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_PCM_NBS_16KHZ | NBS is up/downsampled, use 16 kHz sample rate for NBS | 80 81### ENABLE_* directives {#sec:enableDirectives} 82BTstack properties: 83 84| \#define | Description | 85|-----------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------| 86| ENABLE_CLASSIC | Enable Classic related code in HCI and L2CAP | 87| ENABLE_BLE | Enable BLE related code in HCI and L2CAP | 88| ENABLE_EHCILL | Enable eHCILL low power mode on TI CC256x/WL18xx chipsets | 89| ENABLE_H5 | Enable support for SLIP mode in `btstack_uart.h` drivers for HCI H5 ('Three-Wire Mode') | 90| ENABLE_LOG_DEBUG | Enable log_debug messages | 91| ENABLE_LOG_ERROR | Enable log_error messages | 92| ENABLE_LOG_INFO | Enable log_info messages | 93| ENABLE_SCO_OVER_HCI | Enable SCO over HCI for chipsets (if supported) | 94| ENABLE_SCO_OVER_PCM | Enable SCO ofer PCM/I2S for chipsets (if supported) | 95| ENABLE_HFP_WIDE_BAND_SPEECH | Enable support for mSBC codec used in HFP profile for Wide-Band Speech | 96| ENABLE_HFP_AT_MESSAGES | Enable `HFP_SUBEVENT_AT_MESSAGE_SENT` and `HFP_SUBEVENT_AT_MESSAGE_RECEIVED` events | 97| ENABLE_LE_PERIPHERAL | Enable support for LE Peripheral Role in HCI and Security Manager | 98| ENABLE_LE_CENTRAL | Enable support for LE Central Role in HCI and Security Manager | 99| ENABLE_LE_SECURE_CONNECTIONS | Enable LE Secure Connections | 100| ENABLE_LE_PROACTIVE_AUTHENTICATION | Enable automatic encryption for bonded devices on re-connect | 101| ENABLE_GATT_CLIENT_PAIRING | Enable GATT Client to start pairing and retry operation on security error | 102| ENABLE_MICRO_ECC_FOR_LE_SECURE_CONNECTIONS | Use [micro-ecc library](https://github.com/kmackay/micro-ecc) for ECC operations | 103| ENABLE_LE_DATA_LENGTH_EXTENSION | Enable LE Data Length Extension support | 104| ENABLE_LE_EXTENDED_ADVERTISING | Enable extended advertising and scanning | 105| ENABLE_LE_PERIODIC_ADVERTISING | Enable periodic advertising and scanning | 106| ENABLE_LE_SIGNED_WRITE | Enable LE Signed Writes in ATT/GATT | 107| ENABLE_LE_PRIVACY_ADDRESS_RESOLUTION | Enable address resolution for resolvable private addresses in Controller | 108| ENABLE_CROSS_TRANSPORT_KEY_DERIVATION | Enable Cross-Transport Key Derivation (CTKD) for Secure Connections | 109| ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE | Enable Enhanced Retransmission Mode for L2CAP Channels. Mandatory for AVRCP Browsing | 110| ENABLE_L2CAP_LE_CREDIT_BASED_FLOW_CONTROL_MODE | Enable LE credit-based flow-control mode for L2CAP channels | 111| ENABLE_L2CAP_ENHANCED_CREDIT_BASED_FLOW_CONTROL_MODE | Enable Enhanced credit-based flow-control mode for L2CAP Channels | 112| ENABLE_HCI_CONTROLLER_TO_HOST_FLOW_CONTROL | Enable HCI Controller to Host Flow Control, see below | 113| ENABLE_HCI_SERIALIZED_CONTROLLER_OPERATIONS | Serialize Inquiry, Remote Name Request, and Create Connection operations | 114| ENABLE_ATT_DELAYED_RESPONSE | Enable support for delayed ATT operations, see [GATT Server](profiles/#sec:GATTServerProfile) | 115| ENABLE_BCM_PCM_WBS | Enable support for Wide-Band Speech codec in BCM controller, requires ENABLE_SCO_OVER_PCM | 116| ENABLE_CC256X_ASSISTED_HFP | Enable support for Assisted HFP mode in CC256x Controller, requires ENABLE_SCO_OVER_PCM | 117| Enable_RTK_PCM_WBS | Enable support for Wide-Band Speech codec in Realtek controller, requires ENABLE_SCO_OVER_PCM | 118| ENABLE_CC256X_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND | Enable workaround for bug in CC256x Flow Control during baud rate change, see chipset docs. | 119| ENABLE_CYPRESS_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND | Enable workaround for bug in CYW2070x Flow Control during baud rate change, similar to CC256x. | 120| ENABLE_LE_LIMIT_ACL_FRAGMENT_BY_MAX_OCTETS | Force HCI to fragment ACL-LE packets to fit into over-the-air packet | 121| 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 | 122| ENABLE_TLV_FLASH_WRITE_ONCE | Enable storing of emtpy tag instead of overwriting existing tag - required when flash value cannot be overwritten at all | 123| ENABLE_CONTROLLER_WARM_BOOT | Enable stack startup without power cycle (if supported/possible) | 124| ENABLE_SEGGER_RTT | Use SEGGER RTT for console output and packet log, see [additional options](#sec:rttConfiguration) | 125| ENABLE_EXPLICIT_CONNECTABLE_MODE_CONTROL | Disable calls to control