IAR PowerPac RTOS User Guide

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The scheduler deactivates the task to be suspended (Task 0) by saving the processor registers on its stack. It thenactivates the higher-priority task (Task n) by loading the stack pointer (SP) and the processor registers from the valuesstored on Task n's stack.Task 0Task nTask ControlblockStackTask ControlblockStackvariablestemp. storagevariablestemp. storageret. addressesret. addressesSPCPUregistersSPCPUregistersFree StackareaFree StackareaSchedulerCPUChange of task statusA task may be in one of several states at any given time. When a task is created, it is automatically put into the READYstate (TS_READY).A task in the READY state is activated as soon as there is no other READY task with higher priority. Only one taskmay be active at a time. If a task with higher priority becomes READY, this higher priority task is activated and thepreempted task remains in the the READY state.18IAR PowerPac RTOSfor ARM CoresPPRTOS-2
Basic conceptsThe active task may be delayed for or until a specified time; in this case it is put into the DELAY state (TS_DELAY)and the next highest priority task in the READY state is activated.The active task may also have to wait for an event (or semaphore, mailbox, or queue). If the event has not yet occurred,the task is put into the waiting state and the next highest priority task in the READY state is activated.A non-existent task is one that is not yet available to IAR PowerPac RTOS; it has either not been created yet or it hasbeen terminated.The following illustration shows all possible task states and transitions between them.Not existingCREATETASK()Terminate()TS_Ready Scheduler Active taskDelay()Wait for event,mailbox orsemaphoreTS_DELAYHow the OS gains controlWhen the CPU is reset, the special-function registers are set to their respective values. After reset, program executionbegins. The PC register is set to the start address defined by the start vector or start address (depending on the CPU).This start address is in a startup module shipped with the C compiler, and is part of the standard library.The startup code performs the following:● Loads the stack pointers with the default values, which is for most CPUsthe end of the defined stack segment(s)● Initializes all data segments to their respective values● Calls the main() routine.In a single-task-program, the main() routine is part of your program which takes control immediately after the Cstartup. IAR PowerPac RTOS works with the standard C startup module without any modification. If there are anychanges required, they are documented in the startup file which is shipped with IAR PowerPac RTOS.The main() routine is still part of your application program. Basically, main() creates one or more tasks and thenstarts multitasking by calling OS_Start(). From then on, the scheduler controls which task is executed.The main() routine will not be interrupted by any of the created tasks, because those tasks are executed only after thecall to OS_Start(). It is therefore usually recommended to create all or most of your tasks here, as well as your controlstructures such as mailboxes and semaphores. A good practice is to write software in the form of modules which are(up to a point) reusable. These modules usually have an initialization routine, which creates the required task(s) and/orcontrol structures.PPRTOS-219
Page 1 and 2: IAR PowerPac RTOSUser GuidePPRTOS-2
Page 3 and 4: PrefaceWelcome to the IAR PowerPac
Page 5 and 6: ContentsPreface ...................
Page 7 and 8: ContentsOS_WaitCSema() ............
Page 9 and 10: ContentsOS_LeaveInterrupt() .......
Page 11 and 12: Introduction to IAR PowerPacRTOSWha
Page 13 and 14: Basic conceptsTasksIn this context,
Page 15 and 16: Basic conceptsPREEMPTIVES MULTITASK
Page 17: Basic conceptsMAILBOXES AND QUEUESA
Page 21 and 22: Basic conceptsThe flowchart below i
Page 23 and 24: Basic conceptsLIST OF LIBRARIESIn y
Page 25 and 26: Task routinesIntroductionA task tha
Page 27 and 28: Task routinesOS_CREATETASK() can be
Page 29 and 30: Task routinesExampleThe following e
Page 31 and 32: Task routinesExampleint sec,min;voi
Page 33 and 34: Task routinesAdditional Information
Page 35 and 36: Task routinesReturn valueOS_TASKID:
Page 37 and 38: Software timersSoftware timerA soft
Page 39 and 40: Software timers#define OS_CREATETIM
Page 41 and 42: Software timersOS_SetTimerPeriod()D
Page 43 and 44: Software timersAdditional Informati
Page 45 and 46: Software timersAdditional Informati
Page 47 and 48: Software timersExampleOS_TIMER TIME
Page 49 and 50: Resource semaphoresIntroductionReso
Page 51 and 52: Resource semaphoresResource semapho
Page 53 and 54: Resource semaphoresOS_Request()Desc
Page 55 and 56: Counting SemaphoresIntroductionCoun
Page 57 and 58: Counting SemaphoresPrototypevoid OS
Page 59 and 60: Counting SemaphoresReturn value0: I
Page 61 and 62: MailboxesWhy mailboxes?In the prece
Page 63 and 64: MailboxesMailboxes API function ove
Page 65 and 66: MailboxesExampleSingle-byte mailbox
Page 67 and 68: MailboxesPrototypevoid OS_GetMail (
Page 69 and 70:
MailboxesOS_WaitMail()DescriptionWa
Page 71 and 72:
QueuesWhy queues?In the preceding c
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QueuesReturn valueThe size of the r
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QueuesExamplestatic void MemoryTask
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Task eventsIntroductionTask events
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Task eventsExampleOS_WaitEventTimed
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Task eventsPrototypechar OS_ClearEv
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Event objectsIntroductionEvent obje
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Event objectsExampleif (OS_EVENT_Wa
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Event objectsExampleOS_EVENT_Reset(
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Heap type memory managementANSI C o
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Fixed block size memory poolsIntrod
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Fixed block size memory poolsProtot
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Fixed block size memory poolsProtot
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StacksIntroductionThe stack is the
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InterruptsIntroductionIn this chapt
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InterruptsRules for interrupt handl
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InterruptsOS_LeaveInterruptNoSwitch
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InterruptsNesting interrupt routine
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Critical RegionsIntroductionCritica
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System variablesIntroductionThe sys
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Configuration for your targetsystem
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Time measurementIntroductionIAR Pow
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Time measurementPrototypeU32 OS_Get
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Time measurementPrototypeOS_U32 OS_
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RTOS-aware debuggingThis chapter de
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RTOS-aware debuggingTimersA softwar
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DebuggingRuntime errorsSome error c
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DebuggingValue Define Description17
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Performance and resource usageThis
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Performance and resource usageThe c
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Performance and resource usage*/sta
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ReentranceAll routines that can be
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LimitationsThe following limitation
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Source code of kernel and libraryIn
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Additional modulesKeyboard manager:
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FAQ (frequently asked questions)Q:
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GlossaryActive TaskCooperativemulti
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IndexIndexAAdditional modules . . .
Page 147:
IndexOS_WaitSingleEventTimed(). . .
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IAR PowerPac RTOS User Guide

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