[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

<abstract>
ca65 is a 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.

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 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>

The assembler accepts the following options:

<tscreen><verb>
---------------------------------------------------------------------------
Usage: ca65 [options] file
Short options:
  -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
  -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

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>

Here is a description of all the command line options:

<descrip>

  <tag><tt>--cpu type</tt></tag>

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

        6502, 65C02, 65816 and sunplus

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


  <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/.FEATURE/ command for a list of emulation
  features.


  <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/.CASE/ control command (see section 6).


  <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/.PAGELENGTH/
  directive for more information.


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

  In smart mode (enabled by -s or the <tt/.SMART/ pseudo instruction) the
  assembler will track usage of the REP and 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.


  <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/.AUTOIMPORT/, see control command section below) 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.


  <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 6 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 all valid 6502 mnemonics when in 6502 mode (the
default). The assembler accepts all valid 65SC02 mnemonics when in 65SC02
mode (after a <tt/.PC02/ command is found). The assembler accepts all valid
65816 mnemonics with a few exceptions after a .P816 command is found.
These exceptions are listed below.

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>
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.

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.


<bf>Boolean expressions:</bf>

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.


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
    .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                    2
    .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.

<descrip>


<tag/Numeric constants/

    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>


<tag/Standard labels/

    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.


<tag/Local labels and symbols/

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

    See the description of the <tt/.PROC/ directive for more information.

<tag/Cheap local labels/

    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/.LOCALCHAR/ directive).

    Cheap local labels are visible only between two no cheap labels. As
    soon as a standard symbol is encountered (this may also be a local
    symbol if inside a region defined with the .PROC 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>

<tag/Unnamed labels/

    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.

<tag/Using macros to define labels and constants/

    While there are drawbacks with this approach, it may be handy in some
    situations. Using <tt/.DEFINE/, 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>

</descrip>


If <tt/.DEBUGINFO/ is enabled (or -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

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

<descrip>

<tag><tt><idx>.A16</idx></tt></tag>

  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/.SMART/


<tag><tt><idx>.A8</idx></tt></tag>

  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/.SMART/


<tag><tt><idx>.ADDR</idx></tt></tag>

  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/.FARADDR/. The command must be followed by a
  sequence of (not necessarily constant) expressions.

  Example:

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


<tag><tt><idx>.ALIGN</idx></tt></tag>

  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>


<tag><tt><idx>.ASCIIZ</idx></tt></tag>

  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).


<tag><tt><idx>.AUTOIMPORT</idx></tt></tag>

  Is followd 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>


<tag><tt><idx>.BLANK</idx></tt></tag>

  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>


<tag><tt><idx>.BSS</idx></tt></tag>

  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/.SEGMENT/ command.


<tag><tt><idx>.BYTE</idx></tt></tag>

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

  Example:

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


<tag><tt><idx>.CASE</idx></tt></tag>

  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>


<tag><tt><idx>.CODE</idx></tt></tag>

  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/.SEGMENT/ command.


<tag><tt><idx>.CONCAT</idx></tt></tag>

  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>


<tag><tt><idx>.CONST</idx></tt></tag>

  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>


<tag><tt><idx>.CPU</idx></tt></tag>

  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 -->   65SC816
        3 -->   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)
                txa
                pha
                tya
                pha
        .else
                phx
                phy
        .endif
  </verb></tscreen>


<tag><tt><idx>.DATA</idx></tt></tag>

  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/.SEGMENT/ command.


<tag><tt><idx>.DBYT</idx></tt></tag>

  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.


<tag><tt><idx>.DEBUGINFO</idx></tt></tag>

  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>


<tag><tt><idx>.DEFINE</idx></tt></tag>

  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 separate section about macros.


<tag><tt><idx>.DEF,</idx> <idx>.DEFINED</idx></tt></tag>

  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/.IFDEF/ statement may be replaced by

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


<tag><tt><idx>.DWORD</idx></tt></tag>

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

  Example:

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


<tag><tt><idx>.ELSE</idx></tt></tag>

  Conditional assembly: Reverse the current condition.


<tag><tt><idx>.ELSEIF</idx></tt></tag>

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


<tag><tt><idx>.END</idx></tt></tag>

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


<tag><tt><idx>.ENDIF</idx></tt></tag>

  Conditional assembly: Close a <tt/.IF.../ or <tt/.ELSE/ branch.


<tag><tt><idx>.ENDMAC,</idx> <idx>.ENDMACRO</idx></tt></tag>

  End of macro definition (see separate section).


<tag><tt><idx>.ENDPROC</idx></tt></tag>

  End of local lexical level (see <tt/.PROC/).


<tag><tt><idx>.ENDREP,</idx> <idx>.ENDREPEAT</idx></tt></tag>

  End a <tt/.REPEAT/ block. See the <tt/.REPEAT/ command.


