SLAU131Y October   2004  – June 2021

 

  1.   Read This First
    1.     About This Manual
    2.     How to Use This Manual
    3.     Notational Conventions
    4.     Related Documentation From Texas Instruments
    5.     Trademarks
  2. 1 Introduction to the Software Development Tools
    1. 1.1 Software Development Tools Overview
    2. 1.2 Tools Descriptions
  3. 2 Introduction to Object Modules
    1. 2.1 Object File Format Specifications
    2. 2.2 Executable Object Files
    3. 2.3 Introduction to Sections
      1. 2.3.1 Special Section Names
    4. 2.4 How the Assembler Handles Sections
      1. 2.4.1 Uninitialized Sections
      2. 2.4.2 Initialized Sections
      3. 2.4.3 User-Named Sections
      4. 2.4.4 Current Section
        1. 2.4.4.1 File y.asm
        2. 2.4.4.2 Disassembly of y.obj
      5. 2.4.5 Section Program Counters
      6. 2.4.6 Subsections
      7. 2.4.7 Using Sections Directives
    5. 2.5 How the Linker Handles Sections
      1. 2.5.1 Combining Input Sections
      2. 2.5.2 Placing Sections
    6. 2.6 Symbols
      1. 2.6.1 Global (External) Symbols
      2. 2.6.2 Local Symbols
      3. 2.6.3 Weak Symbols
      4. 2.6.4 The Symbol Table
    7. 2.7 Symbolic Relocations
      1. 2.7.1 Relocation Entries
    8. 2.8 Loading a Program
  4. 3 Program Loading and Running
    1. 3.1 Loading
      1. 3.1.1 Load and Run Addresses
      2. 3.1.2 Bootstrap Loading
        1. 3.1.2.1 Boot, Load, and Run Addresses
        2. 3.1.2.2 Bootloader
        3. 3.1.2.3 Bootloader Routine
          1. 3.1.2.3.1 Sample Bootloader Routine
    2. 3.2 Entry Point
    3. 3.3 Run-Time Initialization
      1. 3.3.1 The _c_int00 Function
      2. 3.3.2 RAM Model vs. ROM Model
        1. 3.3.2.1 Autoinitializing Variables at Run Time (--rom_model)
        2. 3.3.2.2 Initializing Variables at Load Time (--ram_model)
        3. 3.3.2.3 The --rom_model and --ram_model Linker Options
      3. 3.3.3 About Linker-Generated Copy Tables
        1. 3.3.3.1 BINIT
        2. 3.3.3.2 CINIT
    4. 3.4 Arguments to main
    5. 3.5 Run-Time Relocation
    6. 3.6 Additional Information
  5. 4 Assembler Description
    1. 4.1  Assembler Overview
    2. 4.2  The Assembler's Role in the Software Development Flow
    3. 4.3  Invoking the Assembler
    4. 4.4  Controlling Application Binary Interface
    5. 4.5  Naming Alternate Directories for Assembler Input
      1. 4.5.1 Using the --include_path Assembler Option
      2. 4.5.2 Using the MSP430_A_DIR Environment Variable
    6. 4.6  Source Statement Format
      1. 4.6.1 Label Field
      2. 4.6.2 Mnemonic Field
      3. 4.6.3 Operand Field
        1. 4.6.3.1 Operand Syntaxes for Instructions
      4. 4.6.4 Comment Field
    7. 4.7  Literal Constants
      1. 4.7.1 Integer Literals
        1. 4.7.1.1 Binary Integer Literals
        2. 4.7.1.2 Octal Integer Literals
        3. 4.7.1.3 Decimal Integer Literals
        4. 4.7.1.4 Hexadecimal Integer Literals
        5. 4.7.1.5 Character Literals
      2. 4.7.2 Character String Literals
      3. 4.7.3 Floating-Point Literals
    8. 4.8  Assembler Symbols
      1. 4.8.1 Identifiers
      2. 4.8.2 Labels
      3. 4.8.3 Local Labels
        1. 4.8.3.1 Local Labels of the Form $n
        2.       85
        3.       86
      4. 4.8.4 Symbolic Constants
      5. 4.8.5 Defining Symbolic Constants (--asm_define Option)
      6. 4.8.6 Using Symbolic Constants Defined on Command Line
      7. 4.8.7 Predefined Symbolic Constants
      8. 4.8.8 Registers
      9. 4.8.9 Substitution Symbols
    9. 4.9  Expressions
