android for the beaglebone black2.droppdf.com/.../hlk0r/android-for-the-beaglebone-black.pdftable of...

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AndroidfortheBeagleBoneBlack

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TableofContents

Credits

AbouttheAuthors

AbouttheReviewers

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Supportfiles,eBooks,discountoffers,andmore

Whysubscribe?

FreeaccessforPacktaccountholders

Preface

Whatthisbookcovers

Whatyouneedforthisbook

Whothisbookisfor

Conventions

Readerfeedback

Customersupport

Downloadingtheexamplecode

Errata

Piracy

Questions

1.IntroductiontoAndroidandtheBeagleBoneBlack

LookingbackonAndroidandBeagleBoneBlackdevelopment

Shoppingforthehardwareessentials

TheFTDIcable

Powersupply

Breadboardandthemountingplate

MicroSDcards

Learningaboutthehardwareyou’llinterfacewith

General-purposecomponents

TheAdaFruitmemorybreakoutboard

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TheAdaFruitsensorbreakoutboard

Preparingthebreakoutboards

InstallingAndroidontheBeagleBoneBlack

DownloadingapremadeAndroidimage

CreatingyourAndroidmicroSDcardusingWindows

CreatingyourAndroidmicroSDcardusingLinux

Summary

2.InterfacingwithAndroid

UnderstandingtheAndroidHAL

Androidmanagers

TheHALdevelopmentworkflow

WorkingwithPacktHAL

InstallingPacktHAL

PreparingPacktHALunderLinux

PreparingPacktHALunderWindows

ThePacktHALdirectorystructure

PreparingAndroidforPacktHAL

PushingPacktHALfilesunderLinux

PushingPacktHALfilesunderWindows

SettinguptheAndroidNDKforPacktHAL

AddingtheheadertotheNDKunderLinux

AddingtheheadertotheNDKunderWindows

MultiplexingtheBBBpins

ThekernelDeviceTreeandcapemgr

Definingacape

Summary

3.HandlingInputsandOutputswithGPIOs

UnderstandingGPIOs

NutsandboltsofGPIO

GPIOaccessmethodsunderAndroid

ProsandconsofthefileI/Omethod

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Prosandconsofthememory-mappingmethod

PreparingAndroidforGPIOuse

BuildingaGPIO-interfacingcircuit

Constructingthecircuit

Checkingyourwiring

IncludingPacktHALwithinyourapps

UnderstandingtheJavaNativeInterface

CreatinganewappprojectthatusesPacktHAL

BuildingPacktHALunderWindows

BuildingPacktHALunderLinux

ExploringtheGPIOexampleapp

InstallingtheappandsourceunderWindows

InstallingtheappandsourceunderLinux

Theapp’suserinterface

CallingthePacktHALfunctions

UsingthePacktHALGPIOfunctions

Summary

4.StoringandRetrievingDatawithI2C

UnderstandingI2C

DevicesthatuseI2C

MultiplexingforI2ContheBBB

ConnectingtoI2CviatheP9header

MultiplexingforI2C

RepresentingI2CdevicesintheLinuxkernel

PreparingAndroidforFRAMuse

BuildinganI2C-interfacingcircuit

ConnectingtheFRAM

CheckingtheFRAMconnectionwithI2Ctools

ExploringtheI2CFRAMexampleapp

CallingthePacktHALFRAMfunctions

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UnderstandingtheAsyncTaskclass

LearningthedetailsoftheHardwareTaskclass

Summary

5.InterfacingwithHigh-speedSensorsUsingSPI

UnderstandingSPI

MultiplexingforSPIontheBBB

RepresentingSPIdevicesintheLinuxkernel

PreparingAndroidforSPIsensoruse

BuildinganSPIinterfacecircuit

Connectingthesensor

ExploringtheSPIsensorexampleapp

CallingthePacktHALsensorfunctions

UsingtheHardwareTaskclass

Summary

6.CreatingaCompleteInterfacingSolution

Buildingthecompleteinterfacecircuit

Exploringthecompleteexampleapp

Understandinghardwarepollinginanapp

UsingAsyncTaskwithlong-livedthreads

UsingtheHardwareTaskclass

Summary

7.WheretoGofromHere

IntegratingyoursolutionwithAndroid

CreatingacustomkernelandDeviceTree

Addinghardwarecommunicationintothekernel

Integratingintoexistingmanagers

Creatingnewmanagersforcustomhardware

Combiningyourprojectwithotherhardware

Constructingyourownprototypecapes

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CommercialcapesthatinterfacewithAndroid

ExploringtheBBB’sotherinterfaces

Programmablereal-timeunits

Serialcommunications

Controllerareanetwork

Theanalog-to-digitalconverter

Pulsewidthmodulation

Summary

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Allrightsreserved.Nopartofthisbookmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorbyanymeans,withoutthepriorwrittenpermissionofthepublisher,exceptinthecaseofbriefquotationsembeddedincriticalarticlesorreviews.

Everyefforthasbeenmadeinthepreparationofthisbooktoensuretheaccuracyoftheinformationpresented.However,theinformationcontainedinthisbookissoldwithoutwarranty,eitherexpressorimplied.Neithertheauthors,norPacktPublishing,anditsdealersanddistributorswillbeheldliableforanydamagescausedorallegedtobecauseddirectlyorindirectlybythisbook.

PacktPublishinghasendeavoredtoprovidetrademarkinformationaboutallofthecompaniesandproductsmentionedinthisbookbytheappropriateuseofcapitals.However,PacktPublishingcannotguaranteetheaccuracyofthisinformation.

Firstpublished:February2015

Productionreference:1130215

PublishedbyPacktPublishingLtd.

LiveryPlace

35LiveryStreet

BirminghamB32PB,UK.

ISBN978-1-78439-216-1

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CreditsAuthors

AndrewHenderson

AravindPrakash

Reviewers

NathanBurles

GuyCarpenter

AnujDeshpande

CommissioningEditor

AmarabhaBanerjee

AcquisitionEditor

GregWild

ContentDevelopmentEditor

NeetuAnnMathew

TechnicalEditor

TanviBhatt

CopyEditors

DeepaNambiar

VikrantPhadke

ProjectCoordinator

MaryAlex

Proofreaders

SimranBhogal

BernadetteWatkins

Indexer

HemanginiBari

Graphics

SheetalAute

ProductionCoordinator

ManuJoseph

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CoverWork

ManuJoseph

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AbouttheAuthorsAndrewHendersonhasover15yearsofexperiencedevelopingsoftwarefortheLinuxdesktopandembeddedLinuxandAndroidsystems.HeiscurrentlyaPhDcandidateatSyracuseUniversity,withresearchinterestsintheareasofsystemsecurityanddynamicanalysis.HemaintainsmultipleopensourceprojectsfortheBeagleBoardandBeagleBoneplatforms.

IwanttothankCheryl,Olivia,andmyfatherforalloftheirencouragementandsupportduringthetimethatIspentresearchingandwritingthematerialforthisbook.IwouldalsoliketothankDr.HengYin,Dr.WenliangDu,andDr.EhatErcanliofSyracuseUniversityforlendingtheirknowledgeandguidancetomyAndroidOSandBeagleBone/BeagleBoardresearch.

AravindPrakashisaPhDcandidateatSyracuseUniversity.Hisinterestslieinsystemandmobilesecurity,withemphasisonprogramanalysis.Hehaspublishedinmultipletop-tiercomputer-securityconferences.HebringswithhimoveradecadeofprogrammingexperiencefromcompaniessuchasMicrosoft,McAfee,andFireEye.

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AbouttheReviewersNathanBurlesisapost-doctoralresearcherwithaPhDincomputerscience.HeiscurrentlyworkingfortheUniversityofYork,onsubjectsasdiverseasartificialneuralnetworksanddynamic,adaptive,andautomatedsoftwareengineering.

Inhisfreetime,heenjoystinkeringwithembeddedsystemsandelectronics,rangingfromfullsystemssuchastheRaspberryPiandBeagleBoneBlacktosimplemicrocontrollerssuchastheArduino—addingcircuitrytocommunicateusing433MHzRFandinfrared.

Nathanblogsabouthisprojectsaswellastopicsincludingwebsitedevelopment,Android,anddancingathttp://www.nburles.co.uk.

GuyCarpenterisasoftwaredeveloperandveteranhacker.HehascontributedcodetotheBeagleBone,RaspberryPi,Arduino,andChumbyHackersBoardcommunities.HeownsClearwaterSoftwareinBrisbane,Australia.

AnujDeshpandeadorestheBeagleboneBlackandallthingsembeddedwithLinux.Heisanactivepartofthelocalhackerspace,Doo,inPune,andregularlyhostsmeet-upsonavarietyoftopics.

SomeoftheprojectsthathehasbeenapartofareUserspaceArduino,PixHawkFire,andTah.HewasaninternatBeagleboard.org,OneirixLabs,aswellas3DRoboticsforabriefperiodoftime.Anujcompletedhisbachelor’sdegreeincomputersciencefromPICT,Pune.

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PrefaceThebroadavailabilityofAndroid-baseddeviceshasgeneratedalargeamountofinterestindevelopingsoftwareapplications,orapps,thattargetAndroid.Luckily,apowerfulandlow-costhardwareplatformisavailablethatallowsyoutoquicklyandeasilytestyourappsonrealhardware:theBeagleBoneBlack.Withafocusonsmallsizeandawidevarietyofexpansionandinterfacingopportunities,theBeagleBoneBlackprovidesalotofprocessingpowerataverylowprice.Italsoprovidesanopportunitytoappdevelopersthatoncebelongedonlytothosethatwereexperthardwarehackersorownersofexpensivehardwaredevelopmentkits:thechancetowriteAndroidappsthatinteractwithcustomhardwarecircuits.

Whetheryouarebrandnewtohardwareinterfacingoraseasonedexpert,AndroidfortheBeagleBoneBlackprovidesyouwiththetoolsthatyouneedtobegincreatingAndroidappsthatcommunicatedirectlywithyourcustomhardware.Fromtheverybeginning,thisbookwillhelpyouunderstandAndroid’suniqueapproachtohardwareinterfacing.YouwillinstallandcustomizeAndroid,buildcircuitsthatinterfacewithyourBeagleBoneBlackplatform,andbuildnativecodeandAndroidappsthatusethathardwaretocommunicatewiththeoutsideworld.Bysequentiallyworkingthroughtheexamplesineachchapter,youwilllearnhowtocreatemultithreadedappsthatarecapableofinterfacingwithmultiplehardwarecomponentssimultaneously.

Onceyouhaveexploredthevarietyofexamplecircuitsandappsinthisbook,youwillbewellonyourwaytowardbecominganAndroidhardwareinterfacingpro!

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WhatthisbookcoversChapter1,IntroductiontoAndroidandtheBeagleBoneBlack,walksyouthroughtheprocessofinstallingtheAndroidOStoyourBeagleBoneBlackboard.Italsoprovidesyouwithalistofhardwarecomponentsthatyouwillneedtoperformtheactivitiesthroughoutthisbook.

Chapter2,InterfacingwithAndroid,introducesyoutoseveralaspectsoftheBeagleBoneBlack’shardwareandAndroid’sHardwareAbstractionLayer.ItdescribeshowtomakeafewmodificationstobothyourdevelopmentenvironmentandAndroidinstalledonyourBeagleBoneBlacktoallowAndroidappstoaccessthevarioushardwarefeaturesoftheBeagleBoneBlack.

Chapter3,HandlingInputsandOutputswithGPIOs,guidesyouthroughbuildingyourveryfirsthardwareinterfacingcircuitandexplainsthedetailsofabasicAndroidappthatcancommunicatewithit.ThisisyourfirststeptowardbuildingmuchmorecomplexappsthatinteractwiththeworldoutsideyourBeagleBoneBlack.

Chapter4,StoringandRetrievingDatawithI2C,expandsonthebasicsfromChapter3,HandlingInputsandOutputswithGPIOs,andexplainshowasynchronousbackgroundthreadswithinyourappsareusedtocommunicatewithhardware.ItguidesyouthroughbuildingacircuitthatinterfacesanonvolatilememorychiptotheBeagleBoneBlackandtheimplementationdetailsofanappthatinteractswiththechip.

Chapter5,InterfacingwithHigh-speedSensorsUsingSPI,explorescreatingappsthatperformhigh-speedinterfacingusingatemperatureandpressuresensorinterfacedtotheBeagleBoneBlack.

Chapter6,CreatingaCompleteInterfacingSolution,combinesthelessonslearnedaboutGPIO,I2C,andSPIinterfacingfromthepreviouschapterstocreateasingle,complexhardwareandsoftwaresolutionthatusesallthreeinterfacestoreacttohardwareeventsthatoriginatefromtheoutsideworld.

Chapter7,WheretoGofromHere,describesafewmoreofthehardwareinterfacesavailableontheBeagleBoneBlack,explainshowtocreatemorepermanentAndroidhardware/softwaresolutions,andgivesyouafewideasforfutureprojectstoexplore.

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WhatyouneedforthisbookWehaveprovidedinstructionsinthisbookassumingthatyouareusingeitheraWindows-orLinux-basedcomputer.IfyouarealreadyanAndroidappdeveloper,youprobablyhaveallofthesoftwareapplicationsthatyouneedalreadyinstalled.WeexpectyoutohaveboththeEclipseADTandAndroidNDKalreadyinstalled,thoughweprovidelinkstodownloadthesetoolsatthestartofChapter2,InterfacingwithAndroid,intheeventthatyoudonotalreadyhavethem.Chapter1,IntroductiontoAndroidandtheBeagleBoneBlack,providesalistofthevarioushardwarecomponentsandequipmentthatyouwillneedtoimplementtheexampleinterfacingcircuitsusedthroughoutthebook.

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WhothisbookisforIfyouareanAndroidappdeveloperwhowantstobeginexperimentingwiththehardwarecapabilitiesoftheBeagleBoneBlackplatform,thenthisbookisidealforyou.Havingfamiliaritywithbasicelectronicsprinciplesishelpful,andthereaderisexpectedtohavebasicknowledgeindevelopingAndroidappswiththeEclipseADTandAndroidSDK,butnopriorhardwareexperienceisrequired.

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ConventionsInthisbook,youwillfindanumberoftextstylesthatdistinguishbetweendifferentkindsofinformation.Herearesomeexamplesofthesestylesandanexplanationoftheirmeaning.

Codewordsintext,databasetablenames,foldernames,filenames,fileextensions,pathnames,dummyURLs,userinput,andTwitterhandlesareshownasfollows:“Thisavoidshavingtoincludeaspecialmoduleandanoverlaythatloadscommandsinyourinit.{ro.hardware}.rcfile.”

Ablockofcodeissetasfollows:

externintopenFRAM(constunsignedintbus,constunsignedintaddress);

externintreadFRAM(constunsignedintoffset,constunsignedint

bufferSize,constchar*buffer);

externintwriteFRAM(constunsignedintoffset,constunsignedint

constchar*buffer);

externvoidcloseFRAM(void);

Whenwewishtodrawyourattentiontoaparticularpartofacodeblock,therelevantlinesoritemsaresetinbold:

publicvoidonClickSaveButton(Viewview){

hwTask=newHardwareTask();

hwTask.saveToFRAM(this);

publicvoidonClickLoadButton(Viewview){

hwTask.loadFromFRAM(this);

Anycommand-lineinputoroutputiswrittenasfollows:

root@beagleboneblack:/#i2cdetect-y-r2

Newtermsandimportantwordsareshowninbold.Wordsthatyouseeonthescreen,forexample,inmenusordialogboxes,appearinthetextlikethis:“IftheuserclicksontheSamplebuttononcemore,anotherHardwareTaskinstanceisinstantiated.”

NoteWarningsorimportantnotesappearinaboxlikethis.

TipTipsandtricksappearlikethis.

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ErrataAlthoughwehavetakeneverycaretoensuretheaccuracyofourcontent,mistakesdohappen.Ifyoufindamistakeinoneofourbooks—maybeamistakeinthetextorthecode—wewouldbegratefulifyoucouldreportthistous.Bydoingso,youcansaveotherreadersfromfrustrationandhelpusimprovesubsequentversionsofthisbook.Ifyoufindanyerrata,pleasereportthembyvisitinghttp://www.packtpub.com/submit-errata,selectingyourbook,clickingontheErrataSubmissionFormlink,andenteringthedetailsofyourerrata.Onceyourerrataareverified,yoursubmissionwillbeacceptedandtheerratawillbeuploadedtoourwebsiteoraddedtoanylistofexistingerrataundertheErratasectionofthattitle.

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Chapter1.IntroductiontoAndroidandtheBeagleBoneBlackInthisbook,you’lllearnhowtoinstallAndroidtoamicroSDcardforusewiththeBeagleBoneBlackandcreateAndroidappsthatinterfacewithexternalhardwarethatisconnectedtotheBeagleBoneBlack.Youwilldevelopsoftwarethatreceivesinputfromtheoutsideworldviabuttonsandsensors,storesandretrievesdatafromexternalmemorychips,andlightsexternalLEDs.Betteryet,you’lllearnhowtodothisinaflexiblewaythatcanbeeasilyintegratedintoyourapps.

AsyouexploretheworldofinterfacinghardwarewithAndroid,youwilldiscoverthatitencompassesmanydifferentareasofexpertise.UnderstandingelectroniccircuitsandknowinghowtointerfacethemwiththeBeagleBoneBlack,understandingtheLinuxkernel,anddevelopingAndroidappsareafewsuchareas.Luckily,youdon’thavetobeanexpertintheseareastolearnthebasicsofinterfacinghardwarewithAndroid.Wehavedoneourbesttoguideyouthroughtheexamplesinthisbookwithoutrequiringyoutohaveanin-depthknowledgeoftheLinuxkernelorelectronicstheory.

Inthischapter,wewillcoverthefollowingtopics:

LookingbackonAndroidandBeagleBoneBlackdevelopmentShoppingforthehardwareessentialsLearningaboutthehardwareyou’llinterfacewithInstallingAndroidontheBeagleBoneBlack

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LookingbackonAndroidandBeagleBoneBlackdevelopmentTheAndroidoperatingsystemhasbeentakingtheworldbystorm.Eversinceitsintroductiontotheworldinabetareleasein2007,ithasgrowntobecomethedominantmobilephoneOS.Asidefrommobilephones,ithasalsobeenusedfortablets(suchastheBarnes&NobleNookeReaderandtheTescoHudltablet)andavarietyofotherembeddedmultimediadevices.TheOShasaddednewfeaturesandevolvedovertheyears,butitstillhasthesameprimarydesignprinciplesasitdidwhenitwasfirstconceived.ItprovidesalightweightOSwithatouchscreeninterfacethatgivesquickandeasyaccesstomultimediaapplicationswhileusingminimalresources.

Asidefromitsgeneralpopularity,AndroidhasanumberofadvantagesthatmakeitanexcellentOSforyourprojects.ThesourcecodeofAndroidisopensourceandfreelyavailablefromhttp://source.android.com.Itisfreeforyoutouseinanyproductsthatyoucreate.AndroidusesthepopularLinuxkernel,soanyexpertisethatyoualreadyhavewithLinuxwillaidyouinyourAndroiddevelopment.Thereisawell-documentedinterfacingAPIthatmakesdevelopingforAndroidsimpleandstraightforward.

ThebroadavailabilityofAndroid-baseddeviceshasgeneratedalargeamountofinterestindevelopingsoftwareapplications,orapps,thattargetAndroid.IthasbecomeeasiertodevelopAndroidapps.EclipseAndroidDevelopmentTools(ADT)allowsappdeveloperstoprototypesoftwareandthenexecutethatsoftwarewithinanemulatedAndroiddeviceenvironment.However,theemulateddevicediffersfromrealhardwareinsubtle(andsometimesdramatic)waysintermsofspeedandappearance.Luckily,apowerfulandlow-costhardwareplatformisavailablethatallowsyoutoquicklyandeasilytestyourappsonrealhardware:theBeagleBoneBlack.

TheBeagleBoneBlack(BBB)hardwareplatform,producedbyCircuitCofortheBeagleBoard.orgnonprofitorganization,isanewcomertotheopensourcehardwarescene.Firstproducedin2013,thislow-cost,ARM-basedsingleboardcomputerisanimprovementovertheoriginalBeagleBoneplatform.TheBBBisanimprovementovertheoriginalBeagleBoneboardthatoffersincreasedprocessingpower,built-inHDMIvideo,andeithera2or4GB(dependingupontheBBB’srevision)on-boardeMMCmemory.Withafocusonsmallsizeandawidevarietyofexpansionandinterfacingopportunities,theBBBprovidesalotofprocessingpowerataverylowprice.ThefollowingimageshowsatypicalBBB:

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TheBeagleBoneBlack(Source:www.beagleboard.org)

AndroidrunsontheinexpensiveBBB,whichmakesitanexcellenthardwareplatformtousetoexploreAndroidanddevelopyourowncustomAndroidprojects,forexample,ifyouhadanideaforanAndroidkioskdevice,ahand-heldgamingconsole,orsomeothermultimediadevice.ThecombinationofAndroidandtheBBBwillallowyoutoprototypesuchdevicesquicklyandcheaply.

NowthatwehavetakenaquicklookattheBBBandAndroid,let’stakealookatthehardwarethatyouwillneedtomakethemostoutofbothofthem.

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ShoppingforthehardwareessentialsWhenyoupurchaseyourBBB,youwillonlyreceivetheboardandaUSBcabletopowerandcommunicatewithit.Beforeyoubeginanyserioussoftwaredevelopmentforhardware-interfacingprojectswiththeBBB,thereareafewadditionalpiecesofhardwarethatyouwillneed.Inouropinion,thebestplacetopurchasetheseitemsisAdaFruit(www.adafruit.com).Almosteverythinghereisavailablefromthissinglesource,andtheircustomerserviceisverygood.Infact,manyoftheitemslistedhereareavailableasaBeagleBoneBlackstarterkitfromAdaFruit(productID703).Thestarterkitdoesnotcontaina3.3VFutureTechnologyDevicesInternational(FTDI)cable,butitdoesincludetheBeagleBoneBlackitself.

ContentsoftheBeagleBoneBlackstarterkitfromAdaFruit(source:www.adafruit.com)

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TheFTDIcableA3.3voltFTDIcable(productID70)allowsyoutoviewalloftheserialdebugoutputoftheBBB.Ifyouareperforminganyseriousdevelopment,youmusthaveoneofthesecables.ThecableisnecessaryifyouwishtoobservethebootprocessoftheBBB(bothbootloaderandkerneloutputasthesystemisinitialized),anditalsoprovidesaconsoleshellintoLinuxandAndroid.Thisshellhelpsyoutotroubleshootbootproblems,asyouwillalwayshaveamethodofinteractingwiththesystemwhenanetworkconnectionisunavailable,orwhennocommunicationservicesareupandrunning.

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PowersupplyWhiletheBBBcanbepoweredviatheUSBcable,thismethodsuppliesbarelyenoughpowertoruntheBBB.Ifyouareusingexternalcapes,orareotherwiseattachingexternalcircuitsthatdrawpowerfromthe5voltpinsoftheBBB,youmustuseanexternalpowersupply.BeagleBoard.orgspecifiesthatthepowersupplymustbea2amp,5voltDCpowersupplywitha2.1mmbarrelconnectorthatiscenterpositive.AdaFruitsellsapowersupplythatconformstotheBBB’srequirements(productID276).

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BreadboardandthemountingplateExperimentingwithelectronicsbecomesmuchsimplerifyouareabletoeasilyandquicklyconstructcircuitswithouttheworryofsoldering.Becauseofthis,werecommendthatyouinvestinabreadboardandsomebreadboardingjumperwires(productID153).Yourbreadboarddoesn’thavetobeanythingbigorfancy,butyoushoulduseatleastastandardhalf-sizebreadboard(productID64)fortheprojectsgiveninthisbook.

AdaFruitProtoPlate(productID702)isanadditionalitemthatwerecommendthatyoupurchase.ProtoPlateisaplasticplatethatboththeBBBandahalf-sizebreadboardmountonto.ThishelpsyouavoidaccidentallystretchingordisconnectingthewiresthatconnectelectroniccircuitstotheBBB.UsingProtoPlatemakesrelocatingyourBBBandbreadboardsimpleandpainless.

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MicroSDcardsIfyoudomuchworkwiththeBBB,you’llalwayswanttohaveafewextramicroSDcardsaround!Androidwillfitontoan8GBmicroSDcardwithplentyoffreespaceavailabletoholdyourownapps.YoucanwriteanAndroidimagetoalargermicroSDcard,butmostpremadeAndroidsystemimageswillonlyconsumethefirst4–8GBofspaceonthecard.AsmostlaptopsanddesktopPCsdon’tdirectlyacceptmicroSDcards,youshouldownatleastonemicroSD-to-SDcardadapter.Luckily,oneoftheseadaptersistypicallypackagedwitheachmicroSDcardthatyoubuy.

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Learningaboutthehardwareyou’llinterfacewithThebestwaytolearnaboutinterfacingAndroidsoftwarewithhardwareistolearnwhilehavingrealhardwarecomponentsconnectedtoyourBBB.Thisway,yoursoftwarewilltalktoactualhardwareandyoucandirectlyobservehowyourappsrespondtophysicalinteractionwithyoursystem.Wehaveselectedavarietyofelectroniccomponentsthatwillbeusedthroughoutthebooktodemonstratevariousaspectsofhardwareinterfacing.Youarewelcometouseasmanyorasfewofthesecomponentsasyourinterestsandbudgetpermit.Itcanbeexpensivetopurchaseallofthesecomponentsatonce,butmakesuretobuyallofthecomponentsnecessaryforeachchapterifyouareinterestedinimplementingtheexamplesinthatchapter.

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General-purposecomponentsInChapter3,HandlingInputsandOutputswithGPIOs,andChapter6,CreatingaCompleteInterfacingSolution,youwilluseavarietyofelectroniccomponentssuchaspushbuttons,LEDs,andresistorstointerfacewiththeBBB.Manyoftheseitemscanbepurchasedfromanyelectronicssupplier,suchasDigiKey(www.digikey.com),MouserElectronics(www.mouser.com),andSparkFun(www.sparkfun.com).BothDigikeyandMouseroffersomanyvariantsofeachavailablecomponentthatitcanbedifficultforaninexperiencedhardwarehackertopicktherightcomponentstobuy.Becauseofthis,wewillrecommendafewproductsfromSparkFunthatwillgiveyousuitablecomponentsneededtocompletetheexercisesinthisbook.Youarewelcometoselectyourcomponentsfromanothersupplierifusingadifferentoneismoreconvenientforyou.

Ourexamplesrequireonlythreecomponents:aresistor,apushbuttonswitch,andanLED.Wesuggestpurchasinga1Kohm,1/6(or1/4)wattresistor(part#COM-08980),a12mmpushbuttonswitch(part#COM-09190),andanysmallLED(3–10mminsize)thatcanbetriggeredbyaround3voltorless(part#COM-12903isagoodassortmentof5mmLEDs).

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TheAdaFruitmemorybreakoutboardInChapter4,StoringandRetrievingDatawithI2C,andChapter6,CreatingaCompleteInterfacingSolution,youwillinterfacewitha32KBFerroelectricRandomAccessMemory(FRAM),whichisanonvolatilememoryIC,tostoreandretrievedata.WehaveselectedAdaFruitBreakoutBoard(productID1895)thatcontainsthisIC.ThebreakoutboardalreadycontainsallofthenecessarycomponentstointerfacetheICtotheBBB,soyouneednotworryaboutmanyofthelow-leveldetailsinvolvedincreatingaclean,noise-freeconnectionbetweeneachICandtheBBB.

TheFRAMBreakoutBoardwithitsheaderstrip(source:www.adafruit.com)

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TheAdaFruitsensorbreakoutboardInChapter5,InterfacingwithHigh-speedSensorsUsingSPI,andChapter6,CreatingaCompleteInterfacingSolution,youwillinterfacewithasensorICtoreceiveenvironmentaldata.WehaveselectedanAdaFruitbreakoutboard(productID1900)thatcontainstheseICs.ThesebreakoutboardsalreadycontainallofthenecessarycomponentstointerfacetheICstotheBBB,soyouneednotworryaboutmanyofthelow-leveldetailsinvolvedincreatingaclean,noise-freeconnectionbetweeneachICandtheBBB.

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PreparingthebreakoutboardsEachbreakoutboardcomeswithaheaderstrip.Thisheaderstripmustbesolderedintoeachbreakoutboardsothattheycanbeeasilyconnectedtothebreadboard.Thisistheonlysolderingthatisrequiredtocompletetheexercisesinthisbook.Ifyouareunfamiliarwithsoldering,therearenumeroustutorialsonlinethatexplaintechniquesforeffectivesoldering.Ifyoufeeluncomfortablesolderingtheheaderstrips,askafriend,instructor,orcolleaguetoassistyouwiththeprocess.

NoteAfewonlinesolderingtutorialsthatwesuggestthatyoucheckoutare:

https://www.youtube.com/watch?v=BLfXXRfRIzYhttps://learn.sparkfun.com/tutorials/how-to-solder–through-hole-soldering

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InstallingAndroidontheBeagleBoneBlackTheAndroidOSisacomplexpieceofsoftwarethatisconstructedoutofmanycomponentsbuiltfromaverylargecodebase.Itcanbeadifficultandtime-consumingtasktobuildAndroidfromsource,soyouwillbeusingapremadeAndroidimagefromtheBBBAndroidproject(www.bbbandroid.org)throughoutthisbook.

