223cc6685e
git-svn-id: svn://svn.compuextreme.de/Viitor/V963/Viitor_cc65@5933 504e572c-2e33-0410-9681-be2bf7408885
123 lines
3.7 KiB
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123 lines
3.7 KiB
HTML
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<HTML>
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<META NAME="GENERATOR" CONTENT="LinuxDoc-Tools 0.9.20">
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<TITLE>ca65 Users Guide: Porting sources from other assemblers</TITLE>
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<LINK HREF="ca65-17.html" REL=next>
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<LINK HREF="ca65-15.html" REL=previous>
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<LINK HREF="ca65.html#toc16" REL=contents>
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<BODY>
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<A HREF="ca65-17.html">Next</A>
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<A HREF="ca65-15.html">Previous</A>
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<A HREF="ca65.html#toc16">Contents</A>
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<HR>
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<H2><A NAME="s16">16.</A> <A HREF="ca65.html#toc16">Porting sources from other assemblers</A></H2>
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<P>Sometimes it is necessary to port code written for older assemblers to ca65.
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In some cases, this can be done without any changes to the source code by
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using the emulation features of ca65 (see <CODE>
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<A HREF="ca65-10.html#.FEATURE">.FEATURE</A></CODE>). In other cases, it is necessary to make changes to the
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source code.</P>
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<P>Probably the biggest difference is the handling of the <CODE>
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<A HREF="ca65-10.html#.ORG">.ORG</A></CODE> directive. ca65 generates relocatable code, and placement is
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done by the linker. Most other assemblers generate absolute code, placement is
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done within the assembler and there is no external linker.</P>
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<P>In general it is not a good idea to write new code using the emulation
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features of the assembler, but there may be situations where even this rule is
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not valid.</P>
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<H2><A NAME="ss16.1">16.1</A> <A HREF="ca65.html#toc16.1">TASS</A>
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</H2>
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<P>You need to use some of the ca65 emulation features to simulate the behaviour
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of such simple assemblers.</P>
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<P>
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<OL>
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<LI>Prepare your sourcecode like this:
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<BLOCKQUOTE><CODE>
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<PRE>
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; if you want TASS style labels without colons
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.feature labels_without_colons
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; if you want TASS style character constants
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; ("a" instead of the default 'a')
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.feature loose_char_term
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.word *+2 ; the cbm load address
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[yourcode here]
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</PRE>
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</CODE></BLOCKQUOTE>
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notice that the two emulation features are mostly useful for porting
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sources originally written in/for TASS, they are not needed for the
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actual "simple assembler operation" and are not recommended if you are
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writing new code from scratch.
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</LI>
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<LI>Replace all program counter assignments (which are not possible in ca65
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by default, and the respective emulation feature works different from what
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you'd expect) by another way to skip to memory locations, for example the
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<CODE>
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<A HREF="ca65-10.html#.RES">.RES</A></CODE> directive.
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<BLOCKQUOTE><CODE>
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<PRE>
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; *=$2000
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.res $2000-* ; reserve memory up to $2000
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</PRE>
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</CODE></BLOCKQUOTE>
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Please note that other than the original TASS, ca65 can never move the program
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counter backwards - think of it as if you are assembling to disk with TASS.
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</LI>
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<LI>Conditional assembly (<CODE>.ifeq</CODE>/<CODE>.endif</CODE>/<CODE>.goto</CODE> etc.) must be
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rewritten to match ca65 syntax. Most importantly notice that due to the lack
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of <CODE>.goto</CODE>, everything involving loops must be replaced by
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<CODE>
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<A HREF="ca65-10.html#.REPEAT">.REPEAT</A></CODE>.
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</LI>
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<LI>To assemble code to a different address than it is executed at, use the
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<CODE>
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<A HREF="ca65-10.html#.ORG">.ORG</A></CODE> directive instead of
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<CODE>.offs</CODE>-constructs.
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<BLOCKQUOTE><CODE>
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<PRE>
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.org $1800
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[floppy code here]
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.reloc ; back to normal
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</PRE>
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</CODE></BLOCKQUOTE>
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</LI>
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<LI>Then assemble like this:
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<BLOCKQUOTE><CODE>
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<PRE>
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cl65 --start-addr 0x0ffe -t none myprog.s -o myprog.prg
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</PRE>
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</CODE></BLOCKQUOTE>
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Note that you need to use the actual start address minus two, since two bytes
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are used for the cbm load address.
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</LI>
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</OL>
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</P>
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<HR>
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<A HREF="ca65-17.html">Next</A>
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<A HREF="ca65-15.html">Previous</A>
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<A HREF="ca65.html#toc16">Contents</A>
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