xref: /btstack/CHANGELOG.md (revision 7d5c2f20da25e56e90bc87f1f8b57caba59706da)

# Change Log
All notable changes to this project will be documented in this file.

The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).

---

## [Unreleased]

### Fixed
- L2CAP: use connection handle for channel lookups
### Added
### Changed


## Release v1.2

### Fixed
- L2CAP: trigger pairing for outgoing LE Data Channels if security level insufficient
- SM: fix update of sc flag for re-encrypted connection in peripheral role
- SM: send security request on re-connect if bonded and `ENABLE_LE_PROACTIVE_AUTHENTICATION` is defined
- ESP32: fix audio sink driver

### Added
- GAP: `gap_delete_bonding` removes device from LE Resolving List and from discards LE bonding information
- GATT Client: delete bonding information if re-encryption fails and `ENABLE_LE_PROACTIVE_AUTHENTICATION` is not defined
- GATT Client: gatt_client_set_required_security_level allows to set required minimum security level for all GATT requests
- SM: emit events for re-encryption started/complete

### Changed
- AVRCP Controller: allow to send multiple absolute volume commands without waiting for response.
- GAP: replaced `ENABLE_LE_CENTRAL_AUTO_ENCRYPION` with `ENABLE_LE_PROACTIVE_AUTHENTICATION`


## Changes October 2020

### Fixed
- AVDTP Initiator: avoid use of remote seid for stream endpoint lookup, fixes issue with two connected devices
- AVDTP Source: buffer for SBC media codec information got discarded, leading to invalid Set Configuration command in second connection
- SM: only trigger Cross-Transport Key Derivation (CTKD) when bonding is enabled
- SM: set LinkKey flag to request CTKD if enabled
- SM: store CTKD key with Public Identity Address
- SM: only allow CTKD to overwrite existing link key if derived key has same or higher authentication
- SM: start SMP Timeout when sending Security Request
- HFP HF: fix response to AG Codec Selection while waiting for OK of parallel command
- HCI: fix reject of LE remote connection param request via HCI

### Added
- GAP: add `gap_get_link_key_for_bd_addr`
- GAP: add `gap_bonded` to check if bonding information is available for active connection
- SM: support h7 for CTKD

### Changed
- SM: Cross-Transport Key Derivation requires `ENABLE_CROSS_TRANSPORT_KEY_DERIVATION` now
- SM: block connection if encryption fails for bonded devices as Central
- SM: support pairing as Central after failed re-ecnryption


## Release v1.1

### Fixed
- AVRCP/AVCTP: report AVRCP 1.6 and AVCTP 1.4 in SDP record

### Added

### Changed


## Changes September 2020

### Fixed
- HFP: fix parsing of ranges e.g. in +CIND responses
- AVDTP, AVRCP: fix bugs due to transaction id overrun
- A2DP Source: fix issues with stream configuration by sink
- hci_dump: fix tv_us calculation for non-posix / embedded systems with binary output

### Added
- `btstack_ring_buffer`: add `btstack_ring_buffer_reset` to reset it to initial state/empty
- GAP: Support for address resolution of resolvable private addresses by Controller with `ENABLE_LE_PRIVACY_ADDRESS_RESOLUTION`

### Changed
- AVDTP, AVRCP, HSP: schedule SDP query, avoids avoids 'command disallowed' if SDP client is busy
- HSP, HFP: allow to configure usable SCO packet types
- cc256x: update CC256xC init script to v1.4
- A2DP Source: use Get All Capabilities if supported by remote get Delay Reporting capability

## Changes August 2020

### Fixed
- ESP32: fix authentication for incoming Secure Connections
- AVDTP: Fix forwarding of Delay reports
- STM32-F4Discovery: fix pan_lwip_http_server by increasing HCI_ACL_PAYLOAD_SIZE
- tool/create_packet_log: basic support for 16-bit Unicode log files from Windows

