This document provides an introduction to embedded systems and embedded Linux. It begins with definitions of embedded systems as specialized computer systems that perform dedicated functions. It then discusses the typical hardware and software components of embedded systems, including processors, memory, operating systems like Linux, and application software. The document introduces some examples of embedded devices like drones. It also provides an overview of how Linux is customized and built for embedded systems, including the boot process, kernel configuration and building, and creating a root filesystem.

2. 2
Preface
Over the years Linux is being used or
embedded as operating system in many
intelligent and smart electronic devices
starting from mobile phone, refrigerator
to cow milking devices apart from
desktops and server computers. Though
Linux is open source, its often difficult
for a beginner to get started. In this
presentation embedded system and
embedded Linux have been introduced
through examples, animation and short
explanation. This presentation is
targeted to the absolute beginner or
embedded software engineer who wants
to be part of exciting world of Linux and
the enthusiast or even manager who just
wants to get idea about embedded
Linux.

3. 3
About Author
Hossain Reja, a graduate in computer
science and engineering from National Institute of
Technology, Hamirpur, has over seventeen years of
expertise in building embedded systems. He has
experience and working knowledge in multiple
domains – process control, set-top box, cable modems,
mobile domains and vehicle electronics and
infotainment. Hossain is passionate about kernel.

4. 4
Introduction to
Embedded
Systems

5.  Wild Life Preservation is very much
important
 Technology can help to preserve the
wild lives
 One such technology is drone
 Drone is a mini helicopter that can fly
at low altitude and can keep an eye on
the wild lives in a forest
5
Wild Life Preservation

6. 6
Drone – The Flying Machine
 An example of typical drone is a quad-copter
 This drone can take areal images – like wild
lives images in a forest , crop images in a
firming land etc
 These images can be processed to design and
develop various applications like – wild life
preservation, crop pesticide management
 This drone can be controlled by smart phone,
tablet, iPhone and iPad etc

7. 7
Things
Google Glass
A wearable device with optical head mounted
display that helps to navigate, talk to
internet through voice commands and
much more
Nike+ Shoes
This tracks a run and record it and
can communicate with Smart
Phone
Smart Phone
This does not need a description
Smart Watch
A computerized wristwatch that
essentially is a smart phone, phone
app can run on it and it’s application
is bound by your imagination

8. 8
Some more things
In-Vehicle Infotainment System
Provides driver assistance
information, navigation,
entertainment inside car and
much more
Learning Thermostat
An smart thermostat that learns your AC
usage behavior and control it saving
energy and connects to internet so
virtually it can be controlled from
anywhere
Smart Refrigerator
Apart from its basic function of
refrigeration, it learns your food stock
and automatically order for you and
takes instruction from you from
anywhere

9. 9
Embedded Systems
 These devices have at least one thing in common
 They are essentially a computer that runs software to accomplish a
specialized function - learning your AC usage behavior, jogging
behavior, food stock in your refrigerator or entertaining you inside
your car on a along drive
 A computer device with specialized function is an Embedded
System

10. 10
Inside
Embedded
Systems

11. 11
Drone – Tear down
Mechanical
 Chassis
 Propeller
Electrical
 Servo motor
Electronics
 Printed Circuit Board
 Digital Camera

12. 12
Drone – PCB Tear Down
 Main board
 Navigation board
Hardware
Vertical
Camera
Flash ROM
(128MB)
16-bit Micro
& 10-Bit ADC
RAM (128MB)
XY-axis
Gyroscope
WiFi
Processor
(ARM)

13. 13
Hardware Components
Processor : Central
Processing Unit
RAM: Main Memory
ROM: Secondary
(Persistent) Memory
Propeller: Driven by Servo
Motor (Navigation)
Gyroscope: Keeps drone stable
(Navigation)
Camera: Wild Life Image Capture,
Weed Detection at Firm House
WiFi: Wireless communication,
Remote Control through Smart
Phone, iPad etc

14. 14
Embedded Hardware and Software
 Hardware
 Operating System
 Application
Operating System
Applications
Hardware

