MSP430 Assembly Language Tools v15.12.0.LTS User's Guide
SLAU131L - REVISED JANUARY 2016

5 Assembler Directives

Assembler directives supply data to the program and control the assembly process. Assembler directives enable you to do the following:

  • Assemble code and data into specified sections 
  • Reserve space in memory for uninitialized variables
  • Control the appearance of listings
  • Initialize memory
  • Assemble conditional blocks
  • Define global variables
  • Specify libraries from which the assembler can obtain macros
  • Examine symbolic debugging information

This chapter is divided into two parts: the first part (Section 5.1 through Section 5.11) describes the directives according to function, and the second part (Section 5.12) is an alphabetical reference.

5.1 Directives Summary

Table 5-1 through Table 5-16 summarize the assembler directives.

Besides the assembler directives documented here, the MSP430 software tools support the following directives:

  • Macro directives are discussed in Section 6; they are not discussed in this chapter.
  • The C compiler uses directives for symbolic debugging. Unlike other directives, symbolic debugging directives are not used in most assembly language programs. Section A-1 discusses these directives; they are not discussed in this chapter.

NOTE

Labels and Comments Are Not Shown in Syntaxes

Most source statements that contain a directive can also contain a label and a comment. Labels begin in the first column (only labels and comments can appear in the first column), and comments must be preceded by a semicolon, or an asterisk if the comment is the only element in the line. To improve readability, labels and comments are not shown as part of the directive syntax here. See the detailed description of each directive for using labels with directives.

Table 5-1 Directives that Control Section Use

Mnemonic and Syntax Description See
.bss symbol, size in bytes[, alignment] Reserves sizebytes in the .bss (uninitialized data) section .bss topic
.data Assembles into the .data (initialized data) section .data topic
.intvec Creates an interrupt vector entry in a named section that points to an interrupt routine name. .intvec topic
.sect "section name" Assembles into a named (initialized) section .sect topic
.text Assembles into the .text (executable code) section .text topic
symbol .usect "section name", size in bytes
     [, alignment]
Reserves sizebytes in a named (uninitialized) section .usect topic

Table 5-2 Directives that Gather Sections into Common Groups

Mnemonic and Syntax Description See
.endgroup Ends the group declaration .endgroup topic
.gmembersection name Designates section name as a member of the group .gmember topic
.group group section name group type: Begins a group declaration .group topic

Table 5-3 Directives that Affect Unused Section Elimination

Mnemonic and Syntax Description See
.retain " section name " Instructs the linker to include the current or specified section in the linked output file, regardless of whether the section is referenced or not .retain topic
.retainrefs " section name " Instructs the linker to include any data object that references the current or specified section. .retain topic

Table 5-4 Directives that Initialize Values (Data and Memory)

Mnemonic and Syntax Description See
.bits value1[, ..., valuen] Initializes one or more successive bits in the current section .bits topic
.byte value1[, ..., valuen] Initializes one or more successive bytes in the current section .byte topic
.char value1[, ..., valuen] Initializes one or more successive bytes in the current section .char topic
.cstring {expr1|"string1"}[,... , {exprn|"stringn"}] Initializes one or more text strings .string topic
.double value1[, ..., valuen] Initializes one or more 64-bit, IEEE double-precision, floating-point constants .double topic
.field value[, size] Initializes a field of size bits (1-32) with value .field topic
.float value1[, ..., valuen] Initializes one or more 32-bit, IEEE single-precision, floating-point constants .float topic
.half value1[, ... , valuen] Initializes one or more 16-bit integers (halfword) .half topic
.int value1[, ... , valuen] Initializes one or more 16-bit integers .int topic
.long value1[, ... , valuen] Initializes one or more 32-bit integers .long topic
.short value1[, ... , valuen] Initializes one or more 16-bit integers (halfword) .short topic
.string {expr1|"string1"}[,... , {exprn|"stringn"}] Initializes one or more text strings .string topic
.ubyte value1[, ... , valuen] Initializes one or more successive unsigned bytes in the current section .ubyte topic
.uchar value1[, ..., valuen] Initializes one or more successive unsigned bytes in the current section .uchar topic
.uhalf value1[, ... , valuen] Initializes one or more unsigned 16-bit integers (halfword) .uhalf topic
.uint value1[, ... , valuen] Initializes one or more unsigned 32-bit integers .uint topic
.ulong value1[, ... , valuen] Initializes one or more unsigned 32-bit integers .long topic
.ushort value1[, ... , valuen] Initializes one or more unsigned 16-bit integers (halfword) .short topic
.uword value1[, ... , valuen] Initializes one or more unsigned 16-bit integers .uword topic
.word value1[, ... , valuen] Initializes one or more 16-bit integers .word topic

Table 5-5 Directives that Perform Alignment and Reserve Space

Mnemonic and Syntax Description See
.align [size in bytes] Aligns the SPC on a boundary specified by size in bytes, which must be a power of 2; defaults to word (2-byte) boundary .align topic
.bessize Reserves size bytes in the current section; a label points to the end of the reserved space .bes topic
.spacesize Reserves size bytes in the current section; a label points to the beginning of the reserved space .space topic

Table 5-6 Directives that Format the Output Listing

Mnemonic and Syntax Description See
.drlist Enables listing of all directive lines (default) .drlist topic
.drnolist Suppresses listing of certain directive lines .drnolist topic
.fclist Allows false conditional code block listing (default) .fclist topic
.fcnolist Suppresses false conditional code block listing .fcnolist topic
.length [page length] Sets the page length of the source listing .length topic
.list Restarts the source listing .list topic
.mlist Allows macro listings and loop blocks (default) .mlist topic
.mnolist Suppresses macro listings and loop blocks .mnolist topic
.nolist Stops the source listing .nolist topic
.option option1 [, option2 , . . .] Selects output listing options; available options are A, B, H, M, N, O, R, T, W, and X .option topic
.page Ejects a page in the source listing .page topic
.sslist Allows expanded substitution symbol listing .sslist topic
.ssnolist Suppresses expanded substitution symbol listing (default) .ssnolist topic
.tab size Sets tab to size characters .tab topic
.title "string" Prints a title in the listing page heading .title topic
.width [page width] Sets the page width of the source listing .width topic

Table 5-7 Directives that Reference Other Files

Mnemonic and Syntax Description See
.copy ["]filename["] Includes source statements from another file .copy topic
.include ["]filename["] Includes source statements from another file .include topic
.mlib ["]filename["] Specifies a macro library from which to retrieve macro definitions .mlib topic

Table 5-8 Directives that Affect Symbol Linkage and Visibility

Mnemonic and Syntax Description See
.common symbol, size in bytes [, alignment]r
.common symbol, structure tag [, alignment]
Defines a common symbol for a variable. .common topic
.def symbol1[, ... , symboln] Identifies one or more symbols that are defined in the current module and that can be used in other modules .def topic
.global symbol1[, ... , symboln] Identifies one or more global (external) symbols .global topic
.ref symbol1[, ... , symboln] Identifies one or more symbols used in the current module that are defined in another module .ref topic
.symdepend dst symbol name[,src symbol name] Creates an artificial reference from a section to a symbol .symdepend topic
.weak symbol name Identifies a symbol used in the current module that is defined in another module .weak topic

Table 5-9 Directives that Enable Conditional Assembly

Mnemonic and Syntax Description See
.if condition Assembles code block if the condition is true .if topic
.else Assembles code block if the .if condition is false. When using the .if construct, the .else construct is optional. .else topic
.elseifcondition Assembles code block if the .if condition is false and the .elseif condition is true. When using the .if construct, the .elseif construct is optional. .elseif topic
.endif Ends .if code block .endif topic
.loop [count] Begins repeatable assembly of a code block; the loop count is determined by the count. .loop topic
.break [end condition] Ends .loop assembly if end condition is true. When using the .loop construct, the .break construct is optional. .break topic
.endloop Ends .loop code block .endloop topic

Table 5-10 Directives that Define Structure Types

Mnemonic and Syntax Description See
.emember Sets up C-like enumerated types in assembly code  Section 5.9
.endenum Sets up C-like enumerated types in assembly code  Section 5.9
.endstruct Ends a structure definition .struct topic
.enum Sets up C-like enumerated types in assembly code Section 5.9
.struct Begins structure definition .struct topic
.tag Assigns structure attributes to a label .struct topic

Table 5-11 Directives that Define Symbols at Assembly Time

Mnemonic and Syntax Description See
.asg ["]character string["], substitution symbol Assigns a character string to substitution symbol. Substitution symbols created with .asg can be redefined. .asg topic
.define ["]character string["], substitution symbol Assigns a character string to substitution symbol. Substitution symbols created with .define cannot be redefined. .asg topic
symbol .equ value Equates value with symbol .equ topic
.elfsym name, SYM_SIZE(size Provides ELF symbol information .elfsym topic
.evalexpression,
     substitution symbol
Performs arithmetic on a numeric substitution symbol .eval topic
.labelsymbol Defines a load-time relocatable label in a section .label topic
.newblock Undefines local labels .newblock topic
symbol .set value Equates value with symbol .set topic
.unasg symbol Turns off assignment of symbol as a substitution symbol .unasg topic
.undefine symbol Turns off assignment of symbol as a substitution symbol .unasg topic

Table 5-12 Directives that Create or Affect Macros

Mnemonic and Syntax Description See
macname .macro [parameter1 ][,... , parametern ] Begin definition of macro named macname .macro topic
.endm End macro definition .endm topic
.mexit Go to .endm Section 6.2
.mlib filename Identify library containing macro definitions .mlib topic
.var Adds a local substitution symbol to a macro's parameter list .var topic

Table 5-13 Directives that Control Diagnostics

Mnemonic and Syntax Description See
.emsg string Sends user-defined error messages to the output device; produces no .obj file .emsg topic
.mmsgstring Sends user-defined messages to the output device .mmsg topic
.wmsg string Sends user-defined warning messages to the output device .wmsg topic

Table 5-14 Directives that Perform Assembly Source Debug

Mnemonic and Syntax Description See
.asmfunc Identifies the beginning of a block of code that contains a function .asmfunc topic
.endasmfunc Identifies the end of a block of code that contains a function .endasmfunc topic

Table 5-15 Directives that Are Used by the Absolute Lister

Mnemonic and Syntax Description See
.setsect Produced by absolute lister; sets a section Section 9
.setsym Produced by the absolute lister; sets a symbol Section 9

Table 5-16 Directives that Perform Miscellaneous Functions

Mnemonic and Syntax Description See
.cdecls [options,]"filename"[, "filename2"[, ...] Share C headers between C and assembly code .cdecls topic
.end Ends program .end topic

In addition to the assembly directives that you can use in your code, the C/C++ compiler produces several directives when it creates assembly code. These directives are to be used only by the compiler; do not attempt to use these directives.

  • DWARF directives listed in Section A.5
  • The .bound directive is used internally.
  • The .comdat directive is used internally.
  • The .compiler_opts directive indicates that the assembly code was produced by the compiler, and which build model options were used for this file.

5.2 Directives that Define Sections

These directives associate portions of an assembly language program with the appropriate sections:

  • The .bss directive reserves space in the .bss section for uninitialized variables.
  • The .data directive identifies portions of code in the .data section. The .data section usually contains initialized data.
  • The .intvec directive creates an interrupt vector entry that points to an interrupt routine name.
  • The .retain directive can be used to indicate that the current or specified section must be included in the linked output. Thus even if no other sections included in the link reference the current or specified section, it is still included in the link.
  • The .retainrefs directive can be used to force sections that refer to the specified section. This is useful in the case of interrupt vectors.
  • The .sect directive defines an initialized named section and associates subsequent code or data with that section. A section defined with .sect can contain code or data.
  • The .text directive identifies portions of code in the .text section. The .text section usually contains executable code.
  • The .usect directive reserves space in an uninitialized named section. The .usect directive is similar to the .bss directive, but it allows you to reserve space separately from the .bss section.

Section 2 discusses these sections in detail.

Example 5-1 shows how you can use sections directives to associate code and data with the proper sections. This is an output listing; column 1 shows line numbers, and column 2 shows the SPC values. (Each section has its own program counter, or SPC.) When code is first placed in a section, its SPC equals 0. When you resume assembling into a section after other code is assembled, the section's SPC resumes counting as if there had been no intervening code.

The directives in Example 5-1 perform the following tasks:

.text initializes words with the values 1, 2, 3, 4, 5, 6, 7, and 8.
.data initializes words with the values 9, 10, 11, 12, 13, 14, 15, and 16.
var_defs initializes words with the values 17 and 18.
.bss reserves 19 bytes.
xy reserves 20 bytes.

The .bss and .usect directives do not end the current section or begin new sections; they reserve the specified amount of space, and then the assembler resumes assembling code or data into the current section.

