Understanding Embedded Systems

What is a System?

• A system is a way of working, organizing, or performing tasks according to a fixed set of rules, a program, or plan.
• It involves units assembling and working together based on a program or plan.
• Examples include a watch (time display system) and an automatic clothes washing machine

System Definition

• A system comprises functionalities that jointly implement input-output behavior dependably and securely.
• A dependable system delivers services that are justifiably trusted and have accepted dependencies.
• Security includes confidentiality, integrity (absence of improper system alteration), and availability (readiness for correct service).
• A secure system behaves as intended.

What is an Embedded System?

• Software is embedded into computer hardware, dedicating the system to a specific application or part of a larger system.
• An embedded system has dedicated purpose software embedded in computer hardware.
• These systems include a programmable computer not intended as a general-purpose computer
• An embedded system is an information processing system that is application domain specific and tightly coupled to its environment.
• Examples of embedded system application domains include automotive and multimedia.
• Environment refers to the type and properties of input/output information.
• "Tightly coupled" means the system's design and functionality are heavily influenced by its environment.
• Microprocessor-based control systems process a fixed set of instructions to control electromechanical equipment, potentially as part of a larger system.
• These are single or multi-purpose computerized devices embedded within larger engineering equipment or industrial products.
• Examples include personal computers, ATMs, heating/cooling/ventilating systems, security systems, elevators, bar code equipment, and real-time control systems.
• Further examples include telephone exchanges/switches, environmental monitoring equipment, GPS, programmable logic controls, test equipment, and robotics.
• Advanced applications include DVD players, Mars rovers, GPS receivers, and smart watches.

Hardware Units and Devices in an Embedded System

• Hardware elements: power supply, processor, timers, input controllers, input/output devices, memory, communication ports, and application-specific circuits.

Components of a General-Purpose Computer

• Microprocessor, memory, I/O units, input units (keyboard, mouse, scanner), output units (LCD screen, video monitor, printer), networking units (Ethernet card, bus drivers), operating system, and general-purpose software.

Components of an Embedded System

• Microcontroller, a single-chip computer with on-chip RAM, ROM, I/O ports (e.g., Motorola's 6811, Intel's 8051, Atmel, PIC 16X).
• Three main components: embedded application software (generally in flash/ROM) and a real-time operating system (RTOS).
• The application software runs concurrently, and the RTOS supervises tasks and manages system resources according to priorities and timing constraints.

Microprocessor vs. Microcontroller

• Microprocessors are stand-alone, with separate RAM, ROM, I/O, and timers while microcontrollers have RAM, ROM, I/O and timer all on a single chip.
• Microprocessors allow designer to decide the amount of ROM, RAM and I/O ports but microcontrollers offer a fixed amount of on-chip ROM, RAM, I/O ports.
• Microprocessors are expensive, versatile, and general-purpose, while microcontrollers are designed for cost, power, and space-critical applications.
• Microcontrollers are single-purpose and control-oriented.
• Microprocessors have high processing power and consumption, while microcontrollers have low processing power and consumption.
• Microprocessors typically use 32/64-bit instructions with deep pipelines, while microcontrollers use 8/16-bit instructions.

Characteristics of an Embedded System

• Characteristics for a dependable system include: reliability, maintainability, availability, safety, security, and fault tolerance.
• Embedded systems should degrade gracefully by reducing functionality gradually in case of failure.
• Efficiency, are energy, code-size, run-time, weight, and cost efficient
• Being dedicated towards a certain application: Knowledge about behavior at design time can be used to minimize resources and to maximize robustness.
• Contain a dedicated user interface
• Meet real-time constraints:
  • A real-time system must react to stimuli within a time interval dictated by the environment.
  • For real-time systems, right answers arriving too late are wrong.
  • A hard real-time constraint: failure to meet it could result in a catastrophe.
• Reactive systems: continuously interact with environment at pace determined by external events/stimuli.
  • Reactive systems remain in constant communication with their environment and respond based on the timing/occurrence of external inputs

Constraints of an Embedded System Design

• Constraints include available system-memory, processor speed, and limited power dissipation.
• A system design is also constrained by performance, power, size, and non-recurring design and manufacturing costs.

