嵌入式作業系統實作 Implementation of Embedded Operating Systems Introduction

國立台灣大學資訊工程學系

嵌入式作業系統實作 Implementation of

Embedded Operating Systems

Introduction

薛智文[email protected]

http://www.csie.ntu.edu.tw/~cwhsueh/

資工系網媒所 NEWS實驗室

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Outline

Introduction to Embedded System

Introduction to Embedded Operating System

Case Studies

SoCKernel


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Preface

Window 2000, 30M lines.

Netscape Communicator 5, 17M lines.

A 圍棋 program, 0.01M lines.

A SOHO router, 0.6M lines.

What is Embedded (Linux/system)?

Linux image files directories lines bytes

2.6.4 1150K 13400 960 5.6M 167M

2.4.25 1177K 11000 670 5M 149M

2.2.26 507K 5100 280 2.5M 75M

ThreadX 129K 158 1 29K 1.5M

uC/OS-II 55K 13 1 5.5K 0.4M

Tinix’ 0.5K 1 1 20 0.5K


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Embedded OS trends 2001-2002,

sorted by 2001

0%

5%

10%

15%

20%

25%

30%

Hom

e grown

VxW

orks

DO

S

Em

bedded Linux

WinC

E

QN

X

Nucleus

Green H

ills

LynxO

S

Chorus

2001

2002


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Embedded OS trends 2001-2002, sorted by 2002

0%

5%

10%

15%

20%

25%

30%

Em

bedded Linux

VxW

orks

WinC

E

LynxO

S

BSD

Green H

ills

QN

X

DO

S

Chorus

Hom

e grown

2001

2002


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電子書包發展硬體

電子書包作業系統 (OS / UI / CM)

教學 / 同儕群體應用軟體開發工具

系統軟體開發工具 (SDK)相容性測試軟體工具 (TCK)

ICE DDK

開發工具電子書包平台結構

教師教學應用軟體

電子書包教學應用平台

電子書包教學數位內容電子書包數位內容開發工具

同儕群體應用軟體數

位學習輔具

數位學習平台

閱讀程式SCOR

MHTMLXML

數位學習輔具

數位學習平台

Physical•Serial•USB•1394•IrDA•Bluetooth•802.11

Protocol

•SyncML

電子書包與數位學習輔具分工架構圖


org 07c00h ; tell the assembler to load onto 7c00, 0100h for DOS

mov ax, cs

mov ds, ax

mov es, ax

call DispStr ; call string display procedure

jmp $ ; infinite loop

DispStr:

mov ax, BootMessage

mov bp, ax ; ES:BP = string address

mov cx, 16 ; CX = string length

mov ax, 01301h ; AH = 13, AL = 01h

mov bx, 000ch ; page number is 0 (BH = 0) black background red character

; (BL = 0Ch, highlight)

mov dl, 0

int 10h ; the 10h software interrupt

ret

BootMessage: db "Hello, OS world!"

times 510-($-$$) db 0 ; fill the rest of sector (512 bytes) with 0

dw 0xaa55 ; end of sector

Tinix’ -“自己動手寫作業系統 ,” 于淵


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Example

RS485

RS485

Ethernet

Ethernet


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IntroductionUnix SVR4, System V Release 4, AT&T, now owned by Santa Cruz Operation, Inc.;4.4 BSD, UC BerkeleyDigital Unix, DEC Compaq HPAIX, IBMHP-UX, HPSolaris, Sun Microsystems, Stanford UniversityLinux, 1991 Linus Torvalds on 80386 Alpha, SPARC, 680x0, PowerPC, IBM 390, ARM, …

A Unix kernel with other applications available under GNU General Public License GNU’s Not UnixPOSIX, Portable OS based on Unix


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Outline



Software Engineering

Case Studies

SoCKernel

Paper discussion


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What is an Embedded System?

A system designed to perform a specific function, e.g. eBook, PDA, eWatch, …

A combination of computer hardware and software, and perhaps additional mechanical or other parts.Embedded vs. General-Purpose

What is a specific function?Is there a limitation?

Cost, Robust, Low-power, Small, …Using C + Assembly, Java ?