      1. 4.9.1 Mathematical and Logical Operators
      2. 4.9.2 Relational Operators and Conditional Expressions
      3. 4.9.3 Well-Defined Expressions
    10. 4.10 Built-in Functions and Operators
      1. 4.10.1 Built-In Math and Trigonometric Functions
      2. 4.10.2 MSP430 Built-In ELF Relocation Generating Operators
    11. 4.11 Source Listings
    12. 4.12 Debugging Assembly Source
    13. 4.13 Cross-Reference Listings
  6. 5 Assembler Directives
    1. 5.1  Directives Summary
    2. 5.2  Directives that Define Sections
      1. 5.2.1 Sections Directives
    3. 5.3  Directives that Initialize Values
    4. 5.4  Directives that Perform Alignment and Reserve Space
    5. 5.5  Directives that Format the Output Listings
    6. 5.6  Directives that Reference Other Files
    7. 5.7  Directives that Enable Conditional Assembly
    8. 5.8  Directives that Define Union or Structure Types
    9. 5.9  Directives that Define Enumerated Types
    10. 5.10 Directives that Define Symbols at Assembly Time
    11. 5.11 Miscellaneous Directives
    12. 5.12 Directives Reference
      1.      .align
      2.      .asg/.define/.eval
      3.      .asmfunc/.endasmfunc
      4.      .bits
      5.      .bss
      6.      .byte/.ubyte/.char/.uchar
      7.      .cdecls
      8.      .common
      9.      .copy/.include
      10.      .data
      11.      .double/.float
      12.      .drlist/.drnolist
      13.      .elfsym
      14.      .emsg/.mmsg/.wmsg
      15.      .end
      16.      .fclist/.fcnolist
      17.      .field
      18.      .global/.def/.ref
      19.      .group/.gmember/.endgroup
      20.      .half/.short/.uhalf/.ushort
      21.      .if/.elseif/.else/.endif
      22.      .int/.unint/.word/.uword
      23.      .intvec
      24.      .label
      25.      .length/.width
      26.      .list/.nolist
      27.      .long/.ulong
      28.      .loop/.endloop/.break
      29.      .macro/.endm
      30.      .mlib
      31.      .mlist/.mnolist
      32.      .newblock
      33.      .option
      34.      .page
      35.      .retain / .retainrefs
      36.      .sect
      37.      .set/.equ
      38.      .space/.bes
      39.      .sslist/.ssnolist
      40.      .string/.cstring
      41.      .struct/.endstruct/.tag
      42.      .symdepend
      43.      .tab
      44.      .text
      45.      .title
      46.      .unasg/.undefine
      47.      .usect
      48.      .var
      49.      .weak
  7. 6 Macro Language Description
    1. 6.1  Using Macros
    2. 6.2  Defining Macros
    3. 6.3  Macro Parameters/Substitution Symbols
      1. 6.3.1 Directives That Define Substitution Symbols
      2. 6.3.2 Built-In Substitution Symbol Functions
      3. 6.3.3 Recursive Substitution Symbols
      4. 6.3.4 Forced Substitution
      5. 6.3.5 Accessing Individual Characters of Subscripted Substitution Symbols
      6. 6.3.6 Substitution Symbols as Local Variables in Macros
    4. 6.4  Macro Libraries
    5. 6.5  Using Conditional Assembly in Macros
    6. 6.6  Using Labels in Macros
    7. 6.7  Producing Messages in Macros
    8. 6.8  Using Directives to Format the Output Listing
    9. 6.9  Using Recursive and Nested Macros
    10. 6.10 Macro Directives Summary
  8. 7 Archiver Description
    1. 7.1 Archiver Overview
    2. 7.2 The Archiver's Role in the Software Development Flow
    3. 7.3 Invoking the Archiver
    4. 7.4 Archiver Examples
    5. 7.5 Library Information Archiver Description
      1. 7.5.1 Invoking the Library Information Archiver
      2. 7.5.2 Library Information Archiver Example
