嵌入式系统概论

CS4101嵌入式系統概論

DesignsUsingRTOS0CS4101嵌入式系統概論

DesignsUsingSpecificationBeforewecandesignandimplementasystem,weneedtospecifyit

aharderissueSpecifyinganembeddedsystemisharderWhatmustthesystemdo?Howfastmustitdoit?Howcriticaliseachtiming?Hardorsoftreal-time?Knowledgeofsystemhardwareneedede.g.ifaserialportreceives1Kcharacters/secandeachcharactercausesaninterrupt,HWcanhandle?SoftwareengineeringknowledgeneededStructure,modularity,encapsulation,maintainability1SpecificationBeforewecandesUndergroundTankMonitoringMonitorupto8

underground

tanksbyreading

thermometers

andlevelsof

floatsinthem2UndergroundTankMonitoringMonUndergroundTankMonitoringReadingfloatlevel:periodicallySendacommandtohardwaretoreadfromatank;hardwareobtainsthelevelandinterruptsmicroprocessorforlaterreadingReadingtemperature:atanytimeAlarming:Setflagandturnonalarmwhenleveldroppingconsistently(leak)orrisingrapidlyduringrefueling3UndergroundTankMonitoringReaUndergroundTankMonitoringUserInterface:16-buttonkeypad,20-charLCD,thermalprinterKeypad:givecommandslikedisplayinglevels,requestreports,historiesetc.andbuttonsinterruptthemicroprocessorPrinter:interruptsafterprintingeachline,indicatingitisreadyforthenextDisplayshowsmostrecentdata.RetainsdataonscreenuntilchangedbytheprocessorAconnectortoanalarmbelltowarnaboutsystemleaksoroverflows.Turnedoffthroughoneofthekeypadbuttons4UndergroundTankMonitoringUseMoreDetailedSpecificationsMainlyontimingandthisisoftenmostdifficultpart,particularlywhenyoutalktocustomers:Whenafloatinatankisrisingrapidly,howoftendoweneedtoreadit?

severaltimespersecondHowquicklyshouldrespondonpushingbuttons?

0.1secondWhatmicroprocessortouse?8-bitHowmuchtimeforcalculatinggasquantity?

mayneedexperiments;say,4~5sec5MoreDetailedSpecificationsMaThereisaTimingProblem!Ourrequirementsare:MustcheckeachtankinwhichthefloatisrisingseveraltimesasecondBut,ittakesa4or5secondstocalculatethequantityofgasolineinatankAnd,wecanonlyuse8-bitmicroprocessorCanyoubuiltsuchasystemandsatisfythetimingconstraints?Workaround:Detectoverflowsbasedonfloatlevelsaloneandnotcalculatinggasolinevolume6ThereisaTimingProblem!OurDoWeNeedanRTOS?4-5secgasquantitycalculationisthemosttimeconsumingandmustbepre-emptedwhenotherprocessing(mostlyinteractionwithusersoroperationsinemergence)isrequiredtobedoneWithoutanRTOS,ISRsrequiredtodotasks.PossibletomanagewithISRsincurrentcasebutRTOSisabetteroptionNow,wearereadyto“design”thesystem7DoWeNeedanRTOS?4-5secgasDividingWorkintoTasksLevelcalculationtaskCalculatesgasolinevolumeineachtankbasedontemperatureandfloatlevelTakes4-5sec,henceasalowprioritytaskOnetaskforalltanksoronetaskforeachtank?OverflowdetectiontaskHigherprioritythanlevelcalculation&leakdetectionFloathardwaretaskSchedulerequestsfromlevel-calculationandoverflow-detectionformutualexclusivelyaccessingthelevelhardwareneedtomanagerequestqueueAlternatively,canusesemaphoretoprotectlevelHW8DividingWorkintoTasksLevelDividingWorkintoTasksButtonhandlingtaskNeedastatemachinetokeeptrackofsequenceofbuttonspressedputinISR?DisplaytaskNeedtopreventtasksfrominterferingwitheachother’sdisplaycan’tdowithsemaphore(nextpage)AlarmbelltaskmaynotneededSharedhardwareasseveraltaskscanturniton/off.PrintformattingtaskLowerprioritythanbuttonhandlingtasksinceitmighttakemorethan1/10thofasecondtoformatreportswhichmustnotinterferewithbuttonresponse9DividingWorkintoTasksButtonSemaphoreCannotProtectDisplay10SemaphoreCannotProtectDisplSummaryofTaskedNeeded11SummaryofTaskedNeeded11DealingwithSharedDataGasolinelevelissharedbyseveraltasks(levelcalculation,display,printformatting)CanbedealtwitheitherbyhavingasemaphoreoraseparatetaskwithrequestqueueTwoconsiderationsfortheabovedecision:Whatisthelongesttimethatanytaskwillholdontothesemaphore?Caneveryothertaskwaitthatlong?Foroursystem,semaphoremaybesufficient12DealingwithSharedDataGasoliFinalDesign13FinalDesign13ImplementationUsinguC/OSuC/OSAtinyopen-sourcereal-timekernelMemoryfootprintisabout20kforafullyfunctionalkernelSupportingpreemptivepriority-drivenreal-timeschedulingSupportingmanyplatforms:x86,68x,ARM,MIPS…Samplecodeforundergroundtankmonitoring:RunsunderDOS,usesuC/OSservices,andiscompiledwithBorlandC14ImplementationUsinguC/OSuC/OOnHardwarevsOnDOSTankcode+uC/OScodeHardwareTankcode+uC/OScodePCDOSNeedtosimulateHW

