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 75Chipset properties: 76 77| \#define | Description | 78|------------------------|-------------------------------------------------------| 79| HAVE_BCM_PCM2 | PCM2 is used and requires additional configuration | 80| HAVE_BCM_PCM_NBS_16KHZ | NBS is up/downsampled, use 16 kHz sample rate for NBS | 81 82### ENABLE_* directives {#sec:enableDirectives} 83BTstack properties: 84 85| \#define | Description | 86|-----------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------| 87| ENABLE_CLASSIC | Enable Classic related code in HCI and L2CAP | 88| ENABLE_BLE | Enable BLE related code in HCI and L2CAP | 89| ENABLE_EHCILL | Enable eHCILL low power mode on TI CC256x/WL18xx chipsets | 90| ENABLE_H5 | Enable support for SLIP mode in `btstack_uart.h` drivers for HCI H5 ('Three-Wire Mode') | 91| ENABLE_LOG_DEBUG | Enable log_debug messages | 92| ENABLE_LOG_ERROR | Enable log_error messages | 93| ENABLE_LOG_INFO | Enable log_info messages | 94| ENABLE_SCO_OVER_HCI | Enable SCO over HCI for chipsets (if supported) | 95| ENABLE_SCO_OVER_PCM | Enable SCO ofer PCM/I2S for chipsets (if supported) | 96| ENABLE_HFP_WIDE_BAND_SPEECH | Enable support for mSBC codec used in HFP profile for Wide-Band Speech | 97| ENABLE_HFP_AT_MESSAGES | Enable `HFP_SUBEVENT_AT_MESSAGE_SENT` and `HFP_SUBEVENT_AT_MESSAGE_RECEIVED` events | 98| ENABLE_LE_PERIPHERAL | Enable support for LE Peripheral Role in HCI and Security Manager | 99| ENABLE_LE_CENTRAL | Enable support for LE Central Role in HCI and Security Manager | 100| ENABLE_LE_SECURE_CONNECTIONS | Enable LE Secure Connections | 101| ENABLE_LE_SECURE_CONNECTIONS_DEBUG_KEY | Enable support for LE Secure Connection debug keys for testing | 102| ENABLE_LE_PROACTIVE_AUTHENTICATION | Enable automatic encryption for bonded devices on re-connect | 103| ENABLE_GATT_CLIENT_PAIRING | Enable GATT Client to start pairing and retry operation on security error | 104| ENABLE_MICRO_ECC_FOR_LE_SECURE_CONNECTIONS | Use [micro-ecc library](https://github.com/kmackay/micro-ecc) for ECC operations | 105| ENABLE_LE_DATA_LENGTH_EXTENSION | Enable LE Data Length Extension support | 106| ENABLE_LE_ENHANCED_CONNECTION_COMPLETE_EVENT | Enable LE Enhanced Connection Complete Event v1 & v2 | 107| ENABLE_LE_EXTENDED_ADVERTISING | Enable extended advertising and scanning | 108| ENABLE_LE_PERIODIC_ADVERTISING | Enable periodic advertising and scanning | 109| ENABLE_LE_SIGNED_WRITE | Enable LE Signed Writes in ATT/GATT | 110| ENABLE_LE_PRIVACY_ADDRESS_RESOLUTION | Enable address resolution for resolvable private addresses in Controller | 111| ENABLE_CROSS_TRANSPORT_KEY_DERIVATION | Enable Cross-Transport Key Derivation (CTKD) for Secure Connections | 112| ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE | Enable Enhanced Retransmission Mode for L2CAP Channels. Mandatory for AVRCP Browsing | 113| ENABLE_L2CAP_LE_CREDIT_BASED_FLOW_CONTROL_MODE | Enable LE credit-based flow-control mode for L2CAP channels | 114| ENABLE_L2CAP_ENHANCED_CREDIT_BASED_FLOW_CONTROL_MODE | Enable Enhanced credit-based flow-control mode for L2CAP Channels | 115| ENABLE_HCI_CONTROLLER_TO_HOST_FLOW_CONTROL | Enable HCI Controller to Host Flow Control, see below | 116| ENABLE_HCI_SERIALIZED_CONTROLLER_OPERATIONS | Serialize Inquiry, Remote Name Request, and Create Connection operations | 117| ENABLE_ATT_DELAYED_RESPONSE | Enable support for delayed ATT operations, see [GATT Server](profiles/#sec:GATTServerProfile) | 118| ENABLE_BCM_PCM_WBS | Enable support for Wide-Band Speech codec in BCM controller, requires ENABLE_SCO_OVER_PCM | 119| ENABLE_CC256X_ASSISTED_HFP | Enable support for Assisted HFP mode in CC256x Controller, requires ENABLE_SCO_OVER_PCM | 120| Enable_RTK_PCM_WBS | Enable support for Wide-Band Speech codec in Realtek controller, requires ENABLE_SCO_OVER_PCM | 121| ENABLE_CC256X_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND | Enable workaround for bug in CC256x Flow Control during baud rate change, see chipset docs. | 122| ENABLE_CYPRESS_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND | Enable workaround for bug in CYW2070x Flow Control during baud rate change, similar to CC256x. | 123| ENABLE_LE_LIMIT_ACL_FRAGMENT_BY_MAX_OCTETS | Force HCI to fragment ACL-LE packets to fit into over-the-air packet | 124| 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 | 125| ENABLE_TLV_FLASH_WRITE_ONCE | Enable storing of