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

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• Disabling and Enabling the Scheduler– If no shared variables or data structures with an ISR, we candisable and enable schedulingvoid Function (void){OSSchedLock();.. /* You can access shared data in here */.OSSchedUnlock();}– Two or more tasks can share data without contention– While the scheduler is locked, interrupts are enable• If the ISR generates a new event which enables a higherpriority, the higher priority will be run when theOSSchedunlock() is called.2-27Semaphores• Semaphores are used to– Control access to a shared resource (mutual exclusion)– Signal the occurrence of an event– Allow two tasks to synchronize their activities• Two types of semaphores– Binary semaphores– Counting semaphores• Three operations of a semaphore– INITIALIZE (called CREATE)– WAIT (called PEND)– SIGNAL (called POST) --Release semaphore• Highest priority task waiting for the semaphore is activized (uCOS-IIsupports this one)• First task that requested the semaphore is activized (FIFO)2-28
• Accessing shared data by obtaining a semaphoreOS_EVENT *SharedDataSem;void Function (void){INT8U err;OSSemPend(SharedDataSem, 0, &err);.. /* You can access shared data in here (interrupts are recognized) */.OSSemPost(SharedDataSem);}2-29• Control of shared resources (multual exclusion)– e.g., single display devicetask1( ... ){...printf("This is task 1.");...}task2( ... ){...printf("This is task 2.");...}Results may be:ThiThsi siis ttasaks k12..Exclusive usageof certain resources(e.g., shared memory)2-30
Page 1 and 2: Chapter 2Real-Time Systems Concepts
Page 3 and 4: • Resource- EX: I/O, CPU, Memory,
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: • Disabling and enabling interrup
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

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