IAR PowerPac RTOS User Guide

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Return valueType OS_TIME, which is defined as an integer between1 and 2 15 -1 = 0x7FFF = 32767 for 8/16-bit CPUs and as an integer between1 and
Resource semaphoresIntroductionResource semaphores are used for managing resources by avoiding conflicts caused by simultaneous use of a resource.The resource managed can be of any kind: a part of the program that is not reentrant, a piece of hardware like thedisplay, a flash prom that can only be written to by a single task at a time, a motor in a CNC control that can only becontrolled by one task at a time, and a lot more.The basic procedure is as follows:Any task that uses a resource first claims it by calling the OS_Use() or OS_Request() routines of IAR PowerPacRTOS. If the resource is available, the program execution of the task continues, but the resource is blocked for othertasks. If a second task now tries to use the same resource while it is in use by the first task, this second task is suspendeduntil the first task releases the resource. However, if the first task that uses the resource calls OS_Use() again for thatresource, it is not suspended because the resource is blocked only for other tasks.The following diagram illustrates the process of using a resource:USE()Access resourceUNUSE()A resource semaphore contains a counter that keeps track of how many times the resource has been claimed by callingOS_Request() or OS_Use() by a particular task. It is released when that counter reaches 0, which means theOS_Unuse() routine has to be called exactly the same number of times as OS_Use() or OS_Request(). If it is not,the resource remains blocked for other tasks.On the other hand, a task cannot release a resource that it does not own by calling OS_Unuse(). In the debug versionof IAR PowerPac RTOS, a call of OS_Unuse() for a semaphore that is not owned by this task will result in a call tothe error handler OS_Error().Example of using resource semaphoresHere, two tasks access an LC display completely independently from each other. The LCD is a resource that needs tobe protected with a resource semaphore. One task may not interrupt another task which is writing to the LCD, becauseotherwise the following might occur:● Task A positions the cursor● Task B interrupts Task A and repositions the cursor● Task A writes to the wrong place in the LCD' s memory.To avoid this type of situation, every the LCD must be accessed by a task, it is first claimed by a call to OS_Use() (andis automatically waited for if the resource is blocked). After the LCD has been written to, it is released by a call toOS_Unuse().PPRTOS-2 49
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 and 18: Basic conceptsMAILBOXES AND QUEUESA
Page 19 and 20: Basic conceptsThe active task may b
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: Software timersExampleOS_TIMER TIME
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
Page 73 and 74: QueuesReturn valueThe size of the r
Page 75 and 76: QueuesExamplestatic void MemoryTask
Page 77 and 78: Task eventsIntroductionTask events
Page 79 and 80: Task eventsExampleOS_WaitEventTimed
Page 81 and 82: Task eventsPrototypechar OS_ClearEv
Page 83 and 84: Event objectsIntroductionEvent obje
Page 85 and 86: Event objectsExampleif (OS_EVENT_Wa
Page 87 and 88: Event objectsExampleOS_EVENT_Reset(
Page 89 and 90: Heap type memory managementANSI C o
Page 91 and 92: Fixed block size memory poolsIntrod
Page 93 and 94: Fixed block size memory poolsProtot
Page 95 and 96: Fixed block size memory poolsProtot
Page 97 and 98: StacksIntroductionThe stack is the
Page 99 and 100:
InterruptsIntroductionIn this chapt
Page 101 and 102:
InterruptsRules for interrupt handl
Page 103 and 104:
InterruptsOS_LeaveInterruptNoSwitch
Page 105 and 106:
InterruptsNesting interrupt routine
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Critical RegionsIntroductionCritica
Page 109 and 110:
System variablesIntroductionThe sys
Page 111 and 112:
Configuration for your targetsystem
Page 113 and 114:
Time measurementIntroductionIAR Pow
Page 115 and 116:
Time measurementPrototypeU32 OS_Get
Page 117 and 118:
Time measurementPrototypeOS_U32 OS_
Page 119 and 120:
RTOS-aware debuggingThis chapter de
Page 121 and 122:
RTOS-aware debuggingTimersA softwar
Page 123 and 124:
DebuggingRuntime errorsSome error c
Page 125 and 126:
DebuggingValue Define Description17
Page 127 and 128:
Performance and resource usageThis
Page 129 and 130:
Performance and resource usageThe c
Page 131 and 132:
Performance and resource usage*/sta
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ReentranceAll routines that can be
Page 135 and 136:
LimitationsThe following limitation
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Source code of kernel and libraryIn
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Additional modulesKeyboard manager:
Page 141 and 142:
FAQ (frequently asked questions)Q:
Page 143 and 144:
GlossaryActive TaskCooperativemulti
Page 145 and 146:
IndexIndexAAdditional modules . . .
Page 147:
IndexOS_WaitSingleEventTimed(). . .
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IAR PowerPac RTOS User Guide

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