MIPS and Basic Assembly Language - GitHub Pages– Optionally, through a program called QtSPIM (GUI...

MIPSandBasicAssemblyLanguage

CS64:ComputerOrganizationandDesignLogicLecture#4

ZiadMatni

Dept.ofComputerScience,UCSB

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ThisWeekon

“DidjaKnowDat?!”

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WhydoCPUprogrammerscelebrateChristmasandHalloween

onthesameday?

BecauseOct-31=Dec-25

LectureOutline

•  MIPScoreprocessingblocks

•  Basicprogramminginassembly

•  Arithmeticprograms

•  Controllogicprograms

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AnyQuestionsFromLastLecture?

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MIPS

WhyMIPS?•  MIPS:

–  areducedinstructionsetcomputer(RISC)architecturedevelopedbyMIPSTechnologies(1981)

•  Relevantintheembeddedsystemsdomain–  Computersystemswithadedicatedfunctionwithinalarger

mechanicalorelectricalsystem–  Example:lowpowerandlowcostprocessorsinMP3playersor

“Smart”Appliances

•  AllmoderncommercialprocessorssharethesamecoreconceptsasMIPS,justwithextrastuff...butmoreimportantly...

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MIPSisSimpler…

…thanotherinstructionsetsforCPUsSoit’sagreatlearningtool

•  Dozensofinstructions(asopposedtohundreds)•  Lackofredundantinstructionsorspecialcases•  5stagepipelineversus24stages

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Note:PipelininginCPUs

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•  PipeliningisafundamentaldesigninCPUs•  Allowsmultipleinstructionstogoonatonce– a.k.ainstruction-levelparallelism

CodeonMIPS

Originalx=5;y=7;z=x+y;

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MIPSli$t0,5li$t1,7add$t3,$t0,$t1

CodeonMIPS

Originalx=5;y=7;z=x+y;

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MIPSli$t0,5li$t1,7add$t3,$t0,$t1loadimmediate:putthegivenvalueintoaregister$t0:temporaryregister0

CodeonMIPS

Originalx=5;y=7;z=x+y;

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MIPSli$t0,5li$t1,7add$t3,$t0,$t1loadimmediate:putthegivenvalueintoaregister$t1:temporaryregister1

CodeonMIPS

Originalx=5;y=7;z=x+y;

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MIPSli$t0,5li$t1,7add$t3,$t0,$t1add:addtherightmostregisters,puttingtheresultinthefirstregister$t3:temporaryregister3

AvailableRegistersinMIPS

•  32registersinall– Refertoyour

MIPSReferenceCard

•  Forthemoment,let’sonlyconsiderregisters$t0thru$t9

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Assembly

•  ThecodethatyouseeisMIPSassembly

•  Assemblyis*almost*whatthemachinesees.Forthemostpart,itisadirecttranslationtobinaryfromhere(knownasmachinecode)

•  Anassemblertakesassemblycodeandchangesitintotheactual1’sand0’sformachinecode– AnalogoustoacompilerforHLcode

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li$t0,5li$t1,7add$t3,$t0,$t1

MachineCode/Language

•  WhataCPUactuallyacceptsasinput•  Whatactuallygetsexecuted

•  Eachinstructionisrepresentedwith32bits

•  Therearethreedifferentinstructionformats:R,I,andJ–  Theseallowforinstructionstotakeondifferentroles–  R-Formatisusedwhenit’sallaboutregisters–  I-Formatisusedwhenyouinvolvenumbers–  J-Formatisusedwhenyoudocode“jumping”(i.e.branching)

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Sinceallinstructionsare32-bits,thentheyeachoccupy4Bytesofmemory.

MemoryisaddressedinBytes(moreonthislater).

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Sinceallinstructionsare32-bits,thentheyeachoccupy4Bytesofmemory.

MemoryisaddressedinBytes(moreonthislater).

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Sinceallinstructionsare32-bits,thentheyeachoccupy4Bytesofmemory.

