MIPSAssembly:PracticeQuestionsforMidterm1

SavingtoandLoadingfromMemory

CS64:ComputerOrganizationandDesignLogicLecture#6

ZiadMatni

Dept.ofComputerScience,UCSB

•  Tuesday,4/24inthisclassroom•  Startsat11:00AM**SHARP**

–  Pleasestartarriving5-10minutesbeforeclass

•  Imayaskyoutochangeseats•  PleasebringyourUCSBIDswithyou

•  Closedbook:nocalculators,nophones,nocomputers•  OnlytheMIPSReferenceCardisallowed•  Youwillwriteyouranswersontheexamsheetitself.

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What’sontheMidterm??1/2•  DataRepresentation

–  Convertbinßàhexßàdecimalßàbin–  Signedandunsignedbinaries

•  LogicandArithmetic–  Binaryaddition,subtraction

•  CarryandOverflow–  BitwiseAND,OR,NOT,XOR–  GeneralrulesofAND,OR,XOR,usingNORasNOT

•  Alldemosdoneinclass•  Labassignments1and2

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What’sontheMidterm??2/2Assembly•  CorecomponentsofaCPU

–  Howinstructionswork•  Registers($t,$s,$a,$v)•  Arithmeticinassembly(add,subtract,multiply,divide)

–  What’sthedifferencebetweenadd,addi,addu,addui,etc…•  Conditionalsandloopsinassembly•  ConversiontoandfromAssemblyandC/C++•  syscallanditsvarioususes(printingoutput,takinginput,ending

program)•  .dataand.textdeclarations•  MemoryinMIPS•  BigEndianvsLittleEndian4/19/18 Matni,CS64,Wi18 4

ReviewQuestions

•  IwillputupreviewquestionsforMidterm#1upontheclasswebsite– Laterontoday…

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AbouttheMidtermExam•  MadeupofMultipleChoice&ShortAnswers/Coding.EXAMPLES:

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CompletethefollowingMIPSassemblycodethatissupposedtoaddthenumberinregister$t0to15:

li$t0,12_____________

A.  add$t2,$t1,$t2B.  addu$t2,$t1,$t2C.  addi$t2,$t0,FD.  addi$t2,$t0,0xFE.  addui$t2,$t0,0xF

Whatisthe2’scomplementof0x5EC?

A.  1x5ECB.  0x5ECC.  0xA13D.  0xA14E.  0xA15

SampleQuestions

TranslatethisC-stylecodeinto4linesofMIPSassemblycode:intt1=10,t2=3;intt3=t1+2*t2

Whatistheresultoftheseoperations?0xF2&~(0x55)0x102A99D8^0xABA11CAB

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li$t1,10li$t2,3sll$t2,$t2,1add$t3,$t2,$t1

0xA2

00010000001010101001100111011000^10101011101000010001110010101011=10111011100010111000010101110011=0xBB8B8573

SampleQuestionsTranslatethisMIPSassemblycodeintopseudo-code(CorC++accepted):li$s0,2li$s1,6li$t0,2add$s2,$s1,$s0sll$s2,$s2,3mult$s2,$t0mflo$s34/19/18 Matni,CS64,Sp18 8

ints0=2,s1=6,t0=2;ints2=s1+s0;s2*=8;ints3=s2*t0;

SampleQuestions

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.textmain:li$t0,3li$t2,7slt$t3,$t0,$t2beq$t3,$zero,elseadd$t1,t0,$t2;jend

else:add$t1,$t0,$t0

end:li$v0,10syscall

TranslatethisC++codeintoMIPS(justthe.textpart)intt0=3;if(t0<7)t1=7+t0;

elset1=t0+t0;

AnyQuestionsFromLastLecture?

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LargerDataStructures

•  Recall:registersvs.memory– Wherewoulddatastructures,arrays,etc.go?– Whichisfastertoaccess?Why?

•  Somedatastructureshavetobestoredinmemory– Soweneedinstructionsthat“shuttle”datato/fromtheCPUandcomputermemory(RAM)

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AccessingMemory•  Twobaseinstructions:–  load-word(lw)frommemorytoregisters–  store-word(sw)fromregisterstomemory

•  MIPSlacksinstructionsthatdomorewithmemorythanaccessit(e.g.,retrievesomethingfrommemoryandthenadd)–  Operationsaredonestep-by-step– MarkofRISCarchitecture

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MemoryRs

lw

sw

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.datanum1:.word42num2:.word7num3:.space1.textmain:

lw$t0,num1lw$t1,num2add$t2,$t0,$t1sw$t2,num3li$v0,1lw$a0,num3syscall

li$v0,10syscall

Example4Whatdoesthisdo?

MemoryRs

lw

sw

AddressingMemory•  Ifyou’renotusingthe.datadeclarations,thenyouneedstarting

addressesofthedatainmemorywithlwandswinstructionsExample: lw$t0,0x0000400A (ßnotarealaddress)Example: lw$t0,0x0000400A($s0)(ßnotarealaddress)

•  1word=32bits(inMIPS)–  So,ina32-bitunitofmemory,that’s4bytes–  Representedwith8hexadecimals 8x4bits=32bits…checksout…

•  MIPSaddressessequentialmemoryaddresses,butnotin“words”–  AddressesareinBytesinstead–  MIPSwordsmuststartataddressesthataremultiplesof4–  Calledanalignmentrestriction

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ThisisfoundonyourMIPSReferenceCard

NOTE:Notallmemoryaddressescanbeaccessedbytheprogrammer.Althoughtheaddressspaceis32bits,thetopaddressesfrom0x80000000to0xFFFFFFFFarenotavailabletouserprograms.TheyareusedmostlybytheOS.

Howmuchmemorydoesaprogrammergettodirectly

useinMIPS?

MemoryAllocationMap

MappingMIPSMemory(saythat10timesfast!)

•  Imaginecomputermemorylikeabigarrayofwords•  Sizeofcomputermemoryis:

232=4Gbits,or512MBytes(MB)–  Weonlygettouse2Gbits,or256MB–  That’s(256MB/groupsof4B)=64millionwords

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8bits 8bits 8bits 8bitsword

MIPSComputerMemoryAddressingConventions

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1A 80 C5 29

52 00 37 EE

B1 11 1A A5

0x00000x00010x00020x00030x00040x00050x00060x00070x00080x00090x000A0x000B

Aàà

MIPSComputerMemoryAddressingConventions

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1A 80 C5 29

52 00 37 EE

B1 11 1A A5

0x00030x00020x00010x00000x00070x00060x00050x00040x000B0x000A0x00090x0008

Bßß

or...

ATaleof2Conventions…

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BIGEND(MSByte)getsaddressedfirst

LITTLEEND(LSByte)getsaddressedfirst

TheUseofBigEndianvs.LittleEndian

Origin:JonathanSwift(author)in“Gulliver'sTravels”.Somepeoplepreferredtoeattheirhardboiledeggsfromthe“little

end”first(thus,littleendians),whileothersprefertoeatfromthe“bigend”(i.e.bigendians).

•  MIPSuserstypicallygowithBigEndianconvention–  MIPSallowsyoutoprogram“endian-ness”

•  MostIntelprocessorsgowithLittleEndian…

•  It’sjustaconvention–itmakesnodifferencetoaCPU!

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YOURTO-DOs

•  Finishassignment/Lab#2– AssignmentdueonFRIDAY

•  Studyforyourmidterm!!J

•  Relaxalittle

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