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<table class="head">
<tr>
<td class="head-ltitle">RGBASM(5)</td>
<td class="head-vol">File Formats Manual</td>
<td class="head-rtitle">RGBASM(5)</td>
</tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<code class="Nm">rgbasm</code> —
<span class="Nd">language documentation</span>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
This is the full description of the language used by
<a class="Xr" href="rgbasm.1.html">rgbasm(1)</a>. The description of the instructions supported by
the Game Boy CPU is in <a class="Xr" href="gbz80.7.html">gbz80(7)</a>.
<p class="Pp">It is strongly recommended to have some familiarity with the Game
Boy hardware before reading this document. RGBDS is specifically targeted at
the Game Boy, and thus a lot of its features tie directly to its concepts.
This document is not intended to be a Game Boy hardware reference.</p>
<p class="Pp">Generally, “the linker” will refer to
<a class="Xr" href="rgblink.1.html">rgblink(1)</a>, but any program that processes RGB object
files (described in <a class="Xr" href="rgbds.5.html">rgbds(5)</a>) can be used in its
place.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="SYNTAX"><a class="permalink" href="#SYNTAX">SYNTAX</a></h1>
The syntax is line‐based, just as in any other assembler, meaning that
you do one instruction or pseudo‐op per line:
<p class="Pp"></p>
<div class="Bd Bd-indent"><code class="Li">[<var class="Ar">label</var>]
[<var class="Ar">instruction</var>]
[<var class="Ar">; comment</var>]</code></div>
<p class="Pp">Example:</p>
<div class="Bd Pp Bd-indent">
<pre>
John: ld a,87 ;Weee
</pre>
</div>
<p class="Pp">All reserved keywords (pseudo‐ops, mnemonics, registers
etc.) are case‐insensitive, all identifiers (symbol names) are
case-sensitive.</p>
<p class="Pp">Comments are used to give humans information about the code, such
as explanations. The assembler <i class="Em">always</i> ignores comments and
their contents.</p>
<p class="Pp">There are two syntaxes for comments. The most common is that
anything that follows a semicolon ‘<code class="Li">;</code>’
not inside a string, is a comment until the end of the line. The other is
that lines beginning with a ‘<code class="Li">*</code>’ (not
even spaces before it) are ignored. This second syntax is deprecated (will
be removed in a future version) and should be replaced with the first
one.</p>
<p class="Pp">Sometimes lines can be too long and it may be necessary to split
them. To do so, put a backslash at the end of the line:</p>
<div class="Bd Pp Bd-indent">
<pre>
DB 1, 2, 3, \
4, 5, 6, \ ; Put it before any comments
7, 8, 9
</pre>
</div>
<p class="Pp">This works anywhere in the code except inside of strings. To split
strings it is needed to use <code class="Fn">STRCAT</code>() like this:</p>
<div class="Bd Pp Bd-indent">
<pre>
db STRCAT("Hello ", \
"world!")
</pre>
</div>
</section>
<section class="Sh">
<h1 class="Sh" id="EXPRESSIONS"><a class="permalink" href="#EXPRESSIONS">EXPRESSIONS</a></h1>
An expression can be composed of many things. Numerical expressions are always
evaluated using signed 32-bit math. Zero is considered to be the only
"false" number, all non-zero numbers (including negative) are
"true".
<p class="Pp">An expression is said to be "constant" if
<code class="Nm">rgbasm</code> knows its value. This is generally always the
case, unless a label is involved, as explained in the
<a class="Sx" href="#SYMBOLS">SYMBOLS</a> section.</p>
<p class="Pp">The instructions in the macro-language generally require constant
expressions.</p>
<section class="Ss">
<h2 class="Ss" id="Numeric_Formats"><a class="permalink" href="#Numeric_Formats">Numeric
Formats</a></h2>
There are a number of numeric formats.
<table class="Bl-column Bd-indent">
<tr>
<th>Format type</th>
<th>Prefix</th>
<th>Accepted characters</th>
</tr>
<tr>
<td>Hexadecimal</td>
<td>$</td>
<td>0123456789ABCDEF</td>
</tr>
<tr>
<td>Decimal</td>
<td>none</td>
<td>0123456789</td>
</tr>
<tr>
<td>Octal</td>
<td>&</td>
<td>01234567</td>
</tr>
<tr>
<td>Binary</td>
<td>%</td>
<td>01</td>
</tr>
<tr>
<td>Fixed point (16.16)</td>
<td>none</td>
<td>01234.56789</td>
</tr>
<tr>
<td>Character constant</td>
<td>none</td>
<td>"ABYZ"</td>
</tr>
<tr>
<td>Gameboy graphics</td>
<td>`</td>
<td>0123</td>
</tr>
</table>
<p class="Pp">The "character constant" form yields the value the
character maps to in the current charmap. For example, by default (refer to
<a class="Xr">ascii(7)</a>) ‘"A"’ yields 65. See
<a class="Sx" href="#Character_maps">Character maps</a> for information on
charmaps.</p>
<p class="Pp">The last one, Gameboy graphics, is quite interesting and useful.
After the backtick, 8 digits between 0 and 3 are expected, corresponding to
pixel values. The resulting value is the two bytes of tile data that would
produce that row of pixels. For example, ‘`01012323’ is
equivalent to ‘$0F55’.</p>
<p class="Pp">You can also use symbols, which are implicitly replaced with their
value.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="Operators"><a class="permalink" href="#Operators">Operators</a></h2>
A great number of operators you can use in expressions are available (listed
from highest to lowest precedence):
<table class="Bl-column Bd-indent">
<tr>
<th>Operator</th>
<th>Meaning</th>
</tr>
<tr>
<td><a class="permalink" href="#(__&)"><code class="Li" id="(__&)">(
)</code></a></td>
<td>Precedence override</td>
</tr>
<tr>
<td><a class="permalink" href="#FUNC()"><code class="Li" id="FUNC()">FUNC()</code></a></td>
<td>Built-in function call</td>
</tr>
<tr>
<td><a class="permalink" href="#~_+_-"><code class="Li" id="~_+_-">~ +
-</code></a></td>
<td>Unary complement/plus/minus</td>
</tr>
<tr>
<td><a class="permalink" href="#*_/__"><code class="Li" id="*_/__">* /
%</code></a></td>
<td>Multiply/divide/modulo</td>
</tr>
<tr>
<td><a class="permalink" href="#_____"><code class="Li" id="_____"><<
>></code></a></td>
<td>Shift left/right</td>
</tr>
<tr>
<td><a class="permalink" href="#&__&___"><code class="Li" id="&__&___">&
| ^</code></a></td>
<td>Binary and/or/xor</td>
</tr>
<tr>
<td><a class="permalink" href="#+_-"><code class="Li" id="+_-">+
-</code></a></td>
<td>Add/subtract</td>
</tr>
<tr>
<td><a class="permalink" href="#!=_==__=__=____"><code class="Li" id="!=_==__=__=____">!=
== <= >= < ></code></a></td>
<td>Comparison</td>
</tr>
<tr>
<td><a class="permalink" href="#&&___"><code class="Li" id="&&___">&&
||</code></a></td>
<td>Boolean and/or</td>
</tr>
<tr>
<td><a class="permalink" href="#!"><code class="Li" id="!">!</code></a></td>
<td>Unary not</td>
</tr>
</table>
<p class="Pp"><code class="Ic">~</code> complements a value by inverting all its
bits.</p>
<p class="Pp"><code class="Ic">%</code> is used to get the remainder of the
corresponding division. ‘5 % 2’ is 1.</p>
<p class="Pp">Shifting works by shifting all bits in the left operand either
left (‘<<’) or right (‘>>’) by the
right operand's amount. When shifting left, all newly-inserted bits are
reset; when shifting right, they are copies of the original most significant
bit instead. This makes ‘a << b’ and ‘a >>
b’ equivalent to multiplying and dividing by 2 to the power of b,
respectively.</p>
<p class="Pp">Comparison operators return 0 if the comparison is false, and 1
otherwise.</p>
<p class="Pp">Unlike in a lot of languages, and for technical reasons,
<code class="Nm">rgbasm</code> still evaluates both operands of
‘&&’ and ‘||’.</p>
<p class="Pp">! returns 1 if the operand was 0, and 1 otherwise.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="Fixed__u2010_point_Expressions"><a class="permalink" href="#Fixed__u2010_point_Expressions">Fixed‐point
Expressions</a></h2>
Fixed-point numbers are basically normal (32-bit) integers, which count
65536th's instead of entire units, offering better precision than integers but
limiting the range of values. The upper 16 bits are used for the integer part
and the lower 16 bits are used for the fraction (65536ths). Since they are
still akin to integers, you can use them in normal integer expressions, and
some integer operators like ‘+’ and ‘-’ don't care
whether the operands are integers or fixed-point. You can easily truncate a
fixed-point number into an integer by shifting it right by 16 bits. It follows
that you can convert an integer to a fixed-point number by shifting it left.
