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| ENABLE_HCI_COMMAND_STATUS_DISCARDED_FOR_FAILED_CONNECTIONS WORKAROUND | Track connection handle for HCI Commands and assume command has failed if disonnect event for connection is received | 140| ENABLE_MUTUAL_AUTHENTICATION_FOR_LEGACY_SECURE_CONNECTIONS | Re-authentication after connection was encrypted to avoid BIAS Attack. Not needed for min encryption key size of 16 | 141 142Notes: 143 144- 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. 145 146### HCI Controller to Host Flow Control 147In 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. 148 149Host buffer configuration for HCI Controller to Host Flow Control: 150 151| \#define | Description | 152|-------------------------|----------------------------------| 153| HCI_HOST_ACL_PACKET_NUM | Max number of ACL packets | 154| HCI_HOST_ACL_PACKET_LEN | Max size of HCI Host ACL packets | 155| HCI_HOST_SCO_PACKET_NUM | Max number of ACL packets | 156| HCI_HOST_SCO_PACKET_LEN | Max size of HCI Host SCO packets | 157 158### Memory configuration directives {#sec:memoryConfigurationHowTo} 159 160The structs for services, active connections and remote devices can be 161allocated in two different manners: 162 163- statically from an individual memory pool, whose maximal number of 164 elements is defined in the btstack_config.h file. To initialize the static 165 pools, you need to call at runtime *btstack_memory_init* function. An example 166 of memory configuration for a single SPP service with a minimal 167 L2CAP MTU is shown in Listing {@lst:memoryConfigurationSPP}. 168 169- dynamically using the *malloc/free* functions, if HAVE_MALLOC is 170 defined in btstack_config.h file. 171 172For 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. 173 174<!-- a name "lst:memoryConfiguration"></a--> 175<!-- --> 176 177| \#define | Description | 178|-------------------------------------------|----------------------------------------------------------------------------| 179| HCI_ACL_PAYLOAD_SIZE | Max size of HCI ACL payloads | 180| HCI_ACL_CHUNK_SIZE_ALIGNMENT | Alignment of ACL chunk size, can be used to align HCI transport writes | 181| HCI_INCOMING_PRE_BUFFER_SIZE | Number of bytes reserved before actual data for incoming HCI packets | 182| MAX_NR_BNEP_CHANNELS | Max number of BNEP channels | 183| MAX_NR_BNEP_SERVICES | Max number of BNEP services | 184| MAX_NR_GATT_CLIENTS | Max number of GATT clients | 185| MAX_NR_HCI_CONNECTIONS | Max number of HCI connections | 186| MAX_NR_HFP_CONNECTIONS | Max number of HFP connections | 187| MAX_NR_L2CAP_CHANNELS | Max number of L2CAP connections | 188| MAX_NR_L2CAP_SERVICES | Max number of L2CAP services | 189| MAX_NR_RFCOMM_CHANNELS | Max number of RFOMMM connections | 190| MAX_NR_RFCOMM_MULTIPLEXERS | Max number of RFCOMM multiplexers, with one multiplexer per HCI connection | 191| MAX_NR_RFCOMM_SERVICES | Max number of RFCOMM services | 192| MAX_NR_SERVICE_RECORD_ITEMS | Max number of SDP service records | 193| MAX_NR_SM_LOOKUP_ENTRIES | Max number of items in Security Manager lookup queue | 194| MAX_NR_WHITELIST_ENTRIES | Max number of items in GAP LE Whitelist to connect to | 195 196The memory is set up by calling *btstack_memory_init* function: 197 198 btstack_memory_init(); 199 200<!-- a name "lst:memoryConfigurationSPP"></a--> 201<!-- --> 202 203Here's the memory configuration for a basic SPP server. 204 205 #define HCI_ACL_PAYLOAD_SIZE 52 206 #define MAX_NR_HCI_CONNECTIONS 1 207 #define MAX_NR_L2CAP_SERVICES 2 208 #define MAX_NR_L2CAP_CHANNELS 2 209 #define MAX_NR_RFCOMM_MULTIPLEXERS 1 210 #define MAX_NR_RFCOMM_SERVICES 1 211 #define MAX_NR_RFCOMM_CHANNELS 1 212 #define NVM_NUM_LINK_KEYS 3 213 214Listing: Memory configuration for a basic SPP server. {#lst:memoryConfigurationSPP} 215 216In 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. 217 218<!-- --> 219 220### Non-volatile memory (NVM) directives {#sec:nvmConfiguration} 221 222If 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: 223 224<!-- a name "lst:nvmDefines"></a--> 225<!