Connectable Mode by L2CAP | 126| ENABLE_EXPLICIT_IO_CAPABILITIES_REPLY | Let application trigger sending IO Capabilities (Negative) Reply | 127| ENABLE_EXPLICIT_LINK_KEY_REPLY | Let application trigger sending Link Key (Negative) Response, allows for asynchronous link key lookup | 128| ENABLE_EXPLICIT_BR_EDR_SECURITY_MANAGER | Report BR/EDR Security Manager support in L2CAP Information Response | 129| ENABLE_EXPLICIT_DEDICATED_BONDING_DISCONNECT | Keep connection after dedicated bonding is complete | 130| ENABLE_CLASSIC_OOB_PAIRING | Enable support for classic Out-of-Band (OOB) pairing | 131| ENABLE_A2DP_EXPLICIT_CONFIG | Let application configure stream endpoint (skip auto-config of SBC endpoint) | 132| ENABLE_AVDTP_ACCEPTOR_EXPLICIT_START_STREAM_CONFIRMATION | allow accept or reject of stream start on A2DP_SUBEVENT_START_STREAM_REQUESTED | 133| ENABLE_LE_WHITELIST_TOUCH_AFTER_RESOLVING_LIST_UPDATE | Enable Workaround for Controller bug | 134| 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 | 135| ENABLE_CONTROLLER_DUMP_PACKETS | Dump number of packets in Controller per type for debugging | 136 137Notes: 138 139- 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. 140 141### HCI Controller to Host Flow Control 142In 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. 143 144Host buffer configuration for HCI Controller to Host Flow Control: 145 146| \#define | Description | 147|-------------------------|----------------------------------| 148| HCI_HOST_ACL_PACKET_NUM | Max number of ACL packets | 149| HCI_HOST_ACL_PACKET_LEN | Max size of HCI Host ACL packets | 150| HCI_HOST_SCO_PACKET_NUM | Max number of ACL packets | 151| HCI_HOST_SCO_PACKET_LEN | Max size of HCI Host SCO packets | 152 153### Memory configuration directives {#sec:memoryConfigurationHowTo} 154 155The structs for services, active connections and remote devices can be 156allocated in two different manners: 157 158- statically from an individual memory pool, whose maximal number of 159 elements is defined in the btstack_config.h file. To initialize the static 160 pools, you need to call at runtime *btstack_memory_init* function. An example 161 of memory configuration for a single SPP service with a minimal 162 L2CAP MTU is shown in Listing {@lst:memoryConfigurationSPP}. 163 164- dynamically using the *malloc/free* functions, if HAVE_MALLOC is 165 defined in btstack_config.h file. 166 167For 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. 168 169<!-- a name "lst:memoryConfiguration"></a--> 170<!-- --> 171 172| \#define | Description | 173|-------------------------------------------|----------------------------------------------------------------------------| 174| HCI_ACL_PAYLOAD_SIZE | Max size of HCI ACL payloads | 175| HCI_ACL_CHUNK_SIZE_ALIGNMENT | Alignment of ACL chunk size, can be used to align HCI transport writes | 176| HCI_INCOMING_PRE_BUFFER_SIZE | Number of bytes reserved before actual data for incoming HCI packets | 177| MAX_NR_BNEP_CHANNELS | Max number of BNEP channels | 178| MAX_NR_BNEP_SERVICES | Max number of BNEP services | 179| MAX_NR_BTSTACK_LINK_KEY_DB_MEMORY_ENTRIES | Max number of link key entries cached in RAM | 180| MAX_NR_GATT_CLIENTS | Max number of GATT clients | 181| MAX_NR_HCI_CONNECTIONS | Max number of HCI connections | 182| MAX_NR_HFP_CONNECTIONS | Max number of HFP connections | 183| MAX_NR_L2CAP_CHANNELS | Max number of L2CAP connections | 184| MAX_NR_L2CAP_SERVICES | Max number of L2CAP services | 185| MAX_NR_RFCOMM_CHANNELS | Max number of RFOMMM connections | 186| MAX_NR_RFCOMM_MULTIPLEXERS | Max number of RFCOMM multiplexers, with one multiplexer per HCI connection | 187| MAX_NR_RFCOMM_SERVICES | Max number of RFCOMM services | 188| MAX_NR_SERVICE_RECORD_ITEMS | Max number of SDP service records | 189| MAX_NR_SM_LOOKUP_ENTRIES | Max number of items in Security Manager lookup queue | 190| MAX_NR_WHITELIST_ENTRIES | Max number of items in GAP LE Whitelist to connect to | 191| MAX_NR_LE_DEVICE_DB_ENTRIES | Max number of items in LE Device DB | 192 193The memory is set up by calling *btstack_memory_init* function: 194 195 btstack_memory_init(); 196 197<!-- a name "lst:memoryConfigurationSPP"></a--> 198<!-- --> 199 200Here's the memory configuration for a basic SPP server. 