Texas Instruments TMS320C54x, User Manual

Page: 130 / 469

Initialize Field
.field
4-47 Assembler Directives
Syntax
.field value [, size in bits]
Description The .field directive can initialize multiple-bit fields within a single word 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. If the value is relocatable, size must be 16.
-
The size is an optional parameter; it specifies a number from 1 to 32, which
is the number of bits in the field. If you do not specify a size, the assembler
assumes that the size is 16 bits. If you specify a size of 16 or more, the field
will start on a word boundary. If you specify a value that cannot fit into
size
bits, the assembler truncates the value and issues an error message. For
example, .field 3,1 causes the assembler to truncate the value
3 to 1; the
assembler also prints the message:
***warning – value truncated.
Successive .field directives pack values into the specified number of bits start-
ing at the current word. Fields are packed starting at the most significant part
of the word, moving toward the least significant part as more fields are added.
If the assembler encounters a field size that does not fit into the current word,
it writes out the word, increments the SPC, and begins packing fields into the
next word. You can use the .align directive with an operand of 1 to force the
next .field directive to begin packing into a new word.
If you use a label, it points to the word 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 about .struct/
.endstruct, see Section 4.9,
Assembly-Time Symbol Directives, on page 4-21.