MemoryisaddressedinBytes(moreonthislater).

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Sinceallinstructionsare32-bits,thentheyeachoccupy4Bytesofmemory.

MemoryisaddressedinBytes(moreonthislater).

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Sinceallinstructionsare32-bits,thentheyeachoccupy4Bytesofmemory.

MemoryisaddressedinBytes(moreonthislater).

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Sinceallinstructionsare32-bits,thentheyeachoccupy4Bytesofmemory.

MemoryisaddressedinBytes(moreonthislater).

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Sinceallinstructionsare32-bits,thentheyeachoccupy4Bytesofmemory.

MemoryisaddressedinBytes(moreonthislater).

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Sinceallinstructionsare32-bits,thentheyeachoccupy4Bytesofmemory.

MemoryisaddressedinBytes(moreonthislater).

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Sinceallinstructionsare32-bits,thentheyeachoccupy4Bytesofmemory.

MemoryisaddressedinBytes(moreonthislater).

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Sinceallinstructionsare32-bits,thentheyeachoccupy4Bytesofmemory.

MemoryisaddressedinBytes(moreonthislater).

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Sinceallinstructionsare32-bits,thentheyeachoccupy4Bytesofmemory.

MemoryisaddressedinBytes(moreonthislater).

AddingMoreFunctionality

•  Whatabout:displayresults????Yes,that’skindaimportant…•  Whatwouldthisentail?–  EngagingwithInput/Outputpartofthecomputer–  i.e.talkingtodevices

•  Q:Whatusuallyhandlesthis?

•  Soweneedawaytotell theoperatingsystemtokickin

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A:theoperatingsystem

TalkingtotheOS

•  WearegoingtoberunningonMIPSemulatorcalledSPIM–  Optionally,throughaprogramcalledQtSPIM(GUIbased)– Whatisanemulator?

•  We’renotactuallyrunningourcommandsonaMIPSprocessor!!!

…so,inotherwords…we’re“fakingit”

•  Ok,sohowmightweprintsomethingontostd.out?

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SPIMRoutines

•  MIPSfeaturesasyscallinstruction,whichtriggersasoftwareinterrupt,orexception

•  Outsideofanemulator(i.e.intherealworld),theseinstructionspausetheprogramandtelltheOStogodosomethingwithI/O

•  Insidetheemulator,ittellstheemulatortogodosomethingwithI/O

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syscall

•  SowehavetheOS/emulator’sattention,buthowdoesitknowwhatwewant?

•  TheOS/emulatorhasaccesstotheregisters

•  Weputspecialvalues(codes)intheregisterstoindicatewhatwewant–  Thesearecodesthatcan’tbeusedforanythingelse,so

they’reunderstoodtobejustforsyscall

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ProgramFilesforMIPSAssembly

•  Thefileshavetobetext

•  Typicalfileextensiontypeis.asm

•  Toleavecomments, use#atthestartoftheline

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(Finally)PrintinganInteger•  ForSPIM,ifregister$v0contains1andthenweissueasyscall,

thenSPIMwillprintwhateverintegerisstoredinregister$a0ßthisisaspecificruleusingaspecificcode–  Note:$v0isusedforotherstuffaswell–moreonthatlater…–  When$v0=1,syscallisexpectinganinteger!

•  Othervaluesin$v0indicateothertypestosyscallExamples:–  $v0=3meansdouble(orthememaddressofone)in$a0–  $v0=4meansstring(orthememaddressofone)in$a0–  We’llexploresomeoftheselater,butcheckMIPSrefcardforallofthem

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(Finally)PrintinganInteger•  Remember,theusualsyntaxtoloadimmediateavalueintoa

registeris: li<register>,<value>–  Example: li$v0,1 #PUTSTHENUMBER1INTOREG.$v0

•  Tomakesurethattheregister$a0hasthevalueofwhatyouwanttoprintout(let’ssayit’sinanotherregister),usethemovecommand:

move<toregister>,<fromregister>–  Example: move$a0,$t0#PUTSTHEVALUEINREG.$t0INTOREG.$a0