### Added
- `btstack_run_loop_base`: added `btstack_run_loop_base_dump_timer`
- GAP: request role change for classic connection via `gap_request_role`
- GAP: LE Whitelist API with `gap_le_whitelist_x` with x = add, remove, clear and new `gap_connect_with_whitelist`
- SDP Client: add sdp_client_register_query_callback() allows to register query request instead of polling sdp_client_ready()
- BNEP lwIP: add `bnep_lwip_connect` to establish BNEP connection and manage lwIP network interface
- New `btstack_linked_queue` utility, a linked list-based queue with first-in-first-out semantics and constant time enqueue/dequeue operations
- btstack_tlv_posix: add `btstack_tlv_posix_deinit`
- New `btpclient` for use with [auto-pts project](https://github.com/intel/auto-pts)

### Changed
- GAP: treat AES-CCM encrypted connection as mutually authenticated (BIAS)
- GAP: 'gap_auto_connect_x' API deprecated. Please direclty manage LE Whitelist with `gap_le_whitelist_*` functions and call `gap_connect_with_whitelist` instead
- example/hid_host_demo: try to become master for incoming connections
- btstack_run_loop: use btstack_assert instead of local while(true)
- att_db_util: allow to reset att_db via `att_db_util_init`

## Changes July 2020

### Fixed
- AVDTP: fix invalid response for Get Capabilities request if Delay Reporting was supported
- AVDTP: handle concurrent signaling establishment with reject and retry

### Added
- example/hid_host_demo: support reconnect from HID device
- Crypto: support software AES128 for AES-CCM operations
- AVRCP: introduced AVRCP_FEATURE_MASK_* as alternative to avrcp_controller_supported_feature_t and avrcp_target_supported_feature_t enums
- btstack_audio: add set_volume() to sink and set_gain() to source interfaces, minimal volume control for portaudio playback
- AVDTP: renamed definition of supported features from AVDTP_SOURCE_SF_ and AVDTP_SINK_SF_ to AVDTP_SOURCE_FEATURE_MASK_ and AVDTP_SINK_FEATURE_MASK_ respectively
- GAP: Provide gap_get_role to query master/slave role for HCI connection handle
- GAP: Provide gap_pin_code_response_binary to use binary data as PIN, e.g. for pairing with Nintendo Wii Remote

### Changed
- GAP: set minimum required encryption key size for Classic connections back from 16 to 7, matching the Core spec


## Changes June 2020

### Fixed
- HFP: Fix parsing of empty fields, e.g. phone number in +CLCC and other AT commands
- SM: Fix validation of confirm value for secure connection Passkey entry
- AVRCP: handle concurrent signaling establishment with reject and retry

### Added
- GAP: Detect Secure Connection -> Legacy Connection Downgrade Attack by remote features and actual encryption type (BIAS)
- GAP: Mutual authentication: request authentication after Classic connection got encrypted (BIAS)
- Windows port for Dialog DA14585 connected via serial port

## Changes
- CVSD PLC: treat zero frames as good and allow to mark data as bad, e.g. if reported by Controller as erroneous

## Changes May 2020

### Fixed
- hfp_hf, hsp_hs: use eSCO params in accept sco connection only for incoming eSCO connections
- pbap_client: fix PBAP UUID len on connect message
- SM: fix secure connection pairing as peripheral when local user confirmation happens after remote one
- A2DP Source: only connect to remote sink stream endpoints
- btstack_hal_flash_memory: fix write of 0xff bytes to simulated flash
- hsp_hs: fix disconnect if audio not connected
- hsp_ag: fix accept incoming connection

### Added
- example/le_mitm: MITM implementation that forwards ATT PDUs and allows for pairing
- GAP: gap_set_security_level sets required security level for incoming and outgoing connections
- cc256x: allow to specify power vector for each modulation type
- FreeRTOS: btstack_run_loop_freertos_trigger_exit allows to request run loop exit
- SM: support LE Secure Connections Only mode with sm_set_secure_connections_only_mode
- GAP: enable BR/EDR Secure Connections if supported, add gap_secure_connections_enable

