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ARM VERSION 1.2 manual Finding the end of the allocated data

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Writing ARM and Thumb Assembly Language

2.10.4Finding the end of the allocated data

You can use the FIELD directive with an operand of 0 to label a location within a structure. The location is labeled, but the location counter is not incremented.

The size of the data structure defined in Example 2-19 depends on the values of MaxStrLen and ArrayLen. If these values are too large, the structure overruns the end of available memory.

Example 2-19 uses:

•an EQU directive to define the end of available memory

•a FIELD directive with an operand of 0 to label the end of the data structure.

An ASSERT directive checks that the end of the data structure does not overrun the available memory.

Example 2-19

StartOfData	EQU	0x1000
EndOfData	EQU	0x2000
	MAP	StartOfData
Integer	FIELD	4
Integer2	FIELD	4
String	FIELD	MaxStrLen
Array	FIELD	ArrayLen*8
BitMask	FIELD	4
EndOfUsedData	FIELD	0
	ASSERT	EndOfUsedData <= EndOfData

ARM DUI 0068B

Copyright © 2000, 2001 ARM Limited. All rights reserved.

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ARM VERSION 1.2 manual Finding the end of the allocated data

Contents

ARM Developer Suite Assembler Guide ARM Developer SuiteCopyright 2000, 2001 ARM Limited. All rights reserved ARM Developer Suite Assembler Guide Glossary Feedback on About this book onThis book is organized into the following chapters Using this bookAbout this book Intended audienceARM publications Typographical conventionsItalic Further readingOther publications ARM Reference Peripheral Specification ARM DDIFeedback on the ARM Developer Suite FeedbackFeedback on this book ARM DUI 0068B About the ARM Developer Suite assemblers on IntroductionARM Developer Suite ADS has About the ARM Developer Suite assemblersWriting ARM and Thumb Assembly Language Code examples IntroductionOr run the module in AXD with interleaving on See ARM processors always start executing code in ARM state Overview of the ARM architectureArchitecture versions ARM and Thumb stateRegisters Processor modeGeneral-purpose, 32-bit registers Program counter pc Branch instructions ARM instruction set overviewData processing instructions Semaphore instructions Status register access instructionsSingle register load and store instructions Multiple register load and store instructionsFollowing general points apply to ARM instructions Register accessAccess to the inline barrel shifter ARM instruction capabilitiesThumb instruction capabilities Thumb instruction set overviewFollowing general points apply to Thumb instructions Differences between Thumb and ARM instruction sets Access to the barrel shifterSingle register load and store instructions Case rules Structure of assembly language modulesLayout of assembly language source files General form of source lines in assembly language isLocal labels LabelsComments Is a base between 2 Xxx is a number in that base ConstantsELF sections and the Area directive An example ARM assembly language moduleEND directive Entry directiveApplication execution Application terminationCalling subroutines CODE32 and CODE16 directives An example Thumb assembly language moduleBX instruction Example 2-4 Preprocessing an assembly language source file Using the C preprocessorALU status flags Conditional executionExamples Execution conditionsExample of the use of conditional execution Using conditional execution in ARM stateConditional branches only Branch prediction and caches Converting to ThumbLoading constants into registers Right, 2 bits Direct loading with MOV and MVNLoading with LDR Rd, =const Direct loading with MOV in Thumb statePlacing literal pools Loading floating-point constants Direct loading with ADR and Adrl Loading addresses into registersADR Implementing a jump table with ADR Example 2-7 ARM code jump table Example 2-8 Thumb code jump table Loading addresses with LDR Rd, = label R1, =Darea + = LDR R1,PC, #offset into Literal Pool Address registers. For example, the instruction An LDR Rd, =label example string copyingIncrements r1 by Load register Load and store multiple