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

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Figure 2.3 Task StatesWAITINGOSTaskDel()OSMBoxPost()OSQPost()OSQPostFront()OSSemPost()OSTaskResume()OSTimeDlyResume()OSTimeTick()OSMBoxPend()OSQPend()OSSemPend()OSTaskSuspend()OSTimeDly()OSTimeDlyHMSM()DORMANTOSTaskCreate()OSTaskCreateExt()OSTaskDel()READYOSStart()OSIntExit()OS_TASK_SW()RUNNINGInterruptOSIntExit()ISRTask is PreemptedOSTaskDel()2-7Context Switch (or Task Switch)• Each task has its stack to store the associated information• The purpose of context switch– To make sure that the task, which is forced to give up CPU, canresume operation later without lost of any vital information or data• The procedure of interrupt•••MP_addr(n) : instruction(n)MP_addr(n+1) : instruction(n+1)MP_addr(n+2) : instruction(n+2)•••InterruptreturnfrominterruptPush flagsPush MP_addr(n+1)Push CPU registers•• ; isr codes•pop CPU registersreturn ; jump back to; MP_addr(n+1) 2-8
• Foreground/background programming– Context (CPU registers and interrupted program address) save andrestore using one stack• Multi-tasking context switch– Using each task’s own stackCurrent CPU stack pointerTask1’s local variablesReturn address (optional)Task 1 (to be switched from) stackCPU registers whenTask 2 was switchedTask 2’s code addresswhen it was switchedTask 2’s local variableswhen it was switchedReturn address (optional)Task 2 (to be switched to) stack2-9• During context switchTask1’s local variablesReturn address (optional)Task 1 stackCPU registers whenTask 2 was switchedTask 2’s code addresswhen it was switchedTask 2’s local variableswhen it was switchedReturn address (optional)Task 2 stackTask 1 TCBCurrentProgramaddressCurrentCPUregistersTask 2 TCBStack pointerCurrent CPU stack pointerStack pointer2-10
Page 1 and 2: Chapter 2Real-Time Systems Concepts
Page 3: • Resource- EX: I/O, CPU, Memory,
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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