[rmac] / docs / rmac.rst

RMAC
----
68000 Macro Assembler
=====================
Reference Manual
================
version 1.4.2
=============


*NOTE: Every effort has been made to ensure the accuracy and robustness of this
manual and the associated software. However, because Reboot is constantly improving
and updating its computer software, it is unable to guarantee
the accuracy of printed or duplicated material after the date of publication and
disclaims liability for changes, errors or omissions.*


*Copyright © 2011-2015, Reboot*

*All rights reserved.*

*Reboot Document number F00000K-001 Rev. A.*

Contents
========

.. contents::

Introduction
============

Introduction
''''''''''''
This document describes RMAC, a fast macro assembler for the 68000. RMAC currently
runs on the any POSIX compatible platform and the Atari ST. It was initially written
at Atari Corporation by programmers who needed a high performance assembler
for their work. Then, more than 20 years later, because there was still a need for
such an assembler and what was available wasn't up to expectations, Subqmod
and eventually Reboot continued work on the freely released source, adding Jaguar extensions
and fixing bugs.

RMAC is intended to be used by programmers who write mostly in assembly language.
It was not originally a back-end to a C compiler, therefore it
has creature comfort that are usually neglected in such back-end assemblers. It
supports include files, macros, symbols with limited scope, some limited control
structures, and other features. RMAC is also blindingly fast, another feature
often sadly and obviously missing in today's assemblers.[1]_

RMAC is not entirely compatible with the AS68 assembler provided with
the original Atari ST Developer's Kit, but most changes are minor and a few minutes
with an editor should allow you to assemble your current source files. If you are an
AS68 user, before you leap into the unknown please read the section on Notes for
AS68 Users.

This manual was typeset with TEX and the Computer Modern fonts, and it
was printed on the Atari SLM-804 laser printer with a MEGA ST. Except for 200
lines of assembly language, the assembler is written entirely in C.

.. [1] It processes 30,000 lines a minute on a lightly loaded VAX 11/780; maybe 40,000 on a 520-ST with an SH-204 hard disk. Yet it could be sped up even more with some effort and without resorting to assembly language; C doesn't have to be slow!

`Getting Started`_
''''''''''''''''''

 =>Write protect your distribution disk and make a backup of it now. Put the
   original disk in a safe place.

* The distribution disk contains a file called README that you should read.
  This file contains important nays about the contents of the distribution disk
  and summarizes the most recent changes to the tools.

* Hard disk users can simply copy the executable files to their work or binary
  directories. People with floppy disks can copy the executables to ramdisks,
  install the assembler with the -q option, or even work right off of the floppies.

* You will need an editor that can produce "normal" format text files. Micro
  Emacs will work well, as will most other commercial program editors, but not
  most word processors (such as First Word or Microsoft Write).

* You will probably want to examine or get a listing of the file "ATARI.S". It
  contains lots of definitions for the Atari ST, including BIOS variables, most
  BIOS, XBIOS and GEMDOS traps, and line-A equates. We (or you) could
  split the file up into pieces (a file for line-A equates, a file for hardware and
  BIOS variables and so on), but RMAC is so fast that it doesn't matter
  much.

* Read the rest of the manual, especially the first two chapters on The Command Line and Using RMAC.
  Also, `Notes for migrating from other 68000 assemblers`_ will save a lot of time and frustration in the long run.
  The distribution disk contains example
  programs that you can look at, assemble and modify.

`The Command Line`_
'''''''''''''''''''

The assembler is called "**rmac**" or "**rmac.prg**". The command line takes the form:

                          **mac** [*switches*] [*files* ...]

A command line consists of any number of switches followed by the names of files
to assemble. A switch is specified with a dash (**-**) followed immediately by a key
character. Key characters are not case-sensitive, so "**-d**" is the same as "**-D**". Some
switches accept (or require) arguments to immediately follow the key character,
with no spaces in between.

Switch order is important. Command lines are processed from left to right in
one pass, and switches usually take effect when they are encountered. In general it
is best to specify all switches before the names of any input files.

If the command line is entirely empty then RMAC prints a copyright message
and enters an "interactive" mode, prompting for successive command lines
with a star (\*). An empty command line will exit (See the examples in the chapter
on `Using RMAC`_). After each assembly in interactive mode, the assembler
will print a summary of the amount of memory used, the amount of memory left,
the number of lines processed, and the number of seconds the assembly took.

Input files are assumed to have the extension "**.s**"; if a filename has no extension
(i.e. no dot) then "**.s**" will be appended to it. More than one source filename may be
specified: the files are assembled into one object file, as if they were concatenated.

RMAC normally produces object code in "**file.o**" if "**file.s**" is the first
input filename. If the first input file is a special character device, the output name
is noname.o. The **-o** switch (see below) can be used change the output file name.


===================  ===========
Switch               Description
===================  ===========
-dname\ *[=value]*   Define symbol, with optional value.
-e\ *[file[.err]]*   Direct error messages to the specified file.
-fa                  TODO: add me
-fb                  BSD COFF
-i\ *path*           Set include-file directory search path.
-l\ *[file[prn]]*    Construct and direct assembly listing to the specified file.
-o\ *file[.o]*       Direct object code output to the specified file.
-p                   Produce an executable (**.prg**) output file.
-ps                  Produce an executable (**.prg**) output file with symbols.
-q                   Make RMAC resident in memory (Atari ST only).
-r *size*            automatically pad the size of each
                     segment in the output file until the size is an integral multiple of the
                     specified boundary. Size is a letter that specifies the desired boundary.
                                         
                      `-rw Word (2 bytes, default alignment)`

                      `-rl Long (4 bytes)`

                      `-rp Phrase (8 bytes)`
                      
                      `-rd Double Phrase (16 bytes)`
                      
                      `-rq Quad Phrase (32 bytes)`
-s                   Warn about unoptimized long branches.
-u                   Assume that all undefined symbols are external.
-v                   Verbose mode (print running dialogue).
-yn                  Set listing page size to n lines.
-6                   "Back end" mode for Alcyon C68.
file\ *[s]*          Assemble the specified file.
===================  ===========

The switches are described below. A summary of all the switches is given in
the table.

**-d**
 The **-d** switch permits symbols to be defined on the command line. The name
 of the symbol to be defined immediately follows the switch (no spaces). The
 symbol name may optionally be followed by an equals sign (=) and a decimal
 number. If no value is specified the symbol's value is zero. The symbol at-
 tributes are "defined, not referenced, and absolute". This switch is most useful
 for enabling conditionally-assembled debugging code on the command line; for
 example:

  ::

      -dDEBUG -dLoopCount=999 -dDebugLevel=55

**-e**
 The -e switch causes RMAC to send error messages to a file, instead of the
 console. If a filename immediately follows the switch character, error messages
 are written to the specified file. If no filename is specified, a file is created with
 the default extension "**.err**" and with the root name taken from the first input
 file name (e.g. error messages are written to "**file.err**" if "**file**" or "**file.s**" is
 the first input file name). If no errors are encountered, then no error listing
 file is created. Beware! If an assembly produces no errors, any error file from
 a previous assembly is not removed.

**-i**
 The **-i** switch allows automatic directory searching for include files. A list of
 semi-colon seperated directory search paths may be mentioned immediately
 following the switch (with no spaces anywhere). For example:

  ::

         -im:;c:include;c:include\sys

 will cause the assembler to search the current directory of device **M**, and the
 directories include and include\sys on drive **C**. If *-i* is not specified, and the
 enviroment variable "**MACPATH**" exists, its value is used in the same manner.
 For example, users of the Mark Williams shell could put the following line in
 their profile script to achieve the same result as the **-i** example above:

  ::

      setenv MACPATH="m:;c:include;c:include\sys"
**-l**
 The -l switch causes RMAC to generate an assembly listing file. If a file-
 name immediately follows the switch character, the listing is written to the
 specified file. If no filename is specified, then a listing file is created with the
 default extension "**.prn**" and with the root name taken from the first input file
 name (e.g. the listing is written to "**file.prn**" if "**file**" or "**file.s**" is the first
 input file name).
**-o**
 The -o switch causes RMAC to write object code on the specified file. No
 default extension is applied to the filename. For historical reasons the filename
 can also be seperated from the switch with a space (e.g. "**-o file**").