emtpy tag instead of overwriting existing tag - required when flash value cannot be overwritten at all | 126| ENABLE_CONTROLLER_WARM_BOOT | Enable stack startup without power cycle (if supported/possible) | 127| ENABLE_SEGGER_RTT | Use SEGGER RTT for console output and packet log, see [additional options](#sec:rttConfiguration) | 128| ENABLE_EXPLICIT_CONNECTABLE_MODE_CONTROL | Disable calls to control Connectable Mode by L2CAP | 129| ENABLE_EXPLICIT_IO_CAPABILITIES_REPLY | Let application trigger sending IO Capabilities (Negative) Reply | 130| ENABLE_EXPLICIT_LINK_KEY_REPLY | Let application trigger sending Link Key (Negative) Response, allows for asynchronous link key lookup | 131| ENABLE_EXPLICIT_BR_EDR_SECURITY_MANAGER | Report BR/EDR Security Manager support in L2CAP Information Response | 132| ENABLE_EXPLICIT_DEDICATED_BONDING_DISCONNECT | Keep connection after dedicated bonding is complete | 133| ENABLE_CLASSIC_OOB_PAIRING | Enable support for classic Out-of-Band (OOB) pairing | 134| ENABLE_A2DP_EXPLICIT_CONFIG | Let application configure stream endpoint (skip auto-config of SBC endpoint) | 135| ENABLE_AVDTP_ACCEPTOR_EXPLICIT_START_STREAM_CONFIRMATION | allow accept or reject of stream start on A2DP_SUBEVENT_START_STREAM_REQUESTED | 136| ENABLE_LE_WHITELIST_TOUCH_AFTER_RESOLVING_LIST_UPDATE | Enable Workaround for Controller bug | 137| ENABLE_LE_SET_ADV_PARAMS_ON_RANDOM_ADDRESS_CHANGE | Send HCI LE Set Advertising Params after HCI LE Set Random Address - workaround for Controller Bug | 138| ENABLE_CONTROLLER_DUMP_PACKETS | Dump number of packets in Controller per type for debugging | 139 140Notes: 141 142- 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. 143 144### HCI Controller to Host Flow Control 145In 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. 146 147Host buffer configuration for HCI Controller to Host Flow Control: 148 149| \#define | Description | 150|-------------------------|----------------------------------| 151| HCI_HOST_ACL_PACKET_NUM | Max number of ACL packets | 152| HCI_HOST_ACL_PACKET_LEN | Max size of HCI Host ACL packets | 153| HCI_HOST_SCO_PACKET_NUM | Max number of ACL packets | 154| HCI_HOST_SCO_PACKET_LEN | Max size of HCI Host SCO packets | 155 156### Memory configuration directives {#sec:memoryConfigurationHowTo} 157 158The structs for services, active connections and remote devices can be 159allocated in two different manners: 160 161- statically from an individual memory pool, whose maximal number of 162 elements is defined in the btstack_config.h file. To initialize the static 163 pools, you need to call at runtime *btstack_memory_init* function. An example 164 of memory configuration for a single SPP service with a minimal 165 L2CAP MTU is shown in Listing {@lst:memoryConfigurationSPP}. 166 167- dynamically using the *malloc/free* functions, if HAVE_MALLOC is 168 defined in btstack_config.h file. 169 170For 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 recommended. The large ACL buffer is required for 3-DH5 packets to be used. 171 172<!-- a name "lst:memoryConfiguration"></a--> 173<!-- --> 174 175| \#define | Description | 176|-------------------------------------------|----------------------------------------------------------------------------| 177| HCI_ACL_PAYLOAD_SIZE | Max size of HCI ACL payloads | 178| HCI_ACL_CHUNK_SIZE_ALIGNMENT | Alignment of ACL chunk size, can be used to align HCI transport writes | 179| HCI_INCOMING_PRE_BUFFER_SIZE | Number of bytes reserved before actual data for incoming HCI packets | 180| MAX_NR_BNEP_CHANNELS | Max number of BNEP channels | 181| MAX_NR_BNEP_SERVICES | Max number of BNEP services | 182| MAX_NR_GATT_CLIENTS | Max number of GATT clients | 183| MAX_NR_HCI_CONNECTIONS | Max number of HCI connections | 184| MAX_NR_HFP_CONNECTIONS | Max number of HFP connections | 185| MAX_NR_L2CAP_CHANNELS | Max number of L2CAP connections | 186| MAX_NR_L2CAP_SERVICES | Max number of L2CAP services | 187| MAX_NR_RFCOMM_CHANNELS | Max number of RFOMMM connections | 188| MAX_NR_RFCOMM_MULTIPLEXERS | Max number of RFCOMM multiplexers, with one multiplexer per HCI connection | 189| MAX_NR_RFCOMM_SERVICES | Max number of RFCOMM services | 190| MAX_NR_SERVICE_RECORD_ITEMS | Max number of SDP service records | 191| MAX_NR_SM_LOOKUP_ENTRIES | Max number of items in Security Manager lookup queue | 192| MAX_NR_WHITELIST_ENTRIES | Max number of items in GAP LE Whitelist to connect to | 193 194The memory is set up by calling *btstack_memory_init* function: 195 196 btstack_memory_init(); 197 198<!