lec11_jitter0

Lec11_jitter0 - Lecture 11 Jitter jitter = time between actual arrival of a task about to execute and its expected arrival total jitter will be the

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Lecture 11: Jitter jitter = time between actual arrival of a task about to execute and its expected arrival; total jitter will be the quadrature sum of all independent causes of jitter (j i ) on a task’s arrival (ie SQRT[SUM(j i 2 )]. jitter tolerance = largest amount of jitter that can be handled by a task scheduler and still meet its deadlines; typically it is the largest time possible between a task’s actual completion and its deadline. Example: Scheduler has a 8 nsec jitter in scheduling a task and processor has 6 nsec jitter locating task in memory. If these were the only sources of jitter, the total jitter would be SQRT(8 2 + 6 2 ) = 10 nsec. Exercise: Show that if there are a billion transistors in your embedded system, each with its own switching time jitter of 10 psec, that the total jitter of them all is about 315 nsec. Sources of task timing jitter: -poor scheduling -poor priority handling -bad algorithms in support packages (eg printf) -bus contentions (I/O devices) -non-fixed loop iteration count -non-fixed number of recursive calls -garbage collection
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This note was uploaded on 04/07/2010 for the course ELEC ecse 421 taught by Professor Guss during the Winter '10 term at McGill.

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Lec11_jitter0 - Lecture 11 Jitter jitter = time between actual arrival of a task about to execute and its expected arrival total jitter will be the

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