-- --> 226 227| \#define | Description | 228|---------------------------|----------------------------------------------------------------------------------------------| 229| NVM_NUM_LINK_KEYS | Max number of Classic Link Keys that can be stored | 230| NVM_NUM_DEVICE_DB_ENTRIES | Max number of LE Device DB entries that can be stored | 231| NVN_NUM_GATT_SERVER_CCC | Max number of 'Client Characteristic Configuration' values that can be stored by GATT Server | 232 233### HCI Dump Stdout directives {#sec:hciDumpStdout} 234 235Allow to truncate HCI ACL and SCO packets to reduce console output for debugging audio applications. 236 237| \#define | Description | 238|------------------------------|-------------------------------------------| 239| HCI_DUMP_STDOUT_MAX_SIZE_ACL | Max size of ACL packets to log via stdout | 240| HCI_DUMP_STDOUT_MAX_SIZE_SCO | Max size of SCO packets to log via stdout | 241| HCI_DUMP_STDOUT_MAX_SIZE_ISO | Max size of ISO packets to log via stdout | 242 243### SEGGER Real Time Transfer (RTT) directives {#sec:rttConfiguration} 244 245[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. 246 247When 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: 248 249| \#define | Default | Description | 250|----------------------------------|-------------------------------|-------------------------------------------------------------------------------------------------------------------| 251| 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 | 252| SEGGER_RTT_PACKETLOG_CHANNEL | 1 | Channel to use for packet log. Channel 0 is used for terminal | 253| SEGGER_RTT_PACKETLOG_BUFFER_SIZE | 1024 | Size of outgoing ring buffer. Increase if you cannot block but get 'message skipped' warnings. | 254 255## Run-time configuration 256 257To allow code-reuse with different platforms 258as well as with new ports, the low-level initialization of BTstack and 259the hardware configuration has been extracted to the various 260*platforms/PLATFORM/main.c* files. The examples only contain the 261platform-independent Bluetooth logic. But let’s have a look at the 262common init code. 263 264Listing [below](#lst:btstackInit) shows a minimal platform setup for an 265embedded system with a Bluetooth chipset connected via UART. 266 267~~~~ {#lst:btstackInit .c caption="{Minimal platform setup for an embedded system}"} 268 269 int main(){ 270 // ... hardware init: watchdoch, IOs, timers, etc... 271 272 // setup BTstack memory pools 273 btstack_memory_init(); 274 275 // select embedded run loop 276 btstack_run_loop_init(btstack_run_loop_embedded_get_instance()); 277 278 // enable logging 279 hci_dump_init(hci_dump_embedded_stdout_get_instance()); 280 281 282 // init HCI 283 hci_transport_t * transport = hci_transport_h4_instance(); 284 hci_init(transport, NULL); 285 286 // setup example 287 btstack_main(argc, argv); 288 289 // go 290 btstack_run_loop_execute(); 291 } 292 293~~~~ 294 295First, BTstack’s memory pools are set up. Then, the standard run loop 296implementation for embedded systems is selected. 297 298The call to *hci_dump_init* configures BTstack to output all Bluetooth 299packets and its own debug and error message using printf with BTstack's 300millisecond tiomestamps.s as tim. 301The Python 302script *tools/create_packet_log.py* can be used to convert the console 303output into a Bluetooth PacketLogger format that can be opened by the OS 304X PacketLogger tool as well as by Wireshark for further inspection. When 305asking for help, please always include a log created with HCI dump. 306 307The *hci_init* function sets up HCI to use the HCI H4 Transport 308implementation. It doesn’t provide a special transport configuration nor 309a special implementation for a particular Bluetooth chipset. It makes 310use of the *remote_device_db_memory* implementation that allows for 311re-connects without a new pairing but doesn’t persist the bonding 312information. 313 314Finally, it calls *btstack_main()* of the actual example before 315executing the run loop. 316 317 318## Source tree structure {#sec:sourceTreeHowTo} 319 320The source tree has been organized to easily setup new projects. 