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