### Changed
- L2CAP ERTM: send extended features request only once per HCI connection


## Changes April 2020

### Fixed
- hog_mouse_demo/hog_keyboard_demo: handle set protocol mode = boot protocol mode
- HCI: only update BD_ADDR placeholder in shortened and complete name in EIR data, limit device name to 240/248 bytes

### Added
- GAP: gap_set_allow_role_switch allows to prevent role switch in outgoing classic ACL connections
- example: hog_boot_host_demo implements an HID-over-GATT Boot Host that supports keyboard and mouse
- HCI: add ENABLE_LE_LIMIT_ACL_FRAGMENT_BY_MAX_OCTETS that forces fragmentation of ACL-LE packets to fit into over-the-air packet

### Changed
- Broadcom/Cypress: wait 300 ms after PatchRAM update in hci.c to assert Controller is ready
- esp32: provide esp-idf/component/btstack/btstack_port_esp32.c and only minimal app_main in template/main/main.c
- att_db: skip att_read_callback for ATT Read Blob Request if offset == value_len


## Changes March 2020

### Fixed
- GAP: fixed gap_set_scan_parameters() if issued right before gap_start_scan()
- HCI: only send HCI Read Local Encryption Key Size if supported by Controller

### Added
- GATT Client: allow to register for any notification/indication and/or any connection
- HCI: added hci_read_inquiry_scan_activity and hci_write_inquiry_scan_activity commands
- chipset: assert hci packet buffers are suitable for firmware upload or patches (atwilc3000,bcm,cc256x,intel)
- btstack_util: added btstack_replace_bd_addr_placeholder

### Changed
- AVRCP Target: volume in avrcp_target_volume_changed is reported as current value in interim response to register for volume change notifications
- SDP Client: query attributes 0x0000..0xffff instead of 0x0001..0xffff to match other stacks / improve compatibility with bad sdp server implementations


## Changes Februar 2020

### Fixed
- AVRCP Target: fix reporting of PLAYBACK_STATUS_CHANGED
- HCI: handle reconnect request for Classic and LE connections triggered by packet handler for Disconnection Complete Event

### Changed
- hid_host_mode: allow sniff mode

### Added
- port/qt-usb and port/qt-h4: integrate BTstack Qt run loop for Unix- and Win32-based Qt application connected to Bluetooth module via H4 over serial port or USB


## Changes January 2020

### Fixed
- L2CAP ERTM: avoid read-after-free on decline of incoming connection
- GATT Client: set uuid16 to zero when deserializing uuid128 services, characteristics, and descriptors
- att_db_util: fix realloc of att db buffer for large attributes
- btstack_tlv_posix: only keep last value in memory, fix delete operation
- l2cap_signaling: use packet boundary flags 0x00 for LE signaling packets (ignoring hci_non_flushable_packet_boundary_flag_supported())

### Added
- att_db_util: provide GATT Database Hash via att_db_util_hash_calc
- GATT Compiler: provide GATT Database Hash via GATT_DATABASE_HASH Characteristic
- ATT Server: validate request pdu length

### Changed
- Crypto: update AES-CMAC implementation to access all message bytes sequentially


## Changes December 2019

### Fixed
- example/pan_lwip_http_server: use Network Access Point, CoD
- sm: emit pairing complete in master role when no keys are distributed / bonding disabled

### Added

### Changed
- Updated CC256x initscript: CC256xC v1.3
- ESP32: add CMake project files


## Changes November 2019

### Fixed
- AVDTP Source: return correct `avdtp_cid` and `local_seid` in `AVDTP_SUBEVENT_STREAMING_CAN_SEND_MEDIA_PACKET_NOW`
- L2CAP: send LE Data Channel SDUs round robin with other data
- L2CAP ERTM: send ERTM I-frames round robin with other data

