The Performance Design Metric
Performance of a system is a measure of how long the system takes to execute our desired tasks.
The two main measures of performance are:
Latency or response time
This is the time between the start of the task’s execution and the end. For example, processing an image may take 0.25 second.
This is the number of tasks that can be processed per unit time. For example, a camera may be able to process 4 images per second These are the some of the cost measures for developing an RTES. Optimization of the overall cost of design includes each of these factors taken with some multiplying factors depending on their importance. And the importance of each of these factors depends on the type of application. For instance in defense related applications while designing an anti-ballistic system the execution time is the deciding factor. On the other hand, for de-noising a photograph in an embedded camera in your mobile handset the execution time may be little relaxed if it can bring down the cost and complexity of the embedded Digital Signal Processor. The design flow of an RTES involves several steps. The cost and performance is tuned and finetuned in a recursive manner. An overall design methodology is enumerated below.
Design Methodology (Fig. 2.4)
System Requirement and Specifications Define the problem What your embedded system is required to do? Define the requirements (inputs, outputs, control) What are the inputs and outputs of your system? Write down the specifications for them Specify if the signals are in digital or analogue form. Specify the voltage levels, frequency etc. The design task can be further segregated into the following steps
System level Design
Find out the possible subsystems of the system and the interconnections between them.
Sub-system or Node Level design
Each of these subsystems can be termed as the nodes. Elaborate on each of these subsystems and further make the block diagram and component level interconnections.
Processor Level Design
Each subsystem may consist of processor, memory, I/O devices. Specification and design at this level is required now.
Task Level Design
Complete interconnection of these subsystems depending on the tasks they would perform.
• The scope of embedded systems has been encompassing more and more diverse disciplines of technology day by day. Obsolescence of technology occurs at a much faster pace as compared to the same in other areas. The development of Ultra-Low-Power VLSI mixed signal technology is the prime factor in the miniaturization and enhancement of the performance of the existing systems. More and more systems are tending to be compact and portable with the RTES technology. The future course of embedded systems depends on the advancements of sensor technology, mechatronics and battery technology.
• The design of these RTES by and large is application specific. The time-gap between the conception of the design problem and marketing has been the key factor for the industry.
• Most of the cases for very specific applications the system needs to be developed using the available processors rather than going for a custom design.
Version 2 EE IIT, Kharagpur