201 202 #define HCI_ACL_PAYLOAD_SIZE 52 203 #define MAX_NR_HCI_CONNECTIONS 1 204 #define MAX_NR_L2CAP_SERVICES 2 205 #define MAX_NR_L2CAP_CHANNELS 2 206 #define MAX_NR_RFCOMM_MULTIPLEXERS 1 207 #define MAX_NR_RFCOMM_SERVICES 1 208 #define MAX_NR_RFCOMM_CHANNELS 1 209 #define MAX_NR_BTSTACK_LINK_KEY_DB_MEMORY_ENTRIES 3 210 211Listing: Memory configuration for a basic SPP server. {#lst:memoryConfigurationSPP} 212 213In 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. 214 215<!-- --> 216 217### Non-volatile memory (NVM) directives {#sec:nvmConfiguration} 218 219If 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: 220 221<!-- a name "lst:nvmDefines"></a--> 222<!-- --> 223 224| \#define | Description | 225|---------------------------|----------------------------------------------------------------------------------------------| 226| NVM_NUM_LINK_KEYS | Max number of Classic Link Keys that can be stored | 227| NVM_NUM_DEVICE_DB_ENTRIES | Max number of LE Device DB entries that can be stored | 228| NVN_NUM_GATT_SERVER_CCC | Max number of 'Client Characteristic Configuration' values that can be stored by GATT Server | 229 230### HCI Dump Stdout directives {#sec:hciDumpStdout} 231 232Allow to truncate HCI ACL and SCO packets to reduce console output for debugging audio applications. 233 234| \#define | Description | 235|------------------------------|-------------------------------------------| 236| HCI_DUMP_STDOUT_MAX_SIZE_ACL | Max size of ACL packets to log via stdout | 237| HCI_DUMP_STDOUT_MAX_SIZE_SCO | Max size of SCO packets to log via stdout | 238| HCI_DUMP_STDOUT_MAX_SIZE_ISO | Max size of ISO packets to log via stdout | 239 240### SEGGER Real Time Transfer (RTT) directives {#sec:rttConfiguration} 241 242[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. 243 244When 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: 245 246| \#define | Default | Description | 247|----------------------------------|-------------------------------|-------------------------------------------------------------------------------------------------------------------| 248| 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 | 249| SEGGER_RTT_PACKETLOG_CHANNEL | 1 | Channel to use for packet log. Channel 0 is used for terminal | 250| SEGGER_RTT_PACKETLOG_BUFFER_SIZE | 1024 | Size of outgoing ring buffer. Increase if you cannot block but get 'message skipped' warnings. | 251 252## Run-time configuration 253 254To allow code-reuse with different platforms 255as well as with new ports, the low-level initialization of BTstack and 256the hardware configuration has been extracted to the various 257*platforms/PLATFORM/main.c* files. The examples only contain the 258platform-independent Bluetooth logic. But let’s have a look at the 259common init code. 260 261Listing [below](#lst:btstackInit) shows a minimal platform setup for an 262embedded system with a Bluetooth chipset connected via UART. 263 264~~~~ {#lst:btstackInit .c caption="{Minimal platform setup for an embedded system}"} 265 266 int main(){ 267 // ... hardware init: watchdoch, IOs, timers, etc... 268 269 // setup BTstack memory pools 270 btstack_memory_init(); 271 272 // select embedded run loop 273 btstack_run_loop_init(btstack_run_loop_embedded_get_instance()); 274 275 // enable logging 276 hci_dump_init(hci_dump_embedded_stdout_get_instance()); 277 278 279 // init HCI 280 hci_transport_t * transport = hci_transport_h4_instance(); 281 hci_init(transport, NULL); 282 283 // setup example 284 btstack_main(argc, argv); 285 286 // go 287 btstack_run_loop_execute(); 288 } 289 290~~~~ 291 292First, BTstack’s memory pools are set up. Then, the standard run loop 293implementation for embedded systems is selected. 294 295The call to *hci_dump_init* configures BTstack to output all Bluetooth 296packets and its own debug and error message using printf with BTstack's 297millisecond tiomestamps.s as tim. 298The Python 299script *tools/create_packet_log.py* can be used to convert the console 300output into a Bluetooth PacketLogger format that can be opened by the OS 301X PacketLogger tool as well as by Wireshark for further inspection. When 302asking for help, please always include a log created with HCI dump. 303 304The *hci_init* function sets up HCI to use the HCI H4 Transport 305implementation. It doesn’t provide a special transport configuration nor 306a special implementation for a particular Bluetooth chipset. It makes 307use of the *remote_device_db_memory* implementation that allows for 308re-connects without a new pairing but doesn’t persist the bonding 309information. 