### Added
- ATT Server: return error if request to send now for Notification or Indication already registered
- Linked List: return if item was added for `btstack_linked_list_add[_tail]`
- btstack_run_loop_remove: return bool true if timer/data source was removed
- segger-rtt: allow to configure with `SEGGER_RTT_PACKETLOG_*` directives, update to v6.54
- GAP: support setting Link Supervision Timetout for outgoing Classic connections using `gap_set_link_supervision_timeout`
- lwip: add download test files to http server demo

### Changed
- Linked List: return bool true if item was removed


## Changes October 2019

### Fixed

### Added
- `btstack_bool.h`: provide boolean type 'bool' via `<stdbool.h>` or as backport
- provide `btstack_assert(condition)`
- H4 Transport: avoid calling `hci_transport_h4_trigger_next_read` when transport is closed

### Changed
- libusb and posix ports: store bonding information in TLV


## Changes September 2019

### Fixed
- L2CAP ERTM: assert that packet can be stored in fragment buffers in ertm
- L2CAP ERTM: reject incoming connection if ERTM is configured as mandatory but not supported by remote
- GATT Client: allow Write Without Response independent of other requests

### Added
- GAP: allow to reject GAP classic connection via gap_register_classic_connection_filter
- GAP: support reading RSSI for Classic+LE using gap_read_rssi. Emits `GAP_EVENT_RSSI_MEASUREMENT`

### Changed
- Bluetooth and BTstack Error Codes and Events: collect status codes in bluetooth.h and events in btstack_defines.h
- bluetooth.h: extract internal defintitions to respective protocol layers
- Updated CC256x initscripts (CC256xB v1.8, CC256xC v1.2, CC256xC v1.2)


## Changes August 2019

### Fixed
- POSIX, WICED, Windows, FreeRTOS run loops: handle time_ms overrun after 49 days
- RFCOMM: accept incoming L2CAP connection in Basic mode if ERTM is enabled but not requested for this connection
- RFCOMM: limit RFCOMM MTU by local L2CAP MTU for outgoing connections (only revelvant for ERTM)
- L2CAP ERTM: stop timers on disconnect
- L2CAP ERTM: fix sending of segmented SDUs
- L2CAP ERTM: handle unsupported Information Response
- SM: generate local nonce for confirm value in JW+NC+PK in Secure Connections Responder role

### Added
- `btstack_run_loop_base`: portable implementation of timer and data source management as base for platform specific implementations

## Changed
- FreeRTOS: use xQueueCreateStatic (static variant of xQueueCreate) if available for static memory-only setups
- L2CAP ERTM: handle invalid Information Response (assume no extended features supported)
- POSIX: use monotonic clock as timebase if available
- HCI Transport H4/H5/EM9304 SPI: ignore block read/sent from UART driver when closed
- HCI: Read Encryption Key Size after encryption was enabled
- Errata 11838:
  - GAP: gap_set_required_encryption_key_size allows to set the required key size, default = 16 (max)
  - GAP: validate encryption key size to emit GAP Security Levels

## Changes July 2019

### Fixed
- SM: Fixed regression introduced in f3582630
- L2CAP: avoid reading l2cap signaling command len out of bounds
- HCI Transport H4/H5/EM9304 SPI: fix payload size checks (also for 8/16-bit platforms)

### Changed
- SM: Start encryption upon receiving slave securiy request if bonded
- hci: use 2 as HCI_INCOMING_PRE_BUFFER_SIZE in LE-only configuration for GATT Client

---

## Changes June 2019

### Changed
- FreeRTOS: use freertos/.. prefix to include FreeRTOS headers if HAVE_FREERTOS_INCLUDE_PREFIX is defined
- BNEP: add Connection Handle to BNEP_EVENT_CHANNEL_OPENED
- Examples: renamed le_counter to gatt_counter and le_streamer to le_streamer_server to indicate suppport for GATT over BR/EDR

