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_LOG_BTSTACK_EVENTS | Log internal/custom BTstack events | 95| ENABLE_SCO_OVER_HCI | Enable SCO over HCI for chipsets (if supported) | 96| ENABLE_SCO_OVER_PCM | Enable SCO ofer PCM/I2S for chipsets (if supported) | 97| ENABLE_HFP_WIDE_BAND_SPEECH | Enable support for mSBC codec used in HFP profile for Wide-Band Speech | 98| ENABLE_HFP_AT_MESSAGES | Enable `HFP_SUBEVENT_AT_MESSAGE_SENT` and `HFP_SUBEVENT_AT_MESSAGE_RECEIVED` events | 99| ENABLE_LE_PERIPHERAL | Enable support for LE Peripheral Role in HCI and Security Manager | 100| ENABLE_LE_CENTRAL | Enable support for LE Central Role in HCI and Security Manager | 101| ENABLE_LE_SECURE_CONNECTIONS | Enable LE Secure Connections | 102| ENABLE_LE_SECURE_CONNECTIONS_DEBUG_KEY | Enable support for LE Secure Connection debug keys for testing | 103| ENABLE_LE_PROACTIVE_AUTHENTICATION | Enable automatic encryption for bonded devices on re-connect | 104| ENABLE_GATT_CLIENT_PAIRING | Enable GATT Client to start pairing and retry operation on security error | 105| ENABLE_MICRO_ECC_FOR_LE_SECURE_CONNECTIONS | Use [micro-ecc library](https://github.com/kmackay/micro-ecc) for ECC operations | 106| ENABLE_LE_DATA_LENGTH_EXTENSION | Enable LE Data Length Extension support | 107| ENABLE_LE_ENHANCED_CONNECTION_COMPLETE_EVENT | Enable LE Enhanced Connection Complete Event v1 & v2 | 108| ENABLE_LE_EXTENDED_ADVERTISING | Enable extended advertising and scanning | 109| ENABLE_LE_PERIODIC_ADVERTISING | Enable periodic advertising and scanning | 110| ENABLE_LE_SIGNED_WRITE | Enable LE Signed Writes in ATT/GATT | 111| ENABLE_LE_PRIVACY_ADDRESS_RESOLUTION | Enable address resolution for resolvable private addresses in Controller | 112| ENABLE_CROSS_TRANSPORT_KEY_DERIVATION | Enable Cross-Transport Key Derivation (CTKD) for Secure Connections | 113| ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE | Enable Enhanced Retransmission Mode for L2CAP Channels. Mandatory for AVRCP Browsing | 114| ENABLE_L2CAP_LE_CREDIT_BASED_FLOW_CONTROL_MODE | Enable LE credit-based flow-control mode for L2CAP channels | 115| ENABLE_L2CAP_ENHANCED_CREDIT_BASED_FLOW_CONTROL_MODE | Enable Enhanced credit-based flow-control mode for L2CAP Channels | 116| ENABLE_HCI_CONTROLLER_TO_HOST_FLOW_CONTROL | Enable HCI Controller to Host Flow Control, see below | 117| ENABLE_HCI_SERIALIZED_CONTROLLER_OPERATIONS | Serialize Inquiry, Remote Name Request, and Create Connection operations | 118| ENABLE_ATT_DELAYED_RESPONSE | Enable support for delayed ATT operations, see [GATT Server](profiles/#sec:GATTServerProfile) | 119| ENABLE_BCM_PCM_WBS | Enable support for Wide-Band Speech codec in BCM controller, requires ENABLE_SCO_OVER_PCM | 120| ENABLE_CC256X_ASSISTED_HFP | Enable support for Assisted HFP mode in CC256x Controller, requires ENABLE_SCO_OVER_PCM | 121| ENABLE_RTK_PCM_WBS | Enable support for Wide-Band Speech codec in Realtek controller, requires ENABLE_SCO_OVER_PCM | 122| ENABLE_CC256X_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND | Enable workaround for bug in CC256x Flow Control during baud rate change, see chipset docs. | 123| ENABLE_CYPRESS_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND | Enable workaround for bug in CYW2070x Flow Control during baud rate change, similar to CC256x. | 124| ENABLE_LE_LIMIT_ACL_FRAGMENT_BY_MAX_OCTETS | Force HCI to fragment ACL-LE packets to fit into over-the-air packet | 125| 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 | 126| ENABLE_TLV_FLASH_WRITE_ONCE | Enable storing of emtpy tag instead of overwriting existing tag - required when flash value cannot be overwritten at all | 127| ENABLE_CONTROLLER_WARM_BOOT | Enable stack startup without power cycle (if supported/possible) | 128| ENABLE_SEGGER_RTT | Use SEGGER RTT for console output and packet log, see [additional options](#sec:rttConfiguration) | 129| ENABLE_EXPLICIT_CONNECTABLE_MODE_CONTROL | Disable calls to control Connectable Mode by L2CAP | 130| ENABLE_EXPLICIT_IO_CAPABILITIES_REPLY | Let application trigger sending IO Capabilities (Negative) Reply | 131| ENABLE_EXPLICIT_LINK_KEY_REPLY | Let application trigger sending Link Key (Negative) Response, allows for asynchronous link key lookup | 132| ENABLE_EXPLICIT_BR_EDR_SECURITY_MANAGER | Report BR/EDR Security Manager support in L2CAP Information Response | 133| ENABLE_EXPLICIT_DEDICATED_BONDING_DISCONNECT | Keep connection after dedicated bonding is complete | 134| ENABLE_CLASSIC_OOB_PAIRING | Enable support for classic Out-of-Band (OOB) pairing | 135| ENABLE_A2DP_EXPLICIT_CONFIG | Let application configure stream endpoint (skip auto-config of SBC endpoint) | 136| ENABLE_AVDTP_ACCEPTOR_EXPLICIT_START_STREAM_CONFIRMATION | allow accept or reject of stream start on A2DP_SUBEVENT_START_STREAM_REQUESTED | 137| ENABLE_LE_WHITELIST_TOUCH_AFTER_RESOLVING_LIST_UPDATE | Enable Workaround for Controller bug | 138| 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 | 139| ENABLE_CONTROLLER_DUMP_PACKETS | Dump number of packets in Controller per type for debugging | 140| ENABLE_HCI_COMMAND_STATUS_DISCARDED_FOR_FAILED_CONNECTIONS WORKAROUND | Track connection handle for HCI Commands and assume command has failed if disonnect event for connection is received | 141| ENABLE_MUTUAL_AUTHENTICATION_FOR_LEGACY_SECURE_CONNECTIONS | Re-authentication after connection was encrypted to avoid BIAS Attack. Not needed for min encryption key size of 16 | 142 143Notes: 144 145- 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. 146 147### HCI Controller to Host Flow Control 148In 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. 149 150Host buffer configuration for HCI Controller to Host Flow Control: 151 152| \#define | Description | 153|-------------------------|----------------------------------| 154| HCI_HOST_ACL_PACKET_NUM | Max number of ACL packets | 155| HCI_HOST_ACL_PACKET_LEN | Max size of HCI Host ACL packets | 156| HCI_HOST_SCO_PACKET_NUM | Max number of ACL packets | 157| HCI_HOST_SCO_PACKET_LEN | Max size of HCI Host SCO packets | 158 159### Memory configuration directives {#sec:memoryConfigurationHowTo} 160 161The structs for services, active connections and remote devices can be 162allocated in two different manners: 163 164- statically from an individual memory pool, whose maximal number of 165 elements is defined in the btstack_config.h file. To initialize the static 166 pools, you need to call at runtime *btstack_memory_init* function. An example 167 of memory configuration for a single SPP service with a minimal 168 L2CAP MTU is shown in Listing {@lst:memoryConfigurationSPP}. 169 170- dynamically using the *malloc/free* functions, if HAVE_MALLOC is 171 defined in btstack_config.h file. 172 173For 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. 174 175<!-- a name "lst:memoryConfiguration"></a--> 176<!-- --> 177 178| \#define | Description | 179|-------------------------------------------|----------------------------------------------------------------------------| 180| HCI_ACL_PAYLOAD_SIZE | Max size of HCI ACL payloads | 181| HCI_ACL_CHUNK_SIZE_ALIGNMENT | Alignment of ACL chunk size, can be used to align HCI transport writes | 182| HCI_INCOMING_PRE_BUFFER_SIZE | Number of bytes reserved before actual data for incoming HCI packets | 183| MAX_NR_BNEP_CHANNELS | Max number of BNEP channels | 184| MAX_NR_BNEP_SERVICES | Max number of BNEP services | 185| MAX_NR_GATT_CLIENTS | Max number of GATT clients | 186| MAX_NR_HCI_CONNECTIONS | Max number of HCI connections | 187| MAX_NR_HFP_CONNECTIONS | Max number of HFP connections | 188| MAX_NR_L2CAP_CHANNELS | Max number of L2CAP connections | 189| MAX_NR_L2CAP_SERVICES | Max number of L2CAP services | 190| MAX_NR_RFCOMM_CHANNELS | Max number of RFOMMM connections | 191| MAX_NR_RFCOMM_MULTIPLEXERS | Max number of RFCOMM multiplexers, with one multiplexer per HCI connection | 192| MAX_NR_RFCOMM_SERVICES | Max number of RFCOMM services | 193| MAX_NR_SERVICE_RECORD_ITEMS | Max number of SDP service records | 194| MAX_NR_SM_LOOKUP_ENTRIES | Max number of items in Security Manager lookup queue | 195| MAX_NR_WHITELIST_ENTRIES | Max number of items in GAP LE Whitelist to connect to | 196 197The memory is set up by calling *btstack_memory_init* function: 198 199 btstack_memory_init(); 200 201<!-- a name "lst:memoryConfigurationSPP"></a--> 202<!-- --> 203 204Here's the memory configuration for a basic SPP server. 205 206 #define HCI_ACL_PAYLOAD_SIZE 52 207 #define MAX_NR_HCI_CONNECTIONS 1 208 #define MAX_NR_L2CAP_SERVICES 2 209 #define MAX_NR_L2CAP_CHANNELS 2 210 #define MAX_NR_RFCOMM_MULTIPLEXERS 1 211 #define MAX_NR_RFCOMM_SERVICES 1 212 #define MAX_NR_RFCOMM_CHANNELS 1 213 #define NVM_NUM_LINK_KEYS 3 214 215Listing: Memory configuration for a basic SPP server. {#lst:memoryConfigurationSPP} 216 217In 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. 