BBBAndroidisaportofAndroidOpenSourceProject(AOSP)KitKatAndroidtotheBBB.ThereareafewdifferentdistributionsofAndroidavailablefortheBBB,butweselectedBBBAndroidbecauseitusesthe3.8Linuxkernel.ThiskernelincludestheCapeManager(capemgr)functionalityaswellasafewothertoolsthatwillassistyouininterfacinghardwaretoAndroidapps.OtherflavorsofAndroidontheBBBusethe3.2Linuxkernel,whichismucholderandlackscapemgrsupport.Chapter2,InterfacingwithAndroid,discussesthecapemgrfunctionalityinmoredetail.The3.8kernelisagoodbalancebetweenenablingthenewerfeaturesfortheBBBwhileavoidinganypotentiallyunstable,cutting-edgefeatures.

TheBBBcanbootitsOSinafewdifferentways:

OnboardeMMC:TheOSresideswithintheonboardeMMCstorage.TheAngstromorDebianOSthatcomesinstalledonyourBBBbootsfromtheeMMCoutofthebox.MicroSDcard:TheOSresidesonamicroSDcardthatisinsertedintotheBBB.IfabootloaderisinstalledonthemicroSDcard,thebootloaderinstalledontheonboardeMMCnoticesthepresenceofthemicroSDandwillbootfromthatinstead.Inaddition,bootingfromthemicroSDcardisforcedwhentheuserbootbuttonishelddownduringBBBpowerup.Overthenetwork:ThebootloaderiscapableofdownloadingakerneloverthenetworkviaTFTP.TheOScanactuallybedownloadedatboottimethoughthisisusuallyonlydoneduringcommercialproductdevelopment.Thisisanadvancedfeaturethatisoutsidethescopeofthisbook.

TheBBBAndroidimageisdesignedtobewrittentoandbootedfromamicroSDcard.AstheimagecreatesafullybootablesystemonthemicroSDcard,youwillnothavetoholdtheBBB’suserbootbuttonduringpowerontobootintoAndroid.SimplyinsertthemicroSDcardintotheBBBandyou’llbootintoAndroidautomatically.

UsingamicroSDcard-basedOSisadvantageousforusbecauseyoucaneasilymountthecardonaLinuxPCtomodifytheAndroidfilesystemasyouseefit.IftheOSisinstalledintheeMMC,itcanbehardtoaccesstheOStochangearbitraryfilesinthefilesystem.ThesystemmustberunningtoaccesstheeMMCcontents,somakingachangethatcorruptsthesystemormakesitunbootablemakesaccessingtheeMMCtofixtheproblemdifficult.

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DownloadingapremadeAndroidimageThemainpageoftheBBBAndroidwebsiteprovidesadownloadlinkforthemostrecentpremadeimage.Likeanyopensourceproject,detailsabouttheversionnumberandsizeofeachimagearelikelytochangeovertimeasbugsarefoundandchangesaremade.However,thelatestandgreatestwillbeavailableviathewebsite.

BBBAndroid’simagesarecompressedusingthexzcompressorutilitytosavetimewhendownloading,sotheimagemustbedecompressedpriortowritingittoamicroSDcard.ThetoolsusedtodecompressandwritetheimagewillvarydependingupontheOSthatyouareusing.WhilethecompressedimagemightonlybeafewhundredMBinsize,theuncompressedimagewillbe8GB.

NotePriortobeginningthedecompressionoftheimage,makesurethatyouhaveenoughharddrivespacetoholdtheuncompressedimage.

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CreatingyourAndroidmicroSDcardusingWindowsUnderWindows-basedOSes,thecompressedimagecanbeuncompressedusingtoolssuchas7-ZiporWinRARandthenwrittentothemicroSDcardusingthetoolWin32DiskImager.Allofthesetoolsarefreelyavailablefordownload.ToprepareanAndroidmicroSDcard,followthesesteps:

1. Forthisexample,you’llusetheWinRARapplication.DownloadWinRARfromwww.rarlab.comandinstallit.WinRARwillintegratewiththeWindowsExplorershelloftheWindowsdesktop.

2. DownloadandinstalltheWin32DiskImagerapplication.Itisavailablefromtheproject’sSourceForgepageathttp://sourceforge.net/projects/win32diskimager.

3. Right-clickontheBBBAndroidimagethatyoudownloadedandselecttheExtracthereoptionontheExplorershellcontextmenu.Anuncompressedversionoftheimage(8GBinsize)willbewrittentothesamelocationasthecompressedimage.Thedecompressionprocessmighttakeseveralminutes.

Decompressthexz-compressedimagewithWinRAR

4. Insertan8+GBmicroSDcardintothesystem.ThecardwillbedetectedbyWindowsashavingavalidfilesystemonitifitcamepreformatted(mostcardsaresoldpreformattedforyourconvenience).Irrespectiveofwhetherthecardisformattedornot,adriveletterisassignedtoitbyWindows.

5. BrowsetoThisPCandexaminethedevicesshownunderDevicesanddrives.Thecardshouldbeshown.Makeanoteofthedriveletterassignedtothecard.

ThemicroSDcardwillbeshownwithadriveletterunderWindows(driveEintheimage)

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6. LaunchWin32DiskImager.Enterthefilenameandpathtotheuncompressedimageinthetextfield,orclickonthefoldericontonavigatetothefile’slocation.ChangetheDevicedrop-downboxtothedriveletterofthemicroSDcardthatyouidentifiedinstep4.

Win32DiskImagerwiththeimagefilespecified(notethatthedrivelettermatchesthatofthemicroSDcard)

7. Writingtheimagewilltakeseveralminutes.Oncethewritehascompleted,removethemicroSDcardfromyourcomputerandinsertitintoyourBBB.

8. PowerontheBBBandAndroidwillbegintoboot.Onthefirstboot,itwilltakeseveralminutesforthetop-levelUIscreentoappear.Onsubsequentboots,itwilltakeonly30to60secondstoreachthetop-levelUIscreen.

Congratulations!YourBBBisnowrunningtheAndroidOS.

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CreatingyourAndroidmicroSDcardusingLinuxUnderLinux,thecompressedAndroidimagecanbeuncompressedusingthexzcommandandwrittentothemicroSDcardusingtheddcommand.ToprepareanAndroidmicroSDcard,followthesesteps:

1. Makesurethatyouhavexzinstalled.Forsystemsusingapt-get,tryinstallingthexz-utilspackage:

$sudoapt-getinstallxz-utils

2. Decompresstheimageusingxz.Substitutethenameofyourimagefile(withthe.xzfileextension),asshowninthefollowingcommand:

$xz--decompress[IMAGEFILENAME]

3. Onceuncompressed,theimagewillloseits.xzfileextensionandhaveasizeof8GB.InsertyourmicroSDcardintothecomputer.Adeviceinthe/devdirectorywillbeassignedtoyourcard.Todeterminewhichdeviceitis,usefdisk:

$sudofdisk–l

4. Thefdiskutilitywilldisplayallstoragedevicescurrentlyconnectedtoyourcomputer.OneofthedeviceswillreportasbeingthesamesizeasthemicroSDcard.Forexample,ifyouinsertan8GBmicroSDcard,youwillseesomethingsimilartothis:

Disk/dev/sdb:8018MB,8018460672bytes

Theexactstoragecapacityofthecardvariesslightlybetweenmanufacturers,butthesizeisapproximately8GB.Thedeviceassignedtothiscardis/dev/sdb.Otherdeviceslistedbyfdiskwillbesecondarystoragedevices(suchasyourharddrive).Beforeproceedinganyfurther,makecertainthatyouhaveidentifiedtheproperdevicefilethatbelongstoyourmicroSDcard.Ifyouselectthewrongdevice,youwilldestroythefilesystemonthatdevice!

5. WritetheimagetothemicroSDcardusingdd.Assumingthatthedeviceyouidentifiedinstep5is/dev/sdb,usethefollowingcommandtoperformthewrite:

$sudoddif=[NAMEOFIMAGE]of=/dev/sdbbs=4M

6. Writingtheimagewilltakeseveralminutes.Oncethewritehascompleted,removethemicroSDcardfromyourcomputerandinsertitintoyourBBB.

PowerontheBBBandAndroidwillbegintoboot.Onthefirstboot,itwilltakeseveralminutesforthetop-levelUIscreentoappear.Onsubsequentboots,itwilltakeonly30to60secondstoreachthetop-levelUIscreen.

Congratulations!YourBBBisnowrunningtheAndroidOS.

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SummaryInthischapter,youlearnedaboutthehardwarethatyou’llneedtodevelopsoftwarefortheBeagleBoneBlack,theelectronicscomponentsanddevicesthatyouwillneedfortheexercisesinthisbook,andhowtoinstallanAndroiddistributionontoamicroSDcardforuseontheBBB.Inthenextchapter,youwilllearnhowAndroidinteractswithhardwareatthesoftwarelevelandhowtheBBBcanbeconfiguredtointerfacewiththehardwarecomponentsthatyouwillbeusinginthisbook.

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Chapter2.InterfacingwithAndroidInthelastchapter,youinstalledAndroidonyourBBB.Youalsogatheredallofthehardwareandcomponentsthatyouwillneedtotryouttheexercisesinthisbook.NowthatyouhaveaworkingAndroidsystemandthehardwareneededtoexploreit,itistimetodiveintoAndroidandfindouthowtoprepareittointerfacewithcustomhardware.

MostpeoplewouldnotconsiderAndroidandLinuxtobeverysimilar,butthetwohavemoreincommonthanyoumightrealize.UnderneaththepolishedUIsandawidevarietyofapps,AndroidissecretlyLinux.Android’sfilesystemlayoutandservicesarequitedifferentfromthoseofatypicalLinuxsystem,sotherearecertainlymanydifferencesbetweenthetwointermsofuserspace(whereappsandotherprocessesexecute).Intermsofkernelspace(wheredevicedriversexecuteandresourcesareallocatedtoeachrunningprocess),theyarealmostidenticalinfunctionality.UnderstandinghowtheBBBinteractswithLinuxkerneldriversisthekeytocreatingAndroidappsthatcandothesame.

Inthischapter,wewilltellyouaboutAndroid’shardwareabstractionlayer,orHAL.WewillalsointroduceyoutoPacktHAL,aspeciallibrarythatyoucanincludewithinyourappstointerfacewithhardwareontheBBB.WeassumethatyoualreadyhaveEclipseAndroidDeveloperTools(ADT)withtheAndroidSDK,theAndroidNativeDevelopmentKit(NDK),andtheAndroidDebugBridge(ADB)toolsinstalledandworkingonyoursystem.

UnderstandingtheAndroidHALInstallingPacktHALSettinguptheAndroidNDKforPacktHALMultiplexingtheBBBpins

TipAreyoumissingafewtools?

IfyoudonotyethavetheEclipseADTorAndroidNDKtoolsinstalledonyoursystem,youcanfindinstallationinstructionsanddownloadlinksattheselocations:

EclipseADT:http://developer.android.com/sdkAndroidNDK:http://developer.android.com/tools/sdk/ndk

HowtoinstallADBisdiscussedlaterinthischapter.ThischapterassumesthatyouhaveinstalledtheEclipseADTtothec:\adt-bundledirectoryifyouareusingWindows(wemakenoassumptionsforLinux)andthatyouhaveinstalledtheAndroidNDKtothec:\android-ndkdirectory(Windows)orandroid-ndkinyourhomedirectory(Linux).Ifyouhaveinstalledthesetoolstoadifferentlocation,youwillhavetomakeafewsimpleadjustmentstoafewinstructionslaterinthischapter.

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UnderstandingtheAndroidHALAnAndroidkernelcontainsafewadditionalfeaturesthataren’tfoundinatypicalLinuxkernel,suchasBinderIPCandthelow-memorykiller,butotherwiseitisstillLinux.ThisprovidesyouwithoneverybigadvantagewheninterfacinghardwarewithAndroid,thatis,ifaLinuxdriveralreadyexistsinthekernelusedforanAndroidsystem,thenyoualreadyhaveanAndroiddriverforthatdevice.

AndroidappsmustinteractwiththehardwareofanAndroiddevicebygeneratingvideoandaudiodata,receivingbuttonandtouchscreeninputevents,andreceivingsensoreventsfromcameras,accelerometers,andotherdevicesthatgatherinformationfromtheoutsideworld.LeveragingexistingLinuxdriversforthesedevicesmakesAndroidsupportmucheasier.UnlikeatraditionalLinuxdistribution,whichgrantsapplicationspermissiontodirectlyaccessmanydifferentdevicefiles(bydirectlyopeningfilesinthe/devfilesystem),Androiddramaticallylimitstheabilityofprocessestodirectlyaccesshardware.

ConsiderthenumberofdifferentAndroidappsthatusetheaudiofunctionalityofthedevicetoplaysoundsorrecordaudiodata.UnderneathAndroid,theLinuxkernelprovidesthisaudiofunctionalityviaanAdvancedLinuxSoundArchitecture(ALSA)audiodriver.Inmostcases,onlyoneprocessatatimecanopenandcontroltheALSAdriverresource.Ifindividualappswereinchargeoftaking,using,andreleasingtheALSAdriver,itwouldbecomeahugemesstocoordinateaudioresourceusageamongallofthevariousapps.Onemisbehavingappcaneasilytakecontrolofaudioresourcesandblockallotherappsfromusingthem!Buthowcantheallocationandcontroloftheseresourcesbehandled?Tosolvethisproblem,Androidusesmanagers.

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AndroidmanagersManagersarethecomponentsofthesystemthatcontrolhardwaredevicesonbehalfofallapps.Everyapprequiressomesetofresources(suchasaudio,GPS,andnetworkaccess)toperformitsjob.Managersareinchargeofallocatingandinterfacingwitheachoftheseresourcesanddeterminingwhetheranapphaspermissiontousethatresource.

Havingmanagersdealwiththeselow-leveldetailsmakeslifemucheasier.Androidcanbeinstalledonawidevarietyofhardwareplatformsthatvarywildlyintermsofphysicalsizeandinput/outputcapabilities,andappdeveloperscan’tbeexpectedtohaveintimateknowledgeofeachandeveryplatformthattheirappcanbeinstalledon.

Tousearesource,anappmustcreateareferencetothepropermanagerviathegetSystemService()methodoftheandroid.content.Contextclass:

//Createareferencetothesystem"location"manager

LocationManagerlocationManager=(LocationManager)

mContext.getSystemService(LOCATION_SERVICE);

Then,makeinformationandcontrolrequestsviathismanagerreference:

//QuerythelocationmanagertodetermineifGPSisenabled

isGPSEnabled=locationManager.

isProviderEnabled(LocationManager.GPS_PROVIDER);

AppsinteractwithmanagersthroughtheJavaAndroidAPI.WhilemanagersrespondtotheseJavamethods,theymusteventuallyusetheJavanativeinterface(JNI)tocallthenativecodethatdirectlyinteractswiththehardware.Thisiswherethetruecontrolofthehardwaretakesplace.ThebridgebetweentheAndroidAPIandcallstothenativecodethatcontrolthehardwareisknownasthehardwareabstractionlayer(HAL).

ThevariouspiecesoftheHALaretypicallywritteninC/C++,andeachdevice’svendorisresponsibleforimplementingthem.IfsomepiecesoftheHALaremissing,servicesandappswon’tbeabletofullyutilizeallaspectsofthehardwareplatform.VariousAndroidservicesusetheHALtocommunicatewiththehardware,andappsuseIPCtocommunicatewiththeseservicesandgainaccesstothehardware.Theservicesinteractwiththehardwareonanapp’sbehalf(assumingthattheapphastheproperAndroidpermissionstoaccessthatparticularhardwareresource).

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TheHALdevelopmentworkflowTypically,creatingacompleteHALfollowsthesesteps:

1. IdentifyordevelopaLinuxkerneldevicedrivertocontrolthehardware.2. CreateakernelDeviceTreeoverlaythatinstantiatesandconfiguresthedriver.3. Developauserspacelibrarytointerfacewiththekerneldevicedriver.4. DevelopJNIbindingstotheuserspacelibrary.5. DevelopanAndroidmanagerusingtheJNIbindingstointerfacewiththehardware.

Sometimes,itisn’tacleardecisionastowhereaparticularpieceofcustomhardwareshouldbeproperlyintegratedintotheHALandwhichmanagershouldbeinchargeofaccessingthehardware.WhatAndroidpermissionscontrolaccesstothehardware?WilltheAPIhavetobeextendedtooffernewtypesofpermissions?Willacustomservicehavetobecreated?

ImplementingeveryaspectofaproperHALforapieceofcustomhardwareisabitofanoverkillforhobbyists,students,andotherdevelopersinterestedinsimpleexperimentationwithhardwareinterfacing.WhileacommercialAndroidsystemmustaddressallofthesestepstodevelopaproperHAL,wetakeafarmoredirectapproachtohardwareaccessinthisbook.

AsourfocusisonshowinghowyoucaninterfaceAndroidappswithhardware,weskipsteps1through4byprovidingyouwithPacktHAL,anativelibrarythatimplementsaverysimpleHAL.PacktHALwilleaseyouintothedauntingtaskofinterfacingwithhardwareontheBBB,anditprovidesasetoffunctionsthatarecapableofinterfacingwiththehardwareusedintheexamplesthroughoutthisbook.Strictlyspeaking,yourappswillactasthemanagerinchargeofeachhardwareresource.

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WorkingwithPacktHALAppscommunicatewiththenativecallsofPacktHALusingJNI.PacktHALdemonstrateshowtoperformuserspaceinterfacingwithhardwareviathreedifferentinterfacingmethods:GPIO,SPI,andI2C.UsingPacktHAL,youhavedirectaccesstohardwaredevices.Chapters3throughChapter6provideexamplesofhowthisinterfacingworksandhowyoucanuseitwithinyourownAndroidappcode.EachchapterwillexaminethevariouspiecesofPacktHALusedintheappexamplesofthatchapter.

TipHowdoesPacktHALactuallytalktohardware?

Generally,anymethodthatallowsyoutointerfacewithhardwareunderLinuxcanalsobeusedbytheHALforinterfacing.Reading,writing,andmakingioctl()callstofilesinthe/devfilesystemwillwork,asdoesusingmmap()toprovideaccesstomemory-mappedcontrolregisters.PacktHALusesallofthesetechniquestointerfacewiththehardwarethatyouconnecttoyourBBB.

UsingPacktHALisnowherenearassecureasaproperHALimplementationbecausewemustchangethepermissionsonthehardware’suserspaceinterfacessuchthatanyappcanaccessthehardwaredirectly.Thiscanpotentiallymakeyoursystemvulnerabletomaliciousapps,sosuchanapproachshouldneverbeusedinaproductiondevice.Usersthatroot(gainsuperuseraccessto)commercialAndroidphonesandtabletsoftendosotolessenthestrictpermissionsonthesedevicesbydefault.Thisallowsthemtoinstallandenablecustomfeatures,anditprovidesmoreflexibilityandcustomizationfortheirdevices.

AsyouareusingtheBBBasanAndroid-prototypingdevice,suchanapproachistheeasiestwayforyoutointeractwiththehardware.Thisisasteppingstonetowardsdevelopingyourowncustommanagersandservicesthatspeaktoyourhardwareonbehalfofapps.Ideally,onacommercialdevice,onlyanAndroidmanagerwillhavethenecessarypermissionstodirectlyinterfacewiththehardware.

TipOnceyoubecomecomfortablewithusingPacktHALinyourapps,youcanthenexaminePacktHAL’ssourcecodetobetterunderstandhownativecodeinterfaceswiththeLinuxkernel.Eventually,youmightfindyourselfintegratingPacktHALintoyourowncustommanagers.Youmightevenfindyourselfdevelopingcustomcodefortheactualkernel!

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InstallingPacktHALAllofthevariouspiecesofPacktHALarelocatedinthePacktHAL.tgzfile,whichisavailablefordownloadfromPackt’swebsite(http://www.packtpub.com/support).ThisisacompressedtarfilethatcontainsallofthesourcecodeandconfigurationfilesrequiredtomodifyBBBAndroidtousePacktHALandincludePacktHALsupportinyourapps.

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PreparingPacktHALunderLinuxOnceyouhavedownloadedthePacktHAL.tgzfile,youmustdecompressanduntarit.WewillassumethatyouhavecopiedPacktHAL.tgztoyourhomedirectoryafterdownloadingitandwilldecompressitfromthere.Wewillrefertoyourhomedirectoryas$HOME.

UsetheLinuxtarcommandtodecompressanduntarthefile:

$cd$HOME

$tar–xvfPacktHAL.tgz

AdirectorynamedPacktHALnowexistsinyour$HOMEdirectory.AllofthePacktHALfilesarelocatedinthisdirectory.

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PreparingPacktHALunderWindowsOnceyouhavedownloadedthePacktHAL.tgzfile,decompressanduntarit.WewillassumethatyouhavecopiedPacktHAL.tgztotherootdirectoryoftheC:driveafterdownloadingitandwilluseWinRARtodecompressitfromthere.

TipWhereshouldIunpackPacktHAL.tgz?

YoucandecompressanduntarPacktHAL.tgzonthedesktoporwhereverelseyouwish,butyouwillbeperformingsomecommand-linecommandstocopyfilesaroundlater.ItismuchsimplertoperformtheseoperationsifPacktHAL.tgzisdecompressedanduntarredintherootdirectoryoftheC:drive,sowewillassumethatyouareperformingtheseoperationsfromthere.

PerformthefollowingstepstoextractthePacktHAL.tgzfile:

1. OpenafileexplorerwindowandnavigatetotherootoftheC:drive.2. Right-clickonthePacktHAL.tgzfileinfileexplorerandselectExtractHere.

AdirectorynamedC:\PacktHALnowexists.AllofthePacktHALfilesarelocatedinthisdirectory.

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ThePacktHALdirectorystructureThePacktHALdirectoryhasthefollowingstructure:

PacktHAL/

+----cape/

|+----BB-PACKTPUB-00A0.dts

|+----build_cape.sh

+----jni/

|+----(Various.cand.hfiles)

|+----(Various.mkfiles)

+----prebuilt/

|+----BB-PACTPUB-00A0.dtbo

|+----init.genericam33xx(flatteneddevicetr.rc

|+----spi

|+----spidev.h

+----README.txt

ThecapesubdirectorycontainsthesourcecodeandbuildscriptforbuildingaDeviceTreeoverlaythatenablesallofthehardwarefeaturesthatPacktHALneeds.YouwilllearnmoreaboutDeviceTreeoverlayslaterinthischapter.ThejnisubdirectorycontainsthesourcecodefilesthatimplementPacktHAL.ThesesourcefileswillbeaddedtoyourprojectsinlaterchapterstobuildPacktHALsupportintoyourapps.TheprebuiltdirectorycontainsafewpremadefilesthatmustbeaddedtoyourBBBAndroidimageandAndroidNDKtobuildandusePacktHAL.Youwillinstallthefilesintheprebuiltdirectorytotheirrequiredlocationsinthenextfewsections.

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PreparingAndroidforPacktHALBeforeusingPacktHALwithanyapps,youhavetoprepareyourBBBAndroidinstallation.Bydefault,Androidisveryrestrictiveonthepermissionsthatitassignstohardwaredevices.TousePacktHAL,youmustlessenthepermissionrestrictionsandconfigureAndroidforthehardwarethatyouwillinterfacewith.TheseactionsrequirecopyingsomeprebuiltfilesintoyourAndroidsystemtomakeafewconfigurationchangesthatrelaxvariousAndroidpermissionsandconfigurethehardwareproperlyforPacktHAL’suse.

YouwillusetheADBtooltopush(push)thenecessaryfilesovertoyourrunningBBBsystem.Priortopushingthefiles,bootAndroidontheBBBandconnecttheBBBtoyourPCusingtheUSBcablethatcamewithyourBBB.Onceyouhavereachedthispoint,continuewiththeinstructions.

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PushingPacktHALfilesunderLinuxThefollowingstepsareusedinordertopublishPacktHALfilesunderLinux:

1. Beforeyougetstarted,makesurethatADBcanseeyourBBBbyusingtheadbdevicescommand.TheBBBwillreportashavingaserialnumberofBBBAndroid.Executethefollowingcommand:

$adbdevices

Listofdevicesattached

BBBAndroiddevice

2. Ifyouaremissingtheadbcommand,installtheandroid-tools-adbpackageviaapt-get:

$sudoapt-getinstallandroid-tools-adb

TipWhycan’tLinuxfindmyBBB?

IfadbisinstalledonyoursystemandyouareunabletoseetheBBB,youmightneedtoaddaudevruletoyoursystemandperformsomeadditionaltroubleshooting.Googleprovidesdirectionsforaddingthisruleandsometroubleshootingstepsifyourunintoanydifficulty,andthiscanbefoundathttp://developer.android.com/tools/device.html.

BBBAndroidreportstheUSBdeviceIDofitsADBinterfaceas18D1:4E23,whichisthedeviceIDofaGoogleNexusS,sotheUSBvendorIDfortheBBBis18D1(thedeviceIDforGoogledevices).

3. OnceyouhaveverifiedthatadbcanseetheBBB,changeintothePacktHALdirectory,shellintoAndroidviaadb,andremounttheread-onlyrootfsfilesystemasread-write:

$cd$HOME/PacktHAL/prebuilt

$adbshell

root@beagleboneblack:/#mountrootfsrootfs/rw

root@beagleboneblack:/#exit

4. Now,pushthenecessaryfilesintoAndroid’srootfsfilesystem:

$adbpushBB-PACKTPUB-00A0.dtbo/system/vendor/firmware

$adbpushinit.genericam33xx\(flatteneddevicetr.rc/

$adbchmod750/init.genericam33xx\(flatteneddevicetr.rc

5. Finally,shellintoAndroid’srootfsfilesystemtosyncitandremountitasread-only:

$adbshell

root@beagleboneblack:/#sync

root@beagleboneblack:/#mountrootfsrootfs/roremount

6. YouhavenowpreparedyourBBBAndroidimageforPacktHALunderLinux.

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RemovethepowersupplycableandUSBcablefromyourBBBtoshutitdown.7. Then,poweruptheBBBtoverifythatAndroidbootsproperlywiththemodifications

thatyouhavejustmade.

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PushingPacktHALfilesunderWindowsYoumustlocatewhereyouradb.exefileislocated.ItispartoftheplatformtoolsintheAndroidSDK.Inthefollowinginstructions,weareassumingthatyouinstalledtheEclipseADTinthec:\adt-bundledirectory,makingthefullpathtoadbtobec:\adt-bundle\sdk\platform-tools\adb.exe.

ThefollowingstepsareusedinordertopublishPacktHALfilesunderWindows:

1. Beforeyougetstarted,makesurethatadbcanseeyourBBBbyusingtheadbdevicescommand.TheBBBwillreportashavingaserialnumberofBBBAndroid:

$adbdevices

BBBAndroiddevice

TipWhycan’tWindowsfindmyBBB?

ItcanbenotoriouslydifficulttogetadbtoseeAndroiddevicesunderWindows.ThisisbecauseeachhardwaremanufacturerthatcreatesanAndroiddeviceprovidesitsownWindowsADBdevicedriverthatWindowsusestotalktothatdevice.BBBAndroidreportstheUSBdeviceIDofitsADBinterfaceas18D1:4E23,whichisthedeviceIDofaGoogleNexusS.Thisdeviceisoneofthe(many)USBdevicesthataresupportedbyKoushikDutta’sexcellentUniversalADBdriverforWindows.Ifadbcan’tfindyourBBB,installtheUniversalADBdriverandthentryagain.Youcandownloadthedriverfromhttp://www.koushikdutta.com/post/universal-adb-driver.

2. Onceyouhaveverifiedthis,adbcanseetheBBB,shellintoAndroidviaadb,andremounttheread-onlyrootfsfilesystemasread-write:

$adbshell

root@beagleboneblack:/#mountrootfsrootfs/rw

3. Now,pushthenecessaryfilesintoAndroid’srootfsfilesystem:

$adbpushc:\PacktHAL\prebuilt\BB-PACKTPUB-00A0.dtbo

/system/vendor/firmware

$adbpushc:\PacktHAL\prebuilt\init.genericam33xx(flatteneddevicetr.rc

$adbchmod750/init.genericam33xx\flatteneddevicetr.rc

4. Finally,shellintoAndroid’srootfsfilesystemtosyncitandremountitasread-only:

$adbshell

root@beagleboneblack:/#sync

root@beagleboneblack:/#mountrootfsrootfs/roremount

5. YouhavenowpreparedyourBBBAndroidimageforPacktHALunderWindows.

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RemovethepowersupplycableandUSBcablefromyourBBBtoshutitdown.Then,poweruptheBBBtoverifythatAndroidbootsproperlywiththemodificationsthatyouhavejustmade.

TipWhyisitthattheinit.genericam33xx(flatteneddevicetr.rcfileisnamedsooddly?

Androiddeviceshaveasetofread-onlypropertiesthatdescribethehardwareandsoftwareofthesystemtoappsandmanagers.Oneofthesepropertiesisro.hardware,whichdescribesthehardwarethatthekernelisconfiguredfor.Device-specific.rcfilesinAndroidhavetheinit.{ro.hardware}.*rcform.

IntheLinuxkernelsource,thearch/arm/mach-omap2/board-generic.cfileusesaDT_MACHINE_START()macrotospecifythenameoftheBBBplatformasGenericAM33XX(FlattenedDeviceTree).Thistextstringisconvertedtolowercase,spacesareremoved,andthestringistruncatedtoproducethefinalstringthatisstoredinthero.hardwareproperty.