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Embedded System Examples

Computer peripheralsKeyboard, Mouse, …

Information AppliancesSet-Up Boxes, WebTV, …

Monitors and SensorsFire Alarm, Heartbeat Detector, …

Controllers in ElectronicsRefrigerator, Air Conditioner, …

Communication DevicesHub, Router, …

…


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Business Issues of ES

Time-to-market for new devicesDesign to delivery: in weeks

Sustained pressure to reduce costsMany proprietary choices yield low-margins

Life cycle managementNew products overlapping each otherPositioning nightmares

Open platform choices considered risky?Resources expended on “recreating the wheel…” not on product differentiation.


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ES Technology IssuesNeed more complex technology integrated for new services

broadband, wireless, real-time, low-power, …

Multiple emerging standards need to be deployed simultaneously.Product released globally on the same day!Tools, Tools, Tools, …Third party software

No one company can do it all anymoreSupport nightmares

Lack of sources from proprietary choicesOpen sources sound seductive … but risky.


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Real-Time Systems vs. Embedded Systems

RTS ESRTES

.Radar .Calculator.ABS


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Real-Time Systems

Time

Value

Hard RTS

Soft RTS

FirmRTS

Deadline

-Value


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Real-Time Systems (RTS)

Firm RTS

Soft RTSHard RTS

Proprietary

Open

Centralized

Distributed

Embedded


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Outline



Software Engineering

Case Studies

SoCKernel

Paper discussion


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Linux

2.2 Aims to be compliant with IEEE POSIX

Source codes from other Unix-like kernel can be compiled and executed with little efforts, even without patches.

Include modern OS features, i.e. virtual memory, virtual filesystem, lightweight processes, signals, IPC, SMP, …

Was not very innovative except General Public License (GPL).


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Linux vs. Other Unix-Like KernelsLinux kernel is monolithic.

Same as most other Unix variants while Mach 3.0, uses microkernel (task management + semaphore + timer), from CMU

Linux supports modules.Traditional kernels are compiled and linked statically.

Limited kernel threads can not execute user programs, Nonstandard lightweight process, using clone().

Linux is a nonpreemptive kernel.Only Solaris 2.x, Mach 3.0 are fully preemptive.Introduce fixed preemption points to cure.


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Linux vs. Other Unix-Like Kernels (cont.)

Multiprocessor support after 2.2. filesystem and network operation still remain sequential.

Filesystem is standard but is easy to port other filesystem through VFS.

EXT2, EXT3 (Journaling), ReiserFS (small files) IBM AIX, Journaling File SystemSGI Irix, XFS filesystem, for big volume, guaranteed I/O rate, and journaling.

No STREAMS I/O subsystem, from SVR4, popular in other Unix kernels for writing device drivers, terminal drivers, and network protocols.

rejected by Linus because of performance.


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Why Linux?

Free, no charge.Free, fully customizable in all components.Runs on low-end cheap HW platforms.

Embedded Linux is very hot.Powerful.

open source so as to fully utilize HW.High standard for source code quality.

low failure rate and maintenance time.Kernel can be very small and compact.Highly compatible with other OSes.

Filesystem, networking, code executed directly.Well supported.


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Hardware DependencyLinux maintains a neat distinction between hardware-dependent and hardware-independent source code.

alpha Hewlett-Packard's Alpha workstationsarm ARM processor-based computers and embedded devicescris "Code Reduced Instruction Set" CPUs used by Axis in its thin-servers, such as web cameras or development boards i386 IBM-compatible personal computers based on 80 x 86 microprocessors ia64 Workstations based on Intel 64-bit Itanium microprocessorm68k Personal computers based on Motorola MC680 x 0 microprocessors mips Workstations based on MIPS microprocessorsmips64 Workstations based on 64-bit MIPS microprocessorsparisc Workstations based on Hewlett Packard HP 9000 PA-RISC microprocessorsppc Workstations based on Motorola-IBM PowerPC microprocessorss390 32-bit IBM ESA/390 and zSeries mainframess390 x IBM 64-bit zSeries serverssh SuperH embedded computers developed jointly by Hitachi and STMicroelectronics sparc Workstations based on Sun Microsystems SPARC microprocessorssparc64 Workstations based on Sun Microsystems 64-bit Ultra SPARC microprocessors

Taiwan Core


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Power Management

Halting in the idle processidle process executes hlt on Intel

low-power consumption mode

Suspending the systempatches for suspending to disk

APM: Advance Power Managementlaptop standard power management

ACPI: Advanced Configuration and Power Interfacenew comprehensive standard from Intel-Microsoft

Power-management is essential for mobile systems


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Linux 2.6 Highlights

New scheduler

New architectures and processor types have been added – including support for MMU-less systems

New set of drivers for audio and multimedia have been added

Others (kernel core dumping, fast mutex support, an improved I/O subsysem etc.)


