Linux OS Porting on Create XScale-PXA270

Linux kernel porting

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Outline

History and EvolutionOperating system ConceptsLinux versus other Unix-like kernelsDifferences with User ApplicationLinux versionsSteps of portingReference

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History of Linux

First time, the Linux kernel is published at 1991/10/5 “Free minix-like kernel sources for 386-AT”

Linus Torvalds studied MINIX OS first, and learned about hardware knowledge of Intel 80386 process hacking the kernel, trying to port some GNU so

ftware (gcc, bash, ..) on MINIX-386

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History of Linux (cont’)

Linus named his operating system “FREAX” and upload it to the server ‘ftp.funet.fi’

Ari Lemke, the server administrator, doesn’t like this name and changed the directory name to “Linux” for the homophonic of the inventor, Linus

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Evolution of Linux

Linux is a member of the large family of UNIX-like operating system Unix is simple and well-designed Unix consider all the things as ‘files’ in system Kernel and system utilities are written by C

language which is portable very short time to create process easy and stableness inter-process

communication

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Evolution of Linux (cont’)

The kernel aims to be compliant with the IEEE POSIX (Portable Operating System Interface for Computing Systems) a standard to describe API of operating system to promise the applications could porting to

many operating systems without changing the source

based on practice and experience of Unix

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Evolution of Linux (cont’)

Linux isn’t a commercial operating system its source code under GNU General Public

License which is open and available to anyone to study

basic software on Linux is produce from GNU projects

Internet brings Linux to the world hackers from different countries devote their

life to progress Linux on Internet

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Operating system Concepts

An operating system can roughly explain to some components of system ‘system’ contains operating system and any

applications working on the operating system

These components include kernel, device drivers, boot loader, command shell or other user interfaces, and some basic file and system utility tools

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Operating system Concepts (cont’)

Here talks only ‘kernel’, the deepest of an operating system

A kernel needs to provide root services for other parts in system

Kernel also have to manage hardware and allocate system resources

Sometimes a kernel can be explained as ‘supervisor of OS’ or ‘core’

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Operating system Concepts (cont’)

Some special elements of kernel are: interrupt handlers, used to services interrupt

requests scheduler, let many processes to share CPU

slices memory manage system, handle process

address space system utilities like network services or inter-

process communication protocol

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Operating system Concepts (cont’)

In modern system, which has protected memory management units, a kernel program will have higher system state kernel programs have un-limited hardware

access rights and work in a protected memory space named kernel-space

user programs could only access some parts of system resources and could not control hardware directly

user programs are working in user-space

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Operating system Concepts (cont’)

If a user program has to access some kind of hardware, it use system call to ask kernel handle the request action

Almost all the architectures that Linux supported provide the concept of interrupts when hardware want to communicate with

system, it will send a interrupt to let kernel stop and handle it’s request

kernel will use interrupt numbers to choose a specific interrupt handler

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Operating system Concepts (cont’)

In fact, we can induce that CPU are doing one of three things: execute specific process in kernel space handle interrupt request in interrupt context

which independent with other process in kernel space

execute user program process in user space

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Operating system Concepts (cont’)

Here shows the sketch map of transitions between user and kernel mode (space)

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Linux versus other Unix-like kernels

Linux support kernel modules to load and unload dynamically

Linux support symmetrical multiprocessor, which most traditional Unix variants do not support this mechanism

Linux kernel is preemptiveKernel do not separate thread and process,

each procedures are the same just some procedures may share resources

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Linux versus other Unix-like kernels (cont’)

Linux is fully customizable in all its components

Linux kernel can be very small and compact you can fit both a kernel image and full root

filesystem, including all fundamental system programs, on just one 1.4 MB floppy disk

Linux runs on low-end, cheap hardware platforms

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Differences with User Application

Kernel program do not link C library major reason is execution speed and size but also some in common use functions are

implement in kernel source code

Kernel developer use GNU C and ISO C99 to compose kernel the use of inline function and inline assembly

is feasible

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Differences with User Application (cont’)

There is no memory protection mechanism destroy memory data by kernel occurs ‘oops’ kernel memory could not be paged

