embedded linux on arm - pudn.comread.pudn.com/downloads76/ebook/284217/embedded_linux_on_ar… ·...

Home Automation, Networking, and Entertainment Lab

Dept. of Computer Science and Information Engineering National Cheng Kung University

Chia Che Lee

Embedded Linux on ARM

Department of Computer Science and Information EngineeringNational Cheng Kung University 2HANEL

OUTLINETool chainsBootloaderBuilding Linux kernelLinux device driverGUI


Tool chainsA collection of tools used to develop for a particular hardware target (e.g. embedded system)Often used in the context of building software on one system which will be installed or run on someother device (e.g. embedded system) the chain of tools usually consists of such items as a particular version of a compiler, libraries, assembler, special headers, etc.


Tool chainsThe Advantage of understanding tool-chain :

Any project that requires an embedded processor also requires software-development tools.Be advantage to develop new embedded system by developing own tool-chain


Tool chains

The role of toolchain


Tool chains

Compile flow chart

Source code

Source code

Source code

Assembly code

Assembly code

Assembly code

object code

object code

object code

Executable code

code

compiler compiler compiler

Assembler Assembler Assembler

LinkerLibraries


Tool chains

Why using the GNU Tool-chain

GNU is a complete, Unix-like operating system that has been in development for just over twenty yearsGNU software is known for it's stability and standard complianceGNU tool-chain is open source which be easy to modify


Tool chainsThe GNU toolchain consists :

Compiler gccAssembler binutils : asLinker-- binutils : ldLibrary glibcDebugger-- gdb


Tool chains

gcc - GNU Compiler Collection

gcc is a full-featured ANSI C compiler with support for C, C++, Objective C, Java, and FortranGCC provides many levels of source code error checking , produces debugging information, and can perform many different optimizations to the resulting object code


Tool chains

gcc - GNU Compiler Collection

The GNU Compiler for Java is now integrated and supported: GCJ can compile Java source or Java bytecodesto either native code or Java class filesGCC now supports the Intel IA-64 processor, so completely free software systems will be able to run on the IA-64 architecture as soon as it is released.


Tool chains

GNU Binutils

Binutils are a collection of binary tools like assembler, linker, disassembler .Binutils is to create and manipulate binary executable files.The main tools for Binutils

ld - the GNU linker.as - the GNU assembler.


Tool chains

GNU C Library

Any Unix-like operating system needs a C library ( defines the system calls'' and other basic facilities such as open, malloc, printf, exit... )The GNU C library is used as the C library in the GNU system and most systems with the Linux kernel.The GNU C library is a large blob of glue code, which tries to give it's best to hide kernel specific functions from you. (e.g. You can use the same function name and do not care the difference between different kernel )


Tool chains

What is GDB

GDB : The GNU Project DebuggerAllows you to see what is going on `inside' another program while it executes Allows you to see what another program was doing at the moment it crashedGDB can run on most popular UNIX and Microsoft Windows variants.


Tool chains

GDB

Supported LanguagesCC++PascalObjective-CMany other languages


BootloaderBootloader is mainly responsible for loading the kernel, it is an very important componentMany bootloaders can be used with Linux on various hardware

LOIOGRUBLinuxBIOSRedbootU-boot


Bootloader


BootloaderThe simple code will be execute after you power on your target ( Sometimes we call it boot monitor )Embedded System bootloader should do:1. Initialize Hardware: processor and memory2. Loading kernel image and execute kernel

(sometimes it need to transfer parameter to linux kernel)


Bootloader


Bootloader

reset;;Reset Code;(in assembly)Jmp hw_init

Hw_init;Hardware;Initialization;(in assembly).Jmp startup

Startup;;startup code;(in assembly)Call main

NoOS/OS Code

Main(){/*The C/C++ program start here*/}

Boot Loader


Bootloader

Part1Jump 0x00900000

Part2Initialize the actual hardwareSet cpu mode

Part3Disable all interruptsCopy any initialized data from ROM to RAMZero the uninitialized data areaAllocation space for and initialize the stackInitialize the processors stack pointerCreate and initialize the heapExecute the constructors and initializers for all global variables (C++)Enable interruptsCall main

Part4Program C/C++ code


Bootloader


Building Linux kernel

Three different host/target architectures are available for the development of embedded Linux systems:

