Design Of WSN Base Station Platform Based On ARM9 And Windows CE

Wireless sensor network was rooted in military field primitively. As early as in 1978, Carnegie Mellon University has formed Distributed Sensor Net Workshop which was specially used to research the martial supervisory system based on the WSN in the funding of DARPA. With the development of communication and low-power embedded technology, WSN has developed rapidly. Meanwhile, the research and development of the WSN has become a focus in information field. With the characteristics of fast construction and convenient disposition, the WSN can realize real-time information acquisition widely and automatically, which is greatly adapt to the atrocious environment that is not suitable for manual operation or the occasion that needs to collect data automatically. Therefore, the WSN has broad application prospects in the military reconnaissance, environment monitoring, medical wardship, space search, urban traffic management, storage management, Smart Home and so on.In most residential area, billing data of natural gas meters, water meters, electricity meters are read manually, which is time-consuming, laborious, imprecise and not timely. The applications of WSN in wireless meter-reading field will not only be a great saving of human and material resources but also ensure the timeliness and accurateness of data collection. In the future, the Smart Home, environment monitoring and other applications based on WSN will be easily realized by adding new sensors into the WSN merely. In this project, WSN is composed by the base station and a large number of sensor nodes. The sensor nodes installed in the meters are to collect data, while the base station manages all the sensor nodes and communicates with Ethernet. This paper discusses the development of WSN base station system, which is applied in the WSN of gas meter, water meter and electricity meter.The WSN, which is composed of large numbers of low-cost micro-sensor nodes in monitoring area, is a multi-hop self-organized system formed by wireless communication. The purpose of the WSN is to synergically sense, sample and process the information of the objects covered by network, and then the information is sent to observer. This paper is done in the background of which the WSN is used for wireless meter reading. The object of this paper is to design and develop a universal base station system that could be applied to diversiform WSN, such as, gas meter, water meter, and thermal meter and so on.The base station as a data transfer hinge between Ethernet and WSN is critical for the performance of the WSN. The base station needs to process the data not only sampled in the whole sensor network, but also sent by Ethernet, therefore, the base station needs more powerful data processing and communication ability. The paper employs the Samsung S3C2410 microprocessor based on ARM920T kernel as base station. S3C2410 have powerful communication ability and process ability, maximum clock is up to 266 MHz, with the enhanced ARM architecture MMU to support Windows CE EPOC 32 and Linux. All of this make the S3C2410 meet the demand of base station. The base station has 64M SDRAM and 64M NAND Flash, which ensure the function extendibility. Besides, the base station have realized UART, USB, Internet, LCD, JTAG and CC2420 wireless communication module.The base station adopts Windows CE 5.0 embedded operation system. Microsoft Windows CE 5.0 is an open, scalable, 32-bit operating system (OS) that integrates reliable, real time capabilities with advanced Windows technologies. Because of the diversity of the embedded hardware platform, it is needed to transplant Windows CE for different hardware platform. Therefore, the transplantation of Windows CE BSP (Board Support Packet) will be done after the hardware design. The BSP transplantation includes Boot Loader program and OAL (OEM Adapter Layer). Boot Loader is the first code run when the system is powered on, which is similar to the BIOS in the X86 PC. The main function of the Boot Loader is to initial hardware, create memory mapping, copy operating system image from Flash to RAM, enable operating system, and hand the control right of system to operating system at last. OAL that stays between the kernel of Windows CE and the hardware of the object equipment generates executable file connected with kernel library in physics. OAL code is used to process interrupt, timer, power management, bus abstract, universal IO control and other affairs associated to the specific hardware. Moreover, OAL abstracts the accessing for the object platform hardware into function or library. When operating system accesses the hardware, the OAL function or library will be called to complete the access for hardware. In this way, the irrelativeness between Windows CE operating system and specific hardware is realized.On account of that the specific hardware for base station adopted in the paper is CC2420 wireless module, which lacks relevant driver in Windows CE, another key point is to compile driver for CC2420 in Windows CE. According to analysis about the principle of CC2420, we can conclude that its data transmission model is similar to serial interface, which both belong to stream-oriented equipment. So, CC2420 can adopt the most popular stream driving model applied in Windows CE. The driver of stream-oriented equipment is so universal that any equipment's driver can be realized by stream-oriented driver in principle. The stated interface function that realizes stream-oriented driver model is needed in stream-oriented equipment driver, and the interface function is demanded to exposure to Windows CE system kernel, so that operating system will be able to call stream-oriented driver through interface function to implement the access of stream-oriented equipment finally.The analysis and design of the WSN base station platform are mainly discussed in the paper. The paper is organized for five sections as follow: Section 1 introduces the WSN simply, Section 2 discusses the hardware design of the base station system in detail; the transplantation and customization for Windows CE operating system are expounded in Section 3; the development of CC2420wireless transmission module driver in Windows CE is illuminated in Section 4; Section 5 gives conclusions for the full text and proposes some possible problems in practical applications of base station.