It also defines interaction between the above components. It is this low level programming model which makes programmed computations possible.

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1 ProgrammingModel1 A.Introduction Objectives Attheendofthislabyoushouldbeableto: UsetheCPUsimulatortocreatebasicCPUinstructions UsethesimulatortoexecutebasicCPUinstructions UseCPUinstructionstomovedatatoregisters,comparevaluesinregisters, pushdatatothestack,popdatafromthestack,jumptoaddresslocations andaddvaluesheldinregisters. ExplainthefunctionsofspecialCPUregisterssuchasthePC,SRandSP registers. B.Processor(CPU)Simulators Thecomputerarchitecturetutorialsaresupportedbysimulators,whicharecreated tounderpintheoreticalconceptsnormallycoveredduringthelectures.the simulatorsprovidevisualandanimatedrepresentationofmechanismsinvolvedand enablethestudentstoobservethehiddeninnerworkingsofsystems,whichwould bedifficultorimpossibletodootherwise.theaddedadvantageofusingsimulators isthattheyallowthestudentstoexperimentandexploredifferenttechnological aspectsofsystemswithouthavingtoinstallandconfiguretherealsystems. C.BasicTheory Theprogrammingmodelofcomputerarchitecturedefinesthoselowlevel architecturalcomponents,whichincludethefollowing CPUinstructionset CPUregisters Differentwaysofaddressinginstructionsanddataininstructions Italsodefinesinteractionbetweentheabovecomponents.Itisthislowlevel programmingmodelwhichmakesprogrammedcomputationspossible. D.SimulatorDetails Thissectionincludessomebasicinformationonthesimulator,whichshouldenable thestudentstousethesimulator.thetutor(s)willbeavailabletohelpanyone experiencingdifficultyinusingthesimulator.thesimulatorforthislabisan applicationrunningonapcrunningmswindowsoperatingsystem. Themainwindowiscomposedofseveralviews,whichrepresentdifferentfunctional partsofthesimulatedprocessor.theseareshowninimage1belowandare composedof 1

CPUInstructionmemory SpecialCPUregisters CPU(generalpurpose)registers Programstack Programcreationandrunningfeatures CPUInstruction memoryview Addprogram instructionstab Createprogramtab SpecialCPU

2 CPUInstructionmemory SpecialCPUregisters CPU(generalpurpose)registers Programstack Programcreationandrunningfeatures CPUInstruction memoryview Addprogram instructionstab Createprogramtab SpecialCPU registersview Programlistview Image1 CPUSimulatorwindow CPUregistersview Programstackview Thepartsofthesimulatorrelevanttothislabaredescribedbelow.Pleasereadthis informationcarefullyandtrytoidentifythedifferentpartsonthecpusimulator windowbeforeattemptingthefollowingexercises.usethisinformationin conjunctionwiththeexercisesthatfollow. 2

Each instruction is associated with two addresses: the physicaladdress(padd)andthe logical address (LAdd). This view also displays the base address (Base) against each instruction.

3 1.CPUinstructionmemoryview Image2Instructionmemory view Thisviewcontainstheprogram instructions. The instructions are displayed as sequences of lowlevel instruction mnemonics (assemblerlevel format)andnotasbinarycode. This is done for clarity and makes code more readable by humans. Each instruction is associated with two addresses: the physicaladdress(padd)andthe logical address (LAdd). This view also displays the base address (Base) against each instruction. The sequence of instructions belonging to the same program will have the samebaseaddress. 2.SpecialCPUregistersview ThisviewshowsthesetofCPUregisters, whichhavepredefinedspecialistfunctions: PC:ProgramCountercontainstheaddress ofthenextinstructiontobeexecuted. IR:InstructionRegistercontainsthe instructioncurrentlybeingexecuted. SR:StatusRegistercontainsinformation pertainingtotheresultofthelastexecuted instruction. SP:StackPointerregisterpointstothevalue maintainedatthetopoftheprogramstack (seebelow). BR:BaseRegistercontainscurrentbase address. MAR:MemoryAddressRegistercontains Image3SpecialCPU registersview thememoryaddresscurrentlybeing accessed. Statusbits:OV:Overflow;Z:Zero;N: Negative 3

3.CPUregistersview Image4 CPURegistersview The register set view shows the contents of all the generalpurpose registers, which are used to maintain temporary values as the program's

4 3.CPUregistersview Image4 CPURegistersview The register set view shows the contents of all the generalpurpose registers, which are used to maintain temporary values as the program's instructionsareexecuted.registersare very fast memories that hold temporary values while the CPU executesinstructions. Thisarchitecturesupportsfrom8to64 registers. These registers are often used to hold values of a program's variables as defined in highlevel languages. Not all architectures have this many registers. Some have more ( 128 register) and some others have less ( 8 registers). In all cases, these registersservesimilarpurposes. Thisviewdisplayseachregister'sname (Reg),itscurrentvalue(Val)andsome additional values, which are reserved for program debugging. It can also be used to reset the individual register values manually which is often useful for advanced debugging. To manually changearegister scontent,firstselect the register then enter the new value inthetextbox,regvalue,andclickon the CHANGE button in the Registers tab. 4

4.Programstackview Image5Programstackview Theprogramstackisanotherareawhich maintains temporary values as the instructionsareexecuted.