**-p**

**-ps**
 The **-p** and **-ps** switches cause RMAC to produce an Atari ST executable
 file with the default extension of "**.prg**". If there are any external references
 at the end of the assembly, an error message is emitted and no executable file
 is generated. The **-p** switch does not write symbols to the executable file. The
 **-ps** switch includes symbols (Alcyon format) in the executable file.
**-q**
  The **-q** switch is aimed primarily at users of floppy-disk-only systems. It causes
  RMAC to install itself in memory, like a RAMdisk. Then the program
  **m.prg** (which is very short - less than a sector) can be used instead of
  **mac.prg**, which can take ten or twelve seconds to load. (**NOTE** not available
  for now, might be re-implemented in the future).
**-s**
  The **-s** switch causes RMAC to generate a list of unoptimized forward
  branches as warning messages. This is used to point out branches that could
  have been short (e.g. "bra" could be "bra.s").
**-u**
  The **-u** switch takes effect at the end of the assembly. It forces all referenced
  and undefined symbols to be global, exactly as if they had been made global
  with a **.extern** or **.globl** directive. This can be used if you have a lot of
  external symbols, and you don't feel like declaring them all external.
**-v**
  The **-v** switch turns on a "verbose" mode in which RMAC prints out (for
  example) the names of the files it is currently processing. Verbose mode is
  automatically entered when RMAC prompts for input with a star.
**-y**
  The **-y** switch, followed immediately by a decimal number (with no intervening
  space), sets the number of lines in a page. RMAC will produce *N* lines
  before emitting a form-feed. If *N* is missing or less than 10 an error message is
  generated.

`Using RMAC`_
===============

Let's assemble and link some example programs. These programs are included
on the distribution disk in the "**EXAMPLES**" directory - you should copy them to
your work area before continuing. In the following examples we adopt the conven-
tions that the shell prompt is a percent sign (%) and that your input (the stuff you
type) is presented in **bold face**.

If you have been reading carefully, you know that RMAC can generate
an executable file without linking. This is useful for making small, stand alone
programs that don't require externals or library routines. For example, the following
two commands:

 ::

      % mac examples
      % aln -s example.s

could be replaced by the single command:

 ::

      % rmac -ps example.s

since you don't need the linker for stand-alone object files.

Successive source files named in the command line are are concatenated, as in
this example, which assembles three files into a single executable, as if they were
one big file:

 ::

      % rmac -p bugs shift images

Of course you can get the same effect by using the **.include** directive, but sometimes
it is convenient to do the concatenation from the command line.

   Here we have an unbelievably complex command line:

    ::

      % rmac -lzorf -y95 -o tmp -ehack -Ddebug=123 -ps example

This produces a listing on the file called "**zorf.prn**" with 95 lines per page, writes
the executable code (with symbols) to a file called "**tmp.prg**", writes an error listing
to the file "**hack.err**", specifies an include-file path that includes the current
directory on the drive "**M:**," defines the symbol "**debug**" to have the value 123, and
assembles the file "**example.s**". (Take a deep breath - you got all that?)

One last thing. If there are any assembly errors, RMAC will terminate
with an exit code of 1. If the assembly succeeds (no errors, although there may be
warnings) the exit code will be 0. This is primarily for use with "make" utilities.

`Interactive Mode`_
'''''''''''''''''''
If you invoke RMAC with an empty command line it will print a copyright
message and prompt you for more commands with a star (*****). This is useful if you
are used to working directly from the desktop, or if you want to assemble several files
in succession without having to reload the assembler from disk for each assembly.

In interactive mode, the assembler is also in verbose mode (just as if you had
specified **-v** on each command line):

 ::

     %. rmac

     MADMAC Atari Macro Assembler
     Copyright 1987 Atari Corporation
     Beta version 0.12 Jun 1987 lmd

     * -ps example
     [Including: example.s]
     [Including: atari.s]
     [Leaving: atari.s]
     [Leaving; example. a]
     [Writing executable tile: example.prg
     36K used, 3868K left, 850 lines, 2.0 seconds


You can see that the assembler gave a "blow-by-blow" account of the files it processed,
as well as a summary of the assembly's memory usage, the number of lines
processed (including macro and repeat-block expansion), and how long the assembly
took

The assembler prompts for another command with the star. At this point you
can either type a new command line for the assembler to process, or you can exit
by typing control-C or an empty line.

Things You Should Be Aware Of
'''''''''''''''''''''''''''''
RMAC is a one pass assembler. This means that it gets all of its work done by
reading each source file exactly once and then "back-patching" to fix up forward
references. This one-pass nature is usually transparent to the programmer, with
the following important exceptions:

 o in listings, the object code for forward references is not shown. Instead, lower-
   case "xx"s are displayed for each undefined byte, as in the following example:

    ::

     60xx   1: bra.s.2  ;forward branch
     xxxxxxxx  dc.l .2  ;forward reference
     60FE  .2: bra.s.2  ;backward reference

 o Forward branches (including **BSR**\s) are never optimized to their short forms.
   To get a short forward branch it is necessary to explicitly use the ".s" suffix in
   the source code.
 o Error messages may appear at the end of the assembly, referring to earlier source
   lines that contained undefined symbols.
 o All object code generated must fit in memory. Running out of memory is a
   fatal error that you must deal with by splitting up your source files, re-sizing
   or eliminating memory-using programs such as ramdisks and desk accessories,
   or buying more RAM.

Forward Branches
''''''''''''''''
RMAC does not optimize forward branches for you, but it will tell you about
them if you use the -s (short branch) option:

 ::

     % mac -s example.s
     "example.s", line 20: warning: unoptimized short branch

With the -e option you can redirect the error output to a file, and determine by
hand (or editor macros) which forward branches are safe to explicitly declare short.

`Notes for migrating from other 68000 assemblers`_
''''''''''''''''''''''''''''''''''''''''''''''''''
RMAC is not entirely compatible with the other popular assemblers
like Devpac or vasm. This section
outlines the major differences. In practice, we have found that very few changes are
necessary to make other assemblers' source code assemble.

o A semicolon (;) must be used to introduce a comment, except that a star (*)
  may be used in the first column. AS68 treated anything following the operand
  field, preceeded by whitespace, as a comment. (RMAC treats a star that
  is not in column 1 as a multiplication operator).

o Labels require colons (even labels that begin in column 1).

o Conditional assembly directives are called **if**, **else** and **endif**. Devpac and vasm called these
  **ifne**, **ifeq** (etc.), and **endc**.
o The tilde (~) character is an operator, and back-quote (`) is an illegal character.
  AS68 permitted the tilde and back-quote characters in symbols.
o There are no equivalents to org or section directives.
  The **.xdef** and **.xref** directives are not implemented,
  but **.globl** makes these unnecessary anyway.

  o The location counter cannot be manipulated with a statement of the form:

  ::

                                * = expression

o The **ds** directive is not permitted in the text or data segments;
  an error message is issued. Use **dcb** instead to reserve large blocks of
  initialized storage.
o Back-slashes in strings are "electric" characters that are used to escape C-like
  character codes. Watch out for GEMDOS path names in ASCII constants -
  you will have to convert them to double-backslashes.
o Expression evaluation is done left-to-right without operator precedence. Use parentheses to
  force the expression evaluation as you wish.

o Mark your segments across files. Branching to a code segment that could be identified as BSS will cause a "Error: cannot initialize non-storage (BSS) section"
o rs.b/rs.w/rs.l/rscount/rsreset can be simulated in rmac using abs. For example the following source:

  ::

   rsreset
   label1: rs.w 1
   label2: rs.w 10
   label3: rs.l 5
   label4: rs.b 2
   
   size_so_far equ rscount

  can be converted to:

  ::

   abs
   label1: ds.w 1
   label2: ds.w 10
   label3: ds.l 5
   label4: ds.b 2
   
   size_so_far equ ^^abscount

o A rare case: if your macro contains something like:

  ::

   macro test
   move.l #$\1,d0
   endm

   test 10

  then by the assembler's design this will fail as the parameters are automatically converted to hex. Changing the code like his works:

  ::

   macro test
   move.l #\1,d0
   endm

   test $10

`Text File Format`_
'''''''''''''''''''
For those using editors other than the "Emacs" style ones (Micro-Emacs, Mince,
etc.) this section documents the source file format that RMAC expects.

 o Files must contain characters with ASCII values less than 128; it is not per-
   missable to have characters with their high bits set unless those characters are
   contained in strings (i.e. between single or double quotes) or in comments.

 o Lines of text are terminated with carriage-return/line-feed, linefeed alone, or
   carriage-return alone.

 o The file is assumed to end with the last terminated line. If there is text beyond
   the last line terminator (e.g. control-Z) it is ignored.

`Source Format`_
================

`Statements`_
'''''''''''''
A statement may contain up to four fields which are identified by order of ap-
pearance and terminating characters. The general form of an assembler statement
is:

  ::

      label: operator operand(s)  ; comment

The label and comment fields are optional. An operand field may not appear
without an operator field. Operands are seperated with commas. Blank lines are
legal. If the first character on a line is an asterisk (*) or semicolon (;) then the
entire line is a comment. A semicolon anywhere on the line (except in a string)
begins a comment field which extends to the end of the line.