-- a name "lst:memoryConfigurationSPP"></a--> 199<!-- --> 200 201Here's the memory configuration for a basic SPP server. 202 203 #define HCI_ACL_PAYLOAD_SIZE 52 204 #define MAX_NR_HCI_CONNECTIONS 1 205 #define MAX_NR_L2CAP_SERVICES 2 206 #define MAX_NR_L2CAP_CHANNELS 2 207 #define MAX_NR_RFCOMM_MULTIPLEXERS 1 208 #define MAX_NR_RFCOMM_SERVICES 1 209 #define MAX_NR_RFCOMM_CHANNELS 1 210 #define NVM_NUM_LINK_KEYS 3 211 212Listing: Memory configuration for a basic SPP server. {#lst:memoryConfigurationSPP} 213 214In 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 stored in persistent memory. 215 216<!-- --> 217 218### Non-volatile memory (NVM) directives {#sec:nvmConfiguration} 219 220If 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: 221 222<!-- a name "lst:nvmDefines"></a--> 223<!-- --> 224 225| \#define | Description | 226|---------------------------|----------------------------------------------------------------------------------------------| 227| NVM_NUM_LINK_KEYS | Max number of Classic Link Keys that can be stored | 228| NVM_NUM_DEVICE_DB_ENTRIES | Max number of LE Device DB entries that can be stored | 229| NVN_NUM_GATT_SERVER_CCC | Max number of 'Client Characteristic Configuration' values that can be stored by GATT Server | 230 231### HCI Dump Stdout directives {#sec:hciDumpStdout} 232 233Allow to truncate HCI ACL and SCO packets to reduce console output for debugging audio applications. 234 235| \#define | Description | 236|------------------------------|-------------------------------------------| 237| HCI_DUMP_STDOUT_MAX_SIZE_ACL | Max size of ACL packets to log via stdout | 238| HCI_DUMP_STDOUT_MAX_SIZE_SCO | Max size of SCO packets to log via stdout | 239| HCI_DUMP_STDOUT_MAX_SIZE_ISO | Max size of ISO packets to log via stdout | 240 241### SEGGER Real Time Transfer (RTT) directives {#sec:rttConfiguration} 242 243[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. 244 245When 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: 246 247| \#define | Default | Description | 248|----------------------------------|-------------------------------|-------------------------------------------------------------------------------------------------------------------| 249| 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 | 250| SEGGER_RTT_PACKETLOG_CHANNEL | 1 | Channel to use for packet log. Channel 0 is used for terminal | 251| SEGGER_RTT_PACKETLOG_BUFFER_SIZE | 1024 | Size of outgoing ring buffer. Increase if you cannot block but get 'message skipped' warnings. | 252 253## Run-time configuration 254 255To allow code-reuse with different platforms 256as well as with new ports, the low-level initialization of BTstack and 257the hardware configuration has been extracted to the various 258*platforms/PLATFORM/main.c* files. The examples only contain the 259platform-independent Bluetooth logic. But let’s have a look at the 260common init code. 261 262Listing [below](#lst:btstackInit) shows a minimal platform setup for an 263embedded system with a Bluetooth chipset connected via UART. 264 265~~~~ {#lst:btstackInit .c caption="{Minimal platform setup for an embedded system}"} 266 267 int main(){ 268 // ... hardware init: watchdoch, IOs, timers, etc... 269 270 // setup BTstack memory pools 271 btstack_memory_init(); 272 273 // select embedded run loop 274 btstack_run_loop_init(btstack_run_loop_embedded_get_instance()); 275 276 // enable logging 277 hci_dump_init(hci_dump_embedded_stdout_get_instance()); 278 279 280 // init HCI 281 hci_transport_t * transport = hci_transport_h4_instance(); 282 hci_init(transport, NULL); 283 284 // setup example 285 btstack_main(argc, argv); 286 287 // go 288 btstack_run_loop_execute(); 289 } 290 291~~~~ 292 293First, BTstack’s memory pools are set up. Then, the standard run loop 294implementation for embedded systems is selected. 295 296The call to *hci_dump_init* configures BTstack to output all Bluetooth 297packets and its own debug and error message using printf with BTstack's 298millisecond tiomestamps.s as tim. 299The Python 300script *tools/create_packet_log.py* can be used to convert the console 301output into a Bluetooth PacketLogger format that can be opened by the OS 302X PacketLogger tool as well as by Wireshark for further inspection. When 303asking for help, please always include a log created with HCI dump. 304 305The *hci_init* function sets up HCI to use the HCI H4 Transport 306implementation. It doesn’t provide a special transport configuration nor 307a special implementation for a particular Bluetooth chipset. It makes 308use of the *remote_device_db_memory* implementation that allows for 309re-connects without a new pairing but doesn’t persist the bonding 310information. 