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SettinguptheAndroidNDKforPacktHALUnfortunately,theAndroidNativeDevelopmentKit(NDK)ismissingakernelheaderfilethatisneededtobuildPacktHAL.ThemissingheaderdescribestheinterfacebetweenuserspaceappsandthegenericSPIdriver(spidev,whichyouwilluseinChapter5,InterfacingwithHigh-speedSensorsUsingSPI).ItisnotthefaultoftheNDKthatthisheaderfileismissing,asusuallyappswillneverneeddirectaccesstothespidevdriver.

Asyouareusinganapptotalkdirectlytalktothehardware,youwillneedtocopythismissingheaderintoyourNDKinstallation.

TipForyourconvenience,wehaveincludedacopyofthisheaderfileinthePacktHALsourcetarball.YouonlyneedtocopythefileintoyourNDKinstallationpriortobuildingPacktHAL.

BBBAndroidis4.4.4KitKat,andAPIlevel19isthehighestlevelsupportedbythisversion.YouwillbebuildingalloftheexamplesinthisbookforAPIlevel19.EachAPIlevelhasadifferentsetofheadersintheNDK,soyoumustaddthemissingheaderstotheinclude/linuxdirectoryforAPIlevel19.IfyoudecidetobuildappsatlowerAPIlevels,youcanrepeatthefollowingstepstoaddtheadditionalheaderfiletoanyoftheotherAPIlevelsthatyouwishto.

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AddingtheheadertotheNDKunderLinuxIfyouaregoingtobebuildingappsusingEclipseADTunderLinux,youwillneedtohavetheAndroidNDKinstalledonyourLinuxsystem.Fortheseinstructions,wewillassumethatyouhavealreadyinstalledtheNDKtotheandroid-ndkfolderinyour$HOMEdirectory.Asyouhavealreadydownloaded,decompressed,anduntarredthePacktHAL.tgzfiletoyour$HOMEdirectoryearlierinthischapter,wewillassumethatthePacktHALdirectorythatyoucreatedisstillthere:

$cd$HOME/android-ndk/platforms/android-19/arch-arm/usr/include/linux

$cp-rf$HOME/PacktHAL/prebuilt/spi

ThiswillcopythecontentsofthespiheaderfiledirectoryintoyourNDKheaderfiles.YourLinuxNDKinstallationnowhastheextraheaderfilethatitneedstobuildPacktHAL.

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AddingtheheadertotheNDKunderWindowsIfyouaregoingtobebuildingappsusingEclipseADTunderWindows,youwillneedtohavetheAndroidNDKinstalledonyourWindowssystem.Fortheseinstructions,wewillassumethatyouhaveinstalledtheNDKtothec:\android-ndkfolder.Asyouhavealreadydownloaded,decompressed,anduntarredthePacktHAL.tgzfiletoyourc:\directoryearlierinthischapter,wewillassumethatthePacktHALdirectorythatyoucreatedisstillthere:

1. Openafileexplorerwindowandnavigatetothec:\android-ndk\platforms\android-19\arch-arm\usr\include\linuxpath.

2. Openasecondfileexplorerwindowandnavigatetothec:\PacktHAL\prebuiltpath.Right-clickonthespidirectoryandselectCopyfromthecontextmenu.

3. ChangetotheAndroidNDKwindow,right-clickanywherewithinthewhitespaceofthefilelistinthewindow,andselectPastefromthecontextmenu.

ThiswillcopythecontentsofthespiheaderfiledirectoryintoyourNDKheaderfiles.YourWindowsNDKinstallationnowhastheextraheaderfilethatitneedstobuildPacktHAL.

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MultiplexingtheBBBpinsAsaccessinghardwareresourcesfollowsthesameprocessunderAndroidasitdoesunderLinux,itisimportanttounderstandhowtheLinuxkernelconfiguresdevicedriversandallocatesthemtoparticularpiecesofhardware.ItisalsonecessarytounderstandhowthesekerneldriversprovideuserspaceinterfacesthatPacktHALcaninteractwith.

TheBBB’sAM3359processoroffersawidevarietyofsignalsonitshundredsofpins.Thesesignalsincludemanydifferent,specializedinterfacebusesandsensorinputs.Therearefartoomanypotentialsignalsforthenumberofpinsavailabletosupplythesesignalstotheoutsideworld.Toselectwhichsignalsareavailableonthepins,thepinsaremultiplexed,ormuxed,tospecificsignals.

Severaloftheprocessor’spinsarewiredtotheconnectionsoftheBBB’sP8andP9headers.ThemuxingoftheseparticularpinsisofgreatinteresttoBBBusers,asthemuxingdetermineswhichprocessorsignalsandfeaturesareeasilyaccessibletotheuserforhardwareinterfacing.Thereare46pinsoneachoftheBBB’stwoheaders,givingyouatotalof92pinstointerfacewith.Unfortunately,61ofthesepinsareinusebydefault,meaningthatonly31pinscanbechangedaroundforyourprojectswithoutyouhavingtodisableoneormorestandardfeaturesoftheBBBtomakemorepinsavailable.

TheP8andP9expansionheadersoftheBeagleBoneBlack

Somepinsontheheadersarepermanentlyassigned,suchasthepinsthatprovideaccesstovoltage(1.8,3.3,and5VDCareavailable)andgroundsignals.Theotherpinsthough,canbemuxedtomeettheneedsofyourproject.PropermuxingalloftheP8/P9pinsto

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providealloftheresourcesthatyourequirecansometimesbetricky,particularlyifyouareonlybeginningtolearnaboutthehardwareinterfacingaspectsoftheBBB.Luckily,wehavealreadydeterminedapinmuxconfigurationforyouthatwillprovidePacktHALwithallofthehardwareresourcesthatitneedstorunalloftheexercisesinthisbook.

DefaultpinsinuseontheBeagleBoneBlack

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ThekernelDeviceTreeandcapemgrThepinsoftheBBBmustbemuxedinaspecificwaytospeakwithcustomhardware,butwhereandhowisthisactuallydone?Theansweris“thekernel’sDeviceTree.”TheDeviceTreeisahierarchicaldatastructureinsidethekernelthatdescribeswhathardwareispresent,whichresourcesareusedbythathardware,andwhichkerneldriversshouldbeusedtotalktoeachhardwaredevice.Itdescribesdifferentfacetsofthehardware,suchaspinmuxingsettings,clockspeeds,andparametersthatarepassedtokerneldevicedrivers.

Itwouldbeanannoyinghassleiftheuserwasrequiredtoinstallanewkerneleverytimethehardwarechanged.ForahardwareplatformliketheBBB,theusercanchangethehardwareconnectedtotheBBBbetweenpowercycles!ItwouldbeveryusefultobeabletodynamicallychangetheDeviceTreetoaddorremovehardwareonthefly.TheBBB’sLinux3.8kernelhasaspecialsubsystem,calledthecapemanager(capemgr)thatallowsyoutodojustthat.

ThecapemgrdynamicallyaddsandremovespiecesoroverlaysoftheDeviceTree.Itprovidesthreeimportantservices:

ItrecognizesanycapehardwarethatisconnectedtotheBBBItloadstheappropriateDeviceTreeoverlaytoenableandconfigureeachrecognizedcapeItallowsarbitraryDeviceTreeoverlaystobeloadeddynamicallyfromuserspacetoconfigureanyhardwarethatisnotautomaticallydiscovered

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DefiningacapeAcapeisanyhardwareadd-onthatconnectstotheBBB’sP8/P9connectors(similartohowshieldboardsconnecttoanArduino)andcontainsanelectricallyerasableprogrammableread-onlymemory(EEPROM)chipthatreportsthecape’sidentitytothekernel’scapebus.ThecapemgrinthekernelcanthendynamicallyenabletheappropriateDeviceTreeoverlayforthatparticularcape.Thisiswhatallowsyoutoconnectavarietyofdifferent,commerciallyavailablecapeboardstotheBBB,andtheyalljustautomaticallyworkwithoutyouhavingtochangeasingleconfigurationfile.

AmuchlooserdefinitionofacapeisanyexternalcircuitrythatinterfacesviatheP8/P9connectors.WithoutincludinganEEPROMthattellsthecapemgr“IamacapeandmynameisXYZ”,thecapemgrwon’tautomaticallylocateandloadtheproperDeviceTreeoverlayforthecape.Thisisthecaseforalloftheexamplesinthisbook.YoucanstillconsiderthehardwarethatyouconnecttotheBBBtobeacapethatAndroidisinterfacingwith,buttheDeviceTreeoverlaymustbeloadedmanuallyfromuserspace.

Earlierinthischapter,youusedadbtopushafilenamedBB-PACKTPUB-00A0.dtbotoyourAndroidimage.ThisfileistheDeviceTreeoverlaythatconfigurestheBBBforthehardwarethatyouwilluseintheexercisesthroughoutthisbook.Thecustominit.genericam33xx(flatteneddevicetr.rcfilethatyoualsopushedovertotheAndroidimagemanuallyloadsthisoverlayforyouduringAndroid’sbootprocess.

IntheLinuxfilesystem,customoverlaysareplacedintothe/lib/firmwaredirectory.UnderAndroid,however,thereisno/libdirectoryinrootfs,sooverlaysareinsteadplacedintothe/system/vendor/firmwaredirectory.Thisisalsothelocationwherefirmware(.fwfiles)builtduringkernelcompilationisinstalled.WhenusingyourownDeviceTreeoverlaysforyourfutureprojects,remembertoplacethemintothe/system/vendor/firmwaredirectorysothatthecapemgrcanfindthem.

TipWherecanIlearnmoreaboutmultiplexingtheBBB’spins,theDeviceTree,andcreatingcustomoverlays?

LearninghowtoselectthebestpinmuxingforcustomprojectsandcreatingtheappropriateDeviceTreeoverlaysareoutsidethescopeofthisbook,buttherearemanyexcellentresourcesavailablethatcanintroduceyoutotheprocess.Hereareafewgreatresourceswerecommendthatyoureadtolearnmore:

TheBeagleBoneBlackSystemreferencemanual:http://www.adafruit.com/datasheets/BBB_SRM.pdfDerekMolloy’swebsite:http://derekmolloy.ie/category/embedded-systems/beaglebone/AdaFruit’sDeviceTreeOverlaytutorial:https://learn.adafruit.com/introduction-to-the-beaglebone-black-device-tree

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SummaryInthischapter,weexplainedhowAndroidusesaHALtoallowAndroidmanagerstoprovidehardwareaccesstoapps.WeintroducedyoutoPacktHALthatcanbeusedtointerfacewithalloftheexamplesthroughoutthisbook.YouconfiguredyourBBBAndroidimagetousePacktHAL,andyoumodifiedyourNDKinstallationtobuildPacktHALintoyourapps.

WealsoshowedwhichpinsoftheBBB’sP8/P9headerscanbemultiplexed,whattheDeviceTreeisandhowitisusedtomultiplexpins,andhowthecapemgrloadsDeviceTreeoverlaystodynamicallymuxtheBBB’spins.

Inthenextchapter,you’llputPacktHALtoworkandbuildyourfirsthardware-interfacingappusingGPIOs.

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Chapter3.HandlingInputsandOutputswithGPIOsInthelastchapter,youpreparedyourdevelopmentPCandBBBAndroidsystemforthedevelopmentofhardware-interfacingAndroidapps.Nowthatyourdevelopmentenvironmentissetupandreadytogo,youwillbeginexploringyourveryfirstappthatiscapableofdirectcommunicationwithhardwareconnectedtotheBBB.

General-PurposeInput/Output(GPIO)isoneofthemostbasicinterfacesindigitalelectronics.Intheexampleswithinthischapter,youwillbeworkingwithGPIOstoreceivedigitalinputsignalsfromtheoutsideworldandsenddigitaloutputsignalsbackinresponse.Whilethisisasmallstart,itisthefirststepindevelopingandunderstandinghardware-interfacingappsthataremuchmorecomplex.GPIOscanbeusedtoimplementcomplexandpowerfulinterfacinglogic.WewilldiscussboththehardwareandsoftwaresidesofGPIOinterfacingandexplainhowcallingJavamethodsinAndroidappscaninterfacewithlow-levelhardware-interfacingcode.

UnderstandingGPIOsBuildingaGPIOinterfacecircuitIncludingPacktHALwithinyourappsExploringtheGPIOexampleapp

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UnderstandingGPIOsAtitsmostbasiclevel,communicationbetweentwopiecesofhardwarerequiresthetransmissionofdatabackandforthbetweenthem.Incomputersystems,thisdataisrepresentedasvoltagelevelssentoverawirethatconnectsthedevicestogether.Thepatternsandlevelsofvoltagebackandforthformacommunicationprotocolthatthedevicesusetotransmitdatabetweeneachother.

GPIOisthemostbasicinterfacingoptionofferedbymicrocontrollersandmicroprocessors.SomepinsoftheBBB’sprocessorareallocatedasGPIOsthatactasaninput(monitoringvoltageonthewiretoreceivedata)oranoutput(placingaparticularvoltageonthewiretosenddata).TheBBBhasdozensofavailableGPIOpins,whichmakesGPIOaflexibleandsimplewayforAndroidappstointeractwiththeoutsideworldwithoutrequiringfancydevicedriversorextrainterfacinghardware.

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NutsandboltsofGPIODigitallogicoperatesontheconceptthattherearetwodiscretevoltagelevelsthatrepresentanon/highstateandanoff/lowstate.Bytogglingbetweenthesetwostates,binarybitsofdataaretransmittedbetweendevices.TheBBBusesthevoltageof3.3Vforitshighlevelandavoltageof0V(connectedtoaground)forthelowlevel.Thisvoltageschemeisknownasa3.3Vlogiclevel,anditiscommonlyusedforsingle-boardcomputerssuchastheBeagleBoardandRaspberryPi.Manymicrocontrollers(manyArduinos,forexample)usea5Vlogiclevelinstead.

TipNeverapplymorethan3.3VtoanyBBBpin!

Applyinggreaterthan3.3VtoaBBBGPIOcanfrytheBBB’sprocessor,soalwaysmakesurethatyouonlyworkwithamaximumof3.3VwhendesigningtheGPIOinterfacecircuitryfortheBBB.PinsP9.3/4supply3.3V,andpinsP9.5/6supply5V.Itisverysimpletoaccidentallyconnectabreadboardwiretothepinssupplying5Vwhenyouintendedtousethe3.3Vpins.Tohelpavoidthismistake,trycoveringtheP9.5/6pinswithapieceoftape.Thispreventsyoufromaccidentallyinsertingabreadboardwireintothesepins.

TheBBB’sprocessorhasfourbanksofGPIOs,with32individualGPIOsineachbank.Withonly92pinsavailableontheP8/9connectors,itisnotpossibletogiveeveryGPIOaccesstotheoutsideworld.Infact,theBBB’sSystemReferenceManualshowsthatitisonlypossibletomuxabout65uniqueGPIOstoP8/P9atthesametime,evenifeveryotherfeaturebeingmuxedtoP8/9wasdisabled.ThereareafewotherGPIOsthatareusedinternallyfortaskssuchaslightingandblinkingtheBBB’sLEDs,butyoushouldconsideryourselfrestrictedtoonlyusingtheGPIOsthatareaccessibleviaP8/P9andthatdonotconflictwithanyofthestandardBBBfeatures.

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GPIOaccessmethodsunderAndroidTherearetwobasicapproachestointeractingwithGPIOsontheBBB:fileI/Oandmemory-mapping.WiththefileI/O,youpassGPIOrequeststhroughakerneldriverbyreadingandwritingtoGPIOfilesinthefilesystem.Withmemory-mapping,youmaptheGPIOcontrolresistorsintomemoryandthenreadandwritethesemappedmemorylocationstodirectlymanipulatethecontrolresistors.AsbothofthesemethodsaremadepossiblebytheLinuxkernel,theywillbothworkjustaswellunderAndroidastheydounderLinux.

ProsandconsofthefileI/OmethodThefileI/Omethodcanbeperformedbyanyprocessthathastheproperpermissionstoread/writetheGPIOdevicefiles.However,likeanyfileI/Ooperation,thiscanbequiteslow.

Prosandconsofthememory-mappingmethodThememory-mappingmethodallowsyoutodirectlyaccesstheresistorsthatcontroltheGPIOs.Memory-mappingisveryfast(about1000timesfasterthanfileI/O!),butonlyprocesseswithrootpermissionscanuseit.

Asyourappsareunabletoexecutewithrootpermissionswithoutsomeseriouspermissionchanges,youwillbeunabletousememory-mappingtoaccessGPIOs.ThiseffectivelyrestrictsyoutoonlyusingfileI/Oforyourapps.

NotePacktHALimplementsbothmemory-mappingandfileI/OforGPIOaccess.Ifyouareinterestedinthelow-leveldetailsofhowbothoftheseapproacheswork,examinethejni/gpio.cfileinPacktHAL.tgz.

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PreparingAndroidforGPIOuseInChapter2,InterfacingwithAndroid,youusedadbtopushtwoprebuiltfilesfromPacktHALtoyourAndroidsystem.Thesetwofiles,BB-PACKTPUB-00A0.dtboandinit.{ro.hardware}.rc,configureyourAndroidsystemtoenablespecificGPIOsandallowyourappstoaccessthem.

NoteRememberthatwhenwetalkabouttheinit.{ro.hardware}.rcfile,wearereferringtotheinit.genericam33xx(flatteneddevice.trfileintherootdirectoryoftheAndroidfilesystem.

TheBB-PACKTPUB-00A0.dtbofileisaDeviceTreeoverlaythatmuxestheBBBtosupportalloftheexamplesinthisbook.AsfarasGPIOsareconcerned,thisoverlaymuxestheP9.11andP9.13pinsintoGPIOs.InthePacktHAL.tgzfile,thesourcecodefortheoverlayislocatedinthecape/BB-PACKTPUB-00A0.dtsfile.ThecoderesponsibleformuxingthetwoGPIOsislocatedinthebb_gpio_pinsnodewithinfragment@0:

/*AllGPIOpinsarePULLUP,MODE7*/

bb_gpio_pins:pinmux_bb_gpio_pins{

pinctrl-single,pins=<

0x0700x17/*P9.11,gpio0_30,OUTPUT*/

0x0740x37/*P9.13,gpio0_31,INPUT*/

Thedetailsofthehexvaluesusedinthebb_gpio_pinsnodearebeyondthescopeofthisbook.However,thegeneralideaisthattheyspecifywhichpinisofinterest,whichmodethepinshouldbemuxedto,afewdetailsaboutpull-up/pull-downresistors,whetheritisaninputoranoutputpin,andwhetheranyskewingadjustmentsshouldbemadetothesignal.

NoteThedetailsofwhatskewisandhowtoadjustforitarebeyondthescopeofthisbook.Ifyouwouldliketolearnmoreaboutskewing,wesuggesttheWikipediapageonthesubjectasagoodstartingpoint(http://en.wikipedia.org/wiki/Clock_skew).

Atboot,thisoverlayisloadedbytheinit.{ro.hardware}.rcfile.ThekernelthenknowswhichpinsaretreatedasGPIOs.Afterloadingtheoverlay,theinit.{ro.hardware}.rcfilethenexecutesafewcommandsthatexplicitly“unlock”theseGPIOfilesforusebyappsbyexportingthem.ExportingaGPIOpincreatesaseriesoffilesinthe/sysfilesystemthatcanbereadandwrittentointeractwiththatGPIOpin.

ByexportingaGPIOpinandthenchangingthepermissionsoftheproperfilesinthe/sysfilesystemviachmod,anyprocesscanreadfromorwritetoGPIOs.Thisisexactlywhatthecommandsintheinit.{ro.hardware}.rcfiledotoallowAndroidappstointerfacewithGPIOs.Thefollowingportionoftheinit.{ro.hardware}.rcfileperformsthe

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exportandchmodoperations:

#ExportGPIOs30and31(P9.11andP9.13)

write/sys/class/gpio/export30

write/sys/class/gpio/export31

#MakeGPIO30anoutput

write/sys/class/gpio/gpio30/directionout

#MakeGPIOs30and31writeablefromtheFS

chmod777/sys/class/gpio/gpio30/value

chmod777/sys/class/gpio/gpio31/value

EachGPIOhasaspecificintegeridentifierthatisdeterminedbythebanktheGPIObelongstoanditspositionwithinthatbank.Inourcase,theGPIOmuxedtoP9.11isthe30thGPIOinbank0,andP9.13isthe31stGPIOinbank0.Thismakestheirintegeridentifiers30and31,respectively.

NoteTheGPIOpins30and31areonlyavailableviathe/sysfilesystembecausetheywereexplicitlyexportedviathewritecommandsintheinit.{ro.hardware}.rcfile.OtherGPIOpinswillnotbeavailableviathefilesystemunlesstheyarealsoexplicitlyexportedinthesamefashion.

ThisisaveryinsecurewayofallowingGPIOaccessbecauseitopensuptheGPIOsforusebyprocessesthatwemightnotwanttohavedirectaccesstothem.Forexperimentationandprototyping,thisisnotaproblem.However,youcertainlyshouldnotdothisinacommercialsystem.Unlessyoudevelopaproper,privilegedAndroidmanagertohandletheGPIOresources,youmustallowallprocessestoaccesstheGPIOfilesunlessyoutailorthepermissionstoonlybeusablebyappsbelongingtoaspecificuserorgroup.Aseachappisassigneditsownuser,youwouldhavetochowntheGPIOstotheproperuserandgroupafteryouinstalltheapp’s.apkfileontothesystem.

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BuildingaGPIO-interfacingcircuitBeforeyoubegindevelopingsoftwarethatcommunicatesusingGPIOs,youmustfirstconstructahardwarecircuitfortheGPIOstointerfacewith.Forthischapter,youwillbuildasimplecircuitthatconsistsofa1kohmresistor,anLED,andapushbuttonswitch.PartnumbersandsuppliersforthesecomponentswerelistedinChapter1,IntroductiontoAndroidandtheBeagleBoneBlack.Beforegettingstarted,besurethatyouhavealloftheproperpartsandremoveallpowersourcesfromyourBBB(unplugthepowersupplyandUSBcables)priortoconnectinganythingtotheBBB’sP8/P9connector.

TipDon’tdisassembleyourcircuit!

TheGPIOcircuitinthischapterispartofamuchlargercircuitusedinChapter6,CreatingaCompleteInterfacingSolution.Ifyoubuildthecircuitasitispositionedinthefollowingdiagram(towardsthetopofthebreadboard),youcansimplyleavetheGPIOcomponentsandwiresinplaceasyoubuildtheremainingcircuitsinthisbook.Thisway,itwillalreadybeconstructedandworkingwhenyoureachChapter6.

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ConstructingthecircuitThecircuitthatyouwillbuildinterfaceswiththefollowingfourBBB’spins:

P9.1(ground)P9.3(3.3V)P9.11(GPIO)P9.13(GPIO)

TheP9.11pinisconfiguredasanoutputGPIO,anditdrivestheLED.TheP9.13pinisconfiguredasaninputGPIO,anditsetsitsstatedependingupontheinputvoltagethatisappliedtoit.BothGPIOpinsareconfiguredbytheBB-PACKTPUB-00A0.dtbooverlaytouseaninternalpull-upresistor.Ifyouarenotfamiliarwithwhatapull-upresistoris,don’tworry.Forthepurposesoftheseexamples,itsimplymeansthatthelogicleveloftheGPIOswillnot“float”betweenonandoffifnothingisattachedtotheGPIOpins.Instead,thelogiclevelwillbe“pulled-up”totheonstate.

NoteInterestedinlearningmoreaboutwhatapull-upresistorisandhowitworks?Wesuggestthatyoucheckoutthisonlinetutorialonpull-upandpull-downresistors,availableathttp://www.resistorguide.com/pull-up-resistor_pull-down-resistor.

Breadboardstypicallyhavetwoverticalbusesoneithersidethatrunalmosttheentirelengthofthebreadboard.Thesebusesareusedtoprovideconvenientaccesstopowerandgroundsignalsforanycomponentsinsertedintothebreadboard.

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ThecompleteGPIO-interfacingcircuit

Nowwecanstartconstructingourcircuit:

1. ConnecttheBBB’sground(P9.1)and3.3V(P9.3)signalstothetwoverticalbusesonthebreadboard.Thegroundbusistheverticalbustowardsthecenterofthebreadboard.The3.3Vbusistheverticalbustowardstheedgeofthebreadboard.

2. Next,connecttheanode,orthepositivelead,oftheLEDtoP9.11.LEDshaveapolarity,socurrentwillonlyflowthroughtheminonedirection.Currentflowsfromthelongerlead(theanode)oftheLEDtotheshorterlead(thecathode).

3. IftheLED’sleadshavebeencuttothesamelengthandyouareunabletotellwhichleadiswhich,feelaroundtheedgeoftheLED’splasticcasing.Theedgeofthecasingisflatonthecathodesideandroundedontheanodeside.AslongasthecathodeisconnectedtothegroundandtheanodeisconnectedtotheGPIOpin,theLEDwillworkproperly.

4. YoumustlimitthecurrentdrawnbytheLEDtoensurethatyoudonotdamagetheGPIOpin,soplacea1KohmresistorbetweentheLED’scathodeleadandthegroundsignal.ResistorsdonothaveapolaritylikeLEDsdo,sothedirectionthatyouconnectittothebreadboardwillnotmatter.

NoteIfyouwishtolearnmoreaboutusingacurrent-limitingresistorwithanLED,suchasselectingtherightresistorforthetask,wesuggestthatyoureadthetutorialfrom

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SparkFun,availableathttps://www.sparkfun.com/tutorials/219.

5. NowthattheLEDandresistorhavebeenconnectedtotheBBB,youmustconnectthepushbuttonswitch.Differentswitcheshavedifferentnumbersofleads,buttheswitchthatwesuggestedforyourusehasatotaloffourleads.Theseleadsformtwopairsoftwoleadseach.Thetwoleadsineachpairarealwayselectricallyconnectedtoeachother,butonepairwillonlybeelectricallyconnectedtotheotherpairwhenthebuttonisbeingpressed.Twosidesoftheswitcharesmooth,andtheothertwosideshavetwoprotrudingleadsoneachside.Thetwoprotrudingleadsonasinglesideoftheswitchbelongtodifferentpairsofleads.PickonesideoftheswitchwithtwoleadsonitandconnectoneleadtoP9.13andtheotherleadtothebreadboard’sgroundbus.

Yourcircuitisnowcomplete.Double-checkyourwiringagainstthediagramofthecompleteGPIO-interfacingcircuittoensurethateverythingisconnectedproperly.

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CheckingyourwiringOnceyouhavecompletedthewiringoftheGPIOcircuit,youshouldtestittoensurethatitworksproperly.Luckily,youcandothiseasilybyshellingintotheBBBandworkingwiththeexportedGPIOpinfiles.WewillassumethatyouareusingadbtoshellintotheAndroidsystem,butusingtheFTDItoaccesstheconsoleshellwillworkinexactlythesameway.

TipHowdoIusetheFTDIcable?

IfyouhaveneverusedanFTDIcabletocommunicatewithyourBBB,thereisapageonthewww.elinux.orgwiki(maintainedbytheBeagleBoard.orgstaff)thatcanhelpyougetstarted,whichishttp://elinux.org/Beagleboard:Terminal_Shells.

Inthisbook,wewillonlybeusingtheUSBcableandADBshelltoaccesstheBBB.However,learninghowtousetheFTDItomonitorandtroubleshootyourBBBcanreallycomeinhandy.

ConnectpowertoyourBBBandthenusetheUSBcabletoconnecttheBBBtoyourdevelopmentsystem.AftershellingintotheBBB,begintestingyourGPIOcircuitusingthefollowingsteps:

1. ChangeintothedirectoryfortheGPIOpinmuxedtoP9.11(GPIOpin30):

root@beagleboneblack:/#cd/sys/class/gpio/gpio30

2. UsetheechocommandtoturntheLEDonbyforcingthestateofthisGPIOto1:

root@beagleboneblack:/#echo1>value

3. TheLEDwillnowbeturnedon.UsetheechocommandtoturntheLEDoffbyforcingthestateofthisGPIOto0:

root@beagleboneblack:/#echo0>value

4. TheLEDwillnowbeturnedoff.ChangeintothedirectoryfortheGPIOpinmuxedtoP9.13(theGPIOpin31):

root@beagleboneblack:/#cd/sys/class/gpio/gpio31

5. Usethecatcommandtocheckthecurrentstateofthepushbuttonswitch.Whenexecutingthiscommand,makesurethatyouarenotpushingthebutton:

root@beagleboneBlack:/#catvalue

6. Now,executethefollowingcatcommandwhileholdingdownthebutton.Youshouldtypetheentirecommand,pressthebutton,andthenhittheEnterkeytoenterthecommandwhilestillholdingthebuttondown:

root@beagleboneblack:/#catvalue

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NoteThepushbuttonvalueslookreversedbecauseofhowthecircuitiswired.Thepull-upresistoronP9.13willpullthevalueoftheGPIOto1whenthebuttonisnotpressed.Whenthebuttonispressed,theP9.13pinbecomesconnectedtothegroundsignalandchangestheGPIOto0.

IfyousawtheLEDturnonandoffandthecorrectvalueswerereturnedwhentheswitchwaspressedandreleased,youhavecorrectlywiredthecircuit.IftheLEDdidnotlightup,makesurethatyouhavenotaccidentallyswappedtheanodeandcathodeleadsoftheLED.Iftheswitchalwaysreturnsavalueof0,makesurethatyouhaveconnectedthecorrectpairofleadsontheswitchtothegroundsignalbusandP9.13.

