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_MALLOC | Use dynamic memory | 43| HAVE_AES128 | Use platform AES128 engine - not needed usually | 44| HAVE_BTSTACK_STDIN | STDIN is available for CLI interface | 45| HAVE_MBEDTLS_ECC_P256 | mbedTLS provides NIST P-256 operations e.g. for LE Secure Connections | 46 47Embedded platform properties: 48 49| \#define | Description | 50|---------------------------------|--------------------------------------| 51| HAVE_EMBEDDED_TIME_MS | System provides time in milliseconds | 52| HAVE_EMBEDDED_TICK | System provides tick interrupt | 53| HAVE_HAL_AUDIO | Audio HAL is available | 54| HAVE_HAL_AUDIO_SINK_STEREO_ONLY | Duplicate samples for mono playback | 55 56FreeRTOS platform properties: 57 58| \#define | Description | 59|------------------------------|------------------------------------------------------------------| 60| HAVE_FREERTOS_INCLUDE_PREFIX | FreeRTOS headers are in 'freertos' folder (e.g. ESP32's esp-idf) | 61 62POSIX platform properties: 63 64| \#define | Description | 65|--------------------|--------------------------------------| 66| HAVE_POSIX_FILE_IO | POSIX File i/o used for hci dump | 67| HAVE_POSIX_TIME | System provides time function | 68| LINK_KEY_PATH | Path to stored link keys | 69| LE_DEVICE_DB_PATH | Path to stored LE device information | 70 71<!-- a name "lst:btstackFeatureConfiguration"></a--> 72<!-- --> 73 74### ENABLE_* directives {#sec:enableDirectives} 75BTstack properties: 76 77| \#define | Description | 78|-----------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------| 79| ENABLE_CLASSIC | Enable Classic related code in HCI and L2CAP | 80| ENABLE_BLE | Enable BLE related code in HCI and L2CAP | 81| ENABLE_EHCILL | Enable eHCILL low power mode on TI CC256x/WL18xx chipsets | 82| ENABLE_H5 | Enable support for SLIP mode in `btstack_uart.h` drivers for HCI H5 ('Three-Wire Mode') | 83| ENABLE_LOG_DEBUG | Enable log_debug messages | 84| ENABLE_LOG_ERROR | Enable log_error messages | 85| ENABLE_LOG_INFO | Enable log_info messages | 86| ENABLE_SCO_OVER_HCI | Enable SCO over HCI for chipsets (if supported) | 87| ENABLE_SCO_OVER_PCM | Enable SCO ofer PCM/I2S for chipsets (if supported) | 88| ENABLE_HFP_WIDE_BAND_SPEECH | Enable support for mSBC codec used in HFP profile for Wide-Band Speech | 89| ENABLE_HFP_AT_MESSAGES | Enable `HFP_SUBEVENT_AT_MESSAGE_SENT` and `HFP_SUBEVENT_AT_MESSAGE_RECEIVED` events | 90| ENABLE_LE_PERIPHERAL | Enable support for LE Peripheral Role in HCI and Security Manager | 91| ENBALE_LE_CENTRAL | Enable support for LE Central Role in HCI and Security Manager | 92| ENABLE_LE_SECURE_CONNECTIONS | Enable LE Secure Connections | 93| ENABLE_LE_PROACTIVE_AUTHENTICATION | Enable automatic encryption for bonded devices on re-connect | 94| ENABLE_GATT_CLIENT_PAIRING | Enable GATT Client to start pairing and retry operation on security error | 95| ENABLE_MICRO_ECC_FOR_LE_SECURE_CONNECTIONS | Use [micro-ecc library](https://github.com/kmackay/micro-ecc) for ECC operations | 96| ENABLE_LE_DATA_LENGTH_EXTENSION | Enable LE Data Length Extension support | 97| ENABLE_LE_EXTENDED_ADVERTISING | Enable extended advertising and scanning | 98| ENABLE_LE_PERIODIC_ADVERTISING | Enable periodic advertising and scanning | 99| ENABLE_LE_SIGNED_WRITE | Enable LE Signed Writes in ATT/GATT | 100| ENABLE_LE_PRIVACY_ADDRESS_RESOLUTION | Enable address resolution for resolvable private addresses in Controller | 101| ENABLE_CROSS_TRANSPORT_KEY_DERIVATION | Enable Cross-Transport Key Derivation (CTKD) for Secure Connections | 102| ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE | Enable Enhanced Retransmission Mode for L2CAP Channels. Mandatory for AVRCP Browsing | 103| ENABLE_L2CAP_LE_CREDIT_BASED_FLOW_CONTROL_MODE | Enable LE credit-based flow-control mode for L2CAP channels | 104| ENABLE_L2CAP_ENHANCED_CREDIT_BASED_FLOW_CONTROL_MODE | Enable Enhanced credit-based flow-control mode for L2CAP Channels | 105| ENABLE_HCI_CONTROLLER_TO_HOST_FLOW_CONTROL | Enable HCI Controller to Host Flow Control, see below | 106| ENABLE_HCI_SERIALIZED_CONTROLLER_OPERATIONS | Serialize Inquiry, Remote Name Request, and Create Connection operations | 107| ENABLE_ATT_DELAYED_RESPONSE | Enable support for delayed ATT operations, see [GATT Server](profiles/#sec:GATTServerProfile) | 108| ENABLE_BCM_PCM_WBS | Enable support for Wide-Band Speech codec in BCM controller, requires ENABLE_SCO_OVER_PCM | 109| ENABLE_CC256X_ASSISTED_HFP | Enable support for Assisted HFP mode