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2.4 vs. 2.6

Kernel 2.4 hadA Global runqueue.

All CPUs had to wait for other CPUs to finish execution.

An O(n) scheduler.In 2.4, the scheduler used to go through the entire “ global runqueue” to determine the next task to be run.This was an O(n) algorithm where 'n' is the number of processes. The time taken was proportional to the number of active processes in the system.

This lead to large performance hits during heavy workloads.


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Driver Porting to Linux 2.6

Quicker kernel build system

New set of module utilities

Makefiles for 2.4 won’t work in 2.6

.ko module object instead of an .o

module_init and module_exit instead of init_module and cleanup_module

New module loading utility minimize the occurrence of race conditions

The module usage count move to outside of module code


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Workqueue Interface

Used to schedule kernel tasks

Each workqueue has dedicated worker threads associated with it and all the tasks from the run queue run in the context of the process

Driver can use the default workqueue provided by the kernel


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Other Notable Changes

File systemsIBM’s JFS ( journaling file system ) and SGI’s XFS have been merged into 2.6

AudioNew Linux audio architecture ALSA (Advanced Linux Sound Architecture) replaces OSS (Open Sound System)


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Other Notable Changes

Power managementSupport for ACPI (Advanced Configuration and Power Interface), for CPU scalingUnder testing

Networking and IPSecThe IPSec feature uses the new crypto API, including MD4, MD5, DES, etcSupport for the new NFSv4

User interface layerSupport touch screen, braille device, etc


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Downsizing

Why?

1M 500K 300K 100K 46K 16K 5K

How?


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What is a Real-Time System?

A system enforcing timing constraints, e.g. Avionics, Missile Control, …

The correctness of the system depends not only on the logical result of the computation, but also on the time at which the results are produced.

Real-Time vs. High Performance

What is a timing constraint?A constraint of timing requirements, e.g. period, distance, deadline, ready time, …

Functional and temporal correct.


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What is a Real-Time Operating System?

An operating system enforcing timing constraints, Lynx, pSOS, VxWorks, eCOS, uCLinux, LynxOS, RTLinux, KURT, uC/OS-II, QNX, …


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Systems Issues

In RTS, the OS and AP are very tightly coupled, than time-sharing systems.

shared memory, special buses (instruction, data, event, memory, control, invalidate, …).

A RTOS must response to internal and external events deterministically.Low-priority tasks may wait for high-priority task or events indefinitely.System architecture needs to provide high computational speed, high-speed interrupt handling, and high I/O throughput, + fault-tolerance.

國立台灣大學資訊工程學系

TORNADO II ：VxWorks


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TORNADO II ： VxWorks

Embedded Development Tools

VxWorks Real Time Operating System

Wind Microkernel

Snapshoot of Host Development Tools


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The Next Generation of Embedded Development Tools


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VxWorks


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Wind Microkernel


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Embedded Internet


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Virtual Memory


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Multiprocessing


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Graphics


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File Systems


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Networking


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WindView


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Stethoscope


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Tips to be familiar with embedded boards

Buy a new notebook for each of your embedded board.

Lots of notes to be kept.

Search for on-line and off-line manuals.Ask someone who understands the board.Call your vendors.There may be news groups to discuss all kinds questions on your venders’ homepage. Join them!!Search on Google.


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Why Hardware?

A software engineer who writes only applications may spend an entire career and learn nothing about hardware, BUT …

An embedded software engineer must often:understand the hardware in order to write correct software,

must install the software on the hardware,

must figure out whether a problem is a software bug or hardware error, and

read hardware schematic diagram and suggest corrections.


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Overview (1/2)

The Linux is composed of four major subsystems.

User Application

O/S services

Linux Kernel

Hardware controller

User ApplicationO/S ServicesLinux Kernel

Hardware Controller

Decomposion of Linux system


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Overview (2/2)

Before we port Linux into target board, we must know hardware differences between host and target.

Usually, target board has limit hardware support. It might have no MMU or floating point.

Target board might support other special hardware or mechanism that host has not.


