Reference Guide

Chapter 2 37
Program Structure
Macro Processing
Macro Processing
A macro is a user-defined word that is replaced by a sequence of
instructions. Including a macro in a source program causes the sequence
of instructions to be inserted into the program wherever the macro
appears.
A user may define a word as a macro by using the .MACRO directive.
Detailed information about macro arguments, placement and
redefinition of macros, nested macro definitions, and nested macro calls
is in “Assembler Directives and Pseudo-Operations” on page 53.
Defining New Instructions With Macros
If you are testing new CPUs or coprocessors, you may need to use
opcodes that are unknown to the Assembler. A variant of a macro
definition may be used to create a mnemonic for the instruction. After
being defined, the new mnemonic instruction can be invoked as easily as
a standard instruction.
Opcodes, subopcodes, completers, and operands are encoded into the
instruction word in a bit-intensive manner because all PA-RISC
instructions are one word, or 32-bits, in length.
To write a macro, you must specify explicitly which bit fields are to
contain constants and which are to contain macro arguments. The macro
processor has no built-in knowledge of instruction formats. Defining new
instructions through macros is only possible because a convenient way to
delimit bit fields has been provided. It is up to the programmer to choose
the correct bit field.
Bit positions within the 32-bit word are numbered from zero to 31, from
left to right. A bit range is indicated by the starting bit position followed
by the ending bit position. The two bit positions are separated by two
periods and enclosed in braces. The bit field beginning at bit position 6
and ending at bit position 10 is represented as:
{6..10}
If the bit field being assigned from is bigger than the bit field being
assigned to, then a warning is issued and the assigned-from bit field is
truncated on the left. When no bit field is specified for the assigned-from