Example 5-1 Sections Directives

1 ; Comment1 here : Start assembling .... 2 3 0000 .text 4 0000 0001 .word 1,2 0002 0002 5 0004 0003 .word 3,4 0006 0004 6 7 ; Comment 2 8 9 0000 .data 10 0000 0009 .word 9,10 0002 000A 11 0004 000B .word 11,12 0006 000C 12 13 ; Comment 3 14 15 0000 .sect "var_defs" 16 0000 0011 .word 17,18 0002 0012 17 18 ; Comment 4 19 20 0008 .data 21 0008 000D .word 13,14 000a 000E 22 23 0000 .bss sym,19 24 000c 000F .word 15,16 000e 0010 25 26 ; Comment 5 27 28 0008 .text 29 0008 0005 .word 5,6 000a 0006 30 0000 usym .usect "xy",20 31 000c 0007 .word 7,8 000e 0008

5.3 Directives that Initialize Values

Several directives assemble values for the current section. For example:

  • The .byte and .char directives place one or more 8-bit values into consecutive bytes of the current section. These directives are similar to .word, .int, and .long, except that the width of each value is restricted to 8 bits.
  • The .double directive calculates the IEEE format representation of one or more values and stores them in the current section. The stored value is an IEEE 64-bit double-precision floating-point value, and is stored in two words aligned to a word boundary. (MSP430 has no alignment greater than word alignment.)
  • The .field directive places a single value into a specified number of bits in the current word. With .field, you can pack multiple fields into a single word; the assembler does not increment the SPC until a word is filled. If a field will not fit in the space remaining in the current word, .field will insert zeros to fill the current word and then place the field in the next word. See the .field topic.
  • Figure 5-1 shows how fields are packed into a word. Using the following assembled code, notice that the SPC does not change for the first three fields (the fields are packed into the same word):

    1 0000 0003 .field 3,3 2 0000 0043 .field 8,6 3 0000 2043 .field 16,5 4 0002 1234 .field 0x1234,16
Figure 5-1 The .field Directive field1_lau131.gif
  • The .float directive calculates the IEEE format representation of one or more values and stores them in the current section. The stored value is an IEEE 32-bit single-precision floating-point value, and is stored in one word aligned to a word boundary.
  • The .int and .word directives place one or more 16-bit values into consecutive 16-bit values in the current section.
  • The .stringand .cstring directives place 8-bit characters from one or more character strings into the current section. The .string and .cstring directives are similar to .byte, placing an 8-bit character in each consecutive byte of the current section. The .cstring directive adds a NUL character needed by C; the .string directive does not add a NUL character.
  • The .ubyte, .uchar, .uhalf, .uint, .ulong, .ushort, and .uword directives are provided as unsigned versions of their respective signed directives. These directives are used primarily by the C/C++ compiler to support unsigned types in C/C++.

NOTE

Directives that Initialize Constants When Used in a .struct/.endstruct Sequence

The .bits, .byte, .char, .word, .int, .long, .ubyte, .uchar, .uhalf, .uint, .ulong, .ushort, .uword, .string, .double, .float, .half, .short, and .field directives do not initialize memory when they are part of a .struct/ .endstruct sequence; rather, they define a member’s size. For more information, see the .struct/.endstruct directives.

Figure 5-2 compares the .byte, .char, .int, .long, .float, .word, and .string directives using the following assembled code:

1 0000 00AA .byte 0AAh,0BBh 0001 00BB 2 0002 00CC .char 0xCC 3 0004 DDDD .word 0xDDDD 4 0006 FFFF .long 0xEEEEFFFF 0008 EEEE 5 000a DDDD .int 0xDDDD 6 000c FCB9 .float 1.9999 000e 3FFF 7 0010 0048 .string "Help" 0011 0065 0012 006C 0013 0070
Figure 5-2 Initialization Directives initdirs_lau131.gif

5.4 Directives that Perform Alignment and Reserve Space

These directives align the section program counter (SPC) or reserve space in a section:

  • The .align directive aligns the SPC at a 1-byte to 32K-byte boundary. This ensures that the code following the directive begins on the byte value that you specify. If the SPC is already aligned at the selected boundary, it is not incremented. Operands for the .align directive must equal a power of 2 between 20 and 215, inclusive.
  • Figure 5-3 demonstrates the .align directive. Using the following assembled code:

    1 0000 0002 .field 2,3 2 0000 005A .field 11,5 3 .align 2 4 0002 0045 .string "Err" 0003 0072 0004 0072 5 .align 6 0006 0004 .byte 4
    Figure 5-3 The .align Directive align_lau131.gif
  • The .bes and .space directives reserve a specified number of bytes in the current section. The assembler fills these reserved byres with 0s.
    • When you use a label with .space, it points to the first byte that contains reserved bits.
    • When you use a label with .bes, it points to the last byte that contains reserved bits.
  • Figure 5-4 shows how the .space and .bes directives work for the following assembled code:

    1 0000 0100 .word 0x100,0x200 0002 0200 2 0004 Res_1 .space 17 3 0016 000F .word 15 4 002b Res_2 .bes 20 5 002c 00BA .byte 0xBA

    Res_1 points to the first byte in the space reserved by .space. Res_2 points to the last byte in the space reserved by .bes.

    Figure 5-4 The .space and .bes Directives spacebes_lau131.gif

5.5 Directives that Format the Output Listings

These directives format the listing file:

  • The .drlist directive causes printing of the directive lines to the listing; the .drnolist directive turns it off for certain directives. You can use the .drnolist directive to suppress the printing of the following directives. You can use the .drlist directive to turn the listing on again.
  • .asg
    .break
    .emsg
    .eval
    .fclist
    .fcnolist
    .length
    .mlist
    .mmsg
    .mnolist
    .sslist
    .ssnolist
    .var
    .width
    .wmsg
  • The source code listing includes false conditional blocks that do not generate code. The .fclist and .fcnolist directives turn this listing on and off. You can use the .fclist directive to list false conditional blocks exactly as they appear in the source code. You can use the .fcnolist directive to list only the conditional blocks that are actually assembled.
  • The .length directive controls the page length of the listing file. You can use this directive to adjust listings for various output devices.
  • The .list and .nolist directives turn the output listing on and off. You can use the .nolist directive to prevent the assembler from printing selected source statements in the listing file. Use the .list directive to turn the listing on again.
  • The source code listing includes macro expansions and loop blocks. The .mlist and .mnolist directives turn this listing on and off. You can use the .mlist directive to print all macro expansions and loop blocks to the listing, and the .mnolist directive to suppress this listing.
  • The .option directive controls certain features in the listing file. This directive has the following operands:
  • A turns on listing of all directives and data, and subsequent expansions, macros, and blocks.
    B limits the listing of .byte and .char directives to one line.
    H limits the listing of .half and .short directives to one line.
    M turns off macro expansions in the listing.
    N turns off listing (performs .nolist).
    O turns on listing (performs .list).
    R resets the B, H, M, T, and, W directives (turns off the limits of B, H, M, T, and W).
    T limits the listing of .string directives to one line.
    W limits the listing of .word and .int directives to one line.
    X produces a cross-reference listing of symbols. You can also obtain a cross-reference listing by invoking the assembler with the --cross_reference option (see Section 4.3).
  • The .page directive causes a page eject in the output listing.
  • The source code listing includes substitution symbol expansions. The .sslist and .ssnolist directives turn this listing on and off. You can use the .sslist directive to print all substitution symbol expansions to the listing, and the .ssnolist directive to suppress this listing. These directives are useful for debugging the expansion of substitution symbols.
  • The .tab directive defines tab size.
  • The .title directive supplies a title that the assembler prints at the top of each page.
  • The .width directive controls the page width of the listing file. You can use this directive to adjust listings for various output devices.

5.6 Directives that Reference Other Files

These directives supply information for or about other files that can be used in the assembly of the current file:

  • The .copy and .include directives tell the assembler to begin reading source statements from another file. When the assembler finishes reading the source statements in the copy/include file, it resumes reading source statements from the current file. The statements read from a copied file are printed in the listing file; the statements read from an included file are not printed in the listing file.
  • The .def directive identifies a symbol that is defined in the current module and that can be used in another module. The assembler includes the symbol in the symbol table.
  • The .global directive declares a symbol external so that it is available to other modules at link time. (For more information about global symbols, see Section 2.6.1). The .global directive does double duty, acting as a .def for defined symbols and as a .ref for undefined symbols. The linker resolves an undefined global symbol reference only if the symbol is used in the program. The .global directive declares a 16-bit symbol.
  • The .mlib directive supplies the assembler with the name of an archive library that contains macro definitions. When the assembler encounters a macro that is not defined in the current module, it searches for it in the macro library specified with .mlib.
  • The .ref directive identifies a symbol that is used in the current module but is defined in another module. The assembler marks the symbol as an undefined external symbol and enters it in the object symbol table so the linker can resolve its definition. The .ref directive forces the linker to resolve a symbol reference.
  • The .symdepend directive creates an artificial reference from the section defining the source symbol name to the destination symbol. The .symdepend directive prevents the linker from removing the section containing the destination symbol if the source symbol section is included in the output module.
  • The .weak directive identifies a symbol that is used in the current module but is defined in another module. It is equivalent to the .ref directive, except that the reference has weak linkage.

5.7 Directives that Enable Conditional Assembly

Conditional assembly directives enable you to instruct the assembler to assemble certain sections of code according to a true or false evaluation of an expression. Two sets of directives allow you to assemble conditional blocks of code:

  • The .if/.elseif/.else/.endif directives tell the assembler to conditionally assemble a block of code according to the evaluation of an expression.
.if condition marks the beginning of a conditional block and assembles code if the .if condition is true.
[.elseif condition] marks a block of code to be assembled if the .if condition is false and the .elseif condition is true.
.else marks a block of code to be assembled if the .if condition is false and any .elseif conditions are false.
.endif marks the end of a conditional block and terminates the block.

  • The .loop/.break/.endloop directives tell the assembler to repeatedly assemble a block of code according to the evaluation of an expression.
.loop [count] marks the beginning of a repeatable block of code. The optional expression evaluates to the loop count.
.break [end condition] tells the assembler to assemble repeatedly when the .break end condition is false and to go to the code immediately after .endloop when the expression is true or omitted.
.endloop marks the end of a repeatable block.
The assembler supports several relational operators that are useful for conditional expressions. For more information about relational operators, see Section 4.9.2.

5.8 Directives that Define Union or Structure Types

These directives set up specialized types for later use with the .tag directive, allowing you to use symbolic names to refer to portions of a complex object. The types created are analogous to the struct and union types of the C language.

The .struct and .union directives group related data into an aggregate structure which is more easily accessed. These directives do not allocate space for any object. Objects must be separately allocated, and the .tag directive must be used to assign the type to the object.

type .struct ; structure tag definition X .int Y .int T_LEN .endstruct COORD .tag type ; declare COORD (coordinate) COORD .space T_LEN ; actual memory allocation LDR R0, COORD.Y ; load member Y of structure ; COORD into register R0.

5.9 Directives that Define Enumerated Types

These directives set up specialized types for later use in expressions allowing you to use symbolic names to refer to compile-time constants. The types created are analogous to the enum type of the C language. This allows enumerated types to be shared between C and assembly code. See Section 13.

See Section 13.2.10 for an example of using .enum.

5.10 Directives that Define Symbols at Assembly Time

Assembly-time symbol directives equate meaningful symbol names to constant values or strings.

  • The .asg directive assigns a character string to a substitution symbol. The value is stored in the substitution symbol table. When the assembler encounters a substitution symbol, it replaces the symbol with its character string value. Substitution symbols created with .asg can be redefined.
  • .asg "10, 20, 30, 40", coefficients ; Assign string to substitution symbol. .byte coefficients ; Place the symbol values 10, 20, 30, and 40 ; into consecutive bytes in current section.
  • The .define directive assigns a character string to a substitution symbol. The value is stored in the substitution symbol table. When the assembler encounters a substitution symbol, it replaces the symbol with its character string value. Substitution symbols created with .define cannot be redefined.
  • The .eval directive evaluates a well-defined expression, translates the results into a character string, and assigns the character string to a substitution symbol. This directive is most useful for manipulating counters:
  • .asg 1 , x ; x = 1 .loop ; Begin conditional loop. .byte x*10h ; Store value into current section. .break x = 4 ; Break loop if x = 4. .eval x+1, x ; Increment x by 1. .endloop ; End conditional loop.
  • The .label directive defines a special symbol that refers to the load-time address within the current section. This is useful when a section loads at one address but runs at a different address. For example, you may want to load a block of performance-critical code into slower off-chip memory to save space and move the code to high-speed on-chip memory to run. See the .label topic for an example using a load-time address label.
  • The .set and .equ directives set a constant value to a symbol. The symbol is stored in the symbol table and cannot be redefined; for example:
  • bval .set 0100h ; Set bval = 0100h .long bval, bval*2, bval+12 ; Store the values 0100h, 0200h, and 010Ch ; into consecutive words in current section.

    The .set and .equ directives produce no object code. The two directives are identical and can be used interchangeably.

  • The .unasg directive turns off substitution symbol assignment made with .asg.
  • The .undefine directive turns off substitution symbol assignment made with .define.
  • The .var directive allows you to use substitution symbols as local variables within a macro.

5.11 Miscellaneous Directives

These directives enable miscellaneous functions or features:

  • The .asmfunc and .endasmfunc directives mark function boundaries. These directives are used with the compiler --symdebug:dwarf (-g) option to generate debug information for assembly functions.
  • The .cdecls directive enables programmers in mixed assembly and C/C++ environments to share C headers containing declarations and prototypes between C and assembly code.
  • The .end directive terminates assembly. If you use the .end directive, it should be the last source statement of a program. This directive has the same effect as an end-of-file character.
  • The .group, .gmember, and .endgroup directives define an ELF group section to be shared by several sections.
  • The .newblock directive resets local labels. Local labels are symbols of the form $n, where n is a decimal digit, or of the form NAME?, where you specify NAME. They are defined when they appear in the label field. Local labels are temporary labels that can be used as operands for jump instructions. The .newblock directive limits the scope of local labels by resetting them after they are used. See Section 4.8.3 for information on local labels.