218 219<!-- --> 220 221### Non-volatile memory (NVM) directives {#sec:nvmConfiguration} 222 223If 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: 224 225<!-- a name "lst:nvmDefines"></a--> 226<!-- --> 227 228| \#define | Description | 229|---------------------------|----------------------------------------------------------------------------------------------| 230| NVM_NUM_LINK_KEYS | Max number of Classic Link Keys that can be stored | 231| NVM_NUM_DEVICE_DB_ENTRIES | Max number of LE Device DB entries that can be stored | 232| NVN_NUM_GATT_SERVER_CCC | Max number of 'Client Characteristic Configuration' values that can be stored by GATT Server | 233 234### HCI Dump Stdout directives {#sec:hciDumpStdout} 235 236Allow to truncate HCI ACL and SCO packets to reduce console output for debugging audio applications. 237 238| \#define | Description | 239|------------------------------|-------------------------------------------| 240| HCI_DUMP_STDOUT_MAX_SIZE_ACL | Max size of ACL packets to log via stdout | 241| HCI_DUMP_STDOUT_MAX_SIZE_SCO | Max size of SCO packets to log via stdout | 242| HCI_DUMP_STDOUT_MAX_SIZE_ISO | Max size of ISO packets to log via stdout | 243 244### SEGGER Real Time Transfer (RTT) directives {#sec:rttConfiguration} 245 246[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. 247 248When 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: 249 250| \#define | Default | Description | 251|----------------------------------|-------------------------------|-------------------------------------------------------------------------------------------------------------------| 252| 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 | 253| SEGGER_RTT_PACKETLOG_CHANNEL | 1 | Channel to use for packet log. Channel 0 is used for terminal | 254| SEGGER_RTT_PACKETLOG_BUFFER_SIZE | 1024 | Size of outgoing ring buffer. Increase if you cannot block but get 'message skipped' warnings. | 255 256## Run-time configuration 257 258To allow code-reuse with different platforms 259as well as with new ports, the low-level initialization of BTstack and 260the hardware configuration has been extracted to the various 261*platforms/PLATFORM/main.c* files. The examples only contain the 262platform-independent Bluetooth logic. But let’s have a look at the 263common init code. 264 265Listing [below](#lst:btstackInit) shows a minimal platform setup for an 266embedded system with a Bluetooth chipset connected via UART. 267 268~~~~ {#lst:btstackInit .c caption="{Minimal platform setup for an embedded system}"} 269 270 int main(){ 271 // ... hardware init: watchdoch, IOs, timers, etc... 272 273 // setup BTstack memory pools 274 btstack_memory_init(); 275 276 // select embedded run loop 277 btstack_run_loop_init(btstack_run_loop_embedded_get_instance()); 278 279 // enable logging 280 hci_dump_init(hci_dump_embedded_stdout_get_instance()); 281 282 283 // init HCI 284 hci_transport_t * transport = hci_transport_h4_instance(); 285 hci_init(transport, NULL); 286 287 // setup example 288 btstack_main(argc, argv); 289 290 // go 291 btstack_run_loop_execute(); 292 } 293 294~~~~ 295 296First, BTstack’s memory pools are set up. Then, the standard run loop 297implementation for embedded systems is selected. 298 299The call to *hci_dump_init* configures BTstack to output all Bluetooth 300packets and its own debug and error message using printf with BTstack's 301millisecond tiomestamps.s as tim. 302The Python 303script *tools/create_packet_log.py* can be used to convert the console 304output into a Bluetooth PacketLogger format that can be opened by the OS 305X PacketLogger tool as well as by Wireshark for further inspection. When 306asking for help, please always include a log created with HCI dump. 307 308The *hci_init* function sets up HCI to use the HCI H4 Transport 309implementation. It doesn’t provide a special transport configuration nor 310a special implementation for a particular Bluetooth chipset. It makes 311use of the *remote_device_db_memory* implementation that allows for 312re-connects without a new pairing but doesn’t persist the bonding 313information. 