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IncludingPacktHALwithinyourappsBeforedivingintousingPacktHALtointerfacewithGPIOs,youmustunderstandhowtoincludePacktHALsupportinyourapps.WewillwalkyouthroughtheprocessofaddingthePacktHALcodeintoyourappandthenbuildingit.PacktHALwillbepackagedwithyourappinthe.apkappasasharedlibrary.Thesourcecodeforthelibraryexistswithintheapp’sprojectdirectory,butitisbuiltseparatelyfromtheJavacodeoftheapp.YoumustmanuallybuildthePacktHALsharedlibrarybeforeyourappcanincludeitwithinthe.apkappanduseit.

NoteWeincludeaprebuiltversionofthePacktHALlibraryineachoftheexampleappprojectsincludedwiththisbook,soyoucanjumpintobuildingandrunningtheexampleappsrightawaywithoutworryingaboutthedetailsofbuildingPacktHAL.OnceyoubegincreatingyourowncustomappsandmodifyingPacktHALforyourownhardwareprojects,youwillneedtounderstandhowtobuildPacktHALfromsource.

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UnderstandingtheJavaNativeInterfaceAndroidappsarewritteninJava,butthefunctionsinPacktHALarewritteninCnativecode.Nativecodeisthecodethatiscompiledintoanativebinary,suchasasharedlibraryorexecutable,andthenexecuteddirectlybytheAndroidOS.NativecodeisbuiltusingthecompilertoolchainsuppliedwithintheAndroidNDK.Nativebinariesarenotasportableasthe“buildonce,runanywhere”bytecodeofAndroidapps,buttheycanbeusedforlow-levelinterfacinginwaysthatJavacodecannot.UnlikeJavabytecode,whichisexecutableonanyplatformthathasapropervirtualmachine,nativecodeiscompiledforonespecifichardwarearchitecture(suchasARM,x86,orPowerPC)andcanbeexecutedonlyonthatarchitecture.

Functionsimplementedinnativecodearecalledfromanapp’sJavacodeviatheJavaNativeInterface(JNI).JNIisapopularinterfacingmechanismthatJavaapplicationsusetointeractwithnativeC/C++code.Amongotherfeatures,JNIisusedtotranslateJavadatatypesintoCdatatypesandviceversa.

Forexample,considertheJavaStringtype.WhileJavahasaStringimplementation,thereisnoequivalenttypeinC.ThestringmustbesuitablyconvertedtoacompatibletypebeforeitcanbeusedbytheCcode.EachJavatypeisrepresentedinCbyaseriesofequivalenttypes,suchasjint,jstring,andjboolean,whicharedefinedinthestandardjni.hheaderfilethatissuppliedbytheAndroidNDK.

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CreatinganewappprojectthatusesPacktHALThefollowingstepsdemonstratehowyoucancreateanewcustomappthatincludesPacktHAL:

1. LaunchtheEclipseADTandselectthemenuoptionFile,thenNew,thenAndroidApplicationProject.

2. IntheNewAndroidApplicationdialog,entermyappintotheApplicationNamefield.ThiswillautomaticallypopulatetheProjectNameandApplicationNamefields.ChangetheMinimumRequiredSDK,TargetSDK,andCompileWithfieldstoAPI19:Android4.4.Thethemefieldcanbeleftaloneorchangedtowhicheverthemeyouwouldlikeforyourapp.Whenfinished,clickontheNextbutton.

TheNewAndroidApplicationscreen

3. Proceedthroughthesuccessivedialogscreens,retainingthedefaultsettingsforeachscreen,untilyouclickontheFinishbuttononthefinalscreen.

ThenameofthedefaultactivitycreatedforyournewappisMainActivity.Aftercreatingthenewproject,thefolderstructureofyournewmyappprojectwillresideinthemyapp($PROJECT)directoryandhaveadirectorystructuresimilartothefollowing:

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+----.settings/

+----assets/

+----bin/

+----gen/

+----libs/

+----res/

+----src/

+----...

Aftercreatingtheappforthefirsttime,severalnewfolderswillbecreatedtoholdthevariousintermediaryfilescreatedduringthebuildprocess.Onceyouhavecreatedyourapp,youmustaddthePacktHALcodetoitandcompileit.

BuildingPacktHALunderWindowsPacktHALmustbebuiltintoalibraryandincludedwithinyourapp’sprojectcodebasetobeusedbyyourapp.AssumingthatyoudecompressedanduntarredthePacktHAL.tgzfileinc:\,youcancopythePacktHALcodeintoyourapp’sprojectdirectory($PROJECT)usingthefollowingprocess:

1. Openafileexplorerwindowandbrowsetothe$PROJECTdirectory.2. Openasecondfileexplorerwindowandbrowsetoc:\PacktHAL.3. Right-clickonthejnidirectoryinthec:\PacktHALdirectoryandselectCopyfrom

thecontextmenu.4. Right-clickanywhereconvenientonwhitespacewithinthe$PROJECTdirectory

windowandthenselectPastefromthecontextmenu.

Nowthatthejni\directoryexistsinyour$PROJECTdirectory,youcanbuildPacktHALusingtheAndroidNDK.AssumingthatyouinstalledtheAndroidNDKinc:\android-ndk,youcanbuildPacktHALusingthefollowingprocess:

1. Launchcmd.exeforacommandpromptwindow.Usingthecommandprompt,changeintothe$PROJECTdirectory:

c:\>cd$PROJECT\jni

2. BuildthePacktHALlibraryusingtheAndroidNDK:

c:\$PROJECT\jni>c:\android-ndk\ndk-build

[armeabi]Compilethumb:packtHAL<=jni_wrapper.c

[armeabi]Compilethumb:packtHAL<=gpio.c

[armeabi]Compilethumb:packtHAL<=fram.c

[armeabi]Compilethumb:packtHAL<=bmp183.c

[armeabi]SharedLibrary:libpacktHAL.so

[armeabi]Install:libpacktHAL.so=>

libs/armeabi/libpacktHAL.so

ThePacktHALlibraryisnowbuiltandpresentinyourprojectasthefile$PROJECT\libs\armeabi\libpacktHAL.so.

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BuildingPacktHALunderLinuxPacktHALmustbebuiltintoalibraryandincludedwithinyourapp’sprojectcodebasetobeusedbyyourapp.AssumingthatyoudecompressedanduntarredthePacktHAL.tgzfileinyour$HOMEdirectory,youcancopythePacktHALcodeintoyourapp’sprojectdirectory($PROJECT)usingthefollowingcommands:

$cd$PROJECT

$cp–rf$HOME/PacktHAL/jni.

Nowthatthejnidirectoryexistsinyour$PROJECTdirectory,youcanbuildPacktHALusingtheAndroidNDK.AssumingthatyouinstalledtheAndroidNDKin$HOME/android-ndk,youcanbuildPacktHALusingthefollowingprocess:

1. Changeintothe$PROJECT/jnidirectory:

$cd$PROJECT/jni

2. BuildthePacktHALlibraryusingtheAndroidNDK:

$./$HOME/android-ndk/ndk-build

[armeabi]Compilethumb:packtHAL<=jni_wrapper.c

[armeabi]Compilethumb:packtHAL<=gpio.c

[armeabi]Compilethumb:packtHAL<=fram.c

[armeabi]Compilethumb:packtHAL<=bmp183.c

[armeabi]SharedLibrary:libpacktHAL.so

[armeabi]Install:libpacktHAL.so=>

libs/armeabi/libpacktHAL.so

ThePacktHALlibraryisnowbuiltandpresentinyourprojectasthe$PROJECT/libs/armeabi/libpacktHAL.sofile.

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ExploringtheGPIOexampleappInthissection,youwillexaminetheexampleAndroidappthatperformsGPIOinterfacingonBBB.ThepurposeofthisapplicationistodemonstratehowtousePacktHALtoperformGPIOreadandwriteprocessesfromwithinanactualapp.PacktHALprovidesasetofinterfacingfunctionsthatyouwillusetoworkwithGPIOsfromwithinyourAndroidapps.ThesefunctionsallowyoutoreadthevaluesofinputGPIOsandsetthevaluesofoutputGPIOs.Thelow-leveldetailsofthehardwareinterfacingareimplementedinPacktHAL,soyoucanquicklyandeasilygetyourappsinteractingwithGPIOs.

BeforediggingthroughtheGPIOapp’scode,youmustinstallthecodetoyourdevelopmentsystemandinstalltheapptoyourAndroidsystem.Thesourcecodefortheapp,aswellasaprecompiled.apkpackage,arelocatedinthechapter3.tgzfile,whichisavailablefordownloadfromthebook’swebsite.

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InstallingtheappandsourceunderWindowsOnceyouhavedownloadedthechapter3.tgzfile,youmustdecompressanduntarit.Wewillassumethatyouhavecopiedchapter3.tgztotherootdirectoryofc:\afterdownloadingitandwilldecompressitfromthere.Wewillrefertoyourworkspacedirectoryas$WORKSPACE.

Wewillassumethatyouradb.exebinaryisinyourcurrentpath.Ifitisnot,calladbbyusingthefullpathtotheadb.exebinary:

1. Openafileexplorerwindowandnavigatetothedirectory.2. Right-clickonthechapter3.tgzfileinfileexplorerandselectExtractHere.

Adirectorynamedc:\gpionowexists,anditcontainsallofthefilesfortheGPIOexampleapp.YoumustimportthisprojectintoyourEclipseADTworkspace:

1. LaunchEclipseADT.2. OpentheFilemenuandselectImport.3. OntheImportdialog,expandtheAndroidfolderandhighlightExistingAndroid

CodeIntoWorkspace.TheNextbuttonatthebottomofthedialogwillbecomeactive.Clickonittocontinue.

4. OntheImportProjectsdialog,typec:\gpiointheRootDirectorytextfield.Then,clickontheRefreshbutton.Thegpioprojectwillappearonthelistofprojectstoimport.

5. ClickontheSelectAllbutton,thenselectthecheckboxforCopyprojectsintoworkspace.

6. ClickontheFinishbuttontoimportthegpioappprojectintoyourworkspaceandcopythec:\gpiodirectoryintoyour$WORKSPACEdirectory.

AlloftheprojectfilesfortheGPIOapparenowlocatedinthatgpiodirectory.Aprebuilt.apkpackagefortheappisprovidedinthe$WORKSPACE\gpio\bindirectory.Youcaninstallthis.apkpackagedirectlytoyourAndroidsystemusingadb:

1. Launchcmd.exeforacommandpromptwindow.Usingthecommandprompt,changeintothe$WORKSPACE\gpio\bindirectory:

c:\>cd$WORKSPACE\gpio\bin

2. VerifythatadbcanseeyourBBBusingtheadbdevicescommand:

c:\$WORKSPACE\gpio\bin>adbdevices

BBBAndroiddevice

3. Installgpio.apktoyourAndroidsystemviatheinstallcommandinadb:

c:\$WORKSPACE\gpio\bin>adbinstall-dgpio.apk

4. Ifyouhavealreadyinstalledthegpio.apkapponceandarenowreceivingthefailure

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messageofINSTALL_FAILED_ALREADY_EXISTS,useadbtoreinstallgpio.apk:

c:\$WORKSPACE\gpio\bin>adbinstall-d-rgpio.apk

Thegpio.apkappisnowinstalledonyourAndroidsystem,andtheapp’ssourceisnowinstalledinyourEclipseADTworkspace.

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InstallingtheappandsourceunderLinuxOnceyouhavedownloadedthechapter3.tgzfile,youmustdecompressanduntarit.Wewillassumethatyouhavecopiedchapter3.tgztoyour$HOMEdirectoryafterdownloadingitandwilldecompressitfromthere.Wewillrefertoyourworkspacedirectoryas$WORKSPACE.

UsetheLinuxtarcommandtodecompressanduntarthechapter3.tgzfile:

$cd$HOME

$tar–xvfchapter3.tgz

Adirectorynamedgpionowexistsinyour$HOMEdirectory,anditcontainsallofthefilesforthegpioexampleapp.YoumustimportthisprojectintoyourEclipseADTworkspaceasfollows:

1. LaunchEclipseADT.2. OpentheFilemenuandselectImport.3. OntheImportdialog,expandtheAndroidfolderandhighlightExistingAndroid

CodeIntoWorkspace.TheNextbuttonatthebottomofthedialogwillbecomeactive.Clickonittocontinue.

4. OntheImportProjectsdialog,type$HOME/gpio(substitutinginthefullpathfor$HOME)intheRootDirectorytextfield.Then,clickontheRefreshbutton.Thegpioprojectwillappearonthelistofprojectstoimport.

5. ClickontheSelectAllbutton,thenselectthecheckboxforCopyprojectsintoworkspace.

6. ClickontheFinishbuttontoimportthegpioappprojectintoyourworkspaceandcopythe$HOME/gpiodirectoryintoyour$WORKSPACEdirectory.

Alloftheprojectfilesfortheapparenowlocatedinthe$WORKSPACE/gpiodirectory.Aprebuilt.apkpackageforthegpioprojectisprovidedinthegpio/bindirectory.Youcaninstallthis.apkpackagedirectlytoyourAndroidsystemusingadb:

1. Changeintothebindirectoryofthegpioproject:

$cd$WORKSPACE/gpio/bin

2. VerifythatadbcanseeyourBBBusingtheadbdevicescommand:

$adbdevices

BBBAndroiddevice

3. Installgpio.apktoyourAndroidsystemviatheinstallcommandinadb:

$adbinstall-dgpio.apk

4. Ifyouhavealreadyinstalledthegpio.apkapponceandarenowreceivingthefailuremessageofINSTALL_FAILED_ALREADY_EXISTS,useadbtoreinstallgpio.apk:

$adbinstall-d-rgpio.apk

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Thegpio.apkappisnowinstalledonyourAndroidsystem,andtheapp’ssourceisnowinstalledinyourEclipseADTworkspace.

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Theapp’suserinterfaceLaunchthegpioappontheAndroidsystemtoseetheapp’s(UI).Ifyouareusingatouchscreencape,youcansimplytouchthegpioappicononthescreentolaunchtheappandinteractwithitsUI.IfyouareusingtheHDMIforvideo,connectaUSBmousetotheBBB’sUSBportandusethemousetoclickonthegpioappicontolaunchtheapp.

TheappusesaverysimpleUItointeractwiththeGPIOs.Asitissosimple,theonlyactivitythattheapphasisdefaultMainActivity.TheUIconsistsofonlythreebuttonsandtextview.

TheGPIOsampleappscreen

ThePollButtonStatebuttonchecksthecurrentstateofthepushbuttonswitchandupdatesthevalueoftheButtonStatetextviewtoreportthatstate.TheswitchstatewillbereportedasUNKNOWNuntilthePollButtonStatebuttonispressedforthefirsttime.TheTurnlightonbuttonwillturnontheLEDifitisnotalreadyon,andtheTurnlightoffbuttonwillturntheLEDoff.

ThetextviewhasanIDassociatedwithitinres/layout/activity_main.xmlsothattheappcanupdatethetextview’svalueprogrammatically:

<TextView

android:text="@string/button_state"

android:id="@+id/button_state"/>

EachofthethreebuttonshaveanonClick()handlerdefined:

<Button

android:text="@string/button_poll"

android:onClick="onClickButtonPollStatus"/>

<Button

android:text="@string/button_lighton"

android:onClick="onClickButtonLightOn"/>

<Button

android:text="@string/button_lightoff"

android:onClick="onClickButtonLightOff"/>

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EachonClick()handlerwilltriggeroneofthePacktHALGPIOfunctionstoreadthestateofaGPIOorwriteanewstatetoaGPIO.

NoteIfyouneedarefresheronthefinedetailsofthevariousAndroidUIelements,thereareseveralresourcesavailableonlinethatcanhelpyou.WerecommendthatyoustartwiththeofficialAndroidDeveloperwebsiteathttp://developer.android.com/guide/topics/ui/index.html.

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CallingthePacktHALfunctionsTheGPIOinterfacefunctionalityinPacktHALisimplementedinfourCfunctions:

openGPIO()

readGPIO()

writeGPIO()

closeGPIO()

Theprototypesforthesefunctionsarelocatedinthejni/PacktHAL.hheaderfilewithintheapp’sproject:

externintopenGPIO(constintuseMmap);

externintreadGPIO(constunsignedintheader,constunsignedintpin);

externintwriteGPIO(constunsignedintheader,

constunsignedintpin,constunsignedintvalue);

externvoidcloseGPIO(void);

Ideally,youwouldloadthePacktHALsharedlibraryintoyourappandthensimplycallthelibraryfunctionsdirectlytocontroltheGPIOs.TheexampleappactuallydoesloadthePacktHALlibraryviaaSystem.loadLibrary()call,butthenthingsbecomelessstraightforwardbecausetheseCfunctionscannotbecalleddirectly.YoumustspecifyJavamethodsthat,whencalled,actuallycalltheCfunctions.

TheMainActivityclassspecifiesfourmethodswiththenativekeywordtocallthePacktHALCfunctionsinMainActivity.java:

publicclassMainActivityextendsActivity{

privatenativebooleanopenGPIO();

privatenativevoidcloseGPIO();

privatenativebooleanreadGPIO(intheader,intpin);

privatenativevoidwriteGPIO(intheader,intpin,intval);

static{

System.loadLibrary("packtHAL");

ThesefourJavamethodsspecifiedinMainActivityarenotactuallyadirectmappingtotheCfunctionsofthesamenameinPacktHAL.NoticethattheGPIOmethodsinMainActivityareallprivatenativewithinthescopeoftheclass.AnymethoddefinedwiththenativekeywordwillattempttocallanativeJNIwrapperfunctionwhenitisinvoked.However,thenamingoftheinvokedJNIwrapperfunctionfollowssomeveryspecificrulesthatrepresentthescopeofitsJava-sidemethod.ThefollowingfigureshowshowtheseJNIwrapperfunctionsfinallycalltheGPIO-interfacingfunctionsinsideofPacktHAL:

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TheMainActivitymethodsandthePacktHALGPIO-interfacingfunctionsthattheycall

EachnativemethodintheMainActivityclasswiththenamename()willuseJNItocallaJNIwrapperfunctionwiththenameJava_com_packt_gpio_MainActivity_name().Thenameofthiswrapperfunctionisdeterminedbyreplacingeach.inthefullyqualifiednameoftheappwithanunderscore.TheJava_prefixofthefunctionnametellsAndroidthatthefunctionisbeingcalledviaamethodinaJavaclass.ThereareafewexceptionstothisJNInamingconvention,butthisgeneralrulewillgetyouthroughmostcases.

TipDoIneedtoknowallaboutJNItomakemyownAndroidinterfacingprojects?

Notreally.UsingJNIcanbequiteconfusing,andmany,manybooksandtutorialshavebeendedicatedtodescribingitingreatdetail.Fornow,don’tworryaboutnotknowingeverythingthatthereistoknowaboutJNI.WhenyouhavespentsometimeexperimentingwithhardwareinterfacingunderAndroid,youcanrevisitthistopicandlearnmoreofthefinedetailsofhowJNIworks.Inthisbook,wewillfocusonshowingyoujustenoughinformationaboutJNItogetyoustarted.

Asanexample,ourJavaopenGPIO()methodintheMainActivityclassforthecom.packtpub.gpioexampleappusesJNItocallthewrapperCfunctionJava_com_packtpub_gpio_MainActivity_openGPIO().Thisisalittleconfusing,butstillverymanageable.PacktHALimplementstheseJNIwrapperCfunctionsinthejni/packt_native_gpio.cfile.Lookingatthissourcefile,youcanseewheretheJava_com_packtpub_gpio_MainActivity_openGPIO()functioninPacktHALcallstheopenGPIO()CfunctioninPacktHAL:

jbooleanJava_com_packt_gpio_MainActivity_openGPIO(JNIEnv*env,

jobjectthis)

jbooleanret=JNI_TRUE;

if(openGPIO(0)==0){

__android_log_print(ANDROID_LOG_DEBUG,PACKT_NATIVE_TAG,

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"GPIOOpened.");

}else{

__android_log_print(ANDROID_LOG_ERROR,PACKT_NATIVE_TAG,

"openGPIO()failed!");

ret=JNI_FALSE;

returnret;

WhynotjustdoawaywiththeseparateopenGPIO()CfunctionandplaceallofthehardwareinterfacecodeinsideJava_com_packt_gpio_MainActivity_openGPIO()?FunctionssuchasopenGPIO()inPacktHALwillusuallynotchangeonceyouhavethemworkingproperly,andyoucanusethesesamefunctionsunderbothLinuxandAndroid.WrapperfunctionssuchasJava_com_packt_gpio_MainActivity_openGPIO()willchangetheirnameandimplementationdetailsbaseduponhowandwheretheyareinvokedfromanapp’sJavacode.Itisbettertoisolatefunctionalitythatwillnotchangeinitsownfunction.ThisavoidsyouraccidentallybreakingsomethingwhencustomizingorrenamingthefunctionsinvokedviaJNI.

NoteJustrememberthataJavamethodinyourapp,suchasopenGPIO()intheMainActivityclass,makesaJNIcalltoinvokeaPacktHALCfunctionwithalong,manglednamelikeJava_com_packt_gpio_MainActivity_openGPIO().TheJNIwrapperfunctionwillthencalloneofthePacktHALCfunctions,forexample,openGPIO(),thatactuallycontrolsthehardware.Fromtheappdeveloper’spointofview,onceyousortouttheJNIwrapperfunctiondetails,itisalmostlikecallingtheCfunctionthatcontrolsthehardwaredirectlyfromtheJavaappcode!

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UsingthePacktHALGPIOfunctionsNowthatyouhaveseenhowthePacktHALGPIOfunctionsarecalledfromJava,youwillseewhateachofthesefunctionsdoesandhowyoucanusethem.

TheopenGPIO()functioninitializesyourapp’saccesstoGPIOs.ThisfunctionoffersyoutwodifferentmethodsforGPIOinterfacing,ofwhichyouselectonemethodusingopenGPIO()function’suseMmapparameter.ThetwomethodsarefileI/O(bysettinguseMmapto0)andmemory-mapping(bysettinguseMmaptoanynon-zeronumber).Tochangefromoneinterfacingmethodtotheother,youmustcallcloseGPIO()toshutdowntheGPIOportionofPacktHALandthencallopenGPIO()againwithadifferentvalueforuseMmap.

Processesmustrunasroottousememory-mappingtodirectlyaccesstheGPIOcontrolresistors.Asappscannotrunasroot,theJNIwrapperfunctionalwayspasses0astheuseMmapargumenttoopenGPIO()toforcetheuseoffileI/OtointeractwithGPIOs.TheopenGPIO()methodintheMainActivityclassdoesnotacceptanyargumentsbecauseofthis.

TheexampleappcallstheopenGPIO()methodfromtheonCreate()methodoftheMainActivityclass:

protectedvoidonCreate(BundlesavedInstanceState){

...//Existingstatements

TextViewtv=(TextView)findViewById(R.id.button_state);

tv.setText("ButtonState:UNKNOWN");

if(openGPIO()==false){

Log.e("com.packt","UnabletoopenGPIO.");

finish();

ThecomplementarycalltothecloseGPIO()methodismadebytheonDestroy()methodoftheMainActivityclass:

protectedvoidonDestroy(){

closeGPIO();

ThereadGPIO()methodreadsthestateofaparticularinputGPIO.BoththePacktHALreadGPIO()functionandthereadGPIO()methodinMainActivitytakethesametwoparameters.ThefirstparameterisaconnectornumberontheBBB(8or9),andthesecondparameterisapinlocationonthatconnector(1through42).ThereadGPIO()methodiscalledfromwithintheonClick()handlerofthePollStatusbutton:

publicvoidonClickPollStatus(Viewview){

Stringstatus=readGPIO(9,13)==true?"ON":"OFF";

TextViewtv=(TextView)findViewById(R.id.button_state);

tv.setText("ButtonState:"+status);

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InonClickPollStatus(),thereadGPIO()methodcallisreadingthestateoftheGPIOpinP9.13.ThisistheGPIOpinthatyouconnectedtothepushbuttonswitch.IftheswitchispressedwhenthereadGPIO()methodiscalled,trueisreturned.Otherwise,falseisreturned.

ThewriteGPIO()methodisusedtosetthestateofanoutputGPIO.BoththePacktHALwriteGPIO()functionandthewriteGPIO()methodinMainActivitytakethreeparameters.ThefirstparameteristheconnectornumberontheBBB(8or9),thesecondparameterisapinlocationonthatconnector(1through42),andthethirdparameteristhevaluetoset(0or1).ThewriteGPIO()methodiscalledfromwithintheonClickhandlersoftheLightOnandLightOffbuttons:

publicvoidonClickButtonLightOn(Viewview){

writeGPIO(9,11,1);

publicvoidonClickButtonLightOff(Viewview){

writeGPIO(9,11,0);

InbothoftheseonClick()handlers,theGPIObeingsetisP9.11.ThisistheGPIOpinthatyouconnectedtotheLED.TheonClickButtonLightOn()methodsetstheGPIOto1,turningtheLEDon.Likewise,theonClickButtonLightOff()methodsetstheGPIOto0,turningtheLEDoff.

TipAreyoureadyforachallenge?

Nowthatyouhaveseenallofthepiecesofthegpioapp,whynotchangeittoaddnewfunctionality?Forachallenge,trychangingtheapptouseonlyasinglebuttonthattogglesthestateoftheLED.IftheLEDiscurrentlyoff,pressingthebuttonwillturnitonandviceversa.Wehaveprovidedonepossibleimplementationofthisinthechapter3_challenge.tgzfile,whichisavailablefordownloadfromthebook’swebsite.

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SummaryInthischapter,weintroducedyoutoGPIOsandhowtheywork.YouconstructedacircuitthatusesGPIOsforbothinputandoutput,andthenyoudidsomebasictestingonthecircuittoensurethatthecircuitwasconstructedproperlyandthatthekernelisabletointeractwiththecircuitviathefilesystem.YoualsolearnedabouttheportionsofthePacktHALinit.{ro.hardware}.rcfileandBB-PACKTPUB-00A0.dtboDeviceTreeoverlaythatareresponsibleforconfiguringGPIOsandmakingthemavailableforyourapp’suse.

WeshowedyouhowtoaddPacktHALintoanewlycreatedappprojectandhowtobuildPacktHALusingtheAndroidNDK.Then,youlearnedhowJNIintegratesPacktHALintoyourJavaappviaJNIwrapperfunctionsandexploredhoweachGPIOfunctionofPacktHALiscalledandusedfromwithinanapp.

Inthenextchapter,youwilllearnhowtointegrateI2Cbusdevicesintoyourappsandbegininteractingwithhardwarethatismuchmoresophisticatedthanthebasicon/offlogicofGPIOs.

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Chapter4.StoringandRetrievingDatawithI2CInthelastchapter,youusedGPIOstoexchangesimpledigitaldatawiththeoutsideworld.However,whataboutinterfacingwithmoreadvanceddevicesthatrequirecomplexsequencesofbitsorbytesforcommunication?

OneofthemostpopularinterfacingbusesinusetodaywithinembeddedsystemsistheInter-IntegratedCircuitserialbus(commonlyabbreviatedasIIC,I2C,orI2C).Inthischapter,youwilllearnhowtowriteanappthatusestheBBB’sI2CinterfacetostoredatatoandretrievedatafromaFRAMchip.Wewillcoverthefollowingtopics:

UnderstandingI2CMultiplexingforI2ContheBBBRepresentingI2CdevicesintheLinuxkernelBuildinganI2CinterfacecircuitExploringtheI2CFRAMexampleapp

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UnderstandingI2COriginallydevelopedbyPhilipsSemiconductorin1982asabusforcommunicatingwiththeICs,theI2Cprotocolhasbecomeageneral-usebusthatissupportedbyawidevarietyofICmanufacturers.I2Cisamultimasterandmultislavebus,thoughthemostcommonconfigurationisthatofasinglemasterdeviceandoneormoreslavedevicesonasinglebus.AnI2Cmasterdevicesetsthepaceforthebusbygeneratingaclocksignal,anditinitiatescommunicationwiththeslavedevices.Slavedevicesreceivethemaster’sclocksignalandrespondtothemaster’squeries.

OnlyfourwiresarerequiredtocommunicateviaI2C:

Oneclocksignal(SCL)Onedatasignal(SDA)ApositivesupplyvoltageAground

Requiringonlytwopins(fortheSCLandSDAsignals)tocommunicatewithanumberofslavedevicesmakesI2Canenticinginterfacingoption.Oneofthedifficultiesinhardwareinterfacingiseffectivelyallocatingalimitednumberofprocessorpinstobesthandlecommunicatingwithalargenumberofdifferentdevicessimultaneously.Byonlyrequiringtwoprocessorpinstocommunicatewithavarietyofdevices,I2Cfreesuppinsthatcannowbeallocatedtoothertasks.

AnexampleoftheI2Cbuswithasinglemasterdeviceandthreeslavedevices

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DevicesthatuseI2CDuetotheflexibilityandwideusageoftheI2Cbus,therearemanydevicesthatuseitforcommunication.Differentvarietiesofstoragedevices,suchasEEPROMandFRAMICs,arecommonlyinterfacedviaI2C.Forexample,theEEPROMspresentonBBBcapesareallaccessedbytheBBB’sprocessorviaI2C.Sensorsfortemperature,pressure,andhumidity,accelerometers,LCDcontrollers,andsteppermotorcontrollersareallexamplesofdevicesthatareavailablethroughtheI2Cbus.