in CC256x Controller, requires ENABLE_SCO_OVER_PCM | 110| Enable_RTK_PCM_WBS | Enable support for Wide-Band Speech codec in Realtek controller, requires ENABLE_SCO_OVER_PCM | 111| ENABLE_CC256X_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND | Enable workaround for bug in CC256x Flow Control during baud rate change, see chipset docs. | 112| ENABLE_CYPRESS_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND | Enable workaround for bug in CYW2070x Flow Control during baud rate change, similar to CC256x. | 113| ENABLE_LE_LIMIT_ACL_FRAGMENT_BY_MAX_OCTETS | Force HCI to fragment ACL-LE packets to fit into over-the-air packet | 114| 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 | 115| ENABLE_CONTROLLER_WARM_BOOT | Enable stack startup without power cycle (if supported/possible) | 116| ENABLE_SEGGER_RTT | Use SEGGER RTT for console output and packet log, see [additional options](#sec:rttConfiguration) | 117| ENABLE_EXPLICIT_CONNECTABLE_MODE_CONTROL | Disable calls to control Connectable Mode by L2CAP | 118| ENABLE_EXPLICIT_IO_CAPABILITIES_REPLY | Let application trigger sending IO Capabilities (Negative) Reply | 119| ENABLE_EXPLICIT_LINK_KEY_REPLY | Let application trigger sending Link Key (Negative) Response, allows for asynchronous link key lookup | 120| ENABLE_EXPLICIT_BR_EDR_SECURITY_MANAGER | Report BR/EDR Security Manager support in L2CAP Information Response | 121| ENABLE_CLASSIC_OOB_PAIRING | Enable support for classic Out-of-Band (OOB) pairing | 122| ENABLE_A2DP_EXPLICIT_CONFIG | Let application configure stream endpoint (skip auto-config of SBC endpoint) | 123| ENABLE_AVDTP_ACCEPTOR_EXPLICIT_START_STREAM_CONFIRMATION | allow accept or reject of stream start on A2DP_SUBEVENT_START_STREAM_REQUESTED | 124| ENABLE_LE_WHITELIST_TOUCH_AFTER_RESOLVING_LIST_UPDATE | Enable Workaround for Controller bug. | 125| ENABLE_CONTROLLER_DUMP_PACKETS | Dump number of packets in Controller per type for debugging | 126 127Notes: 128 129- 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. 130 131### HCI Controller to Host Flow Control 132In 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. 133 134Host buffer configuration for HCI Controller to Host Flow Control: 135 136| \#define | Description | 137|-------------------------|----------------------------------| 138| HCI_HOST_ACL_PACKET_NUM | Max number of ACL packets | 139| HCI_HOST_ACL_PACKET_LEN | Max size of HCI Host ACL packets | 140| HCI_HOST_SCO_PACKET_NUM | Max number of ACL packets | 141| HCI_HOST_SCO_PACKET_LEN | Max size of HCI Host SCO packets | 142 143### Memory configuration directives {#sec:memoryConfigurationHowTo} 144 145The structs for services, active connections and remote devices can be 146allocated in two different manners: 147 148- statically from an individual memory pool, whose maximal number of 149 elements is defined in the btstack_config.h file. To initialize the static 150 pools, you need to call at runtime *btstack_memory_init* function. An example 151 of memory configuration for a single SPP service with a minimal 152 L2CAP MTU is shown in Listing {@lst:memoryConfigurationSPP}. 153 154- dynamically using the *malloc/free* functions, if HAVE_MALLOC is 155 defined in btstack_config.h file. 156 157For 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. 158 159<!-- a name "lst:memoryConfiguration"></a--> 160<!-- --> 161 162| \#define | Description | 163|-------------------------------------------|----------------------------------------------------------------------------| 164| HCI_ACL_PAYLOAD_SIZE | Max size of HCI ACL payloads | 165| HCI_ACL_CHUNK_SIZE_ALIGNMENT | Alignment of ACL chunk size, can be used to align HCI transport writes | 166| HCI_INCOMING_PRE_BUFFER_SIZE | Number of bytes reserved before actual data for incoming HCI packets | 167| MAX_NR_BNEP_CHANNELS | Max number of BNEP channels | 168| MAX_NR_BNEP_SERVICES | Max number of BNEP services | 169| MAX_NR_BTSTACK_LINK_KEY_DB_MEMORY_ENTRIES | Max number of link key entries cached in RAM | 170| MAX_NR_GATT_CLIENTS | Max number of GATT clients | 171| MAX_NR_HCI_CONNECTIONS | Max number of HCI connections | 172| MAX_NR_HFP_CONNECTIONS | Max number of HFP connections | 173| MAX_NR_L2CAP_CHANNELS | Max number of L2CAP connections | 174| MAX_NR_L2CAP_SERVICES | Max number of L2CAP services | 175| MAX_NR_RFCOMM_CHANNELS | Max number of RFOMMM connections | 176| MAX_NR_RFCOMM_MULTIPLEXERS | Max number of RFCOMM multiplexers, with one multiplexer per HCI connection | 177| MAX_NR_RFCOMM_SERVICES | Max number of RFCOMM services | 178| MAX_NR_SERVICE_RECORD_ITEMS | Max number of SDP service records | 179| MAX_NR_SM_LOOKUP_ENTRIES | Max number of items in Security Manager lookup queue | 180| MAX_NR_WHITELIST_ENTRIES | Max number of items in GAP LE Whitelist to connect to | 181| MAX_NR_LE_DEVICE_DB_ENTRIES | Max number of items in LE Device DB | 182 183The memory is set up by calling *btstack_memory_init* function: 184 185 btstack_memory_init(); 186 187<!