for Assisted HFP mode in CC256x Controller, requires ENABLE_SCO_OVER_PCM | 118| Enable_RTK_PCM_WBS | Enable support for Wide-Band Speech codec in Realtek controller, requires ENABLE_SCO_OVER_PCM | 119| ENABLE_CC256X_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND | Enable workaround for bug in CC256x Flow Control during baud rate change, see chipset docs. | 120| ENABLE_CYPRESS_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND | Enable workaround for bug in CYW2070x Flow Control during baud rate change, similar to CC256x. | 121| ENABLE_LE_LIMIT_ACL_FRAGMENT_BY_MAX_OCTETS | Force HCI to fragment ACL-LE packets to fit into over-the-air packet | 122| ENABLE_TLV_FLASH_EXPLICIT_DELETE_FIELD | Enable use of explicit delete field in TLV Flash implementation - required when flash value cannot be overwritten with zero | 123| ENABLE_TLV_FLASH_WRITE_ONCE | Enable storing of emtpy tag instead of overwriting existing tag - required when flash value cannot be overwritten at all | 124| ENABLE_CONTROLLER_WARM_BOOT | Enable stack startup without power cycle (if supported/possible) | 125| ENABLE_SEGGER_RTT | Use SEGGER RTT for console output and packet log, see [additional options](#sec:rttConfiguration) | 126| ENABLE_EXPLICIT_CONNECTABLE_MODE_CONTROL | Disable calls to control Connectable Mode by L2CAP | 127| ENABLE_EXPLICIT_IO_CAPABILITIES_REPLY | Let application trigger sending IO Capabilities (Negative) Reply | 128| ENABLE_EXPLICIT_LINK_KEY_REPLY | Let application trigger sending Link Key (Negative) Response, allows for asynchronous link key lookup | 129| ENABLE_EXPLICIT_BR_EDR_SECURITY_MANAGER | Report BR/EDR Security Manager support in L2CAP Information Response | 130| ENABLE_EXPLICIT_DEDICATED_BONDING_DISCONNECT | Keep connection after dedicated bonding is complete | 131| ENABLE_CLASSIC_OOB_PAIRING | Enable support for classic Out-of-Band (OOB) pairing | 132| ENABLE_A2DP_EXPLICIT_CONFIG | Let application configure stream endpoint (skip auto-config of SBC endpoint) | 133| ENABLE_AVDTP_ACCEPTOR_EXPLICIT_START_STREAM_CONFIRMATION | allow accept or reject of stream start on A2DP_SUBEVENT_START_STREAM_REQUESTED | 134| ENABLE_LE_WHITELIST_TOUCH_AFTER_RESOLVING_LIST_UPDATE | Enable Workaround for Controller bug | 135| ENABLE_LE_SET_ADV_PARAMS_ON_RANDOM_ADDRESS_CHANGE | Send HCI LE Set Advertising Params after HCI LE Set Random Address - workaround for Controller Bug | 136| ENABLE_CONTROLLER_DUMP_PACKETS | Dump number of packets in Controller per type for debugging | 137 138Notes: 139 140- ENABLE_MICRO_ECC_FOR_LE_SECURE_CONNECTIONS: Only some Bluetooth 4.2+ controllers (e.g., EM9304, ESP32) support the necessary HCI commands for ECC. Other reason to enable the ECC software implementations are if the Host is much faster or if the micro-ecc library is already provided (e.g., ESP32, WICED, or if the ECC HCI Commands are unreliable. 141 142### HCI Controller to Host Flow Control 143In general, BTstack relies on flow control of the HCI transport, either via Hardware CTS/RTS flow control for UART or regular USB flow control. If this is not possible, e.g on an SoC, BTstack can use HCI Controller to Host Flow Control by defining ENABLE_HCI_CONTROLLER_TO_HOST_FLOW_CONTROL. If enabled, the HCI Transport implementation must be able to buffer the specified packets. In addition, it also need to be able to buffer a few HCI Events. Using a low number of host buffers might result in less throughput. 144 145Host buffer configuration for HCI Controller to Host Flow Control: 146 147| \#define | Description | 148|-------------------------|----------------------------------| 149| HCI_HOST_ACL_PACKET_NUM | Max number of ACL packets | 150| HCI_HOST_ACL_PACKET_LEN | Max size of HCI Host ACL packets | 151| HCI_HOST_SCO_PACKET_NUM | Max number of ACL packets | 152| HCI_HOST_SCO_PACKET_LEN | Max size of HCI Host SCO packets | 153 154### Memory configuration directives {#sec:memoryConfigurationHowTo} 155 156The structs for services, active connections and remote devices can be 157allocated in two different manners: 158 159- statically from an individual memory pool, whose maximal number of 160 elements is defined in the btstack_config.h file. To initialize the static 161 pools, you need to call at runtime *btstack_memory_init* function. An example 162 of memory configuration for a single SPP service with a minimal 163 L2CAP MTU is shown in Listing {@lst:memoryConfigurationSPP}. 