<tag><tt><idx>.ERROR</idx></tt></tag>

  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/.WARNING/ and <tt/.OUT/ directives.


<tag><tt><idx>.EXITMAC,</idx> <idx>.EXITMACRO</idx></tt></tag>

  Abort a macro expansion immidiately. This command is often useful in
  recursive macros. See separate chapter about macros.


<tag><tt><idx>.EXPORT</idx></tt></tag>

  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>


<tag><tt><idx>.EXPORTZP</idx></tt></tag>

  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>


<tag><tt><idx>.FARADDR</idx></tt></tag>

  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>


<tag><tt><idx>.FEATURE</idx></tt></tag>

  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><idx>dollar_is_pc</idx></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><idx>labels_without_colons</idx></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><idx>loose_string_term</idx></tt></tag>

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

  <tag><tt><idx>at_in_identifiers</idx></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><idx>dollar_in_identifiers</idx></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><idx>pc_assignment</idx></tt></tag>

    Allow assignments to the PC symbol (`*' or `&dollar;' if dollar_is_pc is
    enabled). Such an assignment is handled identical to the <tt/.ORG/
    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>


<tag><tt><idx>.FILEOPT,</idx> <idx>.FOPT</idx></tt></tag>

  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>


<tag><tt><idx>.GLOBAL</idx></tt></tag>

  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. An additional
  explicit <tt/.IMPORT/ or <tt/.EXPORT/ command for the same symbol is
  allowed.

  Example:

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


<tag><tt><idx>.GLOBALZP</idx></tt></tag>

  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. An
  additional explicit <tt/.IMPORT/ or <tt/.EXPORT/ command for the same
  symbol is explicitly allowed. The symbols in the list are explicitly
  marked as zero page symols.

  Example:

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


<tag><tt><idx>.I16</idx></tt></tag>

  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/.SMART/ command.


<tag><tt><idx>.I8</idx></tt></tag>

  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/.SMART/ command.


<tag><tt><idx>.IF</idx></tt></tag>

  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.


<tag><tt><idx>.IFBLANK</idx></tt></tag>

  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/.ELSE/, <tt/.ELSEIF/ or <tt/.ENDIF/ 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/.BLANK/


<tag><tt><idx>.IFCONST</idx></tt></tag>

  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/.CONST/


<tag><tt><idx>.IFDEF</idx></tt></tag>

  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/.DEFINED/


<tag><tt><idx>.IFNBLANK</idx></tt></tag>

  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/.ELSE/, <tt/.ELSEIF/ or <tt/.ENDIF/ 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/.BLANK/


<tag><tt><idx>.IFNDEF</idx></tt></tag>

  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/.DEFINED/


<tag><tt><idx>.IFNREF</idx></tt></tag>

  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/.REFERENCED/


<tag><tt><idx>.IFP02</idx></tt></tag>

  Conditional assembly: Check if the assembler is currently in 6502 mode
  (see <tt/.P02/ command).


<tag><tt><idx>.IFP816</idx></tt></tag>

  Conditional assembly: Check if the assembler is currently in 65816 mode
  (see <tt/.P816/ command).


<tag><tt><idx>.IFPC02</idx></tt></tag>

  Conditional assembly: Check if the assembler is currently in 65C02 mode
  (see <tt/.PC02/ command).


<tag><tt><idx>.IFREF</idx></tt></tag>

  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/.REFERENCED/


<tag><tt><idx>.IMPORT</idx></tt></tag>

  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>


<tag><tt><idx>.IMPORTZP</idx></tt></tag>

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


<tag><tt><idx>.INCBIN</idx></tt></tag>

  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.

  Example:

  <tscreen><verb>
        .incbin         "sprites.dat"
  </verb></tscreen>


<tag><tt><idx>.INCLUDE</idx></tt></tag>

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

  Example:

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


<tag><tt><idx>.INITIALIZER</idx></tt></tag>

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

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

  An initializer is always exported as an absolute (16 bit) symbol. It may
  have an optional initializer priority that is separated by a comma. If no
  priority is given, the default priority of 24 is used. Priority values 1-15
  are reserved for the runtime and C libraries of the cc65 C compiler.

  Example:

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

  See the C runtime libraries for more examples how to use initializers.


<tag><tt><idx>.LEFT</idx></tt></tag>

  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/.MID/ and <tt/.RIGHT/ builtin functions.


<tag><tt><idx>.LINECONT</idx></tt></tag>

  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>


<tag><tt><idx>.LIST</idx></tt></tag>

  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>


<tag><tt><idx>.LISTBYTES</idx></tt></tag>

  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>


<tag><tt><idx>.LOCAL</idx></tt></tag>

  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/.LOCAL/ 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/.LOCAL/ command is in my eyes a better way to address
  the problem.

