| Advanced Audio Distribution Profile (A2DP) defines the protocols and procedures for sending high-quality audio data to peer Bluetooth devices. The audio payload can be up to 300-400kbps. It's a loss transmission. The quality of transmitted audio which is from a CD source (bit rate:1411kpbs) is similar as the quality that is encoded and decoded by a MP3/ACC codec.A2DP technology is widely used in mobile phone, wireless headphone and car infotainment devices. Most A2DP devices on the market implement the function by integrating a Bluetooth full module. These full modules are made up of Micro Controller Unit (MCU), Digital Signal Processor (DSP), RAM, Flash and communication interface. All these components formed a dedicated sub-system to run the Bluetooth stack and application components. However, for some devices, such as PDA, smart phone and PND, the application processor of the device is much more powerful and capable to run the Bluetooth stack and application components instead of the MCU of the module. So an optimized design by running Bluetooth stack and A2DP components on both high performance processor and Bluetooth controller chip is proposed in this paper.New design is implemented via Host Controller Interface (HCI). This interface is defined in the Bluetooth core specification. It divides the Bluetooth system into two parts, host and controller. And also provides a uniform interface method of accessing the controller from the host. In new design, the Bluetooth device only needs to integrate a Bluetooth controller chip, the host stack and A2DP components run on the application processor of the A2DP device. The new design increased the CPU usage and save the hardware cost of the Bluetooth devices greatly.There is a cross platform issue of this design. The new design is implemented by running host stack, A2DP components and Sub-band codec (SBC) on processors of different Bluetooth devices. So it should be capable of being adapted to different software and hardware environment easily. The design has employed OS, HCI and audio interface abstraction layer to isolate core implementation from detailed embedded system environment. The new A2DP solution can be easily ported to a new embedded platform by modifying these abstraction layers. The design was implemented on PC platform at first. Then be validated on an embedded platform which is made up of Renesas SH77710 MCU, QNX RTOS and Infineon HCI module. Full A2DP function was implemented.Finally, the host side of new A2DP solution is implemented by a modularized design pattern. So it can be easily extended to other Bluetooth profile by changing profile module. |