-- a name "lst:memoryConfigurationSPP"></a--> 188<!-- --> 189 190Here's the memory configuration for a basic SPP server. 191 192 #define HCI_ACL_PAYLOAD_SIZE 52 193 #define MAX_NR_HCI_CONNECTIONS 1 194 #define MAX_NR_L2CAP_SERVICES 2 195 #define MAX_NR_L2CAP_CHANNELS 2 196 #define MAX_NR_RFCOMM_MULTIPLEXERS 1 197 #define MAX_NR_RFCOMM_SERVICES 1 198 #define MAX_NR_RFCOMM_CHANNELS 1 199 #define MAX_NR_BTSTACK_LINK_KEY_DB_MEMORY_ENTRIES 3 200 201Listing: Memory configuration for a basic SPP server. {#lst:memoryConfigurationSPP} 202 203In 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. 204 205<!-- --> 206 207### Non-volatile memory (NVM) directives {#sec:nvmConfiguration} 208 209If 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: 210 211<!-- a name "lst:nvmDefines"></a--> 212<!-- --> 213 214| \#define | Description | 215|---------------------------|----------------------------------------------------------------------------------------------| 216| NVM_NUM_LINK_KEYS | Max number of Classic Link Keys that can be stored | 217| NVM_NUM_DEVICE_DB_ENTRIES | Max number of LE Device DB entries that can be stored | 218| NVN_NUM_GATT_SERVER_CCC | Max number of 'Client Characteristic Configuration' values that can be stored by GATT Server | 219 220### HCI Dump Stdout directives {#sec:hciDumpStdout} 221 222Allow to truncate HCI ACL and SCO packets to reduce console output for debugging audio applications. 223 224| \#define | Description | 225|------------------------------|-------------------------------------------| 226| HCI_DUMP_STDOUT_MAX_SIZE_ACL | Max size of ACL packets to log via stdout | 227| HCI_DUMP_STDOUT_MAX_SIZE_SCO | Max size of SCO packets to log via stdout | 228| HCI_DUMP_STDOUT_MAX_SIZE_ISO | Max size of ISO packets to log via stdout | 229 230### SEGGER Real Time Transfer (RTT) directives {#sec:rttConfiguration} 231 232[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. 233 234When 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: 235 236| \#define | Default | Description | 237|----------------------------------|-------------------------------|-------------------------------------------------------------------------------------------------------------------| 238| 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 | 239| SEGGER_RTT_PACKETLOG_CHANNEL | 1 | Channel to use for packet log. Channel 0 is used for terminal | 240| SEGGER_RTT_PACKETLOG_BUFFER_SIZE | 1024 | Size of outgoing ring buffer. Increase if you cannot block but get 'message skipped' warnings. | 241 242## Run-time configuration 243 244To allow code-reuse with different platforms 245as well as with new ports, the low-level initialization of BTstack and 246the hardware configuration has been extracted to the various 247*platforms/PLATFORM/main.c* files. The examples only contain the 248platform-independent Bluetooth logic. But let’s have a look at the 249common init code. 250 251Listing [below](#lst:btstackInit) shows a minimal platform setup for an 252embedded system with a Bluetooth chipset connected via UART. 253 254~~~~ {#lst:btstackInit .c caption="{Minimal platform setup for an embedded system}"} 255 256 int main(){ 257 // ... hardware init: watchdoch, IOs, timers, etc... 258 259 // setup BTstack memory pools 260 btstack_memory_init(); 261 262 // select embedded run loop 263 btstack_run_loop_init(btstack_run_loop_embedded_get_instance()); 264 265 // enable logging 266 hci_dump_init(hci_dump_embedded_stdout_get_instance()); 267 268 269 // init HCI 270 hci_transport_t * transport = hci_transport_h4_instance(); 271 hci_init(transport, NULL); 272 273 // setup example 274 btstack_main(argc, argv); 275 276 // go 277 btstack_run_loop_execute(); 278 } 279 280~~~~ 281 282First, BTstack’s memory pools are set up. Then, the standard run loop 283implementation for embedded systems is selected. 