  You get an error when using <tt/.LOCAL/ outside a macro.


<tag><tt><idx>.LOCALCHAR</idx></tt></tag>

  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>


<tag><tt><idx>.MACPACK</idx></tt></tag>

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

        generic         Defines generic macros like add and sub.
        longbranch      Defines conditional long jump macros.

  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>

  See separate section about macros packages.


<tag><tt><idx>.MAC,</idx> <idx>.MACRO</idx></tt></tag>

  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 separate section about macros.


<tag><tt><idx>.MATCH</idx></tt></tag>

  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/.XMATCH/ 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/.MATCH/ 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               ; Shit carry into bit 7

        .endmacro
  </verb></tscreen>

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


<tag><tt><idx>.MID</idx></tt></tag>

  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/.LEFT/ and <tt/.RIGHT/ builtin functions.


<tag><tt><idx>.ORG</idx></tt></tag>

  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/.RELOC/ to switch back to relocatable code.

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

  Example:

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


<tag><tt><idx>.OUT</idx></tt></tag>

  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/.WARNING/ and <tt/.ERROR/ directives.


<tag><tt><idx>.P02</idx></tt></tag>

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


<tag><tt><idx>.P816</idx></tt></tag>

  Enable the 65816 instruction set. This is a superset of the 65C02 and
  6502 instruction sets.


<tag><tt><idx>.PAGELEN,</idx> <idx>.PAGELENGTH</idx></tt></tag>

  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 but may be overridden by the <tt/--pagelength/ command line option.
  Beware: Since 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>


<tag><tt><idx>.PARAMCOUNT</idx></tt></tag>

  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>


<tag><tt><idx>.PC02</idx></tt></tag>

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


<tag><tt><idx>.PROC</idx></tt></tag>

  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/.ENDPROC/ 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>


<tag><tt><idx>.REF,</idx> <idx>.REFERENCED</idx></tt></tag>

  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/.IFREF/ statement may be replaced by

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


<tag><tt><idx>.REPEAT</idx></tt></tag>

  Repeat all commands between <tt/.REPEAT/ and <tt/.ENDREPEAT/ a 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>


<tag><tt><idx>.RELOC</idx></tt></tag>

  Switch back to relocatable mode. See the <tt/.ORG/ command.


<tag><tt><idx>.RES</idx></tt></tag>

  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>


<tag><tt><idx>.RIGHT</idx></tt></tag>

  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/.LEFT/ and <tt/.MID/ builtin functions.


<tag><tt><idx>.RODATA</idx></tt></tag>

  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/.SEGMENT/ command.


<tag><tt><idx>.SEGMENT</idx></tt></tag>

  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>


<tag><tt><idx>.SMART</idx></tt></tag>

  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>


<tag><tt><idx>.STRAT</idx></tt></tag>

  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>


<tag><tt><idx>.STRING</idx></tt></tag>

  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>


<tag><tt><idx>.STRLEN</idx></tt></tag>

  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>


<tag><tt><idx>.TCOUNT</idx></tt></tag>

  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>


<tag><tt><idx>.WARNING</idx></tt></tag>

  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/-W0/ 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/.ERROR/ and <tt/.OUT/ directives.


<tag><tt><idx>.WORD</idx></tt></tag>

  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>


<tag><tt><idx>.ZEROPAGE</idx></tt></tag>

  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.

</descrip>



<sect>Macros

<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.

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>

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/.IFBLANK/ 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/.IFNBLANK/ 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/.PARAMCOUNT/. 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>

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/.EXITMACRO/. 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>

Now, with recursive macros, <tt/.IFBLANK/ and <tt/.PARAMCOUNT/, 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
                clc
                lda     addr
                adc     #$01
                sta     addr
                bcc     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
                clc
                lda     addr
                adc     #$01
                sta     addr
                bcc     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/.LOCAL/. <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>

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 speified above, but behaviour is sometimes
different:

<itemize>

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

<item>  Macros defined with <tt/.DEFINE/ 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/.DEFINE/ style macros are allowed anywhere
        in a line. So they are more versatile in some situations.

<item>  <tt/.DEFINE/ style macros may take parameters. While classic macros
        may have empty parameters, this is not true for <tt/.DEFINE/ 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/.DEFINE/ 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).



<sect>Macro packages

<p>
Using the <tt/.MACPACK/ directive, predefined macro packages may be included
with just one command. Available macro packages are:

<descrip>

<tag><tt><idx>generic</idx></tt></tag>

  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>


<tag><tt><idx>longbranch</idx></tt></tag>

  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>

</descrip>


<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 1998-2000 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>