Embedded systems

1. MODULE IV
EMBEDDED SYSTEM

2. • An embedded system is a computer system that does a specific
job within a larger mechanical or electrical system, often with
real-time computing constraints.
• An embedded system is a system that has s/w embedded into
computer h/w which makes the system dedicated for an
application.

4. CHARACTERISTICS FEATURES
• They cannot be programmed to do different things.It is designed to
execute a single program.
• Multifunctioned but single purpose
• They have very limited resources like memory,I/O devices
• They do not have secondary storage device such as CD ROM,floppy
disk etc.The s/w is stored in ROM or in Flash memory
• A specific job has to be done within a specific time(Real time)
• Low power onsuption (most of them are battery operated)
• Highly reliable
• Less space
• Low cost
• Performs functions fast enough

7. • An embedded system has 3 components:
• Embedded system hardware: An embedded system
requires a hardware platform on which to run. The
hardware will be based around a microprocessor or
microcontroller. The embedded system hardware will
also contain other elements including memory, input
output (I/O) interfaces as well as the user interface, and
the display.
• Embedded system software: The embedded system
software (firmware)is written to perform a particular
function. It is typically written in a high level format and
then compiled down to provide code that can be lodged
within a non-volatile memory within the hardware.
• It has an actual real-time operating system (RTOS) that
defines the manner the system works.

8. EMBEDDED OS
• OS acts as an interface b/w the H/W and
application S/W.
• It facilitates the user to format
disks,create,print,copy,....display files,allocate
memory locations,control the i/o operation...
• In multiuser system ,it allows several users to
share the CPU time,provide inter task
communication,memory management......

9. SENSOR:-It measures the quantities that are physical and converts it to an electrical
signal .
A/D CONVERTER:- An analog-to-digital converter that converts the analog signal
sent by the sensor right into a digital signal.
PROCESSOR:- Processors process the digital signaland keep it to the memory.
D-A CONVERTER:- A D/A converter converts the signal fed by the processor to analog
information.
ACTUATOR:-It is a type of motor that is operated by a source of energy, typically
electric current, hydraulic fluid pressure, or pneumatic pressure, and converts that
energy into motion.
BASIC STRUCTURE OF AN EMBEDDED SYSTEM

10. SPECIALITIES
• PERFORMANCE:-Many embedded systems
have time constraints.If the deadlines are
missed ,it may result catastrophe(disaster).
• POWER CONSUMPTION:-Most of the
embedded systems are Battery operated
• COST:-should be minimum in case of office
automation and consumer electronics
• SIZE & WEIGHT:- important parameters in
embedded system used in aircraft,missile etc.
• S/W upgradation capability:- eg.PCO

14. Architecture of the RTOS

15. • The heart or nucleus of any RTOS is the kernel.
Inside the kernel is the scheduler.
• It is basically a set of algorithms which
manage the task running order.
• Multitasking definition comes from the ability
of the kernel to control multiple tasks that
must run within time deadlines.

16. ARCHITECTURE OF KERNEL

17. • Kernel has various functions such as file
management, data transfer between the file
system ,hardware management ,memory
management and also the control of CPU time.
The kernel also handles the Interrupts.
• The Kernel is the first part of the operating system
to load into memory during booting (i.e., system
startup), and it remains there for the entire
duration of the session because its services are
required continuously.
• Kernel Objects : The various kernel objects are
Tasks, Task Scheduler, Interrupt Service Routines,
Semaphores, Mutexes, Mailboxes, Message
Queues, Pipes, Event Registers, Signals and
Timers

18. OS ACTIVITIES(Kernel objects)
• (i).Task:
• A task is a basic unit or atomic unit of execution that can be
scheduled by an RTOS to use the system resources like CPU ,
Memory, I/O devices etc. It starts with reading of the input data and
of the internal state of the task, and terminates with the production
of the results and updating the internal state.
• Task States:
• At any instant of time a task can be in one of the following states :
• (i) Dormant
• (ii).Ready
• (iii).Running and
• (iv).Blocked.
• When a task is first created , it is in the dormant task .When it is
added to RTOS for scheduling ,it is a ready task. If the input or a
resource is not available ,the task gets blocked.

