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Abstract: After briefly introducing the PECOS technology and its characteristics, combined with the basic requirements of the embedded video surveillance system, the main components of the embedded video surveillance system are defined. Combined with the PECOS standard, some examples of serial communication components are given. Finally, several key issues in component programming are discussed.Keywords: video surveillance; CGI; embedded Web; component; PECOS; serial communication
0. introduction
With the maturity of digital video compression technology, embedded video surveillance has become the mainstream of today's surveillance technology, but due to the increasing system functions, changing programming environment and imperfect analysis and design in the early stage, the difficulty of system upgrade and maintenance is increasing. Big [1] , every small change can cause the entire system to be recompiled, linked and debugged, which consumes a lot of manpower, material resources and time. Component design is therefore required, and to simplify the development of components, a standard set of methods is required to build, manage, and maintain components. In the development process of current network video applications, the reusability of the software encountered, the instability of IP network transmission and the diversity of network bandwidth, etc., the best way to solve the problem is to build the application. On the basis of components.
Now the common component model (mainly COM/DCOM, CORBA, JavaBeans, etc.) requires a lot of underlying support at runtime, mainly running on non-embedded platforms [2] . At present, the popular embedded component models in foreign countries mainly include the CCOM model sponsored by the Belgian IWT Association, the Koala component model used by Philips in consumer electronics, and the Delta System platform of Keke Jingcheng in China, which are in the initial stage. These models are not public. It is limited to the technology used internally by the company and requires the corresponding CASE tool support [3] .
In view of the above analysis, this paper carried out the monitoring component design, selected ABB's component model PECOS for field devices as the component standard, and developed the whole system.
1. Introduction to PECOS technology
Elements in the PECOS component model include components, interfaces, and connectors. There are three types of components: active components with their own control threads; passive components that do not have their own control threads, are dispatched by active components [4] ; event components whose functions are triggered by an event. These three components can be combined. An interface indicates that the component is provided to other components or requires data from other components. Includes the type of data to pass (such as floating point), direction (in, out, in/out), and scope. The connector is responsible for connecting compatible types, directions, and ranges of interfaces.
1.1 PECOS component behavior
An application can be comprehensively described by CoCo and the target language class. The connected object is called the RTE runtime environment. RTE is the standard library provided by PECOS. The advantage of RTE is application independence. PECOS components are also platform-independent and can be shared among different projects. A specific application can be divided into the following four layers: RTOS, RTE, Generated Classes, User classes.
1.2 Characteristics of the PECOS component model
User language independence uses interface definition language (IDL) and component definition language (CDL) to describe interfaces and components, so that the model and the specific implementation are separated. In theory, it can be mapped to multiple languages ​​C, C++, Java, and so on.
The portability of the portable embedded system is diverse, so the portability of the component model is very important. In this model, the portability of the underlying interface is well ported.
The ease of maintenance of components enables component maintainability through interface inheritance and optional interfaces.
Compared with other component programming techniques, PECOS has good cross-platform performance and has nothing to do with the programming language. It has better openness, scalability and real-time. So we choose CORBA as the component standard and the whole system. Component programming.
2. Main functional components of embedded monitoring system
The remote monitoring system based on embedded Web mainly consists of three parts: on-site data acquisition equipment, embedded Web server and remote monitoring host [5] . The on-site data acquisition equipment is responsible for on-site data collection and transmits data in a certain protocol standard; the embedded Web server is responsible for the collection and distribution of on-site data, and the monitoring host obtains data in real time via Ethernet, thereby achieving the goal of remote monitoring.
For the whole system, according to the functional requirements, in accordance with the principles of global scalability, reusability, advancement and reliability, the system design is divided into Web Server components, CGI components, serial communication components, data storage components. , alarm components and several other component modules. The interface is divided by service, encapsulated inside the component according to the function, and the system components are made clear, concise and easy to maintain. The relationship between these components is shown in Figure 1:
Figure 1 Main functional components of the embedded monitoring system
The Web Server component refers to the basic content of the TCP/IP protocol (such as the HTTP protocol), the program module that can respond to and process user requests, and implement the opposite communication. Through the implementation of the TCP/IP related protocol, the Web server has a browser and a browser. The ability to interact with clients, process client requests, deliver web messages, and return results to the browser, while working with other applications. Because Boa is a single-tasking small HTTP server, its source code is open, stable, and real-time. Therefore, Boa is selected as the WebServer in this system.
