[cc65] / doc / ca65.sgml

<!doctype linuxdoc system>

<article>
<title>ca65 Users Guide
<author>Ullrich von Bassewitz, <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">
<date>19.07.2000, 29.11.2000, 02.10.2001

<abstract>
ca65 is a powerful macro assembler for the 6502, 65C02 and 65816 CPUs. It is
used as a companion assembler for the cc65 crosscompiler, but it may also be
used as a standalone product.
</abstract>

<!-- Table of contents -->
<toc>

<!-- Begin the document -->

<sect>Overview<p>

ca65 is a replacement for the ra65 assembler that was part of the cc65 C
compiler, originally developed by John R. Dunning. I had some problems with
ra65 and the copyright does not permit some things which I wanted to be
possible, so I decided to write a completely new assembler/linker/archiver
suite for the cc65 compiler. ca65 is part of this suite.

Some parts of the assembler (code generation and some routines for symbol
table handling) are taken from an older crossassembler named a816 written
by me a long time ago.


<sect1>Design criteria<p>

Here's a list of the design criteria, that I considered important for the
development:

<itemize>

<item>  The assembler must support macros. Macros are not essential, but they
        make some things easier, especially when you use the assembler in the
        backend of a compiler.
<item>  The assembler must support the newer 65C02 and 65816 CPUs. I have been
        thinking about a 65816 backend for the C compiler, and even my old
        a816 assembler had support for these CPUs, so this wasn't really a
        problem.
<item>  The assembler must produce relocatable code. This is necessary for the
        compiler support, and it is more convenient.
<item>  Conditional assembly must be supported. This is a must for bigger
        projects written in assembler (like Elite128).
<item>  The assembler must support segments, and it must support more than
        three segments (this is the count, most other assemblers support).
        Having more than one code segments helps developing code for systems
        with a divided ROM area (like the C64).
<item>  The linker must be able to resolve arbitrary expressions. It should
        be able to get things like
<tscreen><verb>
        .import S1, S2
        .export Special
        Special = 2*S1 + S2/7
</verb></tscreen>
        right.
<item>  True lexical nesting for symbols. This is very convenient for larger
        assembly projects.
<item>  "Cheap" local symbols without lexical nesting for those quick, late
        night hacks.
<item>  I liked the idea of "options" as Anre Fachats .o65 format has it, so I
        introduced the concept into the object file format use by the new cc65
        binutils.
<item>  The assembler will be a one pass assembler. There was no real need for
        this decision, but I've written several multipass assemblers, and it
        started to get boring. A one pass assembler needs much more elaborated
        data structures, and because of that it's much more fun:-)
<item>  Non-GPLed code that may be used in any project without restrictions or
        fear of "GPL infecting" other code.
</itemize>
<p>


<sect>Usage<p>


<sect1>Command line option overview<p>

The assembler accepts the following options:

<tscreen><verb>
---------------------------------------------------------------------------
Usage: ca65 [options] file
Short options:
  -D name[=value]       Define a symbol
  -I dir                Set an include directory search path
  -U                    Mark unresolved symbols as import
  -V                    Print the assembler version
  -W n                  Set warning level n
  -g                    Add debug info to object file
  -h                    Help (this text)
  -i                    Ignore case of symbols
  -l                    Create a listing if assembly was ok
  -o name               Name the output file
  -s                    Enable smart mode
  -t sys                Set the target system
  -v                    Increase verbosity

Long options:
  --auto-import         Mark unresolved symbols as import
  --cpu type            Set cpu type
  --debug-info          Add debug info to object file
  --feature name        Set an emulation feature
  --help                Help (this text)
  --ignore-case         Ignore case of symbols
  --include-dir dir     Set an include directory search path
  --listing             Create a listing if assembly was ok
  --pagelength n        Set the page length for the listing
  --smart               Enable smart mode
  --target sys          Set the target system
  --verbose             Increase verbosity
  --version             Print the assembler version
---------------------------------------------------------------------------
</verb></tscreen>


<sect1>Command line options in detail<p>

Here is a description of all the command line options:

<descrip>

  <label id="option--cpu">
  <tag><tt>--cpu type</tt></tag>

  Set the default for the CPU type. The option takes a parameter, which
  may be one of

        6502, 65SC02, 65C02, 65816 and sunplus

  The last one (sunplus) is not available in the freeware version, because the
  instruction set of the sunplus CPU is "proprietary and confidential".


  <label id="option--feature">
  <tag><tt>--feature name</tt></tag>

  Enable an emulation feature. This is identical as using <tt/.FEATURE/
  in the source with two exceptions: Feature names must be lower case, and
  each feature must be specified by using an extra <tt/--feature/ option,
  comma separated lists are not allowed.

  See the discussion of the <tt><ref id=".FEATURE" name=".FEATURE"></tt>
  command for a list of emulation features.


  <label id="option-g">
  <tag><tt>-g, --debug-info</tt></tag>

  When this option (or the equivalent control command <tt/.DEBUGINFO/) is
  used, the assembler will add a section to the object file that contains
  all symbols (including local ones) together with the symbol values and
  source file positions. The linker will put these additional symbols into
  the VICE label file, so even local symbols can be seen in the VICE
  monitor.


  <tag><tt>-h, --help</tt></tag>

  Print the short option summary shown above.


  <tag><tt>-i, --ignore-case</tt></tag>

  This option makes the assembler case insensitive on identifiers and labels.
  This option will override the default, but may itself be overriden by the
  <tt><ref id=".CASE" name=".CASE"></tt> control command.


  <tag><tt>-l, --listing</tt></tag>

  Generate an assembler listing. The listing file will always have the
  name of the main input file with the extension replaced by ".lst". This
  may change in future versions.


  <tag><tt>-o name</tt></tag>

  The default output name is the name of the input file with the extension
  replaced by ".o". If you don't like that, you may give another name with
  the -o option. The output file will be placed in the same directory as
  the source file, or, if -o is given, the full path in this name is used.


  <tag><tt>--pagelength n</tt></tag>

  sets the length of a listing page in lines. See the <tt><ref
  id=".PAGELENGTH" name=".PAGELENGTH"></tt> directive for more information.


  <tag><tt>-s, --smart-mode</tt></tag>

  In smart mode (enabled by -s or the <tt><ref id=".SMART" name=".SMART"></tt>
  pseudo instruction) the assembler will track usage of the <tt/REP/ and
  <tt/SEP/ instructions in 65816 mode and update the operand sizes
  accordingly. If the operand of such an instruction cannot be evaluated by
  the assembler (for example, because the operand is an imported symbol), a
  warning is issued.

  Beware: Since the assembler cannot trace the execution flow this may
  lead to false results in some cases. If in doubt, use the .ixx and .axx
  instructions to tell the assembler about the current settings. Smart
  mode is off by default.


  <label id="option-t">
  <tag><tt>-t sys, --target sys</tt></tag>

  Set the target system. This will enable translation of character strings
  and character constants into the character set of the target platform.
  The default for the target system is "none", which means that no translation
  will take place. The assembler supports the same target systems as the
  compiler, see there for a list.


  <tag><tt>-v, --verbose</tt></tag>

  Increase the assembler verbosity. Usually only needed for debugging
  purposes. You may use this option more than one time for even more
  verbose output.


  <tag><tt>-D</tt></tag>

  This option allows you to define symbols on the command line. Without a
  value, the symbol is defined with the value zero. When giving a value,
  you may use the '&dollar;' prefix for hexadecimal symbols. Please note
  that for some operating systems, '&dollar;' has a special meaning, so
  you may have to quote the expression.


  <tag><tt>-I dir, --include-dir dir</tt></tag>

  Name a directory which is searched for include files. The option may be
  used more than once to specify more than one directory to search. The
  current directory is always searched first before considering any
  additional directores.


  <tag><tt>-U, --auto-import</tt></tag>

  Mark symbols that are not defined in the sources as imported symbols. This
  should be used with care since it delays error messages about typos and such
  until the linker is run. The compiler uses the equivalent of this switch
  (<tt><ref id=".AUTOIMPORT" name=".AUTOIMPORT"></tt>) to enable auto imported
  symbols for the runtime library. However, the compiler is supposed to
  generate code that runs through the assembler without problems, something
  which is not always true for assembler programmers.


  <tag><tt>-V, --version</tt></tag>

  Print the version number of the assembler. If you send any suggestions
  or bugfixes, please include the version number.


  <label id="option-W">
  <tag><tt>-Wn</tt></tag>

  Set the warning level for the assembler. Using -W2 the assembler will
  even warn about such things like unused imported symbols. The default
  warning level is 1, and it would probably be silly to set it to
  something lower.

</descrip>
<p>


<sect>Input format<p>

The assembler accepts the standard 6502/65816 assembler syntax. One line may
contain a label (which is identified by a colon), and, in addition to the
label, an assembler mnemonic, a macro, or a control command (see section <ref
id="control-commands" name="Control Commands"> for supported control
commands). Alternatively, the line may contain a symbol definition using the
'=' token. Everything after a semicolon is handled as a comment (that is, it
is ignored).

Here are some examples for valid input lines:

<tscreen><verb>
        Label:                          ; A label and a comment
                lda     #$20            ; A 6502 instruction plus comment
        L1:     ldx     #$20            ; Same with label
        L2:     .byte   "Hello world"   ; Label plus control command
                mymac   $20             ; Macro expansion
                MySym = 3*L1            ; Symbol definition
        MaSym   = Label                 ; Another symbol
</verb></tscreen>

The assembler accepts

<itemize>
<item>all valid 6502 mnemonics when in 6502 mode (the default or after the
      <tt><ref id=".P02" name=".P02"></tt> command was given).
<item>all valid 65SC02 mnemonics when in 65SC02 mode (after the
      <tt><ref id=".PSC02" name=".PSC02"></tt> command was given).
<item>all valid 65C02 mnemonics when in 65C02 mode (after the
      <tt><ref id=".PC02" name=".PC02"></tt> command was given).
<item>all valid 65618 mnemonics when in 65816 mode (after the
      <tt><ref id=".P816" name=".P816"></tt> command was given).
<item>all valid SunPlus mnemonics when in SunPlus mode (after the
      <tt><ref id=".SUNPLUS" name=".SUNPLUS"></tt> command was given).
</itemize>

In 65816 mode several aliases are accepted in addition to the official
mnemonics:

<tscreen><verb>
        BGE is an alias for BCS
        BLT is an alias for BCC
        CPA is an alias for CMP
        DEA is an alias for DEC A
        INA is an alias for INC A
        SWA is an alias for XBA
        TAD is an alias for TCD
        TAS is an alias for TCS
        TDA is an alias for TDC
        TSA is an alias for TSC
</verb></tscreen>

Evaluation of banked expressions in 65816 mode differs slightly from the
official syntax:

Instead of accepting a 24 bit address (something that is difficult for
the assembler to determine and would have required one more special
.import command), the bank and the absolute address in that bank are
separated by a dot:

<tscreen><verb>
        jsl     3.$1234         ; Call subroutine at $1234 in bank 3
</verb></tscreen>

For literal values, the assembler accepts the widely used number formats:
A preceeding '&dollar;' denotes a hex value, a preceeding '%' denotes a
binary value, and a bare number is interpeted as a decimal. There are
currently no octal values and no floats.
<p>


<sect>Expressions<p>


<sect1>Expression evaluation<p>

All expressions are evaluated with (at least) 32 bit precision. An
expression may contain constant values and any combination of internal and
external symbols. Expressions that cannot be evaluated at assembly time
are stored inside the object file for evaluation by the linker.
Expressions referencing imported symbols must always be evaluated by the
linker.