284 285The call to *hci_dump_init* configures BTstack to output all Bluetooth 286packets and its own debug and error message using printf with BTstack's 287millisecond tiomestamps.s as tim. 288The Python 289script *tools/create_packet_log.py* can be used to convert the console 290output into a Bluetooth PacketLogger format that can be opened by the OS 291X PacketLogger tool as well as by Wireshark for further inspection. When 292asking for help, please always include a log created with HCI dump. 293 294The *hci_init* function sets up HCI to use the HCI H4 Transport 295implementation. It doesn’t provide a special transport configuration nor 296a special implementation for a particular Bluetooth chipset. It makes 297use of the *remote_device_db_memory* implementation that allows for 298re-connects without a new pairing but doesn’t persist the bonding 299information. 300 301Finally, it calls *btstack_main()* of the actual example before 302executing the run loop. 303 304 305## Source tree structure {#sec:sourceTreeHowTo} 306 307The source tree has been organized to easily setup new projects. 308 309| Path | Description | 310|----------|------------------------------------------------------| 311| chipset | Support for individual Bluetooth Controller chipsets | 312| doc | Sources for BTstack documentation | 313| example | Example applications available for all ports | 314| platform | Support for special OSs and/or MCU architectures | 315| port | Complete port for a MCU + Chipset combinations | 316| src | Bluetooth stack implementation | 317| test | Unit and PTS tests | 318| tool | Helper tools for BTstack | 319 320The core of BTstack, including all protocol and profiles, is in *src/*. 321 322Support 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. 323 324To accommodate a particular Bluetooth chipset, the *chipset/* subfolders provide various btstack_chipset_* implementations. 325Please have a look at the existing ports in *port/*. 326 327## Run loop configuration {#sec:runLoopHowTo} 328 329To initialize BTstack you need to [initialize the memory](#sec:memoryConfigurationHowTo) 330and [the run loop](#sec:runLoopHowTo) respectively, then setup HCI and all needed higher 331level protocols. 332 333BTstack uses the concept of a run loop to handle incoming data and to schedule work. 334The run loop handles events from two different types of sources: data 335sources and timers. Data sources represent communication interfaces like 336an UART or an USB driver. Timers are used by BTstack to implement 337various Bluetooth-related timeouts. They can also be used to handle 338periodic events. In addition, most implementations also allow to trigger a poll 339of the data sources from interrupt context, or, execute a function from a different 340thread. 341 342Data sources and timers are represented by the *btstack_data_source_t* and 343*btstack_timer_source_t* structs respectively. Each of these structs contain 344at least a linked list node and a pointer to a callback function. All active timers 345and data sources are kept in link lists. While the list of data sources 346is unsorted, the timers are sorted by expiration timeout for efficient 347processing. Data sources need to be configured upon what event they are called back. 348They can be configured to be polled (*DATA_SOURCE_CALLBACK_POLL*), on read ready (*DATA_SOURCE_CALLBACK_READ*), 349or on write ready (*DATA_SOURCE_CALLBACK_WRITE*). 350 351Timers are single shot: a timer will be removed from the timer list 352before its event handler callback is executed. If you need a periodic 353timer, you can re-register the same timer source in the callback 354function, as shown in Listing [PeriodicTimerHandler]. Note that BTstack 355expects to get called periodically to keep its time, see Section 356[on time abstraction](#sec:timeAbstractionPorting) for more on the 357tick hardware abstraction. 358 359BTstack provides different run loop implementations that implement the *btstack_run_loop_t* interface: 360 361- CoreFoundation: implementation for iOS and OS X applications 362- Embedded: the main implementation for embedded systems, especially without an RTOS. 363- FreeRTOS: implementation to run BTstack on a dedicated FreeRTOS thread 364- POSIX: implementation for POSIX systems based on the select() call. 365- Qt: implementation for the Qt applications 366- WICED: implementation for the Broadcom WICED SDK RTOS abstraction that wraps FreeRTOS or ThreadX. 367- Windows: implementation for Windows based on Event objects and WaitForMultipleObjects() call. 368 369Depending on the platform, data sources are either polled (embedded, FreeRTOS), or the platform provides a way 370to wait for a data source to become ready for read or write (CoreFoundation, POSIX, Qt, Windows), or, 371are not used as the HCI transport driver and the run loop is implemented in a different way (WICED). 