321 322| Path | Description | 323|----------|------------------------------------------------------| 324| chipset | Support for individual Bluetooth Controller chipsets | 325| doc | Sources for BTstack documentation | 326| example | Example applications available for all ports | 327| platform | Support for special OSs and/or MCU architectures | 328| port | Complete port for a MCU + Chipset combinations | 329| src | Bluetooth stack implementation | 330| test | Unit and PTS tests | 331| tool | Helper tools for BTstack | 332 333The core of BTstack, including all protocol and profiles, is in *src/*. 334 335Support 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. 336 337To accommodate a particular Bluetooth chipset, the *chipset/* subfolders provide various btstack_chipset_* implementations. 338Please have a look at the existing ports in *port/*. 339 340## Run loop configuration {#sec:runLoopHowTo} 341 342To initialize BTstack you need to [initialize the memory](#sec:memoryConfigurationHowTo) 343and [the run loop](#sec:runLoopHowTo) respectively, then setup HCI and all needed higher 344level protocols. 345 346BTstack uses the concept of a run loop to handle incoming data and to schedule work. 347The run loop handles events from two different types of sources: data 348sources and timers. Data sources represent communication interfaces like 349an UART or an USB driver. Timers are used by BTstack to implement 350various Bluetooth-related timeouts. They can also be used to handle 351periodic events. In addition, most implementations also allow to trigger a poll 352of the data sources from interrupt context, or, execute a function from a different 353thread. 354 355Data sources and timers are represented by the *btstack_data_source_t* and 356*btstack_timer_source_t* structs respectively. Each of these structs contain 357at least a linked list node and a pointer to a callback function. All active timers 358and data sources are kept in link lists. While the list of data sources 359is unsorted, the timers are sorted by expiration timeout for efficient 360processing. Data sources need to be configured upon what event they are called back. 361They can be configured to be polled (*DATA_SOURCE_CALLBACK_POLL*), on read ready (*DATA_SOURCE_CALLBACK_READ*), 362or on write ready (*DATA_SOURCE_CALLBACK_WRITE*). 363 364Timers are single shot: a timer will be removed from the timer list 365before its event handler callback is executed. If you need a periodic 366timer, you can re-register the same timer source in the callback 367function, as shown in Listing [PeriodicTimerHandler]. Note that BTstack 368expects to get called periodically to keep its time, see Section 369[on time abstraction](#sec:timeAbstractionPorting) for more on the 370tick hardware abstraction. 371 372BTstack provides different run loop implementations that implement the *btstack_run_loop_t* interface: 373 374- CoreFoundation: implementation for iOS and OS X applications 375- Embedded: the main implementation for embedded systems, especially without an RTOS. 376- FreeRTOS: implementation to run BTstack on a dedicated FreeRTOS thread 377- POSIX: implementation for POSIX systems based on the select() call. 378- Qt: implementation for the Qt applications 379- WICED: implementation for the Broadcom WICED SDK RTOS abstraction that wraps FreeRTOS or ThreadX. 380- Windows: implementation for Windows based on Event objects and WaitForMultipleObjects() call. 381 382Depending on the platform, data sources are either polled (embedded, FreeRTOS), or the platform provides a way 383to wait for a data source to become ready for read or write (CoreFoundation, POSIX, Qt, Windows), or, 384are not used as the HCI transport driver and the run loop is implemented in a different way (WICED). 385In any case, the callbacks must be explicitly enabled with the *btstack_run_loop_enable_data_source_callbacks(..)* function. 386 387In your code, you'll have to configure the run loop before you start it 388as shown in Listing [listing:btstackInit]. The application can register 389data sources as well as timers, e.g., for periodical sampling of sensors, or 390for communication over the UART. 391 392The run loop is set up by calling *btstack_run_loop_init* function and providing 393an instance of the actual run loop. E.g. for the embedded platform, it is: 394 395<!-- --> 396 397 btstack_run_loop_init(btstack_run_loop_embedded_get_instance()); 398 399If the run loop allows to trigger polling of data sources from interrupt context, 400*btstack_run_loop_poll_data_sources_from_irq*. 