<p class="Pp">The following functions are designed to operate with fixed-point
numbers:</p>
<table class="Bl-column Bd-indent">
<tr>
<th>Name</th>
<th>Operation</th>
</tr>
<tr>
<td><code class="Fn">DIV</code>(<var class="Fa">x</var>,
<var class="Fa">y</var>)</td>
<td>
<math class="eqn">
<mrow><mi>x</mi><mo>÷</mo><mi>y</mi></mrow>
</math>
</td>
</tr>
<tr>
<td><code class="Fn">MUL</code>(<var class="Fa">x</var>,
<var class="Fa">y</var>)</td>
<td>
<math class="eqn">
<mrow><mi>x</mi><mo>×</mo><mi>y</mi></mrow>
</math>
</td>
</tr>
<tr>
<td><code class="Fn">SIN</code>(<var class="Fa">x</var>)</td>
<td>
<math class="eqn">
<mrow><mi>sin</mi><mo>(</mo><mi>x</mi><mo>)</mo></mrow>
</math>
</td>
</tr>
<tr>
<td><code class="Fn">COS</code>(<var class="Fa">x</var>)</td>
<td>
<math class="eqn">
<mrow><mi>cos</mi><mo>(</mo><mi>x</mi><mo>)</mo></mrow>
</math>
</td>
</tr>
<tr>
<td><code class="Fn">TAN</code>(<var class="Fa">x</var>)</td>
<td>
<math class="eqn">
<mrow><mi>tan</mi><mo>(</mo><mi>x</mi><mo>)</mo></mrow>
</math>
</td>
</tr>
<tr>
<td><code class="Fn">ASIN</code>(<var class="Fa">x</var>)</td>
<td>
<math class="eqn">
<mrow><mi>asin</mi><mo>(</mo><mi>x</mi><mo>)</mo></mrow>
</math>
</td>
</tr>
<tr>
<td><code class="Fn">ACOS</code>(<var class="Fa">x</var>)</td>
<td>
<math class="eqn">
<mrow><mi>acos</mi><mo>(</mo><mi>x</mi><mo>)</mo></mrow>
</math>
</td>
</tr>
<tr>
<td><code class="Fn">ATAN</code>(<var class="Fa">x</var>)</td>
<td>
<math class="eqn">
<mrow><mi>atan</mi><mo>(</mo><mi>x</mi><mo>)</mo></mrow>
</math>
</td>
</tr>
<tr>
<td><code class="Fn">ATAN2</code>(<var class="Fa">x</var>,
<var class="Fa">y</var>)</td>
<td>Angle between
<math class="eqn">
<mrow><mo>(</mo><mi>x</mi><mo>,</mo><mi>y</mi><mo>)</mo></mrow>
</math>
and
<math class="eqn">
<mrow><mo>(</mo><mn>1</mn><mo>,</mo><mn>0</mn><mo>)</mo></mrow>
</math>
</td>
</tr>
</table>
<p class="Pp">These functions are useful for automatic generation of various
tables. Example: assuming a circle has 65536.0 degrees, and sine values are
in range [-1.0 ; 1.0]:</p>
<div class="Bd Pp Bd-indent">
<pre>
; --
; -- Generate a 256-byte sine table with values between 0 and 128
; --
ANGLE = 0.0
REPT 256
db MUL(64.0, SIN(ANGLE) + 1.0) >> 16
ANGLE = ANGLE + 256.0 ; 256 = 65536 / table_len, with table_len = 256
ENDR
</pre>
</div>
</section>
<section class="Ss">
<h2 class="Ss" id="String_Expressions"><a class="permalink" href="#String_Expressions">String
Expressions</a></h2>
The most basic string expression is any number of characters contained in double
quotes (‘<code class="Li">"for instance"</code>’). The
backslash character ‘<code class="Li">\</code>’ is special in
that it causes the character following it to be “escaped”,
meaning that it is treated differently from normal. There are a number of
escape sequences you can use within a string:
<table class="Bl-column Bd-indent">
<tr>
<th>String</th>
<th>Meaning</th>
</tr>
<tr>
<td>‘<code class="Li">\\</code>’</td>
<td>Produces a backslash</td>
</tr>
<tr>
<td>‘<code class="Li">\"</code>’</td>
<td>Produces a double quote without terminating</td>
</tr>
<tr>
<td>‘<code class="Li">\,</code>’</td>
<td>Comma</td>
</tr>
<tr>
<td>‘<code class="Li">\{</code>’</td>
<td>Curly bracket left</td>
</tr>
<tr>
<td>‘<code class="Li">\}</code>’</td>
<td>Curly bracket right</td>
</tr>
<tr>
<td>‘<code class="Li">\n</code>’</td>
<td>Newline ($0A)</td>
</tr>
<tr>
<td>‘<code class="Li">\r</code>’</td>
<td>Carriage return ($0D)</td>
</tr>
<tr>
<td>‘<code class="Li">\t</code>’</td>
<td>Tab ($09)</td>
</tr>
<tr>
<td>“\1” – “\9”</td>
<td>Macro argument (Only the body of a macro, see
<a class="Sx" href="#Invoking_macros">Invoking macros</a>)</td>
</tr>
<tr>
<td>‘<code class="Li">\@</code>’</td>
<td>Label name suffix (Only in the body of macros and REPTs)</td>
</tr>
</table>
(Note that some of those can be used outside of strings, when noted further in
this document.)