372In any case, the callbacks must be explicitly enabled with the *btstack_run_loop_enable_data_source_callbacks(..)* function. 373 374In your code, you'll have to configure the run loop before you start it 375as shown in Listing [listing:btstackInit]. The application can register 376data sources as well as timers, e.g., for periodical sampling of sensors, or 377for communication over the UART. 378 379The run loop is set up by calling *btstack_run_loop_init* function and providing 380an instance of the actual run loop. E.g. for the embedded platform, it is: 381 382<!-- --> 383 384 btstack_run_loop_init(btstack_run_loop_embedded_get_instance()); 385 386If the run loop allows to trigger polling of data sources from interrupt context, 387*btstack_run_loop_poll_data_sources_from_irq*. 388 389On multi-threaded environments, e.g., FreeRTOS, POSIX, WINDOWS, 390*btstack_run_loop_execute_code_on_main_thread* can be used to schedule a callback on the main loop. 391 392The complete Run loop API is provided [here](appendix/apis/#sec:runLoopAPIAppendix). 393 394 395### Run Loop Embedded 396 397In the embedded run loop implementation, data sources are constantly polled and 398the system is put to sleep if no IRQ happens during the poll of all data sources. 399 400The complete run loop cycle looks like this: first, the callback 401function of all registered data sources are called in a round robin way. 402Then, the callback functions of timers that are ready are executed. 403Finally, it will be checked if another run loop iteration has been 404requested by an interrupt handler. If not, the run loop will put the MCU 405into sleep mode. 406 407Incoming data over the UART, USB, or timer ticks will generate an 408interrupt and wake up the microcontroller. In order to avoid the 409situation where a data source becomes ready just before the run loop 410enters sleep mode, an interrupt-driven data source has to call the 411*btstack_run_loop_poll_data_sources_from_irq* function. The call to 412*btstack_run_loop_poll_data_sources_from_irq* sets an 413internal flag that is checked in the critical section just before 414entering sleep mode causing another run loop cycle. 415 416To enable the use of timers, make sure that you defined HAVE_EMBEDDED_TICK or HAVE_EMBEDDED_TIME_MS in the 417config file. 418 419While there is no threading, *btstack_run_loop_poll_data_sources_from_irq* allows to reduce stack size by 420scheduling a continuation. 421 422### Run Loop FreeRTOS 423 424The FreeRTOS run loop is used on a dedicated FreeRTOS thread and it uses a FreeRTOS queue to schedule callbacks on the run loop. 425In each iteration: 426 427- all data sources are polled 428- all scheduled callbacks are executed 429- all expired timers are called 430- finally, it gets the next timeout. It then waits for a 'trigger' or the next timeout, if set. 431 432It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 433 434 435### Run Loop POSIX 436 437The data sources are standard File Descriptors. In the run loop execute implementation, 438select() call is used to wait for file descriptors to become ready to read or write, 439while waiting for the next timeout. 440 441To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 442 443It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 444 445 446### Run loop CoreFoundation (OS X/iOS) 447 448This run loop directly maps BTstack's data source and timer source with CoreFoundation objects. 449It supports ready to read and write similar to the POSIX implementation. The call to 450*btstack_run_loop_execute()* then just calls *CFRunLoopRun()*. 451 452To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 453 454It currently only supports *btstack_run_loop_execute_code_on_main_thread*. 455 456 457### Run Lop Qt 458 459This run loop directly maps BTstack's data source and timer source with Qt Core objects. 460It supports ready to read and write similar to the POSIX implementation. 461 462To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 463 464It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 465 466 467### Run loop Windows 468 469The data sources are Event objects. In the run loop implementation WaitForMultipleObjects() call 470is all is used to wait for the Event object to become ready while waiting for the next timeout. 