<sect1>Size of an expressions result<p>

Sometimes, the assembler must know about the size of the value that is the
result of an expression. This is usually the case, if a decision has to be
made, to generate a zero page or an absolute memory references. In this
case, the assembler has to make some assumptions about the result of an
expression:

<itemize>
<item>  If the result of an expression is constant, the actual value is
        checked to see if it's a byte sized expression or not.
<item>  If the expression is explicitly casted to a byte sized expression by
        one of the '&gt;'/'&lt;' operators, it is a byte expression.
<item>  If this is not the case, and the expression contains a symbol,
        explicitly declared as zero page symbol (by one of the .importzp or
        .exportzp instructions), then the whole expression is assumed to be
        byte sized.
<item>  If the expression contains symbols that are not defined, and these
        symbols are local symbols, the enclosing scopes are searched for a
        symbol with the same name. If one exists and this symbol is defined,
        it's attributes are used to determine the result size.
<item>  In all other cases the expression is assumed to be word sized.
</itemize>

Note: If the assembler is not able to evaluate the expression at assembly
time, the linker will evaluate it and check for range errors as soon as
the result is known.


<sect1>Boolean expressions<p>

In the context of a boolean expression, any non zero value is evaluated as
true, any other value to false. The result of a boolean expression is 1 if
it's true, and zero if it's false. There are boolean operators with extrem
low precedence with version 2.x (where x &gt; 0). The <tt/.AND/ and <tt/.OR/
operators are shortcut operators. That is, if the result of the expression is
already known, after evaluating the left hand side, the right hand side is
not evaluated.


<sect1>Available operators<p>

Available operators sorted by precedence:

<tscreen><verb>
    Op          Description                             Precedence
  -------------------------------------------------------------------
    .CONCAT     Builtin function                        0
    .LEFT       Builtin function                        0
    .MID        Builtin function                        0
    .RIGHT      Builtin function                        0
    .STRING     Builtin function                        0

    *           Builtin pseudo variable (r/o)           1
    .BLANK      Builtin function                        1
    .CONST      Builtin function                        1
    .CPU        Builtin pseudo variable (r/o)           1
    .DEFINED    Builtin function                        1
    .MATCH      Builtin function                        1
    .TCOUNT     Builtin function                        1
    .TIME       Builtin function                        1
    .XMATCH     Builtin function                        1
    .PARAMCOUNT Builtin pseudo variable (r/o)           1
    .REFERENCED Builtin function                        1
    ::          Global namespace override               1
    +           Unary plus                              1
    -           Unary minus                             1
    ~           Unary bitwise not                       1
    .BITNOT     Unary bitwise not                       1
    &lt;           Low byte operator                       1
    &gt;           High byte operator                      1

    *           Multiplication                          2
    /           Division                                2
    .MOD        Modulo operation                        2
    &amp;           Bitwise and                             2
    .BITAND     Bitwise and                             2
    ^           Bitwise xor                             2
    .BITXOR     Bitwise xor                             2
    &lt;&lt;          Shift left operator                     2
    .SHL        Shift left operator                     2
    &gt;&gt;          Shift right operator
    .SHR        Shift right operator                    2

    +           Binary plus                             3
    -           Binary minus                            3
    |           Binary or                               3
    .BITOR      Binary or                               3

    =           Compare operation (equal)               4
    &lt;&gt;          Compare operation (not equal)           4
    &lt;           Compare operation (less)                4
    &gt;           Compare operation (greater)             4
    &lt;=          Compare operation (less or equal)       4
    &gt;=          Compare operation (greater or equal)    4

    &amp;&amp;          Boolean and                             5
    .AND        Boolean and                             5
    .XOR        Boolean xor                             5

    ||          Boolean or                              6
    .OR         Boolean or                              6

    !           Boolean not                             7
    .NOT        Boolean not                             7
</verb></tscreen>


To force a specific order of evaluation, braces may be used as usual.

Some of the pseudo variables mentioned above need some more explanation:

<tscreen><verb>
  *             This symbol is replaced by the value of the program
                counter at start of the current instruction. Note, that
                '*' yields a rvalue, that means, you cannot assign to it.
                Use <tt/.ORG/ to set the program counter in sections with
                absolute code.
</verb></tscreen>
<p>



<sect>Symbols and labels<p>

The assembler allows you to use symbols instead of naked values to make
the source more readable. There are a lot of different ways to define and
use symbols and labels, giving a lot of flexibility.


<sect1>Numeric constants<p>

Numeric constants are defined using the equal sign. After doing

<tscreen><verb>
      two = 2
</verb></tscreen>

may use the symbol "two" in every place where a number is expected, and it is
evaluated to the value 2 in this context. An example would be

<tscreen><verb>
      four = two * two
</verb></tscreen>


<sect1>Standard labels<p>

A label is defined by writing the name of the label at the start of the line
(before any instruction mnemonic, macro or pseudo directive), followed by a
colon. This will declare a symbol with the given name and the value of the
current program counter.


<sect1>Local labels and symbols<p>

Using the <tt><ref id=".PROC" name=".PROC"></tt> directive, it is possible to
create regions of code where the names of labels and symbols are local to this
region. They are not known outside of this region and cannot be accessed from
there. Such regions may be nested like PROCEDUREs in Pascal.

See the description of the <tt><ref id=".PROC" name=".PROC"></tt>
directive for more information.


<sect1>Cheap local labels<p>

Cheap local labels are defined like standard labels, but the name of the
label must begin with a special symbol (usually '@', but this can be
changed by the <tt><ref id=".LOCALCHAR" name=".LOCALCHAR"></tt>
directive).

Cheap local labels are visible only between two non cheap labels. As soon as a
standard symbol is encountered (this may also be a local symbol if inside a
region defined with the <tt><ref id=".PROC" name=".PROC"></tt> directive), the
cheap local symbol goes out of scope.

You may use cheap local labels as an easy way to reuse common label
names like "Loop". Here is an example:

<tscreen><verb>
        Clear:  lda    #$00             ; Global label
                ldy    #$20
        @Loop:  sta    Mem,y            ; Local label
                dey
                bne    @Loop            ; Ok
                rts
        Sub:    ...                     ; New global label
                bne    @Loop            ; ERROR: Unknown identifier!
</verb></tscreen>

<sect1>Unnamed labels<p>

If you really want to write messy code, there are also unnamed
labels. These labels do not have a name (you guessed that already,
didn't you?). A colon is used to mark the absence of the name.

Unnamed labels may be accessed by using the colon plus several minus
or plus characters as a label designator. Using the '-' characters
will create a back reference (use the n'th label backwards), using
'+' will create a forward reference (use the n'th label in forward
direction). An example will help to understand this:

<tscreen><verb>
        :       lda     (ptr1),y        ; #1
                cmp     (ptr2),y
                bne     :+              ; -> #2
                tax
                beq     :+++            ; -> #4
                iny
                bne     :-              ; -> #1
                inc     ptr1+1
                inc     ptr2+1
                bne     :-              ; -> #1

        :       bcs     :+              ; #2 -> #3
                ldx     #$FF
                rts

        :       ldx     #$01            ; #3
        :       rts                     ; #4
</verb></tscreen>

As you can see from the example, unnamed labels will make even short
sections of code hard to understand, because you have to count labels
to find branch targets (this is the reason why I for my part do
prefer the "cheap" local labels). Nevertheless, unnamed labels are
convenient in some situations, so it's your decision.


<sect1>Using macros to define labels and constants<p>

While there are drawbacks with this approach, it may be handy in some
situations. Using <tt><ref id=".DEFINE" name=".DEFINE"></tt>, it is
possible to define symbols or constants that may be used elsewhere. Since
the macro facility works on a very low level, there is no scoping. On the
other side, you may also define string constants this way (this is not
possible with the other symbol types).

Example:

<tscreen><verb>
        .DEFINE two     2
        .DEFINE version "SOS V2.3"

        four = two * two        ; Ok
        .byte   version         ; Ok

        .PROC                   ; Start local scope
        two = 3                 ; Will give "2 = 3" - invalid!
        .ENDPROC
</verb></tscreen>


<sect1>Symbols and <tt>.DEBUGINFO</tt><p>

If <tt><ref id=".DEBUGINFO" name=".DEBUGINFO"></tt> is enabled (or <ref
id="option-g" name="-g"> is given on the command line), global, local and
cheap local labels are written to the object file and will be available in the
symbol file via the linker. Unnamed labels are not written to the object file,
because they don't have a name which would allow to access them.



<sect>Control commands<label id="control-commands">

<p>
Here's a list of all control commands and a description, what they do:


<sect1><tt>.A16</tt><label id=".A16"><p>

  Valid only in 65816 mode. Switch the accumulator to 16 bit.

  Note: This command will not emit any code, it will tell the assembler to
  create 16 bit operands for immediate accumulator adressing mode.

  See also: <tt><ref id=".SMART" name=".SMART"></tt>


<sect1><tt>.A8</tt><label id=".A8"><p>

  Valid only in 65816 mode. Switch the accumulator to 8 bit.

  Note: This command will not emit any code, it will tell the assembler to
  create 8 bit operands for immediate accu adressing mode.

  See also: <tt><ref id=".SMART" name=".SMART"></tt>


<sect1><tt>.ADDR</tt><label id=".ADDR"><p>

  Define word sized data. In 6502 mode, this is an alias for <tt/.WORD/ and
  may be used for better readability if the data words are address values. In
  65816 mode, the address is forced to be 16 bit wide to fit into the current
  segment. See also <tt><ref id=".FARADDR" name=".FARADDR"></tt>. The command
  must be followed by a sequence of (not necessarily constant) expressions.

  Example:

  <tscreen><verb>
        .addr   $0D00, $AF13, _Clear
  </verb></tscreen>

  See: <tt><ref id=".FARADDR" name=".FARADDR"></tt>, <tt><ref id=".WORD"
       name=".WORD"></tt>


<sect1><tt>.ALIGN</tt><label id=".ALIGN"><p>

  Align data to a given boundary. The command expects a constant integer
  argument that must be a power of two, plus an optional second argument
  in byte range. If there is a second argument, it is used as fill value,
  otherwise the value defined in the linker configuration file is used
  (the default for this value is zero).

  Since alignment depends on the base address of the module, you must
  give the same (or a greater) alignment for the segment when linking.
  The linker will give you a warning, if you don't do that.

  Example:

  <tscreen><verb>
        .align  256
  </verb></tscreen>


<sect1><tt>.ASCIIZ</tt><label id=".ASCIIZ"><p>

  Define a string with a trailing zero.

  Example:

  <tscreen><verb>
        Msg:    .asciiz "Hello world"
  </verb></tscreen>

  This will put the string "Hello world" followed by a binary zero into
  the current segment. There may be more strings separated by commas, but
  the binary zero is only appended once (after the last one).


<sect1><tt>.ASSERT</tt><label id=".ASSERT"><p>

  Add an assertion. The command is followed by an expression, an action
  specifier and a message that is output in case the assertion fails. The
  action specifier may be one of <tt/warning/ or <tt/error/. The assertion
  is passed to the linker and will be evaluated when segment placement has
  been done.

  Example:

  <tscreen><verb>
        .assert         * = $8000, error, "Code not at $8000"
  </verb></tscreen>

  The example assertion will check that the current location is at $8000,
  when the output file is written, and abort with an error if this is not
  the case. More complex expressions are possible. The action specifier
  <tt/warning/ outputs a warning, while the <tt/error/ specifier outputs
  an error message. In the latter case, generation if the output file is
  suppressed.


