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BlueZ for Android
*****************
Since Android 4.2 there exists a well standardized HAL interface that the
Bluetooth stack is expected to provide and which enables the easy replacement
of the stack of choice on Android. Android BlueZ is intended as a drop-in
replacement to Android provided Bluetooth stack.
More details about BlueZ for Android architecture and components can be found
in android/hal-ipc-api.txt file.
Supported Android version: 4.4
Building and running on Android
===============================
Steps needed to build and run Android Open Source Project 4.4.2 with
integrated BlueZ.
Build requirements
------------------
- GLib - Android 4.2 or later don't provide GLib and one must provide it in
'external/bluetooth/glib' folder of Android tree. Sample Android GLib port
is available at https://code.google.com/p/aosp-bluez.glib/
- SBC - A2DP code requires SBC library (version 1.2 or higher) present in
'external/bluetooth/sbc' directory. Library is build from Android.mk provided
by BlueZ. SBC code is available at git://git.kernel.org/pub/scm/bluetooth/sbc
- Bionic support - Currently only 'master' branch available at
https://android.googlesource.com/platform/bionic provides all required
functionality and running BlueZ on release branch requires backporting missing
features (currently only epoll_create1 call for Android 4.4.2). Sample
Bionic for Android 4.4.2 with all required features backported is available at
https://code.google.com/p/aosp-bluez.platform-bionic/
Runtime requirements
--------------------
BlueZ HAL library requires 'bluetoothd' and 'bluetoothd-snoop' services to be
available on Android system. Some permissions settings are also required.
This can be done by importing init.bluetooth.rc file in init.rc file of targeted
board:
import init.bluetooth.rc
For convenience examples are provided at:
https://code.google.com/p/aosp-bluez.device-lge-mako/ (Nexus 4)
https://code.google.com/p/aosp-bluez.device-asus-flo/ (Nexus 7 2013)
Downloading and building
------------------------
Building for Android requires full Android AOSP source tree. Sample Android
4.4.2 tree with all required components present is available at
http://code.google.com/p/aosp-bluez/
This tree provides support for Nexus4 (target aosp_mako-userdebug) and
Nexus 7 2013 (target aosp_flo-userdebug). Tree does not provide binary blobs
needed to run Android on supported devices. Those can be obtained from
https://developers.google.com/android/nexus/drivers. Binary blobs needs to be
unpacked (EULA acceptance required) into 'vendor' directory of Android tree.
Downloading:
repo init -u https://code.google.com/p/aosp-bluez.platform-manifest -b kitkat
repo sync
Building:
source build/envsetup.sh
lunch aosp_mako-userdebug or lunch aosp_flo-userdebug
make -j8
Flashing:
adb reboot bootloader
fastboot flashall -w
After full build is done it is possible to rebuild only BlueZ:
'cd external/bluetooth/bluez/android/'
'mm' (or 'mm -B' to force rebuilding of all files)
'adb sync' to update target device.
Linux Kernel requirements
-------------------------
BlueZ for Android uses Linux Bluetooth subsystem and it must be enabled in
kernel. Minimal required version of management interface is 1.3. This
corresponds to Linux 3.9 but latest available version is recommended. Other
requirements include UHID and network bridge support.
Following kernel options should be enabled:
CONFIG_BT
CONFIG_BT_RFCOMM
CONFIG_BT_RFCOMM_TTY
CONFIG_BT_BNEP
CONFIG_BT_BNEP_MC_FILTER
CONFIG_BT_BNEP_PROTO_FILTER
CONFIG_BRIDGE
CONFIG_UHID
Also BT chip driver needs to be enabled e.g:
CONFIG_BT_HCIBTUSB
If it is not possible to use new enough Linux kernel one can use updated
bluetooth subsytem from Backports project. More information about Backports can
be found at https://backports.wiki.kernel.org. Sample kernels using backports
for running BlueZ on Android are available at
https://code.google.com/p/aosp-bluez.
Running with Valgrind
---------------------
BlueZ for Android is preconfigured to be easily run under Valgrind memcheck.
Appropriate configuration and required modules are automatically included when
building either userdebug or eng variant of Android platform.
Valgrind can be enabled in runtime by setting "persist.sys.bluetooth.valgrind"
property to either literal "true" or any numeric value >0. For example:
adb root
adb shell setprop persist.sys.bluetooth.valgrind true
After changing property value Bluetooth need to be restarted to apply changes
(this can be done using UI, just disable and enable it again). Property is
persistent, i.e. there's no need to enable Valgrind again after reboot.
It's recommended to have unstripped libglib.so installed which will enable
complete backtraces in Valgrind output. Otherwise, in many cases backtrace
will break at e.g. g_free() function without prior callers. It's possible to
have proper library installed automatically by appropriate entry in Android.mk,
see https://code.google.com/p/aosp-bluez.glib/ for an example.
Enabling BlueZ debugs
---------------------
BlueZ debug logs can be enabled in runtime by setting "persist.sys.bluetooth.debug"
property to either literal "true" or any numeric value >0. For example:
adb root
adb shell setprop persist.sys.bluetooth.debug 1
After changing property value Bluetooth needs to be restarted to apply changes.