      3. 7.5.3 Listing the Contents of an Index Library
      4. 7.5.4 Requirements
  9. 8 Linker Description
    1. 8.1  Linker Overview
    2. 8.2  The Linker's Role in the Software Development Flow
    3. 8.3  Invoking the Linker
    4. 8.4  Linker Options
      1. 8.4.1  Wildcards in File, Section, and Symbol Patterns
      2. 8.4.2  Specifying C/C++ Symbols with Linker Options
      3. 8.4.3  Relocation Capabilities (--absolute_exe and --relocatable Options)
        1. 8.4.3.1 Producing an Absolute Output Module (--absolute_exe option)
        2. 8.4.3.2 Producing a Relocatable Output Module (--relocatable option)
        3. 8.4.3.3 Producing an Executable, Relocatable Output Module (-ar Option)
      4. 8.4.4  Allocate Memory for Use by the Loader to Pass Arguments (--arg_size Option)
      5. 8.4.5  Compression (--cinit_compression and --copy_compression Option)
      6. 8.4.6  Control Linker Diagnostics
      7. 8.4.7  Automatic Library Selection (--disable_auto_rts Option)
      8. 8.4.8  Do Not Remove Unused Sections (--unused_section_elimination Option)
      9. 8.4.9  Linker Command File Preprocessing (--disable_pp, --define and --undefine Options)
      10. 8.4.10 Error Correcting Code Testing (--ecc Options)
      11. 8.4.11 Define an Entry Point (--entry_point Option)
      12. 8.4.12 Set Default Fill Value (--fill_value Option)
      13. 8.4.13 Define Heap Size (--heap_size Option)
      14. 8.4.14 Hiding Symbols
      15. 8.4.15 Alter the Library Search Algorithm (--library, --search_path, and MSP430_C_DIR )
        1. 8.4.15.1 Name an Alternate Library Directory (--search_path Option)
        2. 8.4.15.2 Name an Alternate Library Directory ( MSP430_C_DIR Environment Variable)
        3. 8.4.15.3 Exhaustively Read and Search Libraries (--reread_libs and --priority Options)
      16. 8.4.16 Change Symbol Localization
        1. 8.4.16.1 Make All Global Symbols Static (--make_static Option)
      17. 8.4.17 Create a Map File (--map_file Option)
      18. 8.4.18 Managing Map File Contents (--mapfile_contents Option)
      19. 8.4.19 Disable Name Demangling (--no_demangle)
      20. 8.4.20 Disable Merging of Symbolic Debugging Information (--no_sym_merge Option)
      21. 8.4.21 Strip Symbolic Information (--no_symtable Option)
      22. 8.4.22 Name an Output Module (--output_file Option)
      23. 8.4.23 Prioritizing Function Placement (--preferred_order Option)
      24. 8.4.24 C Language Options (--ram_model and --rom_model Options)
      25. 8.4.25 Retain Discarded Sections (--retain Option)
      26. 8.4.26 Create an Absolute Listing File (--run_abs Option)
      27. 8.4.27 Scan All Libraries for Duplicate Symbol Definitions (--scan_libraries)
      28. 8.4.28 Define Stack Size (--stack_size Option)
      29. 8.4.29 Enforce Strict Compatibility (--strict_compatibility Option)
      30. 8.4.30 Mapping of Symbols (--symbol_map Option)
      31. 8.4.31 Introduce an Unresolved Symbol (--undef_sym Option)
      32. 8.4.32 Replace Multiply Routine With Hardware Multiplier Routine (--use_hw_mpy)
      33. 8.4.33 Display a Message When an Undefined Output Section Is Created (--warn_sections)
      34. 8.4.34 Generate XML Link Information File (--xml_link_info Option)
      35. 8.4.35 Zero Initialization (--zero_init Option)
    5. 8.5  Linker Command Files
      1. 8.5.1  Reserved Names in Linker Command Files
      2. 8.5.2  Constants in Linker Command Files
      3. 8.5.3  Accessing Files and Libraries from a Linker Command File
      4. 8.5.4  The MEMORY Directive
        1. 8.5.4.1 Default Memory Model