<sect1><tt>.AUTOIMPORT</tt><label id=".AUTOIMPORT"><p>

  Is followed by a plus or a minus character. When switched on (using a
  +), undefined symbols are automatically marked as import instead of
  giving errors. When switched off (which is the default so this does not
  make much sense), this does not happen and an error message is
  displayed. The state of the autoimport flag is evaluated when the
  complete source was translated, before outputing actual code, so it is
  <em/not/ possible to switch this feature on or off for separate sections
  of code. The last setting is used for all symbols.

  You should probably not use this switch because it delays error
  messages about undefined symbols until the link stage. The cc65
  compiler (which is supposed to produce correct assembler code in all
  circumstances, something which is not true for most assembler
  programmers) will insert this command to avoid importing each and every
  routine from the runtime library.

  Example:

  <tscreen><verb>
        .autoimport     +       ; Switch on auto import
  </verb></tscreen>


<sect1><tt>.BLANK</tt><label id=".BLANK"><p>

  Builtin function. The function evaluates its argument in braces and
  yields "false" if the argument is non blank (there is an argument), and
  "true" if there is no argument. As an example, the <tt/.IFBLANK/ statement
  may be replaced by

  <tscreen><verb>
        .if     .blank(arg)
  </verb></tscreen>


<sect1><tt>.BSS</tt><label id=".BSS"><p>

  Switch to the BSS segment. The name of the BSS segment is always "BSS",
  so this is a shortcut for

  <tscreen><verb>
        .segment  "BSS"
  </verb></tscreen>

  See also the <tt><ref id=".SEGMENT" name=".SEGMENT"></tt> command.


<sect1><tt>.BYT, .BYTE</tt><label id=".BYTE"><p>

  Define byte sized data. Must be followed by a sequence of (byte ranged)
  expressions or strings.

  Example:

  <tscreen><verb>
        .byte   "Hello "
        .byt    "world", $0D, $00
  </verb></tscreen>


<sect1><tt>.CASE</tt><label id=".CASE"><p>

  Switch on or off case sensitivity on identifiers. The default is off
  (that is, identifiers are case sensitive), but may be changed by the
  -i switch on the command line.
  The command must be followed by a '+' or '-' character to switch the
  option on or off respectively.

  Example:

  <tscreen><verb>
        .case   -               ; Identifiers are not case sensitive
  </verb></tscreen>


<sect1><tt>.CHARMAP</tt><label id=".CHARMAP"><p>

  Apply a custom mapping for characters. The command is followed by two
  numbers in the range 1..255. The first one is the index of the source
  character, the second one is the mapping. The mapping applies to all
  character and string constants when they generate output, and overrides
  a mapping table specified with the <tt><ref id="option-t" name="-t"></tt>
  command line switch.

  Example:

  <tscreen><verb>
        .charmap        $41, $61        ; Map 'A' to 'a'
  </verb></tscreen>


<sect1><tt>.CODE</tt><label id=".CODE"><p>

  Switch to the CODE segment. The name of the CODE segment is always
  "CODE", so this is a shortcut for

  <tscreen><verb>
        .segment  "CODE"
  </verb></tscreen>

  See also the <tt><ref id=".SEGMENT" name=".SEGMENT"></tt> command.


<sect1><tt>.CONDES</tt><label id=".CONDES"><p>

  Export a symbol and mark it in a special way. The linker is able to build
  tables of all such symbols. This may be used to automatically create a list
  of functions needed to initialize linked library modules.

  Note: The linker has a feature to build a table of marked routines, but it
  is your code that must call these routines, so just declaring a symbol with
  <tt/.CONDES/ does nothing by itself.

  All symbols are exported as an absolute (16 bit) symbol. You don't need to
  use an additional <tt><ref id=".EXPORT" name=".EXPORT"></tt> statement, this
  is implied by <tt/.CONDES/.

  <tt/.CONDES/ is followed by the type, which may be <tt/constructor/,
  <tt/destructor/ or a numeric value between 0 and 6 (where 0 is the same as
  specifiying <tt/constructor/ and 1 is equal to specifying <tt/destructor/).
  The <tt><ref id=".CONSTRUCTOR" name=".CONSTRUCTOR"></tt> and <tt><ref
  id=".DESTRUCTOR" name=".DESTRUCTOR"></tt> commands are actually shortcuts
  for <tt/.CONDES/ with a type of <tt/constructor/ resp. <tt/destructor/.

  After the type, an optional priority may be specified. If no priority is
  given, the default priority of 7 is used. Be careful when assigning
  priorities to your own module constructors so they won't interfere with the
  ones in the cc65 library.

  Example:

  <tscreen><verb>
        .condes         ModuleInit, constructor
        .condes         ModInit, 0, 16
  </verb></tscreen>

  See the <tt><ref id=".CONSTRUCTOR" name=".CONSTRUCTOR"></tt> and <tt><ref
  id=".DESTRUCTOR" name=".DESTRUCTOR"></tt> commands and the separate section
  <ref id="condes" name="Module constructors/destructors"> explaining the
  feature in more detail.


<sect1><tt>.CONCAT</tt><label id=".CONCAT"><p>

  Builtin function. The function allows to concatenate a list of string
  constants separated by commas. The result is a string constant that
  is the concatentation of all arguments. This function is most useful
  in macros and when used together with the <tt/.STRING/ builtin function.
  The function may be used in any case where a string constant is
  expected.

  Example:

  <tscreen><verb>
        .include        .concat ("myheader", ".", "inc")
  </verb></tscreen>

  This is the same as the command

  <tscreen><verb>
        .include        "myheader.inc"
  </verb></tscreen>


<sect1><tt>.CONST</tt><label id=".CONST"><p>

  Builtin function. The function evaluates its argument in braces and
  yields "true" if the argument is a constant expression (that is, an
  expression that yields a constant value at assembly time) and "false"
  otherwise. As an example, the .IFCONST statement may be replaced by

  <tscreen><verb>
        .if     .const(a + 3)
  </verb></tscreen>


<sect1><tt>.CONSTRUCTOR</tt><label id=".CONSTRUCTOR"><p>

  Export a symbol and mark it as a module constructor. This may be used
  together with the linker to build a table of constructor subroutines that
  are called by the startup code.

  Note: The linker has a feature to build a table of marked routines, but it
  is your code that must call these routines, so just declaring a symbol as
  constructor does nothing by itself.

  A constructor is always exported as an absolute (16 bit) symbol. You don't
  need to use an additional <tt/.export/ statement, this is implied by
  <tt/.constructor/. It may have an optional priority that is separated by a
  comma. If no priority is given, the default priority of 7 is used. Be
  careful when assigning priorities to your own module constructors so they
  won't interfere with the ones in the cc65 library.

  Example:

  <tscreen><verb>
        .constructor    ModuleInit
        .constructor    ModInit, 16
  </verb></tscreen>

  See the <tt><ref id=".CONDES" name=".CONDES"></tt> and <tt><ref
  id=".DESTRUCTOR" name=".DESTRUCTOR"></tt> commands and the separate section
  <ref id="condes" name="Module constructors/destructors"> explaining the
  feature in more detail.


<sect1><tt>.CPU</tt><label id=".CPU"><p>

  Reading this pseudo variable will give a constant integer value that
  tells which instruction set is currently enabled. Possible values are:

  <tscreen><verb>
        0 -->   6502
        1 -->   65SC02
        2 -->   65C02
        3 -->   65SC816
        4 -->   SunPlus SPC
  </verb></tscreen>

  It may be used to replace the .IFPxx pseudo instructions or to construct
  even more complex expressions.

  Example:

  <tscreen><verb>
        .if     (.cpu = 0) .or (.cpu = 1) .or (.cpu = 2)
                txa
                pha
                tya
                pha
        .else
                phx
                phy
        .endif
  </verb></tscreen>


<sect1><tt>.DATA</tt><label id=".DATA"><p>

  Switch to the DATA segment. The name of the DATA segment is always
  "DATA", so this is a shortcut for

  <tscreen><verb>
        .segment  "DATA"
  </verb></tscreen>

  See also the <tt><ref id=".SEGMENT" name=".SEGMENT"></tt> command.


<sect1><tt>.DBYT</tt><label id=".DBYT"><p>

  Define word sized data with the hi and lo bytes swapped (use <tt/.WORD/ to
  create word sized data in native 65XX format). Must be followed by a
  sequence of (word ranged) expressions.

  Example:

  <tscreen><verb>
        .dbyt   $1234, $4512
  </verb></tscreen>

  This will emit the bytes

  <tscreen><verb>
        $12 $34 $45 $12
  </verb></tscreen>

  into the current segment in that order.


<sect1><tt>.DEBUGINFO</tt><label id=".DEBUGINFO"><p>

  Switch on or off debug info generation. The default is off (that is,
  the object file will not contain debug infos), but may be changed by the
  -g switch on the command line.
  The command must be followed by a '+' or '-' character to switch the
  option on or off respectively.

  Example:

  <tscreen><verb>
        .debuginfo      +       ; Generate debug info
  </verb></tscreen>


<sect1><tt>.DEFINE</tt><label id=".DEFINE"><p>

  Start a define style macro definition. The command is followed by an
  identifier (the macro name) and optionally by a list of formal arguments
  in braces.
  See section <ref id="macros" name="Macros">.


<sect1><tt>.DEF, .DEFINED</tt><label id=".DEFINED"><p>

  Builtin function. The function expects an identifier as argument in braces.
  The argument is evaluated, and the function yields "true" if the identifier
  is a symbol that is already defined somewhere in the source file up to the
  current position. Otherwise the function yields false. As an example, the
  <tt><ref id=".IFDEF" name=".IFDEF"></tt> statement may be replaced by

  <tscreen><verb>
        .if     .defined(a)
  </verb></tscreen>


<sect1><tt>.DESTRUCTOR</tt><label id=".DESTRUCTOR"><p>

  Export a symbol and mark it as a module destructor. This may be used
  together with the linker to build a table of destructor subroutines that
  are called by the startup code.

  Note: The linker has a feature to build a table of marked routines, but it
  is your code that must call these routines, so just declaring a symbol as
  constructor does nothing by itself.

  A destructor is always exported as an absolute (16 bit) symbol. You don't
  need to use an additional <tt/.export/ statement, this is implied by
  <tt/.destructor/. It may have an optional priority that is separated by a
  comma. If no priority is given, the default priority of 7 is used. Be
  careful when assigning priorities to your own module destructors so they
  won't interfere with the ones in the cc65 library.

  Example:

  <tscreen><verb>
        .destructor     ModuleDone
        .destructor     ModDone, 16
  </verb></tscreen>

  See the <tt><ref id=".CONDES" name=".CONDES"></tt> and <tt><ref
  id=".CONSTRUCTOR" name=".CONSTRUCTOR"></tt> commands and the separate
  section <ref id="condes" name="Module constructors/destructors"> explaining
  the feature in more detail.


<sect1><tt>.DWORD</tt><label id=".DWORD"><p>

  Define dword sized data (4 bytes) Must be followed by a sequence of
  expressions.

  Example:

  <tscreen><verb>
        .dword  $12344512, $12FA489
  </verb></tscreen>


<sect1><tt>.ELSE</tt><label id=".ELSE"><p>

  Conditional assembly: Reverse the current condition.


<sect1><tt>.ELSEIF</tt><label id=".ELSEIF"><p>

  Conditional assembly: Reverse current condition and test a new one.


