chapters 3 arm assembly - sonoma state university...chapters 3 arm assembly embedded systems with...

Chapters3ARMAssemblyEmbeddedSystemswithARMCortext-M

Updated:Wednesday,February7,2018

Programminglanguages-Categories

Efficient,morecomplex

Lesscomplex,notasefficient

Interpretedbasedonthemachine

Programminglanguages-InterpreterVs.Compiler

AssemblerconversinstructionsintoMachineLanguage1sand0s.

CCompiler

AssemblersandCCompilers

AssemblersandCCompilersIDE-

IntegratedDevelopmentEnvironment

ARMAssembly• ModernARMprocessorshaveseveralinstructionsets:• Thefully-featured32-bitARMinstructionset,• Themorerestricted,butspaceefficient,16-bit Thumb instructionset,• Thenewermixed16/32-bit Thumb-2 instructionset,• Jazelle DBX forJavabytecodes,• The NEON 64/128-bitSIMDinstructionset,• The VFP vectorfloatingpointinstructionset.• à Thumb-2istheprogressionofThumb(strictlyitisThumbv3).Itimprovesperformancewhilstkeepingthecodedensitytightbyallowingamixtureof16- and32-bitinstructions.

http://www.davespace.co.uk/arm/introduction-to-arm/instruction-sets.html

LevelsofProgramCodeCCodeà AssemblyàMachineLanguage

8

} High-levellanguage} Levelofabstraction

closertoproblemdomain

} Providesforproductivityandportability

CProgram

Compile Assemble

AssemblyProgram

} Assemblylanguage} Textualrepresentation

ofinstructions

MachineProgram

} Hardwarerepresentation} Binarydigits(bits)} Encodedinstructions

anddata

001000010000000000100000000000001110000000000001010001000000000100011100010000000010100000001010110111001111101110111111000000001110011111111110

int main(void){int i;int total = 0;for (i = 0; i < 10; i++) {total += i;

} while(1); // Dead loop

}

LevelsofProgramCodeCCodeà AssemblyàMachineLanguage

9

MachineProgram

} Hardwarerepresentation} Binarydigits(bits)} Encodedinstructionsand

data

001000010000000000100000000000001110000000000001010001000000000100011100010000000010100000001010110111001111101110111111000000001110011111111110

;MOVSr1,#0x00;MOVSr2,#0x01;ADDSr3,r1,r2;MOVSr0,#0x00;BXlr

21002201188B20004770

InHex

AssemblyInstructionSetsforCortex-M

10fromarm.com

Examples:• ADD• AND• CMP• SUB• MUL• MOV• etc.

AssemblyInstructionsSupported

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• Arithmeticandlogic• Add,Subtract,Multiply,Divide,Shift,Rotate

• Datamovement• Load,Store,Move

• Compareandbranch• Compare,Test,If-then,Branch,compareandbranchonzero

• Miscellaneous• Breakpoints,waitforevents,interruptenable/disable,datamemorybarrier,datasynchronizationbarrier

Compare&Branch DataMovement

Misc. Arithmetic

ARMInstructionFormat

12

label mnemonic operand1, operand2, operand3 ; comments

} Labelisareferencetothememoryaddressofthisinstruction.} Mnemonicrepresentstheoperationtobeperformed(ADD,SUB,etc.).} Thenumberofoperands varies,dependingoneachspecificinstruction.

Someinstructionshavenooperandsatall.} Typically,operand1 isthedestination register,andoperand2 andoperand3 are

sourceoperands.} operand2 isusuallyaregister.} operand3 maybearegister,animmediatenumber,aregistershiftedtoa

constantamountofbits,oraregisterplusanoffset(usedformemoryaccess).

} Everythingafterthesemicolon“;”isacomment,whichisanannotationexplicitlydeclaringprogrammers’intentionsorassumptions.


13


target ADD r0, r2, r3 ; r0 = r2 + r3

label mnemonic commentdestinationoperand

2nd sourceoperand

1st sourceoperand


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Examples:VariantsoftheADDinstructionADD r1, r2, r3 ; r1 = r2 + r3ADD r1, r3 ; r1 = r1 + r3ADD r1, r2, #4 ; r1 = r2 + 4ADD r1, #15 ; r1 = r1 + 15

Remember:Rhastwocomponents:• RegisterAddress• RegisterContent

FirstAssembly

15

AssemblyDirectives

16

AREA Make a new block of data or codeENTRY Declare an entry point where the program execution startsALIGN Align data or code to a particular memory boundaryDCB Allocate one or more bytes (8 bits) of dataDCW Allocate one or more half-words (16 bits) of dataDCD Allocate one or more words (32 bits) of dataSPACE Allocate a zeroed block of memory with a particular sizeFILL Allocate a block of memory and fill with a given value.EQU Give a symbol name to a numeric constantRN Give a symbol name to a registerEXPORT Declare a symbol and make it referable by other source filesIMPORT Provide a symbol defined outside the current source fileINCLUDE/GET Include a separate source file within the current source filePROC Declare the start of a procedureENDP Designate the end of a procedureEND Designate the end of a source file

} DirectivesareNOT instruction;allocatespaceanddefinetypesinmanycases.Theyareusedtoprovidekeyinformationforassembly.