164 165- dynamically using the *malloc/free* functions, if HAVE_MALLOC is 166 defined in btstack_config.h file. 167 168For each HCI connection, a buffer of size HCI_ACL_PAYLOAD_SIZE is reserved. For fast data transfer, however, a large ACL buffer of 1021 bytes is recommended. The large ACL buffer is required for 3-DH5 packets to be used. 169 170<!-- a name "lst:memoryConfiguration"></a--> 171<!-- --> 172 173| \#define | Description | 174|-------------------------------------------|----------------------------------------------------------------------------| 175| HCI_ACL_PAYLOAD_SIZE | Max size of HCI ACL payloads | 176| HCI_ACL_CHUNK_SIZE_ALIGNMENT | Alignment of ACL chunk size, can be used to align HCI transport writes | 177| HCI_INCOMING_PRE_BUFFER_SIZE | Number of bytes reserved before actual data for incoming HCI packets | 178| MAX_NR_BNEP_CHANNELS | Max number of BNEP channels | 179| MAX_NR_BNEP_SERVICES | Max number of BNEP services | 180| MAX_NR_GATT_CLIENTS | Max number of GATT clients | 181| MAX_NR_HCI_CONNECTIONS | Max number of HCI connections | 182| MAX_NR_HFP_CONNECTIONS | Max number of HFP connections | 183| MAX_NR_L2CAP_CHANNELS | Max number of L2CAP connections | 184| MAX_NR_L2CAP_SERVICES | Max number of L2CAP services | 185| MAX_NR_RFCOMM_CHANNELS | Max number of RFOMMM connections | 186| MAX_NR_RFCOMM_MULTIPLEXERS | Max number of RFCOMM multiplexers, with one multiplexer per HCI connection | 187| MAX_NR_RFCOMM_SERVICES | Max number of RFCOMM services | 188| MAX_NR_SERVICE_RECORD_ITEMS | Max number of SDP service records | 189| MAX_NR_SM_LOOKUP_ENTRIES | Max number of items in Security Manager lookup queue | 190| MAX_NR_WHITELIST_ENTRIES | Max number of items in GAP LE Whitelist to connect to | 191 192The memory is set up by calling *btstack_memory_init* function: 193 194 btstack_memory_init(); 195 196<!-- a name "lst:memoryConfigurationSPP"></a--> 197<!-- --> 198 199Here's the memory configuration for a basic SPP server. 200 201 #define HCI_ACL_PAYLOAD_SIZE 52 202 #define MAX_NR_HCI_CONNECTIONS 1 203 #define MAX_NR_L2CAP_SERVICES 2 204 #define MAX_NR_L2CAP_CHANNELS 2 205 #define MAX_NR_RFCOMM_MULTIPLEXERS 1 206 #define MAX_NR_RFCOMM_SERVICES 1 207 #define MAX_NR_RFCOMM_CHANNELS 1 208 #define NVM_NUM_LINK_KEYS 3 209 210Listing: Memory configuration for a basic SPP server. {#lst:memoryConfigurationSPP} 211 212In this example, the size of ACL packets is limited to the minimum of 52 bytes, resulting in an L2CAP MTU of 48 bytes. Only a singleHCI connection can be established at any time. On it, two L2CAP services are provided, which can be active at the same time. Here, these two can be RFCOMM and SDP. Then, memory for one RFCOMM multiplexer is reserved over which one connection can be active. Finally, up to three link keys can be stored in persistent memory. 213 214<!-- --> 215 216### Non-volatile memory (NVM) directives {#sec:nvmConfiguration} 217 218If implemented, bonding information is stored in Non-volatile memory. For Classic, a single link keys and its type is stored. For LE, the bonding information contains various values (long term key, random number, EDIV, signing counter, identity, ...) Often, this is implemented using Flash memory. Then, the number of stored entries are limited by: 219 220<!-- a name "lst:nvmDefines"></a--> 221<!-- --> 222 223| \#define | Description | 224|---------------------------|----------------------------------------------------------------------------------------------| 225| NVM_NUM_LINK_KEYS | Max number of Classic Link Keys that can be stored | 226| NVM_NUM_DEVICE_DB_ENTRIES | Max number of LE Device DB entries that can be stored | 227| NVN_NUM_GATT_SERVER_CCC | Max number of 'Client Characteristic Configuration' values that can be stored by GATT Server | 228 229### HCI Dump Stdout directives {#sec:hciDumpStdout} 230 231Allow to truncate HCI ACL and SCO packets to reduce console output for debugging audio applications. 