### Fixed
- BNEP: Bluetooth address is stored in little-endian format for all BNEP_EVENT_*
- libusb: avoid use-after-free for SCO packets on disconnect

### Added
- example: pan_lwip_http_server using lwIP as network stack to implement PAN NAP service
- platform/lwip/bnep_lwip.c: BNEP lwIP adapter that forwards packets between BNEP service and lwIP
- ENABLE_GATT_OVER_CLASSIC enables support for GATT over BR/EDR in att_server

---

## Changes May 2019

### Changed
- ESP32: Configure SCO over HCI after power up
- btstack_tlv_flash_bank: support targets where a value cannot be overwritten with zero. When ENABLE_TLV_FLASH_EXPLICIT_DELETE_FIELD
  is defined, an explicit delete field is used to indicate an invalid entry.

### Fixed
- SM: Avoid potential use-after-free on immediate disconnect (lookup connection via con handle instead of storing pointer)

### Added
- gatt_client: emit query complete event for signed write operation
- hci_transport_h4: add workaround for flow control bug in CYW2070x, enable with ENABLE_CYPRESS_BAUDRATE_CHANGE_FLOWCONTROL_BUG_WORKAROUND

---

## Changes April 2019

### Changed
- ESP32: use micro-ecc from 3rd-party as esp-idf removed it in their 3.3 release

### Fixed
- hci: pad LE Scan response with zeroes
- SM: store local CSRK
- ATT DB: call write callback for validated signed writes
- ATT Server: abort signed write validation on incoming new request
- Bluetooth SIG web scraping tools updated
- libusb: compiles for FreeBSD

### Added

---

## Changes March 2019

### Changed
- use Makefile for stm32-f4discovery-cc256x port
- le_device_db: add secure_connection argument to le_device_db_encryption_set and le_device_db_encryption_get

### Fixed
- SM: Use provided authentication requirements in slave security request

### Added
- port/stm32-f4discovery-cc256x: add support for built-in MEMS microphone
- SM: Track if connection encryption is based on LE Secure Connection pairing
- ATT DB: Validate if connection encrypted is based on SC if requested
- att_db_util: support ATT_SECURITY_AUTHENTICATED_SC permission flag
- GATT Compiler: support READ_AUTHENTICATED and WRITE_AUTHENTICATED permsission flags
- ESP32: erase nvs flash is newer nvs version found
- libusb: add support for nRF52840-PCA10056 running Zephyr hci_usb example
- port/stm32-l073rz-nucleo-em9304 for Nucleo L073RZ with EM9304 DVK, replaces port/stm32-l053r8-nucleo-em9304

## Changes February 2019

### Changed
- example/a2dp_sink_demo: use linear resampling to fix sample rate drift
- btstack_audio: split interface into sink and source

### Fixed
- Crypto: fix lockup when stack is shutdown while waiting for result of HCI Command, e.g. LE Read Local P256 Public Key
- SM: Avoid SM_EVENT_PAIRING_COMPLETE with ERROR_CODE_REMOTE_USER_TERMINATED_CONNECTION after successful pairing in responder role

### Added
- example/a2dp_sink_demo: add target role, support volume control on both devices
- example/audio_duplex: playback audio audio source on audio sink (test audio path)
- btstack_audio_embedded: implement audio source path

---

## Changes January 2019

### Changed
- L2CAP: provide channel mode (basic/ertm) and fcs option in L2CAP_EVENT_CHANNEL_OPENED
- RFCOMM: support L2CAP ERTM. Callbacks passed to rfcomm_enable_l2cap_ertm() are used to manage ERTM buffers

### Added
- L2CAP: emit L2CAP_EVENT_ERTM_BUFFER_RELEASED if ERTM buffer not needed/used anymore
- L2CAP: add fcs_option to ERTM config l2cap_ertm_config_t
- HCI: validate advertisement data length field when generating GAP_EVENT_ADVERTISING_REPORT
- ad_parser: validate data element length fields in ad_iterator_has_more
- Raspberry Pi 3 A+/B+ port in port/raspi, starts without power cycle