<p class="Pp">A funky feature is
‘<code class="Li">{symbol}</code>’ within a string, called
“symbol interpolation”. This will paste
<var class="Ar">symbol</var>'s contents as a string. If it's a string
symbol, the string is simply inserted. If it's a numeric symbol, its value
is converted to hexadecimal notation with a dollar sign ‘$’
prepended.</p>
<div class="Bd Pp Bd-indent">
<pre>
TOPIC equs "life, the universe, and everything"
ANSWER = 42
; Prints "The answer to life, the universe, and everything is $2A"
PRINTT "The answer to {TOPIC} is {ANSWER}\n"
</pre>
</div>
<p class="Pp">Symbol interpolations can be nested, too!</p>
<p class="Pp">It's possible to change the way numeric symbols are converted by
specifying a print type like so:
‘<code class="Li">{d:symbol}</code>’. Valid print types
are:</p>
<table class="Bl-column Bd-indent">
<tr>
<th>Print type</th>
<th>Format</th>
<th>Example</th>
</tr>
<tr>
<td>‘<code class="Li">d</code>’</td>
<td>Decimal</td>
<td>42</td>
</tr>
<tr>
<td>‘<code class="Li">x</code>’</td>
<td>Lowercase hexadecimal</td>
<td>2a</td>
</tr>
<tr>
<td>‘<code class="Li">X</code>’</td>
<td>Uppercase hexadecimal</td>
<td>2A</td>
</tr>
<tr>
<td>‘<code class="Li">b</code>’</td>
<td>Binary</td>
<td>101010</td>
</tr>
</table>
<p class="Pp">Note that print types should only be used with numeric values, not
strings.</p>
<p class="Pp">HINT: The <code class="Ic">{symbol}</code> construct can also be
used outside strings. The symbol's value is again inserted directly.</p>
<p class="Pp">The following functions operate on string expressions. Most of
them return a string, however some of these functions actually return an
integer and can be used as part of an integer expression!</p>
<table class="Bl-column">
<tr>
<th>Name</th>
<th>Operation</th>
</tr>
<tr>
<td><code class="Fn">STRLEN</code>(<var class="Fa">string</var>)</td>
<td>Returns the number of characters in <var class="Ar">string</var>.</td>
</tr>
<tr>
<td><code class="Fn">STRCAT</code>(<var class="Fa">str1</var>,
<var class="Fa">str2</var>)</td>
<td>Appends <var class="Ar">str2</var> <span class="No">to</span>
<var class="Ar">str1</var>.</td>
</tr>
<tr>
<td><code class="Fn">STRCMP</code>(<var class="Fa">str1</var>,
<var class="Fa">str2</var>)</td>
<td>Returns negative if <var class="Ar">str1</var> <span class="No">is
alphabetically lower than</span> <var class="Ar">str2</var> ,
<span class="No">zero if they match, positive if</span>
<var class="Ar">str1</var> <span class="No">is greater than</span>
<var class="Ar">str2</var>.</td>
</tr>
<tr>
<td><code class="Fn">STRIN</code>(<var class="Fa">str1</var>,
<var class="Fa">str2</var>)</td>
<td>Returns the position of <var class="Ar">str2</var>
<span class="No">in</span> <var class="Ar">str1</var> <span class="No">or
zero if it's not present</span> (first character is position 1).</td>
</tr>
<tr>
<td><code class="Fn">STRSUB</code>(<var class="Fa">str</var>,
<var class="Fa">pos</var>, <var class="Fa">len</var>)</td>
<td>Returns a substring from <var class="Ar">str</var>
<span class="No">starting at</span> <var class="Ar">pos</var> (first
character is position 1) and <var class="Ar">len</var>
<span class="No">characters long.</span></td>
</tr>
<tr>
<td><code class="Fn">STRUPR</code>(<var class="Fa">str</var>)</td>
<td>Converts all characters in <var class="Ar">str</var> <span class="No">to
capitals and returns the new string.</span></td>
</tr>
<tr>
<td><code class="Fn">STRLWR</code>(<var class="Fa">str</var>)</td>
<td>Converts all characters in <var class="Ar">str</var> <span class="No">to
lower case and returns the new string.</span></td>
</tr>
</table>
</section>
<section class="Ss">
<h2 class="Ss" id="Character_maps"><a class="permalink" href="#Character_maps">Character
maps</a></h2>
When writing text that is meant to be displayed in the Game Boy, the characters
used in the source code may have a different encoding than the default of
ASCII. For example, the tiles used for uppercase letters may be placed
starting at tile index 128, which makes it difficult to add text strings to
the ROM.
<p class="Pp">Character maps allow mapping strings up to 16 characters long to
an abitrary 8-bit value:</p>
<div class="Bd Pp Bd-indent">
<pre>
CHARMAP "<LF>", 10
CHARMAP "&iacute", 20
CHARMAP "A", 128
</pre>
</div>
By default, a character map contains ASCII encoding.
<p class="Pp">It is possible to create multiple character maps and then switch
between them as desired. This can be used to encode debug information in
ASCII and use a different encoding for other purposes, for example.
Initially, there is one character map called ‘main’ and it is
automatically selected as the current character map from the beginning.
There is also a character map stack that can be used to save and restore
which character map is currently active.</p>
<table class="Bl-column">
<tr>
<th>Command</th>
<th>Meaning</th>
</tr>
<tr>
<td><a class="permalink" href="#NEWCHARMAP"><code class="Ic" id="NEWCHARMAP">NEWCHARMAP</code></a>
<var class="Ar">name</var></td>
<td>Creates a new, empty character map called
<var class="Ar">name</var>.</td>
</tr>
<tr>
<td><a class="permalink" href="#NEWCHARMAP_2"><code class="Ic" id="NEWCHARMAP_2">NEWCHARMAP</code></a>
<var class="Ar">name</var>, <var class="Ar">basename</var></td>
<td>Creates a new character map called <var class="Ar">name</var>,
<span class="No">copied from character map</span>
<var class="Ar">basename</var>.</td>
</tr>
<tr>
<td><a class="permalink" href="#SETCHARMAP"><code class="Ic" id="SETCHARMAP">SETCHARMAP</code></a>
<var class="Ar">name</var></td>
<td>Switch to character map <var class="Ar">name</var>.</td>
</tr>
<tr>
<td><a class="permalink" href="#PUSHC"><code class="Ic" id="PUSHC">PUSHC</code></a></td>
<td>Push the current character map onto the stack.</td>
</tr>
<tr>
<td><a class="permalink" href="#POPC"><code class="Ic" id="POPC">POPC</code></a></td>
<td>Pop a character map off the stack and switch to it.</td>
</tr>
</table>
<p class="Pp"><b class="Sy">Note:</b> Character maps affect all strings in the
file from the point in which they are defined, until switching to a
different character map. This means that any string that the code may want
to print as debug information will also be affected by it.</p>
<p class="Pp"><b class="Sy">Note:</b> The output value of a mapping can be 0. If
this happens, the assembler will treat this as the end of the string and the
rest of it will be trimmed.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="Other_functions"><a class="permalink" href="#Other_functions">Other
functions</a></h2>
There are a few other functions that do various useful things:
<table class="Bl-column">
<tr>
<th>Name</th>
<th>Operation</th>
</tr>
<tr>
<td><code class="Fn">BANK</code>(<var class="Fa">arg</var>)</td>
<td>Returns a bank number. If <var class="Ar">arg</var> is the symbol
<code class="Ic">@</code>, this function returns the bank of the current
section. If <var class="Ar">arg</var> is a string, it returns the bank of
the section that has that name. If <var class="Ar">arg</var> is a label,
it returns the bank number the label is in. The result may be constant if
<code class="Nm">rgbasm</code> is able to compute it.</td>
</tr>
<tr>
<td><code class="Fn">DEF</code>(<var class="Fa">label</var>)</td>
<td>Returns TRUE (1) if <var class="Ar">label</var> has been defined, FALSE
(0) otherwise. String symbols are not expanded within the
parentheses.</td>
</tr>
<tr>
<td><code class="Fn">HIGH</code>(<var class="Fa">arg</var>)</td>
<td>Returns the top 8 bits of the operand if <var class="Ar">arg</var>
<span class="No">is a label or constant, or the top 8-bit register if it
is a 16-bit register.</span></td>
</tr>
<tr>
<td><code class="Fn">LOW</code>(<var class="Fa">arg</var>)</td>
<td>Returns the bottom 8 bits of the operand if <var class="Ar">arg</var>
<span class="No">is a label or constant, or the bottom 8-bit register if
it is a 16-bit register</span> (<code class="Cm">AF</code>
<span class="No">isn't a valid register for this function</span>).</td>
</tr>
<tr>
<td><code class="Fn">ISCONST</code>(<var class="Fa">arg</var>)</td>
<td>Returns 1 if <var class="Ar">arg</var>'s value is known by RGBASM (e.g.
if it can be an argument to <code class="Ic">IF</code>), or 0 if only
RGBLINK can compute its value.</td>
</tr>
</table>
</section>
</section>
<section class="Sh">
<h1 class="Sh" id="SECTIONS"><a class="permalink" href="#SECTIONS">SECTIONS</a></h1>
Before you can start writing code, you must define a section. This tells the
assembler what kind of information follows and, if it is code, where to put
it.