register instructions Where ARM LDM and STM instructionsSyntax Syntax of the LDM instructions isLDM and STM addressing modes UsageDescending or ascending Implementing stacks with LDM and STMStacking registers for nested subroutines Example 2-11 Block copy Block copy with LDM and STMMovs Thumb-state block copy example Thumb LDM and STM instructionsLDM and STM Push and POPLSR After substitution this becomes Using macrosTest-and-branch macro example This macro can be invoked as followsIf only the remainder is required Unsigned integer division macro exampleRegister that holds the divisor After the instructions are executed, it holds the remainderRatio DivMod r0,r5,r4,r2 Describing data structures with MAP and Field directives Relative maps Register-based maps Program-relative maps Finding the end of the allocated data Forcing correct alignment EndOfChars Defining register-based symbols Using register-based MAP and Field directivesIs equivalent to the C code Setting up a C-type structureIf you want the equivalent of the C code Making faster access possible2-27 for an explanation of these Not This example, the MAP directive isField MAP Using two register-based structures Avoiding problems with MAP and Field directives ArrayBase RN r9 Using frame directives Expressions, literals, and operators on Symbols onCommand syntax Position-independent. The default is /norwpi Specifies that the content of inputfile is read-onlyPosition-independent. The default is /noropi Specifies that the content of inputfile is read-writeSelects no floating-point option. This makes your assembled Assembled for the wrong target FPUSelection of libraries, accordingly Valid options areAllow unaligned LDRs Command-line optionsSets the maximum source cache size to n. The default is 8MB Object file, for use by the debugger see Keep onTurns off warning messages First pass and reads them from memory on the second passAs \n and \t Register namesAssembler Reference Format of source lines Predeclared floating-point register names Predefined register and coprocessor namesPredeclared register names Predeclared program status register namesLists the built-in variables defined by the ARM assembler Built-in variablesExpressions or conditions, for example Determining the armasm version at assembly time Labels on SymbolsSymbol naming rules Numeric constants onNumeric constants VariablesGbls Assembly time substitution of variablesRegister-relative labels Program-relative labelsDCD and Dcdu on Dcfd and Dcfdu on Dcfs and Dcfsu on DCQ and Dcqu on DCW and Dcwu onSyntax of a reference to a local label is Syntax of a local label isAssembler Reference This section contains the following subsections Expressions, literals, and operatorsString literals String expressionsString literals ExampleNumeric expressions Numeric code of the character Is a sequence of characters using only the digits 0 to nNumeric literals Numeric literals can take any of the following formsFloating-point literals can take any of the following forms Floating-point literalsThere are only two logical literals Register-relative and program-relative expressionsLogical expressions Logical literalsString manipulation Operator precedenceOperator precedence in C Precedence Operator Usage Description Unary operatorsExample of use of SBOFFSET1912 and SBOFFSET11 Multiplicative operators Binary operatorsString manipulation operators SHR is a logical shift and does not propagate the sign bit Shift operatorsAddition, subtraction, and logical operators Relational operators 10 shows the Boolean operators Boolean operatorsARM DUI 0068B ARM Instruction Reference Add with carry, Add All Logical Branch Move not All ARM condition codes Q flag LDR and STR, doublewords on ARM memory access instructionsLDR and STR, words and unsigned bytes on LDR and STR, halfwords and signed bytes onLDR and STR, words and unsigned bytes Where Is either LDR Load Register or STR Store RegisterOtherwise, a 32-bit word is transferred Post-indexed offset Zero offsetPre-indexed offset Program-relativeFlexible offset syntax Loading to r15 Address alignment for word transfersArchitectures Saving from r15LDR and STR, halfwords and signed bytes Is often a numeric constant see