310 311Finally, it calls *btstack_main()* of the actual example before 312executing the run loop. 313 314 315## Source tree structure {#sec:sourceTreeHowTo} 316 317The source tree has been organized to easily setup new projects. 318 319| Path | Description | 320|----------|------------------------------------------------------| 321| chipset | Support for individual Bluetooth Controller chipsets | 322| doc | Sources for BTstack documentation | 323| example | Example applications available for all ports | 324| platform | Support for special OSs and/or MCU architectures | 325| port | Complete port for a MCU + Chipset combinations | 326| src | Bluetooth stack implementation | 327| test | Unit and PTS tests | 328| tool | Helper tools for BTstack | 329 330The core of BTstack, including all protocol and profiles, is in *src/*. 331 332Support 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. 333 334To accommodate a particular Bluetooth chipset, the *chipset/* subfolders provide various btstack_chipset_* implementations. 335Please have a look at the existing ports in *port/*. 336 337## Run loop configuration {#sec:runLoopHowTo} 338 339To initialize BTstack you need to [initialize the memory](#sec:memoryConfigurationHowTo) 340and [the run loop](#sec:runLoopHowTo) respectively, then setup HCI and all needed higher 341level protocols. 342 343BTstack uses the concept of a run loop to handle incoming data and to schedule work. 344The run loop handles events from two different types of sources: data 345sources and timers. Data sources represent communication interfaces like 346an UART or an USB driver. Timers are used by BTstack to implement 347various Bluetooth-related timeouts. They can also be used to handle 348periodic events. In addition, most implementations also allow to trigger a poll 349of the data sources from interrupt context, or, execute a function from a different 350thread. 351 352Data sources and timers are represented by the *btstack_data_source_t* and 353*btstack_timer_source_t* structs respectively. Each of these structs contain 354at least a linked list node and a pointer to a callback function. All active timers 355and data sources are kept in link lists. While the list of data sources 356is unsorted, the timers are sorted by expiration timeout for efficient 357processing. Data sources need to be configured upon what event they are called back. 358They can be configured to be polled (*DATA_SOURCE_CALLBACK_POLL*), on read ready (*DATA_SOURCE_CALLBACK_READ*), 359or on write ready (*DATA_SOURCE_CALLBACK_WRITE*). 360 361Timers are single shot: a timer will be removed from the timer list 362before its event handler callback is executed. If you need a periodic 363timer, you can re-register the same timer source in the callback 364function, as shown in Listing [PeriodicTimerHandler]. Note that BTstack 365expects to get called periodically to keep its time, see Section 366[on time abstraction](#sec:timeAbstractionPorting) for more on the 367tick hardware abstraction. 368 369BTstack provides different run loop implementations that implement the *btstack_run_loop_t* interface: 370 371- CoreFoundation: implementation for iOS and OS X applications 372- Embedded: the main implementation for embedded systems, especially without an RTOS. 373- FreeRTOS: implementation to run BTstack on a dedicated FreeRTOS thread 374- POSIX: implementation for POSIX systems based on the select() call. 375- Qt: implementation for the Qt applications 376- WICED: implementation for the Broadcom WICED SDK RTOS abstraction that wraps FreeRTOS or ThreadX. 377- Windows: implementation for Windows based on Event objects and WaitForMultipleObjects() call. 378 379Depending on the platform, data sources are either polled (embedded, FreeRTOS), or the platform provides a way 380to wait for a data source to become ready for read or write (CoreFoundation, POSIX, Qt, Windows), or, 381are not used as the HCI transport driver and the run loop is implemented in a different way (WICED). 382In any case, the callbacks must be explicitly enabled with the *btstack_run_loop_enable_data_source_callbacks(..)* function. 