232 233| \#define | Description | 234|------------------------------|-------------------------------------------| 235| HCI_DUMP_STDOUT_MAX_SIZE_ACL | Max size of ACL packets to log via stdout | 236| HCI_DUMP_STDOUT_MAX_SIZE_SCO | Max size of SCO packets to log via stdout | 237| HCI_DUMP_STDOUT_MAX_SIZE_ISO | Max size of ISO packets to log via stdout | 238 239### SEGGER Real Time Transfer (RTT) directives {#sec:rttConfiguration} 240 241[SEGGER RTT](https://www.segger.com/products/debug-probes/j-link/technology/about-real-time-transfer/) improves on the use of an UART for debugging with higher throughput and less overhead. In addition, it allows for direct logging in PacketLogger/BlueZ format via the provided JLinkRTTLogger tool. 242 243When enabled with `ENABLE_SEGGER_RTT` and `hci_dump_init()` can be called with an `hci_dunp_segger_stdout_get_instance()` for textual output and `hci_dump_segger_binary_get_instance()` for binary output. With the latter, you can select `HCI_DUMP_BLUEZ` or `HCI_DUMP_PACKETLOGGER`, format. For RTT, the following directives are used to configure the up channel: 244 245| \#define | Default | Description | 246|----------------------------------|-------------------------------|-------------------------------------------------------------------------------------------------------------------| 247| SEGGER_RTT_PACKETLOG_MODE | SEGGER_RTT_MODE_NO_BLOCK_SKIP | SEGGER_RTT_MODE_NO_BLOCK_SKIP to skip messages if buffer is full, or, SEGGER_RTT_MODE_BLOCK_IF_FIFO_FULL to block | 248| SEGGER_RTT_PACKETLOG_CHANNEL | 1 | Channel to use for packet log. Channel 0 is used for terminal | 249| SEGGER_RTT_PACKETLOG_BUFFER_SIZE | 1024 | Size of outgoing ring buffer. Increase if you cannot block but get 'message skipped' warnings. | 250 251## Run-time configuration 252 253To allow code-reuse with different platforms 254as well as with new ports, the low-level initialization of BTstack and 255the hardware configuration has been extracted to the various 256*platforms/PLATFORM/main.c* files. The examples only contain the 257platform-independent Bluetooth logic. But let’s have a look at the 258common init code. 259 260Listing [below](#lst:btstackInit) shows a minimal platform setup for an 261embedded system with a Bluetooth chipset connected via UART. 262 263~~~~ {#lst:btstackInit .c caption="{Minimal platform setup for an embedded system}"} 264 265 int main(){ 266 // ... hardware init: watchdoch, IOs, timers, etc... 267 268 // setup BTstack memory pools 269 btstack_memory_init(); 270 271 // select embedded run loop 272 btstack_run_loop_init(btstack_run_loop_embedded_get_instance()); 273 274 // enable logging 275 hci_dump_init(hci_dump_embedded_stdout_get_instance()); 276 277 278 // init HCI 279 hci_transport_t * transport = hci_transport_h4_instance(); 280 hci_init(transport, NULL); 281 282 // setup example 283 btstack_main(argc, argv); 284 285 // go 286 btstack_run_loop_execute(); 287 } 288 289~~~~ 290 291First, BTstack’s memory pools are set up. Then, the standard run loop 292implementation for embedded systems is selected. 293 294The call to *hci_dump_init* configures BTstack to output all Bluetooth 295packets and its own debug and error message using printf with BTstack's 296millisecond tiomestamps.s as tim. 297The Python 298script *tools/create_packet_log.py* can be used to convert the console 299output into a Bluetooth PacketLogger format that can be opened by the OS 300X PacketLogger tool as well as by Wireshark for further inspection. When 301asking for help, please always include a log created with HCI dump. 302 303The *hci_init* function sets up HCI to use the HCI H4 Transport 304implementation. It doesn’t provide a special transport configuration nor 305a special implementation for a particular Bluetooth chipset. It makes 306use of the *remote_device_db_memory* implementation that allows for 307re-connects without a new pairing but doesn’t persist the bonding 308information. 309 310Finally, it calls *btstack_main()* of the actual example before 311executing the run loop. 312 313 314## Source tree structure {#sec:sourceTreeHowTo} 315 316The source tree has been organized to easily setup new projects. 317 318| Path | Description | 319|----------|------------------------------------------------------| 320| chipset | Support for individual Bluetooth Controller chipsets | 321| doc | Sources for BTstack documentation | 322| example | Example applications available for all ports | 323| platform | Support for special OSs and/or MCU architectures | 324| port | Complete port for a MCU + Chipset combinations | 325| src | Bluetooth stack implementation | 326| test | Unit and PTS tests | 327| tool | Helper tools for BTstack | 328 329The core of BTstack, including all protocol and profiles, is in *src/*. 330 331Support for a particular platform is provided by the *platform/* subfolder. For most embedded ports, *platform/embedded/* provides *btstack_run_loop_embedded* and the *hci_transport_h4_embedded* implementation that require *hal_cpu.h*, *hal_led.h*, and *hal_uart_dma.h* plus *hal_tick.h* or *hal_time_ms* to be implemented by the user. 332 333To accommodate a particular Bluetooth chipset, the *chipset/* subfolders provide various btstack_chipset_* implementations. 