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Based on embedded serial device remote monitoring system

LIU Xiaohu, HUANG Yiping

Faculty of mechanical & Electrical Engineering Guilin University of Electronic Technology,GUET

Guili,China

xylxh163@163.com, hyp@guet.edu.cn

Abstract-This article draws on domain of common IT remote

monitoring of the implementation of the plan. From the

application point of view to design a real-time and reliable

serial device remote monitoring system, causes not to have the

networking function originally and to disperse the regional serial devices is connected in the ethernet, make full use of

existing Internet resources for transmission and management

of data. Through studies the embedded S3C2440 the module of

serial port ethernet communication, designed a software program to realize, serial port ethernet communication

applications in the multithreading technology, achieved serial device serial protocol and TCP/IP protocol conversion. In the

program establish a remote tunnel link using OpenVPN, remote login through telnet embedded platform to monitor the

embedded end. The experimental test serial data in remote

monitoring and control of the computer has a good consistency and achieved the monitoring of serial devices.

Keywords-embedded;serial port;ethernet;protocol conversion; multithreading

1. INTRODUCTION

With the rapid development of Internet, the traditional industrial control serial bus technology used in each field for the spread of the serial device it difficult for the centralized management. This requires the serial control bus of traditional upgrade its high-speed Ethernet bus, the serial data into Ethernet transmission of data will facilitate the remote machine to receive and Management. Therefore, we must design a communication protocol conversion mechanisms can conversion RS232/485 serial bus data and Ethernet TCP/IP data format, no need to phase out equipment existing, saving the investment cost and without the need for monitoring procedures any changes can be very efficient and convenient transmission to the traditional serial control bus into the popular Ethernet channel[l].

Modem industrial production continued development of intelligent, not only require the enterprises that will be distributed production equipment and measuring instruments connected achieve to production data or management data sharing, but also the production personnel in the office or more remote devices on the scene instrument for remote monitoring, remote monitoring has become the field of industrial control development trend. Remote monitoring is achieved through the computer network managed objects for remote monitoring and control and is the field of industrial automation control in recent years a hot research topic. In

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LIU Hailang Faculty of mechanical & Electrical Engineering

Guilin University of Electronic Technology,GUET Guili,China

liuhl@guet.edu.cn

response to these circumstances, the paper design s3c2440 and linux operating system based on Ethernet Converter serial port remote monitoring system was implemented. General block diagram shown in Figure 1.

05

Figure I General block diagram shown

II. SERIAL ETHERNET OF BUILDING COMMUNICATION

Serial remote monitoring of embedded systems main function is to carry serial data and network data processing and forwarding. Embedded hardware platform used is s3c2440, s3c2440 is produced by a Samsung 32-bit RISC processor with low power consumption, high performance, low cost and easy to use features, providing three independent asynchronous serial I/O ports, each of which can interrupt or DMA mode, each UART channel contains two 64-byte FIFO components were used to receive data and send data.

Embedded software system design is a major research focus of this paper is mainly network data and serial port forwarding and remote transmission of data between software design. Design of software was apply Client/Server(C/S) model of the target machine Serial Ethernet communication functions and to apply this functionality embedded hardware environment, avoid the software to be redesigned for hardware different[2]. System uses the Linux operating system, it has a mature TCP/IP network protocol support and multi-threaded application processing capabilities, to ensure the reliability of the serial device data and real-time. Data forwarding process is mainly based on communication protocol conversion and multi-threaded programming techniques.

A.Serial Ethernet communication protocol conversion

Embedded serial device remote monitoring system to achieve the first network interface for the serial link and the communication of data between the judge, conversion and transmission of data from serial device to process the frame

to become available in the network transmission of data frames. The data from the network interface frame to judge, converted into serial data frame and sent to a serial device[3]. Programming on the network the data frame must understand serial data frame to achieve transparent transmission network before serial port communication. First we must define serial frame format that transmit Ethernet data must be coupled with IP header and TCP header. Serial network data frame format shown in Table 1.

[ SCI-ial network data framo

l iP hemler l I TCP header I SCI' i a I Data Frame

I Start bit

I Date bit

I Parity bit

I StOP bit

(I) (8) (I) (I)

Table I Serial network data frame format shown Remote machine receive the network data frame, the

parsing out the serial data frame transmission to the appropriate application. Application process to send data, on the contrary, only the serial data into network packets packaged, after long distance transmission on the target machine after the parse data frame sent to the serial port device[ 4].

B. Multithread application Serial Ethernet Communication

Linux is a multi-user, multitasking operating system, have long realized the process mechanism, but there are many disadvantages of using the process, such as inter­process need to adopt some means of data commun

.ication

can be achieved. To achieve two-way between senal and Ethernet data transmission at the same time, this design uses multi-threading under linux. Linux, follow the POSIX thread interface multithreaded, multi-threading a flexible and efficient manner, send and receive independently of each other[5]. The main task to be completed by the four thread: serial port receive data thread, send data thread Ethernet, Ethernet receive data thread, the serial port to send data thread. Communication is used on the thread mutex locks and semaphores control mechanisms. By creating two data buffer to buffer from the network and send and receive serial data[6]. Serial Ethernet Communication multithreaded applications shown in Figure 2.