314 315Finally, it calls *btstack_main()* of the actual example before 316executing the run loop. 317 318 319## Source tree structure {#sec:sourceTreeHowTo} 320 321The source tree has been organized to easily setup new projects. 322 323| Path | Description | 324|----------|------------------------------------------------------| 325| chipset | Support for individual Bluetooth Controller chipsets | 326| doc | Sources for BTstack documentation | 327| example | Example applications available for all ports | 328| platform | Support for special OSs and/or MCU architectures | 329| port | Complete port for a MCU + Chipset combinations | 330| src | Bluetooth stack implementation | 331| test | Unit and PTS tests | 332| tool | Helper tools for BTstack | 333 334The core of BTstack, including all protocol and profiles, is in *src/*. 335 336Support 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. 337 338To accommodate a particular Bluetooth chipset, the *chipset/* subfolders provide various btstack_chipset_* implementations. 339Please have a look at the existing ports in *port/*. 340 341## Run loop configuration {#sec:runLoopHowTo} 342 343To initialize BTstack you need to [initialize the memory](#sec:memoryConfigurationHowTo) 344and [the run loop](#sec:runLoopHowTo) respectively, then setup HCI and all needed higher 345level protocols. 346 347BTstack uses the concept of a run loop to handle incoming data and to schedule work. 348The run loop handles events from two different types of sources: data 349sources and timers. Data sources represent communication interfaces like 350an UART or an USB driver. Timers are used by BTstack to implement 351various Bluetooth-related timeouts. They can also be used to handle 352periodic events. In addition, most implementations also allow to trigger a poll 353of the data sources from interrupt context, or, execute a function from a different 354thread. 355 356Data sources and timers are represented by the *btstack_data_source_t* and 357*btstack_timer_source_t* structs respectively. Each of these structs contain 358at least a linked list node and a pointer to a callback function. All active timers 359and data sources are kept in link lists. While the list of data sources 360is unsorted, the timers are sorted by expiration timeout for efficient 361processing. Data sources need to be configured upon what event they are called back. 362They can be configured to be polled (*DATA_SOURCE_CALLBACK_POLL*), on read ready (*DATA_SOURCE_CALLBACK_READ*), 363or on write ready (*DATA_SOURCE_CALLBACK_WRITE*). 364 365Timers are single shot: a timer will be removed from the timer list 366before its event handler callback is executed. If you need a periodic 367timer, you can re-register the same timer source in the callback 368function, as shown in Listing [PeriodicTimerHandler]. Note that BTstack 369expects to get called periodically to keep its time, see Section 370[on time abstraction](#sec:timeAbstractionPorting) for more on the 371tick hardware abstraction. 372 373BTstack provides different run loop implementations that implement the *btstack_run_loop_t* interface: 374 375- CoreFoundation: implementation for iOS and OS X applications 376- Embedded: the main implementation for embedded systems, especially without an RTOS. 377- FreeRTOS: implementation to run BTstack on a dedicated FreeRTOS thread 378- POSIX: implementation for POSIX systems based on the select() call. 379- Qt: implementation for the Qt applications 380- WICED: implementation for the Broadcom WICED SDK RTOS abstraction that wraps FreeRTOS or ThreadX. 381- Windows: implementation for Windows based on Event objects and WaitForMultipleObjects() call. 382 383Depending on the platform, data sources are either polled (embedded, FreeRTOS), or the platform provides a way 384to wait for a data source to become ready for read or write (CoreFoundation, POSIX, Qt, Windows), or, 385are not used as the HCI transport driver and the run loop is implemented in a different way (WICED). 386In any case, the callbacks must be explicitly enabled with the *btstack_run_loop_enable_data_source_callbacks(..)* function. 387 388In your code, you'll have to configure the run loop before you start it 389as shown in Listing [listing:btstackInit]. The application can register 390data sources as well as timers, e.g., for periodical sampling of sensors, or 391for communication over the UART. 392 393The run loop is set up by calling *btstack_run_loop_init* function and providing 394an instance of the actual run loop. E.g. for the embedded platform, it is: 395 396<!