Texas Instruments TMS320C54x, User Manual

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Symbols
3-20
3.8.5 Substitution Symbols
Symbols can be assigned a string value (variable). This enables you to alias
character strings by equating them to symbolic names. Symbols that
represent character strings are called substitution symbols. When the
assembler encounters a substitution symbol, its string value is substituted for
the symbol name. Unlike symbolic constants, substitution symbols can be
redefined.
A string can be assigned to a substitution symbol anywhere within a program;
for example:
.asg ”errct”, AR2 ;register 2
.asg ”*+”, INC ;indirect auto-increment
.asg ”*–”, DEC ;indirect auto-decrement
When you are using macros, substitution symbols are important because
macro parameters are actually substitution symbols that are assigned a macro
argument. The following code shows how substitution symbols are used in
macros:
add2 .macro ADDRA,ADDRB ;add2 macro definition
LD ADDRA, A
ADD ADDRB, A
STL A, ADDRB
.endm
; add2 invocation
add2 LOC1, LOC2 ;add ”LOC1” argument to a
;second argument ”LOC2”.
; instructions for expanded macro:
;
LD LOC1, A
; ADD LOC2, A
; STL A, LOC2
For more information about macros, see Chapter 5,
Macro Language.