examples below Must be within ±255 bytes of the current instructionIs an offset applied to the value in Rn see Offset syntax Offset syntaxIncorrect example Offset syntax is the same for LDR and STR, doublewords onAddress alignment for halfword transfers You cannot load halfwords or bytes to r15Pre-indexed without writeback LDR and STR, doublewordsIs an optional condition code see Conditional execution on Must be an even numbered register, and not r14Address alignment Not be the same as Rd or Rd+1Incorrect examples Increment address before each transfer Is either LDM or STMIs any one of the following Increment address after each transferLoading or storing the base register, with writeback Non word-aligned addressesIs the register on which the memory address is based 5 PLDAlignment 6 SWP Is swapped with the contents of the memory locationBoth Rd and Rm ARM general data processing instructions Flexible second operand Bits of the register are set to LSR and LSLInstruction substitution Carry flagIs the ARM register holding the first operand 2 ADD, SUB, RSB, ADC, SBC, and RSCIs one of ADD, SUB, RSB, ADC, SBC, or RSC Is the ARM register for the resultUse of r15 Condition flagsMultiword arithmetic examples These instructions subtract one 96-bit integer from another Logical AND, OR, Exclusive or and Bit Clear 3 AND, ORR, EOR, and BICIs one of AND, ORR, EOR, or BIC Orreq Move and Move Not MOV and MVNIs the ARM register for the result Mvnne Compare and Compare Negative CMP and CMNCMN Test and Test Equivalence TST and TEQTEQ Is the operand register 7 CLZCount Leading Zeroes Is the ARM register for the result. Rd must not be r15MUL and MLA on ARM multiply instructionsUMULL, UMLAL, Smull and Smlal on MUL and MLA MUL Is one of UMULL, UMLAL, SMULL, or Smlal UMULL, UMLAL, Smull and SmlalUmull Are the ARM registers holding the values to be multiplied SMULxyUse the top end bits 3116 of Rm Use the top end bits 3116 of RsSmulbt Is the ARM register holding the value to be added SMLAxySmlatb Use the top end bits 3116 of Rs SMULWyAre the ARM registers holding the operands Are the ARM registers holding the values to be multiplied SMLAWyIs the ARM register holding the value to be added Smlawt SMLALxy Smlaltt R15 cannot be used for either Rm or Rs 8 MIA, MIAPH, and MIAxyCurrent processors Use the top end bits 3116 of RmThese instructions are only available in XScale Are the ARM registers holding the operands ARM saturating arithmetic instructionsQADD, QSUB, QDADD, and Qdsub Is one of QADD, QSUB, QDADD, or QdsubQadd ARM branch instructions Branch, and Branch with Link 2 BX 3 BLX Blxmi MCR, MCR2, Mcrr on ARM coprocessor instructions1 CDP, CDP2 2 MCR, MCR2, Mcrr Is p n, where n is an integer in the rangeAre ARM source registers. They must not be r15 Affected 3 MRC, MRC2Mrrc Is the coprocessor register to load or save 5 LDC, STCIs either LDC or STC Is an optional suffix specifying a long transferArchitectures Is either LDC2 or STC2 6 LDC2, STC2Architectures Miscellaneous ARM instructions Software interrupt 1 SWIIs either Cpsr or Spsr 2 MRSWhere Is the destination register. Rd must not be r15Is either Cpsr or Spsr 3 MSRSee MRS on MSR CPSRf, r5 Breakpoint BkptFor current processors 5 MAR, MRAAre general-purpose registers LDR ARM pseudo-instruction on ARM pseudo-instructionsADR ARM pseudo-instructionon Adrl ARM pseudo-instructiononNon word-aligned address within ±255 bytes ADR ARM pseudo-instructionIs an optional condition code Is the register to loadNon word-aligned address within 64KB Adrl ARM pseudo-instructionWord-aligned address within 256KB R4,start + = ADD R4,pc,#0xe800 LDR ARM pseudo-instruction R3,=0xff0 Loads Into = MOV r3,#0xff0 NOP ARM pseudo-instruction Thumb Instruction Reference Add with carry Rotate right LDR and STR, pc or sp relative on Thumb memory access instructionsLDR and STR, immediate offset on LDR and STR, register offset onStore register Where Is eitherLDR and STR, immediate offset Load registerAddress alignment for word and halfword transfers LDR and STR, register offset Strsh 4 in the range 0 to LDR and STR, pc or sp relativeR2,pc,#1016 POP reglist These instructions do not affect the flags POP reglist, pcStore multiple, increment after Ldmia and