<sect1><tt>.END</tt><label id=".END"><p>

  Forced end of assembly. Assembly stops at this point, even if the command
  is read from an include file.


<sect1><tt>.ENDIF</tt><label id=".ENDIF"><p>

  Conditional assembly: Close a <tt><ref id=".IF" name=".IF..."></tt> or
  <tt><ref id=".ELSE" name=".ELSE"></tt> branch.


<sect1><tt>.ENDMAC, .ENDMACRO</tt><label id=".ENDMACRO"><p>

  End of macro definition (see section <ref id="macros" name="Macros">).


<sect1><tt>.ENDPROC</tt><label id=".ENDPROC"><p>

  End of local lexical level (see <tt><ref id=".PROC" name=".PROC"></tt>).


<sect1><tt>.ENDREP, .ENDREPEAT</tt><label id=".ENDREPEAT"><p>

  End a <tt><ref id=".REPEAT" name=".REPEAT"></tt> block.


<sect1><tt>.ERROR</tt><label id=".ERROR"><p>

  Force an assembly error. The assembler will output an error message
  preceeded by "User error" and will <em/not/ produce an object file.

  This command may be used to check for initial conditions that must be
  set before assembling a source file.

  Example:

  <tscreen><verb>
        .if     foo = 1
        ...
        .elseif bar = 1
        ...
        .else
        .error  "Must define foo or bar!"
        .endif
  </verb></tscreen>

  See also the <tt><ref id=".WARNING" name=".WARNING"></tt> and <tt><ref
  id=".OUT" name=".OUT"></tt> directives.


<sect1><tt>.EXITMAC, .EXITMACRO</tt><label id=".EXITMACRO"><p>

  Abort a macro expansion immidiately. This command is often useful in
  recursive macros. See separate section <ref id="macros" name="Macros">.


<sect1><tt>.EXPORT</tt><label id=".EXPORT"><p>

  Make symbols accessible from other modules. Must be followed by a comma
  separated list of symbols to export.

  Example:

  <tscreen><verb>
        .export foo, bar
  </verb></tscreen>

  See: <tt><ref id=".EXPORTZP" name=".EXPORTZP"></tt>


<sect1><tt>.EXPORTZP</tt><label id=".EXPORTZP"><p>

  Make symbols accessible from other modules. Must be followed by a comma
  separated list of symbols to export. The exported symbols are explicitly
  marked as zero page symols.

  Example:

  <tscreen><verb>
        .exportzp  foo, bar
  </verb></tscreen>

  See: <tt><ref id=".EXPORT" name=".EXPORT"></tt>


<sect1><tt>.FARADDR</tt><label id=".FARADDR"><p>

  Define far (24 bit) address data. The command must be followed by a
  sequence of (not necessarily constant) expressions.

  Example:

  <tscreen><verb>
        .faraddr        DrawCircle, DrawRectangle, DrawHexagon
  </verb></tscreen>

  See: <tt><ref id=".ADDR" name=".ADDR"></tt>


<sect1><tt>.FEATURE</tt><label id=".FEATURE"><p>

  This directive may be used to enable one or more compatibility features
  of the assembler. While the use of <tt/.FEATURE/ should be avoided when
  possible, it may be useful when porting sources written for other
  assemblers. There is no way to switch a feature off, once you have
  enabled it, so using

  <tscreen><verb>
        .FEATURE        xxx
  </verb></tscreen>

  will enable the feature until end of assembly is reached.

  The following features are available:

  <descrip>

  <tag><tt>dollar_is_pc</tt></tag>

    The dollar sign may be used as an alias for the star (`*'), which
    gives the value of the current PC in expressions.
    Note: Assignment to the pseudo variable is not allowed.

  <tag><tt>labels_without_colons</tt></tag>

    Allow labels without a trailing colon. These labels are only accepted,
    if they start at the beginning of a line (no leading white space).

  <tag><tt>loose_string_term</tt></tag>

    Accept single quotes as well as double quotes as terminators for string
    constants.

  <tag><tt>loose_char_term</tt></tag>

    Accept single quotes as well as double quotes as terminators for char
    constants.

  <tag><tt>at_in_identifiers</tt></tag>

    Accept the at character (`@') as a valid character in identifiers. The
    at character is not allowed to start an identifier, even with this
    feature enabled.

  <tag><tt>dollar_in_identifiers</tt></tag>

    Accept the dollar sign (`&dollar;') as a valid character in identifiers. The
    at character is not allowed to start an identifier, even with this
    feature enabled.

  <tag><tt>leading_dot_in_identifiers</tt></tag>

    Accept the dot (`.') as the first character of an identifier. This may be
    used for example to create macro names that start with a dot emulating
    control directives of other assemblers. Note however, that none of the
    reserved keywords built into the assembler, that starts with a dot, may be
    overridden. When using this feature, you may also get into trouble if
    later versions of the assembler define new keywords starting with a dot.

  <tag><tt>pc_assignment</tt></tag>

    Allow assignments to the PC symbol (`*' or `&dollar;' if <tt/dollar_is_pc/
    is enabled). Such an assignment is handled identical to the <tt><ref
    id=".ORG" name=".ORG"></tt> command (which is usually not needed, so just
    removing the lines with the assignments may also be an option when porting
    code written for older assemblers).

  </descrip>

  It is also possible to specify features on the command line using the
  <tt><ref id="option--feature" name="--feature"></tt> command line option.
  This is useful when translating sources written for older assemblers, when
  you don't want to change the source code.

  As an example, to translate sources written for Andre Fachats xa65
  assembler, the features

  <verb>
        labels_without_colons, pc_assignment, loose_char_term
  </verb>

  may be helpful. They do not make ca65 completely compatible, so you may not
  be able to translate the sources without changes, even when enabling these
  features. However, I have found several sources that translate without
  problems when enabling these features on the command line.


<sect1><tt>.FILEOPT, .FOPT</tt><label id=".FOPT"><p>

  Insert an option string into the object file. There are two forms of
  this command, one specifies the option by a keyword, the second
  specifies it as a number. Since usage of the second one needs knowledge
  of the internal encoding, its use is not recommended and I will only
  describe the first form here.

  The command is followed by one of the keywords

  <tscreen><verb>
        author
        comment
        compiler
  </verb></tscreen>

  a comma and a string. The option is written into the object file
  together with the string value. This is currently unidirectional and
  there is no way to actually use these options once they are in the
  object file.

  Examples:

  <tscreen><verb>
        .fileopt        comment, "Code stolen from my brother"
        .fileopt        compiler, "BASIC 2.0"
        .fopt           author, "J. R. User"
  </verb></tscreen>


<sect1><tt>.FORCEIMPORT</tt><label id=".FORCEIMPORT"><p>

  Import an absolute symbol from another module. The command is followed by a
  comma separated list of symbols to import. The command is similar to <tt>
  <ref id=".IMPORT" name=".IMPORT"></tt>, but the import reference is always
  written to the generated object file, even if the symbol is never referenced
  (<tt><ref id=".IMPORT" name=".IMPORT"></tt> will not generate import
  references for unused symbols).

  Example:

  <tscreen><verb>
        .forceimport    needthisone, needthistoo
  </verb></tscreen>

  See: <tt><ref id=".IMPORT" name=".IMPORT"></tt>


<sect1><tt>.GLOBAL</tt><label id=".GLOBAL"><p>

  Declare symbols as global. Must be followed by a comma separated list of
  symbols to declare. Symbols from the list, that are defined somewhere in the
  source, are exported, all others are imported. Additional <tt><ref
  id=".IMPORT" name=".IMPORT"></tt> or <tt><ref id=".EXPORT"
  name=".EXPORT"></tt> commands for the same symbol are allowed.

  Example:

  <tscreen><verb>
        .global foo, bar
  </verb></tscreen>


<sect1><tt>.GLOBALZP</tt><label id=".GLOBALZP"><p>

  Declare symbols as global. Must be followed by a comma separated list of
  symbols to declare. Symbols from the list, that are defined somewhere in the
  source, are exported, all others are imported. Additional <tt><ref
  id=".IMPORTZP" name=".IMPORTZP"></tt> or <tt><ref id=".EXPORTZP"
  name=".EXPORTZP"></tt> commands for the same symbol are allowed. The symbols
  in the list are explicitly marked as zero page symols.

  Example:

  <tscreen><verb>
        .globalzp foo, bar
  </verb></tscreen>


<sect1><tt>.I16</tt><label id=".I16"><p>

  Valid only in 65816 mode. Switch the index registers to 16 bit.

  Note: This command will not emit any code, it will tell the assembler to
  create 16 bit operands for immediate operands.

  See also the <tt><ref id=".I8" name=".I8"></tt> and <tt><ref id=".SMART"
  name=".SMART"></tt> commands.


<sect1><tt>.I8</tt><label id=".I8"><p>

  Valid only in 65816 mode. Switch the index registers to 8 bit.

  Note: This command will not emit any code, it will tell the assembler to
  create 8 bit operands for immediate operands.

  See also the <tt><ref id=".I16" name=".I16"></tt> and <tt><ref id=".SMART"
  name=".SMART"></tt> commands.


<sect1><tt>.IF</tt><label id=".IF"><p>

  Conditional assembly: Evalute an expression and switch assembler output
  on or off depending on the expression. The expression must be a constant
  expression, that is, all operands must be defined.

  A expression value of zero evaluates to FALSE, any other value evaluates
  to TRUE.


<sect1><tt>.IFBLANK</tt><label id=".IFBLANK"><p>

  Conditional assembly: Check if there are any remaining tokens in this line,
  and evaluate to FALSE if this is the case, and to TRUE otherwise. If the
  condition is not true, further lines are not assembled until an <tt><ref
  id=".ELSE" name=".ESLE"></tt>, <tt><ref id=".ELSEIF" name=".ELSEIF"></tt> or
  <tt><ref id=".ENDIF" name=".ENDIF"></tt> directive.

  This command is often used to check if a macro parameter was given. Since an
  empty macro parameter will evaluate to nothing, the condition will evaluate
  to FALSE if an empty parameter was given.

  Example:

  <tscreen><verb>
        .macro     arg1, arg2
        .ifblank   arg2
                   lda     #arg1
        .else
                   lda     #arg2
        .endif
        .endmacro
  </verb></tscreen>

  See also: <tt><ref id=".BLANK" name=".BLANK"></tt>


<sect1><tt>.IFCONST</tt><label id=".IFCONST"><p>

  Conditional assembly: Evaluate an expression and switch assembler output
  on or off depending on the constness of the expression.

  A const expression evaluates to to TRUE, a non const expression (one
  containing an imported or currently undefined symbol) evaluates to
  FALSE.

  See also: <tt><ref id=".CONST" name=".CONST"></tt>


<sect1><tt>.IFDEF</tt><label id=".IFDEF"><p>

  Conditional assembly: Check if a symbol is defined. Must be followed by
  a symbol name. The condition is true if the the given symbol is already
  defined, and false otherwise.

  See also: <tt><ref id=".DEFINED" name=".DEFINED"></tt>


<sect1><tt>.IFNBLANK</tt><label id=".IFNBLANK"><p>

  Conditional assembly: Check if there are any remaining tokens in this line,
  and evaluate to TRUE if this is the case, and to FALSE otherwise. If the
  condition is not true, further lines are not assembled until an <tt><ref
  id=".ELSE" name=".ELSE"></tt>, <tt><ref id=".ELSEIF" name=".ELSEIF"></tt> or
  <tt><ref id=".ENDIF" name=".ENDIF"></tt> directive.

