Embedded Systems

Embedded Systems
Dr. Nilesh Bhaskarrao Bahadure
https://www.sites.google.com/site/nileshbbahadure/home
July 25, 2021
Dr. Nilesh Bhaskarrao Bahadure () Unit - V July 25, 2021 1 / 42

Overview I
1 Introduction
Introduction to Embedded Systems
What are Embedded Systems
Embedded Systems and Power Consumption
Embedded Operating Systems
Applications of Embedded Systems
2 Characteristics of Embedded Systems
3 Architecture of Real Embedded Systems
Components of an Embedded systems
Characteristics of Real time embedded systems
4 Embedded Operating System
5 Real Time Operating Systems (RTOS)
Types of Real Time Operating System

Introduction to Embedded Systems
Embedded systems are the platform for the application of microcontrollers.
Embedded systems are omnipresent. These are there in your home, college,
office, shopping mall and so on and so forth. Even when you are on the
move - either on a most basic two wheeler or on an advanced aircraft -
you are still amidst embedded systems. They are a unique combination of
computer hardware, software and perhaps additional mechanical or other
parts, designed to perform a specific function within a given time frame.
The embedded software is required for all real - time applications and de-
veloped using a real time operating system (RTOS), as it helps to schedule
and executes tasks based on the priority in a predictable manner. to cite
just a few examples, embedded software allow your washing machine to
choose speed according to the type of cloth, confer thinking power to the
microwave ovens and propel rocket launchers into space.
Main Slide