StmiaLoad and store multiple registers Load multiple, increment afterR3!, r0,r4 ADC, SBC, and MUL on Thumb arithmetic instructionsADD and SUB, sp on ADD, pc or sp relative onTo +7 ADD and SUB, low registers255 to +255 Restrictions These instructions update the N, Z, C, and V flagsIs a register containing the second operand 2 ADD, high or low registersRange -508 to +508 ADD and SUB, spRange 4 ADD, pc or sp relativeIs the destination register. Rd must be in the range r0- r7 Is either sp or pc5 ADC, SBC, and MUL Where Is one of ADC, SBC, or MULTST on page 5-30 Test bits Thumb general data processing instructionsCMP and CMN on page 5-26 Compare and Compare Negative MOV, MVN, and NEG on page 5-28 Move, Move NOT, and NegateRange r0- r7 Where Is one of AND, ORR, EOR, or BIC1 AND, ORR, EOR, and BIC Bitwise logical operations2 ASR, LSL, LSR, and ROR Immediate shift Register-controlled shiftWhere Is the register containing the first operand Examples Is the source register Where Is the destination register4 MOV, MVN, and NEG Move, Move NOT, and NegateCondition flags Rn and Rm must be in the range r0-r7 Where Is the register containing the first operand5 TST Test bitsThumb branch instructions Label must be within 1 BIs an optional condition code see -2 on 3-23 for more informationCondition codes for Thumb B instruction Long branch with Link 2 BL3 BX BLX label always causes a change to ARM state 4 BLXBranch with Link, and optionally exchange instruction set Instruction clears the T flag in the CPSR. Code atBkpt on Thumb software interrupt and breakpoint instructionsBkpt immed8 Thumb pseudo-instructions 1KB. expr must be defined locally, it cannot be imported ADR Thumb pseudo-instructionIf the value of expr is within range of a MOV instruction, LDR Thumb pseudo-instructionAssembler generates the instruction =labelname Syntax for NOP is NOP Thumb pseudo-instructionARM DUI 0068B Vector Floating-point Programming Absolute value Vector All Negate Vector All Reference Manual Vector floating-point coprocessorVFP architectures Register banks Floating-point registersRestriction on vector length VectorsVector wrap-around Vector strideVector operations Vector and scalar operationsControl of scalar, vector and mixed operations Scalar operationsVFP and condition codes Vector Floating-point Programming FPSCR, the floating-point status and control register VFP system registers0b000 See FMRX, FMXR, and Fmstat on FPEXC, the floating-point exception registerFPSID, the floating-point system ID register Modifying individual bits of a VFP system registerWhen to use flush-to-zero mode Flush-to-zero modeEffects of using flush-to-zero mode Operations not affected by flush-to-zero mode Ftosi and Ftoui on VFP instructionsFmrrs and Fmsrr on FMRX, FMXR, and Fmstat onPage Fabsd d3, d5 Fnegsmi s15, s15 Is the VFP register holding the second operand Fadd and FsubIs the VFP register for the result Is the VFP register holding the first operandFcmp instructions can produce Invalid Operation exceptions FcmpFloating-point compare Fcmp is always scalar With zero instructionIs a double-precision VFP register for the result FcvtdsIs a single-precision VFP register holding the operand Is a single-precision VFP register for the result FcvtsdIs a double-precision VFP register holding the operand Fdiv Address used for the transfer FLD and FSTFloating-point load and store Precision specified in precisionFldsne Fldm and Fstm Following instructions are equivalent Unspecified precisionMust be one of FMAC, FNMAC, FMSC, or Fnmsc FMAC, FNMAC, FMSC, and FnmscFnmscsle These instructions do not produce any exceptions Fmdrr and FmrrdIs the VFP double-precision register Are ARM registers. Do not use r15Is the ARM register. Rd must not be r15 FMDHR, FMDLR, FMRDH, and FmrdlThese instructions are used together as matched pairs Is the VFP single-precision register Fmrs and FmsrAre two consecutive VFP single-precision registers Fmrrs and FmsrrAre the ARM registers. Do not use r15 Is the ARM register FMRX, FMXR, and FmstatFmul and Fnmul Fsito and Fuito Is the VFP register holding the operand FsqrtIs a single-precision VFP register for the integer result Ftosi and FtouiCan be S for single-precision, or D for