Android Bluetooth Introduction

Android Bluetooth Introduction Erin Yueh 2009/06/26

Agenda ● Android Bluetooth architecture ● Related source code ● Init Bluetooth ● Connect with other BT devices (dbus) ● RFCOMM ● OBEX (socket)

Android architecture

The diagram above offers a library-oriented view of the Bluetooth stack.

Related source code ● Bluez 3.36 (user space and kernel) /mydroid/externel/bluez /mydroid/kernel/drivers/bluetooth /mydroid/kernel/net/bluetooth ● Android app framework (java & c++) /mydroid/frameworks/base/core/jni/android_bluetooth_*.cpp /mydroid/frameworks/base/core/java/android/bluetooth/*.java /mydroid/frameworks/base/services/java/com/android/server/ (SystemServer) ● Android UI application /mydroid/packages/apps/Phone/src/com/android/phone/ (Phone App) /mydroid/packages/apps/Settings/src/com/android/settings/bluetooth/ (Settings App)

Init Bluetooth ● /root/init.rc mkdir /data/misc/hcid (store device info) service dbus /system/bin/dbusdaemon service hcid /system/bin/hcid (disabled) service hfag /system/bin/sdptool add channel=10 HFAG (handsfree, disabled, one shot) service hsag /system/bin/sdptool add channel=11 HSAG (headset, disabled, one shot) ● /root/init.trout.rc service hciattach (disabled) ● system server decice BT power On or Off from settings value start related services

ddms: dalvik debug monitor I.

ddms: dalvik debug monitor II.

Bluetooth headset Music player + Dialer

Connect with other BT devices ● Bluez: hcid daemon ● dbus-daemon: connections between hcid and system server ● D-Bus is a simple inter-process communication (IPC) system for software applications to communicate with one another. ● dbus-daemon is the D-Bus message bus daemon. D-Bus is first a library that provides one-to-one communication between any two applications; dbus-daemon is an application that uses this library to implement a message bus daemon. Multiple programs connect to the message bus daemon and can exchange messages with one another. ● debug utility: d-feet, dbus-monitor, dbus-send

BlueZ DBus Architecture

DFeet: DBus viewer and debugger

Dbussend: send a message to a message bus

Scan nearby BT devices in Android ● Bluez utility: hcitool scan ● DiscoverDevices: bluez/util/hcid/dbusapi.txt This method starts the device discovery procedure. This includes an inquiry procedure and remote device name resolving. On start up this process will generate a DiscoveryStarted signal and then return DeviceFound singals. If the procedure has been finished an DiscoveryCompleted signal will be sent. ● Source code: android_server_BluetoothDeviceService.cpp /* Compose the command */ msg = dbus_message_new_method_call(BLUEZ_DBUS_BASE_IFC, nat>adapter, DBUS_CLASS_NAME, "DiscoverDevices"); /* Send the command. */ reply = dbus_connection_send_with_reply_and_block(nat>conn, msg, 1, &err);

Signals

How to pair with a BT device? I. Register Passkey Agent

II. Request PIN code

RFCOMM (Radio Frequency Communication) ● The Bluetooth protocol RFCOMM is a simple set of transport protocols. ● RFCOMM is sometimes called Serial Port Emulation. ● The Bluetooth Serial Port Profile is based on this protocol. ● In the protocol stack, RFCOMM is bound to L2CAP ● RFCOMM provides a simple reliable data stream to the user, similar to TCP. It is used directly by many telephony related profiles as a carrier for AT commands

Send AT commands via bluetooth ● Connect with Nokia N73 phone ● > sdptool browse 00:18:C5:42:18:78 ● > sudo rfcomm connect 0 00:18:C5:42:18:78 2 ● minicom ● > AT ● > AT+CGMR ● > AT+CGMI

OBEX (Object EXchange) ● a communications protocol that facilitates the exchange of binary objects between devices. ● in the protocol stack, OBEX is bound to RFCOMM

SOCKET ● UNIX socket (AF_BLUETOOTH) ● interprocess communication ● like Internet socket recv() send() ● clientserver

Receive files via BT in Android ● openobex + obexpushd ● Run an OBEX data server in Android ● > obexpushd ● listen RFCOMM connections ● File permission

Send files via BT in Android ● Openobex + obexftp ● Connect to a RFCOMM connection ● > obex_test b BTADDR CHANNEL ● > obexftp b BTADDR B CHANNEL list

Thank You!

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Android Bluetooth Introduction

by Erin Yueh

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