What are Embedded Systems
There are many definitions of embedded system but as a general concept
Embedded systems are information processing system that are embedded
into a larger product, embedded system is a special-purpose computer sys-
tem that is used for a particular task. The special computer system is usually
less powerful than general-purpose systems, although some exceptions do
exist where embedded systems are very powerful and complicated. Usually
a low power consumption CPU with a limited amount of memory is used
in embedded systems. Many embedded systems use very small operating
systems; most of these provide very limited operating system capabilities.
However as memory and CPU power is becoming cheap.
Embedded systems are generally not directly visible to the user; it is available
almost in all kind of information processing automated systems. Examples
of embedded systems include information processing systems in telecom-
munication system, in transportation system, in fabrication equipment, in
biomedical instrumentation, aircraft system, and in consumer electronics.
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Embedded Systems and Power Consumption
Power consumption is also an important issue in embedded systems since
most of the devices based on the embedded system are portable devices.
This is also related to the moving parts issue in a sense. Components that
consume more power need cooling, so some type of fan and heat sink must
be attached to the system. For this reason people always prefer CPUs and
other components that use less power and generate less heat. It is also
beneficial for systems that run on batteries to use less power. High power-
consuming components drain batteries quickly.
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Embedded Operating Systems
Since embedded systems are usually not general-purpose systems, they need
not be as sophisticated as commercial general-purpose systems. These oper-
ating systems are smaller in size, prompted in service and quickly bootable.
Most of these operating systems also offer real-time capabilities, which are
missing in general-purpose systems (Microprocessor based systems). Al-
though there are hundreds of operating systems available for the embedded
systems, some of the most commonly used ones are:
1 VxWorks
2 pSOS
3 Embedded Linux
4 QNX
5 Windows CE
6 RTOS (Real time operating system)
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Embedded Operating Systems...
When you use Linux as an embedded operating system, you can take out
many parts of the kernel that are required in the general-purpose Linux
systems. Which parts should be excluded from the kernel depends upon
the requirements of a particular system. For example, you can take out the
entire networking code if the embedded system is not going to be networked.
Similarly, you can take out most of the secondary storage related drivers and
file systems support. Kernel parts that are the most likely candidates for
removal from the embedded Linux are:
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Embedded Operating Systems...
1 Disk drivers
CD-ROM drivers
Most of the networking code. Even if an embedded system is
intended to be networked, you may not need all of the routing code
and drivers for all types of network adapters.
Sound and multimedia related drivers and components. However you
may need these components if the embedded system is used as a
computer game.
Most of the file system support
Any other thing that is not required. You can go through the kernel
configuration process to determine what is not necessary.
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Applications of Embedded Systems
6 Embedded systems are found in a variety of common electronic devices,
such as:
(a) Consumer electronics: Cell phones, pagers, digital cameras, camcorders,
videocassette recorders, portable video games, calculators, Electronics toys,
digital pen, and personal digital assistants;
(b) Home appliances : Microwave ovens, answering machines, thermostat,
home security, washing machines, and lighting systems;
(c) Office automation : Fax machines, copiers, printers, and scanners;
(d) Business equipment: Cash registers, curbside check-in, alarm systems,
card readers, product scanners, and automated teller machines (ATM);
(e) Medical system: There is a huge potential for improving the medical
service by taking advantage of information processing taking place within
medical equipment. The latest EEG and ECG systems are already equipped
with embedded systems.
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Applications of Embedded Systems...
(f) Military applications: Information processing has been used in military
equipment for many years. The RADAR and SONAR systems are already
consisting embedded systems.
Smart buildings: Information processing system can be used to increase
the comfort level in buildings, can reduce the energy consumption within
buildings, and can improve safety and security. For example, energy can be
saved on cooling, heating and lighting rooms which are empty. Available
rooms can be displayed at appropriate places, simplifying ad-hoc meetings
and cleaning.
(g) Robotics: Mechanical aspects are very important for robots. Most of
the characteristics used for the other systems are also equally applicable for
the robotics control.
(h) Trains: Safety features contribute significantly to the total value of
trains, and dependability is extremely important.
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(i) Aircraft electronics: A significant amount of the total value of airplanes
is due to the information processing equipments, including flight control
systems, anti collision systems, pilot information system and others.
(j) Automobiles: Transmission control, cruise control, fuel injection, anti-
lock brakes, car parking system, speed controller, and active suspension.
Modern cars can be sold only if they contain a significant amount of elec-
tronics. These include air bag control systems, engine control systems,
anti braking systems (ABS), air conditioning control, GPS systems, safety
features and many more.
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Figure : Use of Embedded Systems in Automobile
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Characteristics of Embedded Systems
The common characteristics of the embedded systems are as follows
(a) Embedded systems have to be dependable
Most of the embedded systems are used for the safety devices and therefore have to be
dependable. If it is not used for the safety devices, then also dependability must be ensure
for the other systems like two - wheelers, cars, aircraft, rockets, trains, electronics toys
etc.
Dependability encompasses the following aspects of a system:
1 Reliability: Reliability in a sense that a system must not be fail.
2 Maintainability: It is need to ensure that a failing system can be repaired within a
certain time frame. It must be repairable.
3 Availability: The system must be available. To achieve high order of availability,
the system must attain the high order of reliability as well as maintainability.
4 Safety: This is ensure that the system is safe and does not cause any harm
especially a failing system.
5 Security: The system must be secure. Most of the embedded system applications
are found in the communication, so it is need to ensure that confidential data will
remains confidential and that authenticate communication must be guaranteed.
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Characteristics of Embedded Systems...
(b) Embedded system have to be efficient
The efficiency of the embedded systems are evaluated on the following basis
1 Energy: Most of the embedded systems are portable in size and obtaining their
energy or power from the batteries. To ensure the usability of the embedded
system based devices for the longer run, the embedded system must be energy
efficient.
2 Code size: Embedded systems are programmable devices, so the program written
for the embedded system has to be stored with the system (on chip). Generally, in
the embedded system there are no hard discs are available on which the code of
the program may be stored. Also to maintain the portability of the system, the
code size should be as small as possible for the intended application.
3 Run time efficiency: The hardware requirement for implementing the required
functionality should be minimum as possible. The time constraint is meet when
least amount of hardware resources is used for the system. In order to reduce the
power consumption, clock frequencies and supply voltages should be as small as
possible.
4 Weight: Again to meet the portability of the system, the system must be low in
weight.
5 Cost: because of the high volume productivity, the embedded system must be cost
effective, so it is within the reach of the maximum.