334Please have a look at the existing ports in *port/*. 335 336## Run loop configuration {#sec:runLoopHowTo} 337 338To initialize BTstack you need to [initialize the memory](#sec:memoryConfigurationHowTo) 339and [the run loop](#sec:runLoopHowTo) respectively, then setup HCI and all needed higher 340level protocols. 341 342BTstack uses the concept of a run loop to handle incoming data and to schedule work. 343The run loop handles events from two different types of sources: data 344sources and timers. Data sources represent communication interfaces like 345an UART or an USB driver. Timers are used by BTstack to implement 346various Bluetooth-related timeouts. They can also be used to handle 347periodic events. In addition, most implementations also allow to trigger a poll 348of the data sources from interrupt context, or, execute a function from a different 349thread. 350 351Data sources and timers are represented by the *btstack_data_source_t* and 352*btstack_timer_source_t* structs respectively. Each of these structs contain 353at least a linked list node and a pointer to a callback function. All active timers 354and data sources are kept in link lists. While the list of data sources 355is unsorted, the timers are sorted by expiration timeout for efficient 356processing. Data sources need to be configured upon what event they are called back. 357They can be configured to be polled (*DATA_SOURCE_CALLBACK_POLL*), on read ready (*DATA_SOURCE_CALLBACK_READ*), 358or on write ready (*DATA_SOURCE_CALLBACK_WRITE*). 359 360Timers are single shot: a timer will be removed from the timer list 361before its event handler callback is executed. If you need a periodic 362timer, you can re-register the same timer source in the callback 363function, as shown in Listing [PeriodicTimerHandler]. Note that BTstack 364expects to get called periodically to keep its time, see Section 365[on time abstraction](#sec:timeAbstractionPorting) for more on the 366tick hardware abstraction. 367 368BTstack provides different run loop implementations that implement the *btstack_run_loop_t* interface: 369 370- CoreFoundation: implementation for iOS and OS X applications 371- Embedded: the main implementation for embedded systems, especially without an RTOS. 372- FreeRTOS: implementation to run BTstack on a dedicated FreeRTOS thread 373- POSIX: implementation for POSIX systems based on the select() call. 374- Qt: implementation for the Qt applications 375- WICED: implementation for the Broadcom WICED SDK RTOS abstraction that wraps FreeRTOS or ThreadX. 376- Windows: implementation for Windows based on Event objects and WaitForMultipleObjects() call. 377 378Depending on the platform, data sources are either polled (embedded, FreeRTOS), or the platform provides a way 379to wait for a data source to become ready for read or write (CoreFoundation, POSIX, Qt, Windows), or, 380are not used as the HCI transport driver and the run loop is implemented in a different way (WICED). 381In any case, the callbacks must be explicitly enabled with the *btstack_run_loop_enable_data_source_callbacks(..)* function. 382 383In your code, you'll have to configure the run loop before you start it 384as shown in Listing [listing:btstackInit]. The application can register 385data sources as well as timers, e.g., for periodical sampling of sensors, or 386for communication over the UART. 387 388The run loop is set up by calling *btstack_run_loop_init* function and providing 389an instance of the actual run loop. E.g. for the embedded platform, it is: 390 391<!-- --> 392 393 btstack_run_loop_init(btstack_run_loop_embedded_get_instance()); 394 395If the run loop allows to trigger polling of data sources from interrupt context, 396*btstack_run_loop_poll_data_sources_from_irq*. 397 398On multi-threaded environments, e.g., FreeRTOS, POSIX, WINDOWS, 399*btstack_run_loop_execute_code_on_main_thread* can be used to schedule a callback on the main loop. 400 401The complete Run loop API is provided [here](appendix/apis/#sec:runLoopAPIAppendix). 402 403 404### Run Loop Embedded 405 406In the embedded run loop implementation, data sources are constantly polled and 407the system is put to sleep if no IRQ happens during the poll of all data sources. 