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Linux Kernel with MMU (1/5)

The Linux kernel use MMU to manage memory usage. But, Samsung-S3C4 does not have MMU function on it.

We need to consider many part of Linux Kernel for target without MMU.


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ARM MMU functionsTranslate virtual address into physical address

Control memory access permissions

Domain control

Hardware requirement for MMUTLB(Translation look aside buffer)

Access control logic

Translation-table-walking logic


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Virtual memory does more than just make your computer’s memory go further. It provides:

Large address spaces

Protection

Memory mapping

Fair physical memory allocation

Shared virtual memory


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Memory access controlSome memory, such as that containing executable code, naturally read only memory.

The operating system should not allow a process to write data over its executable code.


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Linux page tableNeed to translate a virtual address into a physical one.

Page allocation and de-allocation

ProcessWhile we create a process, Linux uses a technique called “copy on write”.

The read only memory, for example the executable code, will always be shared.

While the new process writes, then Linux would allocate a new page for writing.

Processes use dynamic linking library to share memory.


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Linux Kernel without MMU (1/5)

Linux kernel based on MMU. We must change the Linux kernel to support target devices in which has no MMU.

Virtual memoryThe target has no MMU cannot use virtual memory to allocate memory.

The function that allocate and de-allocate virtual memory are modified into physical memory allocation and de-allocation function.


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Memory access controlThe target has no MMU cannot control memory access permissions and domain.

All of the MMU control, and memory access control functions are masked to support flat memory.

Flat memory model treats the entire memory on your computer the same, without artificial boundaries or special exclusions.


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Page allocation and de-allocationBecause of no MMU, virtual memory can not be used.

All images have to be loaded to memory.

ProcessWithout MMU, processes cannot map image from file directly with ELF or A.OUT format.

We convert ELF into FLAT by using application elf2flat.



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vLinux memory mapvLinux uses very simple memory map to support target without MMU.

Page table entry is not used but reserved for other platform.

Programs are loaded into free memory area when execute.


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Exception Handler

Page Table Entry

Linux Kernel

ROOT File system

Free memory area

DRAM Base


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FireLinux

Developed by Real-Time Systems Laboratory of CS Dept. at CCU

Aims of this systemA flexible interface for run-time dynamic loading/unloading scheduler module

Support both time-driven and priority-driven scheduling approaches

A micro-second resolution one-shot timer

Shorten the task dispatch latency (interval between event and task switching)


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Architecture of FireLinux

Pinwheel RM EDF …

User Space

Kernel Space

Scheduler

Load/Unload

FireTimer

Task1 Task2

Task QueueFlexible Scheduler Interface

Direct Access


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•Configurable OS on SOA•Configurable OS on SOA

System Configuration

Tool

HAL

BSP Tool

SOC

ARM MIPS UniCore …ISS

Porting

MP3 MPEG4 … User Space

HomeControl

DigitalAlbum

COS

Interfaces

Sched

PWRM

EDF

MM

PagingBitmap

Buddy

Task

ThreadNRTTask

RTTask

…

SOA Kernel Space

Kernel


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Overall Architecture

Long way to goFocusTeamwork

SW open kernelHW patented

Taiwan CoreSOC PlatformConfigurablePower-AwareReal-TimeSELF-Verification

xCore

A3:Compiler

A2:RTOS

C1: 多媒體

FU

A1: 結構 &

SOC 平台

B1: 電路設計

C2: 網路

QoS

B3: 電性驗證 B2: 功能驗證


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References

“Understanding the Linux Kernel (2nd Edition),” Daniel P. Bovert & Marco Cesati, O’Reilly, ISBN 0-596-00213-0, 天瓏"MicroC OS II: The Real Time Kernel," Jean J. Labrosse, CMP Books; ISBN 1578201039"Linux Device Drivers," 2nd Edition, Alessandro Rubini, Jonathan Corbet, O’Reilly, ISBN 0-596-00008-1, “Linkers & Loaders” by John Levine Morgan Kaufmann 2000.The official site of uClinux:

http://www.uclinux.org/Arcturus Networks now officially hosting the uClinux project:

http://www.rt-control.com/http://www-106.ibm.com/developerworks/linux/library/l-inside.html#resourceshttp://kernelnewbies.org/documents/kdoc/mousedrivers.pdfhttp://www.cs.ccu.edu.tw/~chsueh

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嵌入式作業系統實作 Implementation of Embedded Operating Systems Introduction