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