摘要
随着电子测试技术的不断发展,测试技术正向自动化、智能化、数字化和网络化的方向发展。同时,数字存储示波器得到越来越广泛的应用,并逐步有取代模拟示波器的趋势。但由于台式数字示波器体积过于庞大,不方便携带进行现场测试和野外作业,己经越来越不能满足人们的生产需要。因此便携式数字存储示波器便孕育而生。
ARM处理器的广泛应用及嵌入式操作系统的发展,使示波器的设计有了新的思路。本文结合ARM处理器的结构及特点,进行了以Intel XScale PXA255处理器为核心的便携式数字存储示波器的设计。在本文中,硬件的设计基于Intel XScale PXA255处理器,同时在外围扩展了FLASH & SDRAM存储、LCD显示、触摸屏输入等模块,并进行了数字示波器数据采集系统电路的设计。本文的软件设计方案基于嵌入式Linux操作系统,进行了Linux 2.4.18内核的移植。同时,为了实现良好的示波器用户图形界面,还进行了MiniGUI图形系统的移植及程序编写。
本设计的实现过程显示了软硬件协同工作的特点,实现了较好的示波器数据采集及波形显示效果,经过对数字存储示波器各个部分仿真、实验及测试,基本达到了设计要求,特别是在用户图形界面GUI的设计上,采用了MiniGUI图形库进行软件开发,实现了良好的示波器人机交互界面。
With the development of the electronic measuring technology, the demand for measurement technique is higher and higher, so the traditional electronic oscillograph can hardly satisfy the need for real works. Measuring technology is geared to automated, intelligent and network directions. Digital storage oscillograph as the important measuring apparatus is widely used in various fields.
The design of digital storage oscillograph is based on the embedded systems. In recent years, the rapid development of digitization technology centering on computer, chip technology and software engineering, greatly boosts the research of embedded technology. Powerful embedded processor and excellent embedded operating system have been developed successively, which makes the application of embedded system more and more widespread and contains each aspect of national economic construction.
Embedded systems include embedded processor and embedded operating system. Embedded processors and the related functional expansion of the system’s circuit structure the hardware platform. Embedded operating systems include the bottom-driven software associated with hardware, system kernel, device driver, communication protocols, a graphical interface, standardization browser and so on. Embedded operating system runs on the embedded processor. Embedded operating system administers the processor and other hardware equipment in the bottom of processor, and it operates all application procedures. It shields the bottom of the details to provide a unified user interface. Application developers only need to split system development into several independent modules. This has greatly simplified the application design and shortened the development cycle, reduced repeating work, improved the efficiency of product development and improved the efficiency of knowledge innovation.
Now the technology of digital storage oscillograph is more advanced overseas, and occupies the great majority of market. So it is indispensable to develop digital storages oscillograph ourselves. However, with the development, it can't meet the need of modern manufacture more and more. As a result, a handhold digital storage oscillograph is studied. According to these requirements, the portable digital oscillograph which can replace the general digital oscillograph is designed and realized in this paper.
General application of ARM processor and development of embedded operating system provide new ideas for oscillograph design.
The portable digital oscillograph designed in this paper is based on the embedded Linux OS and adopts Intel XScale PXA255 processor. It integrates the functions of signal collecting, data calculation, data communication, data storage and signal display. The system design is based on the cooperation of the hardware and the software. The system design and implementation process can be divided into the following steps :
1. This system makes use of the Intel XScale PXA255 processor. We have designed the interface circuit of PXA255 processor and Flash, SDRAM, LCD and the touch screen A/D ADS7843 interface. Synchronously, I have designed the data collecting system hardware and realized the hardware platform of digital storage oscillograph system. Intel XScale PXA255 is a high-powerful embedded ARM processor introduced by Intel Corporation. It supports virtual memory management with MMU, pipelining, cache and the highest working frequency can be up to 400MHz; LCD do the terminals’display; Touch Screen Module uses AD7843; Terminal uses 32M bytes of FLASH and 64M bytes of SDRAM to store date and operate procedures, and the type are E28F128J3A and K4S281632C.
2. This embedded system adopts Linux2.4.18 as the EOS (Embedded Operation System). Linux is organized with layer structure and opens its source code. Its network is power. And it supports many kinds of file systems and can operate on many kinds of embedded processors, including PXA255 processor.
The embedded Linux OS is the heart of the whole system which controlls the operation of the whole system, and distributes the whole resource. The building of the embedded OS is the most important and complicated step which involves whether the whole system could operate reliably.
After studying the boot process of Linux OS and the particularity of the embedded system, this system decides to use host/target cross-platform development mode. In this mode, the host takes charge of building cross-platform development environment and completes most of the development work. At last, the binary code is downloaded to the target platform and run.
Besides, this system uses U-boot1.1.2 as the boot loader and makes JFFS2 (Journaling Flash File System) to be root file system. In software development, NFS (Network File System) is used to share file with PC. The above parts construct the basic embedded system software platform for software development and debugging.
3. After the building of the software platform, I begin to program the applications for the digital storage oscillograph system. The applications mainly achieve the signal collecting, data storage and signal display functions. The study of application is based on the MiniGUI, and the next step is transplanting MiniGUI into the terminal platform to realize the GUI of it.
Through debugging and testing, the hardware and embedded Linux operating system run stably, the GUI is friendly, the system carries out a good result of signal display and ultimately reaches the design request. The applications based on the embedded Linux OS are great transplantable, so we can transplant the applications of this system into other hardware platform. The system can be further expanded in terms of software and hardware to use in many other occasions.
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