This chapter describes the oldstyle syntax module suitable
for some 8-bit CPUs (6502, 680x, 68HC1x, Z80, etc.),
which is available with the extension @code{oldstyle}.

@section Legal

    This module is written in 2002-2018 by Frank Wille and
    is covered by the vasm copyright without modifications.

@section Additional options for this module
 
This syntax module provides the following additional options:
 
@table @option
 
@item -autoexp
 Automatically export all non-local symbols, making them visible
 to other modules during linking.

@item -dotdir
 Directives have to be preceded by a dot (@code{.}).

@item -i
 Ignore everything after a blank in the operand field and treat it as a
 comment. This option is only available when the backend does not separate
 its operands with blanks as well.

@item -noc
 Disable C-style constant prefixes.

@item -noi
 Disable intel-style constant suffixes.

@end table

@section General Syntax

Labels always start at the first column and may be terminated by a
colon (@code{:}), but don't need to. In the last case the mnemonic
needs to be separated from the label by whitespace (not required in
any case, e.g. @code{=}).

Local labels are preceded by '@code{.}' or terminated by '@code{$}'.
For the rest, any alphanumeric character including '@code{_}' is allowed.
Local labels are valid between two global label definitions.

It is allowed, but not recommended, to refer to any local symbol starting with
'@code{.}' in the source, by preceding its name with the name of the last
global symbol, which was defined before it: @code{global_name.local_name}.

The operands are separated from the mnemonic by whitespace. Multiple
operands are separated by comma (@code{,}).

Make sure that you don't define a label on the same line as a
directive for conditional assembly (if, else, endif)! This is not supported.

Some CPU backends may supported multiple statements (directives or
mnemonics) per line, separated by a special character (e.g. @code{:} for Z80).

Comments are introduced by the comment character @code{;}, or the first
blank following the operand field when option @option{-i} was given.
The rest of the line will be ignored.

Example:

@code{mylabel instr op1,op2  ;comment}

In expressions, numbers starting with @code{$} are hexadecimal (e.g.
@code{$fb2c}). For Z80 also @code{&} may be used as a hexadecimal prefix,
but make sure to avoid conflicts with the and-operator (either by using
parentheses or blanks).
@code{%} introduces binary numbers (e.g. @code{%1100101}).
Numbers starting with @code{@@} are assumed to be octal numbers, e.g.
@code{@@237} (except for Z80, where it means binary).
A special case is a digit followed by a @code{#}, which can be used to
define an arbitrary base between 2 and 9 (e.g. @code{4#3012}).
Intel-style constant suffixes are supported: @code{h} for hexadecimal,
@code{d} for decimal, @code{o} or @code{q} for octal and @code{b} for
binary. Hexadecimal intel-style constants must start with a digit (prepend
@code{0}, when required).
Also C-style prefixes are supported for hexadecimal (@code{0x}) and
binary (@code{0b}).
All other numbers starting with a digit are decimal, e.g. @code{1239}.


@section Directives

The following directives are supported by this syntax module (if the
CPU- and output-module allow it):

@table @code
@item <symbol> = <expression>
      Equivalent to @code{<symbol> equ <expression>}.

@item abyte <offset>,<exp1>[,<exp2>,"<string1>"...]
      Write the integer or string constant operands into successive
      bytes of memory in the current section while adding the constant
      <offset> to each byte. Any combination of integer and character
      string constant operands is permitted.

@item addr <exp1>[,<exp2>...]
      Equivalent to @code{word <exp1>[,<exp2>...]}.

@item align <bitcount>
      Insert as much zero bytes as required to reach an address where
      <bit_count> low order bits are zero. For example @code{align 2} would
      make an alignment to the next 32-bit boundary.

@item asc <exp1>[,<exp2>,"<string1>"...]
      Equivalent to @code{byte <exp1>[,<exp2>,"<string1>"...]}.

@item ascii <exp1>[,<exp2>,"<string1>"...]
      See @code{defm}. 

@item asciiz "<string1>"[,"<string2>"...]
      See @code{string}. 

@item assert <expression>[,<message>]
      Display an error with the optional <message> when the expression
      is false.

@item binary <file>
      Inserts the binary contents of <file> into the object code at
      this position. The file will be searched first in the current
      directory, then in all paths defined by @option{-I} or @code{incdir}
      in the order of occurence.

@item blk <exp>[,<fill>]
      Insert <exp> zero or <fill> bytes into the current section.