Linked setupRemovable storage setupStandalone setup

Your actual setup may belong to more than one category or may even change categories over time, depending on your requirements and development methodology



Linked Setup

The target and the host are permanently linked together using a physical cable

This link is typically a serial cable or an Ethernet linkAll transfers occur via the link

*Cross-platform development environment

Host

*Bootloader

*Kernel

*Root filesystem

Target



Linked Setup(cont)

The kernel could be available via Trivial File Transfer Protocol (TFTP)The root filesystem could also be NFS mounted instead of being on a storage media in the target

Using an NFS-mounted root filesystem is actually perfect during development, because it avoids having to constantly copy program modifications between the host and the target

The physical link can also be used for debugging purposes

Many embedded systems provide both Ethernet and RS232 link capabilities



Removable Storage Setup

A storage device is written by the host, is then transferred into the target, and is used to boot the device

*Cross-platform development environment

Host

*Bootloader

Target

*Secondary bootloader

*Kernel

*Root filesystem




(cont)

The target contains only a minimal bootloader

The rest of the components are stored on a removable storage media, such as a CompactFlash IDE device or any other type of drive

Instead of a fixed flash chip, the target could contain a socket where a flash chip could be easily inserted and removed

The chip would be programmed by a flash programmer on the host and inserted into the socket in the target for normal operation




(cont)

This setup is mostly popular during the initial phases of embedded system development

You may find it more practical to move on to a linked setup once the initial development phase is over

you can avoid the need to physically transfer a storage device between the target and the host every time a change has to be made to the kernel or the root filesystem



Standalone Setup

The target is a self-contained development system and includes all the required software to boot, operate, and develop additional software

This setup is similar to an actual workstation, except the underlying hardware is not a conventional workstation but rather the embedded system itself

*Bootloader*Kernel*Full root filesystem*Native development environment

Target



Standalone Setup(cont)

This type of setup is quite popular with developers building high-end PC-based embedded systems, such as high-availability systems

They can use standard off-the-shelf Linux distributions on the embedded systemOnce development is done, they then work at trimming down the distribution and customizing it for their purposes

This gets developers around having to build their own root filesystems and configure the systems' startup

It requires that they know the particular distribution they are using inside out



There are some broad characteristics expected from the hardware to run a Linux system:

1. Linux requires at least a 32-bit CPU containing a memory management unit (MMU)

2. a sufficient amount of RAM must be available to accommodate the system.

3. minimal I/O capabilities are required if any development is to be carried out on the target with reasonable debugging facilities.



There are three different setups used to bootstrap an embedded Linux system:

Solid state storage mediaDiskNetwork



Solid state storage media

Bootloader

Boot parameter

Kernel Root file system



Disk



Networkthe kernel resides on a solid state storage media or a disk, and the root filesystem is mounted via NFSonly the bootloader resides on a local storage media. The kernel is then downloaded via TFTP, and the root filesystem is mounted via NFS



Hardware

Kernel LevelHardware Level

Hardware control (HAL)

Linux

device drivers

character block

buffer cache

file subsystem

System Call InterfaceKernel Level

User Level

Libraries

User program s

IPC

Scheduler

M em ory m anagem ent


Device Driver


Device driverClasses of Devices and Modules

Character devicesBlock devicesNetwork interfaces


Device driver

Character devices

A character (char) device is one that can be accessed as a stream of bytes (like a file)Driver usually implements at least the open, close, read, and write system calls.The text console (/dev/console) and the serial ports (/dev/ttyS0) are examples of char devices.char devices are just data channels, which you can only access sequentially.


Device driver

Block devices

Like char devices, block devices are accessed by filesystem nodes in the /dev directory. A block device is something that can host a filesystem, such as a disk.


Device driver

Network interfaces

Any network transaction is made through an interface, that is, a device that is able to exchange data with other hosts.Network interface was look as a QueueThe Unix way to provide access to interfaces is still by assigning a unique name to them (such as eth0).


Hello World


Kernel module vs

Application

Whereas an application performs a single task from beginning to end, a module registers itself in order to serve future requests, and its main function terminates immediately.

the task of the function init_module(the modules entry point) is to prepare for later invocation of the modules functions.The second entry point of a module, cleanup_module, gets invoked just before the module is unloaded.