383 384In your code, you'll have to configure the run loop before you start it 385as shown in Listing [listing:btstackInit]. The application can register 386data sources as well as timers, e.g., for periodical sampling of sensors, or 387for communication over the UART. 388 389The run loop is set up by calling *btstack_run_loop_init* function and providing 390an instance of the actual run loop. E.g. for the embedded platform, it is: 391 392<!-- --> 393 394 btstack_run_loop_init(btstack_run_loop_embedded_get_instance()); 395 396If the run loop allows to trigger polling of data sources from interrupt context, 397*btstack_run_loop_poll_data_sources_from_irq*. 398 399On multi-threaded environments, e.g., FreeRTOS, POSIX, WINDOWS, 400*btstack_run_loop_execute_code_on_main_thread* can be used to schedule a callback on the main loop. 401 402The complete Run loop API is provided [here](appendix/apis/#sec:runLoopAPIAppendix). 403 404 405### Run Loop Embedded 406 407In the embedded run loop implementation, data sources are constantly polled and 408the system is put to sleep if no IRQ happens during the poll of all data sources. 409 410The complete run loop cycle looks like this: first, the callback 411function of all registered data sources are called in a round robin way. 412Then, the callback functions of timers that are ready are executed. 413Finally, it will be checked if another run loop iteration has been 414requested by an interrupt handler. If not, the run loop will put the MCU 415into sleep mode. 416 417Incoming data over the UART, USB, or timer ticks will generate an 418interrupt and wake up the microcontroller. In order to avoid the 419situation where a data source becomes ready just before the run loop 420enters sleep mode, an interrupt-driven data source has to call the 421*btstack_run_loop_poll_data_sources_from_irq* function. The call to 422*btstack_run_loop_poll_data_sources_from_irq* sets an 423internal flag that is checked in the critical section just before 424entering sleep mode causing another run loop cycle. 425 426To enable the use of timers, make sure that you defined HAVE_EMBEDDED_TICK or HAVE_EMBEDDED_TIME_MS in the 427config file. 428 429While there is no threading, *btstack_run_loop_poll_data_sources_from_irq* allows to reduce stack size by 430scheduling a continuation. 431 432### Run Loop FreeRTOS 433 434The FreeRTOS run loop is used on a dedicated FreeRTOS thread and it uses a FreeRTOS queue to schedule callbacks on the run loop. 435In each iteration: 436 437- all data sources are polled 438- all scheduled callbacks are executed 439- all expired timers are called 440- finally, it gets the next timeout. It then waits for a 'trigger' or the next timeout, if set. 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 POSIX 446 447The data sources are standard File Descriptors. In the run loop execute implementation, 448select() call is used to wait for file descriptors to become ready to read or write, 449while waiting for the next timeout. 450 451To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 452 453It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 454 455 456### Run loop CoreFoundation (OS X/iOS) 457 458This run loop directly maps BTstack's data source and timer source with CoreFoundation objects. 459It supports ready to read and write similar to the POSIX implementation. The call to 460*btstack_run_loop_execute()* then just calls *CFRunLoopRun()*. 461 462To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 463 464It currently only supports *btstack_run_loop_execute_code_on_main_thread*. 465 466 467### Run Lop Qt 468 469This run loop directly maps BTstack's data source and timer source with Qt Core objects. 470It supports ready to read and write similar to the POSIX implementation. 471 472To enable the use of timers, make sure that you defined HAVE_POSIX_TIME in the config file. 473 474It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 475 476 477### Run loop Windows 478 479The data sources are Event objects. In the run loop implementation WaitForMultipleObjects() call 480is all is used to wait for the Event object to become ready while waiting for the next timeout. 481 482It supports both *btstack_run_loop_poll_data_sources_from_irq* as well as *btstack_run_loop_execute_code_on_main_thread*. 483 484 485### Run loop WICED 486 487WICED SDK API does not provide asynchronous read and write to the UART and no direct way to wait for 488one or more peripherals to become ready. Therefore, BTstack does not provide direct support for data sources. 