Uneasy to use floating point numbers in kernel you have to access the floating point registers

and handle your operation by hand

Small and static stack in kernel in 32 bit architecture only 8KB in size

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Differences with User Application (cont’)

Race conditions in kernel: use concurrence control to prevent it care if SMP to access the same resources care if interrupt will access the same resources

with the executing process care if preemptive condition comes true classic ways to prevent these situations are

the use of spinlocks and semaphores

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Linux versions

Linux distinguish stable kernels from development kernels through a simple numbering scheme each version is characterized by three

numbers, separated by periods first two numbers identify the version third number identifies the release new release of a stable version come out

mostly to fix bugs reported by users

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Linux versions (cont’)

If the second number is even, it denotes a stable kernel; otherwise it denotes a development kernel development versions may differ quite

significantly from one another kernel developers experiment with different

solutions which occasionally lead to drastic kernel changes

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Steps of portingSystem requirements:

Linux host: used to compile Linux kernel image, root filesystem,

device driver, user applications, and so on ARM cross-compiler 4.0.2 is needed

Windows host: download and exam your project on Creator Domingo for Linux is needed

Target: Microtime Creator mother board, Creator-XScale-P

XA270 CPU board

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Steps of porting (cont’)

To build a Linux kernel for running on Creator-XSCALE-PXA270, you need: source code of Linux kernel (mt-linux-

2.6.15.3.tar.gz ) patch (linux-2.6.15.3-creator-pxa270.patch) cross compiler (arm-linux-toolchain-bin-

4.0.2.tar.gz )

Then install the cross compiler into your Linux host system

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Steps of porting (cont’)

After install the cross compiler into your system, don’t forget to update your PATH environment variable

When the cross compiler is ready, extract your kernel source and patch it by: cp linux-2.6.15.3-creator-pxa270.patch

/pxa270/pro/devkit/lsp/create-pxa270 patch –p0 < linux-2.6.15.3-creator-

pxa270.patch

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Steps of porting (cont’)

Enter the Linux kernel directory, and type “make menuconfig” to configure your kernel

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Steps of porting (cont’)

Here we use a default configuration file for the Creator XScale-PXA270 board

Choose “Load an Alternate Configuration File” and type “Enter” to select one

The default configuration file is located in “pxa270/linux/arch/arm/configs” and named “creator_pxa270_defconfig”

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Steps of porting (cont’)

After configured the kernel, it’s time to make your kernel image by typing: make dep make clean make zImage

The kernel image could be find at “pxa270/linux/arch/arm/boot/”

To verify the kernel image, you need to copy this image to a Windows host

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Steps of porting (cont’)

Before download and verify your Linux kernel, check the connections between the Creator and your host PC:

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Steps of porting (cont’)

To verify your Linux kernel on PXA270, you need “Domingo for Linux” on Windows system

Check you must have your kernel image in the Windows system

Execute the Domingo on your Windows, and select “No project” to enter a hardware setting page

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Steps of porting (cont’)

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Steps of porting (cont’)

Press the “Config PCM…” to configure the peripheral of XScale PXA270

Choose “Import” to select default one:

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Steps of porting (cont’)

After setting the hardware configuration, you can download your Linux kernel on PXA270 board to see if it work correctly

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Steps of porting (cont’)

Load your kernel into memory addressed 0xa0008000

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Steps of porting (cont’)

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Steps of porting (cont’)

Change the PC register value to A0008000, which the kernel image’s address in RAM

Before click RUN in Domingo, set up your Hyper terminal for receiving Linux kernel debug message and be the shell interface of it

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Steps of porting (cont’)

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Steps of porting (cont’)

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Reference

Web site references:鳥哥的私房菜 Debian 無痛起步 Linux kernel Archives Embedded Linux Training Linux kernel wiki The Linux kernel Kernel trap …

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Reference (cont’)

Book references: Understanding the Linux Kernel, 2/e, O’Reilly Linux 核心開發指南 , 2.6版 , 維科 Linux Kernel 完全剖析 , 博碩文化 …