Assembly Files

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Assembly Files
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Sample program

• .text
• This is an assembler DIRECTIVE, it tells the
  compiler that this section contains assembly
  instructions
• .global main
• This must be present to tell the assembler to
  expect this to be called from external sources.
  It is customary to put it at the beginning of the
  program.
• main
• This is where your program goes.
• init
• Here go the steps to initialise memory locations,
  registers etc. used in the program. Your code
  needs to be sure everything is set correctly to
  begin execution.
• j exit
• This should be the last executable step in your
  program. It returns control of the REX board to
  the monitor program.
• .data
• Comprised of your data items, lookup tables, and
  the like. Initialised when the code is loaded.

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Assembly Language Programs

• Assembly Language Programs consist of
• Assembly Instructions
• Labels
• Directives
• Comments

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Labels

• Labels refer to a location in memory.
• Can associate a label with a WRAMP instruction or
  memory allocated for storage
• e.g.
• All WRAMP programs must start with a main label
• Labels are used so the programmer does not have
  to keep track of memory addresses.

.global main main add 3, 4, 5
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Comments

• WRAMP comments are on a line basis
• Any text on a line after a is treated as
  comments
• e.g.

add 3, 4, 5 This is a comment
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Assembler Directives

• Declarations are examples of Assembler Directives
• Assembler Directives tell a program (assembler or
  compiler) how to create a program and not how to
  execute it
• Directives also exist to allow data and
  instruction to be put in separate areas of Memory

WRAMP
C
.bss int1 .word int2 .word char1 .word
int int1, int2 char char1
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Section Directives

• .text Indicates that this section contains
  assembly instructions
• .data This section contains data, i.e. allocates
  memory space and initialises it to some value.
• .bss This section allocates memory but does not
  initialise it. This allows bigger chunks to be
  allocated than in .data. (bss block started by
  symbol).

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Space Allocation Directives

• .word n Allocates one word of memory and
  initialises it to the value n. Can be used in
  .bss without the n.
• .ascii str Allocates enough space for a string
  and initialises it.
• .asciiz strAllocates and initialises enough
  space for a string plus a null terminating
  character (0x0)
• .space n Allocates n words but does not
  initialise the space in the .bss section

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.global Directive

• .global declares symbols to be accessible by
  outside the current file.
• .global main defined the entry point into the
  program.