MSIT 4B Embedded Systems 1 Chapter 1 Embedded Systems he basic objectives of this chapter is to provide the reader a clear overview of embedded systems. This chapter establishes the distinction between embedded systems and other computing devices. TSome of the basic components of the embedded systems are discussed. 1.0 INTRODUCTION An embedded system is a special-purpose computer system usually built into a small device. An embedded system is required to meet very different requirements than a general-purpose personal computer. It has a processor and specific supporting devices and a compact operating system. These components are just adequate to meet the specific application for which it is designed. In general, an embedded system is a device meant for a specific application. It is a small compact micro computer which renders a specific job. 1.1 DIFFERENCES BETWEEN DESKTOP/LAPTOP COMPUTER AND EMBEDDED SYSTEM A desktop or a laptop computer is a general purpose computing device. We can use this for varieties of applications such as computing, playing games, word processing, software development and so on. The general purpose computer permits addition of new compatible software tools for application development. However the embedded system differs from the laptop/desktop computers in the following ways l Embedded systems do a particular job. They cannot be programmed to do different jobs. MSIT 4B Embedded Systems 1 2 Chapter 1 - Embedded Systems l Embedded Systems have very limited resources, especially memory. They do have only semiconductor memory. Secondary memories such as hard disk or compact disk are not available. l Most of the embedded systems work in real time, i.e., the tasks are usually time synchronized. l Embedded systems normally operate on the battery. So power consumption is highly optimized and hence their hardware have high impact on the power consumption. l Embedded systems are to be highly reliable. There is no compromise on this. Embedded systems are being used in almost all fields such as : l Consumer Electronics l Office Automation l Industrial Automation l Medical Electronics l Computer Networking l Telecommunications l Wireless technologies l Instrumentation l Security l Finance Specific examples of embedded systems l Automatic teller machines (ATMs) l Cellular telephones and Telephone switches l Computer network equipment, including Routers, Switches and Firewalls l Computer printers l Disk drives (floppy disk drives and hard disk drives) l Engine controllers and antilock brake controllers for automobiles l Home automation products, like thermostats, air conditioners, sprinklers, and security monitoring systems MSIT 4B Embedded Systems Chapter 1 - E-Commerce3 l Handheld calculators l Household appliances, including microwave ovens, washing machines, television sets, DVD players/recorders l Inertial guidance systems, flight control hardware/software and other integrated systems in aircraft and missiles l Medical equipments, BP monitor, Sugar level monitor etc l Measurement equipment such as digital storage oscilloscopes, logic analyzers, and spectrum analyzers l Multifunction wrist watches l Personal Digital Assistants (PDAs), i.e. small handheld computers l Programmable logic controllers (PLCs) for industrial automation and monitoring l Stationary videogame consoles and handheld game consoles 1.2 CHARACTERISTICS Two major areas of differences are cost and power consumption. Since many embedded systems are produced in the tens of thousands to millions of units, reducing cost is a major concern. Embedded systems often use a (relatively) slow processor and small memory size to minimize costs. The slowness is not just clock speed. The whole architecture of the computer is often intentionally simplified to lower costs. For example, embedded systems often use peripherals controlled by synchronous serial interfaces, which are ten to hundreds of times slower than comparable peripherals used in PCs. Programs on an embedded system often must run with real-time constraints with limited hardware resources, often there is no disk drive, operating system, keyboard or screen. A flash drive may replace rotating media, and a small keypad and LCD screen may be used instead of a PC’s keyboard and screen. Firmware is the name for software that is embedded in hardware devices, e.g. in one or more ROM/ Flash memory IC chips. Embedded systems are routinely expected to maintain 100% reliability while running continuously for long periods. Firmware is usually developed and tested to much stricter requirements than is general purpose software which can usually be easily restarted if a problem occurs. 1.3 OVERVIEW OF EMBEDDED SYSTEM ARCHITECTURE Every embedded system consists of custom built hardware around a central processing unit (CPU). The hardware also contains memory chips onto which the software is loaded. The software residing on 4 Chapter 1 - Embedded Systems the memory chip is also called firmware. An embedded architecture can be represented as a layered architecture as shown in the figure 1.1. The operating system runs above the hardware and the Application software runs above the operating system. The same layered architecture hold good for general purpose computers also. However the embedded systems sometimes need not posses operating systems, for example, Toys, remote control equipments, etc.,. However some other applications do need the operating system and all applications are to run under it. Usually most embedded systems in computing, mobile and network applications work under a real time operating system. H/W OS App. S/W Figure 1.1 Layered architecture of an Embedded System The hardware block diagram of an embedded system is shown in figure 1.2. The building block comprises of the following l Central processing unit l Memory l Input devices l Output devices l Communication Interfaces l Application specific circuitry MSIT 4B Embedded Systems 5 1.3.1 Central Processing Unit The central Processing unit can be a microcontroller, micro processor or a DSP chip. The microcontroller is a low cost device which has all the necessary components such as Memory, Serial interfaces, Analog and Digital converters etc embedded in one single chip. These microcontrollers can be used for specific applications which work within the specifications of the microcontroller. A microprocessor is more powerful compared to microcontroller and it needs external devices to be interfaced for building an embedded system. The DSP chip is mostly used for signal processing applications. For example, in the design of embedded systems that require audio and video coding. There are many different CPU architectures used in embedded designs. One common configuration for embedded systems is the system on a chip, an application-specific integrated circuit, for which the CPU was purchased as intellectual property to add to the IC’s design. Read Only Random Memory Access Memory Output Input Central Processing Unit Device Device CPU Communication Interface Application Specific Circuitry Figure 1.2 Architecture of an Embedded System 1.3.2 Memory The memory used in the embedded system design is a semiconductor memory. Usually two types of memories are used. The RAM is used for storing temporary information during processing. On the other hand most important memory used in the embedded system is a Read Only Memory called FLASH. 6 Chapter 1 - Embedded Systems Normally the operating system is stored in FLASH. Embedded Systems do not have secondary memory devices interfaced to them. 1.3.3 Input devices Embedded systems have minimal input devices. This means, they don’t have mouse, key board etc. Usually a small key pad with minimal buttons are provided to derive specific commands. 1.3.4 Output devices Most embedded systems have either LED or Small LCD screen interfaced to them to display the information. 1.3.5 Communication Interfaces Embedded systems need to interact with other devices. Based on the requirement, the embedded systems may have one or more of the following interfaces connected to them. l Serial communication interface l Parallel interface l USB l PCMCIA l JTAG l Ethernet l Bluetooth l Infra Red 1.3.6 Application specific circuitry Sensors, transducers and control circuitry may need to be interfaced with the embedded systems for specific applications. MSIT 4B Embedded Systems 7 1.4 SOFTWARE TOOLS USED IN THE EMBEDDED SYSTEMS Like a typical computer programmer, embedded system designers use compilers, assemblers and debuggers to develop an embedded system. These software tools can come from several sources: l Software companies that specialize in the embedded market l Ported from the GNU software development tools. Sometimes, development tools for a personal computer can be used if the embedded processor is a close relative to a common PC processor. Embedded system designers also use a few software tools rarely used by typical computer programmers. l Some designers keep a utility program to turn data files into code, so that they can include any kind of data in a program. l Most designers also have utility programs to add a checksum or CRC to a program, so it can check its program data before executing it. 1.4.1 Operating system The Embedded Systems either have no operating system, or a specialized embedded operating system (often a real-time operating system - RTOS), or the programmer is assigned to port one of these to the new system. The Operating system is a bundle of software which helps the hardware in resource management besides accomplishing