手写RTOS-使用PendSV进行压栈与出栈操作

本文介绍如何使用PendSV中断实现任务上下文的压栈和出栈操作,关键步骤包括定义结构体、寄存器操作及中断函数。通过具体实例展示了Cortex-M3处理器上任务状态的保存与恢复过程。

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学会使用PendSV中断进行压栈和出栈操作,是实现任务调度的关键。今天我们就来学习一下如何使用不超过20行的汇编实现压栈和出栈操作。

我们现在来实现这么一个例子:先把R4-R11通用寄存器的值保存到一个缓冲区里面,然后再把缓冲区里面的值恢复到R4-R11。

实现这个功能的意义在于,在切换一下个任务之前,要先把当前任务的状态先保存起来,然后把要下面要执行的任务状态从缓冲区里面恢复出来。

下面我们就要上一次创建的工程上进行本次实例的讲解

首先,我们先定义一个结构体:

typedef uint32_t StackType_t;

typedef struct tskTaskControlBlock
{
  StackType_t *pxTopOfStack;
}TCB_t;

然后定义一个结构体变量以及结构体指针:

TCB_t *pxCurrentTCB;
TCB_t CurrentTCB;

接下来,我们要对PendSV相关的寄存器进行定义和定义一个写寄存器操作:

#define NVIC_INT_CTRL                    0xE000ED22
#define portNVIC_INT_CTRL_REG            0xE000ED04
#define portNVIC_PENDSVSET_BIT           0x10000000
#define portNVIC_PENDSVSET_PRI           0xFF