These three directives enable you to define your own error and warning messages:

  • The .emsg directive sends error messages to the standard output device. The .emsg directive generates errors in the same manner as the assembler, incrementing the error count and preventing the assembler from producing an object file.
  • The .mmsg directive sends assembly-time messages to the standard output device. The .mmsg directive functions in the same manner as the .emsg and .wmsg directives but does not set the error count or the warning count. It does not affect the creation of the object file.
  • The .wmsg directive sends warning messages to the standard output device. The .wmsg directive functions in the same manner as the .emsg directive but increments the warning count rather than the error count. It does not affect the creation of the object file.

For more information about using the error and warning directives in macros, see Section 6.7.

5.12 Directives Reference

The remainder of this chapter is a reference. Generally, the directives are organized alphabetically, one directive per topic. Related directives (such as .if/.else/.endif), however, are presented together in one topic.

.align
Align SPC on the Next Boundary
Syntax

               .align [size in bytes]

Description

The .align directive aligns the section program counter (SPC) on the next boundary, depending on the size in bytes parameter. The size can be any power of 2 between 20 and 215, inclusive. An operand of 2 aligns the SPC on the next word boundary, and this is the default if no size is given. For example:

2 aligns SPC to word boundary
4 aligns SPC to 2 word boundary
128 aligns SPC to 128-byte boundary

Using the .align directive has two effects:

  • The assembler aligns the SPC on an x-byte boundary within the current section.
  • The assembler sets a flag that forces the linker to align the section so that individual alignments remain intact when a section is loaded into memory.
Example

This example shows several types of alignment, including .align 4, .align 8, and a default .align.

1 0000 0004 .byte 4 2 .align 2 3 0002 0045 .string "Errorcnt" 0003 0072 0004 0072 0005 006F 0006 0072 0007 0063 0008 006E 0009 0074 4 .align 5 000a 0003 .field 3,3 6 000a 002B .field 5,4 7 .align 2 8 000c 0003 .field 3,3 9 .align 8 10 0010 0005 .field 5,4 11 .align 12 0012 0004 .byte 4
.asg/.define/.eval
Assign a Substitution Symbol
Syntax

                .asg " character string ", substitution symbol

                .define " character string ", substitution symbol

                .eval expression , substitution symbol

Description

The .asg and .define directives assign character strings to substitution symbols. Substitution symbols are stored in the substitution symbol table. The .asg directive can be used in many of the same ways as the .set directive, but while .set assigns a constant value (which cannot be redefined) to a symbol, .asg assigns a character string (which can be redefined) to a substitution symbol.

  • The assembler assigns the character string to the substitution symbol.
  • The substitution symbol must be a valid symbol name. The substitution symbol is up to 128 characters long and must begin with a letter. Remaining characters of the symbol can be a combination of alphanumeric characters, the underscore (_), and the dollar sign ($).

The .define directive functions in the same manner as the .asg directive, except that .define disallows creation of a substitution symbol that has the same name as a register symbol or mnemonic. It does not create a new symbol name space in the assembler, rather it uses the existing substitution symbol name space. The .define directive is used to prevent corruption of the assembly environment when converting C/C++ headers. See Section 13 for more information about using C/C++ headers in assembly source.

The .eval directive performs arithmetic on substitution symbols, which are stored in the substitution symbol table. This directive evaluates the expression and assigns the string value of the result to the substitution symbol. The .eval directive is especially useful as a counter in .loop/.endloop blocks.

  • The expression is a well-defined alphanumeric expression in which all symbols have been previously defined in the current source module, so that the result is an absolute expression.
  • The substitution symbol must be a valid symbol name. The substitution symbol is up to 128 characters long and must begin with a letter. Remaining characters of the symbol can be a combination of alphanumeric characters, the underscore (_), and the dollar sign ($).

See the .unasg/.undefine topic for information on turning off a substitution symbol.

Example

This example shows how .asg and .eval can be used.

1 .sslist ; show expanded sub. symbols 2 ; using .asg and .eval 3 4 .asg R12, LOCALSTACK 5 .asg &, AND 6 7 0000 503C ADD #280 AND 255, LOCALSTACK # ADD #280 & 255, R12 0002 0018 8 9 .asg 0,x 10 .loop 5 11 .eval x+1, x 12 .word x 13 .endloop 1 .eval x+1, x # .eval 0+1, x 1 0004 0001 .word x # .word 1 1 .eval x+1, x # .eval 1+1, x 1 0006 0002 .word x # .word 2 1 .eval x+1, x # .eval 2+1, x 1 0008 0003 .word x # .word 3 1 .eval x+1, x # .eval 3+1, x 1 000a 0004 .word x # .word 4 1 .eval x+1, x # .eval 4+1, x 1 000c 0005 .word x # .word 5
.asmfunc/.endasmfunc
Mark Function Boundaries
Syntax

symbol     .asmfunc [stack_usage(num)]

               .endasmfunc

Description

The .asmfunc and .endasmfunc directives mark function boundaries. These directives are used with the compiler -g option (--symdebug:dwarf) to allow assembly code sections to be debugged in the same manner as C/C++ functions.

You should not use the same directives generated by the compiler (see Section A-1) to accomplish assembly debugging; those directives should be used only by the compiler to generate symbolic debugging information for C/C++ source files.

The symbol is a label that must appear in the label field.

The .asmfunc directive has an optional parameter, stack_usage, which indicates that the function may use up to num bytes.

Consecutive ranges of assembly code that are not enclosed within a pair of .asmfunc and .endasmfunc directives are given a default name in the following format:

$ filename : beginning source line : ending source line $

.bits
Initialize Bits
Syntax

                .bits value1[, ... ,valuen ]

Description

The .bits directive places one or more values into consecutive bits of the current section.

The .bits directive is similar to the .field directive (see .field topic ). However, the .bits directive does not allow you to specify the number of bits to fill or increment the SPC.

.bss
Reserve Space in the .bss Section
Syntax

               .bss symbol , size in bytes[, alignment]

Description

The .bss directive reserves space for variables in the .bss section. This directive is usually used to allocate space in RAM.

  • The symbol is a required parameter. It defines a symbol that points to the first location reserved by the directive. The symbol name must correspond to the variable that you are reserving space for.
  • The size in bytes is a required parameter; it must be an absolute constant expression. The assembler allocates size bytes in the .bss section. There is no default size.
  • The alignment is an optional parameter that ensures that the space allocated to the symbol occurs on the specified boundary. The boundary must be set to a power of 2 between 20 and 215, inclusive. If the SPC is already aligned at the specified boundary, it is not incremented.

For more information about sections, see Section 2.

Example

In this example, the .bss directive allocates space for two variables, TEMP and ARRAY. The symbol TEMP points to four bytes of uninitialized space (at .bss SPC = 0). The symbol ARRAY points to 100 bytes of uninitialized space (at .bss SPC = 04h). Symbols declared with the .bss directive can be referenced in the same manner as other symbols and can also be declared external.

1 *********************************************** 2 ** Start assembling into the .text section. ** 3 *********************************************** 4 0000 .text 5 0000 430A MOV #0, R10 6 7 *********************************************** 8 ** Allocate 4 bytes in .bss for TEMP. ** 9 *********************************************** 10 0000 Var_1: .bss TEMP, 4 11 12 *********************************************** 13 ** Still in .text. ** 14 *********************************************** 15 0002 503B ADD #56h, R11 0004 0056 16 0006 5C0B ADD R12, R11 17 18 *********************************************** 19 ** Allocate 100 bytes in .bss for the symbol ** 20 ** named ARRAY. ** 21 *********************************************** 22 0004 .bss ARRAY, 100, 4 23 24 *********************************************** 25 ** Assemble more code into .text. ** 26 *********************************************** 27 0008 4130 RET 28 29 *********************************************** 30 ** Declare external .bss symbols. ** 31 *********************************************** 32 .global ARRAY, TEMP 33 .end
.byte/.ubyte/.char/.uchar
Initialize Byte
Syntax

                .byte value1[, ... ,valuen ]

               .ubyte value1[, ... ,valuen ]

               .char value1[, ... ,valuen ]

               .uchar value1[, ... ,valuen ]

Description

The .byte, .ubyte, .char, and .uchardirectives place one or more values into consecutive bytes of the current section. A value can be one of the following:

  • An expression that the assembler evaluates and treats as an 8-bit signed number
  • A character string enclosed in double quotes. Each character in a string represents a separate value, and values are stored in consecutive bytes. The entire string must be enclosed in quotes.

The assembler truncates values greater than eight bits.

If you use a label, it points to the location of the first byte that is initialized.

When you use these directives in a .struct/.endstruct sequence, they define a member's size; they do not initialize memory. For more information, see the .struct/.endstruct/.tag topic.

Example

In this example, 8-bit values (10, -1, abc, and a) are placed into consecutive bytes in memory with .byte. Also, 8-bit values (8, -3, def, and b) are placed into consecutive bytes in memory with .char. The label STRX has the value 0h, which is the location of the first initialized byte. The label STRY has the value 6h, which is the first byte initialized by the .char directive.

1 0000 .space 100h 2 0100 000A STRX .byte 10, -1, "abc", 'a' 0101 00FF 0102 0061 0103 0062 0104 0063 0105 0061 3 0106 0008 .char 8, -3, "def", 'b' 0107 00FD 0108 0064 0109 0065 010a 0066 010b 0062
.cdecls
Share C Headers Between C and Assembly Code
Syntax

Single Line:

               .cdecls [options,] "filename"[, "filename2"[,...]]

Syntax

Multiple Lines:

               .cdecls [options]

        %{

              /*---------------------------------------------------------------------------------*/

              /* C/C++ code - Typically a list of #includes and a few defines */

              /*---------------------------------------------------------------------------------*/

        %}

Description

The .cdecls directive allows programmers in mixed assembly and C/C++ environments to share C headers containing declarations and prototypes between the C and assembly code. Any legal C/C++ can be used in a .cdecls block and the C/C++ declarations cause suitable assembly to be generated automatically, allowing you to reference the C/C++ constructs in assembly code; such as calling functions, allocating space, and accessing structure members; using the equivalent assembly mechanisms. While function and variable definitions are ignored, most common C/C++ elements are converted to assembly, for instance: enumerations, (non-function-like) macros, function and variable prototypes, structures, and unions.

The .cdecls options control whether the code is treated as C or C++ code; and how the .cdecls block and converted code are presented. Options must be separated by commas; they can appear in any order:

C Treat the code in the .cdecls block as C source code (default).
  CPP Treat the code in the .cdecls block as C++ source code. This is the opposite of the C option.
  NOLIST Do not include the converted assembly code in any listing file generated for the containing assembly file (default).
  LIST Include the converted assembly code in any listing file generated for the containing assembly file. This is the opposite of the NOLIST option.
  NOWARN Do not emit warnings on STDERR about C/C++ constructs that cannot be converted while parsing the .cdecls source block (default).
  WARN Generate warnings on STDERR about C/C++ constructs that cannot be converted while parsing the .cdecls source block. This is the opposite of the NOWARN option.

In the single-line format, the options are followed by one or more filenames to include. The filenames and options are separated by commas. Each file listed acts as if #include "filename" was specified in the multiple-line format.

In the multiple-line format, the line following .cdecls must contain the opening .cdecls block indicator %{. Everything after the %{, up to the closing block indicator %}, is treated as C/C++ source and processed. Ordinary assembler processing then resumes on the line following the closing %}.

The text within %{ and %} is passed to the C/C++ compiler to be converted into assembly language. Much of C language syntax, including function and variable definitions as well as function-like macros, is not supported and is ignored during the conversion. However, all of what traditionally appears in C header files is supported, including function and variable prototypes; structure and union declarations; non-function-like macros; enumerations; and #defines.

The resulting assembly language is included in the assembly file at the point of the .cdecls directive. If the LIST option is used, the converted assembly statements are printed in the listing file.

The assembly resulting from the .cdecls directive is treated similarly to a .include file. Therefore the .cdecls directive can be nested within a file being copied or included. The assembler limits nesting to ten levels; the host operating system may set additional restrictions. The assembler precedes the line numbers of copied files with a letter code to identify the level of copying. An A indicates the first copied file, B indicates a second copied file, etc.

The .cdecls directive can appear anywhere in an assembly source file, and can occur multiple times within a file. However, the C/C++ environment created by one .cdecls is not inherited by a later .cdecls; the C/C++ environment starts new for each .cdecls.

See Section 13 for more information on setting up and using the .cdecls directive with C header files.

Example

In this example, the .cdecls directive is used call the C header.h file.