19. Task Scheduler:
• The task scheduler establishes task time slots. Time slot width and activation
depends on the available resources and priorities.
• A scheduler decides which task will run next in a multitasking system.
• Scheduling Algorithms:
a).First in First out
• (b).Round Robin algorithm
• ©.Round Robin with priority
• (d)Non-preemptive
• (e)Pre-emptive.
• The basic difference between preemptive and non-preemptive scheduling
is that in preemptivescheduling the CPU is allocated to the processes for the
limited time. While in Non-preemptivescheduling, the CPU is allocated to
the process till it terminates or switches to waiting state.
• Every RTOS provides three specific functions.
(i).Scheduling (ii) Dispatching and (iii). Inter-process communication and
synchronization.
• The advantage of using a scheduler is the ease of implementing the sleep
mode in microcontrollers which will reduce the power consumption
considerably (from mA to µA). This is important in battery operated
embedded systems.

20. • context switching (a process switch or a
task switch) is the switching of the CPU from
one process or thread to another.
• A context switch is the process of storing the
state of a process or of a thread, so that it can
be restored and execution resumed from the
same point later. This allows multiple
processes to share a single CPU, and is an
essential feature of a multitasking operating
system.

21. • Semaphores:
• A semaphore is nothing but a value or variable or data
which can control the allocation of a resource among
different tasks in a parallel programming environment.
• Mutex is basically a locking mechanism where a process
locks a resource using mutex. As long as the process has
mutex, no other process can use the same resource.
(Mutual exclusion ). Once process is done with
resource, it releases the mutex. Here comes the concept
of ownership. Mutex is locked and released by the same
process/thread. It cannot happen that mutex is acquired
by one process and released by other.
• So, Unlike semaphores, mutexes have owners. A mutex
can be unlocked only by the thread that owns it

22. Mailboxes
• A Mailbox is basically a pointer size variable. A task
can have a mailbox into which others can post a mail.
A task or ISR sends the message to the mailbox and
also receive messages through the mailbox.
• A task looking for a message from an empty mailbox is
blocked and placed on waiting list for a time (time out
specified by the task) or until a message is received.
When a message is sent to the mail box, the highest
priority task waiting for the message is given the
message in priority-based mailbox
• Similar to our postal mailbox. When someone posts a
message in our mailbox , we take out the message

23. • Message Queues ,are used to send one or more
messages to a task i.e the message queues are used to
establish the Inter task communication. Basically
Queue is an array of mailboxes. Tasks and ISRs can send
and receive messages to the Queue through services
provided by the kernel. Extraction of messages from a
queue follow FIFO(first in first out) or LIFO(last in first
out) structure.
• Applications of message queue are
• • Taking the input from a keyboard
• • To display output
• • Reading voltages from sensors or transducers
• • Data packet transmission in a network
• In each of these applications, a task or an ISR deposits
the message in the message queue. Other tasks can
take the messages.

25. PIPES
• A message pipe is an inter-process task
communication tool used for inserting, deleting
messages between two given interconnected
task or two sets of tasks. ... Pipes are
unidirectional i.e. one thread or task inserts
into it and the other one reads and deletes
from it..

26. Timers:
• A timer is the scheduling of an event according to a predefined time
value
• The kernel has to keep track of different times
• • A particular task may need to be executed periodically, say, every
10ms. A timer is used to keep track of this periodicity.
• • A task may be waiting in a queue for a shared resource. If the
resource is not available for a specified time, an appropriate action
has to be taken.
• The following function calls are provided to manage the timer:
• • Get time
• • Set time
• • Time delay (in system clock ticks)
• • Time delay (in seconds)
• • Reset timer

