General Instructionsx Instructions

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Real‐TimeProgramming,GeneralLabInstructions  March2017,ÖrebroUniversity

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General Information of Lab Instrument and Platform

FarhangNemati,March2017



Real‐TimeProgramming,GeneralLabInstructions  March2017,ÖrebroUniversity

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Introduction

InthelabweuseRaspberryPiB+platformforlabassignments.RaspberryPiisacheap,smallandgeneral

purposecomputermainlyusedforprogrammingembeddedapplications.Itwasoriginallymadeforeducation

purposes,however,itsoonbecameapopularplatformamonghobbyistsandthosewhowishedtolearn

developingembeddedapplications.ThereisabigcommunityforprogrammingonRaspberryPiandthereare

interestingprojectsandworksavailableonline.Usually,adistributionofLinux(Raspbian)isusedasoperating

systemforRaspberryPi.Thismakesitquiteusefulsinceprogramscanbewritteninawiderangeoflanguages,

e.g.,C,C++,Java,andPython.

TheoperatingsystemwehaveinstalledontheseplatformsinthelabisReal‐TimeLinux(Raspbian

compiledwithReal‐Timesettings).TheprogramminglanguagetobeusedisC.WewilluseVisualStudiofor

programminganddebuggingenvironment.Tobeabletoeasilywriteprograms,compile,run,anddebugthem

usingVisualStudio,wehaveinstalledVisualGDBwhichisaconvenientadd‐onforVisualStudio.Oneofthe

usagesofVisualGDBisprogramminganddebuggingC/C++LinuxapplicationsforRaspberryPiandotherLinux

platforms,Androidappsetc.



Raspberry Pi B+

ThemodelB+ofRaspberryPi(Figure1)has40GeneralPurposeInput/Output(GPIO)pins.GPIOpinsare

usedforinput/outputpurposes.However,notallofthe40pinscanbeusedforinput/output;someofthemare

forsupplyingpowerfordevicesconnectingtoRaspberryPi;8pinsforGND(ground),2pinstosupply3.3Volt,

and2pinstosupply5Volt.AsshowninFigure1itisdifficulttorecognizethepins,thereforewehaveconnected

thepinstoaboardwhereeachpinisshownbyalabelnexttoit(Figure2).Exceptthepowersupplypinsthe

restofGPIOpinscanbeusedforeitheroutputorinputpurposes.Thismeansthateachofthesepinscan

GPIOpins

Fi

g

ure1:Ras

p

berr

y

PiB+

Real‐TimeProgramming,GeneralLabInstructions  March2017,ÖrebroUniversity

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programmaticallybesettoeitherinputoroutput.Toeaseworkingwithinput/outputinthelabwehave

providednecessaryfunctionswritteninCwhichcanbedownloadedfromBlackboard.Youhavetobevery

carefulwhenusingGPIO;failureinconnectingandusingthepinsmightdestroythepins.Alwaysaskthelab

assistantforhelptoassistyouconnectingGPIOstootherdevices.Inthefollowingsectionitisexplainedhowto

usetheprovidedCcodetoworkwithGPIO.



ThereisalotofonlineinformationandinterestingprojectsdonebyRaspberryPi.Formoredetails

aboutRaspberryPivisititsofficialwebsiteatwww.raspberrypi.org.

Specifications

• 700MHzBCM2835CPU

• 512MBSDRAM

• 10/100Ethernetport

• Full‐sizeHDMIport

• 4USBports

• MicroSDslot

• Combined3.5mmaudiojackandcompositevideooutput

• Camerainterface(CSI)

• Displayinterface(DSI)

• 40pinsGPIOheader



Starting up Shutting down Raspberry Pi in the Lab

Starting up

ConnecttheelectronicdevicesthatyouaresupposedtoworkwithbeforeturningthePion

(connectingittoelectricity).MakesurethatyouhaveconnectedthePitonetworkusingthenetworkcable.

WhenreadyconnectthePitoelectricitytoturniton.RTLinuxwillbootandafterseveralsecondsthePiwillbe

readytouse.



Fi

g

ure2:GPIOswithlabelsinthe

Real‐TimeProgramming,GeneralLabInstructions  March2017,ÖrebroUniversity

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Shutting down

WhenyouarefinishedwiththePishutdownitproperly.Neverturnitoffbyunpluggingitfromthe

electricitybeforeshuttingitdown.Toshutdownsendthefollowingterminalcommand(forexampleusing

PuTTY)tothePi:

 



Using GPIO

TouseGPIOsalwaysusetheCfunctionsintheprovidedCfiles(piodirect.handpiodirect.c).Foreachlab

whenyoucreateaprojectinVisualStudiofirstdownloadpiodirect.handpiodirect.cfromBlackboard

(“Kursmaterial/Labs/HelperCode”)andaddthemtotheproject.Thedetailsonhowtocreateaprojectfor

RaspberryPiinVisualStudiowillbeexplainedintheinstructionsforthefirstlab.