<p class="Pp"></p>
<div class="Bd Bd-indent"><code class="Li">SECTION <var class="Ar">name</var>,
<var class="Ar">type</var></code></div>
<div class="Bd Bd-indent"><code class="Li">SECTION <var class="Ar">name</var>,
<var class="Ar">type</var>, <var class="Ar">options</var></code></div>
<div class="Bd Bd-indent"><code class="Li">SECTION <var class="Ar">name</var>,
<var class="Ar">type</var>[<var class="Ar">addr</var>]</code></div>
<div class="Bd Bd-indent"><code class="Li">SECTION <var class="Ar">name</var>,
<var class="Ar">type</var>[<var class="Ar">addr</var>],
<var class="Ar">options</var></code></div>
<p class="Pp"><var class="Ar">name</var> is a string enclosed in double quotes,
and can be a new name or the name of an existing section. All sections
assembled at the same time that have the same name are considered to be the
same section, and their code is put together in the object file generated by
the assembler. If the type doesn't match, an error occurs. All other
sections must have a unique name, even in different source files, or the
linker will treat it as an error.</p>
<p class="Pp">Possible section <var class="Ar">type</var>s are as follows:</p>
<dl class="Bl-tag">
<dt><a class="permalink" href="#ROM0"><code class="Ic" id="ROM0">ROM0</code></a></dt>
<dd>A ROM section. <var class="Ar">addr</var> can range from
<span class="Ad">$0000</span> to <span class="Ad">$3FFF</span>, or
<span class="Ad">$0000</span> to <span class="Ad">$7FFF</span> if tiny ROM
mode is enabled in the linker.</dd>
<dt><a class="permalink" href="#ROMX"><code class="Ic" id="ROMX">ROMX</code></a></dt>
<dd>A banked ROM section. <var class="Ar">addr</var> can range from
<span class="Ad">$4000</span> to <span class="Ad">$7FFF</span>.
<var class="Ar">bank</var> can range from 1 to 511. Becomes an alias for
<code class="Ic">ROM0</code> if tiny ROM mode is enabled in the
linker.</dd>
<dt><a class="permalink" href="#VRAM"><code class="Ic" id="VRAM">VRAM</code></a></dt>
<dd>A banked video RAM section. <var class="Ar">addr</var> can range from
<span class="Ad">$8000</span> to <span class="Ad">$9FFF</span>.
<var class="Ar">bank</var> can be 0 or 1, but bank 1 is unavailable if DMG
mode is enabled in the linker.</dd>
<dt><a class="permalink" href="#SRAM"><code class="Ic" id="SRAM">SRAM</code></a></dt>
<dd>A banked external (save) RAM section. <var class="Ar">addr</var> can range
from <span class="Ad">$A000</span> to <span class="Ad">$BFFF</span>.
<var class="Ar">bank</var> can range from 0 to 15.</dd>
<dt><a class="permalink" href="#WRAM0"><code class="Ic" id="WRAM0">WRAM0</code></a></dt>
<dd>A general-purpose RAM section. <var class="Ar">addr</var> can range from
<span class="Ad">$C000</span> to <span class="Ad">$CFFF</span>, or
<span class="Ad">$C000</span> to <span class="Ad">$DFFF</span> if WRAM0
mode is enabled in the linker.</dd>
<dt><a class="permalink" href="#WRAMX"><code class="Ic" id="WRAMX">WRAMX</code></a></dt>
<dd>A banked general-purpose RAM section. <var class="Ar">addr</var> can range
from <span class="Ad">$D000</span> to <span class="Ad">$DFFF</span>.
<var class="Ar">bank</var> can range from 1 to 7. Becomes an alias for
<code class="Ic">WRAM0</code> if WRAM0 mode is enabled in the linker.</dd>
<dt><a class="permalink" href="#OAM"><code class="Ic" id="OAM">OAM</code></a></dt>
<dd>An object attribute RAM section. <var class="Ar">addr</var> can range from
<span class="Ad">$FE00</span> to <span class="Ad">$FE9F</span>.</dd>
<dt><a class="permalink" href="#HRAM"><code class="Ic" id="HRAM">HRAM</code></a></dt>
<dd>A high RAM section. <var class="Ar">addr</var> can range from
<span class="Ad">$FF80</span> to <span class="Ad">$FFFE</span>.
<p class="Pp"><b class="Sy">Note</b>: While <code class="Nm">rgbasm</code>
will automatically optimize <code class="Ic">ld</code> instructions to
the smaller and faster <code class="Ic">ldh</code> (see
<a class="Xr" href="gbz80.7.html">gbz80(7)</a>) whenever possible, it is generally unable to
do so when a label is involved. Using the <code class="Ic">ldh</code>
instruction directly is recommended. This forces the assembler to emit a
<code class="Ic">ldh</code> instruction and the linker to check if the
value is in the correct range.</p>
</dd>
</dl>
<p class="Pp">Since RGBDS produces ROMs, code and data can only be placed in
<code class="Ic">ROM0</code> and <code class="Ic">ROMX</code> sections. To
put some in RAM, have it stored in ROM, and copy it to RAM.</p>
<p class="Pp"><var class="Ar">option</var>s are comma-separated and may
include:</p>
<dl class="Bl-tag">
<dt><a class="permalink" href="#BANK"><code class="Ic" id="BANK">BANK</code></a>[<var class="Ar">bank</var>]</dt>
<dd>Specify which <var class="Ar">bank</var> for the linker to place the
section in. See above for possible values for <var class="Ar">bank</var>,
depending on <var class="Ar">type</var>.</dd>
<dt><a class="permalink" href="#ALIGN"><code class="Ic" id="ALIGN">ALIGN</code></a>[<var class="Ar">align</var>]</dt>
<dd>Place the section at an address whose <var class="Ar">align</var>
least‐significant bits are zero. This option can be used with
<var class="Ar">addr</var>, as long as they don't contradict
eachother.</dd>
</dl>
<p class="Pp">If [<var class="Ar">addr</var>] is not specified, the section is
considered “floating”; the linker will automatically calculate
an appropriate address for the section. Similarly, if
<code class="Ic">BANK</code>[<var class="Ar">bank</var>] is not specified,
the linker will automatically find a bank with enough space.</p>
<p class="Pp">Sections can also be placed by using a linker script file. The
format is described in <a class="Xr" href="rgblink.5.html">rgblink(5)</a>. They allow the user to
place floating sections in the desired bank in the order specified in the
script. This is useful if the sections can't be placed at an address
manually because the size may change, but they have to be together.</p>
<p class="Pp">Section examples:</p>
<ul class="Bl-item">
<li>
<div class="Bd Pp Bd-indent">
<pre>
SECTION "CoolStuff",ROMX
</pre>
</div>
This switches to the section called “CoolStuff”, creating it
if it doesn't already exist. It can end up in any ROM bank. Code and data
may follow.</li>
<li>If it is needed, the the base address of the section can be specified:
<div class="Bd Pp Bd-indent">
<pre>
SECTION "CoolStuff",ROMX[$4567]
</pre>
</div>
</li>
<li>An example with a fixed bank:
<div class="Bd Pp Bd-indent">
<pre>
SECTION "CoolStuff",ROMX[$4567],BANK[3]
</pre>
</div>
</li>
<li>And if you want to force only the section's bank, and not its position
within the bank, that's also possible:
<div class="Bd Pp Bd-indent">
<pre>
SECTION "CoolStuff",ROMX,BANK[7]
</pre>
</div>
</li>
<li>Alignment examples: The first one could be useful for defining an OAM
buffer to be DMA'd, since it must be aligned to 256 bytes. The second
could also be appropriate for GBC HDMA, or for an optimized copy code that
requires alignment.