@item blkw <exp>[,<fill>]
      Insert <exp> zero or <fill> 16-bit words into the current section,
      using the endianess of the target CPU.

@item bsz <exp>[,<fill>]
      Equivalent to @code{blk <exp>[,<fill>]}.

@item byt
      Increases the program counter by one.
      Equivalent to @code{blk 1,0}.

@item byte <exp1>[,<exp2>,"<string1>"...]
      Assign the integer or string constant operands into successive
      bytes of memory in the current section. Any combination of integer
      and character string constant operands is permitted.

@item data <exp1>[,<exp2>,"<string1>"...]
      Equivalent to @code{byte <exp1>[,<exp2>,"<string1>"...]}.

@item db <exp1>[,<exp2>,"<string1>"...]
      Equivalent to @code{byte <exp1>[,<exp2>,"<string1>"...]}.

@item dc <exp>[,<fill>]
      Equivalent to @code{blk <exp>[,<fill>]}.

@item defb <exp1>[,<exp2>,"<string1>"...]
      Equivalent to @code{byte <exp1>[,<exp2>,"<string1>"...]}.

@item defc <symbol> = <expression>
      Define a new program symbol with the name <symbol> and assign to it
      the value of <expression>. Defining <symbol> twice will cause
      an error.

@item defl <exp1>[,<exp2>...]
      Assign the values of the operands into successive 32-bit integers
      of memory in the current section, using the endianess of the target
      CPU.

@item defp <exp1>[,<exp2>...]
      Assign the values of the operands into successive 24-bit integers
      of memory in the current section, using the endianess of the target
      CPU.

@item defm "string"
      Equivalent to @code{text "string"}.

@item defw <exp1>[,<exp2>...]
      Equivalent to @code{word <exp1>[,<exp2>...]}.

@item dfb <exp1>[,<exp2>,"<string1>"...]
      Equivalent to @code{byte <exp1>[,<exp2>,"<string1>"...]}.

@item dfw <exp1>[,<exp2>...]
      Equivalent to @code{word <exp1>[,<exp2>...]}.

@item defs <exp>[,<fill>]
      Equivalent to @code{blk <exp>[,<fill>]}.

@item dephase
      Equivalent to @code{rend}.

@item ds <exp>[,<fill>]
      Equivalent to @code{blk <exp>[,<fill>]}.

@item dsb <exp>[,<fill>]
      Equivalent to @code{blk <exp>[,<fill>]}.

@item dsw <exp>[,<fill>]
      Equivalent to @code{blkw <exp>[,<fill>]}.

@item dw <exp1>[,<exp2>...]
      Equivalent to @code{word <exp1>[,<exp2>...]}.

@item end
      Assembly will terminate behind this line.

@item endif
      Ends a section of conditional assembly.

@item el
      Equivalent to @code{else}.

@item else
      Assemble the following lines when the previous @code{if}-condition
      was false.

@item ei
      Equivalent to @code{endif}. (Not available for Z80 CPU)

@item endm
      Ends a macro definition.

@item endmac
      Ends a macro definition.

@item endmacro
      Ends a macro definition.

@item endr
      Ends a repetition block.

@item endrep
      Ends a repetition block.

@item endrepeat
      Ends a repetition block.

@item endstruct
      Ends a structure definition.

@item endstructure
      Ends a structure definition.

@item <symbol> eq <expression>
      Equivalent to @code{<symbol> equ <expression>}.

@item <symbol> equ <expression>
      Define a new program symbol with the name <symbol> and assign to it
      the value of <expression>. Defining <symbol> twice will cause
      an error.

@item extern  <symbol>[,<symbol>...]
        See @code{global}.

@item even
      Aligns to an even address. Equivalent to @code{align 1}.

@item fail <message>
      Show an error message including the <message> string. Do not generate
      an ouput file.

@item fill <exp>
      Equivalent to @code{blk <exp>,0}.

@item fcb <exp1>[,<exp2>,"<string1>"...]
      Equivalent to @code{byte <exp1>[,<exp2>,"<string1>"...]}.

@item fcc "<string>"
      Equivalent to @code{text}.

@item fdb <exp1>[,<exp2>,"<string1>"...]
      Equivalent to @code{word <exp1>[,<exp2>...]}.

@item global <symbol>[,<symbol>...]
      Flag <symbol> as an external symbol, which means that <symbol> is
      visible to all modules in the linking process. It may be either
      defined or undefined.  

@item if <expression>
      Conditionally assemble the following lines if <expression> is non-zero.

