Research And Design Of MOST Audio Network Based On INIC

MOST is distributed into three generations by network bandwidth. The first generation of MOST is MOST25 whose highest baud rate is 25Mbit/s. The second generation is MOST50 which can transfer data with the bandwidth of 50Mbit/s. The third generation whose highest bandwidth is 150Mbit/s is called MOST150.At present, in foreign markets, many automobile manufacturers have been using MOST25 interface devices to assemble high-end cars, and models with MOST50 network equipment have come out. Because the MOST network technology in our country is behind the times, so we can not develop MOST interface device independently, and we have to import MOST devices to assemble luxury cars. Therefore, studying MOST network standards, research and design MOST interface device independently is meaningful to our country's development of the MOST network technology.Taking design of "MOST audio network based on INIC" as the center, this paper analyzed the transfer principles of MOST Network and the characteristics of INIC, developed an INIC-based MOST audio network system.The MOST network relies on the channel to transmit data, including synchronous channel, asynchronous channel and control channel. Among them, the synchronous channel is used to transmit the real-time data such as multimedia information; the asynchronous channel is used to transmit the aperiodic packet data, such as GPS navigation data, etc; the control channel is used to transmit the information data for network management.According to the ISO/OSI network reference model, MOST interface device model can be divided into the optical physical layer, network interface controller, NetServices basic Layer, NetServices application socket and function block. NetServices software provided by SMSC connects the underlying hardware and application software. NetServices software masks the implementation of underlying hardware, and provides the application interface for the user, so it shortens the development cycle of MOST interface device.Therefore, the focus of developing MOST interface device includes three sections. First, to design the physical layer circuits of optical physical layer and network interface controller; Second, to implement the driver between NetServices software and the physical layer circuit; Third, to realize the application software.The physical layer circuit consists of core circuit and functional circuit. The core circuit which is composed by ATmega128L module, OS81050 module and photoelectric conversion module is used by each MOST interface device. As the external host controller of OS81050. ATmega128L communicates with OS81050 through I2C bus interface; OS81050's stream port is connected to MOST network by optoelectronic component. The functional circuit is mainly used to expand the peripheral function for interface device. The functional circuit of the master node is human-machine interface which is mainly composed by S3C2440 and LCD touch screen, used to show the functions of MOST network and support user's control operations. The functional circuit of DVD device node is the audio encoding circuit which chooses CS5340 as the encoding chip. The functional circuit of audio playback node is the audio decoding circuit which uses CS4341 as the decoding chip.The driver between NetServices software and physical layer circuit is called LLD. NetServices software is divided into two parts which are Layerl and Layer2. Layerl is the basic layer which provides all transport mechanism for accessing to the MOST network. Layer2 which provides a command interpreter and NetBlock is on the top of layerl. NetServices Layerl is divided into two parts called INIC part and EHC part. EHC part is running on the microcontroller ATmega128L, while INIC part is running on OS81050. As both ATmega128L and OS81050 contain software, they can communicate with each other through protocol stack. The control port of OS81050 is connected to the I2C bus interface of ATmega128L, and the interrupt pin of OS81050 is also connected to ATmega128L. If OS81050 has data to send to ATmega128L, it will pull interrupt pin down to notify ATmega128L. The LLD of ATmega128L reads port message and notify MOST NetService that a service request has been received. Similarly, if MOST NetService wants to send data to the underlying hardware, LLD will pack the data into port message and then send to OS81050.The application program is mainly implemented by accomplishing the callback function which is corresponding to FBlock. Taking the DVD device node as an example, if the node needs to respond to the command that the master node control it to playback DVD discs, it is enough to control DVD in callback function corresponding to the DVD playback FBlock.On the basis of the successful development of a single MOST interface device, it is easy to complete the development of the whole network system. The INIC-based MOST audio network is composed of master node, DVD device node and audio playback node. The devices which are connected to each other by optical fiber scatter in different locations to form a logical ring MOST network, the output of one node is the input of another one.The system can provide a good interactive user interface and convenient audio services. At the same time, the system used optical fiber as transmit medium, it has the advantage of anti-interference ability, high bandwidth, high signal fidelity, etc.The experience of designing the INIC-based MOST audio network laid the groundwork for the further study of MOST technology and the development of MOST interface device.