Real-Time Operating Systems

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Cyclic executive approach: example ¿ Actual code that implements the above cyclic executive schedule loop wait_for_interrupt Procedure_For_A Procedure_For_B Procedure_For_C wait_for_interrupt Procedure_For_A Procedure_For_B Procedure_For_D Procedure_For_E wait_for_interrupt Procedure_For_A Procedure_For_B Procedure_For_C wait_for_interrupt Procedure_For_A Procedure_For_B Procedure_For_D end loop 67 Cyclic executive approach ¿ Advantages: ¿ No actual process exists at run-time; each minor cycle is just a sequence of procedure calls. ¿ The procedures share common address space and can pass data between themselves: • No need for data protection, no concurrency ¿ Disadvantages: ¿ All task periods must be multiple of minor cycle time ¿ Difficulty of incorporating sporadic processese or processes with long periods (major cycle time) ¿ Difficult to actually construct CE (equivalent to bin packing) 68 34
Process-based scheduling ¿ Fixed-priority scheduling ¿ Rate-monotonic (RM) scheduling ¿ Deadline-monotonic (DM) scheduling ¿ Dynamic-priority scheduling ¿ EDF 69 Rate Monotonic (RM) Scheduling ¿ Static priority scheduling ¿ Rate monotonic Æ priorities are assigned to tasks according to their request rates. ¿ Each process is assigned a (unique) priority based on its period ¿ the shorter the period, the higher the priority ¿ Given tasks τ i and τ j , T i < T j Æ P i > P j ¿ Intrinsically preemptive: ¿ currently executing task is preempted by a newly released task with shorter period. 70 35
Page 1 and 2: Real-Time Operating Systems 1 Summa
Page 3 and 4: ¿ Real-time Introduction (3) ¿ Ti
Page 5 and 6: RTOS 9 Real-time Operating Systems
Page 7 and 8: Real-time Operating Systems (3) ¿
Page 9 and 10: Achieving predictability: interrupt
Page 11 and 12: Priority inversion (2) ¿ Basic pri
Page 13 and 14: Achieving predictability: memory ma
Page 15 and 16: Processes ¿ Called tasks in the RT
Page 17 and 18: Scheduling constraints ¿ The follo
Page 19 and 20: Periodic and aperiodic tasks ¿ Per
Page 21 and 22: Real-time scheduling 41 ¿ Given: S
Page 23 and 24: Scheduling metrics ¿ n tasks ¿ Av
Page 25 and 26: Jackson’s algorithm [1955] ¿ 1 |
Page 27 and 28: Horn’s algorithm ¿ Example: 53 S
Page 29 and 30: Introduction ¿ Periodic activities
Page 31 and 32: Processor utilization factor (2) ¿
Page 33: Cyclic executive approach ¿ Schedu
Page 37 and 38: RM schedulability test (2) ¿ For l
Page 39 and 40: EDF algorithm ¿ Dynamic scheduling
Page 41 and 42: Deadline monotonic (DM) scheduling
Page 43 and 44: EDF for D
Page 45 and 46: Periodic task scheduling: summary D

Real-Time Operating Systems

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