Embedded System

A special-purpose computer which is completely encapsulated by the device it control. A typical embedded system has a single specialized function.

The computer sits behind the equipment and controls its various components based on the input provided by the user and obtained from number of sensors attached to the system. The way this interaction occurs is usually implemented by the software that run inside the embedded computer. Due to the flexibility and advanced processing capabilities provided by the software, manufacturers of these equipment increasingly prefer to use embedded systems rather than their traditional hardwired controllers.

Cross compiling

The process of compiling a software on a different computer and later using that on a program on a different computer.

Differences with normal computers

• Processing unit is typically a microcontroller
• End users wouldn’t feel the existence of embedded computer most of the time.
• Used over a very long period of time and generally they cannot be programmed or maintained by the end user.
• Have many design constraints such as:
  • limited memory
  • requirement of low cost
  • strict performance guarantee
  • fail-safe operations
  • low power consumption
  • reliability
  • guaranteed real-time behaviour
• Can be optimized as they are dedicated to a specific task.
• Often use simple executives (OS kernels) or real-time OSs, support for real-time scheduling and no hard drives.
• Often interact with their physical environment using a variety of sensors and/or actuators.

Microcontroller

Can be considered as a very simple and a small-scale computer in a single chip.

Has a program memory, a processing unit and a random access memory (registers) which maps to hard disk, CPU and RAM in a typical personal computer respectively. Lightweight.

Programming and designing circuits with microcontrollers are quite complex and not friendly for beginners. Microcontroller programs have to be written separately and inserted into the device using a separate tool (a programmer).

Examples

• thermostats
• calculators
• ATMs
• printers
• video game consoles
• Handheld computers
• PDAs
• cell phones

The line of definition continues to blur as devices get more famous and expanded.

Challenges

Embedded system research field is rich with potential because it combines two factors.

1. First, the system designer usually has control over both the hardware design and the software design.
2. Embedded systems are built upon a wide range of disciplines, including computer architecture (processor architecture and micro architecture, memory system design), compiler, scheduler/operating system, and real-time systems.

Combining these two factors means that barriers between these fields can be broken down, enabling synergy between multiple fields, and resulting in optimizations which are greater than the sum of their parts.

Delivering good performance

Many embedded systems (e.g., anti-lock brakes in a car) have real-time requirements. Unfortunately, many of the performance enhancing features which make personal computers so fast also make it difficult to predict their performance accurately. Such features include pipelined and out-of-order instruction execution in the processor, and caches in the memory system. Hence the challenge for real-time system researchers is to develop approaches to design fast systems with easily predicted performance, or to measure existing complex but fast systems more accurately.