double-precision VFP pseudo-instructionThere is one VFP pseudo-instruction FLD pseudo-instructionD1,=3.12E106 Loads 3.12E106 into d1 Vfpassert Scalar on Vfpassert Vector on VFP directives and vector notationVFP directives and vector notation on Vfpassert Vector on Vfpassert ScalarVFP directives and vector notation on Vfpassert Scalar on Where Is the vector length Is the vector strideR10,FPSCR ARM DUI 0068B Conditional assembly, looping, inclusions, and macros Assembly control directives onLocation of descriptions of directives Alphabetical list of directivesDeclare a global arithmetic, logical, or string variable Symbol definition directivesThis section describes the following directives GBLA, GBLL, and Gbls onGBLA, GBLL, and Gbls Armasm -pd objectsize Seta 0xFF -o objectfile sourcefile LCLA, LCLL, and Lcls SETA, SETL, and Sets Names on RlistEvaluates to a coprocessor register number from 0 to 5 CNCN directive defines a name for a coprocessor register Coprocessor names onEvaluates to a coprocessor number from 0 to 6 CPDN and SN Evaluates to a floating-point register number from 0 to 8 FNDCD and Dcdu on Data definition directivesDCQ and Dcqu on Ltorg During the first pass of the assembler 2 MAPIs a numeric or program-relative expression Set to this addressBy the value of expr FieldStorage counter Expressions on SpaceConsecutive bytes of store 5 DCBTo 255 see Numeric expressions on Quoted string. The characters of the string are loaded intoDCW and Dcwu on DCQ and Dcqu on DCD and DcduNumeric expression see Numeric expressions on Program-relative expressionDcdo Dcfd and Dcfdu Dcfs and Dcfsu Is a numeric expression see Numeric expressions on 10 DCIDCD and Dcdu on DCW and Dcwu on DCQ and DcquData DCW and DcwuTo 65535 see Numeric expressions on DCD and Dcdu on DCQ and Dcqu onIF, ELSE, and Endif on While and Wend on Assembly control directivesMacro and Mend on Mexit onMacro and Mend BGE Mexit Using a macro to produce assembly-time diagnosticsSee Relational operators on 4 IF, ELSE, and EndifExample 7-3 Assembly conditional on a variable being defined While and Wend Frame POP on Frame Push on Frame Register on Frame Restore onFrame description directives Frame Address onCan omit it Is sp unless the function uses a separate frame pointerIs the number of bytes that the stack pointer moves There are two alternative syntaxes for Frame POPThere are two alternative syntaxes for Frame Push Frame PushIs the register in which the value is preserved Frame RegisterFrame Restore Frame Save Frame State Remember Frame State Restore on Function or Proc onFrame State Remember on Function or Proc on Frame State RestoreFunction or Proc Endfunc or Endp Assert Reporting directivesIs an assertion that can evaluate to either True or False Is an expression that evaluates to a string Info3 OPT Where Is the OPT directive setting. -2 lists valid settingsSpecify the -listassembler option to turn on listing OPT Is the title TTL and SubtIs the subtitle GET or Include on Miscellaneous directivesCODE16 and CODE32 on Export or Global onAlign Cacheable, CODE, ALIGN=3 Area Example,CODE,READONLY An example code section CODE16 and CODE32 4 END Entry directive declares an entry point to a program EntryIs optional. type can be any one Is the symbolic name to assign to the value6 EQU Address, or a 32-bit integer constantExport or Global Exportas Extern Nesting directives on GET or IncludeImport File, or library. The symbol name is case-sensitiveGlobal See Export or Global onInclude IncbinSee GET or Include on Keep Symbols are kept except register-relative symbolsRequire directive specifies a dependency between sections Assembly failsNofp RequireREQUIRE8 and PRESERVE8 Evaluates to a register number from 0 to 19 RNRout Platforms See ARM Developer SuiteAmong other things, computer software Thumb stateOtherwise stated Used to find errors in the application program flowDefault thread runs See also Saved Processor Status RegisterSee Read Write Position Independent See also RopiSee also Rwpi See Read Only Position IndependentSee Saved Processor Status Register Normally set to zero on resetBlock of software code or data for an Image By ARM to handle semihostingIndex Align Gbll Adrl Symbols Index-6