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ECE 493T9 Real Time Embedded System Tutorial Set 5 July 14, Spring 2008

ECE 493T9 Real Time Embedded System Tutorial Set 5 July 14, Spring 2008. Clock-Driven Scheduling. Two Main Techniques: Table-Driven Scheduling Input: Periodic Tasks Output: Valid Schedule with Specific Release Time for EVERY Time Slice Method: EDF (or others) Frame-Based Scheduling

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ECE 493T9 Real Time Embedded System Tutorial Set 5 July 14, Spring 2008

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  1. ECE 493T9Real Time Embedded SystemTutorial Set 5July 14, Spring 2008

  2. Clock-Driven Scheduling • Two Main Techniques: • Table-Driven Scheduling • Input: Periodic Tasks • Output: Valid Schedule with Specific Release Time for EVERY Time Slice • Method: EDF (or others) • Frame-Based Scheduling • Input: Periodic Tasks • Output: Valid Schedule with Specific Release Time for EVERY Frame • Method: EDF (or others) • Requirement / Assumptions: • Periodic Tasks (or converted to periodic with worst-case estimations) • Number of tasks is constant throughout the operation of the system • Schedule flexibility is not a major concern

  3. Table-Driven Scheduling • High Predictability, Low Flexibility • All the input tasks must be periodic, or made periodic by worst-case estimation (or other techniques). • Example:Given J1 (1, 2, 2), J2 (2, 6, 6), J3 (2, 12, 12). Construct a Table-Driven Schedule. Since all three jobs are periodic, their schedulibility can be verified with table-driven scheduling technique. In this example we will use EDF as the scheduling method. First, determine the Hyperperiod and Utilization Ratio: Hyperperiod = LCM(Di, i = 1..3) = LCM (4, 6, 12) = 12 Utilization Ratio = 2 / 4 + 2 / 6 + 2 / 12 = 1 After Table-Driven Scheduling, we have the following result: Table:  J1 J2 J1 J2 J1   J3 J1 J2 J1 J2   J1 J3

  4. Frame-Based Scheduling • Set the Scheduler to schedule tasks at periodic time spots rather than at the end of every time slot. • Enable completion of a set of highly related tasks without interruption due to task preemption. • Reduce the complexity of scheduling process and improve the flexibility of Table-Driven Scheduling technique. • Fundamentals: • Based on Table-Driven Scheduling Techniques • During each frame all the included tasks are equally prioritized, and will NOT be preempted by other tasks • Three main frame-size constraints • Major Frame Size must be larger or equal to the process time of every task. • Major Frame Size must divide the Hyperperiod. (To maintain its predictability) • Release Time and Deadline must be separated with at least One Major Frame.

  5. Frame-Based Scheduling • Mathematical Representation of the 3 Frame Size Constraints: • Major Frame Size must be larger or equal to the process time of every task • Major Frame Size must divide the Hyperperiod. (To maintain its predictability)for at least one pi • Release Time and Deadline must be separated with at least One Major Frame

  6. Frame-Based Scheduling • Example 1: Determining Frame Size Given J1(1,15,14), J2 (2, 20, 26), and J3 (3, 22, 22) Notation: J(c, p, D) By constraint one, we know that By constraint two, we know that the possible frame sizes are: Finally, by constraint three, we can narrow down our selection of frame size down to the following:

  7. Frame-Based Scheduling • Example 2: Constructing Frames Given J1(1, 5, 5), J2 (1, 5, 5), J3 (2, 15, 15), J4 (3, 15, 15), and J5 (1, ≥5, ≥5) Please construct a set of frames for scheduling these tasks. Constraint 1: Constraint 2: (Hyperperiod = LCM (5, 15) = 15) Constraint 3: Since both frame sizes are feasible, we will randomly pick f = 5 for demonstration. You can try f = 3 at home.

  8. Frame-Based Scheduling • Example 2: Constructing Frames Given J1(1, 5, 5), J2 (1, 5, 5), J3 (2, 15, 15), J4 (3, 15, 15), and J5 (1, ≥5, ≥5) Please construct a set of frames for scheduling these tasks. Continue… Frame 1:  J1 || J2 || J3 (1) || J4 (1) || J5 (upon event, else pause)Frame 2:  J1 || J2 || J3 (2) || J4 (2) || J5 (upon event, else pause)Frame 3:  J1 || J2 || J4 (3) || J5 (upon event, else pause) || pause Since no precedence is given in this question, the valid schedule of these three frames is: Frame 1 || Frame 2 || Frame 3     (Hyperperiod = 15, f = 5)

  9. Frame-Based Scheduling • Example 3: Frame-Based Scheduling Given J1(2, 5, 5), J2(2,10,10), J3 (5, 15, 15), and J4 (2, 30, 30) as the four jobs in one frame. Please compute a scheduling table for this single frame. Compute Major Frame Length: LCM (pi, i = 1..4) = LCM (5,10,15,30) = 30 Computer Slice Length: GCD (ci, i = 1..4) = GCD(2, 2, 5, 2) = 1 We will use EDF to schedule the 4 tasks in this single frame. Based on EDF, J1 must be scheduled as the first one.

  10. Frame-Based Scheduling • Example 3: Frame-Based Scheduling Continue… Table: J1 J1 Table: J1 J1 J2 J2 Table: J1 J1 J2 J2 J3 J1 J1

  11. Frame-Based Scheduling • Example 3: Frame-Based Scheduling Continue… Table: J1 J1 J2 J2 J3 J1 J1 J3 J3 J3 J1 J1 J3 J2 J2 Table: J1 J1 J2 J2 J3 J1 J1 J3 J3 J3 J1 J1 J3 J2 J2 J1 J1 J3 J3 J3 J1 J1 J3 J3 J4

  12. Frame-Based Scheduling • Example 3: Frame-Based Scheduling Continue… Finally, we will arrive at this Table-Driven Schedule for this single frame: Table: J1 J1 J2 J2 J3 J1 J1 J3 J3 J3 J1 J1 J3 J2 J2 J1 J1 J3 J3 J3 J1 J1 J3 J3 J4 J1 J1 J4 J2 J2

  13. Questions? Questions? Questions?

  14. Project Topic Sign Up!! Midterm Questions

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