<div class="Bd Pp Bd-indent">
<pre>
SECTION "OAM Data",WRAM0,ALIGN[8] ; align to 256 bytes
SECTION "VRAM Data",ROMX,BANK[2],ALIGN[4] ; align to 16 bytes
</pre>
</div>
</li>
</ul>
<section class="Ss">
<h2 class="Ss" id="Section_Stack"><a class="permalink" href="#Section_Stack">Section
Stack</a></h2>
<code class="Ic">POPS</code> and <code class="Ic">PUSHS</code> provide the
interface to the section stack. The number of entries in the stack is limited
only by the amount of memory in your machine.
<p class="Pp"><code class="Ic">PUSHS</code> will push the current section
context on the section stack. <code class="Ic">POPS</code> can then later be
used to restore it. Useful for defining sections in included files when you
don't want to override the section context at the point the file was
included.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="RAM_Code"><a class="permalink" href="#RAM_Code">RAM
Code</a></h2>
Sometimes you want to have some code in RAM. But then you can't simply put it in
a RAM section, you have to store it in ROM and copy it to RAM at some point.
<p class="Pp">This means the code (or data) will not be stored in the place it
gets executed. Luckily, <code class="Ic">LOAD</code> blocks are the perfect
solution to that. Here's an example of how to use them:</p>
<div class="Bd Pp Bd-indent">
<pre>
SECTION "LOAD example", ROMX
CopyCode:
ld de, RAMCode
ld hl, RAMLocation
ld c, RAMLocation.end - RAMLocation
.loop
ld a, [de]
inc de
ld [hli], a
dec c
jr nz, .loop
ret
RAMCode:
LOAD "RAM code", WRAM0
RAMLocation:
ld hl, .string
ld de, $9864
.copy
ld a, [hli]
ld [de], a
inc de
and a
jr nz, .copy
ret
.string
db "Hello World!", 0
.end
ENDL
</pre>
</div>
<p class="Pp">A <code class="Ic">LOAD</code> block feels similar to a
<code class="Ic">SECTION</code> declaration because it creates a new one.
All data and code generated within such a block is placed in the current
section like usual, but all labels are created as if they were placed in
this newly-created section.</p>
<p class="Pp">In the example above, all of the code and data will end up in the
"LOAD example" section. You will notice the
‘RAMCode’ and ‘RAMLocation’ labels. The former
is situated in ROM, where the code is stored, the latter in RAM, where the
code will be loaded.</p>
<p class="Pp">You cannot nest <code class="Ic">LOAD</code> blocks, nor can you
change the current section within them.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="Unionized_Sections"><a class="permalink" href="#Unionized_Sections">Unionized
Sections</a></h2>
When you're tight on RAM, you may want to define overlapping blocks of
variables, as explained in the <a class="Sx" href="#Unions">Unions</a>
section. However, the <code class="Ic">UNION</code> keyword only works within
a single file, which prevents e.g. defining temporary variables on a single
memory area across several files. Unionized sections solve this problem. To
declare an unionized section, add a <code class="Ic">UNION</code> keyword
after the <code class="Ic">SECTION</code> one; the declaration is otherwise
not different. Unionized sections follow some different rules from normal
sections:
<ul class="Bl-bullet Bd-indent">
<li>The same unionized section (= having the same name) can be declared
several times per <code class="Nm">rgbasm</code> invocation, and across
several invocations. Different declarations are treated and merged
identically whether within the same invocation, or different ones.</li>
<li>A section cannot be declared both as unionized or non-unionized.</li>
<li>All declarations must have the same type. For example, even if
<a class="Xr" href="rgblink.1.html">rgblink(1)</a>'s <code class="Fl">-w</code> flag is used,
<code class="Ic">WRAM0</code> and <code class="Ic">WRAMX</code> types are
still considered different.</li>
<li>Different constraints (alignment, bank, etc.) can be specified for each
unionized section declaration, but they must all be compatible. For
example, alignment must be compatible with any fixed address, all
specified banks must be the same, etc.</li>
<li>Unionized sections cannot have type <code class="Ic">ROM0</code> or
<code class="Ic">ROMX</code>.</li>
</ul>
<p class="Pp">Different declarations of the same unionized section are not
appended, but instead overlaid on top of eachother, just like
<a class="Sx" href="#Unions">Unions</a>. Similarly, the size of an unionized
section is the largest of all its declarations.</p>
</section>
</section>
<section class="Sh">
<h1 class="Sh" id="SYMBOLS"><a class="permalink" href="#SYMBOLS">SYMBOLS</a></h1>
RGBDS supports several types of symbols:
<dl class="Bl-hang">
<dt><b class="Sy">Label</b></dt>
<dd>Numerical symbol designating a memory location. May or may not have a
value known at assembly time.</dd>
<dt><b class="Sy">Constant</b></dt>
<dd>Numerical symbol whose value has to be known at assembly time.</dd>
<dt><b class="Sy">Macro</b></dt>
<dd>A block of <code class="Nm">rgbasm</code> code that can be invoked
later.</dd>
<dt><b class="Sy">String equate</b></dt>
<dd>String symbol that can be evaluated, similarly to a macro.</dd>
</dl>
<p class="Pp">Symbol names can contain letters, numbers, underscores, hashes and
‘@’. However, they must begin with either a letter, a number,
or an underscore. Periods are allowed exclusively for labels, as described
below. A symbol cannot have the same name as a reserved keyword.
<i class="Em">In the line where a symbol is defined there mustn't be any
whitespace before it</i>, otherwise <code class="Nm">rgbasm</code> will
treat it as a macro invocation.</p>
<dl class="Bl-tag">
<dt><b class="Sy">Label declaration</b></dt>
<dd>One of the assembler's main tasks is to keep track of addresses for you,
so you can work with meaningful names instead of "magic"
numbers.
<p class="Pp">This can be done in a number of ways:</p>
<div class="Bd Pp Bd-indent">
<pre>
GlobalLabel ; This syntax is deprecated,
AnotherGlobal: ; please use this instead
.locallabel
.yet_a_local:
AnotherGlobal.with_another_local:
ThisWillBeExported:: ; Note the two colons
ThisWillBeExported.too::
</pre>
</div>
<p class="Pp">Declaring a label (global or local) with
‘<code class="Li">::</code>’ does an
<code class="Ic">EXPORT</code> at the same time. (See
<a class="Sx" href="#Exporting_and_importing_symbols">Exporting and
importing symbols</a> below).</p>
<p class="Pp">Any label whose name does not contain a period is a global
label, others are locals. Declaring a global label sets it as the
current label scope until the next one; any local label whose first
character is a period will have the global label's name implicitly
prepended. Local labels can be declared as
‘<code class="Li">scope.local:</code>’ or simply as as
‘<code class="Li">.local:</code>’. If the former notation
is used, then ‘<code class="Li">scope</code>’ must be the
actual current scope.</p>
<p class="Pp">A label's location (and thus value) is usually not determined
until the linking stage, so labels usually cannot be used as constants.
However, if the section in which the label is declared has a fixed base
address, its value is known at assembly time.</p>
<p class="Pp"><code class="Nm">rgbasm</code> is able to compute the
subtraction of two labels either if both are constant as described
above, or if both belong to the same section.</p>
</dd>
<dt><a class="permalink" href="#EQU"><code class="Ic" id="EQU">EQU</code></a></dt>
<dd><a class="permalink" href="#EQU_2"><code class="Ic" id="EQU_2">EQU</code></a>
allows defining constant symbols. Unlike <code class="Ic">SET</code>
below, constants defined this way cannot be redefined. They can, for
example, be used for things such as bit definitions of hardware registers.
<div class="Bd Pp Bd-indent">
<pre>
SCREEN_WIDTH equ 160 ; In pixels
SCREEN_HEIGHT equ 144
</pre>
</div>
<p class="Pp">Note that colons ‘<code class="Li">:</code>’
following the name are not allowed.</p>
</dd>
<dt><a class="permalink" href="#SET"><code class="Ic" id="SET">SET</code></a></dt>
<dd><a class="permalink" href="#SET_2"><code class="Ic" id="SET_2">SET</code></a>,
or its synonym <code class="Ic">=</code>, defines constant symbols like
<code class="Ic">EQU</code>, but those constants can be re-defined. This
is useful for variables in macros, for counters, etc.