### Fixed
- HCI: release outgoing buffer on disconnect if waiting to send another ACL fragment
- POSIX: use correct baudrate enums for baud rates higher than 921600 (Linux)
- Crypto: directly process queued crypto operation on HCI result

---

## Changes December 2018

### Added
- SM: generate and store ER / IR keys in TLV, unless manually set by application
- hci_dump: support PacketLogger or BlueZ format output via SEGGER RTT Channel 1 Up

### Fixed
- SM: fix internal buffer overrun during random address generation

## Changes November 2018

### Added
- GAP: gap_le_connection_interval provides connection interval for conn handle
- Nordic SPP Service Server: GATT service that emulates a serial port over BLE based on Nordic Semiconductor documentation.
- uBlox  SPP Service Server: GATT service that emulates a serial port over BLE based on uBlox documentation.
- SM: ENABLE_LE_CENTRAL_AUTO_ENCRYPTION triggers automatic encryption on connect to bonded devices
- SM: generate and store ER / IR keys in TLV, unless manually set by application

### Fixed
- SM: prevent random address updates if gap_random_address_set was used
- SM: fix internal buffer overrun that can cause storing of bonding information to fail
- SM: ignore Slave Security Request after sending own Pairing Request
- L2CAP: fix use after free on disconnect if ERTM is enabled
- HFP: Handle multiple commands/responses in single RFCOMM packet
- Memory Pools: clear all buffers before use

---

## Changes October 2018

### Added
- SDP Server: queue incoming connections when already connected instead of rejecting them
- GAP: Support enter/exit sniff mode via gap_sniff_mode_enter/exit. gap_set_default_link_policy_settings is needed to enable sniff mode in general.
- HIDS Device: GATT service that exposes HID reports intended for HID Devices, like keyboard and mouse.

### Fixed
- HCI: fix bug in gap_inquiry_stop that triggered additional GAP_EVENT_INQUIRY_COMPLETE instead of stopping the inquiry
- L2CAP: fix issue with outgoing connection before read remote supported complete when other channels exist
- L2CAP ERTM: allow SDU of szie MPS in first packet that contains L2CAP SDU Length
- L2CAP ERTM: fix memory corruption triggered if local_mtu > mps
- L2CAP ERTM: fix outgoing fragment management
- HFP: decline incoming RFCOMM connection after outgoing connection was started
- AVRCP: fix crash on disconnect of connection established by remote

---

## Changes September 2018

### Fixed
- HCI: Error creating outgoing connection (e.g. Connection Limit Exceeded) now handled
- L2CAP: Error creating outgoing connection (e.g. Connection Limit Exceeded) now handled
- L2CAP: Evaluate 'can send now' on HCI Disconnect as ACL buffers in Bluetooth Controller have been used for the closed connection are freed implicitly
- L2CAP: Check can send now before sending extended information requeste needed for ERTM mode
- L2CAP: Use valid signaling identifier for L2CAP Connection Parameter Update Request
- RFCOMM: Trigger l2cap request to send on rfcomm credits when client is waiting to sendtrigger l2cap request to send on rfcomm credits when client is waiting to send
- RFCOMM: Avoid use-after-free on channel finalize
- GATT Client: stop timer on disconnect - fixes use after free / crash

### Added
- A2DP Source: Support stream reconfiguration (a2dp_source_reconfigure_stream_sampling_frequency)
- 3rd-party: yxml is used for PBAP vCard list parsing
- cc256xC: new v1.1 init scripts

---

## Changes August 2018

### Added
- PBAP: added pbap_get_phonebook_size() to get phonebook entry count

### Fixed
- GATT Server: Allow enable Notifications/Indication with Write Command. Fixes issue with some Android devices.
- SM: fix pairing for Secure Connections with Bonding if remote sends additional keys
- SM: drop LTK flag from Pairing Response for Secure Connections
- L2CAP: fix emitted L2CAP_EVENT_CONNECTION_PARAMETER_UPDATE_REQUEST

