Introduction to Realtime Systems (& Embedded Systems)The course will enable you to:For embedded systems it will enable you toExample real-time systemsLets discuss some realtime system (RTS) characteristicsRealtime CharacteristicsRealtime Characteristics (contd.)Embedded SystemReal-time system concepts: Ch.1Real-time system concepts (contd.)DeterminismCPU UtilizationCPU Utilization (Contd.)Sample real-time systemsSlide 15Realtime system characteristics01/14/19 1Introduction to Realtime Systems (& Embedded Systems)B. Ramamurthy01/14/19 2The course will enable you to:Identify the unique characteristics of real-time systems Explain the general structure of a real-time system Define the unique design problems and challenges of real-time systems Apply real-time systems design techniques to various software programs.01/14/19 3For embedded systems it will enable you toUnderstand the basics of an embedded systemProgram an embedded systemDesign, implement and test an embedded system.Ex: realtime + embedded : games on a Gameboy or arcade gamesEx: realtime: Tetris on a laptop01/14/19 4Example real-time systemsDomain ApplicationAvionics Navigation; displaysMultimedia Games; simulatorsMedicine Robot surgery; remote surgery; medical imagingIndustrial systems Robot assembly lines; automated inspectionCivilian Elevator controlAutomotive system; Global positioning system (GPS)01/14/19 5Lets discuss some realtime system (RTS) characteristics01/14/19 6Realtime CharacteristicsRTS have to respond to events in a certain pre-detemined amount of time.The time constraints have to be considered during planning, design, implementation and testing phases.Internal failures due to software and hardware fault have be handled satisfactorily.You cannot simply pop-up a dialog box that says “send report” or “don’t send report”.Also external failures due to outside sources need to be handled.01/14/19 7Realtime Characteristics (contd.)Typical interaction in an RTS is asynchronous. Thus an RTS should have features to handle asynchronous events such as interrupt handlers and dispatcher and associated resources.Potential for race condition: when state of resources are timing dependent race condition may occur.Periodic tasks are common.01/14/19 8Embedded SystemIs a special purpose system designed to perform a few dedicated functions.Small foot prints (in memory)Highly optimized codeCell phones, mp3 players are examples.The components in an mp3 player are highly optimized for storage operations. (For example, no need to have a floating point operation on an mp3 player!)01/14/19 9Real-time system concepts: Ch.1A system is a mapping of a set of input into a set of outputs.A digital camera is an example of a realtime system: set of input including sensors and imaging devices producing control signals and display information.Realtime system can be viewed as a sequence of job to be scheduled.Time between presentation of a set of inputs to a system and the realization of the required behavior, including availability of all associated outputs, is called the response time of the system.01/14/19 10Real-time system concepts (contd.)Real-time system is the one in which logical correctness is based on both the correctness of the output as well as their timeliness.A soft real-time system is one in which performance is degraded by failure to meet response-time constraints.A hard real-time system is one in which failure to meet a single deadline may lead to complete and catastrophic failure.More examples:Automatic teller: softRobot vacuum cleaner: firmMissile delivery system: hard01/14/19 11DeterminismIn every system, and particularly in an embedded system maintaining control is extremely important.Example: (i) a two wheeler going our of control on certain maneuvers. (ii) wheel locks when you enter an unsafe state.It is desirable to avoid such states thorugh proper design.As far as possible, we would like the realtime system to be deterministic.A system is deterministic, if for each possible state and each set of inputs, a unique set of outputs and next state can be detremined.01/14/19 12CPU UtilizationCPU utilization or time loading factor, U, is a measure of the percentage of non-idle processing.Utilization% Zone type Type of application0-25 CPU under utilizedGeneral purpose25-50 Very safe ,,51-68 Safe ,,69 Theoretical limitEmbedded system70-82 Questionable Embedded system83-99 dangerous Embedded system01/14/19 13CPU Utilization (Contd.)Let fi be the frequency of a periodic task.Then period pi = 1/ fi Let ei be the execution time of the task.Then overall utilization of the CPU is:U = nipiei101/14/19 14Sample real-time systemsLets discuss the sample systems listed in the text books.We will also go over the exercises at the end of chapter 1.01/14/19 1501/14/19 16Realtime system
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