471 472It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 473 474 475### Run loop WICED 476 477WICED SDK API does not provide asynchronous read and write to the UART and no direct way to wait for 478one or more peripherals to become ready. Therefore, BTstack does not provide direct support for data sources. 479Instead, the run loop provides a message queue that allows to schedule functions calls on its thread via 480*btstack_run_loop_wiced_execute_code_on_main_thread()*. 481 482The HCI transport H4 implementation then uses two lightweight threads to do the 483blocking read and write operations. When a read or write is complete on 484the helper threads, a callback to BTstack is scheduled. 485 486It currently only supports *btstack_run_loop_execute_code_on_main_thread*. 487 488 489## HCI Transport configuration 490 491The HCI initialization has to adapt BTstack to the used platform. The first 492call is to *hci_init()* and requires information about the HCI Transport to use. 493The arguments are: 494 495- *HCI Transport implementation*: On embedded systems, a Bluetooth 496 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. 497 These are accessed by linking the appropriate file, e.g., 498 [platform/embedded/hci_transport_h4_embedded.c]() 499 and then getting a pointer to HCI Transport implementation. 500 For more information on adapting HCI Transport to different 501 environments, see [here](porting/#sec:hciTransportPorting). 502 503<!-- --> 504 505 hci_transport_t * transport = hci_transport_h4_instance(); 506 507- *HCI Transport configuration*: As the configuration of the UART used 508 in the H4 transport interface are not standardized, it has to be 509 provided by the main application to BTstack. In addition to the 510 initial UART baud rate, the main baud rate can be specified. The HCI 511 layer of BTstack will change the init baud rate to the main one 512 after the basic setup of the Bluetooth module. A baud rate change 513 has to be done in a coordinated way at both HCI and hardware level. 514 For example, on the CC256x, the HCI command to change the baud rate 515 is sent first, then it is necessary to wait for the confirmation event 516 from the Bluetooth module. Only now, can the UART baud rate changed. 517 518<!-- --> 519 520 hci_uart_config_t* config = &hci_uart_config; 521 522After these are ready, HCI is initialized like this: 523 524 hci_init(transport, config); 525 526 527In addition to these, most UART-based Bluetooth chipset require some 528special logic for correct initialization that is not covered by the 529Bluetooth specification. In particular, this covers: 530 531- setting the baudrate 532- setting the BD ADDR for devices without an internal persistent storage 533- upload of some firmware patches. 534 535This is provided by the various *btstack_chipset_t* implementation in the *chipset/* subfolders. 536As an example, the *bstack_chipset_cc256x_instance* function returns a pointer to a chipset struct 537suitable for the CC256x chipset. 538 539<!-- --> 540 541 btstack_chipset_t * chipset = btstack_chipset_cc256x_instance(); 542 hci_set_chipset(chipset); 543 544 545In some setups, the hardware setup provides explicit control of Bluetooth power and sleep modes. 546In this case, a *btstack_control_t* struct can be set with *hci_set_control*. 547 548Finally, the HCI implementation requires some form of persistent storage for link keys generated 549during either legacy pairing or the Secure Simple Pairing (SSP). This commonly requires platform 550specific code to access the MCU’s EEPROM of Flash storage. For the 551first steps, BTstack provides a (non) persistent store in memory. 552For more see [here](porting/#sec:persistentStoragePorting). 553 554<!-- --> 555 556 btstack_link_key_db_t * link_key_db = &btstack_link_key_db_memory_instance(); 557 btstack_set_link_key_db(link_key_db); 558 559 560The higher layers only rely on BTstack and are initialized by calling 561the respective *\*_init* function. These init functions register 562themselves with the underlying layer. In addition, the application can 563register packet handlers to get events and data as explained in the 564following section. 