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MultiplexingforI2ContheBBBTheAM335XprocessoroftheBBBprovidesthreeI2Cbuses:

I2C0I2C1I2C2

TheBBBexposestheI2C1andI2C2busesviaitsP9header,buttheI2C0busisnoteasilyaccessible.I2C0currentlyprovidesthecommunicationchannelbetweentheBBB’sprocessorandtheHDMIframerchipofthebuilt-inHDMIcape,soitshouldbeconsideredunavailableforyouruse(unlessyouwouldliketovoidyourwarrantybysolderingwiresdirectlytothetracesandchippinsontheBBB).

TheI2C1busisavailableforyourgeneraluseandisoftenthegotobusforI2Cinterfacing.IfI2C1isatitsmaximumcapacityorunavailable,theI2C2busisalsoavailableforyouruse.

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ConnectingtoI2CviatheP9headerBydefault,I2C1isnotmuxedtoanypinsandI2C2isavailableviatheP9.19andP9.20pins.I2C2providesI2CcommunicationbetweentheidentificationEEPROMspresentonexternalcapeboardsandthekernel’scapemgr.YoucanmuxI2C2tootherpins,orevendisableitentirely,butifyoudoso,thecapemgrwillnolongerbeabletoautomaticallydetectthepresenceofcapeboardsthatareattachedtotheBBB.Generallyspeaking,youprobablydonotwanttodothis.

ThefollowingfigureshowseachofthepotentialpinsontheP9headerwhereI2Csignalscanbemuxed:

LocationsoftheI2CbusesontheP9headerwithdifferentpinmuxmodes

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MultiplexingforI2CWhendecidinghowyouwouldlikeyourpinstobemuxedwhenusingI2Cinyourprojects,keepthefollowingitemsinmind:

AvoidmuxinganysingleI2Csignaltomorethanonepin.Doingsowastesoneofyourpinsfornogoodreason.AvoidmuxingI2C2awayfromitsdefaultlocation,asthispreventsthecapemgrfromautomaticallydetectingcapeboardsconnectedtotheBBB.YoucanusethedefaultI2C2busforyourownprojects,butnotethatitisclockedat100KHzandtheaddresses0x54through0x57arereservedforcapeEEPROMs.MuxingtheI2C1channeltoP9.17andP9.18conflictswiththeSPI0channel,soyougenerallywouldn’twanttousethisconfigurationifyoualsowishtouseSPI.

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RepresentingI2CdevicesintheLinuxkernelI2Cbusesanddevicesareexposedinuserspaceasfilesinthe/devfilesystem.I2Cbusesareexposedasthe/dev/i2c-Xfile,whereXisthelogicalnumberoftheI2Cchannel.WhilethehardwaresignalsfortheI2Cbusareclearlynumberedas0,1,and2,thelogicalchannelnumberswon’tnecessarilybethesameastheirhardwarecounterparts.

LogicalchannelnumbersareassignedintheorderthattheI2CchannelsareinitializedintheDeviceTree.Forexample,theI2C2channelisusuallythesecondI2Cchannelinitializedbythekernel.Therefore,eventhoughitisphysicalI2Cchannel2,itwillbelogicalI2Cchannel1andaccessibleasthe/dev/i2c-1file.

UnderneathallofthelayersofAndroidAPIsandservices,Androidultimatelyinteractswithdevicedriversinthekernelbyopeningfilesinthe/devand/sysfilesystemsandthenreading,writing,orperformingioctl()callsonthosefiles.WhileitispossibletointeractwithanyI2Cdeviceusingonlytheioctl()callsonthe/dev/i2c-XfilestodirectlycontroltheI2Cbus,thisapproachiscomplicatedandgenerallyshouldbeavoided.Instead,youshouldtrytouseakerneldriverthatcommunicateswithyourdeviceontheI2Cbusforyou.Youcanthenmakeioctl()callsonthefileexposedbythatkerneldrivertoeasilycontrolyourdevice.

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PreparingAndroidforFRAMuseInChapter2,InterfacingwithAndroid,youusedadbtopushtwoprebuiltfilestoyourAndroidsystem.Thesetwofiles,BB-PACKTPUB-00A0.dtboandinit.{ro.hardware}.rc,configureyourAndroidsystemtoenableakerneldevicedriverthathandlesFRAMinterfacing,muxthepinstoenabletheI2C1bus,andallowyourappstoaccessit.

AsfarasI2Cisconcerned,theBB-PACKTPUB-00A0.dtbooverlaymuxestheP9.24andP9.26pinsintotheI2CSCLandSDAsignals.InthePacktHAL.tgzfile,thesourcecodefortheoverlayislocatedinthecape/BB-PACKTPUB-00A0.dtsfile.Thecoderesponsibleformuxingthesetwopinsislocatedinthebb_i2c1a1_pinsnodewithinfragment@0:

/*AllI2C1pinsareSLEWCTRL_SLOW,INPUT_PULLUP,MODE3*/

bb_i2c1a1_pins:pinmux_bb_i2c1a1_pins{

0x1800x73/*P9.26,i2c1_sda*/

0x1840x73/*P9.24,i2c1_scl*/

Whilethissetsupthemuxing,itdoesn’tassignandconfigureadevicedrivertothesepins.Thefragment@1nodeperformsthiskerneldriverallocation:

fragment@1{

target=<&i2c1>;

__overlay__{

status="okay";

pinctrl-names="default";

pinctrl-0=<&bb_i2c1a1_pins>;

clock-frequency=<400000>;

#address-cells=<1>;

#size-cells=<0>;

/*ThisiswherewespecifyeachI2Cdeviceonthisbus*/

adafruit_fram:adafruit_fram0@50{

/*Kerneldriverforthisdevice*/

compatible="at,24c256";

/*I2Cbusaddress*/

reg=<0x50>;

Withoutgoingintotoomuchdetail,therearefoursettingsinfragment@1thatareofinteresttoyou:

Thefirstsettingispinctrl-0,whichtiesthisnodeoftheDeviceTreetothepinsmuxedinthebb_i2c1a1_pinsnodeThesecondsettingisclock-frequency,whichsetstheI2Cbusspeedto400KHzThethirdsettingiscompatible,whichspecifiestheparticularkerneldriver(the24c256driverforEEPROM-likedevices)thatwillhandleourhardwaredeviceThelastsettingisreg,whichspecifiestheaddressontheI2Cbuswherethisdevice

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willreside(0x50,inourcase)

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BuildinganI2C-interfacingcircuitNowthatyouhaveanunderstandingofwhereI2CdevicesareconnectedtotheBBBandhowtheLinuxkernelpresentsaninterfacetothosedevices,itistimetoconnectanI2CdevicetotheBBB.

AswementionedinChapter1,IntroductiontoAndroidandtheBeagleBoneBlack,youwillbeinterfacingwithaFRAMchipinthischapter.Specifically,itisaFujitsuSemiconductorMB85RC256VFRAMchip.This8-pinchipprovides32KBofnonvolatilestorage.Thisparticularchipisonlyavailableinasmalloutlinepackage(SOP),whichisasurfacemountchipthatcanbedifficulttoworkwithwhenbuildingprototypecircuits.Luckilyforus,theAdaFruitbreakoutboardfortheFRAMalreadyhasthechipmounted,whichmakesprototypingsimpleandeasy.

TheFRAMcircuitinthischapterispartofamuchlargercircuitusedinChapter6,CreatingaCompleteInterfacingSolution.Ifyoubuildthecircuitaspositionedinthediagram(towardsthebottomofthebreadboard),youcansimplyleavetheFRAMbreakoutboardandwiresinplaceasyoubuildtheremainingcircuitsinthisbook.Thisway,itwillalreadybeconstructedandworkingwhenyoureachChapter6.

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ConnectingtheFRAMEachI2CdevicemustuseanaddresstoidentifyitselfontheI2Cbus.TheFRAMchipthatweareusingcanbeconfiguredtouseanaddressintherangeof0x50to0x57.ThisisacommonaddressrangeforEEPROMdevices.Theexactaddressissetbyusingtheaddresslines(A0,A1,A2)ofthebreakoutboard.TheFRAMhasabaseaddressof0x50.IftheA0,A1,and/orA2linesareconnectedtoa3.3Vsignal,0x1,0x2,and/or0x4areaddedtotheaddress,respectively.Forthisinterfacingproject,noneoftheaddressinglinesareconnected,whichresultsintheFRAMretainingitsbaseaddressof0x50ontheI2Cbus.

TheFRAMbreakoutboard(theA0,A1,andA2addressinglinesarethethreeright-mostterminalsoftheboard)

NoteTheaddressesofmanyI2Cdevicesareconfigurablebyconnectingtheaddresspinsofthedevicetoeitherthegroundorvoltagesignals.ThisisbecausetherecanbemultiplecopiesofthesamedeviceonasingleI2Cbus.Thecircuitdesignercanassignadifferentaddresstoeachdevicebyrewiringtheaddresspins,ratherthanhavingtobuydifferentpartswithdifferentpre-assignedaddressesthatdonotconflictwitheachother.

ThefollowingfigureshowstheconnectionsbetweentheFRAMbreakoutboardandtheBBB.ThefourmainI2Cbussignals(+3.3V,ground,andI2CSCL/SDA)aremadeusingthepinsoftheP9connector,sowe’veplacedthebreadboardontheP9sideoftheBBB.

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ThecompleteI2C-interfacingcircuit

Let’sgetstarted:

1. ConnectP9.1(ground)totheverticalgroundbusofthebreadboardandconnectP9.3(3.3V)totheverticalVCCbusofthebreadboard.TheseconnectionsareidenticaltotheonesmadefortheGPIObreadboardcircuitthatyoucreatedinChapter3,HandlingInputsandOutputswithGPIOs.

2. TheI2Csignals,SCLandSDA,areontheP9.24andP9.26pins,respectively.WiretheP9.24pintothepinmarkedSCLonthebreakoutboard,andwiretheP9.26pintothepinmarkedSDAonthebreakoutboard.

3. WirethegroundbustotheGNDpinofthebreakoutboardandwiretheVCCbustotheVCCpinofthebreakoutboard.Leavethewriteprotect(WP)pinandthethreeaddresspins(A0,A1,A2)unconnected.

TheFRAMbreakoutboardisnowelectricallyconnectedtotheBBBandisreadyforyouruse.Double-checkyourwiringagainstthediagramofthecompleteFRAMinterfacingcircuittoensurethateverythingisconnectedproperly.

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CheckingtheFRAMconnectionwithI2CtoolsTheI2CtoolsareasetofutilitiesthatallowyoutoprobeandinteractwiththeI2Cbus.ThesetoolsworkonsystemsthatuseaLinuxkernel,andtheyareincludedintheBBBAndroidimage.TheutilitiesinteractwiththeI2Cbusbyopeningthe/dev/i2c-Xdevicefilesandmakingioctl()callsonthem.Bydefault,youmusthaverootaccesstousei2c-tools,butBBBAndroidreducesthepermissionsonthe/dev/i2c-Xfilessothatanyprocess(includingi2c-tools)canreadandwriteinformationabouttheI2Cbuses.

Asanexample,let’stryusingthei2cdetectutilityini2c-tools.i2cdetectwillsweepaspecifiedI2CbusandidentifybusaddresseswhereI2Cdevicesarelocated.UsingtheADBshell,youwillprobethei2c-2physicalbus,whichisalsothesecondlogicalbus(/dev/i2c-1):

0123456789abcdef

00:—--—--—--—--—--—----

10:—--—--—--—--—--—--—--—--

20:—--—--—--—--—--—--—--—--

30:—--—--—--—--—--—--—--—--

40:—--—--—--—--—--—--—--—--

50:—--—--UUUUUUUU—--—--—--—--

60:—--—--—--—--—--—--—--—--

70:—--—--—--—--

NoteTheoutputofi2cdetectshowseverydevicedetectedonthecurrentbus.Anyaddressthatisnotinusehasa--identifier.AnyaddressthatisreservedforadevicedriverintheDeviceTree,butdoesnotcurrentlyhaveadevicelocatedatthataddress,hasaUUidentifier.Ifadeviceisdetectedataparticularaddress,thedevice’stwo-digithexadecimaladdresswillappearasanidentifierinthei2cdetectoutput.

Theoutputofi2cdetectshowsthattheDeviceTreehasallocateddriversforfourI2Cdevicesonthei2c-2physicalbus.ThesefourdevicesaretheEEPROMsataddresses0x54-0x57ofthecapemgr.Thedevicesaren’tactuallypresentbecausenocapeboardsareconnectedtotheBBB,soeachaddresshasaUUidentifier.

AftertheFRAMbreakoutboardiselectricallyconnectedtotheBBB,youmustverifythattheFRAMisavisibledeviceontheI2Cbus.Todothis,usei2cdetecttoexaminethedevicespresentonthei2c-1physicalbus(logicalbus2):

0123456789abcdef

00:—--—--—--—--—--—----

10:—--—--—--—--—--—--—--—--

20:—--—--—--—--—--—--—--—--

30:—--—--—--—--—--—--—--—--

40:—--—--—--—--—--—--—--—--

50:50—--—--—--—--—--—--—----

60:—--—--—--—--—--—--—--—--

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70:—--—--—--—--

TipDouble-checkyourwiring

Ifthei2cdetectoutputshowsaUUatthe0x50addresslocation,youknowthattheI2CbusdoesnotrecognizetheFRAMasbeingattached.Makesurethatyoudon’taccidentallyswaptheSCL(P9.24)andSDA(P9.26)wireswhenconnectingtheFRAMbreakoutboardtotheBBB.

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ExploringtheI2CFRAMexampleappInthissection,wewillexamineourexampleAndroidappthatinterfaceswiththeFRAMusingI2ConBBB.ThepurposeofthisapplicationistodemonstratehowtousePacktHALtoperformFRAMreadsandwritesfromwithinanactualapp.PacktHALprovidesasetofinterfacingfunctionsthatyouwillusetoworkwiththeFRAMfromwithinyourAndroidapps.ThesefunctionsallowyoutoretrieveblocksofdatafromtheFRAMandwritenewdatatobestoredontheFRAM.Thelow-leveldetailsofthehardwareinterfacingareimplementedinPacktHAL,soyoucanquicklyandeasilygetyourappsinteractingwiththeFRAMbreakoutboard.

BeforediggingthroughtheFRAMapp’scode,youmustinstallthecodetoyourdevelopmentsystemandinstalltheapptoyourAndroidsystem.Thesourcecodefortheappaswellastheprecompiled.apkpackage,arelocatedinthechapter4.tgzfile,whichisavailablefordownloadfromthePacktwebsite.FollowthesameprocesstodownloadandaddtheapptoyourEclipseADTenvironmentthatwasdescribedinChapter3,HandlingInputsandOutputswithGPIOs.

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Theapp’suserinterfaceLaunchtheframappontheAndroidsystemtoseetheapp’sUI.Ifyouareusingatouchscreencape,youcansimplytouchtheframappicononthescreentolaunchtheappandinteractwithitsUI.IfyouareusingtheHDMIforvideo,connectaUSBmousetotheBBB’sUSBportandusethemousetoclickontheframappicontolaunchtheapp.Asthisappacceptstextinputfromtheuser,youmightfinditconvenienttoconnectaUSBkeyboardtotheBBB.Otherwise,you’llbeabletousetheonscreenAndroidkeyboardtoinputtext.

Thisapp’sUIisabitmorecomplexthanthatoftheGPIOappinthelastchapter,butitisstillfairlysimple.Asitissosimple,theonlyactivitythattheapphasisthedefaultMainActivity.TheUIconsistsoftwotextfields,twobuttons,andtwotextviews.

TheFRAMsampleappscreen

ThetoptextfieldhasthesaveEditTextidentifierintheactivity_main.xmlfile.ThesaveEditTextfieldacceptsupto60charactersthatwillbestoredtotheFRAM.ThetopbuttonwiththeSavelabelhasthesaveButtonidentifier.ThisbuttonhasanonClick()methodcalledonClickSaveButton()thattriggerstheprocessofinterfacingwiththeFRAMtostorethetextcontainedwithinthesaveEditTexttextfield.

ThebottomtextfieldhastheloadEditTextidentifier.ThistextfieldwilldisplayanydatathatisheldintheFRAM.ThebottombuttonwiththeLoadlabelhastheloadButtonidentifier.ThisbuttonhasanonClick()methodcalledonClickLoadButton()thattriggerstheprocessofinterfacingwiththeFRAMtoloadthefirst60bytesofdataandthenupdatingthetextdisplayedintheloadEditTexttextfield.

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CallingthePacktHALFRAMfunctionsTheFRAMinterfacefunctionalityinPacktHALisimplementedinfourCfunctions:

openFRAM()

readFRAM()

writeFRAM()

closeFRAM()

Theprototypesforthesefunctionsarelocatedinthejni/PacktHAL.hheaderfilewithintheapp’sproject:

externintopenFRAM(constunsignedintbus,constunsignedintaddress);

externintreadFRAM(constunsignedintoffset,constunsignedint

bufferSize,constchar*buffer);

externintwriteFRAM(constunsignedintoffset,constunsignedint

constchar*buffer);

externvoidcloseFRAM(void);

TheopenFRAM()functionopensthefileinthe/devfilesystemthatprovidestheinterfacetothe24c256EEPROMkerneldriver.ItscounterpartfunctioniscloseFRAM(),whichclosesthisfileoncehardwareinterfacingwiththeFRAMisnolongerneeded.ThereadFRAM()functionreadsabufferofdatafromtheFRAM,andthewriteFRAM()functionwritesabufferofdatatotheFRAMforpersistentstorage.Together,thesefourfunctionsprovideallofthenecessaryfunctionalitythatyouneedtointeractwiththeFRAM.

Justlikethegpioappfromthepreviouschapter,theframapploadsthePacktHALsharedlibraryviaaSystem.loadLibrary()calltoaccessthePacktHALFRAMinterfacefunctionsandtheJNIwrapperfunctionsthatcallthem.However,unlikethegpioapp,theMainActivityclassoftheframappdoesnotspecifymethodswiththenativekeywordtocallthePacktHALJNI-wrapperCfunctions.Instead,itleavesthehardwareinterfacingtoanasynchronoustaskclassnamedHardwareTask:

PublicclassMainActivityextendsActivity{

PublicstaticHardwareTaskhwTask;

Static{

System.loadLibrary("packtHAL");

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UnderstandingtheAsyncTaskclassHardwareTaskextendstheAsyncTaskclass,andusingitprovidesamajoradvantageoverthewayhardwareinterfacingisimplementedinthegpioapp.AsyncTasksallowsyoutoperformcomplexandtime-consuminghardware-interfacingtaskswithoutyourappbecomingunresponsivewhilethetasksareexecuted.EachinstanceofanAsyncTaskclasscancreateanewthreadofexecutionwithinAndroid.ThisissimilartohowmultithreadedprogramsfoundonotherOSesspinnewthreadstohandlefileandnetworkI/O,manageUIs,andperformparallelprocessing.

Inthepreviouschapter,thegpioapponlyusedasinglethreadduringitsexecution.ThisthreadisthemainUIthreadthatispartofallAndroidapps.TheUIthreadisdesignedtohandleUIeventsasquicklyaspossible.WhenyouinteractwithaUIelement,thatelement’shandlermethodiscalledbytheUIthread.Forexample,clickingabuttoncausestheUIthreadtoinvokethebutton’sonClick()handler.TheonClick()handlerthenexecutesapieceofcodeandreturnstotheUIthread.

AndroidisconstantlymonitoringtheexecutionoftheUIthread.Ifahandlertakestoolongtofinishitsexecution,AndroidshowsanApplicationNotResponding(ANR)dialogtotheuser.YouneverwantanANRdialogtoappeartotheuser.Itisasignthatyourappisrunninginefficiently(orevennotatall!)byspendingtoomuchtimeinhandlerswithintheUIthread.

TheApplicationNotRespondingdialoginAndroid

ThegpioappinthelastchapterperformedreadsandwritesoftheGPIOstatesveryquicklyfromwithintheUIthread,sotheriskoftriggeringtheANRwasverysmall.InterfacingwiththeFRAMisamuchslowerprocess.WiththeBBB’sI2Cbusclockedatitsmaximumspeedof400KHz,ittakesapproximately25microsecondstoreadorwriteabyteofdatawhenusingtheFRAM.Whilethisisnotamajorconcernforsmallwrites,readingorwritingtheentire32,768bytesoftheFRAMcantakeclosetoafullsecondtoexecute!

MultiplereadsandwritesofthefullFRAMcaneasilytriggertheANRdialog,soitisnecessarytomovethesetime-consumingactivitiesoutoftheUIthread.ByplacingyourhardwareinterfacingintoitsownAsyncTaskclass,youdecoupletheexecutionofthesetime-intensivetasksfromtheexecutionoftheUIthread.ThispreventsyourhardwareinterfacingfrompotentiallytriggeringtheANRdialog.

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LearningthedetailsoftheHardwareTaskclassTheAsyncTaskbaseclassofHardwareTaskprovidesmanydifferentmethods,whichyoucanfurtherexplorebyreferringtotheAndroidAPIdocumentation.ThefourAsyncTaskmethodsthatareofimmediateinterestforourhardware-interfacingeffortsare:

onPreExecute()

doInBackground()

onPostExecute()

execute()

Ofthesefourmethods,onlythedoInBackground()methodexecuteswithinitsownthread.TheotherthreemethodsallexecutewithinthecontextoftheUIthread.OnlythemethodsthatexecutewithintheUIthreadcontextareabletoupdatescreenUIelements.

ThethreadcontextsinwhichtheHardwareTaskmethodsandthePacktHALfunctionsareexecuted

MuchliketheMainActivityclassofthegpioappinthelastchapter,theHardwareTaskclassprovidesfournativemethodsthatareusedtocallPacktHALJNIfunctionsrelatedtoFRAMhardwareinterfacing:

publicclassHardwareTaskextendsAsyncTask<Void,Void,Boolean>{

privatenativebooleanopenFRAM(intbus,intaddress);

privatenativeStringreadFRAM(intoffset,intbufferSize);

privatenativevoidwriteFRAM(intoffset,intbufferSize,

Stringbuffer);

privatenativebooleancloseFRAM();

TheopenFRAM()methodinitializesyourapp’saccesstoaFRAMlocatedonalogicalI2Cbus(thebusparameter)andataparticularbusaddress(theaddressparameter).Oncethe

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connectiontoaparticularFRAMisinitializedviaanopenFRAM()call,allreadFRAM()andwriteFRAM()callswillbeappliedtothatFRAMuntilacloseFRAM()callismade.

ThereadFRAM()methodwillretrieveaseriesofbytesfromtheFRAMandreturnitasaJavaString.AtotalofbufferSizebytesareretrievedstartingatanoffsetofoffsetbytesfromthestartoftheFRAM.ThewriteFRAM()methodwillstoreaseriesofbytestotheFRAM.AtotalofbufferSizecharactersfromtheJavastringbufferarestoredintheFRAMstartedatanoffsetofoffsetbytesfromthestartoftheFRAM.

Intheframapp,theonClick()handlersfortheLoadandSavebuttonsintheMainActivityclasseachinstantiateanewHardwareTask.ImmediatelyaftertheinstantiationofHardwareTask,eithertheloadFromFRAM()orsaveToFRAM()methodiscalledtobegininteractingwiththeFRAM:

publicvoidonClickSaveButton(Viewview){

hwTask.saveToFRAM(this);

publicvoidonClickLoadButton(Viewview){

hwTask.loadFromFRAM(this);

BoththeloadFromFRAM()andsaveToFRAM()methodsintheHardwareTaskclasscallthebaseAsyncTaskclassexecution()methodtobeginthenewthreadcreationprocess:

publicvoidsaveToFRAM(Activityact){

mCallerActivity=act;

isSave=true;

execute();

publicvoidloadFromFRAM(Activityact){

isSave=false;

execute();

NoteEachAsyncTaskinstancecanonlyhaveitsexecute()methodcalledonce.IfyouneedtorunanAsyncTaskasecondtime,youmustinstantiateanewinstanceofitandcalltheexecute()methodofthenewinstance.ThisiswhyweinstantiateanewinstanceofHardwareTaskintheonClick()handlersoftheLoadandSavebuttons,ratherthaninstantiatingasingleHardwareTaskinstanceandthencallingitsexecute()methodmanytimes.

Theexecute()methodautomaticallycallstheonPreExecute()methodoftheHardwareTaskclass.TheonPreExecute()methodperformsanyinitializationthatmustoccurpriortothestartofthenewthread.Intheframapp,thisrequiresdisablingvariousUIelementsandcallingopenFRAM()toinitializetheconnectiontotheFRAMvia

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PacktHAL:

protectedvoidonPreExecute(){

//Somesetupgoeshere

if(!openFRAM(2,0x50)){

Log.e("HardwareTask","Erroropeninghardware");

isDone=true;

//DisabletheButtonsandTextFieldswhiletalkingtothehardware

saveText.setEnabled(false);

saveButton.setEnabled(false);

loadButton.setEnabled(false);

TipDisablingyourUIelements

Whenyouareperformingabackgroundoperation,youmightwishtokeepyourapp’suserfromprovidingmoreinputuntiltheoperationiscomplete.DuringaFRAMreadorwrite,wedonotwanttheusertopressanyUIbuttonsorchangethedataheldwithinthesaveTexttextfield.IfyourUIelementsremainenabledallthetime,theusercanlaunchmultipleAsyncTaskinstancessimultaneouslybyrepeatedlyhittingtheUIbuttons.Topreventthis,disableanyUIelementsrequiredtorestrictuserinputuntilthatinputisnecessary.

OncetheonPreExecute()methodfinishes,theAsyncTaskbaseclassspinsanewthreadandexecutesthedoInBackground()methodwithinthatthread.ThelifetimeofthenewthreadisonlyforthedurationofthedoInBackground()method.OncedoInBackground()returns,thenewthreadwillterminate.

AseverythingthattakesplacewithinthedoInBackground()methodisperformedinabackgroundthread,itistheperfectplacetoperformanytime-consumingactivitiesthatwouldtriggeranANRdialogiftheywereexecutedfromwithintheUIthread.ThismeansthattheslowreadFRAM()andwriteFRAM()callsthataccesstheI2CbusandcommunicatewiththeFRAMshouldbemadefromwithindoInBackground():

protectedBooleandoInBackground(Void…params){

Log.i("HardwareTask","doInBackground:Interfacingwithhardware");

if(isSave){

writeFRAM(0,saveData.length(),saveData);

}else{

loadData=readFRAM(0,61);

}catch(Exceptione){

NoteTheloadDataandsaveDatastringvariablesusedinthereadFRAM()andwriteFRAM()

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callsarebothclassvariablesofHardwareTask.ThesaveDatavariableispopulatedwiththecontentsofthesaveEditTexttextfieldviaasaveEditText.toString()callintheHardwareTaskclass’onPreExecute()method.

TipHowdoIupdatetheUIfromwithinanAsyncTaskthread?

Whiletheframappdoesnotmakeuseoftheminthisexample,theAsyncTaskclassprovidestwospecialmethods,publishProgress()andonPublishProgress(),thatareworthmentioning.TheAsyncTaskthreadusesthesemethodstocommunicatewiththeUIthreadwhiletheAsyncTaskthreadisrunning.ThepublishProgress()methodexecuteswithintheAsyncTaskthreadandtriggerstheexecutionofonPublishProgress()withintheUIthread.Thesemethodsarecommonlyusedtoupdateprogressmeters(hencethenamepublishProgress)orotherUIelementsthatcannotbedirectlyupdatedfromwithintheAsyncTaskthread.YouwillusethepublishProgress()andonPublishProgress()methodsinChapter6,CreatingaCompleteInterfacingSolution.

AfterdoInBackground()hascompleted,theAsyncTaskthreadterminates.ThistriggersthecallingofdoPostExecute()fromtheUIthread.ThedoPostExecute()methodisusedforanypost-threadcleanupandupdatinganyUIelementsthatneedtobemodified.TheframappusesthecloseFRAM()PacktHALfunctiontoclosethecurrentFRAMcontextthatitopenedwithopenFRAM()intheonPreExecute()method.

protectedvoidonPostExecute(Booleanresult){

if(!closeFRAM()){

Log.e("HardwareTask","Errorclosinghardware");

Theusermustnowbenotifiedthatthetaskhasbeencompleted.IftheLoadbuttonwaspressed,thenthestringdisplayedintheloadTextFieldwidgetisupdatedviatheMainActivityclassupdateLoadedData()method.IftheSavebuttonwaspressed,aToastmessageisdisplayedtonotifytheuserthatthesavewassuccessful.

Log.i("HardwareTask","onPostExecute:Completed.");

if(isSave){

Toasttoast=Toast.makeText(mCallerActivity.getApplicationContext(),

"DatastoredtoFRAM",Toast.LENGTH_SHORT);

toast.show();

}else{

((MainActivity)mCallerActivity).updateLoadedData(loadData);

TipGivingToastfeedbacktotheuser

TheToastclassisagreatwaytoprovidequickfeedbacktoyourapp’suser.Itpopsupasmallmessagethatdisappearsafteraconfigurableperiodoftime.Ifyouperformahardware-relatedtaskinthebackgroundandyouwanttonotifytheuserofitscompletion

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withoutchanginganyUIelements,tryusingaToastmessage!ToastmessagescanonlybetriggeredbymethodsthatareexecutingfromwithintheUIthread.