## Changes June 2018

### Added
- btstack_audio.h: application level API for audio playback and recording
- embedded/hal_audio.h: low-level API for audio playback and recording
- HID Device: hid_device_connect(..) function
- ESP32: implement hal_audio
- DA14585: support for Dialog Semiconductor DA14585 LE-only controller
- Raspberry Pi 3 + Raspberry Pi Zero W port in port/raspi

### Changed
- Errata 10734:
  - SM: Generate new EC Public Keypair after each pairing
  - SM: Abort failure with DHKEY_CHECK_FAILED if received public key is invalid (instead of unspecified error)
- btstack.h: only include classic headers if ENABLE_CLASSIC is defined
- windows: ignore virtual Bluetooth adapter provided by VMware
- Replaced HCI_PACKET_BUFFER_SIZE with HCI_INCOMING_PACKET_BUFFER_SIZE and HCI_OUTGOING_PACKET_BUFFER_SIZE

---

## Changes June 2018

### Fixed
- HFP: Fix Wide Band Speech bit in SDP record for both HF/AG. Missing bit prevents macOS from using mSBC
- ATT Server: send ATT_EVENT_HANDLE_VALUE_INDICATION_COMPLETE with status ATT_HANDLE_VALUE_INDICATION_DISCONNECT on disconnect
- AVRCP Controller: fix parsing of now playing info

### Changed
- ATT Server: ATT_HANDLE_VALUE_INDICATION_DISCONNECT is delivered to service handler if registered

### Added
- ATT Server: packet handler field added to att_service_handler_t to receive: connect/disconnect, atu exchange, indication complete

---

## Changes May 2018

### Added
- GAP: re-encrypt outgoing connection if bonded
- ATT Server: wait until re-encryption is complete
- GATT Client: wait until re-encryption is complete
- ATT Server: added att_server_request_to_send_notification and att_server_request_to_send_indication
- GATT Client: if ENABLE_GATT_CLIENT_PAIRING, GATT Client starts pairing and retry operation on security error

### Changed
- ATT Server: att_server_register_can_send_now_callback is deprecated, use att_server_request_to_send_notification/indication instead

### Fixed
- SM: Fix LE Secure Connection pairing in Central role
- le_device_db_tlv: fix seq nr management
- SM: improve le_device_db lookup and storing of IRK
- GATT Server: fix lookup for Client Characteristic Configuration in services with multiple Characteristics
- RFCOMM: emit channel closed on HCI/L2CAP disconnect after sending DISC while expecting UA

---

## Changes April 2018

### Added
- Crypto: btstack_crypo.h provides cryptographic functions for random data generation, AES128, EEC, CBC-MAC (Mesh)
- SM: support pairing using Out-of-Band (OOB) data with LE Secure Connections
- Embedded: support btstack_stdin via SEGGER RTT

### Changed
- att_db_util: added security requirement arguments to characteristic creators
- SM: use btstack_crypto for cryptographpic functions
- GAP: security level for Classic protocols (asides SDP) raised to 2 (encryption)

### Fixed
- HFP: fix answer call command
- HCI: fix buffer overrun in gap_inquiry_explode
- SDP: free service record item on sdp_unregister_service

## Changes March 2018

### Added
- GAP: allow to limit number of connections in LE Peripheral role with gap_set_max_number_peripheral_connections
- ATT Server: support for delayed ATT read response, see example/att_delayed_read_response.c
- ATT Server: allow to specify security requirements seperately for read/writes. .h files need to be regenerated

### Fixed
- RFCOMM: fix infinite loop on L2CAP connection error (regression from 4c3eeed1)
- HSP HS: accept incomming SCO connection
- SM: fix iteration over LE Device DB entries for bonding and address resolving
- SM: store pairing information only if both devices have requested bonding

