CprE 458/558: Real-Time SystemsReal-time SystemsTypical Real-time SystemExample - Car DriverExample - Car Driver (Contd.)Real-time TasksTasks ConstraintsComputing SystemsCprE 458/558: Real-Time Systems (G. Manimaran) 1CprE 458/558: Real-Time Systems Introduction to Real-Time SystemsCprE 458/558: Real-Time Systems (G. Manimaran) 2Real-time SystemsReal-time systems are defined as those systems in which the correctness of the system depends not only on the logical result of computation, but also on the time at which the results are produced.•Hard real-time systems (e.g., Avionic control). •Firm real-time systems (e.g., Banking). •Soft real-time systems (e.g., Video on demand).CprE 458/558: Real-Time Systems (G. Manimaran) 3Typical Real-time SystemCprE 458/558: Real-Time Systems (G. Manimaran) 4Example - Car Driver•Mission: Reaching the destination safely. •Controlled System: Car.•Operating environment: Road conditions and other cars.•Controlling System - Human driver: Sensors - Eyes and Ears of the driver. - Computer: Sensors - Cameras, Infrared receiver, and Laser telemeter. •Controls: Accelerator, Steering wheel, Break-pedal. •Actuators: Wheels, Engines, and Brakes.CprE 458/558: Real-Time Systems (G. Manimaran) 5Example - Car Driver (Contd.)•Critical tasks: Steering and breaking.•Non-critical tasks: Turning on radio. •Performance is not an absolute one. It measures the goodness of the outcome relative to the best outcome possible under a given circumstance. •Cost of fulfilling the mission → Efficient solution. •Reliability of the driver → Fault-tolerance is a must.CprE 458/558: Real-Time Systems (G. Manimaran) 6Real-time Tasks•Periodic tasks - Time-driven. Characteristics are known a priori - Task Ti is characterized by (pi, ci) E.g.: Task monitoring temperature of a patient in an ICU.•Aperiodic tasks - Event-driven. Characteristics are not known a priori - Task Ti is characterized by (ai, ri, ci, di) E.g.: Task activated upon detecting change in patient’s condition.•Sporadic Tasks–Aperiodic tasks with known minimum inter-arrival time. pi : task period << ai : arrival time << ri : ready time di : deadline <<< ci : worst case execution time.CprE 458/558: Real-Time Systems (G. Manimaran) 7Tasks Constraints•Deadline constraint•Resource constraints –Shared access (read-read), Exclusive access (write-x)•Precedence constraints–T1  T2: Task T2 can start executing only after T1 finishes its execution•Fault-tolerant Requirements –To achieve higher reliability for task execution–Redundancy in executionCprE 458/558: Real-Time Systems (G. Manimaran) 8Computing Systems•Uniprocessor •Multiprocessor System (UMA & NUMA) •Distributed