15. ApplicationOS
15
Embedded Hardware and Software
Hardware
Vertical
Camera
Flash ROM
(128MB)
16-bit Micro
& 10-Bit ADC
RAM (128MB)
XY-axis
Gyroscope
WiFi
Processor
(ARM)
Operating System
 Linux
 Android (Linux based)
 Windows
 VxWorks
 iOS
Application Examples
 Navigation
 Video capture and image
processing
 Wild image detection
 Wild Life Protection
 Navigation board

16. 16
Embedded Linux

17. 17
Linux as Embedded OS
Application
Hardware
Linux OS

18. 18
Booting Process – x86
BIOS/EFI/UEFI
Boot Loader
(First Stage) Boot
Loader
(Second
Stage)
(grub, elilo) Kernel
(bzImage)
User
Application
(init)
 Staged booting process
 Main components
 BIOS/EFI/UEFI
(Firmware)
 Boot Loader (First Stage,
optional)
 Boot Loader (elilo, grub
etc)
 Linux Kernel
 User application

19. 19
Booting Process – x86
BIOS/EFI/UEFI
Boot Loader
(First Stage)
Boot Loader
(Second Stage)
(grub, elilo)
Kernel
(bzImage)
User
Application
(init)
* Starts on power
on/reset
* Does basic
initialization
*Does basic test
* Loads and runs First
Stage Boot Loader in
SRAM
* Initialize DRAM
* Loads and run
Second Stage Boot
Loader from DRAM
* Boot loader with
full festuree
*Iinitialize
hardware (DRAM)
* Loads Linux
kernel from a file
system (i.e. SD
card/Flash)
* Runs linux kernel
* Linux kernel
initializes all the
subsystems
(memory manager
scheduler, device
drivers etc)
* Runs first user
space program
* User space start-up
runs
* Mutli-user or
Graphical systems up
and running and ready
to be used
 Staged boot process
 System partially
initialized and
specific task is
achieved at each
stage from power on
to system boot (user
prompt or
application)
 Embedded system
generally prompt for
user login prompt,
it start application
during the boot
process
automatically

20. 20
Boot Process - ARM
ROM Code
init SRAM
Load boot strap on SRAM
Runs SRAM
Boot Strap
Init clock, SDRAM
Load u-boot from Flash to
SDRAM
Runs u-boot
u-boot
Uncompress zImage
Loads it to DRAM
Runs Kernel
Linux Kernel
Initialize all sub-system (clock,
memory manager, scheduler,
device driver, file system etc)
Runs user process init
User space init process
rootfs
Storage ViewExecution View
Flash
(u-boot.bin)
MTD/SD/MMC
(zImage)
SD/MMC/MTD
rootfs
DRAM
(u-boot)
DRAM
kernel
(uncompressed zImage)
DRAM
(init and ...)
Flash
ROMROM
(ROM code)
SRAM
(boot strap)

21. 21
Customization Required for Embedded Linux
ROM Code
Boot Strap
u-boot
Linux Kernel
Provided by chip manufacturer and
available in chip
Provided by chip manufacturer
and available in chip
u-boot project
http://www.denx.de/wiki/U-Boot
main line kernel source code
https://www.kernel.org
No change required
No change required
Customization Required as per
the hardware
Configuration, customization and
extension are required
rootfs Need to build a root file
systems where all required
software will be available
Need to build a root file systems
where all required software will
be available
Actions on Software ComponentsSoftware Components

22. 22
Boot Loader

23. 23
U-boot
 Under Construction

24. 24
EFI
 Under Construction

25. 25
Linux Kernel

26. LinuxKernel
Hardware
26
Linux Kernel Components
Veritical
Camera
Flash ROM
(128MB)
16-bit Micro
& 10-Bit ADC
RAM (128MB)
XY-axis
Gyroscope
WiFi
Memory
Manager
Virtual
Memory
Manager
Network
Drivers
Network
Network
Protocol
Scheduler
Process
Management
Character
Devices
Device
Drivers
Block/MTD
Devices
File System
Virtual File
System
Processor
(ARM)
• Process Management
• Memory Management
• I/O Management
(File system)
• Network
Management
• Device Management