AnexampleoftheToastmessage

Finally,theonPostExecute()methodwillre-enablealloftheUIelementsthatweredisabledinonPreExecute():

saveText.setEnabled(true);

saveButton.setEnabled(true);

loadButton.setEnabled(true);

TheonPostExecute()methodhasnowfinisheditsexecutionandtheappisbacktopatientlywaitingfortheusertomakethenextframaccessrequestbypressingeithertheLoadorSavebutton.

Nowthatyouhaveseenallofthepiecesoftheframapp,whynotchangeittoaddnewfunctionality?Forachallenge,tryaddingacounterthatindicatestotheuserhowmanymorecharacterscanbeenteredintothesaveTexttextfieldbeforethe60-characterlimitisreached.Wehaveprovidedonepossibleimplementationofthisinthechapter4_challenge.tgzfile,whichisavailablefordownloadfromthePackt’swebsite.

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SummaryInthischapter,weintroducedyoutotheI2Cbus.YouconstructedacircuitthatconnectedanI2CFRAMbreakoutboardtotheBBB,andthenyoudidsomebasictestingonthecircuitusingi2cdetectfromi2c-toolstoensurethatthecircuitwasconstructedproperlyandthekernelisabletointeractwiththecircuitviathefilesystem.YoualsolearnedabouttheportionsofthePacktHALinit.{ro.hardware}.rcfileandDeviceTreeoverlaythatareresponsibleforconfiguringandmakingtheI2CbusandI2Cdevicedriversavailableforyourapp’suse.TheframappinthischapterdemonstratedhowtousetheAsyncTaskclasstoperformtime-intensivehardwareinterfacingtaskswithoutstallingtheapp’sUIthreadandtriggeringtheANRdialog.

Inthenextchapter,youwilllearnaboutthehigh-speedserialperipheralinterface(SPI)busanduseittointerfacewithanenvironmentalsensor.

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Chapter5.InterfacingwithHigh-speedSensorsUsingSPIInthepreviouschapter,youworkedwiththeI2CbustocommunicatewithanFRAMdevicethatrequiresfarmorecomplexcommunicationsthanthatofthesimpleon/offdigitalcommunicationsusedbyGPIOs.I2Cisverypowerfulandflexible,butitcanbequiteslow.

Inthischapter,youwilllearnhowtowriteanAndroidappthatusestheBBB’sSPIcapabilitiestoretrieveenvironmentaldatafromahigh-speedsensor.Wewillcoverthefollowingtopics:

UnderstandingSPIMultiplexingforSPIontheBBBRepresentingSPIdevicesintheLinuxkernelBuildinganSPIinterfacecircuitExploringtheSPIsensorexampleapp

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UnderstandingSPITheSerialPeripheralInterface(SPI)busisahigh-speed,serialbusoriginallydevelopedbyMotorola.Itspurposeistofacilitatepoint-to-pointcommunicationbetweenasinglemasterdeviceandoneormoreslavedevice.TheSPIbusistypicallyimplementedusingfoursignals:

LikeI2C,themasterontheSPIbussetsthepaceofcommunicationbetweenthemasterandtheslavebyproducingaclocksignal.WithSPI,thisclocksignaliscalledtheserialclock(SCLK).UnlikethebidirectionaldatabusofI2C,SPIusesdedicatedoutgoingandincomingdatalinesforeachdevice.UsingdedicatedlinesresultsinSPIbeingabletoachievecommunicationspeedsfarhigherthanthoseofI2C.Themastersendsdatatotheslaveviathemasterout,slavein(MOSI)signal,anditreceivesdatafromtheslaveviathemasterin,slaveout(MISO)signal.Theslaveselect(SS)signal,alsocalledchipselect(CS),tellstheslavedevicewhetheritshouldbeawakeandpayingattentionforanyclocksignalsonSCLKanddatabeingsenttoitviaMOSI.Therearevariantsonthisfour-wireSPIbusscheme,suchasathree-wireschemethatomitstheSS/CSsignal,buttheBBBusesafour-wireschemeforitsSPIbuses.

TheSPImasterandslavedevicesonanSPIbus

TheBBBcanactaseitheranSPImasterorslave,soitdoesnotlabelitsdatainputandoutputsignalsforSPIasMISOorMOSI.Instead,itusesthenamesD0andD1forthesesignals.IftheBBBactsasthemasterontheSPIbus,D0istheMISOsignalandD1istheMOSIsignal.IftheBBBactsastheslaveontheSPIbus,thesearereversed(D1isMISO,D0isMOSI).Forthisbook,theBBBwillalwaysbeactingastheSPImaster.

TipHowdoIrememberwhichBBBSPIsignalisinputandwhichisoutput?

ItcanbeconfusingtorememberwhichsignalisMISOandwhichisMOSIwhentheBBBusesthesignalnamesD0andD1.Onewaytorememberistothinkofthe0inD0asanO

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(forslaveoutput)andthe1inD1asanI(forslaveinput).IftheBBBistheSPImaster(whichwillalmostalwaysbethecase),thenD1istheslaveinputsignal(MOSI)andD0istheslaveoutputsignal(MISO).

ThemaximumSCLKspeedforSPIontheBBBis48MHz,butspeedsrangingfrom1MHzto16MHzarecommonlyused.Evenatthesereducedclockspeeds,SPIisfarsuperiortothe400KHzclockspeedofI2Cbuseswhenconsideringtheamountofrawdatathatcanbetransmittedeachsecond.OnlyonedevicecantransmitdataonanI2Cbusatanytime,butboththemasterandslavecantransmitdatasimultaneouslyonanSPIbusbecauseeachdevicehasadedicatedtransmissionsignal.

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MultiplexingforSPIontheBBBTheAM335XprocessoroftheBBBprovidestwoSPIbuses:SPI0andSPI1.BothbusesareaccessibleviatheP9header.Bydefault,noSPIbusesaremuxed.ThefollowingfigureshowseachofthepotentialpinsontheP9headerwhereSPIsignalscanbemuxedindifferentpinmuxmodes:

LocationsoftheSPIbusesontheP9headerwithdifferentpinmuxmodes

WhendecidinghowyouwouldlikeyourpinstobemuxedusingSPIinyourprojects,keepthefollowinginmind:

Whenindoubt,stickwithusingtheSPI0busmuxedtotheP9.17,P9.18,P9.21,andP9.22pins.TheSPI1channelconflictswiththeI2Cbususedbythecapemgr(P9.20)andaudiooutput(P9.28,P9.29,P9.31).BeawarethatmuxingthesepinstouseSPI1candisablesomeotherfunctionalitythatyouaredependinguponforafull-featuredAndroidsystem.

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Ifyouareusingothercapeboardsinyourprojects,makesurethatthesecapesdon’trequiretheuseoftheSPIbuses.OnlyonedevicecanexistoneachSPIbusunlessyouuseaGPIOpinandextralogiccircuitrytomanuallycontroleachSPIdevice’schipselectsignal.

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RepresentingSPIdevicesintheLinuxkernelTheLinuxkernelprovidesageneral-purposeSPIdrivernamedspidev.ThespidevdriverisasimpleinterfacethatabstractsmanyofthehousekeepingdetailsinvolvedinSPIcommunications.Thespidevdriverisexposedviathe/devfilesystemasthe/dev/spidevX.Yfile.MultipleversionsofthesespidevfilescanbepresentdependinguponthenumberofSPIbusesconfiguredintheDeviceTree.TheXvalueinthespidevfilenamereferstotheSPIcontrollernumber(1forSPI0and2forSPI1),andtheYvaluereferstotheSPIbusofthatcontroller(0forthefirstbusand1forthesecondbus).Fortheexamplesinthisbook,youwillonlybeusingthefirstSPIbusoftheSPI0controller,so/dev/spidev1.0istheonlyfilewithwhichPacktHALwillinteract.

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PreparingAndroidforSPIsensoruseInChapter2,InterfacingwithAndroid,youusedadbtopushtwoprebuiltfilestoyourAndroidsystem.Thesetwofiles,BB-PACKTPUB-00A0.dtboandinit.{ro.hardware}.rc,configureyourAndroidsystemtoenablethespidevkerneldevicedriverthathandlesSPIbusinterfacing,muxesthepinstoenabletheSPI0bus,andallowyourappstoaccessthem.

AsfarasSPIisconcerned,theBB-PACKTPUB-00A0.dtbooverlaymuxestheP9.17,P9.18,P9.21,andP9.22pinsintotheSPICS0,D1,D0,andSCLKsignals,respectively.InthePacktHAL.tgzfile,thesourcecodefortheoverlayislocatedinthecape/BB-PACKTPUB-00A0.dtsfile.Thecoderesponsibleformuxingthesetwopinsislocatedinthebb_spi0_pinsnodewithinfragment@0:

/*AllSPI0pinsarePULL,MODE0*/

bb_spi0_pins:pinmux_bb_spi0_pins{

0x1500x30/*P9.22,spi0_sclk,INPUT*/

0x1540x30/*P9.21,spi0_do,INPUT*/

0x1580x10/*P9.18,spi0_d1,OUTPUT*/

0x15c0x10/*P9.17,spi0_cs0,OUTPUT*/

Whilethissetsupthemuxing,itdoesn’tassignandconfigureadevicedrivertothesepins.Thefragment@2nodeperformsthiskerneldriverallocation:

fragment@2{

target=<&spi0>;

__overlay__{

#address-cells=<1>;

#size-cells=<0>;

status="okay";

pinctrl-names="default";

pinctrl-0=<&bb_spi0_pins>;

channel@0{

#address-cells=<1>;

#size-cells=<0>;

/*Kerneldriverforthisdevice*/

compatible="spidev";

reg=<0>;

/*Settingthemaxfrequencyto16MHz*/

spi-max-frequency=<16000000>;

spi-cpha;

Withoutdiggingintothefinedetails,therearethreesettingsinfragment@2thatareofinteresttoyou:

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pinctrl-0

compatible

spi-max-frequency

Thefirstispinctrl-0,whichtiesthisnodeofDeviceTreetothepinsmuxedinthebb_spi0_pinsnode.Thesecondiscompatible,whichspecifiestheparticularkerneldriver,spidev,thatwillhandleourhardwaredevice.Thelastisspi-max-frequency,whichspecifiesthemaximumallowablespeedforthisSPIbus(16MHz).16MHzisthemaximumfrequencyspecifiedforspidevintheDeviceTreeoverlaysprovidedwiththeBBB’skernelsource.

Thecustominit.{ro.hardware}.rcfilethatyoupushedtotheAndroidsystemdoesn’thavetodoanythingspecialforPacktHAL’sSPIinterfacing.Bydefault,BBBAndroiduseschmodtosetthepermissionsofthe/dev/spidev*filesto777(completeaccessforeveryone).Thisisnotasecurepracticesinceanyprocessonthesystemcanpotentiallyopenaspidevdeviceandbeginreadingandwritingtothehardware.Forourpurposes,though,havingthe/dev/spidev*filesaccessibletoeveryprocessisnecessarytoallowourunprivilegedexampleappaccesstotheSPIbus.

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BuildinganSPIinterfacecircuitNowthatyouhaveanunderstandingofwhereSPIdevicesareconnectedtotheBBBandhowtheLinuxkernelpresentsaninterfacetothesedevices,itistimetoconnectanSPIdevicetotheBBB.

AswementionedinChapter1,IntroductiontoAndroidandtheBeagleBoneBlack,youwillbeinterfacingwithasensorinthischapter.Tobespecific,wewillbeusingaBoschSensortecBMP183digitalpressuresensor.This7-pincomponentprovidespressuredatasamples(in16-to19-bitresolution)andtemperaturedatasamples(in16-bitresolution)forapplicationsusedfornavigation,weatherforecasting,andtomeasurechangesinverticalelevationandsoon.

Thisparticularchipisonlyavailableinalandgridarray(LGA),whichisasurfacemountpackagethatcanbedifficulttoworkwithwhenbuildingprototypecircuits.Luckilyforus,theAdaFruitbreakoutboardforthesensoralreadyhasthechipmounted,whichmakesprototypingsimpleandeasy.

Thesensorbreakoutboard(source:www.adafruit.com)

ThebreakoutboardlabelstheSCLKsignalasSCK,MOSIasSDI(serialdatain),MISOasSDO(serialdataout),andSSasCS(chipselect).Topowertheboard,a+3.3VsignalisconnectedtoVCCandagroundisconnectedtoGND.The3Vosignalofthebreakoutboardprovidesa+3.3Vsignalandisnotusedinourexamples.

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ThesensorcircuitinthischapterispartofamuchlargercircuitusedinChapter6,CreatingaCompleteInterfacingSolution.Ifyoubuildthecircuitasitispositionedinthediagram(towardsthemiddleofthebreadboard),youcansimplyleavethesensorbreakoutboardandwiresinplaceasyoubuildtheremainingcircuitsinthisbook.Thisway,itwillalreadybeconstructedandworkingwhenyoureachChapter6.

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ConnectingthesensorThefollowingfigureshowstheconnectionsbetweenthesensorbreakoutboardandtheBBB.ThesixmainSPIbussignals(+3.3V,ground,andtheSPISCLK,MISO,MOSI,andSS)aremadeusingthepinsoftheP9connector,sowehaveplacedthebreadboardontheP9sideoftheBBB.

Thecompletesensorinterfacingcircuit

Let’sgetstarted:

1. ConnectP9.1(ground)totheverticalgroundbusofthebreadboardandP9.3(3.3V)totheverticalVCCbusofthebreadboard.TheseconnectionsareidenticaltotheonesmadefortheGPIOandI2CbreadboardcircuitsyoucreatedinChapter3,HandlingInputsandOutputswithGPIOsandChapter4,StoringandRetrievingDatawithI2C.

2. ThefourSPIbussignals,SCLK,MISO(D0),MOSI(D1),andSSareontheP9.22,P9.21,P9.18,andP9.17pins,respectively.WiretheP9.22pintothepinmarkedSCKonthebreakoutboard,andwiretheP9.21pintothepinmarkedSDO.Then,wiretheP9.18pintothepinmarkedSDI,andwireP9.17tothepinmarkedCS.

3. WirethegroundbustotheGNDpinofthebreakoutboardandtheVCCbustotheVCCpinofthebreakoutboard.Leavethe3Vopinofthebreakoutboardunconnected.

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ThesensorbreakoutboardisnowelectricallyconnectedtotheBBBandisreadyforyouruse.Double-checkyourwiringagainstthediagramofthecompletesensorinterfacingcircuittoensurethateverythingisconnectedproperly.

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ExploringtheSPIsensorexampleappInthissection,youwillexaminetheexampleAndroidappthatperformstheSPIbusinterfacingonBBB.ThepurposeofthisapplicationistodemonstratehowtousePacktHALtoperformSPIreadsandwritesfromwithinanactualappusingasetofinterfacingfunctions.ThesefunctionsallowyoutosendandreceivedatabetweentheSPIbusmaster(theBBB)andtheSPIbusslave(theSPIsensor).Thelow-leveldetailsofthehardwareinterfacingareimplementedinPacktHAL,soyoucanquicklyandeasilygetyourappsinteractingwiththesensor.

BeforediggingthroughtheSPIapp’scode,youmustinstallthecodetoyourdevelopmentsystemandinstalltheapptoyourAndroidsystem.Thesourcecodefortheappandtheprecompiled.apkpackagesarelocatedinthechapter5.tgzfile,whichisavailablefordownloadfromPackt’swebsite.FollowthesameprocesstodownloadandaddtheapptoyourEclipseADTenvironmentthatwasdescribedinChapter3,HandlingInputsandOutputswithGPIOsandChapter4,StoringandRetrievingDatawithI2C.

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Theapp’suserinterfaceTheappusesaverysimpleUItointeractwiththesensor.Asitissosimple,theonlyactivitythattheapphas(bydefault)isMainActivity.TheUIconsistsofonlyonebuttonandtwotextviews.

Thesensorsampleappscreenpriortoreceivingitsfirstsetofsamplesfromthesensor

ThetoptextviewhasthetemperatureTextViewidentifierintheactivity_main.xmlfile,andthebottomtextviewhasthepressureTextViewidentifier.Thesetextviewswilldisplaythetemperatureandpressuredatathatisretrievedfromthesensor.ThebuttonwiththeSamplelabelhasthesampleButtonidentifier.ThisbuttonhasanonClick()methodcalledonClickSampleButton()thattriggerstheprocessofinterfacingwiththesensortosamplethetemperatureandpressuredataandthenupdatingthetextdisplayedinthetemperatureTextViewandpressureTextViewtextviews.

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CallingthePacktHALsensorfunctionsThesensorinterfacefunctionalityinPacktHALisimplementedinavarietyofCfunctionsinthejni/bmp183.cfilewithinthesensorapp’sproject.Thesefunctionsnotonlyinterfacewiththesensor,buttheyalsodoavarietyofconversionandcalibrationtasks.

Theframappinthepreviouschapterusedaspecifickerneldriver(the24c256EEPROMdriver)tointeractwiththeFRAMchip,sotheuser-space-interfacinglogicthatisimplementedinPacktHALisquitesimple.PacktHALdoesnotuseasensor-specifickerneldrivertocommunicatewiththesensor,soitmustusethegenericspidevdrivertocommunicate.ItisuptoPacktHALtoprepare,send,receive,andinterprettheindividualbytesofeverySPImessagethatisgoingtoorfromthesensor.

WhilethereareanumberoffunctionsinPacktHALtohandlethesetasks,onlyfourofthosefunctionsareusedbyoutsidecodetointeractwiththesensor:

openSensor()

getSensorTemperature()

getSensorPressure()

closeSensor()

Theprototypesforthesefunctionsarelocatedinthejni/PacktHAL.hheaderfile:

externintopenSensor(void);

externfloatgetSensorTemperature(void);

externfloatgetSensorPressure(void);

externintcloseSensor(void);

TheopenSensor()functioninitializesaccesstotheSPIbusbyopening/dev/spidev1.0andmakingseveralioctl()callstoconfiguretheSPIbus’communicationparameters(suchastheclockrateofSCLK).

Oncethisconfigurationisperformed,allSPIcommunicationsperformedinsideofPacktHALwillusethisbus.CallingthecounterpartcloseSensor()functionclosesthe/dev/spidev1.0file,whichshutsdowntheSPIbusandfreesitforusebyotherprocessesonthesystem.ThegetSensorTemperature()andgetSensorPressure()functionsperformallofthepreparationoftheSPImessages,SPIcommunication,andsampleconversionlogicrequiredtofetchandconvertthesamplesretrievedfromthesensor.

NoteIfyouwereusingaspecializedkerneldriverdesignedtotalktothespecificsensorthatweareusing,thenthesensor-readinglogicinsidethePacktHALcodewouldbeverysimple(onlyoneortwoioctl()calls).ItisalwaysabalancebetweenplacingHALcodelogicintothekernelversuskeepingitinuserspace.Themorecodethatyoucanpushintothekernel,thesimplerandfastertheuserspacecodewillbe.However,itcanbeverydifficulttodevelopkernelcode,soyoumuststrikeabalancebetweenwhatiseasiesttoimplementandwhatwillprovideyouwiththeperformancenecessaryforyourhardwaredesign.

Thesensorapphasseveralsimilaritiestoappsfrompreviouschapters.Liketheframapp

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fromChapter4,StoringandRetrievingDatawithI2C,thesensorappusesitsownclassderivedfromAsyncTask,HardwareTask,tomakeJNIcallstotheunderlyingsensor-interfacingfunctionsfromPacktHAL.InterfacingwiththehardwareistriggeredbytheonClick()handlerofabuttonpressedbytheapp’suser,similartowhatboththegpioandframappsdo.

MuchliketheGPIO-interfacingfunctionsfromPacktHALthatyouusedinChapter3,HandlingInputsandOutputswithGPIOsandChapter4,StoringandRetrievingDatawithI2C,thesensor-interfacingmethodsinHardwareTaskareveryfasttoexecute.ItisnotactuallynecessarytoexecutethesemethodsfromwithinaseparatethreadsincetheyarenotlikelytotakesolongtoexecutethattheywilltriggertheANRdialog.However,SPIcanbeusedforawidevarietyofdevices,anditispossibletoneedlongerperiodsoftimetosendlargeamountsofdata,sobettersafethansorry.

TipWhenshouldIuseanAsyncTaskforhardwareinterfacing?

Theshortanswertothisis“allofthetime”.WedidnotwanttodistractyouwiththedetailsoftheAsyncTaskclasswhenyouwereworkingwithGPIOsinChapter3,HandlingInputsandOutputswithGPIOs,sothegpioappmademethodcallstoPacktHALfunctionsintheonClick()buttonhandlers.However,thegeneralruletofollowistoalwaysuseAsyncTasktoperformanysortofI/O.I/Oisnotoriouslyslow,soanyI/O(networking,accessingfilesondisk,andhardwareinterfacing)shouldreallytakeplaceinitsownthreadviaAsyncTask.

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UsingtheHardwareTaskclassLikethegpioandframapps,theHardwareTaskclassinthesensorappprovidesfournativemethodsthatareusedtocallthePacktHALJNIfunctionsrelatedtosensorhardwareinterfacing:

privatenativebooleanopenSensor();

privatenativefloatgetSensorTemperature();

privatenativefloatgetSensorPressure();

privatenativebooleancloseSensor();

AsthedetailsoftheSPIbussetupprocessareencapsulatedwithinthePacktHALfunctionsandhiddenfromtheapp,thesemethodstakenoparameters.TheysimplycalltheirPacktHALcounterpartsviathePacktHALJNIwrapperfunctions.

ThethreadcontextsinwhichtheHardwareTaskmethodsandthePacktHALfunctionsareexecuted

Inthesensorapp,theonClick()handlerforthesamplebuttonintheMainActivityclassinstantiatesanewHardwareTaskmethod.Immediatelyafterthisinstantiation,thepollSensor()methodofHardwareTaskiscalledtorequestacurrentsetoftemperatureandpressuredatafromthesensor:

publicvoidonClickSampleButton(Viewview){

hwTask.pollSensor(this);

ThepollSensor()methodbeginsthehardware-interfacingprocessbycallingtheexecution()methodofthebaseAsyncTaskclasstocreateanewthread:

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publicvoidpollSensor(Activityact){

execute();

Theexecute()methodofAsyncTaskcallstheonPreExecute()methodthattheHardwareTaskusestoinitializetheSPIbusviaitsopenSensor()nativemethod.ThesampleButtonmethodisalsodisabledforthedurationofthethreadtopreventthepossibilityofmultiplethreadstryingtousetheSPIbustotalktothesensorsimultaneously:

Log.i("HardwareTask","onPreExecute");

if(!openSensor()){

isDone=true;

//DisabletheButtonwhiletalkingtothehardware

sampleButton.setEnabled(false);

OncetheonPreExecute()methodfinishes,theAsyncTaskbaseclassspinsanewthreadandexecutesthedoInBackground()methodwithinthatthread.Forthesensorapp,thisistheproperplacetoperformanySPIbuscommunicationrequiredtogetthecurrenttemperatureandpressuresamplesfromthesensor.ThegetSensorTemperature()andgetSensorPressure()nativemethodsoftheHardwareTaskclassfetchthelatestsamplesfromthesensorviathegetSensorTemperature()andgetSensorPressure()functionsinPacktHAL:

protectedBooleandoInBackground(Void…params){){

if(isDone){//Wasthehardwareneveropened?

Log.e("HardwareTask","doInBackground:Skippinghardware

interfacing");

returntrue;

Log.i("HardwareTask","doInBackground:Interfacingwithhardware");

temperature=getSensorTemperature();

pressure=getSensorPressure();

}catch(Exceptione){

AfterdoInBackground()iscomplete,theAsyncTaskthreadterminates.ThistriggersthecallingofdoPostExecute()fromtheUIthread.Now,astheapphasfinisheditsSPIcommunicationtasksandreceivedthelatesttemperatureandpressurevaluesfromthesensor,itistimetoclosetheSPIconnection.ThedoPostExecute()methodclosestheSPIbususingthecloseSensor()nativemethodoftheHardwareTaskclass.ThedoPostExecute()methodthenalertstheMainActivityclassofthenewdatareceivedfromthesensorviatheupdateSensorData()method,anditre-enablestheSamplebutton

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ofMainActivity:

if(!closeSensor()){

Toasttoast=

Toast.makeText(mCallerActivity.getApplicationContext(),

"Sensordatareceived",Toast.LENGTH_SHORT);

toast.show();

((MainActivity)mCallerActivity).updateSensorData(temperature,

pressure);

//ReenabletheButtonaftertalkingtothehardware

sampleButton.setEnabled(true);

TheMainActivityclass’updateSensorData()methodisresponsibleforupdatingthedisplayedvaluesinthetemperatureTextViewandpressureTextViewtextviewstoreflectthenewestreceivedsensorvalues:

publicvoidupdateSensorData(floattemperature,floatpressure){

Toasttoast=Toast.makeText(getApplicationContext(),

"Displayingnewsensordata",Toast.LENGTH_SHORT);

TextViewtv=(TextView)findViewById(R.id.temperatureTextView);

tv.setText("Temperature:"+temperature);

tv=(TextView)findViewById(R.id.pressureTextView);

tv.setText("Pressure:"+pressure);

toast.show();

Atthispoint,executionofthesensorapphasreturnedtoitsidlestate.IftheuserclicksontheSamplebuttononcemore,anotherHardwareTaskinstanceisinstantiatedandtheopen-sample-closeinteractioncycleofthehardwarewilloccuragain.

Nowthatyouhaveseenallofthepiecesofthesensorapp,whynotchangeittoaddsomenewfunctionality?Forachallenge,tryaddingacounterthatshowshowmanysampleshavebeentakensofarandtheaveragetemperatureandpressurefromallofthesamplestaken.Wehaveprovidedonepossibleimplementationofthisinthechapter5_challenge.tgzfile,whichisavailablefordownloadfromPackt’swebsite.

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SummaryInthischapter,weintroducedyoutotheSPIbus.YouconstructedacircuitthatconnectedanSPIpressureandtemperaturesensorbreakoutboardtotheBBB,andyoulearnedabouttheportionsofthePacktHALinit.{ro.hardware}.rcfile’sDeviceTreeoverlaythatareresponsibleforconfiguringandmakingtheSPIbusandspidevdevicedriveravailableforyourapp’suse.ThesensorappinthischapterdemonstratedhowcomplextasksintheHALcanbehiddenfromtheappusingasmallsetoffunctionsthathidethelow-leveldetails.ThesesimplifiedPacktHALfunctioncallscanbemadefromaclassderivedfromAsyncTasktoperformmorecomplexinterfacingtaskssimplyfromwithinanapp.

Inthenextchapter,youwilllearnaboutcombiningGPIO,I2C,andSPItogetherintoanappcapableofprovidingacompletehardwaresolutionthatusesalong-livedhardware-interfacingthread.

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Chapter6.CreatingaCompleteInterfacingSolutionInthepreviouschaptersofthisbook,youinterfacedwithdevicesusingGPIOs,I2C,andSPI.YouusedAsyncTaskstoperformhardwareinterfacinginbackgroundthreads,andyouexploredhowtostructureanapptointeractwiththosethreads.

Inthischapter,youwillbringalloftheseconceptstogethertocreateacircuitthatusesallthreeinterfacingmethods,andyouwillexploreanappthatusesalltheinterfacestogethertomakeacomplexsystem.

BuildingthecompleteinterfacecircuitExploringthefinalexampleapp

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BuildingthecompleteinterfacecircuitTheinterfacingcircuitusedinthischapterisacombinationofeachofthecircuitsdescribedinchapters3,4,and5.Ifyouhavesuccessfullyconstructedthecircuitsfromthepreviouschapters,youalreadyhaveagoodunderstandingofhowthecircuitinthischapterwillbeputtogether.Leaveanypreviouslyconstructedcircuitsonthebreadboardtosaveyousomeeffortifyouhaveconstructedthosecircuitsbycloselyfollowingtheinstructionsfromearlierchapters.

Thefollowingdiagramshowstheconnectionsbetweenthesensorbreakoutboard,FRAMbreakoutboard,LED,pushbuttonswitch,resistor,andtheBBB.Revisitchapters3,4,and5fortheexactdetailsonhowtoconstructtheGPIO,FRAM,andSPIportionsofthecircuit,ifyouhavenotyetdoneso.

ThecompletehardwareinterfacingcircuitthatusescomponentswhichinterfacewiththeBBBusingtheGPIOs,I2C,andSPIcomponents

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ExploringthecompleteexampleappInthissection,youwillexaminetheexampleAndroidappthatperformsGPIO,I2C,andinterfacingonBBB.ThepurposeofthisapplicationistodemonstratehowtousePacktHALtoperformavarietyofhardwaretasksfromwithinanactualappusingasetofinterfacingfunctions.Unlikethepreviousexampleapps,whichtakeinputfromtheuser,thisapptakesallofitsinputdirectlyfromthehardwareitself.Thisrequiresaslightlymorecomplexapproachthanthattakenbytheearlierapps.

Beforediggingthroughtheapp’scode,youmustinstallthecodeonyourdevelopmentsystemandinstalltheapponyourAndroidsystem.Thesourcecodefortheappaswellastheprecompiled.apkpackageislocatedinthechapter6.tgzfile,whichisavailablefordownloadfromthePacktwebsite.FollowthesameprocesstodownloadandaddtheapptoyourEclipseADTenvironment,whichwasdescribedinChapter3,HandlingInputsandOutputswithGPIOs.

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Theapp’suserinterfaceLaunchthecompleteappontheAndroidsystemtoseetheapp’sUI.Ifyouareusingatouchscreencape,youcansimplytouchthecompleteapp’sicononthescreentolaunchtheappandinteractwithitsUI.IfyouareusingtheHDMIforvideo,connectaUSBmousetotheBBB’sUSBportandusethemousetoclickonthesensorappicontolaunchtheapp.