489Instead, the run loop provides a message queue that allows to schedule functions calls on its thread via 490*btstack_run_loop_wiced_execute_code_on_main_thread()*. 491 492The HCI transport H4 implementation then uses two lightweight threads to do the 493blocking read and write operations. When a read or write is complete on 494the helper threads, a callback to BTstack is scheduled. 495 496It currently only supports *btstack_run_loop_execute_code_on_main_thread*. 497 498 499## HCI Transport configuration 500 501The HCI initialization has to adapt BTstack to the used platform. The first 502call is to *hci_init()* and requires information about the HCI Transport to use. 503The arguments are: 504 505- *HCI Transport implementation*: On embedded systems, a Bluetooth 506 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. 507 These are accessed by linking the appropriate file, e.g., 508 [platform/embedded/hci_transport_h4_embedded.c]() 509 and then getting a pointer to HCI Transport implementation. 510 For more information on adapting HCI Transport to different 511 environments, see [here](porting/#sec:hciTransportPorting). 512 513<!-- --> 514 515 hci_transport_t * transport = hci_transport_h4_instance(); 516 517- *HCI Transport configuration*: As the configuration of the UART used 518 in the H4 transport interface are not standardized, it has to be 519 provided by the main application to BTstack. In addition to the 520 initial UART baud rate, the main baud rate can be specified. The HCI 521 layer of BTstack will change the init baud rate to the main one 522 after the basic setup of the Bluetooth module. A baud rate change 523 has to be done in a coordinated way at both HCI and hardware level. 524 For example, on the CC256x, the HCI command to change the baud rate 525 is sent first, then it is necessary to wait for the confirmation event 526 from the Bluetooth module. Only now, can the UART baud rate changed. 527 528<!-- --> 529 530 hci_uart_config_t* config = &hci_uart_config; 531 532After these are ready, HCI is initialized like this: 533 534 hci_init(transport, config); 535 536 537In addition to these, most UART-based Bluetooth chipset require some 538special logic for correct initialization that is not covered by the 539Bluetooth specification. In particular, this covers: 540 541- setting the baudrate 542- setting the BD ADDR for devices without an internal persistent storage 543- upload of some firmware patches. 544 545This is provided by the various *btstack_chipset_t* implementation in the *chipset/* subfolders. 546As an example, the *bstack_chipset_cc256x_instance* function returns a pointer to a chipset struct 547suitable for the CC256x chipset. 548 549<!-- --> 550 551 btstack_chipset_t * chipset = btstack_chipset_cc256x_instance(); 552 hci_set_chipset(chipset); 553 554 555In some setups, the hardware setup provides explicit control of Bluetooth power and sleep modes. 556In this case, a *btstack_control_t* struct can be set with *hci_set_control*. 557 558Finally, the HCI implementation requires some form of persistent storage for link keys generated 559during either legacy pairing or the Secure Simple Pairing (SSP). This commonly requires platform 560specific code to access the MCU’s EEPROM of Flash storage. For the 561first steps, BTstack provides a (non) persistent store in memory. 562For more see [here](porting/#sec:persistentStoragePorting). 563 564<!-- --> 565 566 btstack_link_key_db_t * link_key_db = &btstack_link_key_db_memory_instance(); 567 btstack_set_link_key_db(link_key_db); 568 569 570The higher layers only rely on BTstack and are initialized by calling 571the respective *\*_init* function. These init functions register 572themselves with the underlying layer. In addition, the application can 573register packet handlers to get events and data as explained in the 574following section. 575 576 577## Services {#sec:servicesHowTo} 578 579One important construct of BTstack is *service*. A service represents a 580server side component that handles incoming connections. So far, BTstack 581provides L2CAP, BNEP, and RFCOMM services. An L2CAP service handles incoming 582connections for an L2CAP channel and is registered with its protocol 583service multiplexer ID (PSM). Similarly, an RFCOMM service handles 584incoming RFCOMM connections and is registered with the RFCOMM channel 585ID. Outgoing connections require no special registration, they are 586created by the application when needed. 