# © and notes

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.

# 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 reStructuredtext and Sphinx. 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:

> rmac [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
-ipath | Set include-file directory search path.
-l[file[prn]] | Construct and direct assembly listing to the specified file.
-ofile[.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 includesys 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:

>     % rmac 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 BSRs) 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 this 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:

> >     reallyLongSymbolName .reallyLongConfinedSymbolName
> >     a10 ret move dc frog aa6 a9 ????
> >     .a1 .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
>     d0 d1 d2 d3 d4 d5 d6 d7
>     a0 a1 a2 a3 a4 a5 a6 a7
>     r0 r1 r2 r3 r4 r5 r6 r7
>     r8 r9 r10 r11 r12 rl3 r14 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
>     -------------           -----
>     d0-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 ...
>             movea.l d0-d2/a0-a2,-(sp) ; are identical
>             movem.l #keeps,-(sp)    ; save "keep" registers
>             movem.l (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, line1+8
>     line2:  dc.l   line1, line2-8
>     line3:  dc.l   line2-line1, 8
>     error:  dc.l   line1+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.