There is also a possibility to enable mgmt debug logs which also enables debugs
as above. To enable it procced in the same way as described above but use
system properties called: persist.sys.bluetooth.mgmtdbg
Note: Debugs are only available on NON USER build variants
Customization
-------------
It is possible to customize BlueZ for Android through Android system properties.
This may include enabling extra profiles or features inside HALs implementation
These properties are read on Bluetooth stack startup only and require stack
restart if changed. All customization properties names start with
"persist.sys.bluetooth." followed by specific HAL name e.g.
"persist.sys.bluetooth.handsfree". This section list available customization
options.
Property Value Description
-------------------------------------------
handsfree hfp Enable Handsfree Profile (HFP) with narrowband
speech only
hfp_wbs Enable Handsfree Profile (HFP) with narrowband
and wideband speech support
<none> Don't enable Handsfree Profile (HFP)
Building and running on Linux
-----------------------------
It is possible to build and test BlueZ for Android daemon on Linux (eg. PC).
Simply follow instructions available at README file in BlueZ top directory.
Android daemon binary is located at android/bluetoothd. See next section on
how to test Android daemon on Linux.
Testing tool
------------
BT HAL test tools located in android/haltest is provided for HAL level testing
of both Android daemon and HAL library. Start it with '-n' parameter and type
'bluetooth init' in prompt to initialize HAL library. Running without parameter
will make haltest try to initialize all services after start. On Android
required bluetoothd service will be started automatically. On Linux it is
required to start android/bluetoothd manually before init command timeout or
use provided android/system-emulator, which takes care of launching daemon
automatically on HAL library initialization. To deinitialize HAL library and
stop daemon type 'bluetooth cleanup'. Type 'help' for more information. Tab
completion is also supported.
Implementation status
=====================
Summary of HALs implementation status.
complete - implementation is feature complete and Android Framework is able
to use it normally
partial - implementation is in progress and not all required features are
present, Android Framework is able to use some of features
initial - only initial implementations is present, Android Framework is
able to initialize but most likely not able to use it
not started - no implementation, Android Framework is not able to initialize it
Profile ID HAL header Status
---------------------------------------
core bluetooth.h complete
a2dp bt_av.h complete
gatt bt_gatt.h initial
bt_gatt_client.h initial
bt_gatt_server.h not started
handsfree bt_hf.h complete
hidhost bt_hh.h complete
health bt_hl.h initial
pan bt_pan.h complete
avrcp bt_rc.h complete
socket bt_sock.h complete
Implementation shortcomings
===========================
It is possible that some of HAL functionality (although being marked as
complete) is missing implementation due to reasons like feature feasibility or
necessity for latest Android Framework. This sections provides list of such
deficiencies. Note that HAL library is always expected to fully implement HAL
API so missing implementation might happen only in daemon.
HAL Bluetooth
-------------
methods:
dut_mode_send never called from Android Framework
le_test_mode never called from Android Framework
get_remote_service_record never called from Android Framework
callbacks:
dut_mode_recv_cb empty JNI implementation
le_test_mode_cb empty JNI implementation
properties:
BT_PROPERTY_SERVICE_RECORD not supported for adapter and device, for
device this property is to be returned as
response to get_remote_service_record,
not sure what to return on get_property
calls (records of all services?)
BT_PROPERTY_REMOTE_VERSION_INFO information required by this property (LMP
information) are not accessible from mgmt
interface, also marking this property as
settable is probably a typo in HAL header
HAL Socket
----------
Support only for BTSOCK_RFCOMM socket type.
HAL AVRCP
---------
methods:
list_player_app_attr_rsp never called from Android Framework
list_player_app_value_rsp never called from Android Framework
get_player_app_value_rsp never called from Android Framework
get_player_app_attr_text_rsp never called from Android Framework
get_player_app_value_text_rsp never called from Android Framework
set_player_app_value_rsp never called from Android Framework
callbacks:
list_player_app_attr_cb NULL JNI implementation
list_player_app_values_cb NULL JNI implementation
get_player_app_value_cb NULL JNI implementation
get_player_app_attrs_text_cb NULL JNI implementation
get_player_app_values_text_cb NULL JNI implementation
set_player_app_value_cb NULL JNI implementation
Known Android issues
====================
It is possible that BlueZ is triggering bugs on Android Framework that could
affect qualification or user experience. This section provides list of
recommended Android fixes that are not part of latest AOSP release supported by
BlueZ.
https://android-review.googlesource.com/82757
https://android-review.googlesource.com/87670
https://android-review.googlesource.com/88384
Unimplemented Bluetooth features
================================
Some Bluetooth functionality require support from outside of BT stack
eg. telephony stack. This sections describes profiles optional features not
implemented due to lack of support in other Android subsystems or missing API
in respective BT HALs.
Profile Feature Comments
--------------------------------------------------------
HFP Attach a phone number to AT+BINP=1
a voice tag
HFP Enhanced Call Control AT+CHLD={1x,2x}
HFP Explicit Call Transfer AT+CHLD=4
HFP Response and Hold AT+BTRH, +BTRH
HFP In-band Ring Tone +BSIR
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