’ ’

Especially in the market of consumer electronics, where the competitions are very high
and technology is affected very quickly, proper use of hardware resources and the
software development budget are required. Main Slide

(c) Embedded systems must have single functionality.
Embedded systems are generally designed in such a way that it will meet
the requirement of specific task. For example, a pager is always a pager.
In contrast to the general purpose processor system, where it is possible to
run more than one application at a time like word processors, video games,
spreadsheets etc., in the embedded system, only one specific application is
run, so it is designed in this constraint only.
For example, in the car system for monitoring the parking system one ded-
icated embedded system is available and for controlling the airbag another
embedded system is available. In short, for each dedicated applications
theres an embedded system is available.
(d) Embedded systems have a dedicated user interface
(e) Embedded systems must satisfy real - time constraints.
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(f) Embedded systems are hybrid systems.
Hybrid system ensures that the system have both analog and digital parts.
Analog parts are used for accepting the continues signal, especially from the
outside world, but for the processing on the Microcontroller based systems,
where the values are accept only in digital form, the embedded system must
have hybrid system.
(g) Embedded systems are reactive system
Reactive system is a system where the input is accepted continually and
some computations are performed on that, so the output forms a new state.
It is not necessary that all the embedded systems will have all the above
characteristics, but if the systems meeting most of the characteristics listed
above are called embedded systems.
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Architecture of Real Embedded Systems
Figure : Architecture of an Embedded System
Main Slide

Architecture of Real Embedded Systems...
General purpose computers or microprocessor systems have a generic archi-
tecture, but it cannot be defined for real time embedded systems. There
are as many architecture as the number of manufactures. As embedded
systems are specially designed system to perform particular task or opera-
tion generalizing them would severely dilute the purpose of an embedded
system.
However for the sake of our understanding we can discuss some common
form of systems at the block diagram level.
Main Slide

Some of these parts used in the real time embedded systems may be pro-
grammable and therefore must have some place to keep these programs. In
real time embedded systems the on-chip or on-board non-volatile memory
does keep these programs. These programs are the part of the Real Time
Operating System (RTOS) and continually run as long as the device is re-
ceiving power. A part of the RTOS also executes itself in the stand-by mode
while taking a very little power from the battery. This is also called the sleep
mode of the system. One of proposed architecture of an embedded system
may looks as shown in the figure 2
Main Slide

The explanation of various parts as follows:
User Interface: for interacting with users. May consists of keyboard, touch pad etc
ASIC: Application Specific Integrated Circuit: for specific functions like motor control,
data modulation etc.
Microcontroller (µC): A family of microprocessors
Real Time Operating System (RTOS): contains all the software for the system control
and user interface
Controller Process: The overall control algorithm for the external process. It also
provides timing and control for the various units inside the embedded system.
Digital Signal Processor (DSP) a typical family of microprocessors, used for ad-
vanced computing calculations, to process signals etc. Both the DSPs along with their
operating systems and codes are independent of each other. They share the same memory
without interfering with each other. The Real Time Operating System (RTOS) controls
the timing requirement of all the devices.
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DSP assembly code: code for DSP stored in program memory
Dual Ported Memory: Data Memory accessible by two processors at the
same time
CODEC: Compressor/Decompressor of the data
User Interface Process: The part of the RTOS that runs the software
for User Interface activities
Controller Process: The part of the RTOS that runs the software for
Timing and Control amongst the various units of the embedded system
Main Slide

Components of an Embedded systems
From the architecture of an embedded system we have developed some
sense about what type of components used in the design of an embedded
systems.
(a) Processor
The central processing unit is the most important part of the embedded sys-
tem. Depending on the type of application or task to perform the processor
are broadly classified into three major categories.
1. Microprocessors/general purpose microprocessors
2. Microcontroller
3. Digital signal processors
Main Slide