401 402On multi-threaded environments, e.g., FreeRTOS, POSIX, WINDOWS, 403*btstack_run_loop_execute_code_on_main_thread* can be used to schedule a callback on the main loop. 404 405The complete Run loop API is provided [here](appendix/apis/#sec:runLoopAPIAppendix). 406 407 408### Run Loop Embedded 409 410In the embedded run loop implementation, data sources are constantly polled and 411the system is put to sleep if no IRQ happens during the poll of all data sources. 412 413The complete run loop cycle looks like this: first, the callback 414function of all registered data sources are called in a round robin way. 415Then, the callback functions of timers that are ready are executed. 416Finally, it will be checked if another run loop iteration has been 417requested by an interrupt handler. If not, the run loop will put the MCU 418into sleep mode. 419 420Incoming data over the UART, USB, or timer ticks will generate an 421interrupt and wake up the microcontroller. In order to avoid the 422situation where a data source becomes ready just before the run loop 423enters sleep mode, an interrupt-driven data source has to call the 424*btstack_run_loop_poll_data_sources_from_irq* function. The call to 425*btstack_run_loop_poll_data_sources_from_irq* sets an 426internal flag that is checked in the critical section just before 427entering sleep mode causing another run loop cycle. 428 429To enable the use of timers, make sure that you defined HAVE_EMBEDDED_TICK or HAVE_EMBEDDED_TIME_MS in the 430config file. 431 432While there is no threading, *btstack_run_loop_poll_data_sources_from_irq* allows to reduce stack size by 433scheduling a continuation. 434 435### Run Loop FreeRTOS 436 437The FreeRTOS run loop is used on a dedicated FreeRTOS thread and it uses a FreeRTOS queue to schedule callbacks on the run loop. 438In each iteration: 439 440- all data sources are polled 441- all scheduled callbacks are executed 442- all expired timers are called 443- finally, it gets the next timeout. It then waits for a 'trigger' or the next timeout, if set. 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 POSIX 449 450The data sources are standard File Descriptors. In the run loop execute implementation, 451select() call is used to wait for file descriptors to become ready to read or write, 452while waiting for the next timeout. 453 454To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 455 456It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 457 458 459### Run loop CoreFoundation (OS X/iOS) 460 461This run loop directly maps BTstack's data source and timer source with CoreFoundation objects. 462It supports ready to read and write similar to the POSIX implementation. The call to 463*btstack_run_loop_execute()* then just calls *CFRunLoopRun()*. 464 465To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 466 467It currently only supports *btstack_run_loop_execute_code_on_main_thread*. 468 469 470### Run Lop Qt 471 472This run loop directly maps BTstack's data source and timer source with Qt Core objects. 473It supports ready to read and write similar to the POSIX implementation. 474 475To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 476 477It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 478 479 480### Run loop Windows 481 482The data sources are Event objects. In the run loop implementation WaitForMultipleObjects() call 483is all is used to wait for the Event object to become ready while waiting for the next timeout. 484 485It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 486 487 488### Run loop WICED 489 490WICED SDK API does not provide asynchronous read and write to the UART and no direct way to wait for 491one or more peripherals to become ready. Therefore, BTstack does not provide direct support for data sources. 492Instead, the run loop provides a message queue that allows to schedule functions calls on its thread via 493*btstack_run_loop_wiced_execute_code_on_main_thread()*. 494 495The HCI transport H4 implementation then uses two lightweight threads to do the 496blocking read and write operations. When a read or write is complete on 497the helper threads, a callback to BTstack is scheduled. 