-- --> 397 398 btstack_run_loop_init(btstack_run_loop_embedded_get_instance()); 399 400If the run loop allows to trigger polling of data sources from interrupt context, 401*btstack_run_loop_poll_data_sources_from_irq*. 402 403On multi-threaded environments, e.g., FreeRTOS, POSIX, WINDOWS, 404*btstack_run_loop_execute_code_on_main_thread* can be used to schedule a callback on the main loop. 405 406The complete Run loop API is provided [here](appendix/apis/#sec:runLoopAPIAppendix). 407 408 409### Run Loop Embedded 410 411In the embedded run loop implementation, data sources are constantly polled and 412the system is put to sleep if no IRQ happens during the poll of all data sources. 413 414The complete run loop cycle looks like this: first, the callback 415function of all registered data sources are called in a round robin way. 416Then, the callback functions of timers that are ready are executed. 417Finally, it will be checked if another run loop iteration has been 418requested by an interrupt handler. If not, the run loop will put the MCU 419into sleep mode. 420 421Incoming data over the UART, USB, or timer ticks will generate an 422interrupt and wake up the microcontroller. In order to avoid the 423situation where a data source becomes ready just before the run loop 424enters sleep mode, an interrupt-driven data source has to call the 425*btstack_run_loop_poll_data_sources_from_irq* function. The call to 426*btstack_run_loop_poll_data_sources_from_irq* sets an 427internal flag that is checked in the critical section just before 428entering sleep mode causing another run loop cycle. 429 430To enable the use of timers, make sure that you defined HAVE_EMBEDDED_TICK or HAVE_EMBEDDED_TIME_MS in the 431config file. 432 433While there is no threading, *btstack_run_loop_poll_data_sources_from_irq* allows to reduce stack size by 434scheduling a continuation. 435 436### Run Loop FreeRTOS 437 438The FreeRTOS run loop is used on a dedicated FreeRTOS thread and it uses a FreeRTOS queue to schedule callbacks on the run loop. 439In each iteration: 440 441- all data sources are polled 442- all scheduled callbacks are executed 443- all expired timers are called 444- finally, it gets the next timeout. It then waits for a 'trigger' or the next timeout, if set. 445 446It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 447 448 449### Run Loop POSIX 450 451The data sources are standard File Descriptors. In the run loop execute implementation, 452select() call is used to wait for file descriptors to become ready to read or write, 453while waiting for the next timeout. 454 455To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 456 457It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 458 459 460### Run loop CoreFoundation (OS X/iOS) 461 462This run loop directly maps BTstack's data source and timer source with CoreFoundation objects. 463It supports ready to read and write similar to the POSIX implementation. The call to 464*btstack_run_loop_execute()* then just calls *CFRunLoopRun()*. 465 466To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 467 468It currently only supports *btstack_run_loop_execute_code_on_main_thread*. 469 470 471### Run Lop Qt 472 473This run loop directly maps BTstack's data source and timer source with Qt Core objects. 474It supports ready to read and write similar to the POSIX implementation. 475 476To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 477 478It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 479 480 481### Run loop Windows 482 483The data sources are Event objects. In the run loop implementation WaitForMultipleObjects() call 484is all is used to wait for the Event object to become ready while waiting for the next timeout. 485 486It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 487 488 489### Run loop WICED 490 491WICED SDK API does not provide asynchronous read and write to the UART and no direct way to wait for 492one or more peripherals to become ready. Therefore, BTstack does not provide direct support for data sources. 493Instead, the run loop provides a message queue that allows to schedule functions calls on its thread via 494*btstack_run_loop_wiced_execute_code_on_main_thread()*. 