311 312Finally, it calls *btstack_main()* of the actual example before 313executing the run loop. 314 315 316## Source tree structure {#sec:sourceTreeHowTo} 317 318The source tree has been organized to easily setup new projects. 319 320| Path | Description | 321|----------|------------------------------------------------------| 322| chipset | Support for individual Bluetooth Controller chipsets | 323| doc | Sources for BTstack documentation | 324| example | Example applications available for all ports | 325| platform | Support for special OSs and/or MCU architectures | 326| port | Complete port for a MCU + Chipset combinations | 327| src | Bluetooth stack implementation | 328| test | Unit and PTS tests | 329| tool | Helper tools for BTstack | 330 331The core of BTstack, including all protocol and profiles, is in *src/*. 332 333Support 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. 334 335To accommodate a particular Bluetooth chipset, the *chipset/* subfolders provide various btstack_chipset_* implementations. 336Please have a look at the existing ports in *port/*. 337 338## Run loop configuration {#sec:runLoopHowTo} 339 340To initialize BTstack you need to [initialize the memory](#sec:memoryConfigurationHowTo) 341and [the run loop](#sec:runLoopHowTo) respectively, then setup HCI and all needed higher 342level protocols. 343 344BTstack uses the concept of a run loop to handle incoming data and to schedule work. 345The run loop handles events from two different types of sources: data 346sources and timers. Data sources represent communication interfaces like 347an UART or an USB driver. Timers are used by BTstack to implement 348various Bluetooth-related timeouts. They can also be used to handle 349periodic events. In addition, most implementations also allow to trigger a poll 350of the data sources from interrupt context, or, execute a function from a different 351thread. 352 353Data sources and timers are represented by the *btstack_data_source_t* and 354*btstack_timer_source_t* structs respectively. Each of these structs contain 355at least a linked list node and a pointer to a callback function. All active timers 356and data sources are kept in link lists. While the list of data sources 357is unsorted, the timers are sorted by expiration timeout for efficient 358processing. Data sources need to be configured upon what event they are called back. 359They can be configured to be polled (*DATA_SOURCE_CALLBACK_POLL*), on read ready (*DATA_SOURCE_CALLBACK_READ*), 360or on write ready (*DATA_SOURCE_CALLBACK_WRITE*). 361 362Timers are single shot: a timer will be removed from the timer list 363before its event handler callback is executed. If you need a periodic 364timer, you can re-register the same timer source in the callback 365function, as shown in Listing [PeriodicTimerHandler]. Note that BTstack 366expects to get called periodically to keep its time, see Section 367[on time abstraction](#sec:timeAbstractionPorting) for more on the 368tick hardware abstraction. 369 370BTstack provides different run loop implementations that implement the *btstack_run_loop_t* interface: 371 372- CoreFoundation: implementation for iOS and OS X applications 373- Embedded: the main implementation for embedded systems, especially without an RTOS. 374- FreeRTOS: implementation to run BTstack on a dedicated FreeRTOS thread 375- POSIX: implementation for POSIX systems based on the select() call. 376- Qt: implementation for the Qt applications 377- WICED: implementation for the Broadcom WICED SDK RTOS abstraction that wraps FreeRTOS or ThreadX. 378- Windows: implementation for Windows based on Event objects and WaitForMultipleObjects() call. 379 380Depending on the platform, data sources are either polled (embedded, FreeRTOS), or the platform provides a way 381to wait for a data source to become ready for read or write (CoreFoundation, POSIX, Qt, Windows), or, 382are not used as the HCI transport driver and the run loop is implemented in a different way (WICED). 