  This command is often used to check if a macro parameter was given.
  Since an empty macro parameter will evaluate to nothing, the condition
  will evaluate to FALSE if an empty parameter was given.

  Example:

  <tscreen><verb>
        .macro     arg1, arg2
                   lda     #arg1
        .ifnblank  arg2
                   lda     #arg2
        .endif
        .endmacro
  </verb></tscreen>

  See also: <tt><ref id=".BLANK" name=".BLANK"></tt>


<sect1><tt>.IFNDEF</tt><label id=".IFNDEF"><p>

  Conditional assembly: Check if a symbol is defined. Must be followed by
  a symbol name. The condition is true if the the given symbol is not
  defined, and false otherwise.

  See also: <tt><ref id=".DEFINED" name=".DEFINED"></tt>


<sect1><tt>.IFNREF</tt><label id=".IFNREF"><p>

  Conditional assembly: Check if a symbol is referenced. Must be followed
  by a symbol name. The condition is true if if the the given symbol was
  not referenced before, and false otherwise.

  See also: <tt><ref id=".REFERENCED" name=".REFERENCED"></tt>


<sect1><tt>.IFP02</tt><label id=".IFP02"><p>

  Conditional assembly: Check if the assembler is currently in 6502 mode
  (see <tt><ref id=".P02" name=".P02"></tt> command).


<sect1><tt>.IFP816</tt><label id=".IFP816"><p>

  Conditional assembly: Check if the assembler is currently in 65816 mode
  (see <tt><ref id=".P816" name=".P816"></tt> command).


<sect1><tt>.IFPC02</tt><label id=".IFPC02"><p>

  Conditional assembly: Check if the assembler is currently in 65C02 mode
  (see <tt><ref id=".PC02" name=".PC02"></tt> command).


<sect1><tt>.IFPSC02</tt><label id=".IFPSC02"><p>

  Conditional assembly: Check if the assembler is currently in 65SC02 mode
  (see <tt><ref id=".PSC02" name=".PSC02"></tt> command).


<sect1><tt>.IFREF</tt><label id=".IFREF"><p>

  Conditional assembly: Check if a symbol is referenced. Must be followed
  by a symbol name. The condition is true if if the the given symbol was
  referenced before, and false otherwise.

  This command may be used to build subroutine libraries in include files
  (you may use separate object modules for this purpose too).

  Example:

  <tscreen><verb>
        .ifref  ToHex                   ; If someone used this subroutine
        ToHex:  tay                     ; Define subroutine
                lda     HexTab,y
                rts
        .endif
  </verb></tscreen>

  See also: <tt><ref id=".REFERENCED" name=".REFERENCED"></tt>


<sect1><tt>.IMPORT</tt><label id=".IMPORT"><p>

  Import a symbol from another module. The command is followed by a comma
  separated list of symbols to import.

  Example:

  <tscreen><verb>
        .import foo, bar
  </verb></tscreen>

  See: <tt><ref id=".IMPORTZP" name=".IMPORTZP"></tt>


<sect1><tt>.IMPORTZP</tt><label id=".IMPORTZP"><p>

  Import a symbol from another module. The command is followed by a comma
  separated list of symbols to import. The symbols are explicitly imported
  as zero page symbols (that is, symbols with values in byte range).

  Example:

  <tscreen><verb>
        .importzp       foo, bar
  </verb></tscreen>

  See: <tt><ref id=".IMPORT" name=".IMPORT"></tt>


<sect1><tt>.INCBIN</tt><label id=".INCBIN"><p>

  Include a file as binary data. The command expects a string argument
  that is the name of a file to include literally in the current segment.
  In addition to that, a start offset and a size value may be specified,
  separated by commas. If no size is specified, all of the file from the
  start offset to end-of-file is used. If no start position is specified
  either, zero is assume (which means that the whole file is inserted).

  Example:

  <tscreen><verb>
        ; Include whole file
        .incbin         "sprites.dat"

        ; Include file starting at offset 256
        .incbin         "music.dat", $100

        ; Read 100 bytes starting at offset 200
        .incbin         "graphics.dat", 200, 100
  </verb></tscreen>


<sect1><tt>.INCLUDE</tt><label id=".INCLUDE"><p>

  Include another file. Include files may be nested up to a depth of 16.

  Example:

  <tscreen><verb>
        .include        "subs.inc"
  </verb></tscreen>


<sect1><tt>.LEFT</tt><label id=".LEFT"><p>

  Builtin function. Extracts the left part of a given token list.

  Syntax:

  <tscreen><verb>
        .LEFT (&lt;int expr&gt;, &lt;token list&gt;)
  </verb></tscreen>

  The first integer expression gives the number of tokens to extract from
  the token list. The second argument is the token list itself.

  Example:

  To check in a macro if the given argument has a '#' as first token
  (immidiate addressing mode), use something like this:

  <tscreen><verb>
        .macro  ldax    arg
                ...
                .if (.match (.left (1, arg), #))

                ; ldax called with immidiate operand
                ...

                .endif
                ...
        .endmacro
  </verb></tscreen>

  See also the <tt><ref id=".MID" name=".MID"></tt> and <tt><ref id=".RIGHT"
  name=".RIGHT"></tt> builtin functions.


<sect1><tt>.LINECONT</tt><label id=".LINECONT"><p>

  Switch on or off line continuations using the backslash character
  before a newline. The option is off by default.
  Note: Line continuations do not work in a comment. A backslash at the
  end of a comment is treated as part of the comment and does not trigger
  line continuation.
  The command must be followed by a '+' or '-' character to switch the
  option on or off respectively.

  Example:

  <tscreen><verb>
        .linecont       +               ; Allow line continuations

        lda     \
                #$20                    ; This is legal now
  </verb></tscreen>


<sect1><tt>.LIST</tt><label id=".LIST"><p>

  Enable output to the listing. The command must be followed by a boolean
  switch ("on", "off", "+" or "-") and will enable or disable listing
  output.
  The option has no effect if the listing is not enabled by the command line
  switch -l. If -l is used, an internal counter is set to 1. Lines are output
  to the listing file, if the counter is greater than zero, and suppressed if
  the counter is zero. Each use of <tt/.LIST/ will increment or decrement the
  counter.

  Example:

  <tscreen><verb>
        .list   on              ; Enable listing output
  </verb></tscreen>


<sect1><tt>.LISTBYTES</tt><label id=".LISTBYTES"><p>

  Set, how many bytes are shown in the listing for one source line. The
  default is 12, so the listing will show only the first 12 bytes for any
  source line that generates more than 12 bytes of code or data.
  The directive needs an argument, which is either "unlimited", or an
  integer constant in the range 4..255.

  Examples:

  <tscreen><verb>
        .listbytes      unlimited       ; List all bytes
        .listbytes      12              ; List the first 12 bytes
        .incbin         "data.bin"      ; Include large binary file
  </verb></tscreen>


<sect1><tt>.LOCAL</tt><label id=".LOCAL"><p>

  This command may only be used inside a macro definition. It declares a
  list of identifiers as local to the macro expansion.

  A problem when using macros are labels: Since they don't change their name,
  you get a "duplicate symbol" error if the macro is expanded the second time.
  Labels declared with <tt><ref id=".LOCAL" name=".LOCAL"></tt> have their
  name mapped to an internal unique name (<tt/___ABCD__/) with each macro
  invocation.

  Some other assemblers start a new lexical block inside a macro expansion.
  This has some drawbacks however, since that will not allow <em/any/ symbol
  to be visible outside a macro, a feature that is sometimes useful. The
  <tt><ref id=".LOCAL" name=".LOCAL"></tt> command is in my eyes a better way
  to address the problem.

  You get an error when using <tt><ref id=".LOCAL" name=".LOCAL"></tt> outside
  a macro.


<sect1><tt>.LOCALCHAR</tt><label id=".LOCALCHAR"><p>

  Defines the character that start "cheap" local labels. You may use one
  of '@' and '?' as start character. The default is '@'.

  Cheap local labels are labels that are visible only between two non
  cheap labels. This way you can reuse identifiers like "<tt/loop/" without
  using explicit lexical nesting.

  Example:

  <tscreen><verb>
        .localchar      '?'

        Clear:  lda     #$00            ; Global label
        ?Loop:  sta     Mem,y           ; Local label
                dey
                bne     ?Loop           ; Ok
                rts
        Sub:    ...                     ; New global label
                bne     ?Loop           ; ERROR: Unknown identifier!
  </verb></tscreen>


<sect1><tt>.MACPACK</tt><label id=".MACPACK"><p>

  Insert a predefined macro package. The command is followed by an
  identifier specifying the macro package to insert. Available macro
  packages are:

  <tscreen><verb>
        generic         Defines generic macros like add and sub.
        longbranch      Defines conditional long jump macros.
  </verb></tscreen>

  Including a macro package twice, or including a macro package that
  redefines already existing macros will lead to an error.

  Example:

  <tscreen><verb>
        .macpack        longbranch      ; Include macro package

                cmp     #$20            ; Set condition codes
                jne     Label           ; Jump long on condition
  </verb></tscreen>

  Macro packages are explained in more detail in section <ref
  id="macropackages" name="Macro packages">.


<sect1><tt>.MAC, .MACRO</tt><label id=".MAC"><p>

  Start a classic macro definition. The command is followed by an identifier
  (the macro name) and optionally by a comma separated list of identifiers
  that are macro parameters.

  See section <ref id="macros" name="Macros">.


<sect1><tt>.MATCH</tt><label id=".MATCH"><p>

  Builtin function. Matches two token lists against each other. This is
  most useful within macros, since macros are not stored as strings, but
  as lists of tokens.

  The syntax is

  <tscreen><verb>
        .MATCH(&lt;token list #1&gt;, &lt;token list #2&gt;)
  </verb></tscreen>

  Both token list may contain arbitrary tokens with the exception of the
  terminator token (comma resp. right parenthesis) and

  <itemize>
  <item>end-of-line
  <item>end-of-file
  </itemize>

  Often a macro parameter is used for any of the token lists.

  Please note that the function does only compare tokens, not token
  attributes. So any number is equal to any other number, regardless of the
  actual value. The same is true for strings. If you need to compare tokens
  <em/and/ token attributes, use the <tt><ref id=".XMATCH"
  name=".XMATCH"></tt> function.

  Example:

  Assume the macro <tt/ASR/, that will shift right the accumulator by one,
  while honoring the sign bit. The builtin processor instructions will allow
  an optional "A" for accu addressing for instructions like <tt/ROL/ and
  <tt/ROR/. We will use the <tt><ref id=".MATCH" name=".MATCH"></tt> function
  to check for this and print and error for invalid calls.

  <tscreen><verb>
        .macro  asr     arg

                .if (.not .blank(arg)) .and (.not .match (arg, a))
                .error "Syntax error"
                .endif

                cmp     #$80            ; Bit 7 into carry
                lsr     a               ; Shift carry into bit 7

        .endmacro
  </verb></tscreen>

  The macro will only accept no arguments, or one argument that must be the
  reserved keyword "A".

  See: <tt><ref id=".XMATCH" name=".XMATCH"></tt>


<sect1><tt>.MID</tt><label id=".MID"><p>

  Builtin function. Takes a starting index, a count and a token list as
  arguments. Will return part of the token list.