495 496The HCI transport H4 implementation then uses two lightweight threads to do the 497blocking read and write operations. When a read or write is complete on 498the helper threads, a callback to BTstack is scheduled. 499 500It currently only supports *btstack_run_loop_execute_code_on_main_thread*. 501 502 503## HCI Transport configuration 504 505The HCI initialization has to adapt BTstack to the used platform. The first 506call is to *hci_init()* and requires information about the HCI Transport to use. 507The arguments are: 508 509- *HCI Transport implementation*: On embedded systems, a Bluetooth 510 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. 511 These are accessed by linking the appropriate file, e.g., 512 [platform/embedded/hci_transport_h4_embedded.c]() 513 and then getting a pointer to HCI Transport implementation. 514 For more information on adapting HCI Transport to different 515 environments, see [here](porting/#sec:hciTransportPorting). 516 517<!-- --> 518 519 hci_transport_t * transport = hci_transport_h4_instance(); 520 521- *HCI Transport configuration*: As the configuration of the UART used 522 in the H4 transport interface are not standardized, it has to be 523 provided by the main application to BTstack. In addition to the 524 initial UART baud rate, the main baud rate can be specified. The HCI 525 layer of BTstack will change the init baud rate to the main one 526 after the basic setup of the Bluetooth module. A baud rate change 527 has to be done in a coordinated way at both HCI and hardware level. 528 For example, on the CC256x, the HCI command to change the baud rate 529 is sent first, then it is necessary to wait for the confirmation event 530 from the Bluetooth module. Only now, can the UART baud rate changed. 531 532<!-- --> 533 534 hci_uart_config_t* config = &hci_uart_config; 535 536After these are ready, HCI is initialized like this: 537 538 hci_init(transport, config); 539 540 541In addition to these, most UART-based Bluetooth chipset require some 542special logic for correct initialization that is not covered by the 543Bluetooth specification. In particular, this covers: 544 545- setting the baudrate 546- setting the BD ADDR for devices without an internal persistent storage 547- upload of some firmware patches. 548 549This is provided by the various *btstack_chipset_t* implementation in the *chipset/* subfolders. 550As an example, the *bstack_chipset_cc256x_instance* function returns a pointer to a chipset struct 551suitable for the CC256x chipset. 552 553<!-- --> 554 555 btstack_chipset_t * chipset = btstack_chipset_cc256x_instance(); 556 hci_set_chipset(chipset); 557 558 559In some setups, the hardware setup provides explicit control of Bluetooth power and sleep modes. 560In this case, a *btstack_control_t* struct can be set with *hci_set_control*. 561 562Finally, the HCI implementation requires some form of persistent storage for link keys generated 563during either legacy pairing or the Secure Simple Pairing (SSP). This commonly requires platform 564specific code to access the MCU’s EEPROM of Flash storage. For the 565first steps, BTstack provides a (non) persistent store in memory. 566For more see [here](porting/#sec:persistentStoragePorting). 567 568<!-- --> 569 570 btstack_link_key_db_t * link_key_db = &btstack_link_key_db_memory_instance(); 571 btstack_set_link_key_db(link_key_db); 572 573 574The higher layers only rely on BTstack and are initialized by calling 575the respective *\*_init* function. These init functions register 576themselves with the underlying layer. In addition, the application can 577register packet handlers to get events and data as explained in the 578following section. 579 580 581## Services {#sec:servicesHowTo} 582 583One important construct of BTstack is *service*. A service represents a 584server side component that handles incoming connections. So far, BTstack 585provides L2CAP, BNEP, and RFCOMM services. An L2CAP service handles incoming 586connections for an L2CAP channel and is registered with its protocol 587service multiplexer ID (PSM). Similarly, an RFCOMM service handles 588incoming RFCOMM connections and is registered with the RFCOMM channel 589ID. Outgoing connections require no special registration, they are 590created by the application when needed. 