27. Memory Management
• It is a service provided by a kernel which allots
the memory needed ,either static or dynamic
for various processes. The manager optimizes
the memory needs and memory utilization.
• The API provides the following function calls
to manage memory
• • Create a memory block
• • Get data from memory
• • Post data in the memory
• • Query a memory block
• • Free the memory block

28. Handheld Operating Systems
• A handheld operating system, also known as a
mobile OS ,is the operating system that
controls a mobile device.
• The popular handheld operating systems
available are (a) Palm OS (b)Symbian OS
(iii)Windows CE (iv) Windows CE.NET.
• Typical examples of devices running a mobile
operating system are smart phones, personal
digital assistants (PDAs), tablet computers …

29. REAL TIME OS
• Examples for real time operating systems (RTOS) are
VxWorks, µcos, Qnx, Rtlinux, window embedded etc.
these are used when a specific task needs to be done in
a specific time frame.
• Two types
• Soft RTOS:- the performance of the system is not
destroyed if the timing deadlines are not met .
App:- Air conditioner, TV remote or music player, Bus
reservation ,automated teller machine in a bank , A Lift
etc.
• Hard RTOS:-the failure to meet the time dead lines may
lead to a complete catastrophe or damage to the
system
App:- Air navigation system, Nuclear power plant ,
Failure of car brakes , Gas leakage system ,RADAR
operation ,Air traffic control system etc.

30. Concept of AURDINO Board
• Arduino Uno is a microcontroller development board based
on the Atmel ATmega328 MCU. TheArduino Uno has 14
digital input/output pins (of which 6 can be used as PWM
outputs), 6 analog inputs, a 16 MHz crystal oscillator, a USB
connection, a power jack, an ICSP header, and a reset
button.
• Simply connect it to a computer with a USB cable or power
it with a AC-to-DC adapter or battery to get started. The
Arduino Uno differs from all preceding boards in that it does
not use the FTDI(future technology devices international)
USB-to-serial driver chip. Instead, it features the Atmega8U2
programmed as a USB-to-serial converter. The Arduino Uno
MCU board can be powered via the USB connection or with
an external power supply. The power source is selected
automatically.

32. Concept of RASPBERRY Pi
Development Board
• A Raspberry Pi is a credit card-sized computer originally designed for
education
• The Raspberry Pi is slower than a modern laptop or desktop but is still a
complete Linux computer and can provide all the expected abilities that
implies, at a low-power consumption level.
• There are a two Raspberry Pi models, the A and the B, A comes with 256MB
of RAM and one USB port. It is cheaper and uses less power than the B. The
current model B comes with a second USB port, an ethernet port for
connection to a network, and 512MB of RAM
• The Raspberry Pi was designed for the Linux operating system,
• A Raspberry Pi is a compact computer board which offers endless
opportunities. Simply plug in your TV, keyboard, mouse and power supply,
and you are ready to go. There is a whole family of Raspberry Pi’s available
to you, each providing various functionalities. There are also add-on boards
available to enable other uses, such as camera and LCD display modules.
The great thing about Raspberry Pi is that it is suitable for almost all age
groups. Whether it’s introducing programming to children, or used by
engineers to make complex computer-controlled systems, anyone can use
one.

34. • Processor: Broadcom BCM2837 Processor Quad core A53 (ARM v8)
64-bit SoC
Memory: 1GB LPDDR2 SDRAM
Bluetooth: Cypress BLE chip 2.4Ghz/5.0GHz IEEE 802.11ac
Ethernet: Gigabit Ethernet over USB 2.0 (300Mbps max)
USB: Four USB 2.0 ports
Connection: GPIO(general purpose i/o) Header 40-pin
HDMI: 1 x full size
Video: MIPI DSI( Mobile Industry Processor Interface Display Serial
Interface connector) display port, MIPI CSI(camera serial Interface)
camera port & 4 Pole stereo output and composite video port
Multimedia: H.264, MPEG-4 decode (1080p30). H.264 encode
(1080p30). OpenGL ES 1.1, 2.0 graphics.
Storage: microSD card slot for loading operating system and data
storage
Power: USB connector for 5.1V / 2.5A dc