383In any case, the callbacks must be explicitly enabled with the *btstack_run_loop_enable_data_source_callbacks(..)* function. 384 385In your code, you'll have to configure the run loop before you start it 386as shown in Listing [listing:btstackInit]. The application can register 387data sources as well as timers, e.g., for periodical sampling of sensors, or 388for communication over the UART. 389 390The run loop is set up by calling *btstack_run_loop_init* function and providing 391an instance of the actual run loop. E.g. for the embedded platform, it is: 392 393<!-- --> 394 395 btstack_run_loop_init(btstack_run_loop_embedded_get_instance()); 396 397If the run loop allows to trigger polling of data sources from interrupt context, 398*btstack_run_loop_poll_data_sources_from_irq*. 399 400On multi-threaded environments, e.g., FreeRTOS, POSIX, WINDOWS, 401*btstack_run_loop_execute_code_on_main_thread* can be used to schedule a callback on the main loop. 402 403The complete Run loop API is provided [here](appendix/apis/#sec:runLoopAPIAppendix). 404 405 406### Run Loop Embedded 407 408In the embedded run loop implementation, data sources are constantly polled and 409the system is put to sleep if no IRQ happens during the poll of all data sources. 410 411The complete run loop cycle looks like this: first, the callback 412function of all registered data sources are called in a round robin way. 413Then, the callback functions of timers that are ready are executed. 414Finally, it will be checked if another run loop iteration has been 415requested by an interrupt handler. If not, the run loop will put the MCU 416into sleep mode. 417 418Incoming data over the UART, USB, or timer ticks will generate an 419interrupt and wake up the microcontroller. In order to avoid the 420situation where a data source becomes ready just before the run loop 421enters sleep mode, an interrupt-driven data source has to call the 422*btstack_run_loop_poll_data_sources_from_irq* function. The call to 423*btstack_run_loop_poll_data_sources_from_irq* sets an 424internal flag that is checked in the critical section just before 425entering sleep mode causing another run loop cycle. 426 427To enable the use of timers, make sure that you defined HAVE_EMBEDDED_TICK or HAVE_EMBEDDED_TIME_MS in the 428config file. 429 430While there is no threading, *btstack_run_loop_poll_data_sources_from_irq* allows to reduce stack size by 431scheduling a continuation. 432 433### Run Loop FreeRTOS 434 435The FreeRTOS run loop is used on a dedicated FreeRTOS thread and it uses a FreeRTOS queue to schedule callbacks on the run loop. 436In each iteration: 437 438- all data sources are polled 439- all scheduled callbacks are executed 440- all expired timers are called 441- finally, it gets the next timeout. It then waits for a 'trigger' or the next timeout, if set. 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 POSIX 447 448The data sources are standard File Descriptors. In the run loop execute implementation, 449select() call is used to wait for file descriptors to become ready to read or write, 450while waiting for the next timeout. 451 452To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 453 454It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 455 456 457### Run loop CoreFoundation (OS X/iOS) 458 459This run loop directly maps BTstack's data source and timer source with CoreFoundation objects. 460It supports ready to read and write similar to the POSIX implementation. The call to 461*btstack_run_loop_execute()* then just calls *CFRunLoopRun()*. 462 463To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 464 465It currently only supports *btstack_run_loop_execute_code_on_main_thread*. 466 467 468### Run Lop Qt 469 470This run loop directly maps BTstack's data source and timer source with Qt Core objects. 471It supports ready to read and write similar to the POSIX implementation. 472 473To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 474 475It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 476 477 478### Run loop Windows 479 480The data sources are Event objects. In the run loop implementation WaitForMultipleObjects() call 481is all is used to wait for the Event object to become ready while waiting for the next timeout. 482 483It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 484 485 486### Run loop WICED 487 488WICED SDK API does not provide asynchronous read and write to the UART and no direct way to wait for 489one or more peripherals to become ready. Therefore, BTstack does not provide direct support for data sources. 