        2. 8.5.4.2 MEMORY Directive Syntax
        3. 8.5.4.3 Expressions and Address Operators
      5. 8.5.5  The SECTIONS Directive
        1. 8.5.5.1 SECTIONS Directive Syntax
        2. 8.5.5.2 Section Allocation and Placement
          1. 8.5.5.2.1 Example: Placing Functions in RAM
          2. 8.5.5.2.2 Binding
          3. 8.5.5.2.3 Named Memory
          4. 8.5.5.2.4 Controlling Placement Using The HIGH Location Specifier
            1. 8.5.5.2.4.1 Linker Placement With the HIGH Specifier
            2.         256
            3. 8.5.5.2.4.2 Linker Placement Without HIGH Specifier
          5. 8.5.5.2.5 Alignment and Blocking
          6. 8.5.5.2.6 Alignment With Padding
        3. 8.5.5.3 Specifying Input Sections
          1. 8.5.5.3.1 The Most Common Method of Specifying Section Contents
          2.        262
        4. 8.5.5.4 Using Multi-Level Subsections
        5. 8.5.5.5 Specifying Library or Archive Members as Input to Output Sections
          1. 8.5.5.5.1 Archive Members to Output Sections
          2.        266
        6. 8.5.5.6 Allocation Using Multiple Memory Ranges
        7. 8.5.5.7 Automatic Splitting of Output Sections Among Non-Contiguous Memory Ranges
      6. 8.5.6  Placing a Section at Different Load and Run Addresses
        1. 8.5.6.1 Specifying Load and Run Addresses
        2.       271
        3. 8.5.6.2 Referring to the Load Address by Using the .label Directive
      7. 8.5.7  Using GROUP and UNION Statements
        1. 8.5.7.1 Grouping Output Sections Together
        2. 8.5.7.2 Overlaying Sections With the UNION Statement
        3. 8.5.7.3 Using Memory for Multiple Purposes
        4. 8.5.7.4 Nesting UNIONs and GROUPs
        5. 8.5.7.5 Checking the Consistency of Allocators
        6. 8.5.7.6 Naming UNIONs and GROUPs
      8. 8.5.8  Special Section Types (DSECT, COPY, NOLOAD, NOINIT, and VECT_INIT)
      9. 8.5.9  Configuring Error Correcting Code (ECC) with the Linker
        1. 8.5.9.1 Using the ECC Specifier in the Memory Map
        2. 8.5.9.2 Using the ECC Directive
        3. 8.5.9.3 Using the VFILL Specifier in the Memory Map
      10. 8.5.10 Assigning Symbols at Link Time
        1. 8.5.10.1 Syntax of Assignment Statements
        2. 8.5.10.2 Assigning the SPC to a Symbol
        3. 8.5.10.3 Assignment Expressions
        4. 8.5.10.4 Symbols Automatically Defined by the Linker
        5. 8.5.10.5 Assigning Exact Start, End, and Size Values of a Section to a Symbol
        6. 8.5.10.6 Why the Dot Operator Does Not Always Work
        7. 8.5.10.7 Address and Dimension Operators
          1. 8.5.10.7.1 Input Items
          2. 8.5.10.7.2 Output Section
          3. 8.5.10.7.3 GROUPs
          4. 8.5.10.7.4 UNIONs
        8. 8.5.10.8 LAST Operator
      11. 8.5.11 Creating and Filling Holes
        1. 8.5.11.1 Initialized and Uninitialized Sections
        2. 8.5.11.2 Creating Holes
        3. 8.5.11.3 Filling Holes
        4. 8.5.11.4 Explicit Initialization of Uninitialized Sections
    6. 8.6  Linker Symbols
      1. 8.6.1 Using Linker Symbols in C/C++ Applications
      2. 8.6.2 Declaring Weak Symbols
      3. 8.6.3 Resolving Symbols with Object Libraries
    7. 8.7  Default Placement Algorithm
      1. 8.7.1 How the Allocation Algorithm Creates Output Sections
      2. 8.7.2 Reducing Memory Fragmentation
    8. 8.8  Using Linker-Generated Copy Tables
      1. 8.8.1 Using Copy Tables for Boot Loading
      2. 8.8.2 Using Built-in Link Operators in Copy Tables
      3. 8.8.3 Overlay Management Example
      4. 8.8.4 Generating Copy Tables With the table() Operator
