What is an Embedded System?
First, a system is a set of tasks executed against a fixed set of rules, program or plan for a given objective. Embedded System is an application specific computer system comprised of both hardware and software to complete a set of tasks for a given objective. Embedded System runs inside larger system giving it more functionality/features, better performance and reliability.
Key characteristics are:
- Built for a specific application
- Built using Micro controller unit (MCU) – see section below
- Runs inside a larger system with well defined input/output, integration interfaces for other systems and user interface
- Have real time computing constraints of performance, power, cost, size, weight
- Cannot be programmed by end user but end user can provide inputs to get the embedded system to perform a function
Examples of Embedded Systems
The following systems will have one or more embedded systems in them
- Missile – guidance system
- Automobile systems – anti braking system, air bag system and so on
- Household applications – waching machine
- Consumer electronics – cameras
- Telecom – mobile phones
- Healthcare – diagnotic machines
- Drones
Types of ES
Task based embedded system – that complete a specific task in a configured time period. e.g.: washing machine
Real time embedded system – that execute tasks within specified real-time constraints (power, performance, cost, size, weight) based on external input from sensors/actuators
Design contraints of ES
Power – in majority of cases embedded systems are supplied power from a battery hence they should consume as less power as possible to ensure system running longer running on battery
Performance – generally needs to be real time meeting response/execution time requirements of an application
Area – embedded system is a computer in itself hence it should pack in the required hardware, with required resources for the software, in limited space
Cost – needs to be low cost since part of a bigger system which may be made of many different embedded systems
Time to market – getting right the design as per requirements in one go is key to releasing on time a system/product
Building an Embedded System
Steps when building an embedded system
- Requirements gathering
- Writing detailed specification
- Architecture
- Component design
- Development (see figure below for details)
- System integration
The following are the challenges
- How much power is available and how do I limit power consumption?
- What is the time to market?
- What is the target area available in the system in which to embed?
- Testing and ensuring it meets target specification
- Restricted development environment
Components of an Embedded System
Example block diagram of a Chocolate Vending Machine
Micro controller unit (MCU)
MCU is the brain of an embedded system responsible for taking input (eg: sensor data – crash detection in a car, software instructions) and producing output (eg: actions to be performed – launch the airbags in case of crash). It is a hardware made of multiple hardware components that interoperate with each other via a high speed bus. They have a very tiny size varying from 2-10mm
The following are components of a MCU
- Processor – to do required computation to achieve the application objectives
- Memory – to store required program instructions (non volatile – ROM, EEPROM/Flash memory) and data (volatile – RAM)
- Reset circuits and oscillator – reset circuits helps initialize or reset the system including cases of failure, reset oscillator provides timing signals for the operation of micro controller and speed of execution of instructions
- Power Supply
- Analog Digital/Digital Analog Converter – analog sensor to digital, digital output signal to analog actuator (on signal does mechanical action)
- I/O Ports – simple communication analog/digital interface (pins) with external devices (e..g: senors, user interface)
- Communication Interface – complex communication interface (specialized hardware) with external devices
- Interuppt Controllers – manages, prioritizes tasks that require immediate attention
- Timers – used for scheduling tasks, event counting, measuring time intervals
Micro Controller vs Micro processor
| Microprocessor | Microcontroller |
| A silicon chip that is a CPU for arithemetic and logical operations | A integrated chip that is comprises of a CPU, Memory, I/O ports, Interuppt control units and so on |
| Built for general purpose use for processing inside a system | Built for a specific application purpose inside a system |
| Dependent on other hardware devices to input/output and processing | Self contained unit that can independently complete specific application purpose |
| Does not contain an I/O port | Contains multiple I/O ports |
| Limited power saving options | Designed with several power saving features |
Operating System
Operating System is a software that acts as an interface between application software and hardware (MCU). It makes it easier and makes it more efficient to use the hardware of a system.
The main functions of a operating system are:
- Process management
- File management
- Memory management
- Security and protection
- User Interface
- I/O Management