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Figure 2 Serial Ethernet Communication multithreaded applications shown

III. SERIAL REMOTE MONITORING PLATFORM FOR

EMBEDDED NETWORK

Network Monitoring divided into different LANs based on distance control and Internet monitoring. Higher stability of the local area network, technology is very mature, relatively speaking, the actual Internet access and the routing restrictions by the network delay large, substitution and more unstable. Therefore, this paper encrypted VPN tunnel to establish a stable communication technology, to enable Telnet remote login service in the embedded target

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machine, so the server can monitor remote embedded systems.

A. VPN technology in embedded network plaiform

VPN (virtual private network) is the use of open public networks dedicated data transmission channel to establish a special network technology, in essence, is a network interconnect technology, the public Internet network infrastructure to meet business needs and to share network resources and has the same network with professionals to ensure the security of Internet users[7].

There are two different implementations VPN: IPSec VPN and Secure SocketsLayer (SSL) VPN. At present, IPSec VPN provides any transfer of data encryption which can effectively protect the security of IP data packets, so most are used IPSec VPN solutions.

Open VPN provides a realization of all functions SSLVPN solution VPN Program. OpenVPN can use any IP subnet tunnel between the connection can be through a separate TCPIUDP port in any tunnel set up the network card connection. And can configure a scalable, load­balancing functionality with VPN server, it can handle from different places, thousands of dynamic VPN client connection requests.

In the remote monitoring of embedded network platform transplantation OpenVPN, transplant process is as follows:

1) As kernel compile in the Linux, you need to TNU I

TAP device support, you must select the Universal TNU I

TAP device driver support options; 2) Download and install the SSL VPN, SSL VPN main

function is as an algorithm library, through the cross­compiler for the Open VPN provides cryptographic algorithms library;

3) Download and install OpenVPN, generated by cross­compiling the embedded target machine to start the implementation of the document;

4 )Configure Open VPN startup script file to run, including equipment support and certificate path;

5) Start Open VPN in the embedded target machine;

B. TELNET remote login in embedded network plaiform

Upon the completion of the embedded target machine and the remote monitoring server connection, but also on the target machine to enable Telnet remote login service, so that managers can remotely monitor the target machine.

Telnet remote login is used to achieve complete control target machine of the most commonly of form for the Lin�x operating system. The user can connected any target wIth the monitoring system client login to the hosts. Every TCP/IP implementations are to provide a standard Telnet remote login service and run on different operating systems.

Embedded system platform in the application of the service, to migrate Telnet, transplant process is as follows:

1) First download and install busybox, compile-time to choose telnetd;

2) Established ptrnx and pts device, inside inted.conf written the permissions and work patterns of telnetd In the embedded platform;

3) The devpts have associate to pts device; 4) Start telnetd service, so you can login to the

embedded platform. After the above process, the serial device remote

monitoring of embedded network platform construction completed, the remote server PC through the VPN tunnel, remote login through Telnet embedded platform, the implementation of the principle as shown in Figure 3.

Figure 3 Serial device remote monitoring applications

IV. THE VIRTUAL SERIAL PORT OF LINUX PLATFORM

The Ethernet transmission network data and applications can not be directly received on the remote machine, but in reality there is a large number of serial devices are directly manipulate the application serial driver, that is, using the serial port API function or Some packages of the components to interact with the serial device data. Therefore, it is necessary to take some methods to establish an interface between the network driver and serial devices applications, that is virtual serial port, shown in Figure 4. Taking into account the serial device application is running on Linux operating system, so this paper is to be achieved virtual serial port in the Linux platform. Virtual serial port is actually a virtual serial driver responsible for managing the software and convert the information in the Ethernet bus.

PLC

Embedded

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Monitor

PC

Figure 4 Virtual Serial Port applications Virtual serial port software from three components: 1) for the Server service program, is a standard device

driver, is to receive from the Service service program information transmitted on the Ethernet;

2) communication program, will transfer the data stored; 3) Serial port applications providing a standard serial

device interface. The overall framework of the virtual serial

Figure 5 the virtual serial port software of framework

13 1

Virtual serial port and no difference between real serial port, through a virtual serial port, the original site of the serial management software and equipment do not feel the middle of deposit Ethernet bus to realize the original serial communication based on a smooth migration to the management application Ethernet bus system[8,9].

V. THE RESULTS OF TEST

Test Content: serial device sends data to the target machine, target machine program to convert the data, and then sent to the Ethernet; on a host network applications to receive target-side data, and then forwards the data through a virtual serial port to the management process. In this case, must we realize the serial Ethernet protocol conversion and remote monitoring porting to the target, experimental results show that this framework is implemented based on the serial device for remote monitoring, in common Internet network environment, test results normal.

Framework proposed in this paper can be effectively applied in embedded network environment, make up the current serial Ethernet communication in embedded systems have poor portability, and maintainability and scalability in the context has an advantage, but needs to further increase Embedded network security, enhanced interactive features, perfect platform for practicality.

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