<div class="Bd Pp Bd-indent">
<pre>
ARRAY_SIZE EQU 4
COUNT SET 2
COUNT SET ARRAY_SIZE+COUNT
; COUNT now has the value 6
COUNT = COUNT + 1
</pre>
</div>
<p class="Pp">Note that colons ‘<code class="Li">:</code>’
following the name are not allowed.</p>
</dd>
<dt><a class="permalink" href="#RSSET"><code class="Ic" id="RSSET">RSSET</code></a>,
<code class="Ic">RSRESET</code>, <code class="Ic">RB</code>,
<code class="Ic">RW</code></dt>
<dd>The RS group of commands is a handy way of defining structures:
<div class="Bd Pp Bd-indent">
<pre>
RSRESET
str_pStuff RW 1
str_tData RB 256
str_bCount RB 1
str_SIZEOF RB 0
</pre>
</div>
<p class="Pp">The example defines four constants as if by:</p>
<div class="Bd Pp Bd-indent">
<pre>
str_pStuff EQU 0
str_tData EQU 2
str_bCount EQU 258
str_SIZEOF EQU 259
</pre>
</div>
<p class="Pp">There are five commands in the RS group of commands:</p>
<table class="Bl-column">
<tr>
<th>Command</th>
<th>Meaning</th>
</tr>
<tr>
<td><a class="permalink" href="#RSRESET"><code class="Ic" id="RSRESET">RSRESET</code></a></td>
<td>Equivalent to ‘<code class="Li">RSSET 0</code>’.</td>
</tr>
<tr>
<td><a class="permalink" href="#RSSET_2"><code class="Ic" id="RSSET_2">RSSET</code></a>
<var class="Ar">constexpr</var></td>
<td>Sets the <code class="Ic">_RS</code> <span class="No">counter
to</span> <var class="Ar">constexpr</var>.</td>
</tr>
<tr>
<td><a class="permalink" href="#RB"><code class="Ic" id="RB">RB</code></a>
<var class="Ar">constexpr</var></td>
<td>Sets the preceding symbol to <code class="Ic">_RS</code>
<span class="No">and adds</span> <var class="Ar">constexpr</var>
<span class="No">to</span> <code class="Ic">_RS</code>.</td>
</tr>
<tr>
<td><a class="permalink" href="#RW"><code class="Ic" id="RW">RW</code></a>
<var class="Ar">constexpr</var></td>
<td>Sets the preceding symbol to <code class="Ic">_RS</code>
<span class="No">and adds</span> <var class="Ar">constexpr</var>
<span class="No">* 2 to</span> <code class="Ic">_RS</code>.</td>
</tr>
<tr>
<td><a class="permalink" href="#RL"><code class="Ic" id="RL">RL</code></a>
<var class="Ar">constexpr</var></td>
<td>Sets the preceding symbol to <code class="Ic">_RS</code>
<span class="No">and adds</span> <var class="Ar">constexpr</var>
<span class="No">* 4 to</span> <code class="Ic">_RS</code>. (In
practice, this one cannot be used due to a bug).</td>
</tr>
</table>
<p class="Pp">Note that colons ‘<code class="Li">:</code>’
following the name are not allowed.</p>
</dd>
<dt><a class="permalink" href="#EQUS"><code class="Ic" id="EQUS">EQUS</code></a></dt>
<dd><a class="permalink" href="#EQUS_2"><code class="Ic" id="EQUS_2">EQUS</code></a>
is used to define string symbols. Wherever the assembler meets a string
symbol its name is replaced with its value. If you are familiar with C you
can think of it as similar to <code class="Fd">#define .</code>
<div class="Bd Pp Bd-indent">
<pre>
COUNTREG EQUS "[hl+]"
ld a,COUNTREG
PLAYER_NAME EQUS "\"John\""
db PLAYER_NAME
</pre>
</div>
<p class="Pp">This will be interpreted as:</p>
<div class="Bd Pp Bd-indent">
<pre>
ld a,[hl+]
db "John"
</pre>
</div>
<p class="Pp">String symbols can also be used to define small one-line
macros:</p>
<div class="Bd Pp Bd-indent">
<pre>
pusha EQUS "push af\npush bc\npush de\npush hl\n"
</pre>
</div>
<p class="Pp">Note that colons ‘<code class="Li">:</code>’
following the name are not allowed. String equates can't be exported or
imported.</p>
<p class="Pp"><b class="Sy">Important note</b>: An
<code class="Ic">EQUS</code> can be expanded to a string that contains
another <code class="Ic">EQUS</code> and it will be expanded as well. If
this creates an infinite loop, <code class="Nm">rgbasm</code> will error
out once a certain depth is reached. See the <code class="Fl">-r</code>
command-line option in <a class="Xr" href="rgbasm.1.html">rgbasm(1)</a>. Also, a macro can
contain an <code class="Ic">EQUS</code> which calls the same macro,
which causes the same problem.</p>
</dd>
<dt><a class="permalink" href="#MACRO"><code class="Ic" id="MACRO">MACRO</code></a></dt>
<dd>One of the best features of an assembler is the ability to write macros
for it. Macros can be called with arguments, and can react depending on
input using <code class="Ic">IF</code> constructs.
<div class="Bd Pp Bd-indent">
<pre>
MyMacro: MACRO
ld a,80
call MyFunc
ENDM
</pre>
</div>
<p class="Pp">Note that a single colon
‘<code class="Li">:</code>’ following the macro's name is
required. Macros can't be exported or imported.</p>
</dd>
</dl>
<section class="Ss">
<h2 class="Ss" id="Exporting_and_importing_symbols"><a class="permalink" href="#Exporting_and_importing_symbols">Exporting
and importing symbols</a></h2>
Importing and exporting of symbols is a feature that is very useful when your
project spans many source files and, for example, you need to jump to a
routine defined in another file.
<p class="Pp">Exporting of symbols has to be done manually, importing is done
automatically if <code class="Nm">rgbasm</code> finds a symbol it does not
know about.</p>
<p class="Pp">The following will cause <var class="Ar">symbol1</var>,
<var class="Ar">symbol2</var> and so on to be accessible to other files
during the link process:</p>
<div class="Bd Bd-indent"><code class="Li"><code class="Ic">EXPORT</code>
<var class="Ar">symbol1</var> [, <var class="Ar">symbol2</var>,
<span class="No">...</span>]</code></div>
<p class="Pp"><code class="Ic">GLOBAL</code> is a deprecated synonym for
<code class="Ic">EXPORT</code>, do not use it.</p>
<p class="Pp">Note also that only exported symbols will appear in symbol and map
files produced by <a class="Xr" href="rgblink.1.html">rgblink(1)</a>.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="Purging_symbols"><a class="permalink" href="#Purging_symbols">Purging
symbols</a></h2>
<code class="Ic">PURGE</code> allows you to completely remove a symbol from the
symbol table as if it had never existed. <i class="Em">USE WITH EXTREME
CAUTION!!!</i> I can't stress this enough, <b class="Sy">you seriously need to
know what you are doing</b>. DON'T purge a symbol that you use in expressions
the linker needs to calculate. When not sure, it's probably not safe to purge
anything other than string symbols, macros, and constants.