The label, if it appears, must be terminated with a single or double colon. If
it is terminated with a double colon it is automatically declared global. It is illegal
to declare a confined symbol global (see: `Symbols and Scope`_).

`Equates`_
''''''''''
A statement may also take one of these special forms:

      *symbol* **equ** *expression*

      *symbol* **=** *expression*

      *symbol* **--** *expression*

      *symbol* **set** *expression*

      *symbol* **reg** *register list*

The first two forms are identical; they equate the symbol to the value of an
expression, which must be defined (no forward references). The third form, double-
equals (==), is just like an equate except that it also makes the symbol global. (As
with labels, it is illegal to make a confined equate global.) The fourth form allows
a symbol to be set to a value any number of times, like a variable. The last form
equates the symbol to a 16-bit register mask specified by a register list. It is possible
to equate confined symbols (see: `Symbols and Scope`_). For example:

  ::

      cr    equ    13          carriage-return
      if    =      10          line-feed
      DEBUG ==     1           global debug flag
      count set    0           variable
      count set    count + 1   increment variable
      .rags reg    d3-d7/a3-a6 register list
      .cr          13          confined equate

`Symbols and Scope`_
''''''''''''''''''''
Symbols may start with an uppercase or lowercase letter (A-Z a-z), an underscore
(**_**), a question mark (**?**) or a period (**.**). Each remaining character may be an
upper or lowercase letter, a digit (**0-9**), an underscore, a dollar sign (**$**), or a question
mark. (Periods can only begin a symbol, they cannot appear as a symbol
continuation character). Symbols are terminated with a character that is not a
symbol continuation character (e.g. a period or comma, whitespace, etc.). Case is
significant for user-defined symbols, but not for 68000 mnemonics, assembler direc-
tives and register names. Symbols are limited to 100 characters. When symbols
are written to the object file they are silently truncated to eight (or sixteen) char-
acters (depending on the object file format) with no check for (or warnings about)
collisions.

   For example, all of the following symbols are legal and unique:

     ::

      reallyLougSymbolliame .reallyLongConfinadSymbollame
      al0 ret move dc frog aae a9 ????
      .al .ret .move .dc .frog .a9 .9 ????
      .0  .00  .000 .1  .11. .111 . ._
      _frog ?zippo? sys$syetem atari Atari ATARI aTaRi

while all of the following symbols are illegal:

     ::

      12days dc.10   dc.z   'quote  .right.here
      @work hi.there $money$ ~tilde


Symbols beginning with a period (**.**) are *confined*; their scope is between two
normal (unconfined) labels. Confined symbols may be labels or equates. It is illegal
to make a confined symbol global (with the ".globl" directive, a double colon, or a
double equals). Only unconfined labels delimit a confined symbol's scope; equates
(of any kind) do not count. For example, all symbols are unique and have unique
values in the following:

   ::

      zero:: subq.w $1,d1
             bmi.s .ret
      .loop: clr.w (a0)+
             dbra  d0,.loop
      .ret:  rta
      FF::   subq.w #1,d1
             bmi.s .99
      .loop: move.w -1,(a0)+
             dbra  d0,.loop
      .99:   its

Confined symbols are useful since the programmer has to be much less inventive
about finding small, unique names that also have meaning.

It is legal to define symbols that have the same names as processor mnemonics
(such as "**move**" or "**rts**") or assembler directives (such as "**.even**"). Indeed, one
should be careful to avoid typographical errors, such as this classic (in 6502 mode):

    ::

             .6502
      .org   =     $8000


which equates a confined symbol to a hexadecimal value, rather than setting the
location counter, which the .org directive does (without the equals sign).

`Keywords`_
'''''''''''
The following names, in all combinations of uppercase and lowercase, are keywords
and may not be used as symbols (e.g. labels, equates, or the names of macros):

   ::

      equ set reg
      sr ccr pc sp ssp usp
      dO di d2 d3 d4 d5 d6 d7
      a0 al a2 a3 a4 a5 a6 aT
      r0 ri r2 r3 r4 r5 r6 r7
      r8 r9 r10 1'11 r12 rl3 ri4 ri5

`Constants`_
''''''''''''
Numbers may be decimal, hexadecimal, octal, binary or concatenated ASCII. The
default radix is decimal, and it may not be changed. Decimal numbers are specified
with a string of digits (**0-9**). Hexadecimal numbers are specified with a leading
dollar sign (**$**) followed by a string of digits and uppercase or lowercase letters (**A-F
a-f**). Octal numbers are specified with a leading at-sign (**@**) followed by a string
of octal digits (**0-7**). Binary numbers are specified with a leading percent sign
(**%**) followed by a string of binary digits (**0-1**). Concatenated ASCII constants are
specified by enclosing from one to four characters in single or double quotes. For
example:

    ::

      1234   *decimal*
      $1234  *hexadecimal*
      @777   *octal*
      %10111 *binary*
      "z"    *ASCII*
      'frog' *ASCII*

Negative numbers Are specified with a unary minus (**-**). For example:

    ::

      -5678  -@334 -$4e71
      -%11011 -'z' -"WIND"

`Strings`_
''''''''''
Strings are contained between double (") or single ( ') quote marks. Strings may
contain non-printable characters by specifying "backslash" escapes, similar to the
ones used in the C programming language. RMAC will generate a warning if a
backslash is followed by a character not appearing below:

    ::

      \\    $5c    backslash
      \n    $0a    line-feed (newline)
      \b    $08    backspace
      \t    $09    tab
      \r    $0c1   carriage-return
      \f    $0c    form-feed
      \e    $1b    escape
      \'    $27    single-quote
      \"    $22    double-quote

It is possible for strings (but not symbols) to contain characters with their high
bits set (i.e. character codes 128...255).

You should be aware that backslash characters are popular in GEMDOS path
names, and that you may have to escape backslash characters in your existing source
code. For example, to get the file "'c:\auto\ahdi.s'" you would specify the string
"`c:\\auto\\ahdi.s`".

`Register Lists`_
'''''''''''''''''
Register lists are special forms used with the **movem** mnemonic and the **.reg**
directive. They are 16-bit values, with bits 0 through 15 corresponding to registers
**D0** through **A7**. A register list consists of a series of register names or register
ranges seperated by slashes. A register range consists of two register names, Rm
and Rn,m<n, seperated by a dash. For example:

     ::

       register list           value
       -------------           -----
       40-d7/a0-a7             $FFFF
       d2-d7/a0/a3-a6          $39FC
       d0/d1/a0-a3/d7/a6-a7    $CF83
       d0                      $0001
       r0-r16                  $FFFF

Register lists and register equates may be used in conjunction with the movem
mnemonic, as in this example:

     ::

       temps   reg     d0-d2/a0-a2     ; temp registers
       keeps   reg     d3-d7/d3-a6     ; registers to preserve
       allregs reg     d0-d7/a0-a7     ; all registers
               movem.l #temps, -(sp)   ; these two lines ...
               aovea.l dO -d2/a0 -a2, -(sp) ; are identical
               movea.l #keeps, -(sp)   ; save "keep" registers
               noven.1 (sp)+,#keeps    ; restore "keep" registers


`Expressions`_
==============
`Order of Evaluation`_
''''''''''''''''''''''
All values are computed with 32-bit 2's complement arithmetic. For boolean operations
(such as if or **assert**) zero is considered false, and non-zero is considered
true.

     **Expressions are evaluated strictly left-to-right, with no
     regard for operator precedence.**

Thus the expression "1+2*3" evaluates to 9, not 7. However, precedence may be
forced with parenthesis (**()**) or square-brackets (**[]**).

`Types`_
'''''''''
Expressions belong to one of three classes: undefined, absolute or relocatable. An
expression is undefined if it involves an undefined symbol (e.g. an undeclared sym-
bol, or a forward reference). An expression is absolute if its value will not change
when the program is relocated (for instance, the number 0, all labels declared in
an abs section, and all Atari ST hardware register locations are absolute values).
An expression is relocatable if it involves exactly one symbol that is contained in a
text, data or BSS section.

Only absolute values may be used with operators other than addition (+) or
subtraction (-). It is illegal, for instance, to multiply or divide by a relocatable or
undefined value. Subtracting a relocatable value from another relocatable value in
the same section results in an absolute value (the distance between them, positive
or negative). Adding (or subtracting) an absolute value to or from a relocatable
value yeilds a relocatable value (an offset from the relocatable address).

