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