        1. 8.8.4.1 The table() Operator
        2. 8.8.4.2 Boot-Time Copy Tables
        3. 8.8.4.3 Using the table() Operator to Manage Object Components
        4. 8.8.4.4 Linker-Generated Copy Table Sections and Symbols
        5. 8.8.4.5 Splitting Object Components and Overlay Management
      5. 8.8.5 Compression
        1. 8.8.5.1 Compressed Copy Table Format
        2. 8.8.5.2 Compressed Section Representation in the Object File
        3. 8.8.5.3 Compressed Data Layout
        4. 8.8.5.4 Run-Time Decompression
        5. 8.8.5.5 Compression Algorithms
        6.       326
      6. 8.8.6 Copy Table Contents
      7. 8.8.7 General Purpose Copy Routine
    9. 8.9  Linker-Generated CRC Tables and CRC Over Memory Ranges
      1. 8.9.1 Using the crc_table() Operator in the SECTIONS Directive
        1. 8.9.1.1 Restrictions when using the crc_table() Operator
        2. 8.9.1.2 Examples
          1. 8.9.1.2.1 Using crc_table() Operator to Compute the CRC Value for .text Data
          2.        334
          3. 8.9.1.2.2 Specifying an Algorithm in the crc_table() Operator
          4.        336
          5. 8.9.1.2.3 Using a Single Table for Multiple Sections
          6.        338
          7. 8.9.1.2.4 Applying the crc_table() Operator to a GROUP or UNION
          8.        340
        3. 8.9.1.3 Interface When Using the crc_table() Operator
          1. 8.9.1.3.1 The CRC Table Header, crc_tbl.h
      2. 8.9.2 Using the crc() Operator in the MEMORY Directive
        1. 8.9.2.1 Restrictions when Using the crc() Operator
        2. 8.9.2.2 Using the VFILL Specifier within a GROUP
        3. 8.9.2.3 Generate CRC for Most or All of Flash Memory
        4. 8.9.2.4 Computing CRCs for Both Memory Ranges and Sections
        5. 8.9.2.5 Example Specifying Memory Range CRCs
        6. 8.9.2.6 Interface When Using the crc() Operator
      3. 8.9.3 Verification of Linker Computed CRC on MSP430
    10. 8.10 Partial (Incremental) Linking
    11. 8.11 Linking C/C++ Code
      1. 8.11.1 Run-Time Initialization
      2. 8.11.2 Object Libraries and Run-Time Support
      3. 8.11.3 Setting the Size of the Stack and Heap Sections
      4. 8.11.4 Initializing and AutoInitialzing Variables at Run Time
      5. 8.11.5 Initialization of Cinit and Watchdog Timer Hold
    12. 8.12 Linker Example
  10. 9 Absolute Lister Description
    1. 9.1 Producing an Absolute Listing
    2. 9.2 Invoking the Absolute Lister
    3. 9.3 Absolute Lister Example
  11. 10Cross-Reference Lister Description
    1. 10.1 Producing a Cross-Reference Listing
    2. 10.2 Invoking the Cross-Reference Lister
    3. 10.3 Cross-Reference Listing Example
  12. 11Object File Utilities
    1. 11.1 Invoking the Object File Display Utility
    2. 11.2 Invoking the Disassembler
    3. 11.3 Invoking the Name Utility
    4. 11.4 Invoking the Strip Utility
  13. 12Hex Conversion Utility Description
    1. 12.1  The Hex Conversion Utility's Role in the Software Development Flow
    2. 12.2  Invoking the Hex Conversion Utility
      1. 12.2.1 Invoking the Hex Conversion Utility From the Command Line
      2. 12.2.2 Invoking the Hex Conversion Utility With a Command File
    3. 12.3  Understanding Memory Widths
      1. 12.3.1 Target Width
      2. 12.3.2 Specifying the Memory Width
      3. 12.3.3 Partitioning Data Into Output Files
      4. 12.3.4 Specifying Word Order for Output Words
    4. 12.4  The ROMS Directive
      1. 12.4.1 When to Use the ROMS Directive
      2. 12.4.2 An Example of the ROMS Directive
    5. 12.5  The SECTIONS Directive