<div class="Bd Pp Bd-indent">
<pre>
Kamikaze EQUS "I don't want to live anymore"
AOLer EQUS "Me too"
PURGE Kamikaze, AOLer
</pre>
</div>
<p class="Pp">Note that, as an exception, string symbols in the argument list of
a <code class="Ic">PURGE</code> command <i class="Em">will not be
expanded</i>.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="Predeclared_Symbols"><a class="permalink" href="#Predeclared_Symbols">Predeclared
Symbols</a></h2>
The following symbols are defined by the assembler:
<table class="Bl-column Bd-indent">
<tr>
<th>Type</th>
<th>Name</th>
<th>Contents</th>
</tr>
<tr>
<td><a class="permalink" href="#EQU_3"><code class="Ic" id="EQU_3">EQU</code></a></td>
<td><a class="permalink" href="#@"><code class="Dv" id="@">@</code></a></td>
<td>PC value</td>
</tr>
<tr>
<td><a class="permalink" href="#EQU_4"><code class="Ic" id="EQU_4">EQU</code></a></td>
<td><a class="permalink" href="#_PI"><code class="Dv" id="_PI">_PI</code></a></td>
<td>Fixed point π</td>
</tr>
<tr>
<td><a class="permalink" href="#SET_3"><code class="Ic" id="SET_3">SET</code></a></td>
<td><a class="permalink" href="#_RS"><code class="Dv" id="_RS">_RS</code></a></td>
<td>_RS Counter</td>
</tr>
<tr>
<td><a class="permalink" href="#EQU_5"><code class="Ic" id="EQU_5">EQU</code></a></td>
<td><a class="permalink" href="#_NARG"><code class="Dv" id="_NARG">_NARG</code></a></td>
<td>Number of arguments passed to macro</td>
</tr>
<tr>
<td><a class="permalink" href="#EQU_6"><code class="Ic" id="EQU_6">EQU</code></a></td>
<td><a class="permalink" href="#__LINE__"><code class="Dv" id="__LINE__">__LINE__</code></a></td>
<td>The current line number</td>
</tr>
<tr>
<td><a class="permalink" href="#EQUS_3"><code class="Ic" id="EQUS_3">EQUS</code></a></td>
<td><a class="permalink" href="#__FILE__"><code class="Dv" id="__FILE__">__FILE__</code></a></td>
<td>The current filename</td>
</tr>
<tr>
<td><a class="permalink" href="#EQUS_4"><code class="Ic" id="EQUS_4">EQUS</code></a></td>
<td><a class="permalink" href="#__DATE__"><code class="Dv" id="__DATE__">__DATE__</code></a></td>
<td>Today's date</td>
</tr>
<tr>
<td><a class="permalink" href="#EQUS_5"><code class="Ic" id="EQUS_5">EQUS</code></a></td>
<td><a class="permalink" href="#__TIME__"><code class="Dv" id="__TIME__">__TIME__</code></a></td>
<td>The current time</td>
</tr>
<tr>
<td><a class="permalink" href="#EQUS_6"><code class="Ic" id="EQUS_6">EQUS</code></a></td>
<td><a class="permalink" href="#__ISO_8601_LOCAL__"><code class="Dv" id="__ISO_8601_LOCAL__">__ISO_8601_LOCAL__</code></a></td>
<td>ISO 8601 timestamp (local)</td>
</tr>
<tr>
<td><a class="permalink" href="#EQUS_7"><code class="Ic" id="EQUS_7">EQUS</code></a></td>
<td><a class="permalink" href="#__ISO_8601_UTC__"><code class="Dv" id="__ISO_8601_UTC__">__ISO_8601_UTC__</code></a></td>
<td>ISO 8601 timestamp (UTC)</td>
</tr>
<tr>
<td><a class="permalink" href="#EQU_7"><code class="Ic" id="EQU_7">EQU</code></a></td>
<td><a class="permalink" href="#__UTC_YEAR__"><code class="Dv" id="__UTC_YEAR__">__UTC_YEAR__</code></a></td>
<td>Today's year</td>
</tr>
<tr>
<td><a class="permalink" href="#EQU_8"><code class="Ic" id="EQU_8">EQU</code></a></td>
<td><a class="permalink" href="#__UTC_MONTH__"><code class="Dv" id="__UTC_MONTH__">__UTC_MONTH__</code></a></td>
<td>Today's month number, 1–12</td>
</tr>
<tr>
<td><a class="permalink" href="#EQU_9"><code class="Ic" id="EQU_9">EQU</code></a></td>
<td><a class="permalink" href="#__UTC_DAY__"><code class="Dv" id="__UTC_DAY__">__UTC_DAY__</code></a></td>
<td>Today's day of the month, 1–31</td>
</tr>
<tr>
<td><a class="permalink" href="#EQU_10"><code class="Ic" id="EQU_10">EQU</code></a></td>
<td><a class="permalink" href="#__UTC_HOUR__"><code class="Dv" id="__UTC_HOUR__">__UTC_HOUR__</code></a></td>
<td>Current hour, 0–23</td>
</tr>
<tr>
<td><a class="permalink" href="#EQU_11"><code class="Ic" id="EQU_11">EQU</code></a></td>
<td><a class="permalink" href="#__UTC_MINUTE__"><code class="Dv" id="__UTC_MINUTE__">__UTC_MINUTE__</code></a></td>
<td>Current minute, 0–59</td>
</tr>
<tr>
<td><a class="permalink" href="#EQU_12"><code class="Ic" id="EQU_12">EQU</code></a></td>
<td><a class="permalink" href="#__UTC_SECOND__"><code class="Dv" id="__UTC_SECOND__">__UTC_SECOND__</code></a></td>
<td>Current second, 0–59</td>
</tr>
<tr>
<td><a class="permalink" href="#EQU_13"><code class="Ic" id="EQU_13">EQU</code></a></td>
<td><a class="permalink" href="#__RGBDS_MAJOR__"><code class="Dv" id="__RGBDS_MAJOR__">__RGBDS_MAJOR__</code></a></td>
<td>Major version number of RGBDS</td>
</tr>
<tr>
<td><a class="permalink" href="#EQU_14"><code class="Ic" id="EQU_14">EQU</code></a></td>
<td><a class="permalink" href="#__RGBDS_MINOR__"><code class="Dv" id="__RGBDS_MINOR__">__RGBDS_MINOR__</code></a></td>
<td>Minor version number of RGBDS</td>
</tr>
<tr>
<td><a class="permalink" href="#EQU_15"><code class="Ic" id="EQU_15">EQU</code></a></td>
<td><a class="permalink" href="#__RGBDS_PATCH__"><code class="Dv" id="__RGBDS_PATCH__">__RGBDS_PATCH__</code></a></td>
<td>Patch version number of RGBDS</td>
</tr>
</table>
</section>
</section>
<section class="Sh">
<h1 class="Sh" id="DEFINING_DATA"><a class="permalink" href="#DEFINING_DATA">DEFINING
DATA</a></h1>
<section class="Ss">
<h2 class="Ss" id="Declaring_variables_in_a_RAM_section"><a class="permalink" href="#Declaring_variables_in_a_RAM_section">Declaring
variables in a RAM section</a></h2>
<code class="Ic">DS</code> allocates a number of empty bytes. This is the
preferred method of allocating space in a RAM section. You can also use
<code class="Ic">DB</code>, <code class="Ic">DW</code> and
<code class="Ic">DL</code> without any arguments instead (see
<a class="Sx" href="#Defining_constant_data">Defining constant data</a>
below).
<div class="Bd Pp Bd-indent">
<pre>
DS 42 ; Allocates 42 bytes
</pre>
</div>
<p class="Pp">Empty space in RAM sections will not be initialized. In ROM
sections, it will be filled with the value passed to the
<code class="Fl">-p</code> command-line option, except when using overlays
with <code class="Fl">-O</code>.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="Defining_constant_data"><a class="permalink" href="#Defining_constant_data">Defining
constant data</a></h2>
<code class="Ic">DB</code> defines a list of bytes that will be stored in the
final image. Ideal for tables and text. Note that strings are not
zero-terminated!