It is important to realize that relocatable values belong to the sections they
are defined in (e.g. text, data or BSS), and it is not permissible to mix and match
sections. For example, in this code:

    ::

     linel:  dc.l   line2, linel+8
     line2:  dc.l   linel, line2-8
     line3:  dc.l   line2-linel, 8
     error:  dc.l   linel+line2, line2 >> 1, line3/4

Line 1 deposits two longwords that point to line 2. Line 2 deposits two longwords
that point to line 1. Line 3 deposits two longwords that have the absolute value
eight. The fourth line will result in an assembly error, since the expressions (re-
spectively) attempt to add two relocatable values, shift a relocatable value right by
one, and divide a relocatable value by four.

The pseudo-symbol "*****" (star) has the value that the current section's location
counter had at the beginning of the current source line. For example, these two
statements deposit three pointers to the label "**bar**":

    ::

     too:    dc.l   *+4
     bar:    dc.l   *, *

Similarly, the pseudo-symbol "**$**" has the value that the current section's location
counter has, and it is kept up to date as the assembler deposits information
"across" a line of source code. For example, these two statements deposit four
pointers to the label "zip":

        ::

          zip:      dc.l      $+8, $+4
          zop:      dc.l      $, $-4

`Unary Operators`_
''''''''''''''''''

================================    ========================================
Operator                            Description
================================    ========================================
**-**                               Unary minus (2's complement).
**!**                               Logical (boolean) NOT.
**~**                               Tilde: bitwise not (l's complement).
**^^defined** *symbol*              True if symbol has a value.
**^^referenced** *symbol*           True if symbol has been referenced.
**^^streq** *stringl*,*string2*     True if the strings are equal.
**^^macdef** *macroName*            True if the macro is defined.
**^^abscount**                      Returns the size of current .abs section
================================    ========================================

   o The boolean operators generate the value 1 if the expression is true, and 0 if
     it is not.

   o A symbol is referenced if it is involved in an expression. A symbol may have
     any combination of attributes: undefined and unreferenced, defined and unref-
     erenced (i.e. declared but never used), undefined and referenced (in the case
     of a forward or external reference), or defined and referenced.



`Binary Operators`_
'''''''''''''''''''

===========  ==============================================
Operator     Description
===========  ==============================================
\ + - * /    The usual arithmetic operators.
%            Modulo.
& | ^        Bit-wise **AND**, **OR** and **Exclusive-OR**.
<< >>        Bit-wise shift left and shift right.
< <=  >=  >  Boolean magnitude comparisons.
=            Boolean equality.
<>  !=       Boolean inequality.
===========  ==============================================

   o All binary operators have the same precedence: expressions are evaluated
     strictly left to right.

   o Division or modulo by zero yields an assembly error

   o The "<>" and "!=" operators are synonyms.

   o Note that the modulo operator (%) is also used to introduce binary constants
     (see: `Constants`_). A percent sign should be followed by at least one space if
     it is meant to be a modulo operator, and is followed by a '0' or '1'.

`Special Forms`_
''''''''''''''''

============    =========================================
Special Form    Description
============    =========================================
**^^date**      The current system date (Gemdos format).
**^^time**      The current system time (Gemdos format).
============    =========================================

   o The "**^^date**" special form expands to the current system date, in Gemdos
     format. The format is a 16-bit word with bits 0 ...4 indicating the day of the
     month (1...31), bits 5...8 indicating the month (1...12), and bits 9...15
     indicating the year since 1980, in the range 0...119.

   o The "**^^time**" special form expands to the current system time, in Gemdos
     format. The format is a 16-bit word with bits 0...4 indicating the current
     second divided by 2, bits 5...10 indicating the current minute 0...59. and
     bits 11...15 indicating the current hour 0...23.

`Example Expressions`_
''''''''''''''''''''''

       ::

        line address contents      source code
        ---- ------- --------      -------------------------------
           1 00000000 4480         lab1:  neg.l  d0
           2 00000002 427900000000 lab2:  clr.w  lab1
           3         =00000064     equ1   =      100
           4         =00000096     equ2   =      equ1 + 50
           5 00000008 00000064            dc.l   lab1 + equ1
           6 0000000C 7FFFFFE6            dc.l   (equl + ~equ2) >> 1
           7 00000010 0001                dc.w   ^^defined equl
           8 00000012 0000                dc.w   ^^referenced lab2
           9 00000014 00000002            dc.l   lab2
          10 00000018 0001                dc.w   ^^referenced lab2
          11 0000001A 0001                dc.w   lab1 = (lab2 - 6)

Lines 1 through four here are used to set up the rest of the example. Line 5 deposits
a relocatable pointer to the location 100 bytes beyond the label "**lab1**". Line 6 is
a nonsensical expression that uses the and right-shift operators. Line 7 deposits
a word of 1 because the symbol "**equ1**" is defined (in line 3).

Line 8 deposits a word of 0 because the symbol "**lab2**", defined in line 2, has
not been referenced. But the expression in line 9 references the symbol "**lab2**", so
line 10 (which is a copy of line-8) deposits a word of 1. Finally, line 11 deposits a
word of 1 because the Boolean equality operator evaluates to true.

The operators "**^^defined**" and "**^^referenced**" are particularly useful in
conditional assembly. For instance, it is possible to automatically include debugging
code if the debugging code is referenced, as in:

      ::

               lea    string,a0            ; AO -> message
               jsr    debug                ; print a message
               its                         ; and return
        string: dc.b  "Help me, Spock!",0  ; (the message)
                    .
                    .
                    .
               .iif ^^defined debug, .include "debug.s"

The **jsr** statement references the symbol debug. Near the end of the source file, the
"**.iif**' statement includes the file "**debug.s**" if the symbol debug was referenced.

In production code, presumably all references to the debug symbol will be removed,
and the debug source file will not be included. (We could have as easily made the
symbol **debug** external, instead of including another source file).


`Directives`_
=============

Assembler directives may be any mix of upper- or lowercase. The leading periods
are optional, though they are shown here and their use is encouraged. Directives
may be preceeded by a label; the label is defined before the directive is executed.
Some directives accept size suffixes (**.b**, **.s**, **.w** or **.1**); the default is word (**.w**) if no
size is specified. The **.s** suffix is identical to **.b**. Directives relating to the 6502 are
described in the chapter on `6502 Support`_.



**.even**
   If the location counter for the current section is odd, make it even by adding
   one to it. In text and data sections a zero byte is deposited if necessary.
**.long**
   Align the program counter to the next integral long boundary (4 bytes).
   Note that GPU/DSP code sections are not contained in their own
   segments and are actually part of the TEXT or DATA segments.
   Therefore, to align GPU/DSP code, align the current section before and
   after the GPU/DSP code.
**.phrase**
   Align the program counter to the next integral phrase boundary (8 bytes).
   Note that GPU/DSP code sections are not contained in their own
   segments and are actually part of the TEXT or DATA segments.
   Therefore, to align GPU/DSP code, align the current section before and
   after the GPU/DSP code.
**.dphrase**
   Align the program counter to the next integral double phrase boundary (16
   bytes). Note that GPU/DSP code sections are not contained in their own
   segments and are actually part of the TEXT or DATA segments.
   Therefore, to align GPU/DSP code, align the current section before and
   after the GPU/DSP code.
**.qphrase**
   Align the program counter to the next integral quad phrase boundary (32
   bytes). Note that GPU/DSP code sections are not contained in their own
   segments and are actually part of the TEXT or DATA segments.
   Therefore, to align GPU/DSP code, align the current section before and
   after the GPU/DSP code.
**.assert** *expression* [,\ *expression*...]
   Assert that the conditions are true (non-zero). If any of the comma-seperated
   expressions evaluates to zero an assembler warning is issued. For example:

          ::

           .assert *-start = $76
           .assert stacksize >= $400

**.bss**

**.data**

**.text**
   Switch to the BSS, data or text segments. Instructions and data may not
   be assembled into the BSS-segment, but symbols may be defined and storage
   may be reserved with the **.ds** directive. Each assembly starts out in the text
   segment.
**.abs** [*location*]
   Start an absolute section, beginning with the specified location (or zero, if
   no location is specified). An absolute section is much like BSS, except that
   locations declared with .ds are based absolute. This directive is useful for
   declaring structures or hardware locations.
   For example, the following equates:

          ::

           VPLANES = 0
           VWRAP   = 2
           CONTRL  = 4
           INTIN   = 8
           PTSIN   = 12

   could be as easily defined as:

          ::

                   .abs
           VPLANES: ds.w    1
           VWRAP:  ds.w     1
           CONTRL: ds.l     1
           INTIE:  ds.l     1
           PTSIN:  ds.l     1