498 499It currently only supports *btstack_run_loop_execute_code_on_main_thread*. 500 501 502## HCI Transport configuration 503 504The HCI initialization has to adapt BTstack to the used platform. The first 505call is to *hci_init()* and requires information about the HCI Transport to use. 506The arguments are: 507 508- *HCI Transport implementation*: On embedded systems, a Bluetooth 509 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. 510 These are accessed by linking the appropriate file, e.g., 511 [platform/embedded/hci_transport_h4_embedded.c]() 512 and then getting a pointer to HCI Transport implementation. 513 For more information on adapting HCI Transport to different 514 environments, see [here](porting/#sec:hciTransportPorting). 515 516<!-- --> 517 518 hci_transport_t * transport = hci_transport_h4_instance(); 519 520- *HCI Transport configuration*: As the configuration of the UART used 521 in the H4 transport interface are not standardized, it has to be 522 provided by the main application to BTstack. In addition to the 523 initial UART baud rate, the main baud rate can be specified. The HCI 524 layer of BTstack will change the init baud rate to the main one 525 after the basic setup of the Bluetooth module. A baud rate change 526 has to be done in a coordinated way at both HCI and hardware level. 527 For example, on the CC256x, the HCI command to change the baud rate 528 is sent first, then it is necessary to wait for the confirmation event 529 from the Bluetooth module. Only now, can the UART baud rate changed. 530 531<!-- --> 532 533 hci_uart_config_t* config = &hci_uart_config; 534 535After these are ready, HCI is initialized like this: 536 537 hci_init(transport, config); 538 539 540In addition to these, most UART-based Bluetooth chipset require some 541special logic for correct initialization that is not covered by the 542Bluetooth specification. In particular, this covers: 543 544- setting the baudrate 545- setting the BD ADDR for devices without an internal persistent storage 546- upload of some firmware patches. 547 548This is provided by the various *btstack_chipset_t* implementation in the *chipset/* subfolders. 549As an example, the *bstack_chipset_cc256x_instance* function returns a pointer to a chipset struct 550suitable for the CC256x chipset. 551 552<!-- --> 553 554 btstack_chipset_t * chipset = btstack_chipset_cc256x_instance(); 555 hci_set_chipset(chipset); 556 557 558In some setups, the hardware setup provides explicit control of Bluetooth power and sleep modes. 559In this case, a *btstack_control_t* struct can be set with *hci_set_control*. 560 561Finally, the HCI implementation requires some form of persistent storage for link keys generated 562during either legacy pairing or the Secure Simple Pairing (SSP). This commonly requires platform 563specific code to access the MCU’s EEPROM of Flash storage. For the 564first steps, BTstack provides a (non) persistent store in memory. 565For more see [here](porting/#sec:persistentStoragePorting). 566 567<!-- --> 568 569 btstack_link_key_db_t * link_key_db = &btstack_link_key_db_memory_instance(); 570 btstack_set_link_key_db(link_key_db); 571 572 573The higher layers only rely on BTstack and are initialized by calling 574the respective *\*_init* function. These init functions register 575themselves with the underlying layer. In addition, the application can 576register packet handlers to get events and data as explained in the 577following section. 578 579 580## Services {#sec:servicesHowTo} 581 582One important construct of BTstack is *service*. A service represents a 583server side component that handles incoming connections. So far, BTstack 584provides L2CAP, BNEP, and RFCOMM services. An L2CAP service handles incoming 585connections for an L2CAP channel and is registered with its protocol 586service multiplexer ID (PSM). Similarly, an RFCOMM service handles 587incoming RFCOMM connections and is registered with the RFCOMM channel 588ID. Outgoing connections require no special registration, they are 589created by the application when needed. 