Design and implementation of network communication based on ARM11 under Linux platform

With the rapid development of CPU manufacturing technology, more and more high-performance, low-power embedded microprocessors are applied to all aspects of our lives. ARM11 adopts ARM's new generation instruction architecture ARMv6, with a maximum frequency of 1GHz, power consumption as low as 0.4mW/MHz, and 8-level pipeline technology. On the other hand, it improves the memory system to make it more suitable for the hardware requirements of the operating system.

Linux is developed on the basis of Unix. It is a secure, stable, free and portable processor platform for various architectures. Linux is divided into multiple modules, and some minor modules can be cut to reduce the program size, so as to better meet the power consumption and cost requirements of the microprocessor.

1 Construction of embedded Linux software development environment

1.1 Brief Introduction to Embedded Linux Development Environment

The development of embedded Linux drivers needs to be carried out under an operating system with Linux as the kernel. To facilitate data transmission and information feedback during development, VMware virtual machine software is installed, and the Ubuntu 10.10 operating system is installed in it. It should be noted that the operating system version cannot be too low, because if the version is too low, many tools cannot find the corresponding support package, resulting in the failure of some software.

Ubuntu is an operating system based on Linux. When you first install Ubuntu, you will be asked to enter a new account and password. This new account will be used as the default login account when Ubuntu is first started. Ubuntu 10.10 supports a graphical user interface, but there are still many functions in Linux that cannot be expressed in the form of a graphical interface.

Therefore, to learn Linux well, you must have a deeper understanding of the Linux command line.

Ubuntu 10.10 will automatically install VMware tools for file transfer between the virtual machine system and the host machine, that is, users can directly drag files from the host machine to the virtual machine. If it is not installed automatically, select Install VMware Tools under VM to install it.

Linux has certain permissions restrictions for ordinary users. For example, when installing some support packages, you must use the root user's permissions to operate. To log in as the root user every time you start Linux, you can enter the hyperterminal at the first login and open the user configuration file in the /etc/gdm directory: custom.conf. That is, you can log in with root permissions every time you log in.

1.2 Cross-compiler

A cross compiler is a compiler that runs in a computer environment and can compile code that can run in another environment. We call this compiler a cross compiler. In this article, we will write code in an ordinary personal computer with CISC X86 architecture, and the compiled program will run in an ARM11 microprocessor with RISC ARMv6 architecture.

1.3 Network File System

NFS is the abbreviation of Network File System. NFS allows a system to share directories and files with others on the network. By using NFS, users and programs can access files on the remote system just like accessing local files. In embedded development, NFS makes it extremely convenient to transfer files between hardware platforms and computers during development.

1.4 Network Programming Experiment

Implement a typical client/server program. The client-server model requires that each application should consist of two parts: one part is responsible for initiating communication, and the other part is responsible for responding to it. They usually run on different hosts, called client and server respectively. A server is any program that can provide services on the network. A client is an application that a user needs to run in order to get a certain service. A server accepts requests from clients on the network and returns the results to the client after completing the service.

2 Construction of Embedded Linux Hardware Platform

2.1 Linux bootloader

Embedded Linux boot program generally uses u-boot, the full name of which is Universal Boot Loader, which is an open source project that complies with the GPL terms. First, set the DIP switch to configure ARM11 to read u-boot from the SD card, and then use the hyperterminal to copy the read u-boot to the NAND Flash on the ARM11 board, and then set the boot mode to configure ARM11 to boot from Flash. At this point, the loading of the embedded Linux boot program on the ARM11 platform is completed.

2.2 Linux Kernel

After completing the loading of u-boot, the kernel file can be directly transferred from the PC to the embedded development platform through the hyperterminal. Usually, the kernel file is transferred to a specific address of nandflash for temporary storage, and then the kernel file is burned to a specific kernel address through the burning command to complete the burning of the embedded Linux kernel.

2.3 Embedded Linux File System

The files in the embedded Linux file system are a collection of data. The file system contains not only the data in the files but also the structure of the file system. All files, directories, soft links and file protection information seen by all Linux users and programs are stored in it. Commonly used file systems are yaffs2 file system and cramfs file system. Yaffs is the first embedded file system designed specifically for Nandflash memory, suitable for large-capacity storage devices, and is released under the GPL agreement. Cramfs file system is a read-only compressed file system designed specifically for NorFlash, using real-time decompression, compact and fast.

3 Conclusion

The flowchart summary of the network communication program based on ARM11 under the Linux platform is shown in Figure 2.

This article describes the current embedded Linux and its network communication, with embedded as the knowledge background. The design mainly consists of six processes (NFS, cross compiler, network programming experiment, Linux boot program, Linux kernel, embedded Linux file system). The writing process of other embedded Linux applications is similar.