TheappusesaverysimpleUIthatdisplaystwotextviewsinasingleactivity,whichisMainActivitybydefault.

Thecompleteappscreenpriortoreceivingitsfirstsetofsamplesfromthesensor

TherearenobuttonsorotherUIelementsinthisappbecausetheonlyinteractiontheuserhaswiththeappisthroughthecircuit’sGPIOpushbuttonswitch.Whentheuserpressestheswitch,theappperformsaseriesofhardwareinterfacingactions:

TheLEDwillturnontonotifytheuserthattheswitchhasbeenrecognizedaspressed.TheLEDwillremainlituntilalleventsonthelisthaveoccurred.WhiletheLEDison,anyfurtherswitchinputisignored.TemperatureandpressuresamplesarefetchedfromthesensorandwrittenintotheFRAM.TheFRAMisreadtoretrievethestoredtemperatureandpressuresamplevalues.Thevaluesforthetemperatureandpressuresamplesaredisplayedintheapp’sUI.A1-seconddelaywilloccur.TheLEDwillturnoff,andtheswitchcanonceagainbepressedtotriggeranothersample-store-retrieve-displaycycle.

Thevarietyofactionsperformedbytheappmakesitsinterfacingbehaviormorecomplexthanwhatyousawinthepreviousexampleappsinthisbook.Ratherthanfocusingoninterfacingwithasinglehardwarecomponent,thisappinterfaceswiththeGPIO,I2C,andSPIdevicesatthesametimetoprovideacompletesensorsolutionwithpersistentstorage.However,itisbasedonthesamebasicinterfacingconceptsthattheotherexampleappsinthisbookhavedemonstrated.

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UnderstandinghardwarepollinginanappTheearlierappseitherusedtheonClick()handlerofabuttontointerfacedirectlytothehardware(GPIOs)ortriggeredtheinstantiationandexecutionofAsyncTask(I2CandSPI)tointerfacewiththehardware.Inbothofthesecases,interfacingwiththehardwareisinitiatedbyasoftwareevent,theonClick()handler’sexecution,withintheapp.

Inthischapter’sapp,however,wewanttotriggerthehardwareinterfacinginresponsetothehardwareeventcreatedbytheswitchbeingpressed.Listeningforhardwareeventsisanimportantpartofinterfacingbecauseitallowsthehardwaretotelluswheneventsofinterestoccur.Wedonotalwayshavetheluxuryoftellingthehardwaretodosomethingandexpectingthehardwaretodoit.Sometimes,thehardwareneedstonotifyusthataneventhasoccurred.

Wheninterfacingwithhardwarefromakerneldriver,thedrivercanregistertobenotifiedofahardwareeventofinterestbyregisteringfornotificationofthetimeahardwareinterruptoccurs.Ahardwareinterrupttellsthekernelimmediatelythatsomethingnoteworthyhashappenedwiththehardware,andthekernelwillstopwhatitisdoingtoallowtheappropriatekerneldrivertohandletheinterrupt.

Becauseourappsareperformingtheirhigher-levelinterfacinglogicfromuserspace,weareunabletoregisterforaninterrupttonotifyusthetimeaneventofinterestoccurs.Thishardwareeventcanhappenasynchronouslyatanytime,sotheappmustcontinuallypoll,orcheck,thestateoftheswitchtodeterminewhetherithasbeenpressedornot.AppstypicallydonotpollforeventsbecausetheyrelyonbeingnotifiedbytheAndroidframeworkwhensomethinginterestinghappens,butwhenanappisperforminghardwareinterfacingwithouttheassistanceofamanager,pollingbecomesnecessary.

Thefasteranapppollsthehardware,thelesserthechancethattheappwillmisstheoccurrenceofthehardwareeventofinterest.However,constantlypollinginatightloopisabadideabecauseitwillconstantlyconsumeCPUcycles(andbatterylifeinmobiledevices),whichcanbebetterspentelsewhere.Ifyouincludepollinginyourapps,youmustfindagoodbalancebetweenperformanceandusageofresources.

ItisabadideatoplaceapollingloopinsidethecontextoftheUIthread.RememberthatspendingtoomuchtimeexecutingwithinahandlermethodintheUIthreadcontextwillcauseAndroidtotriggertheANRdialog.Toavoidthisproblem,anappmustinstantiateAsyncTask,whichperformsthehardwarepollinginabackgroundthread.TheearlierexampleappsinthisbookusedanAsyncTaskthreadtoperformcommunicationwithhardwaredevices,buttheAsyncTaskthreadwasshort-lived.TheAsyncTaskthread’sbackgroundthreadwasonlyactivewhileitwasinterfacingwiththehardware.Oncetheinterfacingwascompleted,thethreadterminated.Iftheappneededtocommunicatewiththehardwareoncemore,anewAsyncTaskthreadwasinstantiatedandstartedviaitsexecute()method.

BecauseourappmustuseAsyncTasktocontinuallypolltheswitchtocheckforuserinput,theAsyncTaskthreadusedintheappisalong-livedthread.Insteadofinstantiating

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andcallingexecute()forAsyncTaskonlyatthemomentswhentheappneedstocommunicatewiththehardware,theappinstantiatesandexecutesAsyncTaskwheneverittransitionstotheresumedstate.TheAsyncTaskthreadcontinuesexecutinginthebackgrounduntiltheapptransitionstothepausedstate.

NoteTolearnthedetailsofhowAndroidappactivitiestransitionamongthevariouslifecyclestates,suchastheresumedstateandpausedstate,refertotheofficialAndroiddeveloperdocumentationathttp://developer.android.com/training/basics/activity-lifecycle/index.html.

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UsingAsyncTaskwithlong-livedthreadsWehavealreadyusedfourmethodsintheAsyncTaskbaseclassinourpreviousexampleapps.ThesemethodsareusedinAsyncTaskstoimplementbothshort-livedandlong-livedthreads:

onPreExecute()

doInBackground()

onPostExecute()

execute()

Inthischapter,youwillusefiveadditionalmethodsoftheAsyncTaskclass.Theseadditionalmethodscanbeusedforshort-livedthreadstomakethemmorepowerful,andtheywillalmostalwaysbeusedinlong-livedbackgroundthreadstocommunicatewiththethreadandreceivefeedbackfromitwhileitruns:

cancel()

onCancelled()

isCancelled()

publishProgress()

doPublishProgress()

Thecancel(),onCancelled(),andisCancelled()methodsareusedtostopthecurrentlyexecutingAsyncTaskmethodwhentheMainActivityclassofourappleavestheresumedstate.Thecancel()methodiscalledfromwithintheUIthreadcontexttonotifytheAsyncTaskclassthatithasbeencanceledandshouldstopitsexecution.Callingcancel()triggersthecallingoftheonCancelled()methodwithintheAsyncTaskthreadcontext.ThenonCancelled()givestheAsyncTaskclassachancetoperformanynecessarycleanuptasks.TheisCancelled()methodcanbecalledatanytimefromwithintheAsyncTaskthreadcontexttodeterminewhethercancel()andonCancelled()havebeencalled.ThismethodisusuallycalledfromwithinaloopinsideofthedoInBackground()method.

ThepublishProgress()anddoPublishProgress()methodsallowtheAsyncTaskthreadtonotifytheUIthreadofanyinformationthatshouldbedisplayedtotheuserviatheapp’sUI.Forexample,ifanAsyncTaskthreadiscopyingalargefilefromthenetwork,thesetwomethodsnotifytheUIthreadhowmuchofthefilehasbeencopiedandtheestimatedtimeremainingtotransfertheremainderofthefile.TheUIthreadcanthenupdatetheUIwiththisinformationtokeeptheapp’suserinformedoftheAsyncTaskthread’sprogress.

ThesefivenewAsyncTaskmethodswerenotusedintheexampleappsinearlierchaptersbecausethoseappsusedAsyncTaskmethodsthatwereshort-livedthreadsandwhichupdatedthescreenfromtheonPostExecute()method.TheonPostExecute()methodexecutedwithintheUIthread,sotherewasnoneedtousepublishProgress()anddoPublishProgress()inthoseapps.TheAsyncTaskthreadsinthoseappsalsoexecutedwhiletheappwasinaresumedstate,andthethreadsweresoshort-livedthatitwasnotnecessarytousecancel()oronCancelled()toterminatethethreads’execution.Because

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thoseappsdidnotusealoopwithintheirdoInBackground()methods,itwasnotnecessarytouseisCancelled().

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UsingtheHardwareTaskclassSimilartotheexampleappsinpreviouschapters,thecompleteappusesaHardwareTaskclassthatisderivedfromAsyncTask.AllofthehardwareinterfacingisperformedviathemethodsinHardwareTask.

ThethreadcontextsinwhichtheHardwareTaskmethodsandthePacktHALfunctionsareexecuted.TheJNIfunctionsinthisimagehavehadtheirfunctionnameprefixesshortened

toHardwareTask.

TheHardwareTaskclassforthesensorappprovidessevennativemethodsthatareusedtocallthePacktHALJNIfunctionsrelatedtoGPIO,FRAM,andsensorhardwareinterfacing:

privatenativebooleanopenHardware();

privatenativebooleanpollButton();

privatenativebooleanchangeLED(booleanlit);

privatenativebooleanreadSensor();

privatenativefloatgetSensorTemperature();

privatenativefloatgetSensorPressure();

privatenativebooleancloseHardware();

BecausemostofthedetailsofthehardwareinterfacingareencapsulatedwithinthePacktHALfunctionsandhiddenfromthecompleteapp,allbutoneofthesemethodsacceptnoparametersatall.TheysimplycalltheirPacktHALcounterpartsviathePacktHALJNIwrapperfunctions.TheexceptiontothisisthechangeLED()method,whichtakesasingleparametertospecifywhethertheLEDshouldbeturnedonoroff.

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Inthecompleteapp,theonResume()methodoftheMainActivityclassinstantiatesanewHardwareTaskclasswhenMainActivitychangestotheresumedstate:

publicvoidonResume(){

super.onResume();

//Createourbackgroundhardwarecommunicationthread

hwTask.pollHardware(this);

ThepollHardware()methodbeginsthehardwareinterfacingprocessbycallingthebaseAsyncTaskclassexecution()methodtocreateanewthread:

publicvoidpollHardware(Activityact){

execute();

TheonPause()methodoftheMainActivityclasshaltstheAsyncTaskclass’sexecutionwhentheMainActivityclasschangestothepausedstate:

publicvoidonPause(){

super.onPause();

//Releasethehardwarewhentheappispaused

if(hwTask!=null){

hwTask.cancel(true);

hwTask=null;

Thecancel()methodoftheAyncTaskbaseclassbeginstheprocessofcancelingtheexecutingAsyncTaskthreadbycallingtheonCancelled()methodinHardwareTask.InadditiontonotifyingtheAsyncTaskbaseclassthattheexecutionhasbeencanceled,theisDoneBooleanflagissetintheHardwareTaskclass:

protectedvoidonCancelled(){

Log.i("HardwareTask","Cancelled.");

isDone=true;

OnceMainActivityhastransitionedtotheresumedstate,thepollHardware()methodofHardwareTaskbeginstheAsyncTaskthread’sexecution.InonPreExecute(),theisDoneflagisreset,andtheGPIO,I2C,andSPIdevicesareallinitializedviatheopenHardware()method.Ifthehardwareissuccessfullyinitialized,theLEDisthenturnedoffviaachangeLED()call:

Log.i("HardwareTask","onPreExecute");

isDone=false;

if(!openHardware()){

isDone=true;

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}else{

changeLED(false);

AfteronPreExecute()hascompleted,theAsyncTaskbackgroundthreadbeginsrunning.ThedoInBackground()methodbeginsitsexecution.Becausethisisalong-livedthread,thereisawhileloopinsidedoInBackground()thatwillcontinuetoexecuteuntilthethreadiscanceledbythemainUIthread:

protectedBooleandoInBackground(Void…params){

//Pollthebuttonuntilanerrorordone

while(!isDone&&!isCancelled()){

Theloopbeginsbypollingthestateofthepushbuttonswitch.Iftheswitchispressed,thehardwareinterfacinglogicwillbegincommunicatingwiththeFRAMandsensor.Iftheswitchisnotpressed,thentheinterfacinglogicisskipped.Inbothcases,aslightdelayisaddedviaaThread.sleep()methodcalltogivethebackgroundthreadanopportunitytosleepandallowotherthreadstorun.Thislimitstheresourceconsumptionofthebackgroundthreadandgivesotherprocessesandthreadsanopportunitytorun:

while(!isDone&&!isCancelled()){

if(pollButton()){

Thread.sleep(100);

returnfalse;

IfthepollButton()methodstatesthatthebuttonispressed,thehardwareinterfacinglogicbeginsexecuting.ThiscallsthevariousnativemethodsthatinvokethePacktHALJNIfunctions.

First,changeLED()turnsontheLEDtolettheuserknowthatasampleisabouttobetaken:

if(!changeLED(true)){

Log.e("HardwareTask","UnabletoturnLEDon");

Next,thesensorsampleistakenandtheresultisstoredintheFRAM.ThereadSensor()nativemethodinteractswiththesensortoretrievethesampledata,andthenstoresthetemperatureandpressuresamplesinthefirsteightbytesofthememoryoftheFRAM:

if(!readSensor())

Log.e("HardwareTask","Unabletoreadsensor");

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NoteThetemperaturedataisstoredasa4-bytefloatinthefirstfourbytesoftheFRAM,andthepressuredataisstoredasa4-bytefloatinthesecondfourbytesoftheFRAM.Ifyouareinterestedinthedetailsofhowthisisimplementedinthenativecode,takealookattheJava_com_packt_complete_HardwareTask_readSensor()functioninthejni/jni_wrapper.cfileinPacktHAL.

Afterthat,theFRAMisaccessedtoretrievethetemperatureandpressuresamples:

temperature=getSensorTemperature();

pressure=getSensorPressure();

Finally,themainUIthreadisupdatedwiththenewsampledataviathepublishProgress()method.Thethreadsleepsfor1second,andthentheLEDturnsoff.Atthispoint,thepollButton()checkiscompleteandthewhileloopbeginsagain:

publishProgress();

Thread.sleep(1000);

if(!changeLED(false)){

Log.e("HardwareTask","UnabletoturnLEDoff");

}//EndofpollButton()check

ThepublishProgress()methodtriggerstheonProgressUpdate()methodofHardwareTask,whichexecutesintheUIthread.TheonProgressUpdate()methodcallstheMainActivityclassupdateSensorData()method:

protectedvoidonProgressUpdate(Void…values){

((MainActivity)mCallerActivity).

updateSensorData(temperature,pressure);

ThisupdateSensorData()methodintheMainActivityclassupdatestheapp’sUIandprovidesaToastmessagetotheuser:

publicvoidupdateSensorData(floattemperature,floatpressure){

Toasttoast=Toast.makeText(getApplicationContext(),

"Updatingsensordata",Toast.LENGTH_SHORT);

TextViewtv=(TextView)findViewById(R.id.temperatureTextView);

tv.setText("Temperature:"+temperature);

tv=(TextView)findViewById(R.id.pressureTextView);

tv.setText("Pressure:"+pressure);

toast.show();

ThemainpollingwhileloopintheHardwareTaskclass’doInBackground()methodwilleventuallyexitasaresultofeitherthehardwareinterfacingfailingtoinitializeorthebaseAsyncTaskmethodbeingcanceledbyMainActivity.Oncetheloophasfinished,doInBackground()willexitandtheAsyncTaskbackgroundthreadwillterminate.TheonPostExecute()methodwillthenperformanycleanupofitemsrequired,suchas

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shuttingdownthehardwareinterfacing:

if(!closeHardware()){

TheHardwareTaskinstancehasnowcompleteditsbackgroundthread.IftheMainActivityreturnstotheresumedstate,anewHardwareTaskinstancewillbeinstantiated.ThisHardwareTaskinstancewillcreateanotherlong-livedbackgroundthread,andthehardwareinterfacingprocesswillrepeatitself.

Nowthatyouhaveseenallofthepiecesofthecompleteapp,whynotchangeittoaddsomenewfunctionality?Forachallenge,trychangingtheapptocontinuallytakesamplesoncethebuttonhasbeenpressed.Stoptakingsamplesifthebuttonishelddownforashortperiodoftime.Wehaveprovidedonepossibleimplementationofthisinthechapter6_challenge.tgzfile,whichisavailablefordownloadfromthePacktwebsite.

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SummaryInthischapter,weintroducedtheconceptoflong-livedthreadsforhardwareinterfacing.YouconstructedacircuitthatconnectedtheGPIOpushbuttonswitch,GPIOLED,FRAMdevice,andtemperatureandpressuresensorstotheBBB.Unliketheexampleappsinthepreviouschapters,theexampleappinthischapterusedpollingtocontinuallymonitorthestateofthehardware.YoualsoexploredusingfiveadditionalmethodsoftheAsyncTaskclassforcommunicationandcontrolbetweenthebackgroundthreadandthemainUIthreadofyourapp.

NowthatyouhavelearnedmanyofthebasicconceptsofhardwareinterfacingwithAndroidusinganapp,itistimetolookatthebiggerpictureandseehowtoturnyourprototypedsolutionintoamorepermanentsolution.

Inthenextchapter,youwilllearnaboutintegratingyoursolutionwiththeAndroidframework,combiningyoursolutionwithothercapesavailablefortheBBB,andotherinterfacesthatyoucanuseforyourfutureinterfacingprojects.

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Chapter7.WheretoGofromHereInthepreviouschapter,weexaminedhowanAndroidappcaninterfacewithGPIO,I2C,andSPIatthesametimetoprovideacompletehardware-interfacingsolution.WhileyoumightthinkthatthiscoversmostoftheproblemsofhardwareinterfacingunderAndroid,therearestillmanyotherfactorstoconsider.

IntegratingyoursolutionintoAndroidCombiningyourhardwarewithotherhardwareExploringtheBBB’sotherinterfaces

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IntegratingyoursolutionwithAndroidTheBBBoffersawidevarietyofhardwarefeatures,andtheparticularfeaturesthatyouuseinyourprojectswillvaryasyouchangethecapesandoverlaysusedwithinyoursystem.Whilethisgivesyoualotofflexibilityduringprototyping,youmighteventuallyreachapointwhereyouwillfinalizeyourcustomhardwaredesigntoasingle,staticconfigurationanddecidetomakeitapermanentAndroid-basedsolution.

TheexamplesinthisbookmakethedesigndecisionofhavingappsdirectlyaccessthehardwareoftheBBB.Whilethisapproachmakescreatinghardware-interfacingAndroidappssimple,itisnotanidealapproach.Onceyouhaveahardwaredesignthatyoulikeandsoftwarethatproperlyinterfaceswiththehardware,itistimetofullyintegrateyoursolutionwithAndroid.Dependinguponjusthowcomplexyourhardwaresolutionis,youmightendupcreatingcustomkerneldevicedrivers,orevenmodifyingthemanagerswithintheAndroidOSframework!

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CreatingacustomkernelandDeviceTreeThefirststeptocreatingapermanentAndroidsolutionistoensurethateverythingontheLinuxsideofthesystemisasitshouldbe.Thismeansthatallhardwaresupport(suchasLinuxkerneldriversneededforyourproject)shouldbeenabledinthekernelandconfiguredandallocatedwithinthekernel’sDeviceTree(forpinmuxingandresourceallocation).Ideally,everythingthatyouneedwillbestaticallybuiltdirectlyintothekernelandDeviceTree.Thiseliminatestheneedtoloadoverlaysandkernelmodulesforyoursolutionviaexplicitcommandsexecutedfromwithintheinit.{ro.hardware}.rcfile.

OuradviceforpreparingthekernelspaceaspectsofyourprojectistodeveloptheseitemsfromwithinLinux.TheLinuxenvironmentprovidesfarmoretoolsforkerneldriverdevelopmentanddebugging,andyou’llbeabletoquicklyandeasilybuildstandaloneuserspacebinariesthatinteractwithcustomandexistingkerneldriversviatheopen(),read(),write(),andioctl()functioncalls.Thecode-compile-test-debugcycleofLinuxuserspacebinariescanbeperformedveryquicklybecauseafulldevelopmenttoolchain,includingcompilersanddebuggers,areavailableunderLinux.UnderAndroid,youmustbuildsuchtestbinariesusingtheAndroidNDKonyourdevelopmentmachineandthenuseadbtopushthemtoanAndroidsystemfortest.Thismakesthedevelopmentcyclemuchslowerandmoredifficult.

DevelopingastaticDeviceTreeforyoursolutionrequiresasimilarprocess.TheDeviceTreeanditsoverlaysarecompiledusingthedtctool,whichisavailableunderLinux,butnotAndroid.UsingstandardLinuxkerneldebuggingtechniques,youcandevelopandtroubleshootanoverlaythatmuxesthepinsforyourprojectandallocatesthenecessarykerneldriverstothesepins.Onceyouroverlayisworkingproperly,youcanintegratetheoverlayintotheDeviceTreepermanently.

TipWherecanIlearnmoreaboutLinuxdevelopmentfortheBBB?

TherearemanytutorialsandresourcesavailableonthewebtohelpyoulearnaboutdevelopingLinuxsoftwareandDeviceTreeoverlaysfortheBBB.ThebestresourcethatwecanrecommendtoyouistheseriesofBeagleBonevideotutorialscreatedbyDerekMolloy.ThesetutorialscovertopicssuchasthesetupandconfigurationofaC/C++developmentenvironment,debugging,DeviceTreeoverlaycreation,andtroubleshooting.Theyalsohaveavarietyofcodeandcircuitexamplestohelpgetyoustarted.YoucanwatchthesetutorialsfromtheBeagleBonesectionofDerek’swebsiteathttp://derekmolloy.ie/beaglebone.

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AddinghardwarecommunicationintothekernelWhileinterfacingdirectlywithGPIOsandtheI2CandSPIbusesisconvenient,itisnotthemostefficientwaytointerfacewithhardware.TheI2CFRAMexampleinChapter4,StoringandRetrievingDatawithI2C,usesthe24c256kerneldrivertohandlelow-leveldetailsofcommunicationwiththeFRAMchip.CanyouimaginehowdifficultitwouldbetoimplementeverysingledetailneededtodirectlyinterfacewiththeFRAMchip?AsidefromhavingtoknoweverydetailofthecommunicationprotocolbetweentheBBBandtheFRAMchip,suchprotocolscanalsorequirestricttimingguaranteesthataredifficultorimpossibletomeetfromuserspace.

Incaseswhereuserspaceinterfacingwithhardwareisinfeasible,usingakerneldriverisnecessary.Kerneldriversencapsulatethedetailsofcommunicatingwithaspecificpieceofhardware.Thissimplifiesyourinterfacingappsbykeepingthesedetailsoutsideyourapp’simplementation.Kerneldriversalsoprovidemuchstrictertimingguaranteeswhencommunicatingwithhardware.Thisisbecausethekernelhasamuchdeeperunderstandingofschedulingkerneldrivercommunicationeventstomeetthenecessarydeadlines.Inuserspace,aprocesscanbesuspendedatanytimeifthekernel’staskschedulerhasdecidedtogiveanotherprocessanopportunitytoexecute.Evenifauserspaceprocesspriorityisgreatlyincreased,itwillstillalwayshavealowerschedulingprioritywhencomparedtothepriorityofkernel-basedactivities.

Creatingakerneldrivercanbequitecomplex,anditisanactivitythatisfaroutsidethescopeofthisbook.However,ifyoufindyourselftryingtomeetverytighttimingrestrictionswhencommunicatingwithapieceofhardware,youmighteventuallyneedtoexplorethedetailsofkerneldevicedriverdevelopment.

TipWherecanIlearnmoreaboutdevelopingkerneldrivers?

ThebestplacetostartlearningaboutkerneldriverdevelopmentisthebookLinuxDeviceDriversbyCorbet,Rubini,andKroah-Hartman.Thisbookprovidescomprehensiveinstructionsthatwalkyouthroughthedevelopmentprocess.Evenbetter,thethirdeditionofthisbookisfreelyavailablefordownloadathttp://lwn.net/Kernel/LDD3.Thethirdeditionwasoriginallypublishedin2005,soitisabitdated,butthecentralconceptspresentedinthebookarestillvalid.

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IntegratingintoexistingmanagersInChapter5,InterfacingwithHigh-speedSensorsUsingSPI,youinterfacedwithanSPI-basedtemperatureandpressuresensor.Whileyoucommunicatedwiththesensorusingthespidevkerneldriverfromasingleapp,itisfarcleanertohaveamanagercommunicatewiththesensorinstead.Thisway,allappscanrequestaccesstothesensordatabycommunicatingwiththemanager,ratherthanhavingtounderstandthemanydetailsofSPIcommunicationsandcoordinatingaccessamongthemselves.Italsorestrictswhichappshavepermissiontointeractwiththespidevdriver.

Infact,Androidalreadyhasamanager,Android.SensorManager,thatisdesignedtotalkwithhardwaresensorresourcesthatarecommonlyfoundinphonesandtablets.Appscommunicatewiththemanagerbyrequestinganinstanceofthemanagerandthenrequestinganobjectthatrepresentsaparticulartypeofsensor:

PrivatefinalSensorManagermSensorManager;

PrivatefinalSensormPressure;

PrivatefinalSensormTemperature;

PublicSensorActivity(){

mSensorManager=

(SensorManager)getSystemService(SENSOR_SERVICE);mPressure=

mSensorManager.getDefaultSensor(Sensor.TYPE_PRESSURE);

mTemperature=

mSensorManager.getDefaultSensor(Sensor.TYPE_TEMPERATURE);

IfSensorManagerwasextendedtointerfacewiththeSPIsensorthatyouusedinChapter5,InterfacingwithHigh-speedSensorsUsingSPI,yourappcouldhavecommunicatedwiththesensorviaSensorManagerwithonlyafewlinesofJavacode!Evenbetter,thefilesystempermissionsofthespidevdevicewouldnothavetobesettosuchaninsecurestateforappstocommunicatewiththesensor.Unfortunately,itcanbequitedifficulttointegratenewhardwarefunctionalityintoanexistingmanagerforafewreasons:

YoumustrebuildtheappropriatepiecesofAndroid,whichtypicallyrequiresyoutobuildthecompleteAndroidsourcecodebaseatleastonce.Thisisatime-consuming(andoftenquiteconfusing)processfortheinexperienced.TheAndroidOpenSourceProjectprovidesinstructionsonhowtobuildAndroidfromsourceathttps://source.android.com/source.TheadditionalinterfacelogicforyournewhardwaremustbeaddedintotheHALofthemanagerthatyouareintegratingwith.Whilethisisoftenfairlystraightforward,thepiecesofthemanager’sHALmightbescatteredthroughouttheAndroidcodebase.Thenewhardwaremustcomplywiththeframework’sAPImethodsthatareprovidedbythemanager.UnlessyouarewillingtobreakAPIcompatibilitytoaddadditionalattributesandmethodstoaparticularmanager’sclass,youmustensurethatyourhardwarefitstheexistinginterfacesthatthemanagerprovides.

Whilethisintegrationcanbedifficult,itisoftenverystraightforward.AsAndroidis

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designedwithtabletsandphonesinmind,anyhardwarethatcanpotentiallybepartofamobiledeviceplatformprobablyalreadyhasanAndroidmanagerdesignedtointerfacewithit.SensorManagerisagoodexampleofthis.Itisdesignedtoprovidesensorinformationfromavarietyofdifferenttypesofsensorhardware.WhileyouwillneedtointegratesomenativecodeintotheSensorManagerHALtospeakwithyourparticularsensor,thecommunicationbetweentheHALandtheSensorManagerAPImethodsisafairlysimpleprocess.

TipWherecanIfindexamplesofintegratingcustomhardwareintoamanager?

TexasInstrumentsprovidesanumberofevaluationmodules(EVMs)forthevariousprocessorsthattheyproduceandsell.Asmanycommercialproductsarebasedupontheseprocessors,TIfreelyprovidesdocumentationandguidanceonhowtocreatecustomHALcodethatintegratescommonhardwareintoAndroidmanagers.ThebestplacetobeginlookingforthesedetailsisthedocumentationofTI’sSitaraAndroidSDK.TheSDK’swebpageislocatedathttp://www.ti.com/tool/androidsdk-sitara.

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CreatingnewmanagersforcustomhardwareIfyouareintegratingauniquepieceofhardwareintoAndroid,suchastheenvironmentsampleryoucreatedinChapter6,CreatingaCompleteInterfacingSolution,therewillprobablynotbeanystandardAndroidmanagerthatprovidesthenecessaryAPImethodsforappstoproperlycommunicatewiththehardware.Inthiscase,youmightconsidercreatinganewtypeofmanagerthatspecificallydealswiththeuniquehardware.

Anewmanagercanbetailoredspecificallytothehardwarethatitinteractswith.Forexample,theBBBoffersspecializedhardwarethatallowssoftwaretocommunicatewiththecomputersinsidemostmodernvehicles.SuchfunctionalityisnotavailableinstandardAndroidmobiledevices,sonoexiststohandlesuchcommunication.