---

## Changes February 2018

### Added
- GATT Client: gatt_client_request_can_write_without_response_event() causes GATT_EVENT_CAN_WRITE_WITHOUT_RESPONSE
- SM: new event SM_EVENT_PAIRING_COMPLETE
- GAP: support iteration over stored Classic link keys: gap_link_key_iterator_init, gap_link_key_iterator_get_next, gap_link_key_iterator_done
- GAP: add gap_delete_all_link_keys

### Changed
- GATT Client: round robin for multiple connections
- ATT Dispatch: round robin for ATT Server & GATT Client
- L2CAP: round robin for all L2CAP channels (fixed and dynamic)
- btstack_link_key_db: addition functions for link key iteration
- GAP: LE scanning enabled not reset on HCI Reset -> can be enabled before HCI Power Up
- CSR: set all keys in psram instead of default

### Fixed
- tc3556x: fix startup after baud rate change

---

## Changes January 2018

### Added
- Port for Windows with Zephyr HCI Firmware connected via serial port
- em9304: upload patch containers during HCI bootup
- Makefile for STM32-F4Discovery port
- support for console out via SEGGER RTT
- LE Data Channels example in BTstack and [iOS example on GitHub](https://github.com/bluekitchen/CBL2CAPChannel-Demo)
- LE Streamer Client can send as fast as possbile as well
- L2CAP: option to limit ATT MTU via l2cap_set_max_le_mtu

### Changed
- HCI: allow to set hci_set_master_slave_policy (0: try to become master, 1: accept slave)
- GAP: gap_set_connection_parameters includes scan interval and window params
- GATT Client: GATT_EVENT_MTU indicates max MTU
- ATT DB Util: attribute handle is returned for new Services and Characteristics

### Fixed
- Windows: retry serial port operations if not all bytes have been read/written
- HFP: avoid buffer overflows setting up messages
- SBC Decoder: improved error handling for invalid SBC audio data
- GAP: fix Connection Parameter Response in Central role
- ATT DB Util: update pointer to database in case of realloc
- GATT Client: set UUID16 field if 16-bit UUID is stored as UUID128
- GAP: release HCI Connnection after gap_le_conne
- ATT: Exchanged MTU is propagate to ATT Server and GATT Client

---

## Changes December 2017

### Added
- Introduced btstack_network.h network interface abstraction
- btstack_network_posix implementation using Linux tun/tap interface
- WICED: support for btstack_stdin (HAVE_STDIN)
- GATT Server: Writes to GATT Client Characteristic Configuration are stored in TLV and restored on reconnect. The db.h file generated from db.gatt needs to be re-created.
- TLV: global TLV instance available via btstack_tlv_get_instance() (src/btstack_tlv.h)
- TLV: POSIX implementation that appends to a file on disk (platform/posix/btstack_tlv_posix.c
- LE Device DB TLV: overwrite oldest entry if no free entries available
- SM: allow to set fixed passkey in display role using sm_use_fixed_passkey_in_display_role
- Example/hid_host_demo with HID parser and support for basic US keyboard layout
- EM9304: custom HCI Transport implementation for EM9304 on top of btstack_em9304_spi.h platform abstraction only requires hal_em9304_spi.h to be implemented for new ports
- Port for Apollo2 MCU with EM9304 (ports/apollo2-em9304)

### Changed
- panu_demo: uses btstack_network.h now
- WICED: configure printf to replace Linefeed with CRLF
- SBC: split btstack_sbc_bludroid.c into seperate encoder and decoder implementations

### Fixed
- RFCOMM: support connection requests during connection failure
- L2CAP: support connection requests during connection failure
- L2CAP: fix default remote MTU as 672 instead of 48 (Minimal MTU)
- HCI: avoid double free during halting
- SM: fixed reconnect using legacy pairing in slave role