590 591 592## Packet handlers configuration {#sec:packetHandlersHowTo} 593 594 595After the hardware and BTstack are set up, the run loop is entered. From 596now on everything is event driven. The application calls BTstack 597functions, which in turn may send commands to the Bluetooth module. The 598resulting events are delivered back to the application. Instead of 599writing a single callback handler for each possible event (as it is done 600in some other Bluetooth stacks), BTstack groups events logically and 601provides them over a single generic interface. Appendix 602[Events and Errors](generated/appendix/#sec:eventsAndErrorsAppendix) 603summarizes the parameters and event 604codes of L2CAP and RFCOMM events, as well as possible errors and the 605corresponding error codes. 606 607Here is summarized list of packet handlers that an application might 608use: 609 610- HCI event handler - allows to observer HCI, GAP, and general BTstack events. 611 612- L2CAP packet handler - handles LE Connection parameter requeset updates 613 614- L2CAP service packet handler - handles incoming L2CAP connections, 615 i.e., channels initiated by the remote. 616 617- L2CAP channel packet handler - handles outgoing L2CAP connections, 618 i.e., channels initiated internally. 619 620- RFCOMM service packet handler - handles incoming RFCOMM connections, 621 i.e., channels initiated by the remote. 622 623- RFCOMM channel packet handler - handles outgoing RFCOMM connections, 624 i.e., channels initiated internally. 625 626These handlers are registered with the functions listed in Table 627{@tbl:registeringFunction}. 628 629 630| Packet Handler | Registering Function | 631|-------------------------------|--------------------------------------------------------------------------| 632| HCI packet handler | hci_add_event_handler | 633| L2CAP packet handler | l2cap_register_packet_handler | 634| L2CAP service packet handler | l2cap_register_service | 635| L2CAP channel packet handler | l2cap_create_channel | 636| RFCOMM service packet handler | rfcomm_register_service and rfcomm_register_service_with_initial_credits | 637| RFCOMM channel packet handler | rfcomm_create_channel and rfcomm_create_channel_with_initial_credits | 638 639Table: Functions for registering packet handlers. {#tbl:registeringFunction} 640 641HCI, GAP, and general BTstack events are delivered to the packet handler 642specified by *hci_add_event_handler* function. In L2CAP, 643BTstack discriminates incoming and outgoing connections, i.e., event and 644data packets are delivered to different packet handlers. Outgoing 645connections are used access remote services, incoming connections are 646used to provide services. For incoming connections, the packet handler 647specified by *l2cap_register_service* is used. For outgoing 648connections, the handler provided by *l2cap_create_channel* 649is used. RFCOMM and BNEP are similar. 650 651The application can register a single shared packet handler for all 652protocols and services, or use separate packet handlers for each 653protocol layer and service. A shared packet handler is often used for 654stack initialization and connection management. 655 656Separate packet handlers can be used for each L2CAP service and outgoing 657connection. For example, to connect with a Bluetooth HID keyboard, your 658application could use three packet handlers: one to handle HCI events 659during discovery of a keyboard registered by 660*l2cap_register_packet_handler*; one that will be registered to an 661outgoing L2CAP channel to connect to keyboard and to receive keyboard 662data registered by *l2cap_create_channel*; after that 663keyboard can reconnect by itself. For this, you need to register L2CAP 664services for the HID Control and HID Interrupt PSMs using 665*l2cap_register_service*. In this call, you’ll also specify 666a packet handler to accept and receive keyboard data. 667 668All events names have the form MODULE_EVENT_NAME now, e.g., *gap_event_-advertising_report*. 669To facilitate working with 670events and get rid of manually calculating offsets into packets, BTstack provides 671auto-generated getters for all fields of all events in *src/hci_event.h*. All 672functions are defined as static inline, so they are not wasting any program memory 673if not used. If used, the memory footprint should be identical to accessing the 674field directly via offsets into the packet. For example, to access fields address_type 675and address from the *gap_event_advertising_report* event use following getters: 676 677<!