Download Steps of porting (cont

Linux OS Porting on
Create XScale-PXA270
Linux kernel porting
Outline
History and Evolution
Operating system Concepts
Linux versus other Unix-like kernels
Differences with User Application
Linux versions
Steps of porting
Reference
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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
software (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 interprocess 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 preemptive
Kernel 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 porting
System 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-XScalePXA270 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-linux2.6.15.3.tar.gz )
 patch (linux-2.6.15.3-creator-pxa270.patch)
 cross compiler (arm-linux-toolchain-bin4.0.2.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-creatorpxa270.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
無痛起步
 Linux kernel Archives
 Embedded Linux Training
 Linux kernel wiki
 The Linux kernel
 Kernel trap
…
 Debian
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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
…
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