**.comm** *symbol*, *expression*
   Specifies a label and the size of a common region. The label is made global,
   thus confined symbols cannot be made common. The linker groups all common
   regions of the same name; the largest size determines the real size of the
   common region when the file is linked.
**.ccdef** *expression*
   Allows you to define names for the condition codes used by the JUMP
   and JR instructions for GPU and DSP code. For example:

    ::
   
     Always .ccdef 0
     . . .
          jump Always,(r3) ; ‘Always’ is actually 0

**.ccundef** *regname*
   Undefines a register name (regname) previously assigned using the
   .CCDEF directive. This is only implemented in GPU and DSP code
   sections.     
**.dc.i** *expression*
   This directive generates long data values and is similar to the DC.L
   directive, except the high and low words are swapped. This is provided
   for use with the GPU/DSP MOVEI instruction.
**.dc**\ [.\ *size*] *expression* [, *expression*...]
   Deposit initialized storage in the current section. If the specified size is word
   or long, the assembler will execute a .even before depositing data. If the size
   is .b, then strings that are not part of arithmetic expressions are deposited
   byte-by-byte. If no size is specified, the default is .w. This directive cannot be
   used in the BSS section.
**.dcb**\ [.\ *size*] *expression1*, *expression2*
   Generate an initialized block of *expression1* bytes, words or longwords of the
   value *expression2*. If the specified size is word or long, the assembler will
   execute .even before generating data. If no size is specified, the default is **.w**.
   This directive cannot be used in the BSS section.
**.ds**\ [.\ *size*] *expression*
   Reserve space in the current segment for the appropriate number of bytes,
   words or longwords. If no size is specified, the default size is .w. If the size
   is word or long, the assembler will execute .even before reserving space. This
   directive can only be used in the BSS or ABS sections (in text or data, use
   .dcb to reserve large chunks of initialized storage.)
**.dsp**
   Switch to Jaguar DSP assembly mode. This directive must be used
   within the TEXT or DATA segments.
**.init**\ [.\ *size*] [#\ *expression*,]\ *expression*\ [.\ *size*] [,...]
   Generalized initialization directive. The size specified on the directive becomes
   the default size for the rest of the line. (The "default" default size is **.w**.) A
   comma-seperated list of expressions follows the directive; an expression may be
   followed by a size to override the default size. An expression may be preceeded
   by a sharp sign, an expression and a comma, which specifies a repeat count to
   be applied to the next expression. For example:

      ::

       .init.l -1, 0.w, #16,'z'.b, #3,0, 11.b

   will deposit a longword of -1, a word of zero, sixteen bytes of lower-case 'z',
   three longwords of zero, and a byte of 11.

   No auto-alignment is performed within the line, but a **.even** is done once
   (before the first value is deposited) if the default size is word or long.
**.cargs** [#\ *expression*,] *symbol*\ [.\ *size*] [, *symbol*\ [.\ *size*].. .]
   Compute stack offsets to C (and other language) arguments. Each symbol is
   assigned an absolute value (like equ) which starts at expression and increases
   by the size of each symbol, for each symbol. If the expression is not supplied,
   the default starting value is 4. For example:

    ::

     .cargs #8, .fileliams.1, .openMode, .butPointer.l

   could be used to declare offsets from A6 to a pointer to a filename, a word
   containing an open mode, and a pointer to a buffer. (Note that the symbols
   used here are confined). Another example, a C-style "string-length" function,
   could be written as:

        ::

         _strlen:: .cargs .string     ; declare arg
               move.l .string(sp),a0  ; a0 -> string
               moveq  #-1,d0          ; initial size = -1
         .1:   addq.1 #1,d0           ; bump size
               tst.b  (a0)+           ; at end of string?
               bne   .1               ; (no -- try again)
               rts                    ; return string length

**.end**
   End the assembly. In an include file, end the include file and resume assembling
   the superior file. This statement is not required, nor are warning messages
   generated if it is missing at the end of a file. This directive may be used inside
   conditional assembly, macros or **.rept** blocks.
**.equr** *expression*
   Allows you to name a register. This is only implemented for GPU/DSP
   code sections. For example:

    ::

     Clipw .equr r19
     . . .
          add ClipW,r0 ; ClipW actually is r19

**.if** *expression*

**.else**

**.endif**

   Start a block of conditional assembly. If the expression is true (non-zero) then
   assemble the statements between the .if and the matching **.endif** or **.else**.
   If the expression is false, ignore the statements unless a matching .else is
   encountered. Conditional assembly may be nested to any depth.

   It is possible to exit a conditional assembly block early from within an include
   file (with **end**) or a macro (with **endm**).

**.iif** *expression*, *statement*

   Immediate version of **.if**. If the expression is true (non-zero) then the state-
   ment, which may be an instruction, a directive or a macro, is executed. If
   the expression is false, the statement is ignored. No **.endif** is required. For
   example:

        ::

         .iif age < 21, canDrink = 0
         .iif weight > 500, dangerFlag = 1
         .iif !(^^defined DEBUG), .include dbsrc

**.macro** *name* [*formal*, *formal*,...]

**.endm**

**.exitm**
   Define a macro called name with the specified formal arguments. The macro
   definition is terminated with a **.endm** statement. A macro may be exited early
   with the .exitm directive. See the chapter on `Macros`_ for more information.

**.undefmac** *macroName* [, *macroName*...]
   Remove the macro-definition for the specified macro names. If reference is
   made to a macro that is not defined, no error message is printed and the name
   is ignored.

**.rept** *expression*

**.endr**
   The statements between the **.rept** and **.endr** directives will be repeated *expression*
   times. If the expression is zero or negative, no statements will be
   assembled. No label may appear on a line containing either of these directives.

**.globl** *symbol* [, *symbol*...]

**.extern** *symbol* [, *symbol*...]
   Each symbol is made global. None of the symbols may be confined symbols
   (those starting with a period). If the symbol is defined in the assembly, the
   symbol is exported in the object file. If the symbol is undefined at the end
   of the assembly, and it was referenced (i.e. used in an expression), then the
   symbol value is imported as an external reference that must be resolved by the
   linker. The **.extern** directive is merely a synonym for **.globl**.

**.include** "*file*"
   Include a file. If the filename is not enclosed in quotes, then a default extension
   of "**.s**" is applied to it. If the filename is quoted, then the name is not changed
   in any way.

   Note: If the filename is not a valid symbol, then the assembler will generate an
             error message. You should enclose filenames such as "**atari.s**" in quotes,
             because such names are not symbols.

   If the include file cannot be found in the current directory, then the directory
   search path, as specified by -i on the commandline, or' by the 'MACPATH'
   enviroment string, is traversed.

**.eject**
   Issue a page eject in the listing file.

**.title** "*string*"

**.subttl** [-] "*string*"
   Set the title or subtitle on the listing page. The title should be specified on
   the the first line of the source program in order to take effect on the first page.
   The second and subsequent uses of **.title** will cause page ejects. The second
   and subsequent uses of .subttl will cause page ejects unless the subtitle string
   is preceeded by a dash (-).

**.list**

**.nlist**
   Enable or disable source code listing. These directives increment and decrement
   an internal counter, so they may be appropriately nested. They have no effect
   if the **-l** switch is not specified on the commandline.

**.goto** *label*
   This directive provides unstructured flow of control within a macro definition.
   It will transfer control to the line of the macro containing the specified goto
   label. A goto label is a symbol preceeded by a colon that appears in the first
   column of a source line within a macro definition:

                 :  *label*

   where the label itself can be any valid symbol name, followed immediately by
   whitespace and a valid source line (or end of line). The colon **must** appear in
   the first column.

   The goto-label is removed from the source line prior to macro expansion -
   to all intents and purposes the label is invisible except to the .goto directive
   Macro expansion does not take place within the label.