587 588 589## Packet handlers configuration {#sec:packetHandlersHowTo} 590 591 592After the hardware and BTstack are set up, the run loop is entered. From 593now on everything is event driven. The application calls BTstack 594functions, which in turn may send commands to the Bluetooth module. The 595resulting events are delivered back to the application. Instead of 596writing a single callback handler for each possible event (as it is done 597in some other Bluetooth stacks), BTstack groups events logically and 598provides them over a single generic interface. Appendix 599[Events and Errors](generated/appendix/#sec:eventsAndErrorsAppendix) 600summarizes the parameters and event 601codes of L2CAP and RFCOMM events, as well as possible errors and the 602corresponding error codes. 603 604Here is summarized list of packet handlers that an application might 605use: 606 607- HCI event handler - allows to observer HCI, GAP, and general BTstack events. 608 609- L2CAP packet handler - handles LE Connection parameter requeset updates 610 611- L2CAP service packet handler - handles incoming L2CAP connections, 612 i.e., channels initiated by the remote. 613 614- L2CAP channel packet handler - handles outgoing L2CAP connections, 615 i.e., channels initiated internally. 616 617- RFCOMM service packet handler - handles incoming RFCOMM connections, 618 i.e., channels initiated by the remote. 619 620- RFCOMM channel packet handler - handles outgoing RFCOMM connections, 621 i.e., channels initiated internally. 622 623These handlers are registered with the functions listed in Table 624{@tbl:registeringFunction}. 625 626 627| Packet Handler | Registering Function | 628|-------------------------------|--------------------------------------------------------------------------| 629| HCI packet handler | hci_add_event_handler | 630| L2CAP packet handler | l2cap_register_packet_handler | 631| L2CAP service packet handler | l2cap_register_service | 632| L2CAP channel packet handler | l2cap_create_channel | 633| RFCOMM service packet handler | rfcomm_register_service and rfcomm_register_service_with_initial_credits | 634| RFCOMM channel packet handler | rfcomm_create_channel and rfcomm_create_channel_with_initial_credits | 635 636Table: Functions for registering packet handlers. {#tbl:registeringFunction} 637 638HCI, GAP, and general BTstack events are delivered to the packet handler 639specified by *hci_add_event_handler* function. In L2CAP, 640BTstack discriminates incoming and outgoing connections, i.e., event and 641data packets are delivered to different packet handlers. Outgoing 642connections are used access remote services, incoming connections are 643used to provide services. For incoming connections, the packet handler 644specified by *l2cap_register_service* is used. For outgoing 645connections, the handler provided by *l2cap_create_channel* 646is used. RFCOMM and BNEP are similar. 647 648The application can register a single shared packet handler for all 649protocols and services, or use separate packet handlers for each 650protocol layer and service. A shared packet handler is often used for 651stack initialization and connection management. 652 653Separate packet handlers can be used for each L2CAP service and outgoing 654connection. For example, to connect with a Bluetooth HID keyboard, your 655application could use three packet handlers: one to handle HCI events 656during discovery of a keyboard registered by 657*l2cap_register_packet_handler*; one that will be registered to an 658outgoing L2CAP channel to connect to keyboard and to receive keyboard 659data registered by *l2cap_create_channel*; after that 660keyboard can reconnect by itself. For this, you need to register L2CAP 661services for the HID Control and HID Interrupt PSMs using 662*l2cap_register_service*. In this call, you’ll also specify 663a packet handler to accept and receive keyboard data. 664 665All events names have the form MODULE_EVENT_NAME now, e.g., *gap_event_-advertising_report*. 666To facilitate working with 667events and get rid of manually calculating offsets into packets, BTstack provides 668auto-generated getters for all fields of all events in *src/hci_event.h*. All 669functions are defined as static inline, so they are not wasting any program memory 670if not used. If used, the memory footprint should be identical to accessing the 671field directly via offsets into the packet. For example, to access fields address_type 672and address from the *gap_event_advertising_report* event use following getters: 673 674<!