TheCPUinstructionsPSH(push)andPOP areusedtostorevaluesontopofstack and pop values from top of stack respectively. 5.

buttontoremovealltheprogramsfrom the list. Note that when a program is removed, its instructions are also removed from the Instruction Memory Viewtoo. 6.

5 4.Programstackview Image5Programstackview Theprogramstackisanotherareawhich maintains temporary values as the instructionsareexecuted.thestackisa LIFO(lastinfirstout)datastructure.Itis often used for efficient interrupt handling and subroutine calls. Each programhasitsownindividualstack. TheCPUinstructionsPSH(push)andPOP areusedtostorevaluesontopofstack and pop values from top of stack respectively. 5.Programlistview Image6 ProgramListView Use the REMOVE PROGRAM button to remove the selected program from the list; use the REMOVE ALL PROGRAMS buttontoremovealltheprogramsfrom the list. Note that when a program is removed, its instructions are also removed from the Instruction Memory Viewtoo. 6.Programcreation Image7 Createprogramtab Tocreateanewprogramenterits nameintheprogramnamebox anditsbaseaddressinthebase AddressboxthenclickontheADD button.thenewprogram sname willappearintheprogramlistview (seeimage6). 5

Image8 Addprogram instructionstab UseADDNEW buttontoadda new instruction; use EDIT button to edit the selected instruction; use MOVE DOWN/ MOVE UP buttons to move the selected instruction down or up;

6 Image8 Addprogram instructionstab UseADDNEW buttontoadda new instruction; use EDIT button to edit the selected instruction; use MOVE DOWN/ MOVE UP buttons to move the selected instruction down or up; use INSERT ABOVE /INSERT BELOW buttonstoinsertanew instruction above or below the selectedinstructionrespectively. E. Lab Exercises - Investigate and Explore Thelabexercisesareaseriesofactivities,whicharecarriedoutbythestudents underbasicguidelines.so,howisthistutorialconducted?thestudentsareexpected tofollowtheinstructionsgiveninordertoidentifyandlocatetherequired information,toactuponitandmakenotesoftheirobservations.inordertobeable todotheseactivitiesyoushouldconsulttheinformationinsectiondaboveandalso frequentlyrefertotheappendixforinformationonvariouscpuinstructionsyouwill beaskedtocreateanduse.remember,youneedtocarefullyreadandunderstand theinstructionsbeforeyoucanattempteachactivity. Now,letusstart.FirstyouneedtoplacesomeinstructionsintheInstruction MemoryView(seeImage2),representingtheRAMintherealmachine,before executinganyinstructions.todothis,followthestepsbelow: IntheProgramtab(seeImage7),firstenteraProgramName,andthenenteraBase Address(thiscanbeanynumber,butforthisexerciseuse100).ClickontheADD button.anewprogramnamewillbeenteredintheprogramlistview(seeimage6). YoucanusetheSAVE buttontosaveinstructionsinafile.youcanalsousethe LOAD buttontoloadinstructionsfromafile. YouarenowreadytoenterinstructionsintotheCPUSimulator.Youdothisby clickingontheaddnew buttonintheinstructionstab(seeimage8).thiswill displaytheinstructions:cpu0window.youusethiswindowtoselectandenterthe CPUinstructions.Appendixlistssomeoftheinstructionsthissimulatorusesandalso givesexamplesoftheirusage. Now,haveagoatthefollowingactivities(enteryouranswersinthetextboxes provided).awordofcaution:regularlysaveyourcodeinafileincasethesimulator crashesinwhichcaseyoucanrestartthesimulatorandreloadyourfile. 6

7 1. Createaninstruction,whichmovesnumber5toregisterR Executetheaboveinstruction(todothissimplydoubleclickonitinthe InstructionMemoryView).ObservetheresultintheCPURegistersview(Image 4). 3. Createaninstruction,whichmovesnumber8toregisterR Executeit(Youdothisbydoubleclickingontheinstruction) 5. ObservethecontentsofR00andR01intheCPURegistersview(Image4). 6. Createaninstruction,whichaddsthecontentsofR00andR Executeit. 8. Observewhichregistertheresultisputin. 9. Createaninstruction,whichpushestheaboveresulttothetopof thehardwarestack,andthenexecuteit. 10. Createaninstructiontopushnumber2ontopofthestackandexecuteit. ObservethevalueinProgramStack(Image5). 11. ObservethevalueintheSPregister(SpecialCPURegistersview Image3). WheneveryoupushavalueonProgramStack,theSPregisterisupdated. 12. CreateaninstructiontocomparethevaluesinregistersR00andR01. 7

