Real Time and Embedded Systems

Real Time and Embedded Systems

• This chapter serves as an introduction to real-time and embedded systems
• The outlines cover definitions, characteristics, examples, models, tasks, timing constraints, computer organization, memory, and the design process

What is a System?

• A system organizes tasks according to rules, programs, or plans
• Systems arrange for units to work together following a plan
• Examples include a watch (time display system) and an automatic washing machine

System Definition

• A system comprises functionalities implementing input-output behavior dependably and securely
• A dependable system reliably delivers justifiable and trusted services
• Security involves:
  • Confidentiality
  • Integrity
  • Availability
• A secure system behaves as intended

Embedded System Definitions

• An embedded system has embedded software that makes it dedicated to an application, specific part, or larger system
• An embedded system is also defined as having dedicated purpose software inside computer hardware
• An embedded system is any device with a programmable computer for a specific purpose, rather than general use

More on Embedded Systems

• Embedded systems are application domain-specific information processing systems
• These systems are tightly coupled to their environment
• Application domains:
  • Automotive
  • Multimedia
• Environment: input/output information type and properties
• Tightly coupled: system design and functionality heavily influenced by the environment

Embedded System Characteristics

• Embedded systems process a fixed set of programmed instructions to manage electromechanical equipment
• They are single or multi-purpose devices embedded within equipment or industrial products

Examples of Embedded Systems:

• Personal Computers (PCs)
• ATMs
• Heating, Cooling and Ventilating Systems
• Security Systems
• Elevators
• Bar Code Equipment
• Real Time Control Systems
• Telephone Exchanges and Switches (PBXs)
• Environmental Monitoring Equipment
• Global Positioning System (GPSs)
• Programmable Logic Controls (PLCs)
• Test Equipment
• Robotics

Hardware Units in Embedded Systems

• Hardware elements include:
  • Input/Output interfacing/Driver circuits
  • Power supply
  • Processor
  • Timers
  • Program/Data Memory
  • Serial/Parallel Communication Ports
  • System Application Specific Circuits
  • Input Controllers

Components of a General Purpose Computer

• Components of a general-purpose computer:
  • Microprocessor
  • Memory
  • Input/Output (I/O) units (keyboard, mouse, scanner, etc.)
  • Output units (LCD screen, video monitor, printer, etc.)
  • Networking units (Ethernet card, bus drivers, etc.)
  • Operating system (OS)
  • General purpose user interfaces and application software

Components of an Embedded System

• Key component: a microcontroller (single-chip computer)
  • Includes on-chip RAM, ROM, and I/O ports
  • Examples: Motorola's 6811, Intel's 8051, Atmel, PIC 16X
• An embedded system has three main components:
  • Application Software
  • Real Time Operating System (RTOS)

Microprocessor vs. Microcontroller

• Microprocessors:
  • RAM, ROM, I/O, timer are separate
  • Designer decides ROM/RAM/I/O amount
  • Expensive, versatile, general-purpose
  • High processing/power consumption
  • Instruction sets focus on processing-intensive operations
  • Typically 32/64-bit, deep pipeline (5-20 stages)
• Microcontrollers:
  • RAM, ROM, I/O, and timer are all on a single chip
  • Fixed on-chip ROM/RAM/I/O
  • Suited for cost, power, and space-critical applications
  • Single-purpose (control-oriented)
  • Low processing power and consumption
  • Bit-level operations focus
  • Typically 8/16 bit, single/two-stage pipeline

Characteristics of an Embedded System

• Dependable
• Efficient
• Dedicated
• Reactive
• Cost-effective

Dependability in Embedded Systems

• Reliability: System works correctly from the start
• Maintainability: System recovers after errors
• Availability: System works at a given time
• Safety: Causes no harm
• Security: Confidential and authentic communication
• Fault tolerant
• Degrades gracefully

Efficiency in Embedded Systems

• Energy efficient
• Code-size efficient (especially for systems on a chip)
• Run-time efficient
• Weight efficient
• Cost efficient

Application and Interfaces for Embedded Systems

• Dedicated towards a certain application, which maximizes robustness
• Knowledge about behavior at design time can be used to minimize resources
• Dedicated user interface

Real-Time Constraints in Embedded Systems

• Embedded systems must meet real-time constraints
• A real-time system reacts to stimuli within a time interval
• Late arrivals are incorrect for real-time systems
• A hard real-time constraint is catastrophic if unmet

Reactive Systems

• Embedded Systems are typically reactive
• Systems are characterized by continuous interaction with their environment at a pace set by external events or stimuli
• Reactive System Definition: A system that remains in constant communication with its environment and responds based on the timing and occurrence of external inputs

Constraints of Embedded System Design

• Embedded System design considerations:
  • Available system-memory
  • Available processor speed
  • Limited power dissipation
• System Design also considers:
  • performance
  • power
  • size
  • non-recurring design costs and manufacturing cost