Startofnewdataset;Atleastonecodeareaisrequiredperprogram;couldbe

READONLYorREADWRITE

ReferstoPROCEDUREandEndofPROCEDURE;itdefinesthefunction;

similartomain()inC

ENDofsourcefile

Typically2^N

INCLUDE constants.s ; Load Constant Definitions

ForExampleINCLUDE constants.s; Load Constant Definitions

Let’sPracticeFirst….

AssemblyEmulator

• Gotohttps://salmanarif.bitbucket.io/visual/index.html• Downloadtheappropriateversionforyourcomputer• Thisisthelistofsupportedinstructions:https://salmanarif.bitbucket.io/visual/supported_instructions.html

CODE

CPUREGISTORS

RunyourAssemblyCode MoveONEinstructionatatime

WhatisyourfinalPCvalue?

TryThis&AnswertheQuestions…..

Let’sContinuewithSomeSimpleCommands….

Let’sTakeaMOV&MVNCommands

• MOVr0,#42• Movetheconstant42intoregisterR0.

• MOVr2,r3• MovethecontentsofregisterR3intoregisterR2.

• MVNr1,r0• R1=NOT(R0)=-43

• MOVr0,r0• ANOP(nooperation)instruction.

• <operation>• MOV – move• Rd:=Operand2

• MVN – moveNOT• Rd:=0xFFFFFFFFEOROperand2

ArithmeticOperation

• <operation>• ADD – Add

• Rd:=Rn+Operand2• ADC – AddwithCarry

• Rd:=Rn+Operand2+Carry• SUB – Subtract

• Rd:=Rn−Operand2• SBC – SubtractwithCarry

• Rd:=Rn−Operand2−NOT(Carry)• RSB – ReverseSubtract

• Rd:=Operand2−Rn• RSC – ReverseSubtractwithCarry

• Rd:=Operand2−Rn−NOT(Carry)

• ADDr0,r1,r2• R0=R1+R2

• SUBr5,r3,#10• R5=R3−10

• RSBr2,r5,#0xFF00• R2=0xFF00−R5

RSB and RSC subtract in reverse order (e.g. y - x not x - y).

LogicalInstructions

• AND – logicalAND• Rd:=RnANDOperand2

• EOR – ExclusiveOR• Rd:=RnEOROperand2

• ORR – logicalOR• Rd:=RnOROperand2

• BIC – BitwiseClear• Rd:=RnANDNOTOperand2

• ANDr8,r7,r2• R8=R7&R2

• ORRr11,r11,#1• R11|=1

• BICr11,r11,#1• R11&=~1

• EORr11,r11,#1• R11^=1

CompareInstructions:<operation>{cond}Rn,Operand2• <operation>• CMP – compare

• Flagssettoresultof(Rn−Operand2).• CMN – comparenegative

• Flagssettoresultof(Rn+Operand2).• TST – bitwisetest

• Flagssettoresultof(RnANDOperand2).

• TEQ – testequivalence• Flagssettoresultof(RnEOROperand2).

• CMPr0,#42• CompareR0to42.

• CMNr2,#42• CompareR2to-42.

• TSTr11,#1• Testbitzero.

• TEQr8,r9• TestR8equalsR9.

• SUBSr1,r0,#42• CompareR0to42,withresult.

•CMP is like SUB.•CMN is like ADD – subtract of a negative number is the same as add.•TST is like AND.•TEQ is like EOR – exclusive or of identical numbers gives result of zero.

Directive:AREA

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AREA myData, DATA, READWRITE ; Define a data sectionArray DCD 1, 2, 3, 4, 5 ; Define an array with five integers

AREA myCode, CODE, READONLY ; Define a code sectionEXPORT __main ; Make __main visible to the linkerENTRY ; Mark the entrance to the entire program

__main PROC ; PROC marks the begin of a subroutine... ; Assembly program starts here.ENDP ; Mark the end of a subroutineEND ; Mark the end of a program

• TheAREAdirectiveindicatestotheassemblerthestartofanewdataorcodesection.

• Areasarethebasicindependentandindivisibleunitprocessedbythelinker.

• Eachareaisidentifiedbyanameandareaswithinthesamesourcefilecannotsharethesamename.

