Introduction To Real Time Systems

Today, when we are surrounded by highly efficient, intelligent (as considered) and fast gadgets all around us, it is hard to think of a world without electronics. Yet if we try to think of a time like that, it would be a time around 50's when there were no technology interfering our decisions, but as time continued, human kind got webbed in technology. Let us see, how technology evolved with time, by technology I mean software and computing technology.
DECADE TECHNOLOGY
'60s Mainframes
'70s Mini Computers
'80s Personal Computers
'90s Internet And Mobile Phones
'00s REAL TIME SYSTEMS

The first question that should be asked under this heading must be "What is a real time system?" but, to understand the meaning of Real Time and Real Time System, we must know what is a non-Real Time system.
So, the systems in which there is a qualitative notion of time i.e. the machines in which time is expressed using notions before, after, sometime, eventually etc. Here we can see a concept of relative timing.
Now, we can understand what is real time. Unlike relative time, it is a quantitative notion of time, measured using a physical clock. For ex. After a certain event occurs (temperature exceeds 500 degrees ) the corresponding action (coolant shower) must complete within 100ms.
Next question that arises in our mind is, What are the key recent trends, that are motivating real time systems. So,these are:
⦁ Increasing computation demands (e.g. Video conferencing, Mobile TV)
⦁ Increasingly networked systems (Remotely monitor or debug, embedded web browsers, cameras and disks that sit directly on the network).
⦁ Increasing need for reducing time- to -market under ever changing standards.
Basic Model Of An Embedded Real Time System

Let us look at this model in more detail.
Every embedded RTS senses the change in its environment and converts them into electrical signals(using sensors). Some example of sensors are:
⦁ A photovoltaic cell (operation based on photoelectric effect)
⦁ A temperature sensor(operation based on principle of thermocouple)
⦁ A pressure sensor(operation based on piezoelectric principle)
These sensors are available in market as IR proximity, shaft encoder, GPS, sonar, IR distance, electronic compass, CMOS camera.
Input conditioning unit converts these analog signals into digital signals by voltage amplification, voltage level shifting and filtering. These signals are sent to the RTOS (Real Time Operating System) by input interface. RTOS processes the input and computes the output and send these digital signal to conditioning unit via output interface. The conditioning unit converts these digital signals to analog signals and actuators convert these electrical signals into some physical actions. These physical actions may be (motion, change of thermal, electrical, pneumatic or physical characteristic of some object). Some example of actuators are motors, heaters, hydraulic and pneumatic actuators.
Now, the next question that may arise in our mind is "How might a Real time embedded system be designed". Though the answer of this question requires a one semester course on Design and Analysis of Real Time System, yet we can briefly answer this question by recalling how the behavior of a system is described.
The inputs and corresponding outputs of a system (to be designed) are listed first, then the corresponding sensors and actuators are chosen. An RTOS is programmed as per the requirement of computing the output. And conditioning units and interfaces are connected with them.This completes a Real Time embedded system.
In next articles we will look at various Real Time Systems how do they work and how RTOS is designed for different RTSs.
Thank you.