490Instead, the run loop provides a message queue that allows to schedule functions calls on its thread via 491*btstack_run_loop_wiced_execute_code_on_main_thread()*. 492 493The HCI transport H4 implementation then uses two lightweight threads to do the 494blocking read and write operations. When a read or write is complete on 495the helper threads, a callback to BTstack is scheduled. 496 497It currently only supports *btstack_run_loop_execute_code_on_main_thread*. 498 499 500## HCI Transport configuration 501 502The HCI initialization has to adapt BTstack to the used platform. The first 503call is to *hci_init()* and requires information about the HCI Transport to use. 504The arguments are: 505 506- *HCI Transport implementation*: On embedded systems, a Bluetooth 507 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. 508 These are accessed by linking the appropriate file, e.g., 509 [platform/embedded/hci_transport_h4_embedded.c]() 510 and then getting a pointer to HCI Transport implementation. 511 For more information on adapting HCI Transport to different 512 environments, see [here](porting/#sec:hciTransportPorting). 513 514<!-- --> 515 516 hci_transport_t * transport = hci_transport_h4_instance(); 517 518- *HCI Transport configuration*: As the configuration of the UART used 519 in the H4 transport interface are not standardized, it has to be 520 provided by the main application to BTstack. In addition to the 521 initial UART baud rate, the main baud rate can be specified. The HCI 522 layer of BTstack will change the init baud rate to the main one 523 after the basic setup of the Bluetooth module. A baud rate change 524 has to be done in a coordinated way at both HCI and hardware level. 525 For example, on the CC256x, the HCI command to change the baud rate 526 is sent first, then it is necessary to wait for the confirmation event 527 from the Bluetooth module. Only now, can the UART baud rate changed. 528 529<!-- --> 530 531 hci_uart_config_t* config = &hci_uart_config; 532 533After these are ready, HCI is initialized like this: 534 535 hci_init(transport, config); 536 537 538In addition to these, most UART-based Bluetooth chipset require some 539special logic for correct initialization that is not covered by the 540Bluetooth specification. In particular, this covers: 541 542- setting the baudrate 543- setting the BD ADDR for devices without an internal persistent storage 544- upload of some firmware patches. 545 546This is provided by the various *btstack_chipset_t* implementation in the *chipset/* subfolders. 547As an example, the *bstack_chipset_cc256x_instance* function returns a pointer to a chipset struct 548suitable for the CC256x chipset. 549 550<!-- --> 551 552 btstack_chipset_t * chipset = btstack_chipset_cc256x_instance(); 553 hci_set_chipset(chipset); 554 555 556In some setups, the hardware setup provides explicit control of Bluetooth power and sleep modes. 557In this case, a *btstack_control_t* struct can be set with *hci_set_control*. 558 559Finally, the HCI implementation requires some form of persistent storage for link keys generated 560during either legacy pairing or the Secure Simple Pairing (SSP). This commonly requires platform 561specific code to access the MCU’s EEPROM of Flash storage. For the 562first steps, BTstack provides a (non) persistent store in memory. 563For more see [here](porting/#sec:persistentStoragePorting). 564 565<!-- --> 566 567 btstack_link_key_db_t * link_key_db = &btstack_link_key_db_memory_instance(); 568 btstack_set_link_key_db(link_key_db); 569 570 571The higher layers only rely on BTstack and are initialized by calling 572the respective *\*_init* function. These init functions register 573themselves with the underlying layer. In addition, the application can 574register packet handlers to get events and data as explained in the 575following section. 576 577 578## Services {#sec:servicesHowTo} 579 580One important construct of BTstack is *service*. A service represents a 581server side component that handles incoming connections. So far, BTstack 582provides L2CAP, BNEP, and RFCOMM services. An L2CAP service handles incoming 583connections for an L2CAP channel and is registered with its protocol 584service multiplexer ID (PSM). Similarly, an RFCOMM service handles 585incoming RFCOMM connections and is registered with the RFCOMM channel 586ID. Outgoing connections require no special registration, they are 587created by the application when needed. 