YASKAWA JANCD-MIF01 随着微电子技术的不断创新和发展，嵌入式系统已经广泛渗透到科学研究､工程设计､国防军事､自动化控制领域以及人们日常生活的方方面面｡由嵌入式微控制器组成的系统其最明显的优势就是可以嵌入到任何微型或小型仪器和设备中｡
嵌入式系统是指将应用程序､操作系统与计算机硬件集成在一起的系统｡它以应用为中心､以计算机技术为基础，而且软硬件可以裁剪，因而是能满足应用系统对功能､可靠性､成本､体积和功耗的严格要求的专用计算机系统？1？｡嵌入式系统与通信､网络技术的结合可以极大地增强网络的智能化与灵活性，拓展通信功能，从而实现各种通信系统之间的互联互通｡本文给出一种适合于中/低端应用的通信平台设计方案，它可支持Ethernet网络之间的数据传输，并且具有RS232､ RS485､ USB等接口｡文中围绕嵌入式uClinux环境设计了基于嵌入式通信微处理器S3C44B0X的硬件通信平台，从而实现了嵌入式Socket通信｡
1 嵌入式网络通信系统结构
作为一类特殊的计算机系统， 嵌入式系统通常由嵌入式处理器､嵌入式外围设备､嵌入式操作系统和嵌入式应用软件等几大部分组成｡嵌入式处理器是嵌入式系统的核心部件，它可分为嵌入式微处理器､嵌入式微控制器､嵌入式DSP（Digital Signal Processor）和高度集成的嵌入式SoC（System on Chip）｡嵌入式外围设备是指嵌入式硬件系统中除中心控制部件以外的存储､通信､保护､调试､显示等其它辅助部件｡嵌入式操作系统一般在比较大型或需要多任务的应用场合才考虑使用，它可方便嵌入式应用软件的设计，大大提高嵌入式系统的功能，但同时也要占用宝贵的嵌入式资源｡嵌入式应用软件和普通的应用软件有一定的区别，它是针对特定的实际专业领域､基于相应的嵌入式硬件平台､能完成用户预期任务的计算机软件｡
嵌入式处理器有许多种流行的处理器核，本文主要介绍采用Samsung公司基于ARM公司32位RISC的ARM7TDMI核的S3C44B0X处理器来进行Socket通信的软硬件平台的设计和实现方法｡
S3C44B0X是高性价比､高性能的微控制器，它采用ARM7TDMI核，可工作在66MHz｡ARM7TDMI是一种32位嵌入式RISC处理器，但也配备了16位压缩指令集Thumb｡它支持片上调试，允许处理器响应调试请求暂停，芯片内的增强型乘法器（multiplier）可进行两个32位数相乘从而直接产生64位结果，也可为嵌入式ICE硬件提供片上断点和调试点支持｡此外，它还可以提供三级流水线及冯？诺依曼结构｡实际上，S3C44B0X已在ARM7TDMI内容基础上扩展了一系列完整的通用外围器件｡图1所示是一种嵌入式网络通信系统的硬件体系结构｡
2 外围电路设计
作为优秀的网络控制器，基于S3C44B0X处理器的系统必须要有一个与之匹配的控制芯片｡这里，笔者选用了Cirrus logic公司的CS8900A｡CS8900A是一个单芯片全双工的以太网解决方案，片内集成了用于完成以太网电路所必需的所有模拟和数字电路｡图2为系统中的CS8900A以太网接口电路｡图中的信号发送和接收端通过网络隔离变压器和RJ45接口接入传输媒体｡另外，为了系统能够正常工作，还需要外接一个20MHz的晶振｡
3 基于uCliunx的Socket通信
本系统的软件是基于嵌入式操作系统uClinux而设计的｡uClinux是一个完全符合GNU/GPL公约的操作系统，它与UNIX系统兼容，其代码完全开放｡uClinux是在标准Linux基础上进行适当裁剪和优化后的操作系统，uClinux是一个高度优化､代码紧凑的Linux的嵌入式子集｡虽然体积很小，但仍然保留了Linux的大多数优点，如：稳定､良好的移植性;优秀的网络功能;对各种文件系统的完备支持，以及标准丰富的API等｡uClinux是专门面向没有存储器管理单元（MMU）的处理器的嵌入式操作系统，并且专为嵌入式系统做了许多小型化工作，它可以直接在Flash上运行，也可以加载到内存中运行｡u-Cliunx带有一个完整的TCP/IP协议，同时也支持其他许多网络协议，对于嵌入式系统来说，它是一个网络完备的操作系统，因此得到了广泛的应用｡
YASKAWA JANCD-MIF01
YASKAWA JANCD-MIF01
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