408 409The complete run loop cycle looks like this: first, the callback 410function of all registered data sources are called in a round robin way. 411Then, the callback functions of timers that are ready are executed. 412Finally, it will be checked if another run loop iteration has been 413requested by an interrupt handler. If not, the run loop will put the MCU 414into sleep mode. 415 416Incoming data over the UART, USB, or timer ticks will generate an 417interrupt and wake up the microcontroller. In order to avoid the 418situation where a data source becomes ready just before the run loop 419enters sleep mode, an interrupt-driven data source has to call the 420*btstack_run_loop_poll_data_sources_from_irq* function. The call to 421*btstack_run_loop_poll_data_sources_from_irq* sets an 422internal flag that is checked in the critical section just before 423entering sleep mode causing another run loop cycle. 424 425To enable the use of timers, make sure that you defined HAVE_EMBEDDED_TICK or HAVE_EMBEDDED_TIME_MS in the 426config file. 427 428While there is no threading, *btstack_run_loop_poll_data_sources_from_irq* allows to reduce stack size by 429scheduling a continuation. 430 431### Run Loop FreeRTOS 432 433The FreeRTOS run loop is used on a dedicated FreeRTOS thread and it uses a FreeRTOS queue to schedule callbacks on the run loop. 434In each iteration: 435 436- all data sources are polled 437- all scheduled callbacks are executed 438- all expired timers are called 439- finally, it gets the next timeout. It then waits for a 'trigger' or the next timeout, if set. 440 441It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 442 443 444### Run Loop POSIX 445 446The data sources are standard File Descriptors. In the run loop execute implementation, 447select() call is used to wait for file descriptors to become ready to read or write, 448while waiting for the next timeout. 449 450To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 451 452It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 453 454 455### Run loop CoreFoundation (OS X/iOS) 456 457This run loop directly maps BTstack's data source and timer source with CoreFoundation objects. 458It supports ready to read and write similar to the POSIX implementation. The call to 459*btstack_run_loop_execute()* then just calls *CFRunLoopRun()*. 460 461To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 462 463It currently only supports *btstack_run_loop_execute_code_on_main_thread*. 464 465 466### Run Lop Qt 467 468This run loop directly maps BTstack's data source and timer source with Qt Core objects. 469It supports ready to read and write similar to the POSIX implementation. 470 471To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 472 473It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 474 475 476### Run loop Windows 477 478The data sources are Event objects. In the run loop implementation WaitForMultipleObjects() call 479is all is used to wait for the Event object to become ready while waiting for the next timeout. 480 481It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 482 483 484### Run loop WICED 485 486WICED SDK API does not provide asynchronous read and write to the UART and no direct way to wait for 487one or more peripherals to become ready. Therefore, BTstack does not provide direct support for data sources. 488Instead, the run loop provides a message queue that allows to schedule functions calls on its thread via 489*btstack_run_loop_wiced_execute_code_on_main_thread()*. 490 491The HCI transport H4 implementation then uses two lightweight threads to do the 492blocking read and write operations. When a read or write is complete on 493the helper threads, a callback to BTstack is scheduled. 494 495It currently only supports *btstack_run_loop_execute_code_on_main_thread*. 496 497 498## HCI Transport configuration 499 500The HCI initialization has to adapt BTstack to the used platform. The first 501call is to *hci_init()* and requires information about the HCI Transport to use. 502The arguments are: 503 504- *HCI Transport implementation*: On embedded systems, a Bluetooth 505 module can be connected via USB or an UART port. On embedded, BTstack implements HCI UART Transport Layer (H4) and H4 with eHCILL support, a lightweight low-power variant by Texas Instruments. For POSIX, there is an implementation for HCI H4, HCI H5 and H2 libUSB, and for WICED HCI H4 WICED. 