Chapter 2 Real-Time Systems Concepts Foreground/Background ...

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Critical Section• The critical section– A piece of code which cannot be interrupted during execution• Cases of critical sections– Modifying a block of memory shared by multiple kernel services• Process table• Ready queue, waiting queue, delay queue, etc.– Modifying global variables used by kernel• Entering a critical section– Disable global interrupt - disable()• Leaving a critical section– Enable global interrupt - enable()2-32-4
• Resource– EX: I/O, CPU, Memory, Printer, …• Shared Resource– The resources which are shared among the tasks– Each task should gain exclusive access to the shared resource toprevent data corruption è Mutual exclusion• Task and Thread (herein both terminology represent asame thing)– A simple program that thinks it has the CPU all to itself– Each task is an infinite loop– It has five state: Dormant, Ready, Running, Waiting, and ISR(Interrupted)2-5TASK #1 TASK #2 TASK #nStack Stack StackFigure 2.2Multiple TaskTask Control BlockStatusTask Control BlockStatusTask Control BlockStatusSPSPSPPriorityPriorityPriorityMEMORYCPUCPU RegistersSPContext2-6
Page 1: Chapter 2Real-Time Systems Concepts
Page 5 and 6: • Foreground/background programmi
Page 7 and 8: Scheduler• Also called the dispat
Page 9 and 10: Figure 2.5 Preemptive kernelLow Pri
Page 11 and 12: Figure 2.7 Priority Inversion probl
Page 13 and 14: • Disabling and enabling interrup
Page 15 and 16: • Accessing shared data by obtain
Page 17 and 18: BUF * BufReq(void){BUF *ptr;Acquire
Page 19 and 20: Event Flags (uCOS-II does not suppo
Page 21 and 22: Message queues• Is used to send o
Page 23 and 24: Figure 2.21 non-preemptive kernelIn
Page 25 and 26: Clock Tick• A special interrupt t
Page 27: • Reduce the execution jitter of

Chapter 2 Real-Time Systems Concepts Foreground/Background ...

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