1 Introduction
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With the continuous development of communication technologies and the increasing popularity of high-definition applications, traditional multimedia information publishing terminals have been unable to meet the playback requirements of high-definition media. In view of the complexity of the existing technology, high cost, poor playback quality, this paper introduces a high-definition media information publishing terminal design scheme, which uses embedded platform architecture and hardware decoding technology to support multiple audio and video and pictures. The format enables the combined playback of multimedia information such as video, audio, pictures and scrolling subtitles, and the playback quality can achieve excellent HDTV quality. As the terminal node of the high-definition media publishing system, under the management and control of the remote central control system, the system can display information such as advertisements, news, weather forecasts and property notifications in a timely or instant manner, and the most fresh information will be available in the first time. Delivered to the audience; this decentralized communication model can segment audiences, differentiate audience needs, optimize the communication process, and improve the accuracy of audience coverage, so as to optimize the communication effect, in building TV, banking, community, The advertising and information distribution markets such as stations and airports have broad application prospects.
2 hardware system structure
The main processor of this system selects the professional-grade high-definition video decoding chip EM8623L from Sigma Designs. The chip also integrates V ideo Decoder ( R ISC ), ARM, DSP three chips, including MPEG - 1 /2 / 4 SD / HD, WMV9 SD / HD, D ivx, H 264, VC - 1 and so on. Multiple video format decoding, audio: MPEG-1, Layer1 /2 /3 (MP3), AC-3, AAC, PCM, WMA9, etc. The embedded 200MHz ARM is responsible for the core master, memory bandwidth of 32 bits, and supports up to 256MB of DDR, supporting 64MB of flash expansion. The 32-bit DSP is dedicated to audio processing and the 16-bit R ISC processor is responsible for video decoding. The EM8623L also features a 2D graphics engine and rich interface support such as IDE, DV I, PC I, and U SB. This embedded architecture and hard decoding based chip solution meets the needs of HD media playback terminal equipment in terms of cost, power consumption and efficiency.
The hardware system structure of the HD media information publishing terminal described in this paper mainly includes: HD decoding chip EM 8623L; 128MB SDRAM and 8MB flash memory; network interface controller; front panel control circuit; built-in 25-inch notebook SATA hard disk interface; providing high-definition digital multimedia Interface (HDM I), high definition video color difference component (YPbPr), composite video signal interface (V IDEO) and other video interfaces, optical digital audio interface (S / PD IF), coaxial digital audio interface (COAX IAL), dual Audio interface such as channel stereo audio interface (R- AUD IO - L). In addition, a USB2 0 interface is provided, which can be connected to an external mobile storage device, play audio and video resources therein, and provide firmware upgrade function.
3 software design
3.1 Software Architecture Design
The software system is designed according to the embedded system principle and multimedia information publishing application requirements. The system architecture is shown in Figure 1. It consists mainly of hardware driver layer, real-time operating system layer, middle layer and application layer. The hardware driver layer is the most closely connected software layer, including audio and video output interface, N IC, SATA controller, USB0 0 controller, Flash, RS232 and front panel / remote control, and access hardware address. The API of the register is an important basis for the stable and efficient operation of the system. Device driver loading can be loaded in the kernel as the operating system starts. It can also be loaded separately after the operating system is up. The driver loading can be set at the time of kernel compilation, making the kernel size setting flexible. , to make appropriate adjustments according to the lash space.
Figure 1 system software structure diagram
The real-time operating system is a core part of embedded device software. uC linux is a real-time operating system designed for embedded processor features. It inherits the powerful network functions and multi-tasking management functions of standard Linux, supports multiple file systems, provides standard rich APIs, and has high execution efficiency. Small footprint, scalability and good portability. In addition, he designed the processor without MMU and rewrote the memory management and process management of the Linux to meet the development requirements of the MMU-free processor. Since the EM8623L is a processor without an MMU, this system uses uC linux as the operating system kernel.