  Syntax:

  <tscreen><verb>
        .MID (&lt;int expr&gt;, &lt;int expr&gt;, &lt;token list&gt;)
  </verb></tscreen>

  The first integer expression gives the starting token in the list (the
  first token has index 0). The second integer expression gives the number
  of tokens to extract from the token list. The third argument is the
  token list itself.

  Example:

  To check in a macro if the given argument has a '<tt/#/' as first token
  (immidiate addressing mode), use something like this:

    <tscreen><verb>
        .macro  ldax    arg
                ...
                .if (.match (.mid (0, 1, arg), #))

                ; ldax called with immidiate operand
                ...

                .endif
                ...
        .endmacro
  </verb></tscreen>

  See also the <tt><ref id=".LEFT" name=".LEFT"></tt> and <tt><ref id=".RIGHT"
  name=".RIGHT"></tt> builtin functions.


<sect1><tt>.ORG</tt><label id=".ORG"><p>

  Start a section of absolute code. The command is followed by a constant
  expression that gives the new PC counter location for which the code is
  assembled. Use <tt><ref id=".RELOC" name=".RELOC"></tt> to switch back to
  relocatable code.

  Please note that you <em/do not need/ this command in most cases. Placing
  code at a specific address is the job of the linker, not the assembler, so
  there is usually no reason to assemble code to a specific address.

  You may not switch segments while inside a section of absolute code.

  Example:

  <tscreen><verb>
        .org    $7FF            ; Emit code starting at $7FF
  </verb></tscreen>


<sect1><tt>.OUT</tt><label id=".OUT"><p>

  Output a string to the console without producing an error. This command
  is similiar to <tt/.ERROR/, however, it does not force an assembler error
  that prevents the creation of an object file.

  Example:

  <tscreen><verb>
        .out    "This code was written by the codebuster(tm)"
  </verb></tscreen>

  See also the <tt><ref id=".WARNING" name=".WARNING"></tt> and <tt><ref
  id=".ERROR" name=".ERROR"></tt> directives.


<sect1><tt>.P02</tt><label id=".P02"><p>

  Enable the 6502 instruction set, disable 65SC02, 65C02 and 65816
  instructions. This is the default if not overridden by the
  <tt><ref id="option--cpu" name="--cpu"></tt> command line option.

  See: <tt><ref id=".PC02" name=".PC02"></tt>, <tt><ref id=".PSC02"
  name=".PSC02"></tt> and <tt><ref id=".P816" name=".P816"></tt>


<sect1><tt>.P816</tt><label id=".P816"><p>

  Enable the 65816 instruction set. This is a superset of the 65SC02 and
  6502 instruction sets.

  See: <tt><ref id=".P02" name=".P02"></tt>, <tt><ref id=".PSC02"
  name=".PSC02"></tt> and <tt><ref id=".PC02" name=".PC02"></tt>


<sect1><tt>.PAGELEN, .PAGELENGTH</tt><label id=".PAGELENGTH"><p>

  Set the page length for the listing. Must be followed by an integer
  constant. The value may be "unlimited", or in the range 32 to 127. The
  statement has no effect if no listing is generated. The default value is -1
  (unlimited) but may be overridden by the <tt/--pagelength/ command line
  option. Beware: Since ca65 is a one pass assembler, the listing is generated
  after assembly is complete, you cannot use multiple line lengths with one
  source. Instead, the value set with the last <tt/.PAGELENGTH/ is used.

  Examples:

  <tscreen><verb>
        .pagelength     66              ; Use 66 lines per listing page

        .pagelength     unlimited       ; Unlimited page length
  </verb></tscreen>


<sect1><tt>.PARAMCOUNT</tt><label id=".PARAMCOUNT"><p>

  This builtin pseudo variable is only available in macros. It is replaced by
  the actual number of parameters that were given in the macro invocation.

  Example:

  <tscreen><verb>
        .macro  foo     arg1, arg2, arg3
        .if     .paramcount <> 3
        .error  "Too few parameters for macro foo"
        .endif
        ...
        .endmacro
  </verb></tscreen>

  See section <ref id="macros" name="Macros">.


<sect1><tt>.PC02</tt><label id=".PC02"><p>

  Enable the 65C02 instructions set. This instruction set includes all
  6502 and 65SC02 instructions.

  See: <tt><ref id=".P02" name=".P02"></tt>, <tt><ref id=".PSC02"
  name=".PSC02"></tt> and <tt><ref id=".P816" name=".P816"></tt>


<sect1><tt>.POPSEG</tt><label id=".POPSEG"><p>

  Pop the last pushed segment from the stack, and set it.

  This command will switch back to the segment that was last pushed onto the
  segment stack using the <tt><ref id=".PUSHSEG" name=".PUSHSEG"></tt>
  command, and remove this entry from the stack.

  The assembler will print an error message if the segment stack is empty
  when this command is issued.

  See: <tt><ref id=".PUSHSEG" name=".PUSHSEG"></tt>


<sect1><tt>.PROC</tt><label id=".PROC"><p>

  Start a nested lexical level. All new symbols from now on are in the local
  lexical level and are not accessible from outside. Symbols defined outside
  this local level may be accessed as long as their names are not used for new
  symbols inside the level. Symbols names in other lexical levels do not
  clash, so you may use the same names for identifiers. The lexical level ends
  when the <tt><ref id=".ENDPROC" name=".ENDPROC"></tt> command is read.
  Lexical levels may be nested up to a depth of 16.

  The command may be followed by an identifier, in this case the
  identifier is declared in the outer level as a label having the value of
  the program counter at the start of the lexical level.

  Note: Macro names are always in the global level and in a separate name
  space. There is no special reason for this, it's just that I've never
  had any need for local macro definitions.

  Example:

  <tscreen><verb>
        .proc   Clear           ; Define Clear subroutine, start new level
                lda     #$00
        L1:     sta     Mem,y   ; L1 is local and does not cause a
                                ; duplicate symbol error if used in other
                                ; places
                dey
                bne     L1      ; Reference local symbol
                rts
        .endproc                ; Leave lexical level
  </verb></tscreen>

  See: <tt><ref id=".ENDPROC" name=".ENDPROC"></tt>


<sect1><tt>.PSC02</tt><label id=".PSC02"><p>

  Enable the 65SC02 instructions set. This instruction set includes all
  6502 instructions.

  See: <tt><ref id=".P02" name=".P02"></tt>, <tt><ref id=".PC02"
  name=".PC02"></tt> and <tt><ref id=".P816" name=".P816"></tt>


<sect1><tt>.PUSHSEG</tt><label id=".PUSHSEG"><p>

  Push the currently active segment onto a stack. The entries on the stack
  include the name of the segment and the segment type. The stack has a size
  of 16 entries.

  <tt/.PUSHSEG/ allows together with <tt><ref id=".POPSEG" name=".POPSEG"></tt>
  to switch to another segment and to restore the old segment later, without
  even knowing the name and type of the current segment.

  The assembler will print an error message if the segment stack is already
  full, when this command is issued.

  See: <tt><ref id=".POPSEG" name=".POPSEG"></tt>


<sect1><tt>.REF, .REFERENCED</tt><label id=".REFERENCED"><p>

  Builtin function. The function expects an identifier as argument in braces.
  The argument is evaluated, and the function yields "true" if the identifier
  is a symbol that has already been referenced somewhere in the source file up
  to the current position. Otherwise the function yields false. As an example,
  the <tt><ref id=".IFREF" name=".IFREF"></tt> statement may be replaced by

  <tscreen><verb>
        .if     .referenced(a)
  </verb></tscreen>

  See: <tt><ref id=".DEFINED" name=".DEFINED"></tt>


<sect1><tt>.REPEAT</tt><label id=".REPEAT"><p>

  Repeat all commands between <tt/.REPEAT/ and <tt><ref id=".ENDREPEAT"
  name=".ENDREPEAT"></tt> constant number of times. The command is followed by
  a constant expression that tells how many times the commands in the body
  should get repeated. Optionally, a comma and an identifier may be specified.
  If this identifier is found in the body of the repeat statement, it is
  replaced by the current repeat count (starting with zero for the first time
  the body is repeated).

  <tt/.REPEAT/ statements may be nested. If you use the same repeat count
  identifier for a nested <tt/.REPEAT/ statement, the one from the inner
  level will be used, not the one from the outer level.

  Example:

  The following macro will emit a string that is "encrypted" in that all
  characters of the string are XORed by the value $55.

  <tscreen><verb>
        .macro  Crypt   Arg
                .repeat .strlen(Arg), I
                .byte   .strat(Arg, I) .xor $55
                .endrep
        .endmacro
  </verb></tscreen>

  See: <tt><ref id=".ENDREPEAT" name=".ENDREPEAT"></tt>


<sect1><tt>.RELOC</tt><label id=".RELOC"><p>

  Switch back to relocatable mode. See the <tt><ref id=".ORG"
  name=".ORG"></tt> command.


<sect1><tt>.RES</tt><label id=".RES"><p>

  Reserve storage. The command is followed by one or two constant
  expressions. The first one is mandatory and defines, how many bytes of
  storage should be defined. The second, optional expression must by a
  constant byte value that will be used as value of the data. If there
  is no fill value given, the linker will use the value defined in the
  linker configuration file (default: zero).

  Example:

  <tscreen><verb>
        ; Reserve 12 bytes of memory with value $AA
        .res    12, $AA
  </verb></tscreen>


<sect1><tt>.RIGHT</tt><label id=".RIGHT"><p>

  Builtin function. Extracts the right part of a given token list.

  Syntax:

  <tscreen><verb>
        .RIGHT (&lt;int expr&gt;, &lt;token list&gt;)
  </verb></tscreen>

  The first integer expression gives the number of tokens to extract from
  the token list. The second argument is the token list itself.

  See also the <tt><ref id=".LEFT" name=".LEFT"></tt> and <tt><ref id=".MID"
  name=".MID"></tt> builtin functions.


<sect1><tt>.RODATA</tt><label id=".RODATA"><p>

  Switch to the RODATA segment. The name of the RODATA segment is always
  "RODATA", so this is a shortcut for

  <tscreen><verb>
        .segment  "RODATA"
  </verb></tscreen>

  The RODATA segment is a segment that is used by the compiler for
  readonly data like string constants.

  See also the <tt><ref id=".SEGMENT" name=".SEGMENT"></tt> command.


<sect1><tt>.SEGMENT</tt><label id=".SEGMENT"><p>

  Switch to another segment. Code and data is always emitted into a
  segment, that is, a named section of data. The default segment is
  "CODE". There may be up to 254 different segments per object file
  (and up to 65534 per executable). There are shortcut commands for
  the most common segments ("CODE", "DATA" and "BSS").

  The command is followed by a string containing the segment name (there
  are some constraints for the name - as a rule of thumb use only those
  segment names that would also be valid identifiers). There may also be
  an optional attribute separated by a comma. Valid attributes are
  "<tt/zeropage/" and "<tt/absolute/".

  When specifying a segment for the first time, "absolute" is the
  default. For all other uses, the attribute specified the first time
  is the default.

  "absolute" means that this is a segment with absolute addressing. That
  is, the segment will reside somewhere in core memory outside the zero
  page. "zeropage" means the opposite: The segment will be placed in the
  zero page and direct (short) addressing is possible for data in this
  segment.

  Beware: Only labels in a segment with the zeropage attribute are marked
  as reachable by short addressing. The `*' (PC counter) operator will
  work as in other segments and will create absolute variable values.

