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