506 These are accessed by linking the appropriate file, e.g., 507 [platform/embedded/hci_transport_h4_embedded.c]() 508 and then getting a pointer to HCI Transport implementation. 509 For more information on adapting HCI Transport to different 510 environments, see [here](porting/#sec:hciTransportPorting). 511 512<!-- --> 513 514 hci_transport_t * transport = hci_transport_h4_instance(); 515 516- *HCI Transport configuration*: As the configuration of the UART used 517 in the H4 transport interface are not standardized, it has to be 518 provided by the main application to BTstack. In addition to the 519 initial UART baud rate, the main baud rate can be specified. The HCI 520 layer of BTstack will change the init baud rate to the main one 521 after the basic setup of the Bluetooth module. A baud rate change 522 has to be done in a coordinated way at both HCI and hardware level. 523 For example, on the CC256x, the HCI command to change the baud rate 524 is sent first, then it is necessary to wait for the confirmation event 525 from the Bluetooth module. Only now, can the UART baud rate changed. 526 527<!-- --> 528 529 hci_uart_config_t* config = &hci_uart_config; 530 531After these are ready, HCI is initialized like this: 532 533 hci_init(transport, config); 534 535 536In addition to these, most UART-based Bluetooth chipset require some 537special logic for correct initialization that is not covered by the 538Bluetooth specification. In particular, this covers: 539 540- setting the baudrate 541- setting the BD ADDR for devices without an internal persistent storage 542- upload of some firmware patches. 543 544This is provided by the various *btstack_chipset_t* implementation in the *chipset/* subfolders. 545As an example, the *bstack_chipset_cc256x_instance* function returns a pointer to a chipset struct 546suitable for the CC256x chipset. 547 548<!-- --> 549 550 btstack_chipset_t * chipset = btstack_chipset_cc256x_instance(); 551 hci_set_chipset(chipset); 552 553 554In some setups, the hardware setup provides explicit control of Bluetooth power and sleep modes. 555In this case, a *btstack_control_t* struct can be set with *hci_set_control*. 556 557Finally, the HCI implementation requires some form of persistent storage for link keys generated 558during either legacy pairing or the Secure Simple Pairing (SSP). This commonly requires platform 559specific code to access the MCU’s EEPROM of Flash storage. For the 560first steps, BTstack provides a (non) persistent store in memory. 561For more see [here](porting/#sec:persistentStoragePorting). 562 563<!-- --> 564 565 btstack_link_key_db_t * link_key_db = &btstack_link_key_db_memory_instance(); 566 btstack_set_link_key_db(link_key_db); 567 568 569The higher layers only rely on BTstack and are initialized by calling 570the respective *\*_init* function. These init functions register 571themselves with the underlying layer. In addition, the application can 572register packet handlers to get events and data as explained in the 573following section. 574 575 576## Services {#sec:servicesHowTo} 577 578One important construct of BTstack is *service*. A service represents a 579server side component that handles incoming connections. So far, BTstack 580provides L2CAP, BNEP, and RFCOMM services. An L2CAP service handles incoming 581connections for an L2CAP channel and is registered with its protocol 582service multiplexer ID (PSM). Similarly, an RFCOMM service handles 583incoming RFCOMM connections and is registered with the RFCOMM channel 584ID. Outgoing connections require no special registration, they are 585created by the application when needed. 586 587 588## Packet handlers configuration {#sec:packetHandlersHowTo} 589 590 591After the hardware and BTstack are set up, the run loop is entered. From 592now on everything is event driven. The application calls BTstack 593functions, which in turn may send commands to the Bluetooth module. The 594resulting events are delivered back to the application. Instead of 595writing a single callback handler for each possible event (as it is done 596in some other Bluetooth stacks), BTstack groups events logically and 597provides them over a single generic interface. Appendix 598[Events and Errors](generated/appendix/#sec:eventsAndErrorsAppendix) 599summarizes the parameters and event 600codes of L2CAP and RFCOMM events, as well as possible errors and the 601corresponding error codes. 