The Development Of The Gateway In Networked Digital Home

With the rapid development of the computer, communications technology, embedded technology and information appliances, more and more families called for the establishment of a home network. The "digital home" concept was proposed extensively at home and abroad. Family Gateway is the core of the entire family networks, its function is achive Internet access for remote control, as well as the function of connecting the family's internal network. Based on Jilin province's science and technology projects "The key technology research in networked digital home", the paper designed a kind of embedded home gateway which is based on Freescale's 16-bit production MC9S12NE64 microcontroller. Ccompared with the multi-chip design with the same function, it has many advantages such as small size, simple structure, high integration and reliability.The main purpose of the design is to achieve MC9S12NE64's Ethernet access for network data transmission. Currently there are different types of popular network protocol, although each has its own advantages, but only TCP/IP allows full connectivity with the Internet, it is more focused on the Internet data transmission between equipments. The TCP/IP protocol stack, run on General computer is too complicated and demand large system resources. Embedded systems, because of its CPU processing power and storage capacity are subject to system cost limit, making full use of resources and improving the system's cost-effective development are the fundamental characteristics of embedded applications. Embedded systems are generally in order to meet a specific demand, and network support requirements are relatively low. Any agreement on the need to add the corresponding module, without the use of complete TCP/IP protocol, we shall, in accordance with the needs, reduct the TCP/IP protocol appropriately. The most critical question in achieving embedded TCP/IP protocol stack is how to combine the limited system resources: embedded systems hardware and software environment, as well as specific applications of embedded Internet simply the standard TCP/IP protocol stack. The paper, comparing several embedded protocol stack, choose OpenTCP protocol stack, and made some changes with characteristics of processors MC9S12NE64. The changes follows: Based on the characteristics of MC9S12NE64, OpenTCP optimized the key part of buffer District management deciding the TCP/IP protocol's capability. High-level protocol (TCP/UDP, IP, ICMP, ARP)'s disposal directly based on the MAC address of the buffer layer. Achieve a zero-copy data. Enhance the performance of the protocol stack. ARP packet transmission rate could reach 87 Mb/s in Fast Ethernet. Cancel all the IP options and TCP options. TCP flow control window length is set to 1. That is, a two-way message transmission is based on stopping and waiting model. Cancell IP sub-group package mechanism; IC2MP agreement only provides Echo services. TFTP, HTTP, and other application layer protocol is not a must, in order to save space and Guarantee the efficiency of operating procedures, application layer protocols will be removed, retaining only the TCP/UDP, IP, ICMP, ARP, and other core agreement. Provide services to application procedures directly. The reduction work includes the deletion of part of the source code, modification of parameters'configuration of certain documents. In hardware design, MC9S12NE64 physical port and the isolation transformer are connected with the IEEE802.3's requirements to physical layer specification. Such as the interval between RJ45 jack and isolation transformer should be as small as possible, the output and input differential signal should be isolated, and ensure that the rated load current of power supply is not less than 300 mA. Attention should be paid to the requirements of the system clock, MC9S12NE64 supports only the Pierce oscillator circuit, the accuracy of crystal should be higher than 25 ppm. MC9S12NE64 in the systerm works in the normal single-chip mode, the internal power supply should be in working state.Software design goes in the integrated development environment Codewarrior, using ANSI C and Assembly Language. In accordance with the principles of modular design, the entire control procedures are divided into a number of sub-procedures. It is not only readable, convenient debugging, but also has a strong Universal, Facilitating future software transplantation, version updating, improving and perfect. From two aspects, Development costs and System Stability, of a comprehensive consideration, selectμC/OS-Ⅱas the operating system. In view of the characteristics of MC9S12NE64, transplantμC/OS-Ⅱ. The main work of the paper include:(1)The establishment of MC9S12NE64 hardware development platforms. Research on real-time embedded operating systemμC/OS-II and completed its transplant on MC9S12NE64. Established software development platform based on a standardized driver libraries and real-time embedded operating systemμC/OS-II. (2) In-depth research and analysis the TCP / IP network protocol. Reduce open-source protocol stack OpenTCP appropriately and transplant it on MC9S12NE64 on the basis of the characteristics for embedded systems. (3)Introduced MC9S12NE64 integrated software development platform Codewarrior and BDM debugging systems. On the development platform, completed the debugging of the embedded gateway desighed in the paper to prove the feasibility of the design.Experiments show that the embedded home gateway which has the advantages of small size, simple structure, high integration and reliability, meet the requirements of family information on the long-distance transmission and remote control of home appliances.