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The code comes from the RGBDS source and documentation zip files found on this website: http://www.otakunozoku.com/1999/08/01/rednex-gameboy-development-system/ The same website reports: "Best of all, it’s free! That’s right! Free! The executables are free to use, either for personal hobby use, or full blown commercial productions — I know of at least a dozen commercial games you can purchase that are written with RGBDS — and the source code is free to modify. "The only thing I ask is that you do not charge for either distributing the executables or source code, and any derivative works you give credit to the original authors of the tools. That means you have to say “Thanks” to the original authors SurfSmurf and Otaku." Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
120 lines
4.3 KiB
HTML
120 lines
4.3 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<HTML>
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<HEAD>
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<TITLE>xAsm MACRO/ENDM</TITLE>
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</HEAD>
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<BODY BGCOLOR="#692764" TEXT="#F5A0D8" LINK="#8AAEE6" VLINK="#2B9DA4" ALINK="#95F0DA">
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<I><H2>MACRO<BR>
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ENDM</H2></I><HR>
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<P>One of the best features of an assembler is the ability to write macros for it. Macros also provide a method of passing
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arguments to them and they can then react to the input using IF-constructs.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE>MyMacro: MACRO
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ld a,80
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call MyFunc
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ENDM</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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<P>The above example is a very simple macro. You execute the macro by typing its name.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE> add a,b
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ld sp,hl
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MyMacro ;This will be expanded
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sub a,87</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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<P>When the assembler meets MyMacro it will insert the macrodefinition (the text enclosed in <B>MACRO/ENDM</B>).
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<P><A NAME="labelsuffix"></A>Suppose your macro contains a loop.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE>LoopyMacro: MACRO
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xor a,a
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.loop ld [hl+],a
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dec c
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jr nz,.loop
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ENDM</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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<A TARGET="#labelsuffix"></A><P>This is fine. That is, if you only use the macro once per <A HREF="labels.htm">scope</A>. To get around this problem there is a special label string equate called <B>\@</B> that you can append to your labels and it will then expand to a unique string.
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<B>\@</B> also works in <A HREF="rept.htm">REPT-blocks</A> should you have any loops there.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE>LoopyMacro: MACRO
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xor a,a
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.loop\@ ld [hl+],a
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dec c
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jr nz,.loop\@
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ENDM</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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<H4>Arguments</H4>
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<P>I'd like <I>LoopyMacro</I> a lot better if I didn't have to pre-load the registers with values and <I>then</I> call it.
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What I'd like is the ability to pass it arguments and it then loaded the registers itself.
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<P>And I can do that. In macros you can get the arguments by using the special macro string equates <B>\1</B> through
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<B>\9</B>, <B>\1</B> being the first argument specified on the calling of the macro.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE>LoopyMacro: MACRO
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ld hl,\1
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ld c,\2
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xor a,a
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.loop\@ ld [hl+],a
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dec c
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jr nz,.loop\@
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ENDM</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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<P>Now I can call the macro specifying two arguments. The first being the address and the second being a bytecount.
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The macro will then reset all bytes in this range.<BR>
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<BR>
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<TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE> LoopyMacro MyVars,54</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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<P> You can specify up to nine arguments when calling a
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macro. Arguments are passed as string equates. There's no need to enclose them in quotes. Parameter passing has changed a bit since v1.03 in that an expression will not be evaluated first but passed directly. This means that it's probably a very good idea to use
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brackets around \1-\9 if you perform further calculations on them. For instance if you pass 1+2 as the first argument and then do
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<P><TABLE BORDER=0 BGCOLOR="Black" CELLPADDING=8 WIDTH="50%">
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<TR>
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<TD><FONT COLOR="#00FF00">
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<PRE> PRINTV \1*2
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</PRE>
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</FONT></TD>
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</TR>
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</TABLE>
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you will get the value 5 on screen and not 6 as you might have expected..<BR>
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<P>Note that a colon (:) following the macro-name is required. Macros can't be exported or imported. It's valid to call a macro from a macro (yes, even the same one).<BR>
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<H3>See also:</H3>
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<UL>
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<LI><A HREF="shift.htm">SHIFT</A>
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</UL>
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<BR><HR>
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<FONT SIZE="-1"><I><P ALIGN=RIGHT>Last updated 02 July 1997 by <A HREF="mailto:surfsmurf@matilde.demon.co.uk">Carsten Sorensen</A></P></I></FONT>
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