Embedded systems and Real Time Operating systems (RTOS)

Embedded systems and Real Time Operating systems (RTOS)

Introduction

Embedded systems and Real Time Operating systems (RTOS) are two among the several technologies that will play a major role in making these concepts possible. A large number of people are already depending on operating systems for real time applications, these 'eyes in the sky' are now going to make an impact on our every day lives in a more significant manner.Even Nostradamus would have been hard pressed to answer this question. Embedded systems are pre-designed without connections and operate as per the required task. But in operating systems instruction is design-oriented. These systems are basically platform-less systems. Embedded systems are the unsung heroes of much of the technology we use today — the video game we play, or the CD player or the washing machines we use employ them. Without an embedded system we would not even be able to go online using modem.

Design Orientation

Embedded systems are usually low cost and are easily available off the shelf for most applications. They usually have low design risks, since it is easy to verify the design using tools fueling the growth of embedded systems.

Embedded systems have received a major shot in the arm as the result of three developments:

The first was the development of standard run-time platforms like java, which enabled their use in myriad ways that were unimaginable in the past.

The second was the coming together of embedded systems and the Internet, which made possible the networking of several embedded systems to operate as part of a large system across networks.

The third was the emergence of several integrated software environments, which simplified the implementations of these applications.

During operation, the design structure may be changed as per our tasks. For example, consider two transistors; we can mould them using other passive elements as emitter coupled circuit, Darlington pair, etc., as per instruction.

Real Time Applications Automobiles

Almost every car that rolls off the production line these days makes use of embedded technology in one form or the other; most of the embedded systems in automobiles are rugged in nature, as most of these systems are made up of a single chip. No driver clashes or 'systems busy' conditions happen in these systems. Their compact profiles enable them to fit easily under the cramped hood of a car. These systems can be used to implement features ranging from adjustment of the suspension to suit road conditions and the octane content in the fuel to antilock braking systems (ABS) and security systems.

Embedded systems can also make drive-less vehicle control a reality. Major automobile manufacturers are already engaged in work on these concepts. One such technology is Adaptive Cruise control (ACC) from Ford. ACC allows cars to keep safe distances from other vehicles on busy highways. The driver can set the speed of his car and the distance between his car and others. He can over side the system anytime he wants by braking. Each car with ACC has a microwave radar unit or laser transceivers fixed in front of it to determine the distance and relative speed of any vehicle in its path. The ACC computer constantly controls the throttle and brakes of the car.

Another revolution is the way Internet services will be integrated into the car. So when you drive past your mechanic's, you will be reminded that that your engine oil needs a refill, and when you cross the city limits, the toll will automatically get deducted from your bank account. And while passing the shopping mail, your PDA, which is connected to the Net via the car, will inform you about a new scale. In fact, the automatic to;l deduction concept is already in effect in several countries around the globe.

Hybrid verification of the controller and analysis of timing properties are conducted through the use of third party tools.

The approach is applied to Adaptive Cruise Control (ACC) and Cooperative ACC systems. While regular cruise control systems track a desired vehicle speed, Adaptive Cruise Control (ACC) systems adapt their behavior if there is a vehicle ahead on the roadway, and follow the leader vehicle at a driver requested time gap using line-of-sight sensors such as radar and/or Lidar.

Vehicle Model And Controller Design

The vehicle model used for controller development is an eleven-state model, which includes vehicle state dynamics, throttle and brake system dynamics, a two-state model for the spark-ignition engine including external data maps which require interpolation, and models of the torque converter, transmission and wheel slip, as shown in the figure.

The vehicle state dynamics have two continuous states, vehicle position and velocity, and consider vehicle mass, air drag and rolling resistance. The throttle and brake dynamics are both first-order, with one continuous state for each representing actuator dynamics for the throttle and time response lag for the brakes. The controller design process stems from system requirements. Vehicles may be heterogeneous, that is of different types, makes and models. The controller was split hierarchically between an upper level controller that has several modes, namely cruise control (CC), adaptive cruise control (ACC) and coordinated adaptive cruise control (CACC). In ACC mode we use only information from the host vehicle's forward-looking sensors, and in CACC mode we supplement this information with data from the wireless communication system.

The upper control generates a desired host vehicle acceleration, which is sent to the lower-level controller. The lower-level controller converts this desired acceleration to a desired torque, then chooses whether to apply the brakes or throttle, and in what amount. Both controllers are run on separate control computers.

In the following equations, the following variables are used:

Fa is the aerodynamic drag force

Mrr is the rolling resistance moment

Rg is the gear ratio (related to engine and Vehicle speeds)

ades is the desired synthetic acceleration

ct is the control torque

h is the effective wheel radius

1) Throttle control From the desired torque, the desired throttle angle is computed using an engine map.
2) Brake control

From the desired torque, two different brake control strategies have been implemented. In the first strategy, the master cylinder pressure is controlled. A pressure regulator valve controls the pressure applied on the hydraulic actuator. Seal friction exists in the master cylinder and the actuator, and a small amount of hysteresis is present in the pressure regulation