CreatinganewmanagertohandlethespecificdetailsofusingthisinterfaceandprovidingacustomAPItousethismanagerfreesappsfromhavingtoknowthedetailsofsuchcommunication.However,thisshouldbeconsideredasalastresortforthefollowingreasons:

Thereisnoexistingmanagercodetobuildupon.Atbest,youmightfindasimplemanagerfromwhichtocopythecodeasastartingpoint.TheAndroidbuildprocessmustbemodifiedtoincludebuildingthenewmanagercode.ThisrequiresaddingthesourcefilesforthenewmanagertotheAndroidmakefilesandthenverifyingthattheAndroidframeworkisnotbroken.BuildingAndroidisalargeandcomplextask,somakinganychangestotheprocessshouldnotbeundertakenlightly.YoumustdesignaproperAPItointerfacewiththenewmanager.AsthisnewinterfaceadditionisnotpartofthestandardAndroidAPI,appswillbeunabletoincludetheseAPIcallsunlessyouspecificallyaddthemtoyourEclipseADTinstallation.Youmustalsoaugmentandroid.Manifest.permissiontoincludeoneormorenewpermissionsettingsthatallowanapptoaccessthefunctionalityofthenewmanager.Asanalternative,youcanpiggybackonanexistingpermissionorchoosetoforegousingpermissionsentirely.

Overall,buildingacustommanagerisalotofworkandnotforthefainthearted.TheprocesstouchesmanydifferentpiecesoftheAndroidframeworkandrequiresexpertiseinthefunctionalityofallofthosepieces.IfyoufindyourselfinapositionwhereyouthinkyouabsolutelyneedtocreateanewmanagertohandleyourhardwareproperlyviatheAndroidframework,youshouldconsiderskippingthemanagerandusinganapproachsimilartotheexamplesinthisbook:haveyourappcommunicatedirectlywithyourhardwareusingJNI.

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CombiningyourprojectwithotherhardwareNowthatyouhaveconsideredhowtobestmodifythesoftwaresideofyourAndroidsystemtofullyintegrateyourcustomhardwareproject,let’slookatthehardwaresideofthings.Breadboardsdoagreatjobofallowingyoutorapidlycreateandchangeyourhardwareprojectdesigns.Hardwareandsoftwareco-designisaniterativeprocess,soyoumightfindyourselfchangingyourhardwaredesignsasyoudevelopinterfacingsoftware.However,carryingaroundabreadboardtoshowoffyourhardwareprojectsisfarfromideal.

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ConstructingyourownprototypecapesWhynotcreateyourowncustomcapeboardproject?IfyouhavedevelopedtheperfecthardwareprojectforyourAndroidsystem,youshouldconsidermakingitastand-alonecapeboard.Puttingyourprojectintoacapeformfactormakesiteasytointegrateitwithothercapeboards.Italsoallowsyoutomoveyourprojectfromplacetoplacewithoutworryingaboutdisturbingthecircuitoraccidentallydisconnectinganybreadboardwires.

Creatingaprofessionallylaid-outPCBforacustomcapeisaverydifficulttaskfortheinexperienced.However,youcanstillconstructyourowncapeboardwithalittlesolderingandplanning.Adafruit’sProtoCapeKit(productID572)isagreatplacetostart.ProtoCapeislittlemorethanagenericPCBtoholdcomponentsthataresolderedintosemipermanentcircuits.IfyoupurchasedtheBeagleBoneBlackStarterPack(productID703)thatwementionedinChapter1,IntroductiontoAndroidandtheBeagleBoneBlack,youalreadyhaveProtoCape,asitisincludedinthatkit.

ProtoCapeKitforconstructingsemipermanentcapecircuits(source:www.adafruit.com)

NoteProtoCapealsoofferstheimportantadvantageofremovingthebreadboardwiresthatblocktheopeningsoftheP8/P9connectors.Uptofourcapescanbeconnectedsimultaneouslybystackingthecapes(pluggingonecapeintoanotherviapass-throughP8/P9connectorsoneachcape).ThisprovidestheopportunitytocombinedifferentcombinationsofcapestocreateacustomAndroidsystemthatmakesthemostoutofthecustomhardwarethatyouhavedesigned.IfbreadboardwiresareblockingtheP8/P9connections,othercapescannolongerbeinsertedintotheconnectorsandstackedontopoftheBBB.Thismakesitimpossibletouseabreadboarddesignifthetop-mostcapeinthestackdoesn’thaveapass-throughP8/P9connector(likemostLCDcapes).

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CommercialcapesthatinterfacewithAndroidThereareanumberofpremadeBBBcapesthatareavailableforpurchaseandwillworkwellwithAndroid.4DSystems(http://www.4dsystems.com.au/)providesseveraldifferentreasonablypricedLCDcapesofvarioussizesandresolutionsthatareavailableinbothtouchscreenandnon-touchscreenmodels.BeagleBoardToys(http://www.beagleboardtoys.com/)alsoprovidesawidevarietyofcapes,suchasLCD,audio,andbatterycapes.BycombiningavarietyofdifferentcapeswithyourBBB,youcanturnyourAndroidsystemintoaportableAndroiddevice!

The4DCAPE-70T(800x480pixels,left)and4DCAPE-43T(480x272pixels,right)4DSystemstouchscreenLCDcapes(source:www.4dsystems.com.au)

TipWhataboutUSBdevices?

OtherhardwarecomponentstoconsiderareUSBdevicessuchasaudiodevices,mice,keyboards,Wi-Fiadapters,Bluetoothadapters,gamepads,andwebcams.AstheLinuxkernelcontainsdriversforallofthesedevices,youcaneasilyexperimentwiththemtoextendyourAndroidplatformanddevelopavarietyofcreativeapps.TheBBBonlyhasasingleUSBport,thoughyoucanconnectaUSBhubtothatporttosupportusingmultipleUSBdevicessimultaneously.

PerhapsyoucancreateanAndroid-basedhand-heldgamingconsolewithGPIOcontrollerinputsandanSPI-orI2C-basedaccelerometer.OryoucandesignacustomautomotivecontrolconsolewithatouchscreenLCDthatgathersreal-timedatafromyourvehicle.Youhavecontrolofboththehardwareandsoftwareoftheentireplatform,andtheAndroidappdevelopmenttoolsareexcellentforcreatingUIsquicklyandeasily.Thepossibilitiesareendless!

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The5VDCbattery(left)andaudioCODEC(right)CircuitCocapes(source:www.beagleboardtoys.com)

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ExploringtheBBB’sotherinterfacesSofar,wehaveusedtheBBB’sGPIO,SPI,andI2Cfunctionalityforourinterfacing.ThesearenottheonlyinterfacingoptionsthattheBBBoffers,though.ThefollowingareafewotherinterfacesthatyoushouldkeepinmindasyouconsiderAndroidprojectsontheBBB.

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Programmablereal-timeunitsEmbeddedwithintheBBB’sAM335Xprocessorareapairofprogrammablereal-timeunits(PRUs).Theseunitsareclockedat200MHz,sotheyexecuteprogramsattherateofasingleinstructionevery5ns.ThekernelloadsprogramsintoaPRUandtheninstructsthePRUtobeginexecution.CommunicationbetweenthePRUandthekerneloccursviasharedmemory.TheexecutionofPRUsiscompletelyseparatefromthatofthemainprocessor,sopushingthePRUstotheirlimitwillnothaveaperformanceimpactonthemainprocessorunlesssomecoordinationbetweentheprocessorandaPRUisrequired.

ThereareanumberofGPIOpinsthatcanbemuxedsothattheyfallunderthedirectcontrolofaPRU.ThePRUcancheckorsetthevalueoftheseGPIOsoneachinstruction,meaningthatPRU-controlledGPIOscantogglefastenoughto“bit-bang”implementationsofcomplexdigitalinterfaces(suchasSPIandI2C).Ifyouhaveacustompieceofhardwareandneedtoimplementahigh-speedinterfacetoit,usingoneorbothofthePRUsisanoption.

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SerialcommunicationsTheBBBoffersfiveserialcommunicationUARTsthatcanbemuxedtothepinsoftheP8andP9connectors.ThereisalsoasixthUART(UART0)thatprovidestheserialdebugoutputviatheFTDIcable.IfyouareusingtheBBBtocontrolalargenumberofserial-controlleddevices,theseUARTsareaveryusefulresource.

Unfortunately,severaloftheseUARTs(UARTs3,4,and5)conflictwithpinsthatareinusebytheLCDinterfacebusthatprovidesvideodatatoLCDcapesandtheinternalHDMIcape.AsmuchofAndroid’sstrengthcomesfromitsuserinterface,disablingtheLCDinterfacetoreceivemoreUARTsisusuallyaverypoortrade-off.IfyoufindthatyouabsolutelyneedtheseUARTsunderAndroid,alloftheUARTscanbeaccessedusingthestandardLinuxkernelserialdriverandexistingNDKlibrariesthataccessthe/dev/TTYS*filesinthefilesystem.

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ControllerareanetworkTherearetwocontrollerareanetwork(CAN)busesontheBBB.CANisaserialprotocolthatformsoneofthefiveprotocolsusedintheon-boarddiagnostics(OBD)standardforvehicleinterfacing.VehiclediagnosticshardwareandsoftwareuseCANtocommunicatewiththehostcontrollerofmostmodernautomobiles.TheCANdriverintheLinuxkernelexposeseachCANbusasanetworkinterfacethatcanbecommunicatedwithvianetworksocketprogramming.IfyouareinterestedincreatinganAndroiddevicecapableofcommunicatingwithyourvehicle,suchasastatusdisplayinyourcarorahand-helddiagnosticunit,theCANbusisexactlywhatyouneed.

TheCAN0busismuxedtotheP9.19andP9.20pins,whicharethesamepinsusedbytheI2C2bususedbythecapemgrtodiscovertheidentityofanyconnectedcapes.MuxingtheCAN1bustotheP9.24andP9.26pinscanconflictwithI2C1dependinguponhowyouhavemuxedyourI2Cchannels.Ingeneral,youwon’tbeabletouseSPI,I2C,andCANatthesametime.

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Theanalog-to-digitalconverterTheBBBisn’tlimitedtoonlydigitalcommunications.Italsoprovidesan8-channel,12-bitanalog-to-digitalconverter(ADC)thatallowstheBBBtoreceiveanalogvoltagelevelsbetween0and1.8V.Thisisusefulwheninteractingwithreal-worldsensorsaswellasmanytouchscreendisplays.However,youmustbeverycarefultoensurethatthevoltageappliedtothesepinsneverexceeds1.8voltsoryouwilldamagetheBBB.

PinsP9.32throughP9.40arepermanentlymuxedwithADC,soyouarefreetousethemforyourownprojects.TheCircuitCoand4DSystemsLCDcapeswithtouchscreensupportpresentlyuseADCchannels4-7forthetouchscreen,leavingchannels0-3availableforyouruse.

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PulsewidthmodulationTheAM3359processorontheBBBhasaPulseWidthModulation(PWM)subsystemthatisusedfortheprecisecontrolofelectricmotors.PWMsetstheperiodanddutycyclewherevoltageissuppliedtoamotortocontrolitsrotationspeed.ThePWMsubsystemcontainsthreeEnhancedHighResolutionPulseWidthModulator(eHRPWM)modulesandanEnhancedQuadratureEncoderPulse(eQEP)module.Altogether,thesefourmodulesprovideeightPWMchannelsfordrivingmotors.

WhilePWMisoftenseenincontrolofindustrialmanufacturingequipment,roboticservomotors,andvariousothermechanicalsystems,itcanalsobeusedtocontrolthebrightnessoflightingandothertasksthatcanmakeuseofthevariabledutycycleofPWMtoemulatepower/brightness/speedlevelsbetweenoffandonatfullintensity.IfyouareinterestedincontrollingmechanicalsystemswiththeAndroidOS,PWMisdefinitelyafeatureoftheBBBthatyoushouldexplorefurther.

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SummaryInthischapter,welookedathowtofullyintegrateyourcustomhardwareprojectsintoAndroidontheBBB.WediscussedhowyourcustomdevicedriversshouldbebuiltdirectlyintoyourLinuxkernelandhowyourcustomDeviceTreeoverlaysshouldbecompileddirectlyintothemainDeviceTree.Thisavoidshavingtoincludeaspecialmoduleandanoverlaythatloadscommandsinyourinit.{ro.hardware}.rcfile.

WealsoexploredhowtocustomizethestandardAndroidsoftwareframeworktoincludesupportforyourcustomhardwareprojects.ExistingAndroidmanagerscanbeextendedtosupportcustomhardware.

WelookedatmakingyourcustomhardwaredesignsemipermanentusingProtoCape.Thisallowsyoutoavoidaccidentallydisconnectingbreadboardwireswhenmovingyourprojectaround.ItalsoallowsforeasierintegrationwithcommerciallyavailableBBBcapesbyavoidingtheproblemofblockingtheP8/P9connectorswithbreadboardwires.WealsomentionedthattherearemanytypesofUSBdevicesthatarealsosupportedbyAndroidandareworthexploringwhenconsideringnewprojects.

Finally,weexploredsomeoftheotherBBBinterfacesthatwerenotcoveredbytheexamplesintheearlierchaptersofthisbook.TheBBB’sPRUs,serialUARTs,CANbuses,ADCs,andPWMsubsystemsallofferadditionalfunctionalitytointerfacewiththeoutsideworld.

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IndexA

AdaFruitURL/Shoppingforthehardwareessentials

AdaFruitProtoPlateabout/Breadboardandthemountingplate

AdvancedLinuxSoundArchitecture(ALSA)driver/UnderstandingtheAndroidHALanalog-to-digitalconverter(ADC)

about/Theanalog-to-digitalconverterAndroid

about/LookingbackonAndroidandBeagleBoneBlackdevelopmentURL,forsourcecode/LookingbackonAndroidandBeagleBoneBlackdevelopmentpreparing,forPacktHAL/PreparingAndroidforPacktHALpreparing,forGPIO/PreparingAndroidforGPIOusecustomhardwareprojects,integratingwith/IntegratingyoursolutionwithAndroid

Android,interfacingwithAndroidHAL/UnderstandingtheAndroidHALPacktHAL,installing/InstallingPacktHALAndroidNDK,settingupforPacktHAL/SettinguptheAndroidNDKforPacktHALBeagleBoneBlackpins,multiplexing/MultiplexingtheBBBpins

Android.4DSystemsURL/CommercialcapesthatinterfacewithAndroid

AndroidHALabout/UnderstandingtheAndroidHALAndroidmanagers/Androidmanagersdevelopmentworkflow/TheHALdevelopmentworkflowPacktHAL,workingwith/WorkingwithPacktHAL

Androidinstallation,onBBBabout/InstallingAndroidontheBeagleBoneBlackpremadeAndroidimage,downloading/DownloadingapremadeAndroidimageAndroidmicroSDcard,creatingwithWindows/CreatingyourAndroidmicroSDcardusingWindowsAndroidmicroSDcard,creatingwithLinux/CreatingyourAndroidmicroSDcardusingLinux

Androidmanagersabout/Androidmanagers

AndroidmicroSDcardcreating,Windowsused/CreatingyourAndroidmicroSDcardusingWindows

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creating,Linuxused/CreatingyourAndroidmicroSDcardusingLinuxAndroidNativeDevelopmentKit(NDK)

settingup,forPacktHAL/SettinguptheAndroidNDKforPacktHALheader,addingunderLinux/AddingtheheadertotheNDKunderLinuxheader,addingunderWindows/AddingtheheadertotheNDKunderWindows

AndroidOpenSourceProject(AOSP)KitKatAndroid/InstallingAndroidontheBeagleBoneBlackApplicationNotResponding(ANR)/UnderstandingtheAsyncTaskclassAsyncTask

about/Understandinghardwarepollinginanappusing,withlong-livedthreads/UsingAsyncTaskwithlong-livedthreadsisCancelled()method/UsingAsyncTaskwithlong-livedthreadscancel()method/UsingAsyncTaskwithlong-livedthreadsonCancelled()method/UsingAsyncTaskwithlong-livedthreadspublishProgress()method/UsingAsyncTaskwithlong-livedthreadsdoPublishProgress()method/UsingAsyncTaskwithlong-livedthreads

AsyncTaskmethodsdoInBackground()/LearningthedetailsoftheHardwareTaskclassexecute()/LearningthedetailsoftheHardwareTaskclassonPreExecute()/LearningthedetailsoftheHardwareTaskclassonPostExecute()/LearningthedetailsoftheHardwareTaskclass

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BBB-PACKTPUB-00A0.dtbofile/PreparingAndroidforGPIOuseBBBAndroid

URL/InstallingAndroidontheBeagleBoneBlackabout/InstallingAndroidontheBeagleBoneBlack

BBBAndroidimageabout/InstallingAndroidontheBeagleBoneBlack

BeagleBoardToysURL/CommercialcapesthatinterfacewithAndroid

BeagleBoneBlack(BBB)about/LookingbackonAndroidandBeagleBoneBlackdevelopmenthardware/Shoppingforthehardwareessentialshardwarecomponents/Learningaboutthehardwareyou’llinterfacewithAndroid,installing/InstallingAndroidontheBeagleBoneBlackbootingoptions/InstallingAndroidontheBeagleBoneBlackinterfaces/ExploringtheBBB’sotherinterfaces

BeagleBoneBlackpinsmultiplexing/MultiplexingtheBBBpinskernelDeviceTree/ThekernelDeviceTreeandcapemgrcapemanager(capemgr)/ThekernelDeviceTreeandcapemgrcape,defining/Definingacape

BinderIPC/UnderstandingtheAndroidHALbootingoptions,BeagleBoneBlack(BBB)

onboardeMMC/InstallingAndroidontheBeagleBoneBlackmicroSDcard/InstallingAndroidontheBeagleBoneBlackoverthenetwork/InstallingAndroidontheBeagleBoneBlack

breadboard,BeagleBoneBlack(BBB)about/Breadboardandthemountingplate

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defining/Definingacapecapemanager(capemgr)

about/ThekernelDeviceTreeandcapemgrservices/ThekernelDeviceTreeandcapemgr

CapeManager(capemgr)functionalityabout/InstallingAndroidontheBeagleBoneBlack

chipselect(CS)signal/UnderstandingSPICircuitCo/LookingbackonAndroidandBeagleBoneBlackdevelopmentcompleteexampleapp

about/Exploringthecompleteexampleappuserinterface/Theapp’suserinterfacehardwarepolling/UnderstandinghardwarepollinginanappAsyncTask,usingwithlong-livedthreads/UsingAsyncTaskwithlong-livedthreadsHardwareTaskclass,using/UsingtheHardwareTaskclass

completeinterfacecircuitbuilding/Buildingthecompleteinterfacecircuit

controllerareanetwork(CAN)about/Controllerareanetwork

customappcreating,includingPacktHAL/CreatinganewappprojectthatusesPacktHALPacktHAL,buildingunderWindows/BuildingPacktHALunderWindowsPacktHAL,buildingunderLinux/BuildingPacktHALunderLinux

customhardwareprojectsintegration,withAndroidperforming/IntegratingyoursolutionwithAndroidcustomkernel,creating/CreatingacustomkernelandDeviceTreeDeviceTree,creating/CreatingacustomkernelandDeviceTreehardwarecommunication,addingintokernel/Addinghardwarecommunicationintothekernelexistingmanagers,integratinginto/Integratingintoexistingmanagersnewmanagers,creating/Creatingnewmanagersforcustomhardwarehardware/Combiningyourprojectwithotherhardwarecustomprototypecapes,constructing/Constructingyourownprototypecapescommercialcapes/CommercialcapesthatinterfacewithAndroid

customkernelcreating/CreatingacustomkernelandDeviceTree

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Ddevelopmentworkflow,AndroidHAL

about/TheHALdevelopmentworkflowDeviceTree

creating/CreatingacustomkernelandDeviceTreedirectorystructure,PacktHAL

about/ThePacktHALdirectorystructure

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EEclipseAndroidDevelopmentTools(ADT)/LookingbackonAndroidandBeagleBoneBlackdevelopmentelectricallyerasableprogrammableread-onlymemory(EEPROM)chip/DefiningacapeEnhancedHighResolutionPulseWidthModulatormodule(eHRPWM)

about/PulsewidthmodulationEnhancedQuadratureEncoderPulse(eQEP)module

about/Pulsewidthmodulationevaluationmodules(EVMs)/Integratingintoexistingmanagers

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FfileI/Omethod

about/GPIOaccessmethodsunderAndroidpros/ProsandconsofthefileI/Omethodcons/ProsandconsofthefileI/Omethod

FRAMchip/AddinghardwarecommunicationintothekernelFTDIcable,BeagleBoneBlack(BBB)

about/TheFTDIcableFutureTechnologyDevicesInternational(FTDI)cable/Shoppingforthehardwareessentials

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about/UnderstandingGPIOsvoltagelevels/NutsandboltsofGPIOon/highstate/NutsandboltsofGPIOoff/lowstate/NutsandboltsofGPIOaccessmethods,underAndroid/GPIOaccessmethodsunderAndroidAndroid,preparingfor/PreparingAndroidforGPIOuse

GPIO-interfacingcircuitbuilding/BuildingaGPIO-interfacingcircuit,ConstructingthecircuitP9.11pin/ConstructingthecircuitP9.13pin/Constructingthecircuitwiring,checking/Checkingyourwiring

GPIOaccessmethodsabout/GPIOaccessmethodsunderAndroidfileI/Omethod/GPIOaccessmethodsunderAndroid,ProsandconsofthefileI/Omethodmemory-mappingmethod/GPIOaccessmethodsunderAndroid,Prosandconsofthememory-mappingmethod

GPIOexampleappabout/ExploringtheGPIOexampleappinstalling,underWindows/InstallingtheappandsourceunderWindowssource,installingunderWindows/InstallingtheappandsourceunderWindowsinstalling,underLinux/InstallingtheappandsourceunderLinuxsource,installingunderLinux/InstallingtheappandsourceunderLinuxuserinterface/Theapp’suserinterfacePacktHALfunctions,calling/CallingthePacktHALfunctionsPacktHALGPIOfunctions,using/UsingthePacktHALGPIOfunctions

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Hhardware,BeagleBoneBlack(BBB)

about/ShoppingforthehardwareessentialsFTDIcable/TheFTDIcablepowersupply/Powersupplybreadboard/Breadboardandthemountingplatemountingplate/BreadboardandthemountingplatemicroSDcards/MicroSDcards

hardwarecomponents,interfacingwithabout/Learningaboutthehardwareyou’llinterfacewithgeneral-purposecomponents/General-purposecomponentsAdaFruitmemorybreakoutboard/TheAdaFruitmemorybreakoutboardAdaFruitsensorbreakoutboard/TheAdaFruitsensorbreakoutboardbreakoutboards,preparing/Preparingthebreakoutboards

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about/UnderstandingI2Cdevices/DevicesthatuseI2Cmultiplexing,onBeagleBoneBlack/MultiplexingforI2ContheBBB

I2C-interfacingcircuitbuilding/BuildinganI2C-interfacingcircuitFRAM,connecting/ConnectingtheFRAMFRAMconnection,checkingwithI2C-tools/CheckingtheFRAMconnectionwithI2Ctools

I2Cdevicesrepresenting,inLinuxkernel/RepresentingI2CdevicesintheLinuxkernelAndroid,preparingforFRAM/PreparingAndroidforFRAMuse

I2CFRAMexampleappabout/ExploringtheI2CFRAMexampleappuserinterface/Theapp’suserinterfacePacktHALFRAMfunctions,calling/CallingthePacktHALFRAMfunctionsAsyncTaskclass,using/UnderstandingtheAsyncTaskclassHardwareTaskclass,using/LearningthedetailsoftheHardwareTaskclass

installation,PacktHALabout/InstallingPacktHALPacktHAL,preparingunderLinux/PreparingPacktHALunderLinuxPacktHAL,preparingunderWindows/PreparingPacktHALunderWindowsPacktHALdirectorystructure/ThePacktHALdirectorystructureAndroid,preparingforPacktHAL/PreparingAndroidforPacktHALPacktHALfiles,pushingunderLinux/PushingPacktHALfilesunderLinuxPacktHALfiles,pushingunderWindows/PushingPacktHALfilesunderWindows

interfaces,BeagleBoneBlack(BBB)programmablereal-timeunits(PRUs)/Programmablereal-timeunitsserialcommunications/Serialcommunicationscontrollerareanetwork(CAN)/Controllerareanetworkanalog-to-digitalconverter(ADC)/Theanalog-to-digitalconverterPulseWidthModulation(PWM)subsystem/Pulsewidthmodulation

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JJavaNativeInterface(JNI)

about/UnderstandingtheJavaNativeInterface

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KkernelDeviceTree

about/ThekernelDeviceTreeandcapemgrkerneldrivers/Addinghardwarecommunicationintothekernel

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Llandgridarray(LGA)/BuildinganSPIinterfacecircuitLinux

used,forcreatingAndroidmicroSDcard/CreatingyourAndroidmicroSDcardusingLinux

LinuxkernelI2Cdevices,representing/RepresentingI2CdevicesintheLinuxkernelSPIdevices,representing/RepresentingSPIdevicesintheLinuxkernel

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Mmasterin,slaveout(MISO)signal/UnderstandingSPImasterout,slavein(MOSI)signal/UnderstandingSPImemory-mappingmethod

about/GPIOaccessmethodsunderAndroidpros/Prosandconsofthememory-mappingmethodcons/Prosandconsofthememory-mappingmethod

microSDcards,BeagleBoneBlack(BBB)about/MicroSDcards

mountingplate,BeagleBoneBlack(BBB)about/Breadboardandthemountingplate

multiplexing,forI2ConBeagleBoneBlackabout/MultiplexingforI2ContheBBBI2C,connectingviaP9header/ConnectingtoI2CviatheP9headerperforming/MultiplexingforI2C

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Oon-boarddiagnostics(OBD)

about/Controllerareanetwork

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PPacktHAL

about/TheHALdevelopmentworkflowworkingwith/WorkingwithPacktHALinstallation/InstallingPacktHALpreparing,underLinux/PreparingPacktHALunderLinuxpreparing,underWindows/PreparingPacktHALunderWindowsdirectorystructure/ThePacktHALdirectorystructureAndroid,preparingfor/PreparingAndroidforPacktHALfiles,pushingunderLinux/PushingPacktHALfilesunderLinuxfiles,pushingunderWindows/PushingPacktHALfilesunderWindows

PacktHAL,addingtoappsabout/IncludingPacktHALwithinyourappsJavaNativeInterface/UnderstandingtheJavaNativeInterface

PacktHALFRAMfunctionsopenFRAM()function/CallingthePacktHALFRAMfunctionscloseFRAM()function/CallingthePacktHALFRAMfunctionsreadFRAM()function/CallingthePacktHALFRAMfunctionswriteFRAM()function/CallingthePacktHALFRAMfunctions

PacktHALfunctionscalling/CallingthePacktHALfunctions

PacktHALGPIOfunctionsopenGPIO()function/UsingthePacktHALGPIOfunctionscloseGPIO()function/UsingthePacktHALGPIOfunctionsreadGPIO()function/UsingthePacktHALGPIOfunctionswriteGPIO()method/UsingthePacktHALGPIOfunctionsonClickButtonLightOn()method/UsingthePacktHALGPIOfunctionsonClickButtonLightOff()method/UsingthePacktHALGPIOfunctions

PacktHALsensorfunctionsopenSensor()function/CallingthePacktHALsensorfunctionscloseSensor()function/CallingthePacktHALsensorfunctionsgetSensorTemperature()function/CallingthePacktHALsensorfunctionsgetSensorPressure()function/CallingthePacktHALsensorfunctions

pausedstate/Understandinghardwarepollinginanapppowersupply,BeagleBoneBlack(BBB)

about/PowersupplypremadeAndroidimage

downloading/DownloadingapremadeAndroidimageprogrammablereal-timeunits(PRUs)

about/Programmablereal-timeunitsPulseWidthModulation(PWM)

about/Pulsewidthmodulation

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Rresumedstate/Understandinghardwarepollinginanapp

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Sserialclock(SCLK)signal/UnderstandingSPIserialcommunications

about/Serialcommunicationsslaveselect(SS)signal/UnderstandingSPIsmalloutlinepackage(SOP)/BuildinganI2C-interfacingcircuitSparkFun

URL/ConstructingthecircuitSPI

about/UnderstandingSPIserialclock(SCLK)signal/UnderstandingSPImasterout,slavein(MOSI)signal/UnderstandingSPImasterin,slaveout(MISO)signal/UnderstandingSPIslaveselect(SS)signal/UnderstandingSPIchipselect(CS)signal/UnderstandingSPImultiplexing,forBeagleBoneBlack/MultiplexingforSPIontheBBB

SPIdevicesrepresenting,inLinux/RepresentingSPIdevicesintheLinuxkernel

SPIinterfacecircuitbuilding/BuildinganSPIinterfacecircuitsensor,connecting/Connectingthesensor

SPIsensorAndroid,preparingfor/PreparingAndroidforSPIsensoruse

SPIsensorexampleappabout/ExploringtheSPIsensorexampleappuserinterface/Theapp’suserinterfacePacktHALsensorfunctions,calling/CallingthePacktHALsensorfunctionsHardwareTaskclass,using/UsingtheHardwareTaskclass

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Tthreadofexecution/UnderstandingtheAsyncTaskclass

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Uusing

HardwareTaskclass/UsingtheHardwareTaskclass

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V3.3Vlogiclevel

about/NutsandboltsofGPIO

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WWin32DiskImagerapplication

URL/CreatingyourAndroidmicroSDcardusingWindowsWindows

used,forcreatingAndroidmicroSDcard/CreatingyourAndroidmicroSDcardusingWindows

WinRARURL/CreatingyourAndroidmicroSDcardusingWindows

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