27. UserSpace
27
Kernel Space & User Space
System Call (Linux Kernel Gateway)
System Software, Middleware, Application
Scheduler
Block/MTD
Devices
Character
Devices
Network
Drivers
Memory
Manager
Process
ManagementFile
System
Device
Drivers
NetworkVirtual
Memory
Manager Network
Protocol
Virtual File System
KernelSpace
(Privileged)
Hardware
Hardware
• Kernel Space
• User Space
• System Calls – gateway to
kernel from user space

28. 28
Kernel Space & User Space
UserSpace
System Calls (Kernel Gateway)
System Software (glibc, libudev, ...)
Hardware
Hardware
Kernel
Kernel
Space
Middleware
Network
Services ()
Internet
Services
(Webkit)
Graphics
Services
(Qt)
Media
Services
(pulseaudio,
gstreamer...)

29. KernelComponents
29
Kernel Code Organization
Scheduler
Process
Manage-
ment
Character
Devices
Device
Drivers
Memory
Manager
Virtual
Memory
Manager
Network
Drivers
Network
Network
Protocol
Block/M
TD
Devices
File
System
Virtual File System
Hardware
HardwareKernelCode
ConfigurationConfiguration
mmdrivers
i2c
mmc
fs
ext4
jffs2
net
wireless
ipv4
kernel
sched
timer

30. 30
Kernel Source Organization

31. KernelComponents
31
Kernel Configuration
SchedulerBlock/MT
D Devices
Character
Devices
Network
Drivers
Memory
Manager
Process
Manage-
mentFile
System
Device
Drivers
NetworkVirtual
Memory
Manager Network
Protocol
Virtual File System
Hardware (ARM, USB, SD, Flash...)
Hardware
....
CONFIG_ARM=y
CONFIG_USB=y
CONFIG_EXT4=y
....
CONFIG_MTD=y
• Configure kernel based on
hardware and features
required
• Eliminate kernel
components or features
that are not required to
optimize the image size

32. 32
Linux System Build
Environment

33. 33
Build Environment
Host (Development PC) Target
• Cross Development
Platform

34. 34
Build Tools
gcc - Compiler, Assembler, Linker
binutils - binary manipulation apps
gdb - software debugger
Host (Development PC)

35. 35
Tools Brief Note
arm-linux-gnueabi-gcov Coverage testing tool
arm-linux-gnueabi-gprof Display call graph profile
arm-linux-gnueabi-nm List symbols from object files
arm-linux-gnueabi-objcopy Copy and translate object files
arm-linux-gnueabi-objdump Display information from object file
arm-linux-gnueabi-readelf Display information from elf file
arm-linux-gnueabi-strip Discard symbols from object files
binutils for ARM architecture with EABI

36. 36
Tools Brief Note
arm-linux-gnueabi-gcc C compiler
arm-linux-gnueabi-cpp C++ compiler
arm-linux-gnueabi-ld Linker & Loader
arm-linux-gnueabi-as Assembler
Complier tool chain for ARM architecture
with EABI

37. 37
Building Blocks (ARM…)
Host PC
tool chain-
Compiler,
Assembler
, Linker
root file
system
source
kernel
source
u-boot
source
Target
bzImage
u-boot.bin
rootfs

38. 38
Embedded Linux Building Activities
Kernel Configuration - Genrally configuration are supplied by the board supplier to start with, however some
changes may require to meet some specification
Board Specific Changes - Hardware configuration that depends on the user setting like device address, IRQ etc
SoC Specific Changes - The kernel may have support to the SoC, however some configuration may be required
Device Specific Drivers - If new devices are available and the driver is not present in the mainline kernel, driver
for that device need to be devloped
Kernel Optimization - Kernel may be optimized for space, some unnecessary modules or features may be
disabled
Kernel Debugging - Kernel provides may debugging features built int he kernel code, one need to enable those
features int he kernel configuration

39. 39
Embedded Linux Components Build Process
Get sources
Configure and Apply patches
Build