588 589 590## Packet handlers configuration {#sec:packetHandlersHowTo} 591 592 593After the hardware and BTstack are set up, the run loop is entered. From 594now on everything is event driven. The application calls BTstack 595functions, which in turn may send commands to the Bluetooth module. The 596resulting events are delivered back to the application. Instead of 597writing a single callback handler for each possible event (as it is done 598in some other Bluetooth stacks), BTstack groups events logically and 599provides them over a single generic interface. Appendix 600[Events and Errors](generated/appendix/#sec:eventsAndErrorsAppendix) 601summarizes the parameters and event 602codes of L2CAP and RFCOMM events, as well as possible errors and the 603corresponding error codes. 604 605Here is summarized list of packet handlers that an application might 606use: 607 608- HCI event handler - allows to observer HCI, GAP, and general BTstack events. 609 610- L2CAP packet handler - handles LE Connection parameter requeset updates 611 612- L2CAP service packet handler - handles incoming L2CAP connections, 613 i.e., channels initiated by the remote. 614 615- L2CAP channel packet handler - handles outgoing L2CAP connections, 616 i.e., channels initiated internally. 617 618- RFCOMM service packet handler - handles incoming RFCOMM connections, 619 i.e., channels initiated by the remote. 620 621- RFCOMM channel packet handler - handles outgoing RFCOMM connections, 622 i.e., channels initiated internally. 623 624These handlers are registered with the functions listed in Table 625{@tbl:registeringFunction}. 626 627 628| Packet Handler | Registering Function | 629|-------------------------------|--------------------------------------------------------------------------| 630| HCI packet handler | hci_add_event_handler | 631| L2CAP packet handler | l2cap_register_packet_handler | 632| L2CAP service packet handler | l2cap_register_service | 633| L2CAP channel packet handler | l2cap_create_channel | 634| RFCOMM service packet handler | rfcomm_register_service and rfcomm_register_service_with_initial_credits | 635| RFCOMM channel packet handler | rfcomm_create_channel and rfcomm_create_channel_with_initial_credits | 636 637Table: Functions for registering packet handlers. {#tbl:registeringFunction} 638 639HCI, GAP, and general BTstack events are delivered to the packet handler 640specified by *hci_add_event_handler* function. In L2CAP, 641BTstack discriminates incoming and outgoing connections, i.e., event and 642data packets are delivered to different packet handlers. Outgoing 643connections are used access remote services, incoming connections are 644used to provide services. For incoming connections, the packet handler 645specified by *l2cap_register_service* is used. For outgoing 646connections, the handler provided by *l2cap_create_channel* 647is used. RFCOMM and BNEP are similar. 648 649The application can register a single shared packet handler for all 650protocols and services, or use separate packet handlers for each 651protocol layer and service. A shared packet handler is often used for 652stack initialization and connection management. 653 654Separate packet handlers can be used for each L2CAP service and outgoing 655connection. For example, to connect with a Bluetooth HID keyboard, your 656application could use three packet handlers: one to handle HCI events 657during discovery of a keyboard registered by 658*l2cap_register_packet_handler*; one that will be registered to an 659outgoing L2CAP channel to connect to keyboard and to receive keyboard 660data registered by *l2cap_create_channel*; after that 661keyboard can reconnect by itself. For this, you need to register L2CAP 662services for the HID Control and HID Interrupt PSMs using 663*l2cap_register_service*. In this call, you’ll also specify 664a packet handler to accept and receive keyboard data. 665 666All events names have the form MODULE_EVENT_NAME now, e.g., *gap_event_-advertising_report*. 