Components of an Embedded systems...
(b) Memory
Compactness, speed and low power consumption are the characteristics re-
quired for the memory to be used in an embedded system. Therefore, very
low power semiconductor memories are used in almost all such devices. For
housing the operating system Read Only Memory (ROM) is used. For ex-
ample you may like to change the ring tone of your mobile device and keep
it for some time. You may like to change the screen color etc. In these cases
the memory should be capable of retaining the information even after the
power is removed. In other words the memory should be non-volatile and
should be easily programmable too. It is achieved by using Flash memories.
Flash memories are also faster in operation compare to other similar kind of
memories so it highly suited to the embedded systems.
Main Slide

(c) Input - output devices and interfaces
Input/output interfaces are necessary to make the embedded systems in-
teract with the external world. They could be Visual Display Units such as
TFT screens in a mobile phone, touch pad key board, antenna, microphones,
speakers etc. These embedded systems should also have open interfaces to
other devices such as Desktop Computers, Local Area Networks (LAN) and
other embedded systems. For example you may like to download your ad-
dress book into your personal digital assistant (PDA). Or you may like to
download some mp3 songs from your favorite internet site into your mp3
player. These input/output devices along with standard software protocols
in the RTOS provide the necessary interface to these standards.
Main Slide

(d) Software as operating system
The embedded system is just the physical body as long as it is not pro-
grammed. Whenever you switch on your mobile device you might have
marked some activities on the screen. Whenever you move from one city to
the other you might have noticed the changes on your screen. Or sometimes
you might have noticed the no-signal sign on the mobile device. These ac-
tivities are taken care of by the Real Time Operating System sitting on the
non-volatile memory of the embedded systems.
Main Slide

(e) Application software
Application software is designed to perform the specific task or operation
on an embedded system. Application software may also be referred to as
users program.
Main Slide

Real-time systems cover such an enormous range of applications and products that a
generalization of the characteristics into a set that is applicable to each and every system
is difficult. Different categories of real-time systems may exhibit the characteristics that
we identify to different extents or may not even exhibit some of the characteristics at all.
1. Time constraints: Every real-time task is associated with some time constraints.
One form of time constraints that is very common is deadlines associated with tasks. A
task deadline specifies the time before which the task must complete and produce the
results. Other types of timing constraints are delay and duration. It is the responsibility
of the real-time operating system (RTOS) to ensure that all tasks meet their respective
time constraints.
2. New Correctness Criterion: The notion of correctness in real-time systems is
different from that used in the context of traditional systems. In real-time systems,
correctness implies not only logical correctness of the results, but the time at which the
results are produced is important. If the result is produced after the deadline then this
result is considered as the incorrect or inappropriate result.
Main Slide

3. Safety-Criticality: For traditional non-real-time systems safety
and reliability are independent issues. However, in many real-time systems
these two issues are intricately bound together making them safety-critical.
Note that a safe system is one that does not cause any damage even when
it fails. A reliable system on the other hand, is one that can operate for
long durations of time without exhibiting any failures.
4. Concurrency: A real-time system usually needs to respond to several
independent events within very short and strict time bounds. For instance,
if the motor car met in the accident then safety air bag must open within a
time frame, otherwise it is useless. These systems can be considered to be
non-deterministic, since the behavior of the system depends on the exact
timing of its inputs.
Main Slide

5. Task Criticality: Task criticality is a measure of the cost of failure
of a task. Task criticality is determined by examining how critical are the
results produced by the task to the proper functioning of the system. A
real-time system may have tasks of very different criticalities. It is there-
fore natural to expect that the criticalities of the different tasks must be
taken into consideration while designing for fault-tolerance. The higher the
criticality of a task, the more reliable it should be made. Further, in the
event of a failure of a highly critical task, immediate failure detection and
recovery are important. However, it should be realized that task priority is
a different concept and task criticality does not solely determine the task
priority or the order in which various tasks are to be executed.
Main Slide

6. Reactive: Real-time systems are often reactive. A reactive system is
one in which an on-going interaction between the computer and the envi-
ronment is maintained. Ordinary systems compute functions on the input
data to generate the output data
Main Slide