591 592 593## Packet handlers configuration {#sec:packetHandlersHowTo} 594 595 596After the hardware and BTstack are set up, the run loop is entered. From 597now on everything is event driven. The application calls BTstack 598functions, which in turn may send commands to the Bluetooth module. The 599resulting events are delivered back to the application. Instead of 600writing a single callback handler for each possible event (as it is done 601in some other Bluetooth stacks), BTstack groups events logically and 602provides them over a single generic interface. Appendix 603[Events and Errors](generated/appendix/#sec:eventsAndErrorsAppendix) 604summarizes the parameters and event 605codes of L2CAP and RFCOMM events, as well as possible errors and the 606corresponding error codes. 607 608Here is summarized list of packet handlers that an application might 609use: 610 611- HCI event handler - allows to observer HCI, GAP, and general BTstack events. 612 613- L2CAP packet handler - handles LE Connection parameter requeset updates 614 615- L2CAP service packet handler - handles incoming L2CAP connections, 616 i.e., channels initiated by the remote. 617 618- L2CAP channel packet handler - handles outgoing L2CAP connections, 619 i.e., channels initiated internally. 620 621- RFCOMM service packet handler - handles incoming RFCOMM connections, 622 i.e., channels initiated by the remote. 623 624- RFCOMM channel packet handler - handles outgoing RFCOMM connections, 625 i.e., channels initiated internally. 626 627These handlers are registered with the functions listed in Table 628{@tbl:registeringFunction}. 629 630 631| Packet Handler | Registering Function | 632|-------------------------------|--------------------------------------------------------------------------| 633| HCI packet handler | hci_add_event_handler | 634| L2CAP packet handler | l2cap_register_packet_handler | 635| L2CAP service packet handler | l2cap_register_service | 636| L2CAP channel packet handler | l2cap_create_channel | 637| RFCOMM service packet handler | rfcomm_register_service and rfcomm_register_service_with_initial_credits | 638| RFCOMM channel packet handler | rfcomm_create_channel and rfcomm_create_channel_with_initial_credits | 639 640Table: Functions for registering packet handlers. {#tbl:registeringFunction} 641 642HCI, GAP, and general BTstack events are delivered to the packet handler 643specified by *hci_add_event_handler* function. In L2CAP, 644BTstack discriminates incoming and outgoing connections, i.e., event and 645data packets are delivered to different packet handlers. Outgoing 646connections are used access remote services, incoming connections are 647used to provide services. For incoming connections, the packet handler 648specified by *l2cap_register_service* is used. For outgoing 649connections, the handler provided by *l2cap_create_channel* 650is used. RFCOMM and BNEP are similar. 651 652The application can register a single shared packet handler for all 653protocols and services, or use separate packet handlers for each 654protocol layer and service. A shared packet handler is often used for 655stack initialization and connection management. 656 657Separate packet handlers can be used for each L2CAP service and outgoing 658connection. For example, to connect with a Bluetooth HID keyboard, your 659application could use three packet handlers: one to handle HCI events 660during discovery of a keyboard registered by 661*l2cap_register_packet_handler*; one that will be registered to an 662outgoing L2CAP channel to connect to keyboard and to receive keyboard 663data registered by *l2cap_create_channel*; after that 664keyboard can reconnect by itself. For this, you need to register L2CAP 665services for the HID Control and HID Interrupt PSMs using 666*l2cap_register_service*. In this call, you’ll also specify 667a packet handler to accept and receive keyboard data. 668 669All events names have the form MODULE_EVENT_NAME now, e.g., *gap_event_-advertising_report*. 670To facilitate working with 671events and get rid of manually calculating offsets into packets, BTstack provides 672auto-generated getters for all fields of all events in *src/hci_event.h*. All 673functions are defined as static inline, so they are not wasting any program memory 674if not used. If used, the memory footprint should be identical to accessing the 675field directly via offsets into the packet. For example, to access fields address_type 676and address from the *gap_event_advertising_report* event use following getters: 677 678<!