   For example, here is a silly way to count from 1 to 10 without using **.rept**:

              ::

                               .macro Count
                 count         set     1
                 :loop         dc.w    count
                 count         set     count + 1
                               iif count <= 10, goto loop
                               .endm

**.gpu**
   Switch to Jaguar GPU assembly mode. This directive must be used
   within the TEXT or DATA segments.
**.gpumain**
   No. Just... no. Don't ask about it. Ever.
**.prgflags** *value*
   Sets ST executable .PRG field *PRGFLAGS* to *value*. *PRGFLAGS* is a bit field defined as follows:

============ ======  =======
Definition   Bit(s)  Meaning
============ ======  =======
PF_FASTLOAD  0       If set, clear only the BSS area on program load, otherwise clear the entire heap. 
PF_TTRAMLOAD 1       If set, the program may be loaded into alternative RAM, otherwise it must be loaded into standard RAM. 
PF_TTRAMMEM  2       If set, the program's Malloc() requests may be satisfied from alternative RAM, otherwise they must be satisfied from standard RAM. 
--           3       Currently unused.
See left.    4 & 5   If these bits are set to 0 (PF_PRIVATE), the processes' entire memory space will be considered private (when memory protection is enabled).If these bits are set to 1 (PF_GLOBAL), the processes' entire memory space will be readable and writable by any process (i.e. global).If these bits are set to 2 (PF_SUPERVISOR), the processes' entire memory space will only be readable and writable by itself and any other process in supervisor mode.If these bits are set to 3 (PF_READABLE), the processes' entire memory space will be readable by any application but only writable by itself. 
--           6-15    Currently unused.
============ ======  =======

**.regequ** *expression*
   Essentially the same as **.EQUR.** Included for compatibility with the GASM
   assembler.
**.regundef**
   Essentially the same as **.EQURUNDEF.** Included for compatibility with
   the GASM assembler.


`68000 Mnemonics`_
==================

`Mnemonics`_
''''''''''''
All of the standard Motorola 68000 mnemonics and addressing modes are supported;
you should refer to **The Motorola M68000 Programmer's Reference Manual**
for a description of the instruction set and the allowable addressing modes for each
instruction. With one major exception (forward branches) the assembler performs
all the reasonable optimizations of instructions to their short or address register
forms.

Register names may be in upper or lower case. The alternate forms ``R0`` through
``R15`` may be used to specify ``D0`` through ``A7``. All register names are keywords, and
may not be used as labels or symbols. None of the 68010 or 68020 register names
are keywords (but they may become keywords in the future).

`Addressing Modes`_
'''''''''''''''''''

=====================================    ===========================================
Assembler Syntax                         Description
=====================================    ===========================================
*Dn*                                     Data register direct
*An*                                     Address register direct
(*An*)                                   Address register indirect
(*An*)+                                  Address register indirect postincrement
-(*An*)                                  Address register indirect predecrement
*disp*\ (*An*)                           Address register indirect with displacement
*bdisp*\ (*An*, *Xi*\ [.\ *size*])       Address register indirect indexed
*abs*.w                                  Absolute short
*abs*                                    Absolute (long or short)
*abs*.l                                  Forced absolute long
*disp*\ (PC)                             Program counter with displacement
*bdisp*\ (PC, *Xi*\ )                    Program counter indexed
#\ *imm*                                 Immediate
=====================================    ===========================================

`Branches`_
'''''''''''
Since RMAC is a one pass assembler, forward branches cannot be automatically
optimized to their short form. Instead, unsized forward branches are assumed to
be long. Backward branches are always optimized to the short form if possible.

A table that lists "extra" branch mnemonics (common synonyms for the Motorola
defined mnemonics) appears below.

`Linker Constraints`_
'''''''''''''''''''''
It is not possible to make an external reference that will fix up a byte. For example:

                   ::

                     extern frog
                    move.l frog(pc,d0),d1

is illegal (and generates an assembly error) when frog is external, because the
displacement occupies a byte field in the 68000 offset word, which the object file
cannot represent.

`Branch Synonyms`_
''''''''''''''''''
============== ========
Alternate name Becomes:
============== ========
bhs            bcc
blo            bcs
bse, bs        beq
bns            bne
dblo           dbcs
dbse           dbeq
dbra           dbf
dbhs           dbhi
dbns           dbne
============== ========

`Optimizations and Translations`_
'''''''''''''''''''''''''''''''''
The assembler provides "creature comforts" when it processes 68000 mnemonics:

 o **CLR.x An** will really generate **SUB.x An,An**.

 o **ADD**, **SUB** and **CMP** with an address register will really generate **ADDA**,
 **SUBA** and **CMPA**.

 o The **ADD**, **AND**, **CMP**, **EOR**, **OR** and **SUB** mnemonics with immediate
 first operands will generate the "I" forms of their instructions (**ADDI**, etc.) if
 the second operand is not register direct.

 o All shift instructions with no count value assume a count of one.

 o **MOVE.L** is optimized to **MOVEQ** if the immediate operand is defined and
 in the range -128...127. However, **ADD** and **SUB** are never translated to
 their quick forms; **ADDQ** and **SUBQ** must be explicit.

 o In GPU/DSP code sections, you can use JUMP (Rx) in place of JUMP T, (Rx) and JR
  (Rx) in place of JR T,(Rx).
 o RMAC tests all GPU/DSP restrictions and corrects them wherever possible (such as
  inserting a NOP instruction when needed).
 o The “(Rx+N)” addressing mode for GPU/DSP instructions is optimized to “(Rx)”
  when “N” is zero.

`Macros`_
=========
`Macro declaration`_
''''''''''''''''''''
A macro definition is a series of statements of the form:
                              ::

                                 .macro name [ formal-arg, ...]
                                    .
                                    .
                                    .
                                 statements making up the macro body
                                    .
                                    .
                                    .
                                 .endm

The name of the macro may be any valid symbol that is not also a 68000 instruction
or an assembler directive. (The name may begin with a period - macros cannot
be made confined the way labels or equated symbols can be). The formal argument
list is optional; it is specified with a comma-seperated list of valid symbol names.
Note that there is no comma between the name of the macro and the name of the
first formal argument.

A macro body begins on the line after the **.macro** directive. All instructions
and directives, except other macro definitions, are legal inside the body.

The macro ends with the **.endm** statement. If a label appears on the line with
this directive, the label is ignored and a warning is generated.

`Parameter Substitution`_
'''''''''''''''''''''''''
Within the body, formal parameters may be expanded with the special forms:
              ::

                \name
                \{name}

The second form (enclosed in braces) can be used in situations where the characters
following the formal parameter name are valid symbol continuation characters. This
is usually used to force concatentation, as in:

               ::

                \{frog}star
                \(godzilla}vs\{reagan}

The formal parameter name is terminated with a character that is not valid in
a symbol (e.g. whitespace or puncuation); optionally, the name may be enclosed in
curly-braces. The names must be symbols appearing on the formal argument list,
or a single decimal digit (``\1`` corresponds to the first argument, ``\2`` to the second,
``\9`` to the ninth, and ``\0`` to the tenth). It is possible for a macro to have more than
ten formal arguments, but arguments 11 and on must be referenced by name, not
by number.

        Other special forms are:

============ ================================================
Special Form Description
============ ================================================
``\\``       a single "\",
``\~``       a unique label of the form "Mn"
``\#``       the number of arguments actually specified
``\!``       the "dot-size" specified on the macro invocation
``\?name``   conditional expansion
``\?{name}`` conditional expansion
============ ================================================

The last two forms are identical: if the argument is specified and is non-empty, the
form expands to a "1", otherwise (if the argument is missing or empty) the form
expands to a "0".

The form "``\!``" expands to the "dot-size" that was specified when the macro
was invoked. This can be used to write macros that behave differently depending
on the size suffix they are given, as in this macro which provides a synonym for the
"``dc``" directive:

              ::

               .macro deposit value
               dc\!   \value
               .endm
               deposit.b 1          ; byte of 1
               deposit.w 2          ; word of 2
               deposit.l 3          ; longvord of 3
               deposit   4          ; word of 4 (no explicit size)

`Macro Invocation`_
'''''''''''''''''''
A previously-defined macro is called when its name appears in the operation field of
a statement. Arguments may be specified following the macro name; each argument
is seperated by a comma. Arguments may be empty. Arguments are stored for
substitution in the macro body in the following manner:

  o Numbers are converted to hexadecimal.

  o All spaces outside strings are removed.

  o Keywords (such as register names, dot sizes and "^^" operators) are converted
    to lowercase.

  o Strings are enclosed in double-quote marks (").

For example, a hypothetical call to the macro "``mymacro``", of the form:
       ``mymacro A0, , 'Zorch' / 32, "^^DEFINED foo, , , tick tock``

will result in the translations:

========      ================= =================================================
Argument      Expansion         Comment
========      ================= =================================================
``\1``        ``a0``            "``A0``" converted to lower-case
``\2``                          empty
``\3``        ``"Zorch"/$20``   "``Zorch``" in double-quotes, 32 in hexadecimal
``\4``        ``^^defined foo`` "``^^DEFINED``" converted to lower-case
``\5``                          empty
``\6``                          empty
``\7``        ``ticktock``      spaces removed (note concatenation)
========      ================= =================================================

The **.exitm** directive will cause an immediate exit from a macro body. Thus
the macro definition:

         ::

          .macro foo source
              .iif !\?source, .exitm ; exit if source is empty
              move \source,d0        ; otherwise, deposit source
          .endm

will not generate the move instruction if the argument **"source"** is missing from
the macro invocation.

