11-04-2011, 04:32 PM
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EMBEDDED SYSTEMS
1.1 Introduction:
An embedded system is a system which is going to do a predefined specified task is the embedded system and is even defined as combination of both software and hardware. A general-purpose definition of embedded systems is that they are devices used to control, monitor or assist the operation of equipment, machinery or plant. "Embedded" reflects the fact that they are an integral part of the system. At the other extreme a general-purpose computer may be used to control the operation of a large complex processing plant, and its presence will be obvious.
All embedded systems are including computers or microprocessors. Some of these computers are however very simple systems as compared with a personal computer.
The very simplest embedded systems are capable of performing only a single function or set of functions to meet a single predetermined purpose. In more complex systems an application program that enables the embedded system to be used for a particular purpose in a specific application determines the functioning of the embedded system. The ability to have programs means that the same embedded system can be used for a variety of different purposes. In some cases a microprocessor may be designed in such a way that application software for a particular purpose can be added to the basic software in a second process, after which it is not possible to make further changes. The applications software on such processors is sometimes referred to as firmware.
The simplest devices consist of a single microprocessor (often called a "chip”), which may itself be packaged with other chips in a hybrid system or Application Specific Integrated Circuit (ASIC). Its input comes from a detector or sensor and its output goes to a switch or activator which (for example) may start or stop the operation of a machine or, by operating a valve, may control the flow of fuel to an engine.
As the embedded system is the combination of both software and hardware
Software deals with the languages like ALP, C, and VB etc., and Hardware deals with Processors, Peripherals, and Memory.
Memory: It is used to store data or address.
Peripherals: These are the external devices connected
Processor: It is an IC which is used to perform some task
1.1.1 Applications of embedded systems
• Manufacturing and process control
• Construction industry
• Transport
• Buildings and premises
• Domestic service
• Communications
• Office systems and mobile equipment
• Banking, finance and commercial
• Medical diagnostics, monitoring and life support
• Testing, monitoring and diagnostic systems
1.2 Processors are classified into four types like:
Micro Processor (µp)
Micro controller (µc)
Digital Signal Processor (DSP)
Application Specific Integrated Circuits (ASIC)
1.3 Micro Processor (µp):
A silicon chip that contains a CPU. In the world of personal computers, the terms microprocessor and CPU are used interchangeably. At the heart of all personal computers and most workstations sits a microprocessor. Microprocessors also control the logic of almost all digital devices, from clock radios to fuel-injection systems for automobiles.
1.3.1 Three basic characteristics differentiate microprocessors:
Instruction set: The set of instructions that the microprocessor can execute.
Bandwidth : The number of bits processed in a single instruction.
Clock speed : Given in megahertz (MHz), the clock speed determines how many instructions per second the processor can execute.
In both cases, the higher the value, the more powerful the CPU. For example, a 32-bit microprocessor that runs at 50MHz is more powerful than a 16-bit microprocessor that runs at 25MHz. In addition to bandwidth and clock speed, microprocessors are classified as being either RISC (reduced instruction set computer) or CISC (complex instruction set computer).
A microprocessor has three basic elements, as shown above. The ALU performs all arithmetic computations, such as addition, subtraction and logic operations (AND, OR, etc). It is controlled by the Control Unit and receives its data from the Register Array. The Register Array is a set of registers used for storing data. These registers can be accessed by the ALU very quickly. Some registers have specific functions - we will deal with these later. The Control Unit controls the entire process. It provides the timing and a control signal for getting data into and out of the registers and the ALU and it synchronizes the execution of instructions (we will deal with instruction execution at a later date).
1.4 Micro Controller (µc):
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications.
1.5 Digital Signal Processors (DSPs):
Digital Signal Processors is one which performs scientific and mathematical operation. Digital Signal Processor chips - specialized microprocessors with architectures designed specifically for the types of operations required in digital signal processing. Like a general-purpose microprocessor, a DSP is a programmable device, with its own native instruction code. DSP chips are capable of carrying out millions of floating point operations per second, and like their better-known general-purpose cousins, faster and more powerful versions are continually being introduced. DSPs can also be embedded within complex "system-on-chip" devices, often containing both analog and digital circuitry.
1.6 Application Specific Integrated Circuit (ASIC)
ASIC is a combination of digital and analog circuits packed into an IC to achieve the desired control/computation function
1.6.1 ASIC typically contains
CPU cores for computation and control
Peripherals to control timing critical functions
Memories to store data and program
Analog circuits to provide clocks and interface to the real world which is analog in nature
I/Os to connect to external components like LEDs, memories, monitors etc.
1.7 Computer Instruction Set
There are two different types of computer instruction set there are:
1. RISC (Reduced Instruction Set Computer) and
2. CISC (Complex Instruction Set computer)
1.7.1 Reduced Instruction Set Computer (RISC)
A RISC (reduced instruction set computer) is a microprocessor that is designed to perform a smaller number of types of computer instruction so that it can operate at a higher speed (perform more million instructions per second, or millions of instructions per second). Since each instruction type that a computer must perform requires additional transistors and circuitry, a larger list or set of computer instructions tends to make the microprocessor more complicated and slower in operation.
Besides performance improvement, some advantages of RISC and related design improvements are:
A new microprocessor can be developed and tested more quickly if one of its aims is to be less complicated.
Operating system and application programmers who use the microprocessor's instructions will find it easier to develop code with a smaller instruction set.
The simplicity of RISC allows more freedom to choose how to use the space on a microprocessor.
Higher-level language compilers produce more efficient code than formerly because they have always tended to use the smaller set of instructions to be found in a RISC computer.
1.7.1.1 RISC characteristics
Simple instruction set:
In a RISC machine, the instruction set contains simple, basic instructions, from which more complex instructions can be composed.
Same length instructions.
Each instruction is the same length, so that it may be fetched in a single operation.
1 machine-cycle instructions.
Most instructions complete in one machine cycle, which allows the processor to handle several instructions at the same time. This pipelining is a key technique used to speed up RISC machines.
1.7.2 Complex Instruction Set Computer (CISC)
CISC, which stands for Complex Instruction Set Computer, is a philosophy for designing chips that are easy to program and which make efficient use of memory. Each instruction in a CISC instruction set might perform a series of operations inside the processor. This reduces the number of instructions required to implement a given program, and allows the programmer to learn a small but flexible set of instructions.