@item ifdef <symbol>
      Conditionally assemble the following lines if <symbol> is defined.

@item ifndef <symbol>
      Conditionally assemble the following lines if <symbol> is undefined.

@item ifd <symbol>
      Conditionally assemble the following lines if <symbol> is defined.

@item ifnd <symbol>
      Conditionally assemble the following lines if <symbol> is undefined.

@item ifeq <expression>
      Conditionally assemble the following lines if <expression> is zero.

@item ifne <expression>
      Conditionally assemble the following lines if <expression> is non-zero.

@item ifgt <expression>
      Conditionally assemble the following lines if <expression> is
      greater than zero.

@item ifge <expression>
      Conditionally assemble the following lines if <expression> is
      greater than zero or equal.

@item iflt <expression>
      Conditionally assemble the following lines if <expression> is
      less than zero.

@item ifle <expression>
      Conditionally assemble the following lines if <expression> is
      less than zero or equal.

@item ifused <symbol>
      Conditionally assemble the following lines if <symbol> has been
      previously referenced in an expression or in a parameter of an opcode.
      Issue a warning, when <symbol> is already defined.
      Note that @code{ifused} does not work, when the symbol has only been
      used in the following lines of the source.

@item incbin <file>[,<offset>[,<nbytes>]]
      Inserts the binary contents of <file> into the object code at
      this position. When <offset> is specified, then the given number
      of bytes will be skipped at the beginning of the file. The optional
      <nbytes> argument specifies the maximum number of bytes to be read
      from that file.
      The file will be searched first in the current directory, then in all
      paths defined by @option{-I} or @code{incdir} in the order of occurence.

@item incdir <path>
      Add another path to search for include files to the list of
      known paths. Paths defined with @option{-I} on the command line are
      searched first.

@item include <file>
      Include source text of <file> at this position. The include file
      will be searched first in the current directory, then in all
      paths defined by @option{-I} or @code{incdir} in the order of
      occurence.

@item mac <name>
      Equivalent to @code{macro <name>}.

@item list
      The following lines will appear in the listing file, if it was
      requested.

@item local <symbol>[,<symbol>...]
      Flag <symbol> as a local symbol, which means that <symbol> is
      local for the current file and invisible to other modules in
      the linking process.

@item macro <name>[,<argname>...]
      Defines a macro which can be referenced by <name>. The <name>
      may also appear on the left side of the @code{macro} directive,
      starting at the first column. The macro definition is closed
      by an @code{endm} directive. When calling a macro you may pass
      up to 9 arguments, separated by comma. Those arguments are
      referenced within the macro context as @code{\1} to @code{\9},
      or optionally by named arguments, which you have to specify in
      the operand.
      Argument @code{\0} is set to the macro's first qualifier
      (mnemonic extension), when given.
      The special argument @code{\@@} inserts an underscore followed by
      a six-digit unique id, useful for defining labels.
      @code{\()} may be used as a separator between the name of a macro
      argument and the subsequent text.
      @code{\<symbolname>} inserts the current decimal value of the absolute
      symbol @code{symbolname}.

@item mdat <file>
      Equivalent to @code{incbin <file>}.

@item nolist
      The following lines will not be visible in a listing file.

@item org <expression>
      Sets the base address for the subsequent code. This is equivalent
      to @code{*=<expression>}.

@item phase <expression>
      Equivalent to @code{rorg <expression>}.

@item repeat <expression>
      Equivalent to @code{rept <expression>}.

@item rept <expression>
      Repeats the assembly of the block between @code{rept} and @code{endr}
      <expression> number of times. <expression> has to be positive.

@item reserve <exp>
      Equivalent to @code{blk <exp>,0}.

@item rend
      Ends a @code{rorg} block of label relocation. Following labels will
      be based on @code{org} again.

@item rmb <exp>[,<fill>]
      Equivalent to @code{blk <exp>[,<fill>]}. (Not available for 6502 CPU.)

@item roffs <expression>
      Sets the program counter <expression> bytes behind the start of the
      current section. The new program counter must not be smaller than the
      current one. The space will be padded with zeros.

@item rorg <expression>
      Relocate all labels between @code{rorg} and @code{rend} based on the
      new origin from @code{<expression>}.