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Ok…SoAboutThoseRegistersMIPShas32registers,each32bits

AugmentingwithPrinting#Mainprogramli$t0,5li$t1,7add$t3,$t0,$t1#Printanintegertostd.outputli$v0,1move$a0,$t3syscall

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We’reNotQuiteDoneYet!ExitinganAssemblyPrograminSPIM•  IfyouareusingSPIM,thenyouneedtosaywhen

youaredoneaswell–  MostHLLprogramsdothisforyouautomatically

•  Howisthisdone?–  Issueasyscallwithaspecialvaluein$v0=10(decimal)

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AugmentingwithExiting#Mainprogramli$t0,5li$t1,7add$t3,$t0,$t1#Printtostd.outputli$v0,1move$a0,$t3syscall#Endprogramli$v0,10syscall

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MIPSSystemServicesExamplesWe’veSeenSoFar…

stdout

stdin

FileI/O

NowLet’sMakeitaFullProgram(almost)

•  Weneedtotelltheassembler(anditssimulator)whichbitsshouldbeplacedwhereinmemory–  Bits?

(remember:everythingendsupbeingabunchof1’sand0’s!)

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AllocatedasprogramRUN

AllocatedatprogramLOAD

Constantstobeusedintheprogram(likestrings)

mutableglobalvariables

thetextoftheprogram

MarkingtheCode

•  Forthesimulator,you’llneeda.textdirectivetospecifycode

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AllocatedasprogramRUN

AllocatedatprogramLOAD

Constantstobeusedintheprogram(likestrings)

mutableglobalvariables

thetextoftheprogram

.text#Mainprogramli$t0,5li$t1,7add$t3,$t0,$t1#Printtostandardoutputli$v0,1move$a0,$t3syscall#Endprogramli$v0,10syscall

Themoveinstruction

•  ThemoveinstructiondoesnotactuallyshowupinSPIM

•  Itisapseudo-instructionforustouse,butit’sactuallytranslatedintoanactualinstruction

ORIGINAL: move$a0,$t3ACTUAL: addu$a0,$zero,$t3 #what’saddu?what’s$zero?

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WhyPseudocodes?Andwhat’sthis$zero??

•  $zero–  Specifiedlikeanormalregister,

butdoesnotbehavelikeanormalregister–  Writesto$zeroarenotsaved–  Readsfrom$zeroalwaysreturn0value

•  Whyhavemoveasapseudo-instructioninsteadofasanactualinstruction?–  It’sonelessinstructiontoworryabout–  OnedesigngoalofRISCistocutoutredundancy–  moveisn’ttheonlyone!liisanotheronetoo!

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ListofallCoreInstructionsinMIPS

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ListoftheArithmeticCoreInstructionsinMIPS

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ListofallPsuedoInstructionsinMIPSThatYouAreAllowedtoUseinCS64!!!

ALLOFTHISANDMOREISONYOURHANDY“MIPSREFERENCECARD”NOWFOUNDONTHECLASSWEBSITE

MIPSPeculiarity:NORusedaNOT

•  HowtomakeaNOTfunctionusingNORinstead•  Recall:NOR=NOTOR•  Truth-Table:

•  So,intheabsenceofaNOTfunction, useaNORwitha0asoneoftheinputs!

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A B ANORB0 00 11 01 1

1

000

Notethat:0NORxx=NOTxx

Let’sRunThisProgramAlready!UsingSPIM

•  We’llcallitsimpleadd.asm•  RunitonCSILas:$spim–fsimpleadd.asm

•  We’llalsorunotherarithmeticprogramsandexplainthemaswegoalong– TAKENOTES!

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YOURTO-DOs

•  ReviewALLthedemocode– Availableviatheclasswebsite

•  Assignment#1– DueFriday

•  Assignment/Lab#2–  LabonMONDAY–  Submititviaturnin

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