Bluetooth in Android 4.2 and 4.3 (a): overview

starting with Android 4.2, a major change has taken place in the Bluetooth stack: from BlueZ to Bluedroid, which was developed jointly by Google and Broadcom (of course, the core part is Broadcom, Google is mostly doing the parts related to the upper framework). the http://source.android.com/devices/bluetooth.html can be used to understand the architecture of the new Bluetooth stack in general, with few related documents, Read the code for a deeper understanding. compared with BlueZ, Bluedroid has the following advantages:

• The hierarchy is clearly structured. Each profile is unified on the upper layer to facilitate the addition of new profiles, and the HAL layer is added to facilitate portability.

• Removed the dbus,framework Java code directly into the Bluedroid native code.
  

But bluedroid in Android 4.2 is less powerful than BlueZ in Android 4.1, for example, AVRCP 1.3 is not supported; Many bugs, such as some Bluetooth headsets, cannot redial the last call. The most important thing is that the 4.2 bluedroid does not support ble. However, there has been a lot of improvement in the newly released Android 4.3, and AVRCP 1.3 and BLE have been supported.
There are currently some Android 4.1 or 4.2 devices that support BLE, but are all using the vendor own solution, such as Bluetooth stack using BlueZ 5.x, and then provide vendor BLE Android SDK. Now Android 4.3 has been released, from the future trend of development, if someone to learn Bluetooth in Android, it is recommended not to study BlueZ, it is better to turn to bluedroid.
Here is the distribution of Bluetooth-related code in Android 4.2:

Android.bluetooth	Frameworks/base/core/java/android/bluetooth	Implements public API for the Bluetooth adapter and profiles
Bluetooth system Service	Packages/apps/bluetooth/src	Implements service and profiles at the Android fraework layer
Bluetooth JNI	Packages/apps/bluetooth/jni	Defines Bluetooth adapter and profiles service Jni:calls to Hal and receives callback from HAL
Bluetooth HAL	hardware/libhardware/include/hardware/bt_*.h files	Defines the standard interface, the Android.bluetooth adapter and Profiles APIs
Bluetooth Stack	External/bluetooth/bluedroid	Implement Bluetooth Stack:core and profiles

In the case of pan profile, we can look at the specific distribution of the code and how the class and file are named:

Android.bluetooth	Frameworks	public class Bluetoothpan implements Bluetoothprofile
Bluetooth System Service	Packages/apps	public class Panservice extends ProfileService
Bluetooth JNI	Packages/apps	Com_android_bluetooth_pan.cpp
Bluetooth HAL	Hardware/libhardware	Include/hardware/bt_pan.h
Bluetooth Stack	External/bluetooth	BLUEDROID/BTIF/SRC/BTIF_PAN.C (Implements Bt_pan.h)
		Bluedroid/bta/pan (Broadcom BTA)
		Bluedroid/stack/pan (Broadcom BTE)