C header file:

#define WANT_ID 10 #define NAME "John\n"extern int a_variable; extern float cvt_integer(int src); struct myCstruct { int member_a; float member_b; }; enum status_enum { OK = 1, FAILED = 256, RUNNING = 0 };

Source file:

.cdecls C,LIST,"myheader.h"size: .int $sizeof(myCstruct) aoffset: .int myCstruct.member_a boffset: .int myCstruct.member_b okvalue: .int status_enum.OK failval: .int status_enum.FAILED .if $defined(WANT_ID) id .cstring NAME .endif

Listing File:

1 .cdecls C,LIST,"myheader.h"A 1 ; ------------------------------------------ A 2 ; Assembly Generated from C/C++ Source Code A 3 ; ------------------------------------------ A 4 A 5 ; =========== MACRO DEFINITIONS =========== A 6 .define "1",WANT_ID A 7 .define """John\n""",NAME A 8 .define "1",_OPTIMIZE_FOR_SPACE A 9 A 10 ; =========== TYPE DEFINITIONS =========== A 11 status_enum .enum A 12 0001 OK .emember 1 A 13 0100 FAILED .emember 256 A 14 0000 RUNNING .emember 0 A 15 .endenum A 16 A 17 myCstruct .struct 0,2 ; struct size=(6 bytes|48 bits), alignment=2 A 18 0000 member_a .field 16 ; int member_a - offset 0 bytes, size (2 bytes|16 bits) A 19 0002 member_b .field 32 ; float member_b-offset 2 bytes, size (4 bytes|32 bits) A 20 0006 .endstruct ; final size=(6 bytes|48 bits) A 21 A 22 ; =========== EXTERNAL FUNCTIONS =========== A 23 .global cvt_integer A 24 A 25 ; =========== EXTERNAL VARIABLES =========== A 26 .global a_variable 2 3 0000 0006 size: .int $sizeof(myCstruct) 4 0002 0000 aoffset: .int myCstruct.member_a 5 0004 0002 boffset: .int myCstruct.member_b 6 0006 0001 okvalue: .int status_enum.OK 7 0008 0100 failval: .int status_enum.FAILED 8 .if $defined(WANT_ID) 9 000a 004A id .cstring NAME 000b 006F 000c 0068 000d 006E 000e 000A 000f 0000 10 .endif
.common
Create a Common Symbol
Syntax

               .common symbol , size in bytes[, alignment]

               .common symbol , structure tag[, alignment]

Description

The .common directive creates a common symbol in a common block, rather than placing the variable in a memory section.

This directive is used by the compiler when the --common option is enabled (the default), which causes uninitialized file scope variables to be emitted as common symbols. The benefit of common symbols is that generated code can remove unused variables that would otherwise increase the size of the .bss section. (Uninitialized variables of a size larger than 32 bytes are separately optimized through placement in separate subsections that can be omitted from a link.) This optimization happens for C/C++ code by default unless you use the --common=off compiler option.

  • The symbol is a required parameter. It defines a name for the symbol created by this directive. The symbol name must correspond to the variable that you are reserving space for.
  • The size in bytes is a required parameter; it must be an absolute expression. The assembler allocates size bytes in the section used for common symbols. There is no default size.
  • A structure tag can be used in place of a size to specify a structure created with the .struct directive. Either a size or a structure tag is required for this argument.
  • The alignment is an optional parameter that ensures that the space allocated to the symbol occurs on the specified boundary. The boundary must be set to a power of 2 between 20 and 215, inclusive. If the SPC is already aligned at the specified boundary, it is not incremented.

Common symbols are symbols that are placed in the symbol table of an ELF object file. They represent an uninitialized variable. Common symbols do not reference a section. (In contrast, initialized variables need to reference a section that contains the initialized data.) The value of a common symbol is its required alignment; it has no address and stores no address. While symbols for an uninitialized common block can appear in executable object files, common symbols may only appear in relocatable object files. Common symbols are preferred over weak symbols. See the section on the "Symbol Table" in the System V ABI specification for more about common symbols.

When object files containing common symbols are linked, space is reserved in an uninitialized section for each common symbol. A symbol is created in place of the common symbol to refer to its reserved location.

.copy/.include
Copy Source File
Syntax

              .copy"filename"

              .include"filename"

Description

The .copy and .include directives tell the assembler to read source statements from a different file. The statements that are assembled from a copy file are printed in the assembly listing. The statements that are assembled from an included file are not printed in the assembly listing, regardless of the number of .list/.nolist directives assembled.

When a .copy or .include directive is assembled, the assembler:

  1. Stops assembling statements in the current source file
  2. Assembles the statements in the copied/included file
  3. Resumes assembling statements in the main source file, starting with the statement that follows the .copy or .include directive

The filename is a required parameter that names a source file. It is enclosed in double quotes and must follow operating system conventions.

You can specify a full pathname (for example, /320tools/file1.asm). If you do not specify a full pathname, the assembler searches for the file in:

  1. The directory that contains the current source file
  2. Any directories named with the --include_path assembler option
  3. Any directories specified by the MSP430_A_DIR environment variable
  4. Any directories specified by the MSP430_C_DIR environment variable

For more information about the --include_path option and MSP430_A_DIR, see Section 4.5. For more information about MSP430_C_DIR, see the MSP430 Optimizing C/C++ Compiler User's Guide.

The .copy and .include directives can be nested within a file being copied or included. The assembler limits nesting to 32 levels; the host operating system may set additional restrictions. The assembler precedes the line numbers of copied files with a letter code to identify the level of copying. A indicates the first copied file, B indicates a second copied file, etc.

Example 1

In this example, the .copy directive is used to read and assemble source statements from other files; then, the assembler resumes assembling into the current file.

The original file, copy.asm, contains a .copy statement copying the file byte.asm. When copy.asm assembles, the assembler copies byte.asm into its place in the listing (note listing below). The copy file byte.asm contains a .copy statement for a second file, word.asm.

When it encounters the .copy statement for word.asm, the assembler switches to word.asm to continue copying and assembling. Then the assembler returns to its place in byte.asm to continue copying and assembling. After completing assembly of byte.asm, the assembler returns to copy.asm to assemble its remaining statement.

copy.asm
(source file)
byte.asm
(first copy file)
word.asm
(second copy file)
     .space 29
     .copy "byte.asm"
 ** Back in original file
     .string "done"
 ** In byte.asm
     .byte 32,1+ 'A'
     .copy "word.asm"
 ** Back in byte.asm
     .byte 67h + 3q
 ** In word.asm
     .word 0ABCDh, 56q

Listing file:

1 0000 .space 29 2 .copy "byte.asm"A 1 ** In byte.asm A 2 001d 0020 .byte 32,1+ 'A' 001e 0042 A 3 .copy "word.asm"B 1 ** In word.asm B 2 0020 ABCD .word 0ABCDh, 56q 0022 002E A 4 ** Back in byte.asm A 5 0024 006A .byte 67h + 3q 3 4 ** Back in original file 5 0025 0064 .string "done" 0026 006F 0027 006E 0028 0065
Example 2

In this example, the .include directive is used to read and assemble source statements from other files; then, the assembler resumes assembling into the current file. The mechanism is similar to the .copy directive, except that statements are not printed in the listing file.

include.asm
(source file)
byte2.asm
(first copy file)
word2.asm
(second copy file)
     .space 29
     .include "byte2.asm"
 ** Back in original file
     .string "done"
 ** In byte2.asm
     .byte 32,1+ 'A'
     .include "word2.asm"
 ** Back in byte2.asm
     .byte 67h + 3q
 ** In word2.asm
     .word 0ABCDh, 56q

 

Listing file:

1 0000 .space 29 2 .include "byte2.asm" 3 4 **Back in original file 5 0025 0064 .string "done" 0026 006F 0027 006E 0028 0065
.data
Assemble Into the .data Section
Syntax

               .data

Description

The .data directive sets .data as the current section; the lines that follow will be assembled into the .data section. The .data section is normally used to contain tables of data or preinitialized variables.

For more information about sections, see Section 2.

Example

In this example, code is assembled into the .data and .text sections.

1 ; Comments here 2 0000 .data 3 0000 .space 0xCC 4 5 6 ; Comments here 7 0000 .text 8 0000 INDEX .set 0 9 0000 430B MOV #INDEX,R11 10 11 12 13 ; Comments here 14 00cc Table: .data 15 00cc FFFF .word -1 16 00ce 00FF .byte 0xFF 17 18 19 20 ; Comments here 21 0002 .text 22 0002 00CC! con .field Table,16 23 0004 421B MOV &con,R11 0006 0002! 24 0008 5B1C ADD 0(R11),R12 000a 0000 25 26 00cf .data
.double/.float
Initialize Single- or Double-Precision Floating-Point Value
Syntax

               .double value1 [, ... ,valuen]

               .float  value [, ... ,valuen ]

Description

The .double directive places the IEEE double-precision floating-point representation of one or more floating-point values into the current section.

Each value must be an absolute constant expression with an arithmetic type or a symbol equated to an absolute constant expression with an arithmetic type. Each constant is converted to a floating-point value in IEEE single-precision 32-bit format for .float and 64-bit format for .double. Floating point constants are aligned on word boundaries.

The 32-bit value is stored exponent byte first, most significant byte of fraction second, and least significant byte of fraction third, in the format shown in Figure 5-5.

Figure 5-5 32-Bit Single-Precision Floating-Point Format single_tdz072.gif

The 64-bit value is stored in the format shown in Figure 5-6.

Figure 5-6 64-Bit Double-Precision Floating-Point Format double_tdz072.gif

When you use .double or .float in a .struct/.endstruct sequence, they define a member's size; they do not initialize memory. For more information, see the .struct/.endstruct/.tag topic.

Example

Following are examples of the .float and .double directives:

1 0000 5951 .double -2.0e25 0002 E984 2 0004 5951 .float -1.0e25 0006 E904 3 0008 0000 .double 6 000a 40C0 4 000c 0000 .float 3 000e 4040

.drlist/.drnolist
Control Listing of Directives
Syntax

                .drlist

               .drnolist

Description

Two directives enable you to control the printing of assembler directives to the listing file:

The .drlist directive enables the printing of all directives to the listing file.

The .drnolist directive suppresses the printing of the following directives to the listing file. The .drnolist directive has no affect within macros.

  • .asg
  • .break
  • .emsg
  • .eval
  • .fclist

  • .fcnolist
  • .mlist
  • .mmsg
  • .mnolist
  • .sslist

  • .ssnolist
  • .var
  • .wmsg

By default, the assembler acts as if the .drlist directive had been specified.

Example

This example shows how .drnolist inhibits the listing of the specified directives.

Source file:

.asg 0, x .loop 2 .eval x+1, x .endloop .drnolist .asg 1, x .loop 3 .eval x+1, x .endloop

Listing file:

1 .asg 0, x 2 .loop 2 3 .eval x+1, x 4 .endloop 1 .eval 0+1, x 1 .eval 1+1, x 5 6 .drnolist 7 9 .loop 3 10 .eval x+1, x 11 .endloop
.elfsym
ELF Symbol Information
Syntax

                .elfsym name, SYM_SIZE(size)

Description

The .elfsym directive provides additional information for symbols in the ELF format. This directive is designed to convey different types of information, so the type, data pair is used to represent each type. Currently, this directive only supports the SYM_SIZE type.

SYM_SIZE indicates the allocation size (in bytes) of the symbol indicated by name.

Example

This example shows the use of the ELF symbol information directive.

.sect ".examp" .alignment 4 .elfsym ex_sym, SYM_SIZE(4) ex_sym: .word 0
.emsg/.mmsg/.wmsg
Define Messages
Syntax

                .emsg string

               .mmsg string

               .wmsg string

Description

These directives allow you to define your own error and warning messages. When you use these directives, the assembler tracks the number of errors and warnings it encounters and prints these numbers on the last line of the listing file.

The .emsg directive sends an error message to the standard output device in the same manner as the assembler. It increments the error count and prevents the assembler from producing an object file.

The .mmsg directive sends an assembly-time message to the standard output device in the same manner as the .emsg and .wmsg directives. It does not, however, set the error or warning counts, and it does not prevent the assembler from producing an object file.

The .wmsg directive sends a warning message to the standard output device in the same manner as the .emsg directive. It increments the warning count rather than the error count, however. It does not prevent the assembler from producing an object file.

Example

This example sends the message ERROR -- MISSING PARAMETER to the standard output device.

Source file:

MSG_EX .macro parm1 .if $symlen(parm1) = 0 .emsg "ERROR -- MISSING PARAMETER" .else ADD parm1, r7, r8 .endif .endm MSG_EX R11 MSG_EX

Listing file:

1 MSG_EX .macro parm1 2 .if $symlen(parm1)=0 3 .emsg "ERROR -- MISSING PARAMETER" 4 .else 5 ADD parm1, r7 6 .endif 7 .endm 8 9 0000 MSG_EX R11 1 .if $symlen(parm1)=0 1 .emsg "ERROR -- MISSING PARAMETER"1 .else 1 0000 5B07 ADD R11, r7 1 .endif 10 11 0002 MSG_EX 1 .if $symlen(parm1)=0 1 .emsg "ERROR -- MISSING PARAMETER" "emsg.asm", ERROR! at line 11: [ ***** USER ERROR ***** - ] ERROR -- MISSING PARAMETER 1 .else 1 ADD parm1, r7 1 .endif 1 Assembly Error, No Assembly Warnings

In addition, the following messages are sent to standard output by the assembler:

*** ERROR! line 11: ***** USER ERROR ***** - : ERROR -- MISSING PARAMETER .emsg "ERROR -- MISSING PARAMETER" 1 Error, No Warnings Errors in source - Assembler Aborted

.end
End Assembly
Syntax

              .end

Description

The .end directive is optional and terminates assembly. The assembler ignores any source statements that follow a .end directive. If you use the .end directive, it must be the last source statement of a program.

This directive has the same effect as an end-of-file character. You can use .end when you are debugging and you want to stop assembling at a specific point in your code.

NOTE

Ending a Macro

Do not use the .end directive to terminate a macro; use the .endm macro directive instead.

Example

This example shows how the .end directive terminates assembly. Any source statements that follow the .end directive are ignored by the assembler.

Source file:

START: .space 300 TEMP .set 15 .bss LOC1,0x48 LOCL_n .word LOC1 MOV #TEMP,R11 MOV &LOCL_n,R12 MOV 0(R12),R13 .end .byte 4 .word 0xCCC

Listing file:

1 0000 START: .space 300 2 000F TEMP .set 15 3 0000 .bss LOC1,0x48 4 012c 0000! LOCL_n .word LOC1 5 012e 403B MOV #TEMP,R11 0130 000F 6 0132 421C MOV &LOCL_n,R12 0134 012C! 7 0136 4C1D MOV 0(R12),R13 0138 0000 8 .end
.fclist/.fcnolist
Control Listing of False Conditional Blocks
Syntax

                .fclist

               .fcnolist

Description

Two directives enable you to control the listing of false conditional blocks:

The .fclist directive allows the listing of false conditional blocks (conditional blocks that do not produce code).

