Linux Community Magazine

Abstract: This paper describes the use of embedded Linux PowerPC405 on digital video playback system to build the process of software platform to explore the embedded Linux system in cross-compiler, bootloader, Linux kernel, root file system, and several other major part of the the build process. Keywords: PowerPC405; embedded Linux; digital video player; U-BOOT Introduction: Digital video playback devices in recent years developed very rapidly in a wide variety. Traditional video playback device (such as DVD player) software system is generally a simple control loop system, no operating system extensions and upgrades limited. This study is a portable digital video playback device is built on top of the embedded 32-bit PowerPC405CPU, running Linux operating system to large capacity hard disk as a storage medium, with networking capabilities. IBM, launched PowerPC405 is a specialized RISC processor for embedded applications, is widely used. Embedded Linux [1] as an open-sou rce operating system software with free of charge, to support a number of CPU, can be cut, support networks, rich software resources and so on. Use of embedded Linux to build a digital video playback system software platform allows the player low cost, easy to upgrade and manage, support multiple interfaces such as USB, enabling easy exchange of video programming and other advantages, the kind of equipment on behalf of the future development of a direction. This paper discusses the construct used in embedded digital video player Linux system bootloader, Linux kernel porting process and may be the major problems encountered, the corresponding solution. 1 digital video playback system block diagram (Chart 1-1 Stream Play System hardware block diagram) Figure 1-1 based players in the system diagram, the core control system PowerPC405-based embedded Linux, through the application process to the data storage system in the treatment program after a certain move to the stream contr ol system in the FPGA, the complete decrypted by the FPGA to give decoding system, decoding system extracted through the output RGB signal to the display device to display. Which we are concerned about is the core control system set up in embedded Linux systems. Player embedded Linux system hierarchy shown in Figure 1-2, the hardware after power, CPU's program first pointer to point to a specific memory address, the address stored with general office bootloader, bootloader initialization complete CPU and memory and other equipment, the Linux kernel in moving from the general ROM device to extract the memory and then jump to the kernel process pointer in memory of the beginning of the Department, by the Linux kernel to complete the rest of the system continue to guide the work. Re-initialize the system kernel, after completion, it loads the root file system, run user applications. The embedded Linux system platform construction process can refer to the system boot process, th e major construction work to do bootloader, Linux kernel, root file system these parts. 2 platform to build embedded Linux systems preparation (Figure 1-2 software system structure chart) To build embedded Linux platform, first of all be prepared to cross-platform development tool chain. It runs on local host, the compiler links the binary executable generated will run on the development board's CPU and operating system. Construction includes a compiler, gcc, linker ld, C library glibc toolchain, etc. There are many ways you can download the source code to the related sites compiled by hand, and the most convenient way was a good use of sound development has been compiled package, such as Germany denx company ELDK development kit, use the method, see [2]. 3bootloader and Kernel Selection Ready development tool chain, you can begin the development of embedded Linux system, first bootloader choice. 3.1bootloader choice Normal PC, after the first boot into the BIOS, the system through the BIOS for some initialization, then boot the operating system such as Windows or Linux, embedded systems in general no BIOS, but it also needs to achieve a similar function module, which is the bootloader (boot loader), its main function is to initialize the CPU, memory and other hardware devices, and into the operating system. Bootloader many different types, such as blob, lilo, grub, U-BOOT so. Currently the most widely used in embedded field is free and open source software denx's U-BOOT, it supports PowerPC, ARM, MIPS, x86 and other CPU, more than 100 kinds development board, a clear source structure, transplant easily, development rich document, users may encounter problems using general can quickly be resolved. Therefore, we use U-BOOT as a development board bootloader. According to different development boards, flash size, and model different kind of memory sizes, different ways so start making use of U-BOOT need to do some appropriate changes to meet the u ser's own development board, specific transplantation Methods and FAQs can be found in [3]. 3.2Linux kernel porting Bootloader initialization complete system hardware, put the Linux kernel from an external storage medium into memory, then, it will control to the Linux kernel, the kernel to continue to complete the system's guidance. If the kernel does not support the users to use the development board, the user needs to manually modify the Linux kernel itself to do some work related to migration, to pay attention to is on the development board's hardware peripheral parts of the deal, including the kernel basic information on the hardware board processing, on-board hardware initialization, interrupt the distribution. Development Board-level Linux kernel porting the most convenient way is to use the existing kernel and the user hardware platform closest to the development board as a template, do changes on this basis. We use the development board and IBMwalnut development boar d similar to the major peripherals, including hard drives, USB devices are using PCI bus interface adapter (PCI switch to IDE, PCI transfer USB), so the kernel of the migration work has two parts, one for the bootloader and kernel information transfer between the hardware board, two PCI peripherals for the initialization. 3.2.1U-BOOT and Linux kernel with U-BOOT complete hardware initialization after the kernel into memory,