565 566 567## Services {#sec:servicesHowTo} 568 569One important construct of BTstack is *service*. A service represents a 570server side component that handles incoming connections. So far, BTstack 571provides L2CAP, BNEP, and RFCOMM services. An L2CAP service handles incoming 572connections for an L2CAP channel and is registered with its protocol 573service multiplexer ID (PSM). Similarly, an RFCOMM service handles 574incoming RFCOMM connections and is registered with the RFCOMM channel 575ID. Outgoing connections require no special registration, they are 576created by the application when needed. 577 578 579## Packet handlers configuration {#sec:packetHandlersHowTo} 580 581 582After the hardware and BTstack are set up, the run loop is entered. From 583now on everything is event driven. The application calls BTstack 584functions, which in turn may send commands to the Bluetooth module. The 585resulting events are delivered back to the application. Instead of 586writing a single callback handler for each possible event (as it is done 587in some other Bluetooth stacks), BTstack groups events logically and 588provides them over a single generic interface. Appendix 589[Events and Errors](generated/appendix/#sec:eventsAndErrorsAppendix) 590summarizes the parameters and event 591codes of L2CAP and RFCOMM events, as well as possible errors and the 592corresponding error codes. 593 594Here is summarized list of packet handlers that an application might 595use: 596 597- HCI event handler - allows to observer HCI, GAP, and general BTstack events. 598 599- L2CAP packet handler - handles LE Connection parameter requeset updates 600 601- L2CAP service packet handler - handles incoming L2CAP connections, 602 i.e., channels initiated by the remote. 603 604- L2CAP channel packet handler - handles outgoing L2CAP connections, 605 i.e., channels initiated internally. 606 607- RFCOMM service packet handler - handles incoming RFCOMM connections, 608 i.e., channels initiated by the remote. 609 610- RFCOMM channel packet handler - handles outgoing RFCOMM connections, 611 i.e., channels initiated internally. 612 613These handlers are registered with the functions listed in Table 614{@tbl:registeringFunction}. 615 616 617| Packet Handler | Registering Function | 618|-------------------------------|--------------------------------------------------------------------------| 619| HCI packet handler | hci_add_event_handler | 620| L2CAP packet handler | l2cap_register_packet_handler | 621| L2CAP service packet handler | l2cap_register_service | 622| L2CAP channel packet handler | l2cap_create_channel | 623| RFCOMM service packet handler | rfcomm_register_service and rfcomm_register_service_with_initial_credits | 624| RFCOMM channel packet handler | rfcomm_create_channel and rfcomm_create_channel_with_initial_credits | 625 626Table: Functions for registering packet handlers. {#tbl:registeringFunction} 627 628HCI, GAP, and general BTstack events are delivered to the packet handler 629specified by *hci_add_event_handler* function. In L2CAP, 630BTstack discriminates incoming and outgoing connections, i.e., event and 631data packets are delivered to different packet handlers. Outgoing 632connections are used access remote services, incoming connections are 633used to provide services. For incoming connections, the packet handler 634specified by *l2cap_register_service* is used. For outgoing 635connections, the handler provided by *l2cap_create_channel* 636is used. RFCOMM and BNEP are similar. 637 638The application can register a single shared packet handler for all 639protocols and services, or use separate packet handlers for each 640protocol layer and service. A shared packet handler is often used for 641stack initialization and connection management. 642 643Separate packet handlers can be used for each L2CAP service and outgoing 644connection. For example, to connect with a Bluetooth HID keyboard, your 645application could use three packet handlers: one to handle HCI events 646during discovery of a keyboard registered by 647*l2cap_register_packet_handler*; one that will be registered to an 648outgoing L2CAP channel to connect to keyboard and to receive keyboard 649data registered by *l2cap_create_channel*; after that 650keyboard can reconnect by itself. For this, you need to register L2CAP 651services for the HID Control and HID Interrupt PSMs using 652*l2cap_register_service*. In this call, you’ll also specify 653a packet handler to accept and receive keyboard data. 654 655All events names have the form MODULE_EVENT_NAME now, e.g., *gap_event_-advertising_report*. 