The .fcnolist directive suppresses the listing of false conditional blocks until a .fclist directive is encountered. With .fcnolist, only code in conditional blocks that are actually assembled appears in the listing. The .if, .elseif, .else, and .endif directives do not appear.

By default, all conditional blocks are listed; the assembler acts as if the .fclist directive had been used.

Example

This example shows the assembly language and listing files for code with and without the conditional blocks listed.

Source file:

AAA .set 1 BB .set 0 .fclist .if AAA ADD #1024,R11 .else ADD #1024*10,R11 .endif .fcnolist .if AAA ADD #1024,R11 .else ADD #1024*10,R11 .endif

Listing file:

1 0001 AAA .set 1 2 0000 BB .set 0 3 .fclist 4 .if AAA 5 0000 503B ADD #1024,R11 0002 0400 6 .else 7 ADD #1024*10,R11 8 .endif 9 .fcnolist 11 0004 503B ADD #1024,R11 0006 0400
.field
Initialize Field
Syntax

               .field value[, size in bits]

Description

The .field directive initializes a multiple-bit field within a single word (16 bits) of memory. This directive has two operands:

  • The value is a required parameter; it is an expression that is evaluated and placed in the field. The value must be absolute.
  • The size in bits is an optional parameter; it specifies a number from 1 to 32, which is the number of bits in the field. The default size is 16 bits. If you specify a value that cannot fit in size in bits, the assembler truncates the value and issues a warning message. For example, .field 3,1 causes the assembler to truncate the value 3 to 1; the assembler also prints the message:
  • *** WARNING! line 21: W0001: Field value truncated to 1 .field 3, 1

Successive .field directives pack values into the specified number of bits.

The .field directive is similar to the .bits directive (see the .bits topic). However, the .bits directive does not allow you to specify the number of bits in the field and does not automatically increment the SPC when a word boundary is reached.

Use the .align directive to force the next .field directive to begin packing a new word.

If you use a label, it points to the byte that contains the specified field.

When you use .field in a .struct/.endstruct sequence, .field defines a member's size; it does not initialize memory. For more information, see the .struct/.endstruct/.tag topic.

Example

This example shows how fields are packed into a word. The SPC does not change until a word is filled and the next word is begun.

1 ************************************ 2 ** Initialize a 14-bit field. ** 3 ************************************ 4 0000 0ABC .field 0ABCh, 14 5 6 ************************************ 7 ** Initialize a 5-bit field ** 8 ** in the same word. ** 9 ************************************ 10 0002 000A L_F: .field 0Ah, 5 11 12 ************************************ 13 ** Write out the word. ** 14 ************************************ 15 .align 4 16 17 ************************************ 18 ** Initialize a 4-bit field. ** 19 ** This fields starts a new word. ** 20 ************************************ 21 0004 000C x: .field 0Ch, 4 22 23 ************************************ 24 ** 16-bit relocatable field ** 25 ** in the next word. ** 26 ************************************ 27 0006 0004! .field x 28 29 ************************************ 30 ** Initialize a 16-bit field. ** 31 ************************************ 32 0008 4321 .field 04321h, 16

Figure 5-7 shows how the directives in this example affect memory.

Figure 5-7 The .field Directive field2_lau131.gif
.global/.def/.ref
Identify Global Symbols
Syntax

                .global symbol1[, ... ,symboln]

               .def symbol1[, ... ,symboln]

               .ref symbol1[, ... ,symboln]

Description

Three directives identify global symbols that are defined externally or can be referenced externally:

The .def directive identifies a symbol that is defined in the current module and can be accessed by other files. The assembler places this symbol in the symbol table.

The .ref directive identifies a symbol that is used in the current module but is defined in another module. The linker resolves this symbol's definition at link time.

The .global directive acts as a .ref or a .def, as needed.

A global symbol is defined in the same manner as any other symbol; that is, it appears as a label or is defined by the .set, .equ, .bss, or .usect directive. If a global symbol is defined more than once, the linker issues a multiple-definition error. (The assembler can provide a similar multiple-definition error for local symbols.) The .ref directive always creates a symbol table entry for a symbol, whether the module uses the symbol or not; .global, however, creates an entry only if the module actually uses the symbol.

A symbol can be declared global for either of two reasons:

  • If the symbol is not defined in the current module (which includes macro, copy, and include files), the .global or .ref directive tells the assembler that the symbol is defined in an external module. This prevents the assembler from issuing an unresolved reference error. At link time, the linker looks for the symbol's definition in other modules.
  • If the symbol is defined in the current module, the .global or .def directive declares that the symbol and its definition can be used externally by other modules. These types of references are resolved at link time.
Example

This example shows four files. The file1.lst and file2.lst refer to each other for all symbols used; file3.lst and file4.lst are similarly related.

The file1.lst and file3.lst files are equivalent. Both files define the symbol INIT and make it available to other modules; both files use the external symbols X, Y, and Z. Also, file1.lst uses the .global directive to identify these global symbols; file3.lst uses .ref and .def to identify the symbols.

The file2.lst and file4.lst files are equivalent. Both files define the symbols X, Y, and Z and make them available to other modules; both files use the external symbol INIT. Also, file2.lst uses the .global directive to identify these global symbols; file4.lst uses .ref and .def to identify the symbols.

file1.lst

1 ; Global symbol defined in this file 2 .global INIT 3 ; Global symbols defined in file2.lst 4 .global X, Y, Z 5 0000 INIT: 6 0000 503B ADD #56h, R11 0002 0056 7 0004 0000! .word X 8 ; . 9 ; . 10 ; . 11 .end

 

file2.lst

1 ; Global symbols defined in this file 2 .global X, Y, Z 3 ; Global symbol defined in file1.lst 4 .global INIT 5 0001 X: .set 1 6 0002 Y: .set 2 7 0003 Z: .set 3 8 0000 0000! .word INIT 9 ; . 10 ; . 11 ; . 12 .end

file3.lst

1 ; Global symbol defined in this file 2 .def INIT 3 ; Global symbols defined in file2.lst 4 .ref X, Y, Z 5 0000 INIT: 6 0000 503B ADD #56h, R11 0002 0056 7 0004 0000! .word X 8 ; . 9 ; . 10 ; . 11 .end

file4.lst

1 ; Global symbols defined in this file 2 .def X, Y, Z 3 ; Global symbol defined in file3.lst 4 .ref INIT 5 0001 X: .set 1 6 0002 Y: .set 2 7 0003 Z: .set 3 8 0000 0000! .word INIT 9 ; . 10 ; . 11 ; . 12 .end
.group/.gmember/.endgroup
Define Common Data Section
Syntax

                .group   group section name group type

               .gmember section name

               .endgroup

Description

Three directives instruct the assembler to make certain sections members of an ELF group section (see the ELF specification for more information on group sections).

The .group directive begins the group declaration. The group section name designates the name of the group section. The group type designates the type of the group. The following types are supported:

0x0 Regular ELF group
0x1 COMDAT ELF group

Duplicate COMDAT (common data) groups are allowed in multiple modules; the linker keeps only one. Creating such duplicate groups is useful for late instantiation of C++ templates and for providing debugging information.

The .gmember directive designates section name as a member of the group.

The .endgroup directive ends the group declaration.

.half/.short/.uhalf/.ushort
Initialize 16-Bit Integers
Syntax

                .half value1[, ... ,valuen ]

               .short value1[, ... ,valuen ]

                .uhalf value1[, ... ,valuen ]

               .ushort value1[, ... ,valuen ]

Description

The .half and .short directives place one or more values into consecutive halfwords in the current section. A value can be either:

  • An expression that the assembler evaluates and treats as a 16-bit signed or unsigned number
  • A character string enclosed in double quotes. Each character in a string represents a separate value and is stored alone in the least significant eight bits of a 16-bit field, which is padded with 0s.

The assembler truncates values greater than 16 bits.

If you use a label with .half or .short, it points to the location where the assembler places the first byte.

These directives perform a word (16-bit) alignment before data is written to the section.

When you use .half or .short in a .struct/.endstruct sequence, they define a member's size; they do not initialize memory. For more information, see the .struct/.endstruct/.tag topic.

Example

In this example, .half is used to place 16-bit values (10, -1, abc, and a) into consecutive halfwords in memory; .short is used to place 16-bit values (8, -3, def, and b) into consecutive halfwords in memory. The label STRN has the value 100ch, which is the location of the first initialized halfword for .short.

1 0000 .space 100h * 16 2 1000 000A .half 10, -1, "abc", "a' 1002 FFFF 1004 0061 1006 0062 1008 0063 100a 0061 3 100c 0008 STRN .short 8, -3, "def", 'b' 100e FFFD 1010 0064 1012 0065 1014 0066 1016 0062
.if/.elseif/.else/.endif
Assemble Conditional Blocks
Syntax

               .if condition

             [.elseifcondition]

             [.else]

              .endif

Description

These directives provide conditional assembly:

The .if directive marks the beginning of a conditional block. The condition is a required parameter.

  • If the expression evaluates to true (nonzero), the assembler assembles the code that follows the expression (up to a .elseif, .else, or .endif).
  • If the expression evaluates to false (0), the assembler assembles code that follows a .elseif (if present), .else (if present), or .endif (if no .elseif or .else is present).

The .elseif directive identifies a block of code to be assembled when the .if expression is false (0) and the .elseif expression is true (nonzero). When the .elseif expression is false, the assembler continues to the next .elseif (if present), .else (if present), or .endif (if no .elseif or .else is present). The .elseif is optional in a conditional block, and more than one .elseif can be used. If an expression is false and there is no .elseif, the assembler continues with the code that follows a .else (if present) or a .endif.

The .else directive identifies a block of code that the assembler assembles when the .if expression and all .elseif expressions are false (0). The .else directive is optional in the conditional block; if an expression is false and there is no .else statement, the assembler continues with the code that follows the .endif. The .elseif and .else directives can be used in the same conditional assembly block.

The .endif directive terminates a conditional block.

See Section 4.9.2 for information about relational operators.

Example

This example shows conditional assembly:

1 0001 SYM1 .set 1 2 0002 SYM2 .set 2 3 0003 SYM3 .set 3 4 0004 SYM4 .set 4 5 6 If_4: .if SYM4 = SYM2 * SYM2 7 0000 0004 .byte SYM4 ; Equal values 8 .else 9 .byte SYM2 * SYM2 ; Unequal values 10 .endif 11 12 If_5: .if SYM1 <= 10 13 0001 000A .byte 10 ; Equal values 14 .else 15 .byte SYM1 ; Unequal values 16 .endif 17 18 If_6: .if SYM3 * SYM2 != SYM4 + SYM2 19 .byte SYM3 * SYM2 ; Unequal value 20 .else 21 0002 0008 .byte SYM4 + SYM4 ; Equal values 22 .endif 23 24 If_7: .if SYM1 = SYM2 25 .byte SYM1 26 .elseif SYM2 + SYM3 = 5 27 0003 0005 .byte SYM2 + SYM3 28 .endif
.int/.unint/.word/.uword
Initialize 16-Bit Integers
Syntax

                .int value1[, ... ,valuen ]

               .uint value1[, ... ,valuen ]

               .word value1[, ... ,valuen ]

               .uword value1[, ... ,valuen ]

Description

The .int, .unint, .word, and .uword directives place one or more values into consecutive words in the current section. Each value is placed in a 16-bit word by itself and is aligned on a word boundary. A value can be either:

  • An expression that the assembler evaluates and treats as a 16-bit signed or unsigned number
  • A character string enclosed in double quotes. Each character in a string represents a separate value and is stored alone in the least significant eight bits of a 16-bit field, which is padded with 0s.

A value can be either an absolute or a relocatable expression. If an expression is relocatable, the assembler generates a relocation entry that refers to the appropriate symbol; the linker can then correctly patch (relocate) the reference. This allows you to initialize memory with pointers to variables or labels.

If you use a label with these directives, it points to the first word that is initialized.

When you use these directives in a .struct/.endstruct sequence, they define a member's size; they do not initialize memory. See the .struct/.endstruct/.tag topic.

Example

In this example, the .int and .word directives are used to initialize words. The symbol WORDX points to the first word that is reserved by .word.

1 0000 .space 73h 2 0000 .bss PAGE, 128 3 0080 .bss SYMPTR, 4 4 0074 403B INST: MOV #056h, R11 0076 0056 5 0078 000A .int 10, SYMPTR, -1, 35 + 'a', INST, "abc" 007a 0080! 007c FFFF 007e 0084 0080 0074! 0082 0061 0084 0062 0086 0063 6 0000 0C80 WORDX: .word 3200, 1 + 'AB', -0AFh, 'X' 0002 4242 0004 FF51 0006 0058

.intvec
Create an Interrupt Vector
Syntax

               .intvec "section_name", routine_name

Description

The .intvec directive creates an interrupt vector with a pointer to an interrupt function. It defines a named section and specifies the ISR routine to be run for the interrupt. The .intvec directive is equivalent to performing the .sect directive followed by the .short directive.

The section_name identifies the section for the interrupt vector pointer to the interrupt routine. The name must be of the form .intxx where xx is the number of the interrupt vector. The section name must be enclosed in double quotes. See Section 2.4.3 for information about named sections.

