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MIPSandBasicAssemblyLanguage
CS64:ComputerOrganizationandDesignLogicLecture#4
ZiadMatni
Dept.ofComputerScience,UCSB
4/12/18 Matni,CS64,Sp18 2
ThisWeekon
“DidjaKnowDat?!”
4/12/18 Matni,CS64,Sp18 3
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$zeroalwaysreturn0value
• Whyhavemoveasapseudo-instructioninsteadofasanactualinstruction?– It’sonelessinstructiontoworryabout– OnedesigngoalofRISCistocutoutredundancy– moveisn’ttheonlyone!liisanotheronetoo!
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ListofallCoreInstructionsinMIPS
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ListoftheArithmeticCoreInstructionsinMIPS
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ListofallPsuedoInstructionsinMIPSThatYouAreAllowedtoUseinCS64!!!
ALLOFTHISANDMOREISONYOURHANDY“MIPSREFERENCECARD”NOWFOUNDONTHECLASSWEBSITE
MIPSPeculiarity:NORusedaNOT
• HowtomakeaNOTfunctionusingNORinstead• Recall:NOR=NOTOR• Truth-Table:
• So,intheabsenceofaNOTfunction, useaNORwitha0asoneoftheinputs!
4/12/18 Matni,CS64,Sp18 47
A B ANORB0 00 11 01 1
1
000
Notethat:0NORxx=NOTxx
Let’sRunThisProgramAlready!UsingSPIM
• We’llcallitsimpleadd.asm• RunitonCSILas:$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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