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