The routine_name identifies the ISR trap routine that should be run as a result of this interrupt.

The linker command file must specify output sections that map to the physical memory location for each interrupt vector. The standard linker command files are set up to handle the .intxx naming convention used by the .intvec directive.

If you do not specify an ISR routine for some interrupt vectors, an ISR routine will be provided for those vectors from the RTS library and the RTS library will automatically be linked with your application. The default ISR routine puts the device in low power mode. You can override the ISR provided by the RTS by using the .intvec directive with the "default_isr" section name as shown in the following example.

.intvec "default_isr", isr_trap_function
Example

This example creates an interrupt vector in the .int55 section that runs a routine called ADC12_ISR.

.intvec ".int55", ADC12_ISR
.label
Create a Load-Time Address Label
Syntax

               .label symbol

Description

The .label directive defines a special symbol that refers to the load-time address rather than the run-time address within the current section. Most sections created by the assembler have relocatable addresses. The assembler assembles each section as if it started at 0, and the linker relocates it to the address at which it loads and runs.

For some applications, it is desirable to have a section load at one address and run at a different address. For example, you may want to load a block of performance-critical code into slower memory to save space and then move the code to high-speed memory to run it. Such a section is assigned two addresses at link time: a load address and a run address. All labels defined in the section are relocated to refer to the run-time address so that references to the section (such as branches) are correct when the code runs. See Section 3.5 for more information about run-time relocation.

The .label directive creates a special label that refers to the load-time address. This function is useful primarily to designate where the section was loaded for purposes of the code that relocates the section.

Example

This example shows the use of a load-time address label.

sect ".examp" .label examp_load ; load address of section start: ; run address of section <code>finish: ; run address of section end .label examp_end ; load address of section end

See Section 8.5.6 for more information about assigning run-time and load-time addresses in the linker.

.length/.width
Set Listing Page Size
Syntax

                .length [page length]

               .width [page width]

Description

Two directives allow you to control the size of the output listing file.

The .length directive sets the page length of the output listing file. It affects the current and following pages. You can reset the page length with another .length directive.

  • Default length: 60 lines. If you do not use the .length directive or if you use the .length directive without specifying the page length, the output listing length defaults to 60 lines.
  • Minimum length: 1 line
  • Maximum length: 32 767 lines

The .width directive sets the page width of the output listing file. It affects the next line assembled and the lines following. You can reset the page width with another .width directive.

  • Default width: 132 characters. If you do not use the .width directive or if you use the .width directive without specifying a page width, the output listing width defaults to 132 characters.
  • Minimum width: 80 characters
  • Maximum width: 200 characters

The width refers to a full line in a listing file; the line counter value, SPC value, and object code are counted as part of the width of a line. Comments and other portions of a source statement that extend beyond the page width are truncated in the listing.

The assembler does not list the .width and .length directives.

Example

The following example shows how to change the page length and width.

******************************************** ** Page length = 65 lines ** ** Page width = 85 characters ** ******************************************** .length 65 .width 85 ******************************************** ** Page length = 55 lines ** ** Page width = 100 characters ** ******************************************** .length 55 .width 100
.list/.nolist
Start/Stop Source Listing
Syntax

                .list

               .nolist

Description

Two directives enable you to control the printing of the source listing:

The .list directive allows the printing of the source listing.

The .nolist directive suppresses the source listing output until a .list directive is encountered. The .nolist directive can be used to reduce assembly time and the source listing size. It can be used in macro definitions to suppress the listing of the macro expansion.

The assembler does not print the .list or .nolist directives or the source statements that appear after a .nolist directive. However, it continues to increment the line counter. You can nest the .list/.nolist directives; each .nolist needs a matching .list to restore the listing.

By default, the source listing is printed to the listing file; the assembler acts as if the .list directive had been used. However, if you do not request a listing file when you invoke the assembler by including the --asm_listing option on the command line (see Section 4.3), the assembler ignores the .list directive.

Example

This example shows how the .copy directive inserts source statements from another file. The first time this directive is encountered, the assembler lists the copied source lines in the listing file. The second time this directive is encountered, the assembler does not list the copied source lines, because a .nolist directive was assembled. The .nolist, the second .copy, and the .list directives do not appear in the listing file. Also, the line counter is incremented, even when source statements are not listed.

Source file:

* Back in original file NOP .nolist .copy "copy2.asm" .list * Back in original file .string "Done"

Listing file:

1 .copy "copy2.asm"A 1 * In copy2.asm (copy file) A 2 0000 0020 .word 32, 1 + 'A' 0002 0042 2 * Back in original file 3 0004 4303 NOP 7 * Back in original file 8 000a 0044 .string "Done" 000b 006F 000c 006E 000d 0065
.long/.ulong
Initialize 32-Bit Integer
Syntax

               .long value1[, ... ,valuen]

               .ulong value1[, ... ,valuen]

Description

The .long directive places one or more values into consecutive words in the current section. A value can be either:

  • An expression that the assembler evaluates and treats as a 32-bit signed or unsigned number
  • A character string enclosed in double quotes. Each character in a string represents a separate value and is stored alone in the least significant eight bits of a 32-bit field, which is padded with 0s.

A value can be either an absolute or a relocatable expression. If an expression is relocatable, the assembler generates a relocation entry that refers to the appropriate symbol; the linker can then correctly patch (relocate) the reference. This allows you to initialize memory with pointers to variables or labels.

The .long directive performs a word (16-bit) alignment before any data is written to the section.

When you use .long directive in a .struct/.endstruct sequence, it defines a member's size; it does not initialize memory. See the .struct/.endstruct/.tag topic.

Example

This example shows how the .long directive initializes words. The symbol DAT1 points to the first word that is reserved.

1 0000 ABCD DAT1: .long 0ABCDh, 'A' + 100h, 'g', 'o' 0002 0000 0004 0141 0006 0000 0008 0067 000a 0000 000c 006F 000e 0000 2 0010 0000! .long DAT1, 0AABBCCDDh 0012 0000 0014 CCDD 0016 AABB 3 0018 DAT2:
.loop/.endloop/.break
Assemble Code Block Repeatedly
Syntax

                .loop [count]

               .break [end-condition]

               .endloop

Description

Three directives allow you to repeatedly assemble a block of code:

The .loop directive begins a repeatable block of code. The optional count operand, if used, must be a well-defined integer expression. The count indicates the number of loops to be performed (the loop count). If count is omitted, it defaults to 1024. The loop will be repeated count number of times, unless terminated early by a .break directive.

The optional .break directive terminates a .loop early. You may use .loop without using .break. The .break directive terminates a .loop only if the end-condition expression is true (evaluates to nonzero). If the optional end-condition operand is omitted, it defaults to true. If end-condition is true, the assembler stops repeating the .loop body immediately; any remaining statements after .break and before .endloop are not assembled. The assembler resumes assembling with the statement after the .endloop directive. If end-condition is false (evaluates to 0), the loop continues.

The .endloop directive marks the end of a repeatable block of code. When the loop terminates, whether by a .break directive with a true end-condition or by performing the loop count number of iterations, the assembler stops repeating the loop body and resumes assembling with the statement after the .endloop directive.

Example

This example illustrates how these directives can be used with the .eval directive. The code in the first six lines expands to the code immediately following those six lines.

1 .eval 0,x 2 COEF .loop 3 .word x*100 4 .eval x+1, x 5 .break x = 6 6 .endloop 1 0000 0000 .word 0*100 1 .eval 0+1, x 1 .break 1 = 6 1 0002 0064 .word 1*100 1 .eval 1+1, x 1 .break 2 = 6 1 0004 00C8 .word 2*100 1 .eval 2+1, x 1 .break 3 = 6 1 0006 012C .word 3*100 1 .eval 3+1, x 1 .break 4 = 6 1 0008 0190 .word 4*100 1 .eval 4+1, x 1 .break 5 = 6 1 000a 01F4 .word 5*100 1 .eval 5+1, x 1 .break 6 = 6
.macro/.endm
Define Macro
Syntax

macname  .macro [parameter1[, ... ,parametern]]

                 model statements or macro directives

                 .endm

Description

The .macro and .endm directives are used to define macros.

You can define a macro anywhere in your program, but you must define the macro before you can use it. Macros can be defined at the beginning of a source file, in an .include/.copy file, or in a macro library.

macname names the macro. You must place the name in the source statement's label field.
.macro identifies the source statement as the first line of a macro definition. You must place .macro in the opcode field.
[parameters] are optional substitution symbols that appear as operands for the .macro directive.
model statements are instructions or assembler directives that are executed each time the macro is called.
macro directives are used to control macro expansion.
.endm marks the end of the macro definition.

Macros are explained in further detail in Section 6.

.mlib
Define Macro Library
Syntax

               .mlib " filename "

Description

The .mlib directive provides the assembler with the filename of a macro library. A macro library is a collection of files that contain macro definitions. The macro definition files are bound into a single file (called a library or archive) by the archiver.

Each file in a macro library contains one macro definition that corresponds to the name of the file. The filename of a macro library member must be the same as the macro name, and its extension must be .asm. The filename must follow host operating system conventions; it can be enclosed in double quotes. You can specify a full pathname (for example, c:\320tools\macs.lib). If you do not specify a full pathname, the assembler searches for the file in the following locations in the order given:

  1. The directory that contains the current source file
  2. Any directories named with the --include_path assembler option
  3. Any directories specified by the MSP430_A_DIR environment variable
  4. Any directories specified by the MSP430_C_DIR environment variable

See Section 4.5 for more information about the --include_path option.

A .mlib directive causes the assembler to open the library specified by filename and create a table of the library's contents. The assembler stores names of individual library members in the opcode table as library entries. This redefines any existing opcodes or macros with the same name. If one of these macros is called, the assembler extracts the library entry and loads it into the macro table. The assembler expands the library entry as it does other macros, but it does not place the source code in the listing. Only macros called from the library are extracted, and they are extracted only once. See Section 6.

Example

The code creates a macro library that defines two macros, inc4.asm and dec4.asm. The file inc4.asm contains the definition of inc4 and dec4.asm contains the definition of dec4.

inc4.asm dec4.asm
* Macro for incrementing
inc4 .macro reg
    ADD.W #1, reg
    ADD.W #1, reg
    ADD.W #1, reg
    ADD.W #1, reg
    .endm
* Macro for decrementing
dec4 .macro reg
    SUB.W #1, reg
    SUB.W #1, reg
    SUB.W #1, reg
    SUB.W #1, reg
    .endm

Use the archiver to create a macro library:

ar430 -a mac inc4.asm dec4.asm

Now you can use the .mlib directive to reference the macro library and define the inc4.asm and dec4.asm macros:

1 .mlist 2 .mlib "mac.lib" 3 ; Macro call 4 0000 inc4 R11, R12, R13, R14 1 0000 531B ADD.W #1,R11 1 0002 531C ADD.W #1,R12 1 0004 531D ADD.W #1,R13 1 0006 531E ADD.W #1,R14 5 6 ; Macro call 7 0008 dec4 R11, R12, R13, R14 1 0008 831B SUB.W #1,R11 1 000a 831C SUB.W #1,R12 1 000c 831D SUB.W #1,R13 1 000e 831E SUB.W #1,R14
.mlist/.mnolist
Start/Stop Macro Expansion Listing
Syntax

                .mlist

               .mnolist

Description

Two directives enable you to control the listing of macro and repeatable block expansions in the listing file:

The .mlist directive allows macro and .loop/.endloop block expansions in the listing file.

The .mnolist directive suppresses macro and .loop/.endloop block expansions in the listing file.

By default, the assembler behaves as if the .mlist directive had been specified.

See Section 6 for more information on macros and macro libraries. See the .loop/.break/.endloop topic for information on conditional blocks.

Example

This example defines a macro named STR_3. The first time the macro is called, the macro expansion is listed (by default). The second time the macro is called, the macro expansion is not listed, because a .mnolist directive was assembled. The third time the macro is called, the macro expansion is again listed because a .mlist directive was assembled.

1 STR_3 .macro P1, P2, P3 2 .string ":p1:", ":p2:", ":p3:" 3 .endm 4 5 0000 STR_3 "as", "I", "am" ; Invoke STR_3 macro. 1 0000 003A .string ":p1:", ":p2:", ":p3:" 0001 0070 0002 0031 0003 003A 0004 003A 0005 0070 0006 0032 0007 003A 0008 003A 0009 0070 000a 0033 000b 003A 6 .mnolist ; Suppress expansion. 7 000c STR_3 "as", "I", "am" ; Invoke STR_3 macro. 8 .mlist ; Show macro expansion. 9 0018 STR_3 "as", "I", "am" ; Invoke STR_3 macro. 1 0018 003A .string ":p1:", ":p2:", ":p3:" 0019 0070 001a 0031 001b 003A 001c 003A 001d 0070 001e 0032 001f 003A 0020 003A 0021 0070 0022 0033 0023 003A

.newblock
Terminate Local Symbol Block
Syntax

               .newblock

Description

The .newblock directive undefines any local labels currently defined. Local labels, by nature, are temporary; the .newblock directive resets them and terminates their scope.

A local label is a label in the form $n, where n is a single decimal digit, or name?, where name is a legal symbol name. Unlike other labels, local labels are intended to be used locally, and cannot be used in expressions. They can be used only as operands in 8-bit jump instructions. Local labels are not included in the symbol table.

After a local label has been defined and (perhaps) used, you should use the .newblock directive to reset it. The .text, .data, and .sect directives also reset local labels. Local labels that are defined within an include file are not valid outside of the include file.

