1. Linux OS Porting on Create XScale-PXA270
Linux kernel porting

2. Outline History and Evolution Operating system Concepts
Linux versus other Unix-like kernels
Differences with User Application
Linux versions
Steps of porting
Reference

3. 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 process
hacking the kernel, trying to port some GNU software (gcc, bash, ..) on MINIX-386

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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’

10. 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

11. 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

12. 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

13. 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

14. Operating system Concepts (cont’)
Here shows the sketch map of transitions between user and kernel mode (space)

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. Steps of porting System requirements: Linux host: Windows host:
used to compile Linux kernel image, root filesystem, device driver, user applications, and so on
ARM cross-compiler is needed
Windows host:
download and exam your project on Creator
Domingo for Linux is needed
Target:
Microtime Creator mother board, Creator-XScale-PXA270 CPU board

23. Steps of porting (cont’)
To build a Linux kernel for running on Creator-XSCALE-PXA270, you need:
source code of Linux kernel (mt-linux tar.gz )
patch (linux creator-pxa270.patch)
cross compiler (arm-linux-toolchain-bin tar.gz )
Then install the cross compiler into your Linux host system

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

25. Steps of porting (cont’)
Enter the Linux kernel directory, and type “make menuconfig” to configure your kernel

26. 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”

27. 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

28. Steps of porting (cont’)
Before download and verify your Linux kernel, check the connections between the Creator and your host PC:

29. 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

30. Steps of porting (cont’)

31. Steps of porting (cont’)
Press the “Config PCM…” to configure the peripheral of XScale PXA270
Choose “Import” to select default one:

32. Steps of porting (cont’)
After setting the hardware configuration, you can download your Linux kernel on PXA270 board to see if it work correctly

33. Steps of porting (cont’)
Load your kernel into memory addressed 0xa

34. Steps of porting (cont’)

35. Steps of porting (cont’)
Change the PC register value to A , 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

36. Steps of porting (cont’)

37. Steps of porting (cont’)

38. 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 …

39. 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 …