ARM VERSION 1.2

Writing ARM and Thumb Assembly Language

Setting up a C-type structure

There are two stages to using structures in C:

1. Declaring the fields that the structure contains.

2. Generating the structure in memory and using it.

For example, the following

typedef

statement defines a point stru cture that contains

three

float

fields named

and

, but it does not allocate any memory. The second

statement allocates th ree structures of type

Point

in memory, named

origin

oldloc

, and

newloc

typedef struct Point

{

float x,y,z;

} Point;

Point origin,oldloc,newloc;

The following assembly language code is equivalent to the

typedef

statement above:

PointBase RN r11

MAP 0,PointBase

Point_x FIELD 4

Point_y FIELD 4

Point_z FIELD 4

The following assembly language code allocates space in memory. This is equivalent to

the last line of C code:

origin SPACE 12

oldloc SPACE 12

newloc SPACE 12

You must load the base address of the data structure into the base register before you

can use the labels defined in the map. For example:

LDR PointBase,=origin

MOV r0,#0

STR r0,Point_x

MOV r0,#2

STR r0,Point_y

MOV r0,#3

STR r0,Point_z

is equivalent to the C code:

origin.x = 0;

origin.y = 2;

origin.z = 3;