667To facilitate working with 668events and get rid of manually calculating offsets into packets, BTstack provides 669auto-generated getters for all fields of all events in *src/hci_event.h*. All 670functions are defined as static inline, so they are not wasting any program memory 671if not used. If used, the memory footprint should be identical to accessing the 672field directly via offsets into the packet. For example, to access fields address_type 673and address from the *gap_event_advertising_report* event use following getters: 674 675<!-- --> 676 uint8_t address type = gap_event_advertising_report_get_address_type(event); 677 bd_addr_t address; 678 gap_event_advertising_report_get_address(event, address); 679 680 681## Bluetooth HCI Packet Logs {#sec:packetlogsHowTo} 682 683If things don't work as expected, having a look at the data exchanged 684between BTstack and the Bluetooth chipset often helps. 685 686For this, BTstack provides a configurable packet logging mechanism via hci_dump.h and the following implementations: 687 688 void hci_dump_init(const hci_dump_t * hci_dump_implementation); 689 690| Platform | File | Description | 691|----------|------------------------------|----------------------------------------------------| 692| POSIX | `hci_dump_posix_fs.c` | HCI log file for Apple PacketLogger and Wireshark | 693| POSIX | `hci_dump_posix_stdout.c` | Console output via printf | 694| Embedded | `hci_dump_embedded_stdout.c` | Console output via printf | 695| Embedded | `hci_dump_segger_stdout.c` | Console output via SEGGER RTT | 696| Embedded | `hci_dump_segger_binary.c` | HCI log file for Apple PacketLogger via SEGGER RTT | 697 698On POSIX systems, you can call *hci_dump_init* with a *hci_dump_posix_fs_get_instance()* and 699configure the path and output format with *hci_dump_posix_fs_open(const char * path, hci_dump_format_t format)* 700where format can be *HCI_DUMP_BLUEZ* or *HCI_DUMP_PACKETLOGGER*. 701The resulting file can be analyzed with Wireshark or the Apple's PacketLogger tool. 702 703On embedded systems without a file system, you either log to an UART console via printf or use SEGGER RTT. 704For printf output you pass *hci_dump_embedded_stdout_get_instance()* to *hci_dump_init()*. 705With RTT, you can choose between textual output similar to printf, and binary output. 706For textual output, you can provide the *hci_dump_segger_stdout_get_instance()*. 707 708It will log all HCI packets to the UART console via printf or RTT Terminal. 709If you capture the console output, incl. your own debug messages, you can use 710the create_packet_log.py tool in the tools folder to convert a text output into a 711PacketLogger file. 712 713For less overhead and higher logging speed, you can directly log in binary format by 714passing *hci_dump_segger_rtt_binary_get_instance()* and selecting the output format by 715calling *hci_dump_segger_rtt_binary_open(hci_dump_format_t format)* with the same format as above. 716 717 718In addition to the HCI packets, you can also enable BTstack's debug information by adding 719 720 #define ENABLE_LOG_INFO 721 #define ENABLE_LOG_ERROR 722 723to the btstack_config.h and recompiling your application. 724 725## Bluetooth Power Control {#sec:powerControl} 726 727In 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. 728The 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. 729 730To enable/disable discoverability, you can call: 731 732 /** 733 * @brief Allows to control if device is discoverable. OFF by default. 734 */ 735 void gap_discoverable_control(uint8_t enable); 736 737If 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. 738 739To enable/disable connectability, you can call: 740 741 /** 742 * @brief Override page scan mode. Page scan mode enabled by l2cap when services are registered 743 * @note Might be used to reduce power consumption while Bluetooth module stays powered but no (new) 744 * connections are expected 745 */ 746 void gap_connectable_control(uint8_t enable); 747 748For Bluetooth Low Energy, the radio is periodically used to broadcast advertisements that are used for both discovery and connection establishment. 749 750To enable/disable advertisements, you can call: 751 752 /** 753 * @brief Enable/Disable Advertisements. OFF by default. 754 * @param enabled 755 */ 756 void gap_advertisements_enable(int enabled); 757 758If 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. 759 760Finally, 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: 761 762 /** 763 * @brief Requests the change of BTstack power mode. 764 */ 765 int hci_power_control(HCI_POWER_MODE mode); 766 767with 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. 768