-- --> 679 uint8_t address type = gap_event_advertising_report_get_address_type(event); 680 bd_addr_t address; 681 gap_event_advertising_report_get_address(event, address); 682 683 684## Bluetooth HCI Packet Logs {#sec:packetlogsHowTo} 685 686If things don't work as expected, having a look at the data exchanged 687between BTstack and the Bluetooth chipset often helps. 688 689For this, BTstack provides a configurable packet logging mechanism via hci_dump.h and the following implementations: 690 691 void hci_dump_init(const hci_dump_t * hci_dump_implementation); 692 693| Platform | File | Description | 694|----------|------------------------------|----------------------------------------------------| 695| POSIX | `hci_dump_posix_fs.c` | HCI log file for Apple PacketLogger and Wireshark | 696| POSIX | `hci_dump_posix_stdout.c` | Console output via printf | 697| Embedded | `hci_dump_embedded_stdout.c` | Console output via printf | 698| Embedded | `hci_dump_segger_stdout.c` | Console output via SEGGER RTT | 699| Embedded | `hci_dump_segger_binary.c` | HCI log file for Apple PacketLogger via SEGGER RTT | 700 701On POSIX systems, you can call *hci_dump_init* with a *hci_dump_posix_fs_get_instance()* and 702configure the path and output format with *hci_dump_posix_fs_open(const char * path, hci_dump_format_t format)* 703where format can be *HCI_DUMP_BLUEZ* or *HCI_DUMP_PACKETLOGGER*. 704The resulting file can be analyzed with Wireshark or the Apple's PacketLogger tool. 705 706On embedded systems without a file system, you either log to an UART console via printf or use SEGGER RTT. 707For printf output you pass *hci_dump_embedded_stdout_get_instance()* to *hci_dump_init()*. 708With RTT, you can choose between textual output similar to printf, and binary output. 709For textual output, you can provide the *hci_dump_segger_stdout_get_instance()*. 710 711It will log all HCI packets to the UART console via printf or RTT Terminal. 712If you capture the console output, incl. your own debug messages, you can use 713the create_packet_log.py tool in the tools folder to convert a text output into a 714PacketLogger file. 715 716For less overhead and higher logging speed, you can directly log in binary format by 717passing *hci_dump_segger_rtt_binary_get_instance()* and selecting the output format by 718calling *hci_dump_segger_rtt_binary_open(hci_dump_format_t format)* with the same format as above. 719 720 721In addition to the HCI packets, you can also enable BTstack's debug information by adding 722 723 #define ENABLE_LOG_INFO 724 #define ENABLE_LOG_ERROR 725 726to the btstack_config.h and recompiling your application. 727 728## Bluetooth Power Control {#sec:powerControl} 729 730In 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. 731The 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. 732 733To enable/disable discoverability, you can call: 734 735 /** 736 * @brief Allows to control if device is discoverable. OFF by default. 737 */ 738 void gap_discoverable_control(uint8_t enable); 739 740If 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. 741 742To enable/disable connectability, you can call: 743 744 /** 745 * @brief Override page scan mode. Page scan mode enabled by l2cap when services are registered 746 * @note Might be used to reduce power consumption while Bluetooth module stays powered but no (new) 747 * connections are expected 748 */ 749 void gap_connectable_control(uint8_t enable); 750 751For Bluetooth Low Energy, the radio is periodically used to broadcast advertisements that are used for both discovery and connection establishment. 752 753To enable/disable advertisements, you can call: 754 755 /** 756 * @brief Enable/Disable Advertisements. OFF by default. 757 * @param enabled 758 */ 759 void gap_advertisements_enable(int enabled); 760 761If 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. 762 763Finally, 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: 764 765 /** 766 * @brief Requests the change of BTstack power mode. 767 */ 768 int hci_power_control(HCI_POWER_MODE mode); 769 770with 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. 771