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