<title>ca65 Users Guide
<author><url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz">,<newline>
<url url="mailto:greg.king5@verizon.net" name="Greg King">
-<date>2016-06-11
<abstract>
ca65 is a powerful macro assembler for the 6502, 65C02, and 65816 CPUs. It is
<sect1>Address sizes of symbols<p>
+The address size of a symbol can be specified with a prefix:
+<itemize>
+<item>z: zeropage addressing (8 bits).
+<item>a: absolute addressing (16 bits).
+<item>f: far addressing (24 bits).
+</itemize>
+
+The zeropage addressing override can be used to ensure the use of optimal
+zeropage instructions, or correct cases where the size isn't yet known
+due to the single-pass assembly model.
+
+The larger addressing overrides can be used to promote a smaller address
+to absolute or far addressing, instead of being automatically fit into
+a smaller addressing type.
<sect1>Memory models<p>
<tscreen><verb>
; Reserve space for the larger of two data blocks
- savearea: .max (.sizeof (foo), .sizeof (bar))
+ savearea: .res .max (.sizeof (foo), .sizeof (bar))
</verb></tscreen>
See: <tt><ref id=".MIN" name=".MIN"></tt>
Example:
<tscreen><verb>
- ; Reserve space for some data, but 256 bytes minimum
- savearea: .min (.sizeof (foo), 256)
+ ; Reserve space for some data, but 256 bytes maximum
+ savearea: .res .min (.sizeof (foo), 256)
</verb></tscreen>
See: <tt><ref id=".MAX" name=".MAX"></tt>
<tag><tt>at_in_identifiers</tt><label id="at_in_identifiers"></tag>
- Accept the at character (`@') as a valid character in identifiers. The
+ Accept the at character ('@') as a valid character in identifiers. The
at character is not allowed to start an identifier, even with this
feature enabled.
<tag><tt>dollar_in_identifiers</tt><label id="dollar_in_identifiers"></tag>
- Accept the dollar sign (`$') as a valid character in identifiers. The
+ Accept the dollar sign ('$') as a valid character in identifiers. The
dollar character is not allowed to start an identifier, even with this
feature enabled.
<tag><tt>dollar_is_pc</tt><label id="dollar_is_pc"></tag>
- The dollar sign may be used as an alias for the star (`*'), which
+ 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>leading_dot_in_identifiers</tt><label id="leading_dot_in_identifiers"></tag>
- Accept the dot (`.') as the first character of an identifier. This may be
+ Accept the dot ('.') as the first character of an identifier. This may be
used for example to create macro names that start with a dot emulating
control directives of other assemblers. Note however, that none of the
reserved keywords built into the assembler, that starts with a dot, may be
<tag><tt>pc_assignment</tt><label id="pc_assignment"></tag>
- Allow assignments to the PC symbol (`*' or `$' if <tt/dollar_is_pc/
+ Allow assignments to the PC symbol ('*' or '$' if <tt/dollar_is_pc/
is enabled). Such an assignment is handled identical to the <tt><ref
id=".ORG" name=".ORG"></tt> command (which is usually not needed, so just
removing the lines with the assignments may also be an option when porting
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
+ as reachable by short addressing. The '*' (PC counter) operator will
work as in other segments and will create absolute variable values.
Please note that a segment cannot have two different address sizes. A
some things may be done with both macro types, each type has special
usages. The types complement each other.
+<item> Parentheses work differently from C macros.
+ The common practice of wrapping C macros in parentheses may cause
+ unintended problems here, such as accidentally implying an
+ indirect addressing mode. While the definition of a macro requires
+ parentheses around its argument list, when invoked they should not be
+ included.
+
</itemize>
Let's look at a few examples to make the advantages and disadvantages
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:
+Note that, while formal parameters have to be placed in parentheses,
+the actual argument used when invoking the macro should not be.
+The invoked arguments are separated by commas only, if parentheses are
+used by accident they will become part of the replaced token.
+
+If you wish to have an expression follow the macro invocation, the
+last parameter can be enclosed in curly braces {} to indicate the end of that
+argument.
+
+Examples:
<tscreen><verb>
-.macro DEBUG message
- .out message
-.endmacro
+.define COMBINE(ta,tb,tc) ta+tb*10+tc*100
+
+.word COMBINE 5,6,7 ; 5+6*10+7*100 = 765
+.word COMBINE(5,6,7) ; (5+6*10+7)*100 = 7200 ; incorrect use of parentheses
+.word COMBINE 5,6,7+1 ; 5+6*10+7+1*100 = 172
+.word COMBINE 5,6,{7}+1 ; 5+6*10+7*100+1 = 766 ; {} encloses the argument
+.word COMBINE 5,6-2,7 ; 5+6-2*10+7*100 = 691
+.word COMBINE 5,(6-2),7 ; 5+(6-2)*10+7*100 = 745
+.word COMBINE 5,6,7+COMBINE 0,1,2 ; 5+6*10+7+0+1*10+2*100*100 = 20082
+.word COMBINE 5,6,{7}+COMBINE 0,1,2 ; 5+6*10+7*100+0+1*10+2*100 = 975
</verb></tscreen>
-(That is an example where a problem can be solved with both macro types).
+With C macros it is common to enclose the results in parentheses to
+prevent unintended interactions with the text of the arguments, but
+additional care must be taken in this assembly context where parentheses
+may alter the meaning of a statement. In particular, indirect addressing modes
+may be accidentally implied:
+
+<tscreen><verb>
+.define DUO(ta,tb) (ta+(tb*10))
+
+ lda DUO(5,4), Y ; LDA (indirect), Y
+ lda 0+DUO(5,4), Y ; LDA absolute indexed, Y
+</verb></tscreen>
<sect1>Characters in macros<p>
<itemize>
<item><tt/__APPLE2__/ - Target system is <tt/apple2/ or <tt/apple2enh/
<item><tt/__APPLE2ENH__/ - Target system is <tt/apple2enh/
+<item><tt/__ATARI2600__/ - Target system is <tt/atari2600/
<item><tt/__ATARI5200__/ - Target system is <tt/atari5200/
<item><tt/__ATARI__/ - Target system is <tt/atari/ or <tt/atarixl/
<item><tt/__ATARIXL__/ - Target system is <tt/atarixl/
projects / cc65 / blobdiff