8 13. Executeit. 14. ObservethevalueintheSRregister(SpecialCPURegistersview Image3). 15. ObservethestatusoftheOV/Z/Npartsofthestatusregister.Whichboxesare checkedandwhicharenot?whatdotheyindicate? 16. Createaninstructiontounconditionallyjumptothefirstinstruction. 17. Executeit. 18. ObservethevalueinthePCregister.Thisistheaddressofthenextinstructionto beexecuted.makeanoteofwhichinstructionitispointingto? 19. ObservethevaluesinthePAddandLAddcolumns.Whatdothesevalues indicate?aretheydifferent(hint:checkoutthebaseaddressvalue)? 20. WhatisthedifferencebetweentheLAddvalueofthefirstinstructionandthe LAddvalueofthesecondinstruction?Whatdoesthisvalueindicate(Hint:Think oftheinstructionlengthsinbytes)? 21. CreateaninstructiontopopthevalueontopoftheProgramStackintoregister R02. 8

9 22. Executeit. 23. ObservethevalueintheSPregister. 24. CreateaninstructiontopopthevalueontopoftheProgramStackintoregister R Executeit. 26. ObservethevalueintheSPregister. 27. Executethelastinstructionagain.Whathappened?Explain. 28. Createacompareinstruction,whichcomparesvaluesinregistersR04andR ManuallyinserttwoequalvaluesinregistersR04andR05(Image4). 30. Oneagainexecutethecompareinstructioninstep28above. 31. WhichofthestatusflagsOV/Z/Nisset(i.e.boxischecked)?Why? 32. ManuallyinsertavalueinregisterR05greaterthanthatinregisterR Executethecompareinstructioninstep28above. 34. WhichofthestatusflagsOV/Z/Nisset?Why? 35. ManuallyinsertavalueinregisterR04greaterthanthatinregisterR Executethecompareinstructioninstep28above. 37. WhichofthestatusflagsOV/Z/Nisset?Why? 9

10 38. Createaninstruction,whichwilljumptothefirstinstructionifthevaluesin registersr04andr05areequal. 39. TesttheaboveinstructionbymanuallyputtingequalvaluesinregistersR04 andr05,thenfirstexecutingthecompareinstructionfollowedbyexecutingthe jumpinstruction(remember:youexecuteaninstructionbydoubleclickingon it).diditwork? 40. SavetheinstructionsintheInstructionMemoryViewinafilebyclickingon thesave button(image7). ***Endofexercises*** 10

11 Instruction Data transfer instructions MOV LDB LDW STB STW PSH POP Appendix - Simulator Instruction Sub-set Description Move data to register; move register to register MOV #2, R01 moves number 2 into register R01 MOV R01, R03 moves contents of register R01 into register R03 Load a byte from memory to register Load a word (2 bytes) from memory to register Store a byte from register to memory Store a word (2 bytes) from register to memory Push data to top of hardware stack (TOS); push register to TOS PSH #6 pushes number 6 on top of the stack PSH R03 pushes the contents of register R03 on top of the stack Pop data from top of hardware stack to register Arithmetic instructions ADD SUB MUL DIV POP R05 pops contents of top of stack into register R05 Note: If you try to POP from an empty stack you will get the error message Stack overflow. Add number to register; add register to register ADD #3, R02 adds number 3 to contents of register R02 and stores the result in register R02. ADD R00, R01 adds contents of register R00 to contents of register R01 and stores the result in register R01. Subtract number from register; subtract register from register Multiply number with register; multiply register with register Divide number with register; divide register with register Control transfer instructions JMP Jump to instruction address unconditionally 11

12 JLT JGT JEQ JNE CAL RET SWI HLT JMP 100 unconditionally jumps to address location 100 Jump to instruction address if less than (after last comparison) Jump to instruction address if greater than (after last comparison) Jump to instruction address if equal (after last comparison instruction) JEQ 200 jumps to address location 200 if the previous comparison instruction result indicates that the two numbers are equal, i.e. the Z status flag is set (the Z box will be checked in this case). Jump to instruction address if not equal (after last comparison) Jump to subroutine address Return from subroutine Software interrupt (used to request OS help) Halt simulation Comparison instruction CMP Compare number with register; compare register with register CMP #5, R02 compare number 5 with the contents of register R02 CMP R01, R03 compare the contents of registers R01 and R03 Note: Input, output instructions IN OUT If R01 = R03 then the status flag Z will be set, i.e. the Z box is checked. If R03 > R01 then non of the status flags will be set, i.e. none of the status flag boxes are checked. If R01 > R03 then the status flag N will be set, i.e. the N status box is checked. Get input data (if available) from an external IO device Output data to an external IO device 12

Tutorial 1: Programming Model 1

Tutorial 1: Programming Model 1 Introduction Objectives At the end of this lab you should be able to: Use the CPU simulator to create basic CPU instructions Use the simulator to execute the basic CPU instructions