Setting up GPIO

AlwayscallgpioSetup()atthebeginningoffunctionmain()inanyproject:

intmain(intargc,char*argv[])

{

gpioSetup();

...

}

Setting a GPIO pin as input or output

Forsettingapinasaninputoroutputcallthefollowingfunction:

GPIOcreate(enumPinpin,intdirection)



PutthereturnedGPIOtypeinavariableoftypeGPIO.Fromthatpointyouwillusethisvariabletowork

withthepin.

Parameterpinisthenameofpin(writtenonthelabelnexttothepin)followedby“_”.ForexampleGPIO

pin#17isenteredas_17

Thedirectionsetsthepintoeitherinputoroutput;enterIN_PINifthepinistobeaninput,andenter

OUT_PINifthepinisgoingtobeanoutputpin.



Examples:

GPIOgpio4=create(_4,OUT_PIN);/*setspin#4(seeFigure2)asoutputpin*/

GPIOgpioScl=create(_SCL,OUT_IN);/*setspinSCL(seeFigure2)asinputpin*/



Writing a value to an output GPIO pin

Thevalueofanoutputpincanbesettohigh(1)orlow(0).Whenitishighthevoltageofthepinis

around3.3Voltandwhenitislowitsvoltageisaround0Volts(GND).Toputanoutputpintohighcallthe

followingfunction:

Real‐TimeProgramming,GeneralLabInstructions  March2017,ÖrebroUniversity

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intonOff(GPIOgpio_,intonOff);



ParameteronOffhastobeONtoputthepinonhighandOFFtoputthepinonlow.

Example:

GPIOgpio17=create(_17,OUT_PIN);

onOff(gpio17,ON);/*setspin#17tohigh*/

onOff(gpio17,OFF);/*setspin#17tolow*/



Reading the value of an input GPIO pin

ToreadavaluefromaGPIOpinthatissetasinput,callthefollowingfunction:

intreadIn(GPIOgpio_);



Ifthereturnvalueis1itmeanstheinputishigh,ifthereturnvalueis0thevalueofinputpinislow.



Example:

intvalue;



GPIOgpio4=create(_4,IN_PIN);

value=readIn(gpio4);





Using a GPIO pin for buttons and switches



WhenusingabuttonwithRaspberryPi,onepinofthebuttonhastobeconnectedtoaGNDandits

otherpinhastobeconnectedtoaninputGPIOpin.FirstofalltheGPIOpinhastobecreatedasinputpinand

thenfunctionpullUpDown(GPIOgpio_,intpud)hastobecalledonthatpin.Thevalueofparameterpudcan

beeitherPUD_UPorPUD_DOWN.IfPUD_UP(pullup)isgivenasthevalueofpudtheGPIOpinbydefaultis

high(1)andwhenthebuttonispushedtheinputvaluebecomeslow(0).OntheothersideifPUD_DOWN(pull

down)isgiven,thedefaultvalueoftheGPIOpinbydefaultislowandwhenthebuttonispushedtheinput

valueoftheGPIOpinbecomeshigh.



Example1:

GPIOgpio17=create(_17,IN_PIN);

pullUpDown(gpio17,PUD_UP);



while(1)

{

if(readIn(gpio17)==0)

{

printf("Buttonpushed!\n");

break;

}

else

{

printf("Buttonreleased!\n");

}

usleep(20000);

}

destroy(gpio17);

Real‐TimeProgramming,GeneralLabInstructions  March2017,ÖrebroUniversity

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

Thereisafunctionthatdoestheworkofbothcreate()andpullUpDown()together.Itispreferredto

usethisfunctionforbuttons:

GPIOcreateWithPullUpDown(enumPinpin,intup);







Example2:

GPIOgpio17=createWithPullUpDown(_17,PUD_UP);

while(1)

{

if(!readIn(gpio17))

{

printf("Buttonpushed!\n");

break;

}

else

{

printf("Buttonreleased!\n");

}

usleep(20000);

}

destroy(gpio17);



Example3:



GPIOgpio17=createWithPullUpDown(_17,PUD_DOWN);/*NoticethatitisPullDown!*/

while(1)

{

if(readIn(gpio17))

{

printf("Buttonpushed!\n");

break;

}

else

{

printf("Buttonreleased!\n");

}

usleep(20000);

}

destroy(gpio17);



Unset a GPIO pin

Whenyouarefinishedworkingwithapinandyoudon’tneeditanymorecallthefollowingfunction

(alwaysdoit!):

voiddestroy(GPIOgpio_);



Example:

destroy(gpio17);