-- --> 675 uint8_t address type = gap_event_advertising_report_get_address_type(event); 676 bd_addr_t address; 677 gap_event_advertising_report_get_address(event, address); 678 679 680## Bluetooth HCI Packet Logs {#sec:packetlogsHowTo} 681 682If things don't work as expected, having a look at the data exchanged 683between BTstack and the Bluetooth chipset often helps. 684 685For this, BTstack provides a configurable packet logging mechanism via hci_dump.h and the following implementations: 686 687 void hci_dump_init(const hci_dump_t * hci_dump_implementation); 688 689| Platform | File | Description | 690|----------|------------------------------|----------------------------------------------------| 691| POSIX | `hci_dump_posix_fs.c` | HCI log file for Apple PacketLogger and Wireshark | 692| POSIX | `hci_dump_posix_stdout.c` | Console output via printf | 693| Embedded | `hci_dump_embedded_stdout.c` | Console output via printf | 694| Embedded | `hci_dump_segger_stdout.c` | Console output via SEGGER RTT | 695| Embedded | `hci_dump_segger_binary.c` | HCI log file for Apple PacketLogger via SEGGER RTT | 696 697On POSIX systems, you can call *hci_dump_init* with a *hci_dump_posix_fs_get_instance()* and 698configure the path and output format with *hci_dump_posix_fs_open(const char * path, hci_dump_format_t format)* 699where format can be *HCI_DUMP_BLUEZ* or *HCI_DUMP_PACKETLOGGER*. 700The resulting file can be analyzed with Wireshark or the Apple's PacketLogger tool. 701 702On embedded systems without a file system, you either log to an UART console via printf or use SEGGER RTT. 703For printf output you pass *hci_dump_embedded_stdout_get_instance()* to *hci_dump_init()*. 704With RTT, you can choose between textual output similar to printf, and binary output. 705For textual output, you can provide the *hci_dump_segger_stdout_get_instance()*. 706 707It will log all HCI packets to the UART console via printf or RTT Terminal. 708If you capture the console output, incl. your own debug messages, you can use 709the create_packet_log.py tool in the tools folder to convert a text output into a 710PacketLogger file. 711 712For less overhead and higher logging speed, you can directly log in binary format by 713passing *hci_dump_segger_rtt_binary_get_instance()* and selecting the output format by 714calling *hci_dump_segger_rtt_binary_open(hci_dump_format_t format)* with the same format as above. 715 716 717In addition to the HCI packets, you can also enable BTstack's debug information by adding 718 719 #define ENABLE_LOG_INFO 720 #define ENABLE_LOG_ERROR 721 722to the btstack_config.h and recompiling your application. 723 724## Bluetooth Power Control {#sec:powerControl} 725 726In 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. 727The 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. 728 729To enable/disable discoverability, you can call: 730 731 /** 732 * @brief Allows to control if device is discoverable. OFF by default. 733 */ 734 void gap_discoverable_control(uint8_t enable); 735 736If 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. 737 738To enable/disable connectability, you can call: 739 740 /** 741 * @brief Override page scan mode. Page scan mode enabled by l2cap when services are registered 742 * @note Might be used to reduce power consumption while Bluetooth module stays powered but no (new) 743 * connections are expected 744 */ 745 void gap_connectable_control(uint8_t enable); 746 747For Bluetooth Low Energy, the radio is periodically used to broadcast advertisements that are used for both discovery and connection establishment. 748 749To enable/disable advertisements, you can call: 750 751 /** 752 * @brief Enable/Disable Advertisements. OFF by default. 753 * @param enabled 754 */ 755 void gap_advertisements_enable(int enabled); 756 757If 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. 758 759Finally, 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: 760 761 /** 762 * @brief Requests the change of BTstack power mode. 763 */ 764 int hci_power_control(HCI_POWER_MODE mode); 765 766with 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. 767