  Example:

  <tscreen><verb>
        .segment "ROM2"                 ; Switch to ROM2 segment
        .segment "ZP2", zeropage        ; New direct segment
        .segment "ZP2"                  ; Ok, will use last attribute
        .segment "ZP2", absolute        ; Error, redecl mismatch
  </verb></tscreen>

  See: <tt><ref id=".BSS" name=".BSS"></tt>, <tt><ref id=".CODE"
  name=".CODE"></tt>, <tt><ref id=".DATA" name=".DATA"></tt> and <tt><ref
  id=".RODATA" name=".RODATA"></tt>


<sect1><tt>.SETCPU</tt><label id=".SETCPU"><p>

  Switch the CPU instruction set. The command is followed by a string that
  specifies the CPU. Possible values are those that can also be supplied to
  the <tt><ref id="option--cpu" name="--cpu"></tt> command line option,
  namely: 6502, 65SC02, 65C02, 65816 and sunplus. Please note that support
  for the sunplus CPU is not available in the freeware version, because the
  instruction set of the sunplus CPU is "proprietary and confidential".

  See: <tt><ref id=".CPU" name=".CPU"></tt>,
       <tt><ref id=".IFP02" name=".IFP02"></tt>,
       <tt><ref id=".IFP816" name=".IFP816"></tt>,
       <tt><ref id=".IFPC02" name=".IFPC02"></tt>,
       <tt><ref id=".IFPSC02" name=".IFPSC02"></tt>,
       <tt><ref id=".P02" name=".P02"></tt>,
       <tt><ref id=".P816" name=".P816"></tt>,
       <tt><ref id=".PC02" name=".PC02"></tt>,
       <tt><ref id=".PSC02" name=".PSC02"></tt>


<sect1><tt>.SMART</tt><label id=".SMART"><p>

  Switch on or off smart mode. The command must be followed by a '+' or
  '-' character to switch the option on or off respectively. The default
  is off (that is, the assembler doesn't try to be smart), but this
  default may be changed by the -s switch on the command line.

  In smart mode the assembler will track usage of the <tt/REP/ and <tt/SEP/
  instructions in 65816 mode and update the operand sizes accordingly. If
  the operand of such an instruction cannot be evaluated by the assembler
  (for example, because the operand is an imported symbol), a warning is
  issued. Beware: Since the assembler cannot trace the execution flow this
  may lead to false results in some cases. If in doubt, use the <tt/.Inn/ and
  <tt/.Ann/ instructions to tell the assembler about the current settings.

  Example:

  <tscreen><verb>
        .smart                          ; Be smart
        .smart  -                       ; Stop being smart
  </verb></tscreen>


<sect1><tt>.STRAT</tt><label id=".STRAT"><p>

  Builtin function. The function accepts a string and an index as
  arguments and returns the value of the character at the given position
  as an integer value. The index is zero based.

  Example:

  <tscreen><verb>
        .macro  M       Arg
                ; Check if the argument string starts with '#'
                .if (.strat (Arg, 0) = '#')
                ...
                .endif
        .endmacro
  </verb></tscreen>


<sect1><tt>.STRING</tt><label id=".STRING"><p>

  Builtin function. The function accepts an argument in braces and converts
  this argument into a string constant. The argument may be an identifier, or
  a constant numeric value.

  Since you can use a string in the first place, the use of the function may
  not be obvious. However, it is useful in macros, or more complex setups.

  Example:

  <tscreen><verb>
        ; Emulate other assemblers:
        .macro  section name
                .segment        .string(name)
        .endmacro
  </verb></tscreen>


<sect1><tt>.STRLEN</tt><label id=".STRLEN"><p>

  Builtin function. The function accepts a string argument in braces and
  eveluates to the length of the string.

  Example:

  The following macro encodes a string as a pascal style string with
  a leading length byte.

  <tscreen><verb>
        .macro  PString Arg
                .byte   .strlen(Arg), Arg
        .endmacro
  </verb></tscreen>


<sect1><tt>.SUNPLUS</tt><label id=".SUNPLUS"><p>

  Enable the SunPlus instructions set. This command will not work in the
  freeware version of the assembler, because the instruction set is
  "proprietary and confidential".

  See: <tt><ref id=".P02" name=".P02"></tt>, <tt><ref id=".PSC02"
  name=".PSC02"></tt>, <tt><ref id=".PC02" name=".PC02"></tt>, and 
  <tt><ref id=".P816" name=".P816"></tt>


<sect1><tt>.TCOUNT</tt><label id=".TCOUNT"><p>

  Builtin function. The function accepts a token list in braces. The
  function result is the number of tokens given as argument.

  Example:

  The <tt/ldax/ macro accepts the '#' token to denote immidiate addressing (as
  with the normal 6502 instructions). To translate it into two separate 8 bit
  load instructions, the '#' token has to get stripped from the argument:

  <tscreen><verb>
        .macro  ldax    arg
                .if (.match (.mid (0, 1, arg), #))
                ; ldax called with immidiate operand
                lda     #<(.right (.tcount (arg)-1, arg))
                ldx     #>(.right (.tcount (arg)-1, arg))
                .else
                ...
                .endif
        .endmacro
  </verb></tscreen>


<sect1><tt>.TIME</tt><label id=".TIME"><p>

  Reading this pseudo variable will give a constant integer value that
  represents the current time in POSIX standard (as seconds since the
  Epoch).

  It may be used to encode the time of translation somewhere in the created
  code.

  Example:

  <tscreen><verb>
        .dword  .time   ; Place time here
  </verb></tscreen>


<sect1><tt>.WARNING</tt><label id=".WARNING"><p>

  Force an assembly warning. The assembler will output a warning message
  preceeded by "User warning". This warning will always be output, even if
  other warnings are disabled with the <tt><ref id="option-W" name="-W0"></tt>
  command line option.

  This command may be used to output possible problems when assembling
  the source file.

  Example:

  <tscreen><verb>
        .macro  jne     target
                .local L1
                .ifndef target
                .warning "Forward jump in jne, cannot optimize!"
                beq     L1
                jmp     target
        L1:
                .else
                ...
                .endif
        .endmacro
  </verb></tscreen>

  See also the <tt><ref id=".ERROR" name=".ERROR"></tt> and <tt><ref id=".OUT"
  name=".OUT"></tt> directives.


<sect1><tt>.WORD</tt><label id=".WORD"><p>

  Define word sized data. Must be followed by a sequence of (word ranged,
  but not necessarily constant) expressions.

  Example:

  <tscreen><verb>
        .word   $0D00, $AF13, _Clear
  </verb></tscreen>


<sect1><tt>.XMATCH</tt><label id=".XMATCH"><p>

  Builtin function. Matches two token lists against each other. This is
  most useful within macros, since macros are not stored as strings, but
  as lists of tokens.

  The syntax is

  <tscreen><verb>
        .XMATCH(&lt;token list #1&gt;, &lt;token list #2&gt;)
  </verb></tscreen>

  Both token list may contain arbitrary tokens with the exception of the
  terminator token (comma resp. right parenthesis) and

  <itemize>
  <item>end-of-line
  <item>end-of-file
  </itemize>

  Often a macro parameter is used for any of the token lists.

  The function compares tokens <em/and/ token values. If you need a function
  that just compares the type of tokens, have a look at the <tt><ref
  id=".MATCH" name=".MATCH"></tt> function.

  See: <tt><ref id=".MATCH" name=".MATCH"></tt>


<sect1><tt>.ZEROPAGE</tt><label id=".ZEROPAGE"><p>

  Switch to the ZEROPAGE segment and mark it as direct (zeropage) segment.
  The name of the ZEROPAGE segment is always "ZEROPAGE", so this is a
  shortcut for

  <tscreen><verb>
        .segment  "ZEROPAGE", zeropage
  </verb></tscreen>

  Because of the "zeropage" attribute, labels declared in this segment are
  addressed using direct addressing mode if possible. You <em/must/ instruct
  the linker to place this segment somewhere in the address range 0..$FF
  otherwise you will get errors.

  See: <tt><ref id=".SEGMENT" name=".SEGMENT"></tt>



<sect>Macros<label id="macros"><p>


<sect1>Introduction<p>

Macros may be thought of as "parametrized super instructions". Macros are
sequences of tokens that have a name. If that name is used in the source
file, the macro is "expanded", that is, it is replaced by the tokens that
were specified when the macro was defined.


<sect1>Macros without parameters<p>

In it's simplest form, a macro does not have parameters. Here's an
example:

<tscreen><verb>
        .macro  asr             ; Arithmetic shift right
                cmp     #$80    ; Put bit 7 into carry
                ror             ; Rotate right with carry
        .endmacro
</verb></tscreen>

The macro above consists of two real instructions, that are inserted into
the code, whenever the macro is expanded. Macro expansion is simply done
by using the name, like this:

<tscreen><verb>
        lda     $2010
        asr
        sta     $2010
</verb></tscreen>


<sect1>Parametrized macros<p>

When using macro parameters, macros can be even more useful:

<tscreen><verb>
        .macro  inc16   addr
                clc
                lda     addr
                adc     #$01
                sta     addr
                lda     addr+1
                adc     #$00
                sta     addr+1
        .endmacro
</verb></tscreen>

When calling the macro, you may give a parameter, and each occurence of
the name "addr" in the macro definition will be replaced by the given
parameter. So

<tscreen><verb>
        inc16   $1000
</verb></tscreen>

will be expanded to

<tscreen><verb>
                clc
                lda     $1000
                adc     #$01
                sta     $1000
                lda     $1000+1
                adc     #$00
                sta     $1000+1
</verb></tscreen>

A macro may have more than one parameter, in this case, the parameters
are separated by commas. You are free to give less parameters than the
macro actually takes in the definition. You may also leave intermediate
parameters empty. Empty parameters are replaced by empty space (that is,
they are removed when the macro is exanded). If you have a look at our
macro definition above, you will see, that replacing the "addr" parameter
by nothing will lead to wrong code in most lines. To help you, writing
macros with a variable parameter list, there are some control commands:

<tt><ref id=".IFBLANK" name=".IFBLANK"></tt> tests the rest of the line and
returns true, if there are any tokens on the remainder of the line. Since
empty parameters are replaced by nothing, this may be used to test if a given
parameter is empty. <tt><ref id=".IFNBLANK" name=".IFNBLANK"></tt> tests the
opposite.