See Section 4.8.3 for more information on the use of local labels.

Example

This example shows how the local label $1 is declared, reset, and then declared again.

1 .global ADDRA,ADDRB,ADDRC 2 3 0000 403B Label1: MOV #ADDRA, R11 ; Load Address A to R11 0002 0000! 4 0004 803B SUB #ADDRB, R11 ; Subtract Address B. 0006 0000! 5 0008 3803 JL $1 ; If < 0, branch to $1 6 000a 403B MOV #ADDRB, R11 ; otherwise, load ADDRB to R11 000c 0000! 7 000e 3C02 JMP $2 ; and branch to $2 8 0010 403B $1 MOV #ADDRA, R11 ; $1: load ADDRA to AC0. 0012 0000! 9 0014 503B $2 ADD #ADDRC, R11 ; $2: add ADDRC. 0016 0000! 10 .newblock ; Undefine $1 so can be used again. 11 0018 3C02 JMP $1 ; If less than zero, branch to $1. 12 001a 4B82 MOV R11,&ADDRC ; Store AC0 low in ADDRC. 001c 0000! 13 001e 4303 $1 NOP
.option
Select Listing Options
Syntax

                .option option1[, option2,. . .]

Description

The .option directive selects options for the assembler output listing. The options must be separated by commas; each option selects a listing feature. These are valid options:

A turns on listing of all directives and data, and subsequent expansions, macros, and blocks.
B limits the listing of .byte and .char directives to one line.
H limits the listing of .half and .short directives to one line.
L limits the listing of .long directives to one line.
M turns off macro expansions in the listing.
N turns off listing (performs .nolist).
O turns on listing (performs .list).
R resets any B, H, M, T, and, W (turns off the limits of B, H, M, T, and, W).
T limits the listing of .string directives to one line.
W limits the listing of .word and .int directives to one line.
X produces a cross-reference listing of symbols. You can also obtain a cross-reference listing by invoking the assembler with the --cross_reference option (see Section 4.3).

Options are not case sensitive.

Example

This example shows how to limit the listings of the .byte, .char, .int, long, .word, and .string directives to one line each.

1 ***************************************************** 2 ** Limit the listing of .byte, .char, .int, .long, ** 3 ** .word, and .string directives to 1 line each. ** 4 ***************************************************** 5 .option B, W, T 6 0000 00BD .byte -'C', 0B0h, 5 7 0003 00BC .char -'D', 0C0h, 6 8 0006 000A .int 10, 35 + 'a', "abc" 9 0010 CCDD .long 0AABBCCDDh, 536 + 'A' 0012 AABB 0014 0259 0016 0000 10 0018 15AA .word 5546, 78h 11 001c 0045 .string "Extended Registers" 12 13 **************************************************** 14 ** Reset the listing options. ** 15 **************************************************** 16 .option R 17 002e 00BD .byte -'C', 0B0h, 5 002f 00B0 0030 0005 18 0031 00BC .char -'D', 0C0h, 6 0032 00C0 0033 0006 19 0034 000A .int 10, 35 + 'a', "abc" 0036 0084 0038 0061 003a 0062 003c 0063 20 003e CCDD .long 0AABBCCDDh, 536 + 'A' 0040 AABB 0042 0259 0044 0000 21 0046 15AA .word 5546, 78h 0048 0078 22 004a 0045 .string "Extended Registers" 004b 0078 004c 0074 004d 0065 004e 006E 004f 0064 0050 0065 0051 0064 0052 0020 0053 0052 0054 0065 0055 0067 0056 0069 0057 0073 0058 0074 0059 0065 005a 0072 005b 0073
.page
Eject Page in Listing
Syntax

                .page

Description

The .page directive produces a page eject in the listing file. The .page directive is not printed in the source listing, but the assembler increments the line counter when it encounters the .page directive. Using the .page directive to divide the source listing into logical divisions improves program readability.

Example

This example shows how the .page directive causes the assembler to begin a new page of the source listing.

Source file:

Source file (generic) .title "**** Page Directive Example ****"; . ; . ; . .page

Listing file:

MSP430 Assembler PC vx.x.x Day Time Year Tools Copyright (c) 2003-2011 Texas Instruments Incorporated **** Page Directive Example **** PAGE 1 2 ; . 3 ; . 4 ; . MSP430 Assembler PC vx.x.x Day Time Year Tools Copyright (c) 2003-2011 Texas Instruments Incorporated **** Page Directive Example ****
.retain / .retainrefs
Conditionally Retain Sections In Object Module Output
Syntax

               .retain["section name"]

               .retainrefs["section name"]

Description

The .retain directive indicates that the current or specified section is not eligible for removal via conditional linking. You can also override conditional linking for a given section with the --retain linker option. You can disable conditional linking entirely with the --unused_section_elimination=off linker option.

The .retainrefs directive indicates that any sections that refer to the current or specified section are not eligible for removal via conditional linking. For example, applications may use an .intvecs section to set up interrupt vectors. The .intvecs section is eligible for removal during conditional linking by default. You can force the .intvecs section and any sections that reference it to be retained by applying the .retain and .retainrefs directives to the .intvecs section.

The section name identifies the section. If the directive is used without a section name, it applies to the current initialized section. If the directive is applied to an uninitialized section, the section name is required. The section name must be enclosed in double quotes. A section name can contain a subsection name in the form section name:subsection name.

The linker assumes that all sections by default are eligible for removal via conditional linking. (However, the linker does automatically retain the .reset section.) The .retain directive is useful for overriding this default conditional linking behavior for sections that you want to keep included in the link, even if the section is not referenced by any other section in the link. For example, you could apply a .retain directive to an interrupt function that you have written in assembly language, but which is not referenced from any normal entry point in the application.

.sect
Assemble Into Named Section
Syntax

                .sect " section name "

Description

The .sect directive defines a named section that can be used like the default .text and .data sections. The .sect directive sets section name to be the current section; the lines that follow are assembled into the section name section.

The section name identifies the section. The section name must be enclosed in double quotes. A section name can contain a subsection name in the form section name:subsection name. See Section 2 for more information about sections.

Example

This example defines a special-purpose section named Vars and assembles code into it.

1 *************************************************** 2 ** Begin assembling into .text section. ** 3 *************************************************** 4 0000 .text 5 0000 403B MOV #0x78,R11 0002 0078 6 0004 503B ADD #0x78,R11 0006 0078 7 *************************************************** 8 ** Begin assembling into Vars section. ** 9 *************************************************** 10 0000 .sect "Vars" 11 0000 CCCD .float 0.05 0002 3D4C 12 0004 00AA X: .word 0xAA 13 *************************************************** 14 ** Resume assembling into .text section. ** 15 *************************************************** 16 0008 .text 17 0008 5B0C ADD R11,R12 18 *************************************************** 19 ** Resume assembling into Vars section. ** 20 *************************************************** 21 0006 .sect "Vars" 22 0006 000D .field 13 23 0008 000A .field 0xA 24 000a 0010 .field 0x10
.set/.equ
Define Assembly-Time Constant
Syntax

symbol  .set   value

symbol  .equ  value

Description

The .setand .equ directives equate a constant value to a .set/.equ symbol. The symbol can then be used in place of a value in assembly source. This allows you to equate meaningful names with constants and other values. The .set and .equ directives are identical and can be used interchangeably.

  • The symbol is a label that must appear in the label field.
  • The value must be a well-defined expression, that is, all symbols in the expression must be previously defined in the current source module.

Undefined external symbols and symbols that are defined later in the module cannot be used in the expression. If the expression is relocatable, the symbol to which it is assigned is also relocatable.

The value of the expression appears in the object field of the listing. This value is not part of the actual object code and is not written to the output file.

Symbols defined with .set or .equ can be made externally visible with the .def or .global directive (see the .global/.def/.ref topic). In this way, you can define global absolute constants.

Example

This example shows how symbols can be assigned with .set and .equ.

1 ***************************************************** 2 ** Equate symbol ACCUM to register R11 and use ** 3 ** it instead of the register. ** 4 ***************************************************** 5 000B ACCUM .set R11 6 0000 401B MOV 0x56, ACCUM 0002 0054 7 8 ***************************************************** 9 ** Set symbol INDEX to an integer expression ** 10 ** and use it as an immediate operand. ** 11 ***************************************************** 12 0035 INDEX .equ 100/2 + 3 13 0004 503B ADD #INDEX, ACCUM 0006 0035 14 15 ***************************************************** 16 ** Set symbol SYMTAB to a relocatable expression ** 17 ** and use it as a relocatable operand. ** 18 ***************************************************** 19 0008 000A LABEL .word 10 20 0009! SYMTAB .set LABEL + 1 21 22 ***************************************************** 23 ** Set symbol NSYMS equal to the symbol INDEX ** 24 ** and use it as you would INDEX. ** 25 ***************************************************** 26 0035 NSYMS .set INDEX 27 000a 0035 .word NSYMS
.space/.bes
Reserve Space
Syntax

[label]   .space  size in bytes

[label]   .bes      size in bytes

Description

The .spaceand .bes directives reserve the number of bytes given by size in bytes in the current section and fill them with 0s. The section program counter is incremented to point to the word following the reserved space.

When you use a label with the .space directive, it points to the first byte reserved. When you use a label with the .bes directive, it points to the last reserved.

Example

This example shows how memory is reserved with the .space and .bes directives.

1 ************************************************** 2 ** Begin assembling into the .text section. ** 3 ************************************************** 4 0000 .text 5 6 ************************************************** 7 ** Reserve 0F0 bytes in the .text section. ** 8 ************************************************** 9 0000 .space 0F0h 10 00f0 0100 .word 100h, 200h 00f2 0200 11 ************************************************** 12 ** Begin assembling into the .data section. ** 13 ************************************************** 14 0000 .data 15 0000 0049 .string "In .data" 0001 006E 0002 0020 0003 002E 0004 0064 0005 0061 0006 0074 0007 0061 16 *************************************************** 17 ** Reserve 100 bytes in the .data section; RES_1 ** 18 ** points to the first byte that contains ** 19 ** reserved bytes. ** 20 *************************************************** 21 0008 RES_1: .space 100 22 006c 000F .word 15 23 006e 0008! .word RES_1 24 *************************************************** 25 ** Reserve 20 bits in the .data section; RES_2 ** 26 ** points to the last byte that contains ** 27 ** reserved bytes. ** 28 *************************************************** 29 0083 RES_2: .bes 20 30 0084 0036 .word 36h 31 0086 0083! .word RES_2
.sslist/.ssnolist
Control Listing of Substitution Symbols
Syntax

                .sslist

               .ssnolist

Description

Two directives allow you to control substitution symbol expansion in the listing file:

The .sslist directive allows substitution symbol expansion in the listing file. The expanded line appears below the actual source line.

The .ssnolist directive suppresses substitution symbol expansion in the listing file.

By default, all substitution symbol expansion in the listing file is suppressed; the assembler acts as if the .ssnolist directive had been used.

Lines with the pound (#) character denote expanded substitution symbols.

Example

This example shows code that, by default, suppresses the listing of substitution symbol expansion, and it shows the .sslist directive assembled, instructing the assembler to list substitution symbol code expansion.

1 SHIFT .macro dst,amount 2 .loop amount 3 RLA dst 4 .endloop 5 .endm 6 7 .global value 8 9 0000 SHIFT R5,3 1 .loop 3 1 RLA dst 1 .endloop 2 0000 5505 RLA R5 2 0002 5505 RLA R5 2 0004 5505 RLA R5 10 0006 5582 ADD R5,&value 0008 0000! 11 12 .sslist 13 14 000a SHIFT R5,3 1 .loop amount # .loop 3 1 RLA dst 1 .endloop 2 000a 5505 RLA dst # RLA R5 2 000c 5505 RLA dst # RLA R5 2 000e 5505 RLA dst # RLA R5
.string/.cstring
Initialize Text
Syntax

                .string   {expr1 | "string1"} [, ... , {exprn | "stringn"} ]

               .cstring   {expr1 | "string1"} [, ... , {exprn | "stringn"} ]

Description

The .string and .cstring directives place 8-bit characters from a character string into the current section. The expr or string can be one of the following:

  • An expression that the assembler evaluates and treats as an 8-bit signed number.
  • A character string enclosed in double quotes. Each character in a string represents a separate value, and values are stored in consecutive bytes. The entire string must be enclosed in quotes.

The .cstring directive adds a NUL character needed by C; the .string directive does not add a NUL character. In addition, .cstring interprets C escapes (\\ \a \b \f \n \r \t \v \<octal>).

The assembler truncates any values that are greater than eight bits. Operands must fit on a single source statement line.

If you use a label, it points to the location of the first byte that is initialized.

When you use .string and .cstring in a .struct/.endstruct sequence, the directive only defines a member's size; it does not initialize memory. For more information, see the .struct/.endstruct/.tag topic.

Example

In this example, 8-bit values are placed into consecutive words in the current section.

1 0000 0041 Str_Ptr: .string "ABCD" 0001 0042 0002 0043 0003 0044 2 0004 0041 .string 41h, 42h, 43h, 44h 0005 0042 0006 0043 0007 0044 3 0008 0041 .string "Austin", "Houston", "Dallas" 0009 0075 000a 0073 000b 0074 000c 0069 000d 006E 000e 0048 000f 006F 0010 0075 0011 0073 0012 0074 0013 006F 0014 006E 0015 0044 0016 0061 0017 006C 0018 006C 0019 0061 001a 0073 4 001b 0030 .string 36 + 12
.struct/.endstruct/.tag
Declare Structure Type
Syntax

[stag]         .struct           [expr]

[mem0]       element         [expr0]
[mem1]       element         [expr1]
       .                 .                 
      .                 .                 
      .                 .                 

