Lec19Time - Lecture 19 Timing Considerations Outline Why...

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ECE 471 19-Time-1 Outline Why timing needs to be considered? How to specify the timing requirement? How to satisfy the timing requirement? How to ensure the timing requirement is satisfied? Discussion Summary Lecture 19 Timing Considerations
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ECE 471 19-Time-2 Why Timing Needs to be Considered? Many embedded systems are reactive systems. The system reaction to an external input may need to be fast; Otherwise, some external information may be lost or the system may malfunction. For example, a car radio may need to read knob input, to process the data from serial communication ports, to process the voice signal from the A/D converter, and to control the tuner, cassette, phone, etc. The user will not be satisfied if the system does not react to input in a timely manner.
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ECE 471 19-Time-3 How to Specify the Timing Requirement Frequency of execution How often a program component needs to be executed? E.g., the radio volume knob must be read once in every 20ms Latency How soon a program component needs to be executed when an event occur? E.g., the interrupt must be processed within 1ms
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ECE 471 19-Time-4 How to Specify the Timing Requirement (cont.) Two types of timing requirement hard deadline - all timing requirements must be satisfied. soft deadline - some timing requirement can be violated temporarily. All timing requirement must be satisfied statistically.
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ECE 471 19-Time-5 How to Satisfy the Frequency Requirement? Determine the frequency of execution of each functional module If the timing deadline is a hard deadline, define c i as the worst execution CPU time for module i If the timing deadline is a soft deadline, define c i as the average execution CPU time for module i Define T i as the period of task i Define n as the number of tasks
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