@item section <name>[,"<attributes>"]
      Starts a new section named <name> or reactivate an old one. If
      attributes are given for an already existing section, they must
      match exactly. The section's name will also be defined as a new
      symbol, which represents the section's start address.
      The "<attributes>" string may consist of the following characters:

      Section Contents:
@table @code
@item c 
         section has code

@item d 
         section has initialized data

@item u 
         section has uninitialized data

@item i 
         section has directives (info section)

@item n 
         section can be discarded
            
@item R 
         remove section at link time
            
@item a 
         section is allocated in memory
@end table

      Section Protection:

@table @code          
@item r
         section is readable
            
@item w
         section is writable
           
@item x
         section is executable
           
@item s
         section is sharable
@end table

@item <symbol> set <expression>
      Create a new symbol with the name <symbol> and assign
      the value of <expression>. If <symbol> is already assigned, it will
      contain a new value from now on.

@item spc <exp>
      Equivalent to @code{blk <exp>,0}.

@item string "<string1>"[,"<string2>"...]
      Like @code{text}, but adds a terminating zero-byte.

@item struct <name>
      Defines a structure which can be referenced by <name>. Labels within
      a structure definitation can be used as field offsets. They will be
      defined as local labels of @code{<name>} and can be referenced through
      @code{<name>.<label>}. All directives are allowed, but instructions will
      be ignored when such a structure is used. Data definitions can be used as
      default values when the structure is used as initializer. The structure
      name, <name>, is defined as a global symbol with the structure's size.
      A structure definition is ended by @code{endstruct}.

@item structure <name>
      Equivalent to @code{struct <name>}.

@item text "<string>"
      Places a single string constant operands into successive bytes of
      memory in the current section. The string delimiters may be any
      printable ASCII character.

@item weak <symbol>[,<symbol>...]
      Flag <symbol> as a weak symbol, which means that <symbol> is
      visible to all modules in the linking process and may be replaced
      by any global symbol with the same name.
      When a weak symbol remains undefined its value defaults to 0.

@item wor <exp1>[,<exp2>...]
      Equivalent to @code{word <exp1>[,<exp2>...]}.

@item wrd
      Increases the program counter by two.
      Equivalent to @code{blkw 1,0}.

@item word <exp1>[,<exp2>...]
      Assign the values of the operands into successive 16-bit words
      of memory in the current section, using the endianess of the target
      CPU.

@item xdef  <symbol>[,<symbol>...]
        See @code{global}.

@item xlib  <symbol>[,<symbol>...]
        See @code{global}.

@item xref  <symbol>[,<symbol>...]
        See @code{global}.

@item zmb <exp>[,<fill>]
      Equivalent to @code{blk <exp>[,<fill>]}.
@end table


@section Structures
The oldstyle syntax is able to manage structures.
Structures can be defined in two ways:
@example 
mylabel struct[ure]
        <fields>
        endstruct[ure]
@end example  
        or:    
@example      
        struct[ure] mylabel
        <fields>
        endstruct[ure]
@end example  

Any directive is allowed to define the structure fields. Labels can be used
to define offsets into the structure. The initialized data is used as default
value, whenever no value is given for a field when the structure is referenced.

Some examples of structure declarations:
@example
  struct point
x    db 4
y    db 5
z    db 6
  endstruct
@end example

This will create the following labels:
@example
point.x  ; 0   offsets
point.y  ; 1
point.z  ; 2
point    ; 3   size of the structure
@end example

The structure can be used by optionaly redefining the fields value:
@example
point1 point
point2 point 1, 2, 3
point3 point ,,4
@end example
is equivalent to
@example
point1  
               db 4
               db 5
               db 6
point2
               db 1
               db 2
               db 3
point3
               db 4
               db 5
               db 4
@end example


@section Known Problems

    Some known problems of this module at the moment:

@itemize @minus

@item Addresses assigned to @code{org} or to the current pc symbol @code{'*'}
(on the z80 the pc symbol is @code{'$'}) must be constant.

@item Expressions in an @code{if} directive must be constant.

@end itemize

@section Error Messages

This module has the following error messages:

@itemize @minus
@item 1001: syntax error
@item 1002: invalid extension
@item 1003: no space before operands
@item 1004: too many closing parentheses
@item 1005: missing closing parentheses
@item 1006: missing operand
@item 1007: garbage at end of line
@item 1008: %c expected
@item 1009: invalid data operand
@item 1010: , expected
@item 1011: identifier expected
@item 1012: illegal escape sequence %c
@item 1013: unexpected "%s" without "%s"
@item 1021: cannot open binary file "%s"
@item 1023: alignment too big
@item 1024: label <%s> has already been defined
@item 1025: skipping instruction in struct init
@item 1026: last %d bytes of string constant have been cut

@end itemize