Init_module()Init_module()for each facility, there is a specific kernel function that accomplishes this registration. The arguments passed to the kernel registration functions are usually a pointer to a data structure describing the new facility and the name of the facility being registered.


cleanup_module

cleanup_module()To unload a module, use the rmmodcommand. Its task is much simpler thanloading, since no linking has to be performed. The command invokes the delete_module system call, which calls cleanup_module in the module itself if the usage count is zero or returns an error otherwise.


I/O RegionsThe job of a typical driver is, for the most part, writing and reading I/O ports and I/O memory. Access to I/O ports and I/O memory (collectively called I/O regions) happens both at initialization time and during normal operations.


I/O Port

A typical /proc/ioports file on a recent PC that is running version 2.4 of the kernel will look like the following:0000-001f : dma10020-003f : pic10040-005f : timer0060-006f : keyboard0080-008f : dma page reg00a0-00bf : pic200c0-00df : dma200f0-00ff : fpu0170-0177 : ide101f0-01f7 : ide002f8-02ff : serial(set)0300-031f : NE20000376-0376 : ide103c0-03df : vga+03f6-03f6 : ide003f8-03ff : serial(set)1000-103f : Intel Corporation 82371AB PIIX4 ACPI1000-1003 : acpi1004-1005 : acpi1008-100b : acpi100c-100f : acpi1100-110f : Intel Corporation 82371AB PIIX4 IDE1300-131f : pcnet_cs1400-141f : Intel Corporation 82371AB PIIX4 ACPI1800-18ff : PCI CardBus #021c00-1cff : PCI CardBus #045800-581f : Intel Corporation 82371AB PIIX4 USBd000-dfff : PCI Bus #01d000-d0ff : ATI Technologies Inc 3D Rage LT Pro AGP-133


I/O MemoryI/O memory information is available in the /proc/iomem file.


Chars DriversMajor and Minor NumbersSpecial files for char drivers are Major and Minor Numbers identified by a cin the first column of the output of ls l. Block devices appear in /dev as well, but they are identified by a b.Use ls l /dev commend to check.


Chars DriversThe kernel uses the major number at open time to dispatch execution to the appropriate driverThe minor number is used only by the driver specified by the major number

mknod /dev/scull0 c 254 0

creates a char device (c) whose major number is 254 and whose minor number is 0.


GUIQT & QT EmbeddedDirectFB


GUI

QT & QT Embedded

Qt is a C++ class library for writing GUI applications that run on UNIX, Windows 95/98, and Windows NT platforms Qt/Embedded, the embedded Linux port of Qt, is a complete and self-contained C++ GUI and platform development tool for Linux-based embedded development.


GUI

QT & QT Embedded


GUI

DirectFB


GUI

DirectFB

Embedded Linux on ARMOUTLINETool chainsTool chainsTool chainsThe role of toolchainTool chainsCompile flow chartTool chains Why using the GNU Tool-chainTool chainsTool chainsgcc - GNU Compiler CollectionTool chainsgcc - GNU Compiler CollectionTool chainsGNU BinutilsTool chains GNU C LibraryTool chains What is GDBTool chainsGDBBootloaderBootloaderBootloaderBootloaderBootloaderBootloaderBootloaderBuilding Linux kernelBuilding Linux kernel Linked SetupBuilding Linux kernel Linked Setup(cont)Building Linux kernel Removable Storage SetupBuilding Linux kernel Removable Storage Setup(cont)Building Linux kernel Removable Storage Setup(cont)Building Linux kernel Standalone SetupBuilding Linux kernel Standalone Setup(cont)Building Linux kernelBuilding Linux kernelBuilding Linux kernelBuilding Linux kernelBuilding Linux kernelBuilding Linux kernelBuilding Linux kernelDevice DriverDevice driverDevice driver Character devicesDevice driver Block devicesDevice driver Network interfacesHello WorldKernel module vs ApplicationInit_module()cleanup_moduleI/O RegionsI/O PortI/O MemoryChars DriversChars DriversGUIGUI QT & QT EmbeddedGUI QT & QT EmbeddedGUIDirectFBGUIDirectFB

embedded linux on arm - pudn.comread.pudn.com/downloads76/ebook/284217/embedded_linux_on_ar… ·...

Documents