A CGI component is a program module with independent functions designed according to the CGI standard. It is a standard interface for the embedded web server to interact with external extension applications. It passes the data of the field device to the embedded web server in real time. Thereby realizing dynamic data interaction between the remote client and the field device.
A data storage component is a functional module that can store data collected in the field and provide read and write methods for other functional components. The alarm component is a program module that provides an alarm function.
Among these components, the WebServer component and the CGI program component are combined with the serial communication component, the data storage component, and the alarm component to perform functions such as data collection, storage, display, and alarm.
3. Serial communication component instance
The following uses the serial communication component module as an example to illustrate how to implement its functions with PECOS.
The serial communication component refers to a separate program module that completes the serial communication function. This module mainly includes hardware devices such as a PTZ camera. Camera control mainly includes controlling its focal length, lens concave and convex, aperture; PTZ control mainly includes controlling its automatic rotation and direction, which completes the data transmission of the field device, that is, the PTZ camera to the CGI component [6] , which interacts with the CGI program components. Cooperate to complete the data update to the embedded web server.
The following is the definition of the interface definition language IDL of the serial communication component module. The constants and data definitions are omitted here, and only the presidential framework of the entire module is provided.
Module SerialPort{
Interface Camera{
SetFocus(in int FocusValue, out int Result);// Set the focus value
SetLens(in int LensValue, out int Result);//Set lens convergence and divergence values
SetAperture(in int ApertureValue, out int Result);//Set aperture value
}
Interface Console //PTZ interface
{
SetAuto(in Boolean isAuto, out int Result);//Set whether the gimbal rotates automatically
SetDirection(in int Direction, out int Result);//Incoming direction values ​​from 1-8, representing up, down, left, right, bottom left, top right, bottom right
....
} After designing the IDL, use the IDL compiler to compile them into a server framework, insert them into the project, declare the classes, and write the server program.
The serial communication component module can be easily disassembled and expanded. If you want to add a new hardware device, you only need to add a new interface to define the function, without changing the entire program, which greatly improves the programming efficiency. The entire program is easy to maintain.
4. Several key issues to be aware of in component design
Using a componentized design approach requires addressing the following key issues:
(1) Establishing a reasonable system model and component model is the basis of component design. Reasonable decomposition of the system function model, based on relatively independent functional modules to define components, the boundaries between components should be clear.
(2) Standardization is a prerequisite for ensuring compatibility of components. The interface and operational definitions for each component should be standardized as much as possible, including the property access to the component and the operation of the component.
(3) Components should be easy to reuse. Component technology and its supporting tools should support component version management because reusability is an important aspect when introducing a component-based development model.
5. Conclusion
The author's innovative view is the model design of the video surveillance component and implements simple functions. The next step is to further refine its functionality, using existing embedded components to define video surveillance components or the basis of existing components. Design a new componentized model.
references
[1] Fang Hongzheng Zhao Guigen Liu Kejun Research on Embedded Component Model [J] Microcomputer Application 2005 26(6)521-523
[2] Zhang Yishan CGI Programming Guide [M] China Water Resources and Hydropower Press 1998
[3] Chen Congsheng, Zhu Mingri, Ma Xuewen Based on the CGI Interface Design and Application of uCliunx[J] Journal of Guilin University of Technology 2005
[4].Bastiaan Schonhaage Model mapping to C++ or Java-based ultra-light environment Technical Report Deliveralbe D2.2.9-1.Pecos, 2001.
[5] Seeking technology, Tan Siliang Visual c++ serial communication development example navigation [M] People's Posts and Telecommunications Press, 2003, 132-189
[6] Feng Hongcai, Deng Hualai, Liu Nianbo Realize remote control of pan/tilt and lens with Active X control [J] Computer Application Research 2004 (6) 234-236
[7] Li Wei, Yan Qizheng, Image Acquisition Application Based on S3C2410 Platform and Embedded Linux[J] Microcomputer Information 2006(6)125-128
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