• Anassemblyprogrammusthaveatleastonecodearea.

• Bydefault,acodeareacanonlyberead(READONLY)andadataareamaybereadfromandwrittento(READWRITE).

Directive:ENTRY

27




• TheENTRYdirectivemarksthefirstinstructiontobeexecutedwithinanapplicationprogram.

• Theremustbeexactlyone ENTRYdirectiveinanapplication,nomatterhowmanysourcefilestheapplicationhas.

Directive:END

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• TheENDdirectiveindicatestheendofasourcefile.

• Eachassemblyprogrammustendwiththisdirective.

Directive:PROC andENDP

29




• PROC andENDP aretomarkthestartandendofafunction(alsocalledsubroutineorprocedure).

• Asinglesourcefilecancontainmultiplesubroutines,witheachofthemdefinedbyapairofPROC andENDP.

• PROC andENDP cannotbenested.Wecannotdefineafunctionwithinanotherfunction.

Directive:EXPORTandIMPORT

30




• TheEXPORTdeclaresasymbolandmakesthissymbolvisibletothelinker.

• TheIMPORTgivestheassemblerasymbolthatisnotdefinedlocallyinthecurrentassemblyfile.Thesymbolmustbedefinedinanotherfile.

• TheIMPORTissimilartothe“extern”keywordinC.

Directive:DataAllocation

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Directive Description Memory SpaceDCB Define Constant Byte Reserve 8-bit valuesDCW Define Constant Half-word Reserve 16-bit valuesDCD Define Constant Word Reserve 32-bit valuesDCQ Define Constant Reserve 64-bit valuesDCFS Definesingle-precision

floating-pointnumbersReserve 32-bit values

DCFD Definedouble-precisionfloating-pointnumbers

Reserve 64-bit values

SPACE Defined Zeroed Bytes Reserve a number of zeroed bytesFILL Defined Initialized Bytes Reserve and fill each byte with a value

Directive:DataAllocation

32

AREA myData, DATA, READWRITEhello DCB "Hello World!",0 ; Allocate a string that is null-terminated

dollar DCB 2,10,0,200 ; Allocate integers ranging from -128 to 255

scores DCD 2,3.5,-0.8,4.0 ; Allocate 4 words containing decimal values

miles DCW 100,200,50,0 ; Allocate integers between –32768 and 65535

Pi DCFS 3.14 ; Allocate a single-precision floating number

Pi DCFD 3.14 ; Allocate a double-precision floating number

p SPACE 255 ; Allocate 255 bytes of zeroed memory space

f FILL 20,0xFF,1 ; Allocate 20 bytes and set each byte to 0xFF

binary DCB 2_01010101 ; Allocate a byte in binary

octal DCB 8_73 ; Allocate a byte in octal

char DCB ‘A’ ; Allocate a byte initialized to ASCII of ‘A’

Directive:EQU andRN

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• TheEQU directiveassociatesasymbolicnametoanumericconstant.Similartotheuseof#defineinaCprogram,theEQU canbeusedtodefineaconstantinanassemblycode.

• TheRNdirectivegivesasymbolicnametoaspecificregister.

; Interrupt Number Definition (IRQn)BusFault_IRQn EQU -11 ; Cortex-M3 Bus Fault Interrupt SVCall_IRQn EQU -5 ; Cortex-M3 SV Call Interrupt PendSV_IRQn EQU -2 ; Cortex-M3 Pend SV Interrupt SysTick_IRQn EQU -1 ; Cortex-M3 System Tick Interrupt

Dividend RN 6 ; Defines dividend for register 6Divisor RN 5 ; Defines divisor for register 5

Directive:ALIGN

34

AREA example, CODE, ALIGN = 3 ; Memory address begins at a multiple of 8ADD r0, r1, r2 ; Instructions start at a multiple of 8

AREA myData, DATA, ALIGN = 2 ; Address starts at a multiple of foura DCB 0xFF ; The first byte of a 4-byte word

ALIGN 4, 3 ; Align to the last byte (3) of a word (4)b DCB 0x33 ; Set the fourth byte of a 4-byte wordc DCB 0x44 ; Add a byte to make next data misaligned

ALIGN ; Force the next data to be alignedd DCD 12345 ; Skip three bytes and store the word

Directive:INCLUDEorGET

35

• TheINCLUDEorGETdirectiveistoincludeanassemblysourcefilewithinanothersourcefile.

• ItisusefultoincludeconstantsymbolsdefinedbyusingEQU andstoredinaseparatesourcefile.

INCLUDE constants.s ; Load Constant DefinitionsAREA main, CODE, READONLYEXPORT __main ENTRY

__main PROC...ENDPEND

chapters 3 arm assembly - sonoma state university...chapters 3 arm assembly embedded systems with...

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