7. Stability: Under overload conditions, real-time systems need to con-
tinue to meet the deadlines of the most critical tasks, though the deadlines
of non-critical tasks may not be met. This is in contrast to the requirement
of fairness for traditional systems even under overload conditions.
8. Exception Handling: Many real-time systems work round-the-clock
and often operate without human operators. For example, consider a small
automated chemical plant that is set up to work non-stop. When there are
no human operators, taking corrective actions on a failure becomes difficult.
Even if no corrective actions can be immediate taken, it is desirable that a
failure does not result in catastrophic situations. A failure should be detected
and the system should continue to operate in a gracefully degraded mode
rather than shutting off abruptly.
Main Slide

Embedded Operating System
Except for very simple systems, scheduling, task switching, and I/O requires
the support of an operating system suited for embedded applications. The
following are the essential features of real time and embedded operating
systems:
(a) Flexible: Due to the large variety of the operating systems, there
is also a large variety of requirements for the functionality of embedded
operating systems. Hence, we need operating systems which can be flexible
towards the application at hand. Configurability is therefore one of the main
characteristics of embedded operating systems.
Main Slide

(b) Compact in size: There are effectively no devices like hard disk, a
keyboard, a screen or a mouse or any other similar peripheral devices that
needs to be supported by all the versions of the operating system, except
maybe the system timer.
(c) Protection mechanisms are not always necessary, since embedded sys-
tems are typically designed for a single or dedicated purpose and untested
programs are hardly ever loaded, it means that the program loaded in the
embedded systems are already tested, it can be assumed to be reliable.
Main Slide

(d) Interrupts can be employed by any process. In desktop computing ap-
plications, interrupts would be a serious source of unreliability to allow any
process to use interrupts directly, whereas in embedded systems it is possible
to let interrupts directly start and stop tasks.
(e) Many embedded systems are real time systems and hence the operating
system used in the embedded systems must be a real time operating system.
Main Slide

Real Time Operating Systems (RTOS)
Real time operating system is an operating system that supports the con-
struction of real - time systems. A RTOS is an operating system intended
to serve real - time application process data as it comes in, typically without
any buffering delays. Processing time requirements are, measured in tenths
of seconds or even shorter.
The following is the key characteristics of the real - time operating systems.
Main Slide

Real Time Operating Systems (RTOS)...
Main Slide

1. The timing behavior of the operating system (OS) must be predictable.
For each service of the OS, an upper bound on the execution time must be
guaranteed.
2. The OS must manage the timing and scheduling of tasks. Scheduling
can be defined as mapping from the set of tasks to intervals of execution
time, including the mapping to start times as a special case. Also, the OS
possibly has to aware of task deadlines so that the OS can apply appropriate
techniques.
Main Slide

3. The OS must be fast. In addition to being predictable, the OS must
be capable of supporting applications with deadlines that are fractions of a
second.
Each RTOS includes a so called real time OS kernel. This kernel manages
the resources which are found in every system, including the processor, the
memory and the system timer. In fact, kernel will take care of all kind
of resources of the operating system. Protection mechanisms need not be
present.
Main Slide

Types of Real Time Operating System
There are two types of RTOSs: General purpose OS and real time kernel.
(a) General purpose OS type RTOSs: for these operating systems, some
drivers, such as disk, network drivers, or audio drivers are implicitly assumed
to be present, and they are embedded into the kernel. The application soft-
ware and middleware are implemented on top of the application program-
ming interface, which is standard for all applications.
Figure : General Purpose operating system
Main Slide

Types of Real Time Operating System...
(b) Real - time kernel type RTOSs: Since there is hardly any stan-
dard device in embedded systems, device drivers are not deeply embedded
into the kernel, but are implemented on the top of the kernel. Only the
necessary drivers are included. Application software and middleware may
be implemented on top of the appropriate drivers, not on top of a standard
API of the OS.
Figure : Real time operating system
Main Slide

Thank you
Please send your feedback at nbahadure@gmail.com
For more details and updates kindly visit
https://sites.google.com/site/nileshbbahadure/home
Main Slide

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