602 603Here is summarized list of packet handlers that an application might 604use: 605 606- HCI event handler - allows to observer HCI, GAP, and general BTstack events. 607 608- L2CAP packet handler - handles LE Connection parameter requeset updates 609 610- L2CAP service packet handler - handles incoming L2CAP connections, 611 i.e., channels initiated by the remote. 612 613- L2CAP channel packet handler - handles outgoing L2CAP connections, 614 i.e., channels initiated internally. 615 616- RFCOMM service packet handler - handles incoming RFCOMM connections, 617 i.e., channels initiated by the remote. 618 619- RFCOMM channel packet handler - handles outgoing RFCOMM connections, 620 i.e., channels initiated internally. 621 622These handlers are registered with the functions listed in Table 623{@tbl:registeringFunction}. 624 625 626| Packet Handler | Registering Function | 627|-------------------------------|--------------------------------------------------------------------------| 628| HCI packet handler | hci_add_event_handler | 629| L2CAP packet handler | l2cap_register_packet_handler | 630| L2CAP service packet handler | l2cap_register_service | 631| L2CAP channel packet handler | l2cap_create_channel | 632| RFCOMM service packet handler | rfcomm_register_service and rfcomm_register_service_with_initial_credits | 633| RFCOMM channel packet handler | rfcomm_create_channel and rfcomm_create_channel_with_initial_credits | 634 635Table: Functions for registering packet handlers. {#tbl:registeringFunction} 636 637HCI, GAP, and general BTstack events are delivered to the packet handler 638specified by *hci_add_event_handler* function. In L2CAP, 639BTstack discriminates incoming and outgoing connections, i.e., event and 640data packets are delivered to different packet handlers. Outgoing 641connections are used access remote services, incoming connections are 642used to provide services. For incoming connections, the packet handler 643specified by *l2cap_register_service* is used. For outgoing 644connections, the handler provided by *l2cap_create_channel* 645is used. RFCOMM and BNEP are similar. 646 647The application can register a single shared packet handler for all 648protocols and services, or use separate packet handlers for each 649protocol layer and service. A shared packet handler is often used for 650stack initialization and connection management. 651 652Separate packet handlers can be used for each L2CAP service and outgoing 653connection. For example, to connect with a Bluetooth HID keyboard, your 654application could use three packet handlers: one to handle HCI events 655during discovery of a keyboard registered by 656*l2cap_register_packet_handler*; one that will be registered to an 657outgoing L2CAP channel to connect to keyboard and to receive keyboard 658data registered by *l2cap_create_channel*; after that 659keyboard can reconnect by itself. For this, you need to register L2CAP 660services for the HID Control and HID Interrupt PSMs using 661*l2cap_register_service*. In this call, you’ll also specify 662a packet handler to accept and receive keyboard data. 663 664All events names have the form MODULE_EVENT_NAME now, e.g., *gap_event_-advertising_report*. 665To facilitate working with 666events and get rid of manually calculating offsets into packets, BTstack provides 667auto-generated getters for all fields of all events in *src/hci_event.h*. All 668functions are defined as static inline, so they are not wasting any program memory 669if not used. If used, the memory footprint should be identical to accessing the 670field directly via offsets into the packet. For example, to access fields address_type 671and address from the *gap_event_advertising_report* event use following getters: 672 673<!-- --> 674 uint8_t address type = gap_event_advertising_report_get_address_type(event); 675 bd_addr_t address; 676 gap_event_advertising_report_get_address(event, address); 677 678 679## Bluetooth HCI Packet Logs {#sec:packetlogsHowTo} 680 681If things don't work as expected, having a look at the data exchanged 682between BTstack and the Bluetooth chipset often helps. 