The middle layer includes a private protocol stack module, a PPPOE (Po int-to-po intpro tocol over E thernet) module, an audio and video decoding module, and a 2D graphics accelerator module. These modules are located between the real-time operating system layer and the application layer, providing an API interface provider call up, and implementing the mapping of the API interface function to the hardware driver layer through the real-time operating system. The private protocol stack module is a private and reliable datagram protocol based on UDP, designed to support remote large data volume download. The protocol stack can adopt adaptive fault retransmission and retransmission mechanisms according to different network packet loss rates, and overcomes the unreliability of UDP protocol data transmission. In the network environment with high network packet loss rate, it can display relatively strong data receiving capability, and better meet the high-speed and reliable download task of large data volume HD media. The effective data download rate can reach more than 80% of the existing bandwidth. . The PPPOE module supports the system ADSL network access function by porting the PPPOE code on the open source standard Linux to the embedded uC linux kernel. The audio and video decoding module is a complete file player developed by Sigma Designs for playing multi-standard audio and video files supported by EM86231 hard decoding and advanced display processing functions (supporting HDM I/YPbPr/AV and other video output and S / PDIF , two-channel audio output). The 2D graphics accelerator supports high-speed OSD and GU I to provide high-quality images for high-definition displays.
The application layer is at the top level of the software system, and implements the main functions of the system application software, including remote control receiving processing, graphical user interface display, high-definition media file local download, online online upgrade, system login remote server registration authentication, video/ Time-sharing control and combined playback of audio/picture/flying characters, etc.
3.2 System Task Design
For the accuracy, real-time and immediacy required for HD media information release, the system mainly designed four system tasks, namely: main control task, timing thread, network task thread and flying word play thread. The main control task is mainly responsible for each task scheduling, monitoring the control commands issued by the server to the main window and the flying word window (such as suspending, fast forwarding, rewinding, stopping, continuing, etc.), and making various programs according to downloading to the local hard disk. Single-playing of corresponding media programs can achieve sequential playback, insert control, time-by-time playback, and manual playback. The network task thread includes a control information sending and receiving thread and a data downloading thread. The control information sending and receiving thread and the data thread complete the remote downloading and local storage of the high-definition media file, and the control information sending and receiving thread is mainly responsible for the handshake of the protocol, that is, the protocol information originating end does not wait for the arrival of the agreed protocol information within 200 ms, and then determines that the information times out and proceeds. Retransmission; The data thread is primarily responsible for the local download and storage of media files pushed by the network.
The timing thread is mainly responsible for obtaining the current system time, and then comparing the system time with the playing time of each record in the local time control list and the playing time of each record of the insertion control list, if there is a recorded playing time, then proceeding The corresponding playback processing, the playback processing is divided into a main window and a flying word window. The flying word playing thread realizes the corresponding flying word playing operation according to the flying word loop play list, the flying word insertion list, and the program sequence in the flying word time control list. The specific steps of the overall workflow of the system are as follows:
(1) Start the bootloader and perform the necessary hardware initialization;
(2) Starting rom fs from flash;
(3) Determine whether the startup is successful. If successful, extract the app bin gz, initialize the kernel, load the corresponding device driver, and start the upper application.
(4) If it is unsuccessful, read rom fs b in from the hard disk, write it to the ROM, and repeat (3) operation;
(5) Read the default configuration parameters in flash and set the corresponding parameters;
(6) Start DHCP, obtain IP address, gateway, DNS server IP, subnet mask, etc.
(7) Start the network thread task, perform the docking of the terminal and the server, register the authentication; download the media data, etc.; if the connection with the server is successful, synchronize the terminal system time;
(8) Start the main control task and play the specified broadcast list program according to the playback priority. The main control task flow chart is shown in Figure 2. 
Figure 2 main control task flow
4 Conclusion
This paper designs a high-definition media publishing terminal based on EM8623L, featuring low power consumption, compact structure and high stability. Supports efficient and reliable high-definition media program local download; Supports sequential playback, instant playback and timed playback functions; Supports smooth playback of almost all HD video media; Enables combined playback of multimedia information such as video, audio, pictures and scrolling subtitles; Real-time monitoring of the front-end control system; with a variety of audio and video output interfaces, support 1080P pure HD display. At present, the front-end control system has been widely promoted and applied in banks, airports and other places.
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Yangzhou Heli Photoelectric Co., Ltd. , http://www.heli-eee.com