Popular Embedded Microcontroller Manufacturers

• Atmel, Microchip, Intel, Philips/Signetics, Zilog, Dallas, Freescale Semiconductors, Texas, Hitachi and ARM.
• Small scale (8/16 bit) microcontrollers include Intel 8051, AVR ATmega8, PIC16F8x FAMILY, ARM8, Hitachi H8, and Freescale Semiconductors 68HC11xx.
• Medium scale (16 bit) microcontrollers: Intel 8051MX, AVR XMEGA 8/16, PIC16F876/PIC18, ARM16, Hitachi D64F2336FA, Freescale Semiconductors 68HC12xx/68HC16xx.
• Large scale (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

• A real-time embedded system is a real-time computer system (hardware/software) within a larger real-time or cyber-physical system
• Components include mechanical and/or electrical parts, such as in airplanes or automobiles.
• The devices interface to the external environment through sensors and actuators.
• Ex: a robot controller with mechanical arms, servomechanisms, multiple sensors, and actuators
• Real-time systems are computer systems responding to timing constraints.
• Real-time systems comprises the real-time application, real-time OS, and I/O subsystem, interfacing with sensors and actuators.
• Combination of embedded systems and real-time computing creates a real-time embedded system.
• These systems are used where results are needed within a specific time period, such as military applications.

Examples of Real-Time Embedded Systems

• Medical Sector: MRI, CT scanners, ultrasound, laboratory analytical equipment, radiation therapy, patient monitoring, and defibrillation.
• Manufacturing: advance plants and factories like as robotics, Al systems and IoT devices performing various processes.
• Monitoring sensors control assembly-line operation.
• Include Specific machinery working conditions like as temperature, humidity, pressure, vibration and other variables, predicting possible failures
• Examples include process control, power plants, chemical plants, and consumer products like soft drinks and beer.
• Defense: weapons, tracking, command/control, and advanced houses and cities.
• Smart homes and cities are gaining popularity due to the Internet of Things, using smart lighting, heating, and air conditioning.
• Systems used for parking, communication, digital signage, and surveillance.
• Transportation: for use in modern vehicles (cars, trucks, ships, trains, planes) along with numerous sensors.
• Includes GPS trackers, Anti-lock Braking Systems (ABS), control systems, and airbags.
• Applied in traffic control for airspace, highways, railway tracks, and shipping lanes

Types of Real-Time Embedded Systems

• Soft Real Time Embedded Systems: consider processes like as main task, and control the entirely task.
• Examples: personal computers, audio/video systems, set-top boxes, DVD players, and weather monitoring systems.
• Hard Real Time Embedded Systems: Timelines must be met in all circumstances & Complete processes properly in the first time itself.
• Must generate accurate responses to events within specified time
• Examples: flight control, missile guidance, and weapons defense systems.

Characteristics of a Real-Time Embedded System

• Constant Response: Responds in the same manner to a certain situation
• Deadline: Missed deadlines can cost lives and finances.
• Accuracy: system failure can cause havoc
• Quick Response: Respond to the changing external environment with immediate effect.
• Correctness: Correctness of result is to obtain result in time,
• Embedded: Combine hardware and software for a specific purpose.
• Safety: provide critical safety. and recover quickly from failures.
• Concurrency: Respond to several concurrent processes and tasks.
• Distributed: Components are connected in a distributed way in different geographical locations.

Components of Real-Time Embedded Systems

• Hardware: includes a microcontroller or microprocessor, Input and Output ports, sensors, actuators, relays, power supply or batteries and several other peripheral parts
• Software: consists of embedded operating systems (OS) that includes task scheduling to operates within a defined timeframe

Computer Organization and Architecture Concepts

• A computer system combines a processor, random access memory (RAM), read only memory (ROM), and input/output (I/O) ports.
• Software consists of specific instructions stored in memory, defining what and when tasks are performed.
• -The processor executes the software by retrieving and interpreting these instructions one at a time.
• A microprocessor is a small processor, where small refers to size (it fits in a hand) and not computational ability

Design Requirements (Constraints)

• Include: Timing, Size & Weight, Safety & Reliability (low cost reliability with minimal redundancy), Cost sensitivity and Power consumption
• Others: component acquisition, upgrades, and compatibility.

Design Process

• A top-down process analyzes the problem, creating high level and engineering designs, implements and tests hardware and software.
• Includes specifications, constraints and block diagrams