Look at this example:

<tscreen><verb>
        .macro  ldaxy   a, x, y
        .ifnblank       a
                lda     #a
        .endif
        .ifnblank       x
                ldx     #x
        .endif
        .ifnblank       y
                ldy     #y
        .endif
        .endmacro
</verb></tscreen>

This macro may be called as follows:

<tscreen><verb>
        ldaxy   1, 2, 3         ; Load all three registers

        ldaxy   1, , 3          ; Load only a and y

        ldaxy   , , 3           ; Load y only
</verb></tscreen>

There's another helper command for determining, which macro parameters are
valid: <tt><ref id=".PARAMCOUNT" name=".PARAMCOUNT"></tt> This command is
replaced by the parameter count given, <em/including/ intermediate empty macro
parameters:

<tscreen><verb>
        ldaxy   1               ; .PARAMCOUNT = 1
        ldaxy   1,,3            ; .PARAMCOUNT = 3
        ldaxy   1,2             ; .PARAMCOUNT = 2
        ldaxy   1,              ; .PARAMCOUNT = 2
        ldaxy   1,2,3           ; .PARAMCOUNT = 3
</verb></tscreen>


<sect1>Recursive macros<p>

Macros may be used recursively:

<tscreen><verb>
        .macro  push    r1, r2, r3
                lda     r1
                pha
        .if     .paramcount > 1
                push    r2, r3
        .endif
        .endmacro
</verb></tscreen>

There's also a special macro to help writing recursive macros: <tt><ref
id=".EXITMACRO" name=".EXITMACRO"></tt> This command will stop macro expansion
immidiately:

<tscreen><verb>
        .macro  push    r1, r2, r3, r4, r5, r6, r7
        .ifblank        r1
                ; First parameter is empty
                .exitmacro
        .else
                lda     r1
                pha
        .endif
                push    r2, r3, r4, r5, r6, r7
        .endmacro
</verb></tscreen>

When expanding this macro, the expansion will push all given parameters
until an empty one is encountered. The macro may be called like this:

<tscreen><verb>
        push    $20, $21, $32           ; Push 3 ZP locations
        push    $21                     ; Push one ZP location
</verb></tscreen>


<sect1>Local symbols inside macros<p>

Now, with recursive macros, <tt><ref id=".IFBLANK" name=".IFBLANK"></tt> and
<tt><ref id=".PARAMCOUNT" name=".PARAMCOUNT"></tt>, what else do you need?
Have a look at the inc16 macro above. Here is it again:

<tscreen><verb>
        .macro  inc16   addr
                clc
                lda     addr
                adc     #$01
                sta     addr
                lda     addr+1
                adc     #$00
                sta     addr+1
        .endmacro
</verb></tscreen>

If you have a closer look at the code, you will notice, that it could be
written more efficiently, like this:

<tscreen><verb>
        .macro  inc16   addr
                inc     addr
                bne     Skip
                inc     addr+1
        Skip:
        .endmacro
</verb></tscreen>

But imagine what happens, if you use this macro twice? Since the label
"Skip" has the same name both times, you get a "duplicate symbol" error.
Without a way to circumvent this problem, macros are not as useful, as
they could be. One solution is, to start a new lexical block inside the
macro:

<tscreen><verb>
        .macro  inc16   addr
        .proc
                inc     addr
                bne     Skip
                inc     addr+1
        Skip:
        .endproc
        .endmacro
</verb></tscreen>

Now the label is local to the block and not visible outside. However,
sometimes you want a label inside the macro to be visible outside. To make
that possible, there's a new command that's only usable inside a macro
definition: <tt><ref id=".LOCAL" name=".LOCAL"></tt>. <tt/.LOCAL/ declares one
or more symbols as local to the macro expansion. The names of local variables
are replaced by a unique name in each separate macro expansion. So we could
also solve the problem above by using <tt/.LOCAL/:

<tscreen><verb>
        .macro  inc16   addr
                .local  Skip            ; Make Skip a local symbol
                clc
                lda     addr
                adc     #$01
                sta     addr
                bcc     Skip
                inc     addr+1
        Skip:                           ; Not visible outside
        .endmacro
</verb></tscreen>


<sect1>C style macros<p>

Starting with version 2.5 of the assembler, there is a second macro type
available: C style macros using the <tt/.DEFINE/ directive. These macros are
similar to the classic macro type described above, but behaviour is sometimes
different:

<itemize>

<item>  Macros defined with <tt><ref id=".DEFINE" name=".DEFINE"></tt> may not
        span more than a line. You may use line continuation (see <tt><ref
        id=".LINECONT" name=".LINECONT"></tt>) to spread the definition over
        more than one line for increased readability, but the macro itself
        may not contain an end-of-line token.

<item>  Macros defined with <tt><ref id=".DEFINE" name=".DEFINE"></tt> share
        the name space with classic macros, but they are detected and replaced
        at the scanner level. While classic macros may be used in every place,
        where a mnemonic or other directive is allowed, <tt><ref id=".DEFINE"
        name=".DEFINE"></tt> style macros are allowed anywhere in a line. So
        they are more versatile in some situations.

<item>  <tt><ref id=".DEFINE" name=".DEFINE"></tt> style macros may take
        parameters. While classic macros may have empty parameters, this is
        not true for <tt><ref id=".DEFINE" name=".DEFINE"></tt> style macros.
        For this macro type, the number of actual parameters must match
        exactly the number of formal parameters.

        To make this possible, formal parameters are enclosed in braces when
        defining the macro. If there are no parameters, the empty braces may
        be omitted.

<item>  Since <tt><ref id=".DEFINE" name=".DEFINE"></tt> style macros may not
        contain end-of-line tokens, there are things that cannot be done. They
        may not contain several processor instructions for example. So, while
        some things may be done with both macro types, each type has special
        usages. The types complement each other.

</itemize>

Let's look at a few examples to make the advantages and disadvantages
clear.

To emulate assemblers that use "<tt/EQU/" instead of "<tt/=/" you may use the
following <tt/.DEFINE/:

<tscreen><verb>
        .define EQU     =

        foo     EQU     $1234           ; This is accepted now
</verb></tscreen>

You may use the directive to define string constants used elsewhere:

<tscreen><verb>
        ; Define the version number
        .define VERSION         "12.3a"

        ; ... and use it
        .asciiz VERSION
</verb></tscreen>

Macros with parameters may also be useful:

<tscreen><verb>
        .define DEBUG(message)  .out    message

        DEBUG   "Assembling include file #3"
</verb></tscreen>

Note that, while formal parameters have to be placed in braces, this is
not true for the actual parameters. Beware: Since the assembler cannot
detect the end of one parameter, only the first token is used. If you
don't like that, use classic macros instead:

<tscreen><verb>
        .macro  message
                .out    message
        .endmacro
</verb></tscreen>

(This is an example where a problem can be solved with both macro types).


<sect1>Characters in macros<p>

When using the <ref id="option-t" name="-t"> option, characters are translated
into the target character set of the specific machine. However, this happens
as late as possible. This means that strings are translated if they are part
of a <tt><ref id=".BYTE" name=".BYTE"></tt> or <tt><ref id=".ASCIIZ"
name=".ASCIIZ"></tt> command. Characters are translated as soon as they are
used as part of an expression.

This behaviour is very intuitive outside of macros but may be confusing when
doing more complex macros. If you compare characters against numeric values,
be sure to take the translation into account.




<sect>Macro packages<label id="macropackages"><p>

Using the <tt><ref id=".MACPACK" name=".MACPACK"></tt> directive, predefined
macro packages may be included with just one command. Available macro packages
are:


<sect1><tt>.MACPACK generic</tt><p>

This macro package defines macros that are useful in almost any program.
Currently, two macros are defined:

<tscreen><verb>
        .macro  add     Arg
                clc
                adc     Arg
        .endmacro

        .macro  sub     Arg
                sec
                sbc     Arg
        .endmacro
</verb></tscreen>


<sect1><tt>.MACPACK longbranch</tt><p>

This macro package defines long conditional jumps. They are named like the
short counterpart but with the 'b' replaced by a 'j'. Here is a sample
definition for the "<tt/jeq/" macro, the other macros are built using the same
scheme:

<tscreen><verb>
        .macro  jeq     Target
                .if     .def(Target) .and ((*+2)-(Target) <= 127)
                beq     Target
                .else
                bne     *+5
                jmp     Target
                .endif
        .endmacro
</verb></tscreen>

All macros expand to a short branch, if the label is already defined (back
jump) and is reachable with a short jump. Otherwise the macro expands to a
conditional branch with the branch condition inverted, followed by an absolute
jump to the actual branch target.

The package defines the following macros:

<tscreen><verb>
        jeq, jne, jmi, jpl, jcs, jcc, jvs, jvc
</verb></tscreen>



<sect>Module constructors/destructors<label id="condes"><p>

<em>Note:</em> This section applies mostly to C programs, so the explanation
below uses examples from the C libraries. However, the feature may also be
useful for assembler programs.


<sect1>Module overview<p>

Using the <tt><ref id=".CONSTRUCTOR" name=".CONSTRUCTOR"></tt> and <tt><ref
id=".DESTRUCTOR" name=".DESTRUCTOR"></tt> keywords it it possible to export
functions in a special way. The linker is able to generate tables with all
functions of a specific type. Such a table will <em>only</em> include symbols
from object files that are linked into a specific executable. This may be used
to add initialization and cleanup code for library modules.

The C heap functions are an example where module initialization code is used.
All heap functions (<tt>malloc</tt>, <tt>free</tt>, ...) work with a few
variables that contain the start and the end of the heap, pointers to the free
list and so on. Since the end of the heap depends on the size and start of the
stack, it must be initialized at runtime. However, initializing these
variables for programs that do not use the heap are a waste of time and
memory.

So the central module defines a function that contains initialization code and
exports this function using the <tt/.CONSTRUCTOR/ statement. If (and only if)
this module is added to an executable by the linker, the initialization
function will be placed into the table of constructors by the linker. The C
startup code will call all constructors before <tt/main/ and all destructors
after <tt/main/, so without any further work, the heap initialization code is
called once the module is linked in.

While it would be possible to add explicit calls to initialization functions
in the startup code, the new approach has several advantages:

<enum>
<item>
If a module is not included, the initialization code is not linked in and not
called. So you don't pay for things you don't need.

<item>
Adding another library that needs initialization does not mean that the
startup code has to be changed. Before we had module constructors and
destructors, the startup code for all systems had to be adjusted to call the
new initialization code.

<item>
The feature saves memory: Each additional initialization function needs just
two bytes in the table (a pointer to the function).

</enum>


<sect1>Pitfalls<p>

When creating and using module constructors and destructors, please take care
of the following:

<itemize>

<item>
The linker will only generate function tables, it will not generate code to
call these functions. If you're using the feature in some other than the
existing C environments, you have to write code to call all functions in a
linker generated table yourself. See the <tt>condes</tt> module in the C
runtime for an example on how to do this.

<item>
The linker will only add addresses of functions that are in modules linked to
the executable. This means that you have to be careful where to place the
condes functions. If initialization is needed for a group of functions, be
sure to place the initialization function into a module that is linked in
regardless of which function is called by the user.

<item>
The linker will generate the tables only when requested to do so by the
<tt/FEATURE CONDES/ statement in the linker config file. Each table has to
be requested separately.

<item>
Constructors and destructors may have priorities. These priorities determine
the order of the functions in the table. If your intialization or cleanup code
does depend on other initialization or cleanup code, you have to choose the
priority for the functions accordingly.

<item>
Besides the <tt><ref id=".CONSTRUCTOR" name=".CONSTRUCTOR"></tt> and <tt><ref
id=".DESTRUCTOR" name=".DESTRUCTOR"></tt> statements, there is also a more
generic command: <tt><ref id=".CONDES" name=".CONDES"></tt>. This allows to
specify an additional type. Predefined types are 0 (constructor) and 1
(destructor). The linker generates a separate table for each type on request.

</itemize>





<sect>Bugs/Feedback<p>

If you have problems using the assembler, if you find any bugs, or if
you're doing something interesting with the assembler, I would be glad to
hear from you. Feel free to contact me by email
(<htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">).



<sect>Copyright<p>

ca65 (and all cc65 binutils) are (C) Copyright 1998-2001 Ullrich von
Bassewitz. For usage of the binaries and/or sources the following
conditions do apply:

This software is provided 'as-is', without any expressed or implied
warranty.  In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

<enum>
<item>  The origin of this software must not be misrepresented; you must not
        claim that you wrote the original software. If you use this software
        in a product, an acknowledgment in the product documentation would be
        appreciated but is not required.
<item>  Altered source versions must be plainly marked as such, and must not
        be misrepresented as being the original software.
<item>  This notice may not be removed or altered from any source
        distribution.
</enum>



</article>