40. 40
Boot Loader
Build

41. 41
U-boot
Boot Loader Build
hr@ed# wget https://www.kernel.org/pub/linux/kernel/v3.0/linux-
3.13.tar.xz
hr@ed# tar xJvf linux-3.13.tar.xz
hr@ed# cd linux-3.13
hr@ed# make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-
vexpress_defconfig
hr@ed# make menuconfig
hr@ed# make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-
vexpress_defconfig
hr@ed# patch -l < [patch files]
Get
BusyBox
source
Configure
& Patch
Build

42. 42
See Your Freshly Baked u-boot Run…
Run u-boot…
# qemu-system-arm -M vexpress-a9 -m 256 M -nographic -kernel uboot.bin
Run u-boot
with qemu
See your u-
boot run

43. 43
Linux Kernel
Build

44. 44
Kernel Configuration
Linux Kernel Source
Kernel Config (.config)
(Drone)
Kernel Config (.config)
(Learning Thermostat)
Kernel Image
(zImage)
- Drone
Kernel Image
(bzImage)
- Learning Thermostat

45. 45
Kernel Configuration
 Add Text

46. 46
Kernel Patch
Linux Kernel Source
(Base kernel)
Kernel Patch
(customization,
extension on base
kernel)
Resultant Kernel
Source Code
Kernel Config
(.config)
(Drone)
Resultant Kernel
Source Code
Kernel Build Image
(bzImage/zImage)
apply patch
build

47. 47
Linux Kernel Build
Linux Kernel Build
hr@ed# wget https://www.kernel.org/pub/linux/kernel/v3.0/linux-
3.13.tar.xz
hr@ed# tar xJvf linux-3.13.tar.xz
hr@ed# cd linux-3.13
hr@ed# make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-
vexpress_defconfig
hr@ed# make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- menuconfig
hr@ed# make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi-
vexpress_defconfig
hr@ed# patch -l < [patch files]
Get
Kernel
source
Configure
& Patch
Build

48. 48
See Your Freshly Baked Kernel Run…
 Add Text
Run Linux kernel…
# qemu-system-arm -M vexpress-a9 -m 256 M -nographic -kernel zImage
Run Linux
kernel with
qemu
See your
Linux
kernel run

49. 49
Root File
System Build

50. 50
Root File System
C Library (glibc.so)
Kernelboot
loader
cp, mv, ls, modprobe, ...
init and init
script
shell
device filesprocfs, sysfs
/bin, /usr, /lib, /sbin
...
Minimal Root File System
• C library (glibc)
• Basic Linux commands
• Linux Shell
• Device files
• procfs and sysfs
• Init Script

51. 51
C Library
glibc (POSIX interfaces)
C standard library (string operations, )
folder pipestimer
filesprocess signal
memory
manager
mutexthread
semaphore
shared memory
C Library (glibc)
• Process management
• Memory management
• File Management
• Process Synchronization

52. 52
Root File System - BusyBox
 Update
C Library (glibc.so)
BusyBox

53. 53
BusyBox Build
hr@ed# wget http://www.busybox.net/downloads/busybox-1.20.0.tar.bz2
hr@ed# tar xjf busybox-1.20.0.tar.bz2
hr@ed# cd busybox- busybox-1.20.0
hr@ed# $ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- defconfig
hr@ed# make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi- menuconfig
hr@ed# make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi- install
Apply patch if any
Get
BusyBox
source
Configure
& Patch
Build
Root File System with BusyBox

54. 54
Root File System
Rootfs with BusyBox
# cd _install
# mkdir proc sys dev etc etc/init.d
# mknod /dev/tty2 c 4 2
# mknod /dev/tty3 c 4 3
# mknod /dev/tty4 c 4 4
# chmod +x etc/init.d/rcS
# find . | cpio -o --format=newc > ../rootfs.img
#!/bin/sh
#File : /etc/init.d/rcS
mount -t proc none /proc
mount -t sysfs none /sys
/sbin/mdev -s
Create
folders
Create
device
node
Create
rootfs cpio
image
Create
/etc/init.d/
rcS

55. 55
Root File System
Rootfs with busybox
# qemu-system-arm -M vexpress-a9 -m 256M -kernel zImage -initrd rootfs.img -
append "root=/dev/ram rdinit=/sbin/init"
Run Linux
with
BusyBox
rootfs
# Welcome to myLinux
See your
Linux with
BusyBox
run