Design and Implementation of ADSL2+ Tester Based on ARM

Introduction

In recent years, asymmetric digital subscriber line (ADSL) has been widely used worldwide as an ideal solution to the "last mile" problem of the network. In China, ADSL services have become one of the main growth points of operators' revenue. However, since the existing telephone lines are designed specifically for transmitting low-frequency voice signals, which is not conducive to high-frequency signal transmission, and the surrounding environment of the lines is harsh and complex and changeable, a series of complex tests are required for both the opening of ADSL services and normal operation and maintenance. Most of the existing test instruments are foreign brands and are expensive. Domestic products generally have limited test frequency bands and one-sided test results. In addition, due to the limited processing power of the core chip, the embedded operating system is not advanced, the software package functions are not perfect, and the management of test results is also relatively chaotic. With the continuous growth of the market, especially after the launch of ADSL2/2+ based on the ITU G.992.3/G.992.5 standard, reasonably priced, fully functional, and easy-to-operate test tools have become an urgent need for broadband operators. Based on this situation, this paper proposes a new ADSL2+ tester, which uses ARM9 processor and Windows CE operating system, comprehensively improves the processing capability and reliability of the product, and uses LCD touch screen to provide users with an intuitive and simple friendly interface, which can evaluate the network service quality at different locations of the user loop.
System hardware design

The system hardware structure is shown in Figure 1, which mainly consists of three parts: ARM control processing module, built-in Modem module and related simulation test module. The control processing module is the core part of the tester, responsible for the overall system control and related data processing.

Control processing module

This instrument requires LCD display and touch screen, so it requires high-speed data processing capability and considerable control capability. The ARM9 series 32-bit microcontroller S3C2410X used in the system has a frequency of up to 203MHz, which can easily run WinCE, Linux and other operating systems and perform more complex information processing. At the same time, a 5-inch STN LCD screen is used to intuitively display various test indicators, which makes up for the defects of the display effect of existing test tools. The use of a touch screen instead of a keyboard input part makes the portability advantage more prominent. Considering the needs of operating system operation and large-scale high-speed data processing, the system uses two 32M SDRAMs, one 32M NAND Flash and one 2M NOR Flash. The program, operating system and test data are stored in the NAND Flash, and the system boots from the 16-bit NOR Flash.

Built-in Modem module

When testing the line transmission performance parameters, the system can be directly connected to the local end without the user Modem. The ADSL/ADSL2/2+ data frame is converted by the built-in Modem and sent to the CPU for decoding and analysis. Therefore, it is also very important to choose a reliable and excellent Modem chip. This system uses the BCM6338 chip based on the latest ADSL2+ standard from BROADCOM, USA, which is suitable for various types of networks such as ADSL/ADSL2/ADSL2+, ensuring the reliability of the test results.

Analog test module The

physical layer test mainly includes voltage, resistance, capacitance test, etc., and has an embedded time domain reflectometer (TDR) for line fault location. All test functions are implemented by an independent board, and sent to the CPU for processing and storage through the general I/O port and A/D conversion port. The voltage, resistance, capacitance and other tests are calculated after measuring the voltage. S3C2410 integrates an 8-channel 10-bit ADC conversion module. The A/D converter works in on-chip sampling and holding mode, supports power-down mode, and its measured analog input voltage range is 0~3.3V. It can realize the conversion of external analog signals to digital signals in Windows CE environment. Figure 2 is a typical application of voltage measurement.

TEST0/TEST1 is the analog voltage to be measured. After 10 times voltage division, it is connected to a subtraction amplifier, and then connected to the 6th branch AD6 pin of 2410 for signal transmission and filtering. The 10-bit ADC value can be obtained through the device driver. Based on this value, the analog voltage VAD6 of AD6 is calculated as: *3.3. According to the schematic diagram, the voltage of the external test point TEST0 can be obtained. The calculation formula is: VTEST=
system software design

The system software development uses Platform Builder 4.2 and Embedded Visual C++ 4.0 (EVC).

Operating system kernel

The key to this development task is to select a real-time operating system that meets the application requirements and has the best cost-effectiveness. Taking into account the operating system's support for hardware and the ease of secondary development, the system uses Microsoft's Windows CE.

Customization and porting of the operating system is an important step in project development. We use the Platform Builder integrated development environment. After selecting the BSP, we cut the kernel and delete unnecessary system components according to project needs and memory capacity limitations. After establishing an operating system image project, we add custom module components to the corresponding project of Platform Builder to generate an operating system image. The Windows CE feature directory is extensible, and you can add your own features such as driver files to the feature directory. Platform Builder uses .cec files to create a feature directory, which allows Platform Builder to display this feature in the integrated development environment and add this feature to an operating system.

Application

The application to be developed in this project mainly includes data calculation display and system control, which are developed and debugged using EVC. The main test items of the system are physical layer test and network layer test.

Physical layer test is used to test the physical layer parameters of ADSL/ADSL2/2+ lines, including ADSL/ADSL2/2+ connection status, connection mode, uplink/downlink rate, noise margin, line attenuation, output power, CRC error, HEC error, FEC error, OCD error, NCD error and channel bitmap.

Through the built-in ADSL2+ Modem of the instrument, PPPoE dial-up is performed. After establishing the PPPoE dial-up connection, the network layer Ping, Ipconfig, Tracert and Route tests can be performed.

Device driver

Platform Builder comes with some standard BSPs and some general drivers, but for some special devices and functions, the drivers that come with Platform Builder cannot meet the requirements. In order to facilitate the communication and control with the simulation test part and the use of the LCD touch screen, it is also necessary to write the corresponding interface driver, mainly including the I/O port driver with PWM function for TDR test, etc., which is written in C language.

PWM is a method of digitally encoding the level of an analog signal. By using a high-resolution counter, the duty cycle of a square wave is modulated to encode the level of a specific analog signal. S3C2410X integrates 4 timers with PWM function. When the PWM function is required, the driver can adjust the PWM control register to control the I/O port to output pulses of equal amplitude and different widths to equal the ideal waveform. The PWM driver source code is omitted. For details, please see the website of this magazine.
Conclusion

The above design and system programming, after a series of field tests, have met the requirements of functional design. The system runs well and can successfully complete the test tasks in ADSL/ADSL2/ADSL2+ networks. It has been successfully industrialized with its excellent performance and has been partially applied to the business development of major broadband operators.

References:
1. Sun Tianze, Yuan Wenju, et al. Embedded Design and Linux Driver Development Guide - Based on ARM9 Processor. Beijing: Publishing House of Electronics Industry, 2004
2. Zhou Yulin, Ning Yang, et al. Windows CE.net Kernel Customization and Application Development. Beijing: Publishing House of Electronics Industry, 2004
3. ITU-T Recmmendation G.992.2/G.992.3/ G.992.5
4. Guo Shiqiu. ADSL Broadband Network Technology. Beijing: Tsinghua University Press, 2001