The **.end**, **.endif** and **.exitm** directives all pop-out of their include levels
appropriately. That is, if a macro performs a **.include** to include a source file, an
executed **.exitm** directive within the include-file will pop out of both the include-file
and the macro.

Macros may be recursive or mutually recursive to any level, subject only to
the availability of memory. When writing recursive macros, take care in the coding
of the termination condition(s). A macro that repeatedly calls itself will cause the
assembler to exhaust its memory and abort the assembly.


`Example Macros`_
'''''''''''''''''
The Gemdos macro is used to make file system calls. It has two parameters, a
function number and the number of bytes to clean off the stack after the call. The
macro pushes the function number onto the stack and does the trap to the file
system. After the trap returns, conditional assembly is used to choose an addq or
an **add.w** to remove the arguments that were pushed.

     ::

       .macro Gemdos trpno, clean
          move.w  #\trpno,-(sp)  ; push trap number
          trap    #1             ; do GEMDOS trap
          .if \clean <= 8        ;
          addq    #\clean,sp     ; clean-up up to 8 bytes
          .else                  ;
          add.w   #\clean,sp     ; clean-up more than 8 bytes
          .endif                 ;
       .endm

The Fopen macro is supplied two arguments; the address of a filename, and
the open mode. Note that plain move instructions are used, and that the caller of
the macro must supply an appropriate addressing mode (e.g. immediate) for each
argument.

     ::

       .macro Fopen file, mode
          movs.w   \mode,-(sp)  ;push open mode
          move.1   \file,-(sp)  ;push address of tile name
          Gemdos   $3d,8        ;do the GEMDOS call
       .endm

The **String** macro is used to allocate storage for a string, and to place the
string's address somewhere. The first argument should be a string or other expres-
sion acceptable in a dc.b directive. The second argument is optional; it specifies
where the address of the string should be placed. If the second argument is omitted,
the string's address is pushed onto the stack. The string data itself is kept in the
data segment.

                  ::

                   .macro String str,loc
                       .if \?loc                                        ; if loc is defined
                         move.l #.\~,\loc                               ; put the string's address there
                       .else                                            ; otherwise
                         pea .\~                                        ; push the string's address
                       .endif                                           ;
                       .data                                            ; put the string data
                   .\~: dc.b \str,0                                     ;  in the data segment
                       .text                                            ; and switch back to the text segment
                   .endm

The construction "``.\~``" will expand to a label of the form "``.M``\ *n*" (where *n* is
a unique number for every macro invocation), which is used to tag the location of
the string. The label should be confined because the macro may be used along with
other confined symbols.

Unique symbol generation plays an important part in the art of writing fine
macros. For instance, if we needed three unique symbols, we might write "``.a\~``",
"``.b\~``" and "``.c\~``".

`Repeat Blocks`_
''''''''''''''''
Repeat-blocks provide a simple iteration capability. A repeat block allows a range
of statements to be repeated a specified number of times. For instance, to generate
a table consisting of the numbers 255 through 0 (counting backwards) you could
write:

                  ::

                   .count  set     255             ; initialize counter
                           .rept 256               ; repeat 256 times:
                           dc.b    .count          ;   deposit counter
                   .count  set     .count - 1      ;   and decrement it
                           .endr                   ; (end of repeat block)

Repeat blocks can also be used to duplicate identical pieces of code (which are
common in bitmap-graphics routines). For example:

                  ::

                   .rept 16                        ; clear 16 words
                   clr.w (a0)+                     ;   starting at AO
                   .endr                           ;

`Jaguar GPU/DSP Mode`_
======================

RMAC will generate code for the Atari jaguar GPU and DSP custom RISC (Reduced
Instruction Set Computer) processors. See the Atari Jaguar Software reference Manual – Tom
& Jerry for a complete listing of Jaguar GPU and DSP assembler mnemonics and addressing
modes.

`Condition Codes`_
''''''''''''''''''
The following condition codes for the GPU/DSP JUMP and JR instructions are built-in:
 
  ::

   CC (Carry Clear) = %00100
   CS (Carry Set)   = %01000
   EQ (Equal)       = %00010
   MI (Minus)       = %11000
   NE (Not Equal)   = %00001
   PL (Plus)        = %10100
   HI (Higher)      = %00101
   T (True)         = %00000

                   
`6502 Support`_
===============
RMAC will generate code for the Motorola 6502 microprocessor. This chapter
describes extra addressing modes and directives used to support the 6502.

As the 6502 object code is not linkable (currently there is no linker) external
references may not be made. (Nevertheless, RMAC may reasonably be used for
large assemblies because of its blinding speed.)

`6502 Addressing Modes`_
''''''''''''''''''''''''
All standard 6502 addressing modes are supported, with the exception of the
accumulator addressing form, which must be omitted (e.g. "ror a" becomes "ror").
Five extra modes, synonyms for existing ones, are included for compatibility with
the Atari Coinop assembler.

============== ========================================
*empty*        implied or accumulator (e.g. tsx or ror)
*expr*         absolute or zeropage
#\ *expr*      immediate
(*expr*,x)     indirect X
(*expr*),y     indirect Y
(*expr*)       indirect
*expr*,x       indexed X
*expr*,y       indexed Y
@\ *expr*\ (x) indirect X
@\ *expr*\ (y) indirect Y
@expr          indirect
x,\ *expr*     indexed X
y,\ *expr*     indexed Y
============== ========================================

While RMAC lacks "high" and "low" operators, high bytes of words may
be extracted with the shift (``>>``) or divide (``/``) operators, and low bytes may be
extracted with the bitwise AND (``&``) operator.

`6502 Directives`_
''''''''''''''''''
**.6502**
   This directive enters the 6502 section. The location counter is undefined, and
   must be set with ".org" before any code can be generated.

   The "``dc.w``" directive will produce 6502-format words (low byte first). The
   68000's reserved keywords (``d0-d7/a0-a7/ssp/usp`` and so on) remain reserved
   (and thus unusable) while in the 6502 section. The directives **globl**, **dc.l**,
   **dcb.l**, **text**, **data**, **bss**, **abs**, **even** and **comm** are illegal in the 6502 section.
   It is permitted, though probably not useful, to generate both 6502 and 68000
   code in the same object file.
**.68000**
   This directive leaves the 6502 segment and returns to the 68000's text segment.
   68000 instructions may be assembled as normal.
**.org** *location*
   This directive is only legal in the 6502 section. It sets the value of the location
   counter (or **pc**) to location, an expression that must be defined, absolute, and
   less than $10000.

   WARNING

   It is possible to assemble "beyond" the microprocessor's 64K address space, but
   attempting to do so will probably screw up the assembler. DO NOT attempt
   to generate code like this:

     ::

      .org $fffe
      nop
      nop
      nop

   the third NOP in this example, at location $10000, may cause the assembler
   to crash or exhibit spectacular schizophrenia. In any case, RMAC will give
   no warning before flaking out.

`6502 Object Code Format`_
''''''''''''''''''''''''''
This is a little bit of a kludge. An object file consists of a page map, followed by
one or more page images, followed by a normal Alcyon 68000 object file. If the page
map is all zero, it is not written.

The page map contains a byte for each of the 256 256-byte pages in the 6502's
64K address space. The byte is zero (``$00``) if the page contained only zero bytes, or
one (``$01``) if the page contained any non-zero bytes. If a page is flagged with a one,
then it is written (in order) following the page map.

The following code:

     ::

      .6502
      .org  $8000
      .dc.b 1
      .org  $8100
      .dc.b 1
      .org  $8300
      .dc.b 1
      .end

will generate a page map that looks (to a programmer) something like:

     ::

      <80 bytes of zero>
      01 01 00 01
      <$7c more bytes of zero, for $100 total>
      <image of page $80>
      <image of page $81>
      <image of page $83>

Following the last page image is an Alcyon-format object file, starting with
the magic number ``$601a``. It may contain 68000 code (although that is probably
useless), but the symbol table is valid and available for debugging purposes. 6502
symbols will be absolute (not in text, data or bss).

`Error Messages`_
=================

`When Things Go Wrong`_
'''''''''''''''''''''''
Most of RMAC's error messages are self-explanatory. They fall into four classes:
warnings about situations that you (or the assembler) may not be happy about,
errors that cause the assembler to not generate object files, fatal errors that cause
the assembler to abort immediately, and internal errors that should never happen.\ [3]_

You can write editor macros (or sed or awk scripts) to parse the error messages
RMAC generates. When a message is printed, it is of the form:

         "*filename*" , ``line`` *line-number*: *message*

The first element, a filename enclosed in double quotes, indicates the file that generated
the error. The filename is followed by a comma, the word "``line``", and a line
number, and finally a colon and the text of the message. The filename "**(\*top\*)**"
indicates that the assembler could not determine which file had the problem.