656To facilitate working with 657events and get rid of manually calculating offsets into packets, BTstack provides 658auto-generated getters for all fields of all events in *src/hci_event.h*. All 659functions are defined as static inline, so they are not wasting any program memory 660if not used. If used, the memory footprint should be identical to accessing the 661field directly via offsets into the packet. For example, to access fields address_type 662and address from the *gap_event_advertising_report* event use following getters: 663 664<!-- --> 665 uint8_t address type = gap_event_advertising_report_get_address_type(event); 666 bd_addr_t address; 667 gap_event_advertising_report_get_address(event, address); 668 669 670## Bluetooth HCI Packet Logs {#sec:packetlogsHowTo} 671 672If things don't work as expected, having a look at the data exchanged 673between BTstack and the Bluetooth chipset often helps. 674 675For this, BTstack provides a configurable packet logging mechanism via hci_dump.h and the following implementations: 676 677 void hci_dump_init(const hci_dump_t * hci_dump_implementation); 678 679| Platform | File | Description | 680|----------|------------------------------|----------------------------------------------------| 681| POSIX | `hci_dump_posix_fs.c` | HCI log file for Apple PacketLogger and Wireshark | 682| POSIX | `hci_dump_posix_stdout.c` | Console output via printf | 683| Embedded | `hci_dump_embedded_stdout.c` | Console output via printf | 684| Embedded | `hci_dump_segger_stdout.c` | Console output via SEGGER RTT | 685| Embedded | `hci_dump_segger_binary.c` | HCI log file for Apple PacketLogger via SEGGER RTT | 686 687On POSIX systems, you can call *hci_dump_init* with a *hci_dump_posix_fs_get_instance()* and 688configure the path and output format with *hci_dump_posix_fs_open(const char * path, hci_dump_format_t format)* 689where format can be *HCI_DUMP_BLUEZ* or *HCI_DUMP_PACKETLOGGER*. 690The resulting file can be analyzed with Wireshark or the Apple's PacketLogger tool. 691 692On embedded systems without a file system, you either log to an UART console via printf or use SEGGER RTT. 693For printf output you pass *hci_dump_embedded_stdout_get_instance()* to *hci_dump_init()*. 694With RTT, you can choose between textual output similar to printf, and binary output. 695For textual output, you can provide the *hci_dump_segger_stdout_get_instance()*. 696 697It will log all HCI packets to the UART console via printf or RTT Terminal. 698If you capture the console output, incl. your own debug messages, you can use 699the create_packet_log.py tool in the tools folder to convert a text output into a 700PacketLogger file. 701 702For less overhead and higher logging speed, you can directly log in binary format by 703passing *hci_dump_segger_rtt_binary_get_instance()* and selecting the output format by 704calling *hci_dump_segger_rtt_binary_open(hci_dump_format_t format)* with the same format as above. 705 706 707In addition to the HCI packets, you can also enable BTstack's debug information by adding 708 709 #define ENABLE_LOG_INFO 710 #define ENABLE_LOG_ERROR 711 712to the btstack_config.h and recompiling your application. 713 714## Bluetooth Power Control {#sec:powerControl} 715 716In 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. 717The 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. 718 719To enable/disable discoverability, you can call: 720 721 /** 722 * @brief Allows to control if device is discoverable. OFF by default. 723 */ 724 void gap_discoverable_control(uint8_t enable); 725 726If 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. 727 728To enable/disable connectability, you can call: 729 730 /** 731 * @brief Override page scan mode. Page scan mode enabled by l2cap when services are registered 732 * @note Might be used to reduce power consumption while Bluetooth module stays powered but no (new) 733 * connections are expected 734 */ 735 void gap_connectable_control(uint8_t enable); 736 737For Bluetooth Low Energy, the radio is periodically used to broadcast advertisements that are used for both discovery and connection establishment. 738 739To enable/disable advertisements, you can call: 740 741 /** 742 * @brief Enable/Disable Advertisements. OFF by default. 743 * @param enabled 744 */ 745 void gap_advertisements_enable(int enabled); 746 747If 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. 748 749Finally, 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: 750 751 /** 752 * @brief Requests the change of BTstack power mode. 753 */ 754 int hci_power_control(HCI_POWER_MODE mode); 755 756with 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. 757