andpresentaDOSinterface15OnHardwarevsOnDOSTankcodeStartupDBGMAIN.C:allofDOSscreenandkeyboardinterfacevoidmain(void){/*Settimer&uC/OSinterruptonDOS*/ .../*Starttherealsystem*/

vEmbeddedMain();}16StartupDBGMAIN.C:allofDOSsStartupMAIN.C:mainroutineofHWindependentcodevoidvEmbeddedMain(void){OSInit();/*initializeuC/OS*/vTankDataInit();vTimerInit();vDisplaySystemInit();vFloatInit();

vButtonSystemInit();

vLevelsSystemInit();vPrinterSystemInit();vHardwareInit();vOverflowSystemInit();

OSStart();/*startuC/OS*/}17StartupMAIN.C:mainroutineofInsideuC/OS-OSinit()InitinternalstructuresofuC/OSTaskreadylistPrioritytableTaskcontrolblocks(TCB)EventcontrolblocksQueuecontrolblocksCreatehousekeepingtasksTheidletask

OSTaskCreate(OSTaskIdle,(void*)0,

(void*)&OSTaskIdleStk[OS_TASK_IDLE_STK_TOP],

OS_LO_PRIO);18InsideuC/OS-OSinit()InitinInsideuC/OS-OSinit()OSTaskCreate(): OSTaskCreate( OSTaskIdel, (void*)0, &TaskStartStk[TASK_STK_SIZE-1], 0 );Entrypointofthetask(apointertofunction)ParameterofthetaskStackofthetaskPriority(0=highest)19InsideuC/OS-OSinit()OSTaskCInternalStructureofuC/OS-II20InternalStructureofuC/OS-IITaskControlBlock(TCB)21TaskControlBlock(TCB)21BacktoMAIN.CvButtonSystemInit()ThetaskthatinitializesthebuttontaskvoidvButtonSystemInit(void){/*Initializethequeueforthistask*/QButtonTask=OSQCreate(&a_pvQData[0],Q_SIZE);/*Startthetaskthathandlesbuttonstatemachine*/OSTaskCreate(vButtonTask,NULLP,(void*)&ButtonTaskStk[STK_SIZE],TASK_PRIORITY_BUTTON);}22BacktoMAIN.CvButtonSystemIniBacktoMAIN.CvLevelsSystemInit()ThetaskthatinitializesthelevelstaskvoidvLevelsSystemInit(void){/*Initializethequeueforthistask*/QLevelsTask=OSQCreate(&a_pvQData[0],Q_SIZE);/*Startthetaskthatcalculatesthetanklevels*/OSTaskCreate(vLevelsTask,NULLP,(void*)&LevelsTaskStk[STK_SIZE],TASK_PRIORITY_LEVELS);}23BacktoMAIN.CvLevelsSystemIniInsideuC/OS-OSstart()StartmultitaskingofuC/OSNeverreturnstomain()NeedtocreateatleastonetaskbeforecallingOSstart()ThatisthereasonwhyweneedtocreateOSTaskIdel()Runthehighest-priorityreadytaskWehavealreadyhadtaskssuchasOSTaskIdel(),vButtonTask(),vLevelsTask(),...readytorun24InsideuC/OS-OSstart()StartvButtonTaskThetaskthathandlesthebuttonstatemachinestaticvoidvButtonTask(){...while(TRUE){/*Waitforabuttonpress*/wMsg=(int)OSQPend(QButtonTask,WAIT_FOREVER,&byErr);switch(iCmdState){caseCMD_NONE:switch(wMsg){case'1':case'2':case'3':vDisplayTankLevel(wMsg-'1');break;

...Taskblockedwaitingforrequestsinqueue25vButtonTaskThetaskthathandlvButtonInterruptThisisthebuttoninterruptroutinevoidvButtonInterrupt(void){/*GotoHW,seewhatbuttonwaspushed*/wButton=wHardwareButtonFetch();/*Putbuttononthetask’squeue*/OSQPost(QButtonTask,(void*)wButton);}WakeupvButtonTask()26vButtonInterruptThisisthebuvLevelsTaskThetaskthatcalculatesthetanklevelsstaticvoidfarvLevelsTask(){/*Startwiththefirsttank*/iTank=0;while(TRUE){/*Getfloatsandfindlevelintank*/

vReadFloats(iTank,vFloatCallback);/*Waitfortheresult.*/wFloatLevel=(WORD)OSQPend(QLevelsTask,WAIT_FOREVER,&byErr)-MSG_LEVEL_VALUE;/*Dothe"calculation"–looong*/27vLevelsTaskThetaskthatcalcuvLevelsTask/*Adddatatothedatabank*/vTankDataAdd(iTank,wFloatLevel);/*Nowtestforleaks*/if(iTankDataGet(iTank,a_iLevels,NULLP,3)…{if/*thelevelsgodownconsistently.*/{