[memn]      .tag stag        [exprn]
       .                 .                 
      .                 .                 
      .                 .                 

[memN]       element         [exprN]

[size]          .endstruct

label            .tag               stag

Description

The .struct directive assigns symbolic offsets to the elements of a data structure definition. This allows you to group similar data elements together and let the assembler calculate the element offset. This is similar to a C structure or a Pascal record. The .struct directive does not allocate memory; it merely creates a symbolic template that can be used repeatedly.

The .endstruct directive terminates the structure definition.

The .tag directive gives structure characteristics to a label, simplifying the symbolic representation and providing the ability to define structures that contain other structures. The .tag directive does not allocate memory. The structure tag (stag) of a .tag directive must have been previously defined.

Following are descriptions of the parameters used with the .struct, .endstruct, and .tag directives:

  • The stag is the structure's tag. Its value is associated with the beginning of the structure. If no stag is present, the assembler puts the structure members in the global symbol table with the value of their absolute offset from the top of the structure. The stag is optional for .struct, but is required for .tag.
  • The expr is an optional expression indicating the beginning offset of the structure. The default starting point for a structure is 0.
  • The memn/N is an optional label for a member of the structure. This label is absolute and equates to the present offset from the beginning of the structure. A label for a structure member cannot be declared global.
  • The element is one of the following descriptors: .byte, .char, .word, .int, .long, .string, .double, .float, .half, .short, .field, and .tag. All of these except .tag are typical directives that initialize memory. Following a .struct directive, these directives describe the structure element's size. They do not allocate memory. The .tag directive is a special case because stag must be used (as in the definition of stag).
  • The exprn/N is an optional expression for the number of elements described. This value defaults to 1. A .string element is considered to be one byte in size, and a .field element is one bit.
  • The size is an optional label for the total size of the structure.

NOTE

Directives that Can Appear in a .struct/.endstruct Sequence

The only directives that can appear in a .struct/.endstruct sequence are element descriptors, conditional assembly directives, and the .align directive, which aligns the member offsets on word boundaries. Empty structures are illegal.

The following examples show various uses of the .struct, .tag, and .endstruct directives.

Example 1
1 REAL_REC .struct ;stag 2 0000 NOM .int ;member1 = 0 3 0002 DEN .int ;member2 = 2 4 0004 REAL_LEN .endstruct ;real_len = 4 5 6 0000 .bss REAL, REAL_LEN 7 8 0000 .text 9 0000 521B ADD.W &REAL + REAL_REC.DEN,R11 0002 0002! 10
Example 2
11 0000 .data 12 CPLX_REC .struct 13 0000 REALI .tag REAL_REC ; stag 14 0004 IMAGI .tag REAL_REC ; member1 = 0 15 0008 CPLX_LEN .endstruct ; cplx_len = 8 16 17 COMPLEX .tag CPLX_REC ; assign structure attrib 18 19 0004 .bss COMPLEX, CPLX_LEN 20 21 0004 .text 22 0004 521B ADD &COMPLEX.REALI,R11 ; access structure 0006 0004!
Example 3
1 0000 .data 2 .struct ; no stag puts mems into 3 ; global symbol table 4 0000 X .int ; create 3 dim templates 5 0002 Y .int 6 0004 Z .int 7 0006 .endstruct
Example 4
1 0000 .data 2 BIT_REC .struct ; stag 3 0000 STREAM .string 64 4 0040 BIT7 .field 7 ; bits1 = 64 5 0040 BIT9 .field 9 ; bits2 = 64 6 0042 BIT10 .field 10 ; bits3 = 65 7 0044 X_INT .int ; x_int = 66 8 0046 BIT_LEN .endstruct ; length = 67 9 10 BITS .tag BIT_REC 11 12 0000 .bss BITS, BIT_REC 13 14 0000 .text 15 0000 521B ADD &BITS.BIT7,R11 ; move into R11 0002 0040! 16 0004 F03B AND #127,R11 ; mask off garbage bits 0006 007F

.symdepend/.weak
Affect Symbol Linkage and Visibility
Syntax

                .symdepend dst symbol name[,src symbol name]

               .weak symbol name

Description

These directives are used to affect symbol linkage and visibility.

The .symdepend directive creates an artificial reference from the section defining src symbol name to the symbol dst symbol name. This prevents the linker from removing the section containing dst symbol name if the section defining src symbol name is included in the output module. If src symbol name is not specified, a reference from the current section is created.

The .weak directive identifies a symbol that is used in the current module but is defined in another module. The linker resolves this symbol's definition at link time. Instead of including a weak symbol in the output file's symbol table by default (as it would for a global symbol), the linker only includes a weak symbol in the output of a "final" link if the symbol is required to resolve an otherwise unresolved reference. See Section 2.6.2 for details about how weak symbols are handled by the linker.

The .weak directive is equivalent to the .ref directive, except that the reference has weak linkage.

A global symbol is defined in the same manner as any other symbol; that is, it appears as a label or is defined by the .set, .equ, .bss, or .usect directive. If a global symbol is defined more than once, the linker issues a multiple-definition error. (The assembler can provide a similar multiple-definition error for local symbols.) The .weak directive always creates a symbol table entry for a symbol, whether the module uses the symbol or not; .symdepend, however, creates an entry only if the module actually uses the symbol.

A symbol can be declared global in either of the following ways:

  • If the symbol is not defined in the current module (which includes macro, copy, and include files), use the .weak directive to tell the assembler that the symbol is defined in an external module. This prevents the assembler from issuing an unresolved reference error. At link time, the linker looks for the symbol's definition in other modules.
  • If the symbol is defined in the current module, use the .symdepend directive to declare that the symbol and its definition can be used externally by other modules. These types of references are resolved at link time.

For example, use the .weak and .set directives in combination as shown in the following example, which defines a weak absolute symbol "ext_addr_sym":

.weak ext_addr_sym ext_addr_sym .set 0x12345678

If you assemble such assembly source and include the resulting object file in the link, the "ext_addr_sym" in this example is available as a weak absolute symbol in a final link. It is a candidate for removal if the symbol is not referenced elsewhere in the application.

.tab
Define Tab Size
Syntax

                .tab size

Description

The .tab directive defines the tab size. Tabs encountered in the source input are translated to size character spaces in the listing. The default tab size is eight spaces.

Example

In this example, each of the lines of code following a .tab statement consists of a single tab character followed by an NOP instruction.

Source file:

; default tab size NOP NOP NOP .tab 4 NOP NOP NOP .tab 16 NOP NOP NOP

Listing file:

1 ; default tab size 2 0000 4303 NOP 3 0002 4303 NOP 4 0004 4303 NOP 5 7 0006 4303 NOP 8 0008 4303 NOP 9 000a 4303 NOP 10 12 000c 4303 NOP 13 000e 4303 NOP 14 0010 4303 NOP
.text
Assemble Into the .text Section
Syntax

                .text

Description

The .text sets .text as the current section. Lines that follow this directive will be assembled into the .text section, which usually contains executable code. The section program counter is set to 0 if nothing has yet been assembled into the .text section. If code has already been assembled into the .text section, the section program counter is restored to its previous value in the section.

The .text section is the default section. Therefore, at the beginning of an assembly, the assembler assembles code into the .text section unless you use a .data or .sect directive to specify a different section.

For more information about sections, see Section 2.

Example

This example assembles code into the .text and .data sections.

1 ******************************************** 2 * Begin assembling into the .data section. * 3 ******************************************** 4 0000 .data 5 0000 000A .byte 0Ah, 0Bh 0001 000B 6 0002 0011 coeff .word 011h,0x22,0x33 0004 0022 0006 0033 7 8 ******************************************** 9 * Begin assembling into the .text section. * 10 ******************************************** 11 0000 .text 12 0000 0041 START: .string "A", "B", "C" 0001 0042 0002 0043 13 0003 0058 $END: .string "X", "Y", "Z" 0004 0059 0005 005A 14 0006 403A MOV.W #0x1234,R10 0008 1234 15 000a 521A ADD.W &coeff+1,R10 000c 0003! 16 17 ******************************************** 18 * Resume assembling into .data section. * 19 ******************************************** 20 0008 .data 21 0008 000C .byte 0Ch, 0Dh 0009 000D 22 23 ******************************************** 24 * Resume assembling into .text section. * 25 ******************************************** 26 000e .text 27 000e 0051 .string "QUIT" 000f 0055 0010 0049 0011 0054
.title
Define Page Title
Syntax

                .title " string "

Description

The .title directive supplies a title that is printed in the heading on each listing page. The source statement itself is not printed, but the line counter is incremented.

The string is a quote-enclosed title of up to 64 characters. If you supply more than 64 characters, the assembler truncates the string and issues a warning:

*** WARNING! line x: W0001: String is too long - will be truncated

The assembler prints the title on the page that follows the directive and on subsequent pages until another .title directive is processed. If you want a title on the first page, the first source statement must contain a .title directive.

Example

In this example, one title is printed on the first page and a different title is printed on succeeding pages.

Source file:

.title "**** Fast Fourier Transforms ****"; . ; . ; . .title "**** Floating-Point Routines ****" .page

Listing file:

MSP430 Assembler PC vx.x.x Day Time Year Tools Copyright (c) 2003-2011 Texas Instruments Incorporated **** Fast Fourier Transforms **** PAGE 1 2 ; . 3 ; . 4 ; . MSP430 Assembler PC vx.x.x Day Time Year Tools Copyright (c) 2003-2011 Texas Instruments Incorporated **** Floating-Point Routines **** PAGE 2 No Errors, No Warnings
.usect
Reserve Uninitialized Space
Syntax

symbol  .usect "section name", size in bytes[, alignment]

Description

The .usect directive reserves space for variables in an uninitialized, named section. This directive is similar to the .bss directive; both simply reserve space for data and that space has no contents. However, .usect defines additional sections that can be placed anywhere in memory, independently of the .bss section.

  • The symbol points to the first location reserved by this invocation of the .usect directive. The symbol corresponds to the name of the variable for which you are reserving space.
  • The section name must be enclosed in double quotes. This parameter names the uninitialized section. A section name can contain a subsection name in the form section name:subsection name.
  • The size in bytes is an expression that defines the number of bytes that are reserved in section name.
  • The alignment is an optional parameter that ensures that the space allocated to the symbol occurs on the specified boundary. The boundary can be set to a power of 2 between 20 and 215, inclusive. If the SPC is already aligned at the specified boundary, it is not incremented.

Initialized sections directives (.text, .data, and .sect) tell the assembler to pause assembling into the current section and begin assembling into another section. A .usect or .bss directive encountered in the current section is simply assembled, and assembly continues in the current section.

Variables that can be located contiguously in memory can be defined in the same specified section; to do so, repeat the .usect directive with the same section name and the subsequent symbol (variable name).

For more information about sections, see Section 2.

Example

This example uses the .usect directive to define two uninitialized, named sections, var1 and var2. The symbol ptr points to the first byte reserved in the var1 section. The symbol array points to the first byte in a block of 100 bytes reserved in var1, and dflag points to the first byte in a block of 50 bytes in var1. The symbol vec points to the first byte reserved in the var2 section.

Figure 5-8 shows how this example reserves space in two uninitialized sections, var1 and var2.

1 ****************************************************** 2 ** Assemble into the .text section. ** 3 ****************************************************** 4 0000 .text 5 0000 403B MOV #0x3,R11 0002 0003 6 7 ****************************************************** 8 ** Reserve 2 bytes in the var1 section. ** 9 ****************************************************** 10 0000 ptr .usect "var1",2 11 12 ****************************************************** 13 ** Reserve 100 bytes in the var1 section. ** 14 ****************************************************** 15 0002 array .usect "var1",100 16 17 0004 503B ADD #37,R11 0006 0025 18 19 ****************************************************** 20 ** Reserve 50 bytes in the var1 section. ** 21 ****************************************************** 22 0066 dflag .usect "var1",50 23 24 0008 503C ADD #dflag-array,R12 000a 0064 25 26 ****************************************************** 27 ** Reserve 100 bytes in the var2 section. ** 28 ****************************************************** 29 0000 vec .usect "var2",100 30 31 000c 5C0B ADD R12,R11 32 33 ****************************************************** 34 ** Declare a .usect symbol to be external. ** 35 ****************************************************** 36 .global array
Figure 5-8 The .usect Directive usect_tdz072.gif
.unasg/.undefine
Turn Off Substitution Symbol
Syntax

                .unasg symbol

                .undefine symbol

Description

The .unasg and .undefine directives remove the definition of a substitution symbol created using .asg or .define. The named symbol will removed from the substitution symbol table from the point of the .undefine or .unasg to the end of the assembly file. See Section 4.8.8 for more information on substitution symbols.

These directives can be used to remove from the assembly environment any C/C++ macros that may cause a problem. See Section 13 for more information about using C/C++ headers in assembly source.

   

.var
Use Substitution Symbols as Local Variables
Syntax

                .var sym1 [, sym2 , ... , symn ]

Description

The .var directive allows you to use substitution symbols as local variables within a macro. With this directive, you can define up to 32 local macro substitution symbols (including parameters) per macro.

The .var directive creates temporary substitution symbols with the initial value of the null string. These symbols are not passed in as parameters, and they are lost after expansion.

See Section 4.8.8 for more information on substitution symbols .See Section 6 for information on macros.

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