683 684For this, BTstack provides a configurable packet logging mechanism via hci_dump.h and the following implementations: 685 686 void hci_dump_init(const hci_dump_t * hci_dump_implementation); 687 688| Platform | File | Description | 689|----------|------------------------------|----------------------------------------------------| 690| POSIX | `hci_dump_posix_fs.c` | HCI log file for Apple PacketLogger and Wireshark | 691| POSIX | `hci_dump_posix_stdout.c` | Console output via printf | 692| Embedded | `hci_dump_embedded_stdout.c` | Console output via printf | 693| Embedded | `hci_dump_segger_stdout.c` | Console output via SEGGER RTT | 694| Embedded | `hci_dump_segger_binary.c` | HCI log file for Apple PacketLogger via SEGGER RTT | 695 696On POSIX systems, you can call *hci_dump_init* with a *hci_dump_posix_fs_get_instance()* and 697configure the path and output format with *hci_dump_posix_fs_open(const char * path, hci_dump_format_t format)* 698where format can be *HCI_DUMP_BLUEZ* or *HCI_DUMP_PACKETLOGGER*. 699The resulting file can be analyzed with Wireshark or the Apple's PacketLogger tool. 700 701On embedded systems without a file system, you either log to an UART console via printf or use SEGGER RTT. 702For printf output you pass *hci_dump_embedded_stdout_get_instance()* to *hci_dump_init()*. 703With RTT, you can choose between textual output similar to printf, and binary output. 704For textual output, you can provide the *hci_dump_segger_stdout_get_instance()*. 705 706It will log all HCI packets to the UART console via printf or RTT Terminal. 707If you capture the console output, incl. your own debug messages, you can use 708the create_packet_log.py tool in the tools folder to convert a text output into a 709PacketLogger file. 710 711For less overhead and higher logging speed, you can directly log in binary format by 712passing *hci_dump_segger_rtt_binary_get_instance()* and selecting the output format by 713calling *hci_dump_segger_rtt_binary_open(hci_dump_format_t format)* with the same format as above. 714 715 716In addition to the HCI packets, you can also enable BTstack's debug information by adding 717 718 #define ENABLE_LOG_INFO 719 #define ENABLE_LOG_ERROR 720 721to the btstack_config.h and recompiling your application. 722 723## Bluetooth Power Control {#sec:powerControl} 724 725In most BTstack examples, the device is set to be discoverable and connectable. In this mode, even when there's no active connection, the Bluetooth Controller will periodically activate its receiver in order to listen for inquiries or connecting requests from another device. 726The ability to be discoverable requires more energy than the ability to be connected. Being discoverable also announces the device to anybody in the area. Therefore, it is a good idea to pause listening for inquiries when not needed. Other devices that have your Bluetooth address can still connect to your device. 727 728To enable/disable discoverability, you can call: 729 730 /** 731 * @brief Allows to control if device is discoverable. OFF by default. 732 */ 733 void gap_discoverable_control(uint8_t enable); 734 735If you don't need to become connected from other devices for a longer period of time, you can also disable the listening to connection requests. 736 737To enable/disable connectability, you can call: 738 739 /** 740 * @brief Override page scan mode. Page scan mode enabled by l2cap when services are registered 741 * @note Might be used to reduce power consumption while Bluetooth module stays powered but no (new) 742 * connections are expected 743 */ 744 void gap_connectable_control(uint8_t enable); 745 746For Bluetooth Low Energy, the radio is periodically used to broadcast advertisements that are used for both discovery and connection establishment. 747 748To enable/disable advertisements, you can call: 749 750 /** 751 * @brief Enable/Disable Advertisements. OFF by default. 752 * @param enabled 753 */ 754 void gap_advertisements_enable(int enabled); 755 756If a Bluetooth Controller is neither discoverable nor connectable, it does not need to periodically turn on its radio and it only needs to respond to commands from the Host. In this case, the Bluetooth Controller is free to enter some kind of deep sleep where the power consumption is minimal. 757 758Finally, if that's not sufficient for your application, you could request BTstack to shutdown the Bluetooth Controller. For this, the "on" and "off" functions in the btstack_control_t struct must be implemented. To shutdown the Bluetooth Controller, you can call: 759 760 /** 761 * @brief Requests the change of BTstack power mode. 762 */ 763 int hci_power_control(HCI_POWER_MODE mode); 764 765with mode set to *HCI_POWER_OFF*. When needed later, Bluetooth can be started again via by calling it with mode *HCI_POWER_ON*, as seen in all examples. 766