-- --> 678 uint8_t address type = gap_event_advertising_report_get_address_type(event); 679 bd_addr_t address; 680 gap_event_advertising_report_get_address(event, address); 681 682 683## Bluetooth HCI Packet Logs {#sec:packetlogsHowTo} 684 685If things don't work as expected, having a look at the data exchanged 686between BTstack and the Bluetooth chipset often helps. 687 688For this, BTstack provides a configurable packet logging mechanism via hci_dump.h and the following implementations: 689 690 void hci_dump_init(const hci_dump_t * hci_dump_implementation); 691 692| Platform | File | Description | 693|----------|------------------------------|----------------------------------------------------| 694| POSIX | `hci_dump_posix_fs.c` | HCI log file for Apple PacketLogger and Wireshark | 695| POSIX | `hci_dump_posix_stdout.c` | Console output via printf | 696| Embedded | `hci_dump_embedded_stdout.c` | Console output via printf | 697| Embedded | `hci_dump_segger_stdout.c` | Console output via SEGGER RTT | 698| Embedded | `hci_dump_segger_binary.c` | HCI log file for Apple PacketLogger via SEGGER RTT | 699 700On POSIX systems, you can call *hci_dump_init* with a *hci_dump_posix_fs_get_instance()* and 701configure the path and output format with *hci_dump_posix_fs_open(const char * path, hci_dump_format_t format)* 702where format can be *HCI_DUMP_BLUEZ* or *HCI_DUMP_PACKETLOGGER*. 703The resulting file can be analyzed with Wireshark or the Apple's PacketLogger tool. 704 705On embedded systems without a file system, you either log to an UART console via printf or use SEGGER RTT. 706For printf output you pass *hci_dump_embedded_stdout_get_instance()* to *hci_dump_init()*. 707With RTT, you can choose between textual output similar to printf, and binary output. 708For textual output, you can provide the *hci_dump_segger_stdout_get_instance()*. 709 710It will log all HCI packets to the UART console via printf or RTT Terminal. 711If you capture the console output, incl. your own debug messages, you can use 712the create_packet_log.py tool in the tools folder to convert a text output into a 713PacketLogger file. 714 715For less overhead and higher logging speed, you can directly log in binary format by 716passing *hci_dump_segger_rtt_binary_get_instance()* and selecting the output format by 717calling *hci_dump_segger_rtt_binary_open(hci_dump_format_t format)* with the same format as above. 718 719 720In addition to the HCI packets, you can also enable BTstack's debug information by adding 721 722 #define ENABLE_LOG_INFO 723 #define ENABLE_LOG_ERROR 724 725to the btstack_config.h and recompiling your application. 726 727## Bluetooth Power Control {#sec:powerControl} 728 729In 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. 730The 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. 731 732To enable/disable discoverability, you can call: 733 734 /** 735 * @brief Allows to control if device is discoverable. OFF by default. 736 */ 737 void gap_discoverable_control(uint8_t enable); 738 739If 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. 740 741To enable/disable connectability, you can call: 742 743 /** 744 * @brief Override page scan mode. Page scan mode enabled by l2cap when services are registered 745 * @note Might be used to reduce power consumption while Bluetooth module stays powered but no (new) 746 * connections are expected 747 */ 748 void gap_connectable_control(uint8_t enable); 749 750For Bluetooth Low Energy, the radio is periodically used to broadcast advertisements that are used for both discovery and connection establishment. 751 752To enable/disable advertisements, you can call: 753 754 /** 755 * @brief Enable/Disable Advertisements. OFF by default. 756 * @param enabled 757 */ 758 void gap_advertisements_enable(int enabled); 759 760If 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. 761 762Finally, 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: 763 764 /** 765 * @brief Requests the change of BTstack power mode. 766 */ 767 int hci_power_control(HCI_POWER_MODE mode); 768 769with 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. 770