Popular Embedded System Makers

• Atmel, Microchip, Intel, Philips/Signetics, Zilog, Dallas, Freescale Semiconductors, Texas, Hitachi, ARM
• Small Scale ES with 8/16 bit Microcontrollers:
  • Intel 8051 family
  • AVR ATmega8 family
  • PIC16F8x FAMILY
  • ARM8
  • Hitachi H8
  • Freescale Semiconductors 68HC11xx
• Medium Scale ES with 16 bit Microcontrollers:
  • Intel 8051MX
  • AVR XMEGA 8/16
  • PIC16F876, PIC18
  • ARM16
  • Hitachi D64F2336FA
  • Freescale Semiconductors 68HC12xx, 68HC16xx
• Large Scale ES with 36 bit Microcontrollers:
  • Intel 8051MX
  • AVR AT91 series
  • PIC16F876, PIC18
  • ARM Cortex-M3
  • Philips LPC2000 series
  • Hitachi SH704FY
  • Freescale Semiconductors 68HC12xx, 68HC16xx

Real-Time Embedded System Design

• Real-time embedded systems include both hardware and software.
• They are a part of a larger real-time or cyber physical system with mechanical and/or electrical components.
• Real-time embedded system uses sensors and actuators to interface with external environment
• Example: a robot controller with mechanical arms, servomechanisms, sensors, and actuators
• Real-time systems are computer systems with timing constraints
• Real time embedded system combines embedded systems and real-time computing
• They are used where results are needed in a specific timely manner

Examples of Real Time Embedded Systems

• Medical Sector: Magnetic resonance imaging, CT scanners, ultrasound scans, laboratory analytical equipment, radiation therapy, patient monitoring, defibrillation
• Manufacturing: Real time embedded systems are also used into advance plants and factories like as robotics, Al systems and IoT devices perform various processes, monitoring sensors control assembly-line operation, Specific machinery working conditions like as temperature, humidity, pressure, vibration and other variables, predicting possible failures, Process Control, Power plants, Chemical plants, Consumer products such as soft drinks and beer
• Defense Sector: Firing weapons, Tracking, Command and control, Advance houses and Cities Smart homes and cities are getting more popularity due to introduce of Internet of Things techniques and real-time embedded systems, Smart lighting, heating and air conditioning which people can manage through smart phone, Smart parking, communication systems, digital signage with multimedia content, surveillance systems all utilize real-time embedded systems to function.
• Transportation: These embedded systems are used into modern vehicles (cars, trucks, ships, trains, planes) along with numerous sensors, GPS (Global Positioning System) trackers, Anti – lock Braking System or ABS and control systems as well as airbags, Traffic control for airspace, highways, railway tracks, and shipping lanes

Types of Real Time Embedded Systems

• Two Types: Soft Real Time and Hard Real Time Systems
• Soft Real Time Embedded Systems:
  • Processes are considered as the main task
  • Examples: Personal computer, Audio and video systems, Set top boxes , DVD Players, Weather Monitoring Systems
• Hard Real Time Embedded Systems:
  • Focus on timelines, they should not be omitted in any circumstances
  • No use of permanent memory, so processes must be complete properly
  • System must generate accurate responses to events
  • Examples: Flight Control Systems, Missile Guidance Systems Weapons Defense System

Characteristics of a Real-Time Embedded System

• Constant Response: Responds the same to a situation
• Deadline: a missed deadline can cost lives and finances
• Accuracy: causes havoc if the embedded system doesn't work
• Quick Response: Must be swift to respond to external effects
• Correctness: Correctness of result is to obtain correct result in time
• Embedded: Embedded system means that combination of hardware and software designed for a specific purpose. Real-time systems collect the data from the environment and passes to other components of the system for processing. Safety: Safety is necessary for any system but real-time systems provide critical safety. Real-time systems also can perform for a long time without failures. It also recovers very soon when failure occurs int he system and it does not cause any harm to the data and information.
• Concurrency: Real-time systems are concurrent that means it can respond to a several number of processes at a time. There are several different tasks going on within the system and it responds accordingly to every task in short intervals. This makes the real-time systems concurrent systems.
• Distributed: In various real-time systems, all the components of the systems are connected in a distributed way. The real-time systems are connected in such a way that different components are at different geographical locations. Thus all the operations of real-time systems are operated in distributed ways.
• Stability: In real-time, the system will divide the result off tasks even when the real-time systems is busy.

Components of a Real Time Embedded System

• Hardware: contains microcontroller, microprocessor, Input/Output ports, sensors, etc
• Software: Contains embedded software which direct the system, contains task scheduling

Computer Organization and Architecture Concepts

• A computer system combines the processor, RAM, ROM, and input/output ports
• Software is a sequenced set of instructions, storing, and defining the tasks being performed.
• The process executes by retrieving and interpreting these instructions one at a time
• A microprocessor is a small processor, where small relates to size, not computing ability

Computer Organizations and Architecture

• Basic components of a computer system include:
  • Processor
  • Memory
  • I/O
• General-purpose systems differ from embedded systems because general-purpose include, keyboard, disk, and graphics display, and can be programmed for purposes
• Include word processing, accounting, system computing, and database systems. Has a wide range of functions. Allows programs to be added to the system
• General-purpose machines do not run in real-time. Tasks in real-time are done be embedded systems. I/O interfaces are crucial.

Design process

• It describes the top-down design

Design Requirements:

• Includes timing, sensitivity, weight, safety