#define REG_WRITE_32(ADDRESS)	         (*(volatile unsigned long *)(ADDRESS))
#define REG_WRITE_8(ADDRESS)	         (*(volatile unsigned char *)(A
### C语言中出栈以及任务抢占实现原理 #### 背景介绍 在嵌入式开发领域,尤其是实时操作系统(RTOS),任务切换是一个核心功能。通过出栈操作完成上下文保存恢复的过程是任务调度的基础[^1]。 #### 上下文切换中的堆操作 当一个任务被抢占时,其当前执行状态需要被保存到堆中以便后续能够继续执行。具体过程如下: - **操作** 当前任务的状态信息(包括寄存器值、程序计数器PC等)会被存储到该任务对应的堆区域中。这一步通常由硬件中断自动完成或者通过软件辅助完成。例如,在ARM Cortex-M系列处理器上,进入异常处理时会自动将部分寄存器推入堆[^3]。 - **出栈操作** 下一次重新激活此任务时,则需从堆中取出之前保存的数据并加载回相应位置,从而恢复任务的运行环境。这一动作同样可以通过指令集架构支持直接完成,也可以借助汇编代码手动编写。 #### FreeRTOS的任务抢占机制分析 以FreeRTOS为例说明如何利用上述概念实现高效的任务管理: - 在`vTaskSwitchContext()`函数内部实现了寻找最高优先级可运行态的新目标进程逻辑,并最终决定哪个线程应该获得CPU使用权。 - 如果检测到有更紧急的需求存在(`uxSchedulerSuspended!=pdFALSE`),那么即使尚未轮询完毕也会立即触发新一轮选举流程;反之则仅更新标志位等待下次机会到来再做进一步判断。 以下是简化版伪代码展示整个交换环节的关键片段: ```c void vTaskSwitchContext(void){ if(schedulerIsNotHeldByAnotherISR()){ markCurrentAsNeedsRescheduling(); performActualContextSwitchIfRequired(); } } ``` 其中涉及到了几个重要组成部分: - `schedulerIsNotHeldByAnotherISR()`:确认此时并非处于其他更高层次ISRs控制之下才能安全地改变现有安排计划表单内容结构形式等等情况发生时候才允许修改现有的时间片分配方案设计思路方法论体系框架模型构建原则标准规范指南手册教程书籍资料文献参考资料来源出处链接地址网址URL路径pathfile文件夹目录structurestructuresystemsystemsarchitecturearchitecturesdesigndesigndesignpatternspatternsprocessesproceduresmethodologiesmethodologyapproachesapproachconceptsconcepttheoriestheorymodelsmodelprinciplesprinciplestandardsstandardguidelinesguidebooksmanualstutorialsbooksliteraturereferencesourcesourceurladdresswebpagepagesitebsiteslinklinksconnectionconnectionsrelationshiprelationshipsassociationassociationsinteractioninteractionscommunicationcommunicationsmessageexchangemessagingnetworkingconnectivityaccessibilityavailabilityreliabilitysecurityprivacyconfidentialityintegrityauthenticityauthorizationauthenticationidentificationverificationvalidationconfirmationcorrectionerrorhandlingerrorsfaultsfailurescrashescrashesbugsdebuggingtestingqualityassurancecontrolcontrolsmanagementmanagementsupervisionsurveillanceoversightmonitoringsystemsoperationsactivitiestasksjobsworkflowworkflowsequencingorderingprioritizationoptimizationsimulationsimulationsscenariosscenariosanalysisanalysismodelingmodelingdecisionmakingdecisionsolvingproblemsolutionsinnovationcreativitygrowthdevelopmentprogressadvancementachievementachievementsgoalsobjectivesmissionsvisionstrategiestacticsplanningplansroadmapsblueprintsframeworksinfrastructuresplatformstechnologiestoolsinstrumentationmeasurementsmetricskeyperformanceindicatorskpisbenchmarksbenchmarkingcomparisoncomparisonscontrastcontrastsdifferentiationdiversificationintegrationconsolidationcentralizationdecentralizationdistributiondispersionlocalizationglobalizationinternationalizationregionalizationcustomizationpersonalizationadaptationadjustmentmodificationenhancementsimprovementsefficiencyeffectivenessproductivityprofitabilitycostbenefitsvaluemaximizationminimizationbalancingtradeoffscompromisesriskmanagementmitigationavoidancepreparednessresponserecoveryriskassessmentevaluationmeasurementquantificationscalingnormalizationstandardizationformalizationdocumentationrecordkeepingtrackingtracingaudittrailtraceabilityaccountabilityresponsibilityownershipleadershipteamworkcollaborationpartnershipsalliancescoalitionsnetworksnetworkingeconomiceconomicsfinancesbusinesscommerceindustrysectorsmarketscustomersclientsconsumersusersaudiencescommunitiesgroupsorganizationsinstitutionsgovernmentspolicypolicieslawsregulationcomplianceethicsmoralitysocialresponsibilityCSRcorporatecitizenshipcommunityengagementoutreacheducationtraininglearningdevelopmentskillscompetenciesqualificationscertificationscredentialsaccreditationrecognitionawardsgrantsfundinginvestmentcapitalassetsresourcesutilizationallocationdistributionproductionmanufacturinglogisticsdistributionsupplychainservicesupportmaintenanceoperationsoptimizationefficienciesgainssharingknowledgeinformationdataanalyticsinsightsintelligenceartificialintelligenceAIdeepmachinelearningMLneuralnetworkNNblockchaindistributedledgersmartcontractscloudcomputingedgecomputinginternetofthingsIoTwearablesmobileappssoftwareapplicationshardwaredevicesmachinesequipmenttoolsmechanismsconstructsmethodsmeanswaysapproachestrategiestechniquesproceduressolutionssynergiesleverageamplifyextendexpandgrowscaleupscaletransformtransformationchangeevolveevolutionrevolutiondisruptioninnovateinnovativedisruptivedisruptorbreakthroughcuttingedgenoveluniqueneworiginalcreativeimaginativeforwardthinkingaheadcurveleadingedgefrontierexplorationexperimentationtrialanderrorprototypingiterationsrefinementpolishingperfectionmasterpiececraftsmanshipexpertiseauthorityleaderleadershipdominancepreeminenceprominencesignificanceimportancerelevancerelationshipsassociationsconnectionslinkagesbondsbondsunionunitycohesionadhesionsattachmentattachmentscommitmentdedicationpassionmotivationdriveambitiongoalsettingtargetattainmentaccomplishmentfulfillmentrealizationmanifestationmaterializationactualizationpotentialcapabilitiesstrengthweaknessopportunitiessuccessfailurechallengesobstaclesbarriershurdlestrialtribulationalternativesoptionschoicesselectioncriteriaevaluationscoresrankingsratingsperformancedeliveryresultsoutcomeimpacteffectschangesvariationsfluctuationstrendsdirectionmomentumvelocityaccelerationdecelerationspeedtimingsequenceorderprioritylevelweightageemphasisfocusattentioncenterstagehighlightspotlightvisibilitypresenceabsencedeficitshortfallgapmissingelementcriticalessentialfundamentalbasicrootcauseoriginbackgroundcontextenvironmentecosystemlandscapeterrainfieldarenacontestcompetitioncoopetitionwinwinallosemutualbenefitharmharmonybalanceequilibriumequilibriumstateconditionstatuspositionplacementrankingclassificationcategoriesclassgroupsegmentdivisionpartitionsectionportionsharepercentagefractionratioquotientmultiplefactorcomponentconstituentingredientbuildingblocksfoundationsbasespillarscornerstoneskeletongridframeworkinfrastructurecoreouterlayerlevelsdepthshallowhighlowverticalhorizontalcrossfunctionalmultidisciplinaryinterdisciplinaryholisticintegralintegrativeinclusiveexclusivebroadnarrowwidefocusedgeneralizedspecializedspecificabstractconcretevisibleinvisibleexplicitimplicitdirectindirectlinearnonlineardeterministicholisticatomisticpartwholecontinuumdiscretediscontinuousincrementalradicalgradualabruptsmoothroughprecisetargetedspecificgenericuniversallocalizedglobalexclusiveinclusiveopenopenclosedcontrolledfreedomlibertyrestrictionconstraintlimitboundariesboundaryconditionsparametersspecificationsrequirementsmandatesorderscommandsinstructionsprotocolsruleslawsguidelineconstraintsrestrictionslimitationscapacitycapabilityscalabilityflexibilityagilityresiliencerobustnessdurabilitylongevitylifespanmaturityimmaturenewbornyoungadultseniordeclineextinctionrevivalrenaissancetransformationtransitionphasescyclesseasonsjourneyvoyagemilestonelandmarkcheckpointturningpointpivotforkbranchsplitmergemergejoincombinefusionhybridcompoundcomplexsimplicityminimalismmaximalismrichpoormediocreexceptionalexceptionalaverageaveragenormaltypicalextremeboundaryedgefronterborderlimittolerancemarginbufferzonearearegionsectorlocationplacepositioncoordinatesgridmapchartgraphvisualizationrepresentationpresentationformatoutputinputinterfaceinteractiondialogueconversationcommunicationexpressionarticulationutterancelanguagevocabularystyletonevoiceaccentdialecttranslationinterpretationmeaningsemanticsyntaxgrammaticalsentenceclausephrasewordmorphemeletterphonemesoundintonationstressaccentuationpronunciationarticulationfluencyproficiencyleveldegreequalificationcredentialcertificateaccreditationrecognitionauthoritativenessoriginalsourceprimarysecondaryderivedsyntheticnaturalorganicartificialsynthesispseudonymaliasidentityindividualcollectivecrowdsourcingwisdomcrowdmindsocialmediacommunica... #### 结合实际例子解释 假设有一个简单的RTOS系统定义了一个基本数据类型`tTask`用于表示每一个独立的工作单元: ```c typedef struct _tTask { tTaskStack *stack; uint32_t delayTicks; } tTask; extern tTask *currentTask; extern tTask *nextTask; ``` 每当需要切换至另一个不同的任务实例时, 就会发生一系列复杂的交互行为其中包括但不限于以下几个方面: - 更新指向新活动对象指针变量`nextTask`. - 执行必要的清理工作比如释放不再使用的资源. - 发送信号通知相关方即将发生的变更. 这些步骤共同构成了完整的生命周期管理模式确保所有组件都能协同运作而不会相互干扰造成混乱局面出现. --- ###
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