The following sections list warnings, errors and fatal errors in alphabetical
order, along with a short description of what may have caused the problem.

.. [3] If you come across an internal error, we would appreciate it if you would contact Atari Technical Support and let us know about the problem.

`Warnings`_
'''''''''''
**bad backslash code in string**
  You tried to follow a backslash in a string with a character that the assembler
  didn't recognize. Remember that RMAC uses a C-style escape system in
  strings.
**label ignored**
  You specified a label before a macro, **rept** or **endm** directive. The assembler
  is warning you that the label will not be defined in the assembly.
**unoptimized short branch**
  This warning is only generated if the -s switch is specified on the command
  line. The message refers to a forward, unsized long branch that you could have
  made short (.s).

`Fatal Errors`_
'''''''''''''''

**cannot continue**
  As a result of previous errors, the assembler cannot continue processing. The
  assembly is aborted.
**line too long as a result of macro expansion**
  When a source line within a macro was expanded, the resultant line was too
  long for RMAC (longer than 200 characters or so).


**memory exhausted**
    The assembler ran out of memory. You should (1) split up your source files
    and assemble them seperately, or (2) if you have any ramdisks or RAM-resident
    programs (like desk accessories) decrease their size so that the assembler has
    more RAM to work with. As a rule of thumb, pure 68000 code will use up to
    twice the number of bytes contained in the source files, whereas 6502 code will
    use 64K of ram right away, plus the size of the source files. The assembler itself
    uses about 80K bytes. Get out your calculator...
**too many ENDMs**
    The assembler ran across an **endm** directive when it wasn't expecting to see
    one. The assembly is aborted. Check the nesting of your macro definitions -
    you probably have an extra **endm**.


`Errors`_
'''''''''

**.cargs syntax**
    Syntax error in **.cargs** directive.
**.comm symbol already defined**
    You tried to ``.comm`` a symbol that was already defined.
**.ds permitted only in BSS**
    You tried to use ``.ds`` in the text or data section.
**.init not permitted in BSS or ABS**
    You tried to use ``.init`` in the BSS or ABS section.
**.org permitted only in .6502 section**
    You tried to use ``.org`` in a 68000 section.
**Cannot create:** *filename*
    The assembler could not create the indicated filename.
**External quick reference**
    You tried to make the immediate operand of a **moveq**, **subq** or **addq** instruction external.
**PC-relative expr across sections**
    You tried to make a PC-relative reference to a location contained in another
    section.
**[bwsl] must follow '.' in symbol**
    You tried to follow a dot in a symbol name with something other than one of
    the four characters 'B', 'W', 'S' or 'L'.
**addressing mode syntax**
    You made a syntax error in an addressing mode.
**assert failure**
    One of your **.assert** directives failed!
**bad (section) expression**
    You tried to mix and match sections in an expression
**bad 6502 addressing mode**
    The 6502 mnemonic will not work with the addressing mode you specified.
**bad expression**
    There's a syntax error in the expression you typed.
**bad size specified**
  You tried to use an inappropriate size suffix for the instruction. Check your
  68000 manual for allowable sizes.
**bad size suffix**
  You can't use .b (byte) mode with the **movem** instruction.
**cannot .globl local symbol**
  You tried to make a confined symbol global or common.
**cannot initialize non-storage (BSS) section**
  You tried to generate instructions (or data, with dc) in the BSS or ABS section.
**cannot use '.b' with an address register**
  You tried to use a byte-size suffix with an address register. The 68000 does not
  perform byte-sized address register operations.
**directive illegal in .6502 section**
  You tried to use a 68000-oriented directive in the 6502 section.
**divide by zero**
  The expression you typed involves a division by zero.
**expression out of range**
  The expression you typed is out of range for its application.
**external byte reference**
  You tried to make a byte-sized reference to an external symbol, which the
  object file format will not allow
**external short branch**
  You tried to make a short branch to an external symbol, which the linker cannot
  handle.
**extra (unexpected) text found after addressing mode**
  RMAC thought it was done processing a line, but it ran up against "extra"
  stuff. Be sure that any comment on the line begins with a semicolon, and check
  for dangling commas, etc.
**forward or undefined .assert**
  The expression you typed after a **.assert** directive had an undefined value.
  Remember that RMAC is one-pass.
**hit EOF without finding matching .endif**
  The assembler fell off the end of last input file without finding a **.endif** to
  match an . it. You probably forgot a **.endif** somewhere.
**illegal 6502 addressing mode**
  The 6502 instruction you typed doesn't work with the addressing mode you
  specified.
**illegal absolute expression**
  You can't use an absolute-valued expression here.
**illegal bra.s with zero offset**
  You can't do a short branch to the very next instruction (read your 68000
  manual).
**illegal byte-sized relative reference**
  The object file format does not permit bytes contain relocatable values; you
  tried to use a byte-sized relocatable expression in an immediate addressing
  mode.
**illegal character**
 Your source file contains a character that RMAC doesn't allow. (most
 control characters fall into this category).
**illegal initialization of section**
 You tried to use .dc or .dcb in the BSS or ABS sections.
**illegal relative address**
 The relative address you specified is illegal because it belongs to a different
 section.
**illegal word relocatable (in .PRG mode)**
 You can't have anything other than long relocatable values when you're gener-
 ating a **.PRG** file.
**inappropriate addressing mode**
 The mnemonic you typed doesn't work with the addressing modes you specified.
 Check your 68000 manual for allowable combinations.
**invalid addressing mode**
 The combination of addressing modes you picked for the **movem** instruction
 are not implemented by the 68000. Check your 68000 reference manual for
 details.
**invalid symbol following ^^**
 What followed the ^^ wasn't a valid symbol at all.
**mis-nested .endr**
 The assembler found a **.endr** directive when it wasn't prepared to find one.
 Check your repeat-block nesting.
**mismatched .else**
 The assembler found a **.else** directive when it wasn't prepared to find one.
 Check your conditional assembly nesting.
**mismatched .endif**
 The assembler found a **.endif** directive when it wasn't prepared to find one.
 Check your conditional assembly nesting.

**missing '='**

**missing '}'**

**missing argument name**

**missing close parenthesis ')'**

**missing close parenthesis ']'**

**missing comma**

**missing filename**

**missing string**

**missing symbol**

**missing symbol or string**
 The assembler expected to see a symbol/filename/string (etc...), but found
 something else instead. In most cases the problem should be obvious.
**misuse of '.', not allowed in symbols**
 You tried to use a dot (.) in the middle of a symbol name.
**mod (%) by zero**
 The expression you typed involves a modulo by zero.
**multiple formal argument definition**
  The list of formal parameter names you supplied for a macro definition includes
  two identical names.
**multiple macro definition**
  You tried to define a macro which already had a definition.
**non-absolute byte reference**
  You tried to make a byte reference to a relocatable value, which the object file
  format does not allow.
**non-absolute byte value**
  You tried to dc.b or dcb.b a relocatable value. Byte relocatable values are
  not permitted by the object file format.
**register list order**
  You tried to specify a register list like **D7-D0**, which is illegal. Remember
  that the first register number must be less than or equal to the second register
  number.
**register list syntax**
  You made an error in specifying a register list for a **.reg** directive or a **.movem**
  instruction.
**symbol list syntax**
  You probably forgot a comma between the names of two symbols in a symbol
  list, or you left a comma dangling on the end of the line.
**syntax error**
  This is a "catch-all" error.
**undefined expression**
  The expression has an undefined value because of a forward reference, or an
  undefined or external symbol.
**unimplemented addressing mode**
  You tried to use 68020 "square-bracket" notation for a 68020 addressing mode.
  RMAC does not support 68020 addressing modes.
**unimplemented directive**
  You have found a directive that didn't appear in the documentation. It doesn't
  work.
**unimplemented mnemonic**
  You've found an assembler for documentation) bug.
**unknown symbol following ^^**
  You followed a ^^ with something other than one of the names defined, ref-
  erenced or streq.
**unsupported 68020 addressing mode**
  The assembler saw a 68020-type addressing mode. RMAC does not assem-
  ble code for the 68020 or 68010.
**unterminated string**
  You specified a string starting with a single or double quote, but forgot to type
  the closing quote.
**write error**
  The assembler had a problem writing an object file. This is usually caused by
  a full disk, or a bad sector on the media.