    6. 12.6  The Load Image Format (--load_image Option)
      1. 12.6.1 Load Image Section Formation
      2. 12.6.2 Load Image Characteristics
    7. 12.7  Excluding a Specified Section
    8. 12.8  Assigning Output Filenames
    9. 12.9  Image Mode and the --fill Option
      1. 12.9.1 Generating a Memory Image
      2. 12.9.2 Specifying a Fill Value
      3. 12.9.3 Steps to Follow in Using Image Mode
    10. 12.10 Array Output Format
    11. 12.11 Controlling the ROM Device Address
    12. 12.12 Control Hex Conversion Utility Diagnostics
    13. 12.13 Description of the Object Formats
      1. 12.13.1 ASCII-Hex Object Format (--ascii Option)
      2. 12.13.2 Intel MCS-86 Object Format (--intel Option)
      3. 12.13.3 Motorola Exorciser Object Format (--motorola Option)
      4. 12.13.4 Extended Tektronix Object Format (--tektronix Option)
      5. 12.13.5 Texas Instruments SDSMAC (TI-Tagged) Object Format (--ti_tagged Option)
      6. 12.13.6 TI-TXT Hex Format (--ti_txt Option)
        1. 12.13.6.1 TI-TXT Object Format
  14. 13Sharing C/C++ Header Files With Assembly Source
    1. 13.1 Overview of the .cdecls Directive
    2. 13.2 Notes on C/C++ Conversions
      1. 13.2.1  Comments
      2. 13.2.2  Conditional Compilation (#if/#else/#ifdef/etc.)
      3. 13.2.3  Pragmas
      4. 13.2.4  The #error and #warning Directives
      5. 13.2.5  Predefined symbol __ASM_HEADER__
      6. 13.2.6  Usage Within C/C++ asm( ) Statements
      7. 13.2.7  The #include Directive
      8. 13.2.8  Conversion of #define Macros
      9. 13.2.9  The #undef Directive
      10. 13.2.10 Enumerations
      11. 13.2.11 C Strings
      12. 13.2.12 C/C++ Built-In Functions
      13. 13.2.13 Structures and Unions
      14. 13.2.14 Function/Variable Prototypes
      15. 13.2.15 C Constant Suffixes
      16. 13.2.16 Basic C/C++ Types
    3. 13.3 Notes on C++ Specific Conversions
      1. 13.3.1 Name Mangling
      2. 13.3.2 Derived Classes
      3. 13.3.3 Templates
      4. 13.3.4 Virtual Functions
    4. 13.4 Special Assembler Support
      1. 13.4.1 Enumerations (.enum/.emember/.endenum)
      2. 13.4.2 The .define Directive
      3. 13.4.3 The .undefine/.unasg Directives
      4. 13.4.4 The $defined( ) Built-In Function
      5. 13.4.5 The $sizeof Built-In Function
      6. 13.4.6 Structure/Union Alignment and $alignof( )
      7. 13.4.7 The .cstring Directive
  15.   A Symbolic Debugging Directives
    1.     A.1 DWARF Debugging Format
    2.     A.2 Debug Directive Syntax
  16.   B XML Link Information File Description
    1.     B.1 XML Information File Element Types
    2.     B.2 Document Elements
      1.      B.2.1 Header Elements
      2.      B.2.2 Input File List
      3.      B.2.3 Object Component List
      4.      B.2.4 Logical Group List
      5.      B.2.5 Placement Map
      6.      B.2.6 Far Call Trampoline List
      7.      B.2.7 Symbol Table
  17.   C CRC Reference Implementation
    1.     C.1 Reference CRC Calculation Routine
      1.      C.1.1 Reference Implementation of a CRC Calculation Function: example_c1.c
    2.     C.2 Linker-Generated Copy Tables and CRC Tables
      1.      C.2.1 Main Routine for Example Application: main.c
      2.      C.2.2 Checking CRC Values: check_crc.c
      3.      C.2.3 Task1 Routine: task1.c
      4.      C.2.4 Task2 Routine: task2.c
      5.      C.2.5 Task3 Routine: task3.c
      6.      C.2.6 Command File Addition
  18.   D Glossary
    1.     D.1 Terminology
  19.   E Revision History
  20.   464
  21.   465

.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