<div class="Bd Pp Bd-indent">
<pre>
DB 1,2,3,4,"This is a string"
</pre>
</div>
<p class="Pp"><code class="Ic">DS</code> can also be used to fill a region of
memory with some value. The following produces 42 times the byte $FF:</p>
<div class="Bd Pp Bd-indent">
<pre>
DS 42, $FF
</pre>
</div>
<p class="Pp">Alternatively, you can use <code class="Ic">DW</code> to store a
list of words (16-bit) or <code class="Ic">DL</code> to store a list of
double-words/longs (32-bit). Strings are not allowed as arguments to
<code class="Ic">DW</code> and <code class="Ic">DL</code>.</p>
<p class="Pp">You can also use <code class="Ic">DB</code>,
<code class="Ic">DW</code> and <code class="Ic">DL</code> without arguments,
or leaving empty elements at any point in the list. This works exactly like
<code class="Ic">DS 1</code>, <code class="Ic">DS 2</code> and
<code class="Ic">DS 4</code> respectively. Consequently, no-argument
<code class="Ic">DB</code>, <code class="Ic">DW</code> and
<code class="Ic">DL</code> can be used in a <code class="Ic">WRAM0</code> /
<code class="Ic">WRAMX</code> / <code class="Ic">HRAM</code> /
<code class="Ic">VRAM</code> / <code class="Ic">SRAM</code> section.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="Including_binary_files"><a class="permalink" href="#Including_binary_files">Including
binary files</a></h2>
You probably have some graphics, level data, etc. you'd like to include. Use
<code class="Ic">INCBIN</code> to include a raw binary file as it is. If the
file isn't found in the current directory, the include-path list passed to
<a class="Xr" href="rgbasm.1.html">rgbasm(1)</a> (see the <code class="Fl">-i</code> option) on the
command line will be searched.
<div class="Bd Pp Bd-indent">
<pre>
INCBIN "titlepic.bin"
INCBIN "sprites/hero.bin"
</pre>
</div>
<p class="Pp">You can also include only part of a file with
<code class="Ic">INCBIN</code>. The example below includes 256 bytes from
data.bin, starting from byte 78.</p>
<div class="Bd Pp Bd-indent">
<pre>
INCBIN "data.bin",78,256
</pre>
</div>
</section>
<section class="Ss">
<h2 class="Ss" id="Unions"><a class="permalink" href="#Unions">Unions</a></h2>
Unions allow multiple memory allocations to overlap, like unions in C. This does
not increase the amount of memory available, but allows re-using the same
memory region for different purposes.
<p class="Pp">A union starts with a <code class="Ic">UNION</code> keyword, and
ends at the corresponding <code class="Ic">ENDU</code> keyword.
<code class="Ic">NEXTU</code> separates each block of allocations, and you
may use it as many times within a union as necessary.</p>
<div class="Bd Pp Bd-indent">
<pre>
; Let's say PC = $C0DE here
UNION
; Here, PC = $C0DE
Name: ds 8
; PC = $C0E6
Nickname: ds 8
; PC = $C0EE
NEXTU
; PC is back to $C0DE
Health: dw
; PC = $C0E0
Something: ds 6
; And so on
Lives: db
NEXTU
VideoBuffer: ds 19
ENDU
</pre>
</div>
<p class="Pp">In the example above, ‘Name, Health, VideoBuffer’
all have the same value, as do ‘Nickname’ and
‘Lives’. Thus, keep in mind that <code class="Ic">ld [Health],
a</code> is identical to <code class="Ic">ld [Name], a</code>.</p>
<p class="Pp">The size of this union is 19 bytes, as this is the size of the
largest block (the last one, containing ‘VideoBuffer’).
Nesting unions is possible, with each inner union's size being considered as
described above.</p>
<p class="Pp">Unions may be used in any section, but inside them may only be
<code class="Ic">DS -</code> like commands (see
<a class="Sx" href="#Declaring_variables_in_a_RAM_section">Declaring
variables in a RAM section</a>).</p>
</section>
</section>
<section class="Sh">
<h1 class="Sh" id="THE_MACRO_LANGUAGE"><a class="permalink" href="#THE_MACRO_LANGUAGE">THE
MACRO LANGUAGE</a></h1>
<section class="Ss">
<h2 class="Ss" id="Invoking_macros"><a class="permalink" href="#Invoking_macros">Invoking
macros</a></h2>
You execute the macro by inserting its name.
<div class="Bd Pp Bd-indent">
<pre>
add a,b
ld sp,hl
MyMacro ; This will be expanded
sub a,87
</pre>
</div>
<p class="Pp">It's valid to call a macro from a macro (yes, even the same
one).</p>
<p class="Pp">When <code class="Nm">rgbasm</code> sees
<code class="Ic">MyMacro</code> it will insert the macro definition (the
code enclosed in <code class="Ic">MACRO</code> /
<code class="Ic">ENDM</code>).</p>
<p class="Pp">Suppose your macro contains a loop.</p>
<div class="Bd Pp Bd-indent">
<pre>
LoopyMacro: MACRO
xor a,a
.loop ld [hl+],a
dec c
jr nz,.loop
ENDM
</pre>
</div>
<p class="Pp">This is fine, but only if you use the macro no more than once per
scope. To get around this problem, there is the escape sequence
<code class="Ic">\@</code> that expands to a unique string.</p>
<p class="Pp"><code class="Ic">\@</code> also works in
<code class="Ic">REPT</code> blocks.</p>
<div class="Bd Pp Bd-indent">
<pre>
LoopyMacro: MACRO
xor a,a
.loop\@ ld [hl+],a
dec c
jr nz,.loop\@
ENDM
</pre>
</div>
<p class="Pp"><b class="Sy">Important note</b>: Since a macro can call itself
(or a different macro that calls the first one), there can be circular
dependency problems. If this creates an infinite loop,
<code class="Nm">rgbasm</code> will error out once a certain depth is
reached. See the <code class="Fl">-r</code> command-line option in
<a class="Xr" href="rgbasm.1.html">rgbasm(1)</a>. Also, a macro can have inside an
<b class="Sy">EQUS</b> which references the same macro, which has the same
problem.</p>
<p class="Pp">It's possible to pass arguments to macros as well! You retrieve
the arguments by using the escape sequences <code class="Ic">\1</code>
through <code class="Ic">\9</code>, <code class="Ic">\1</code> being the
first argument specified on the macro invocation.</p>
<div class="Bd Pp Bd-indent">
<pre>
LoopyMacro: MACRO
ld hl,\1
ld c,\2
xor a,a
.loop\@ ld [hl+],a
dec c
jr nz,.loop\@
ENDM
</pre>
</div>
<p class="Pp">Now I can call the macro specifying two arguments, the first being
the address and the second being a byte count. The generated code will then
reset all bytes in this range.</p>
<div class="Bd Pp Bd-indent">
<pre>
LoopyMacro MyVars,54
</pre>
</div>
<p class="Pp">Arguments are passed as string equates, although there's no need
to enclose them in quotes. Thus, an expression will not be evaluated first
but kind of copy-pasted. This means that it's probably a very good idea to
use brackets around <code class="Ic">\1</code> to <code class="Ic">\9</code>
if you perform further calculations on them. For instance, consider the
following:</p>
<div class="Bd Pp Bd-indent">
<pre>
print_double: MACRO
PRINTV \1 * 2
ENDM
print_double 1 + 2
</pre>
</div>
<p class="Pp">The <code class="Ic">PRINTV</code> statement will expand to
‘<code class="Li">PRINTV 1 + 2 * 2</code>’, which will print 5
and not 6 as you might have expected.</p>
<p class="Pp">Line continuations work as usual inside macros or lists of macro
arguments. However, some characters need to be escaped, as in the following
example:</p>
<div class="Bd Pp Bd-indent">
<pre>
PrintMacro: MACRO
PRINTT \1
ENDM
PrintMacro STRCAT("Hello "\, \
"world\\n")
</pre>
</div>
<p class="Pp">The comma needs to be escaped to avoid it being treated as
separating the macro's arguments. The backslash ‘\’ (from
‘\n’) also needs to be escaped because of the way
<code class="Nm">rgbasm</code> processes macro arguments.</p>
<p class="Pp">In reality, up to 256 arguments can be passed to a macro, but you
can only use the first 9 like this. If you want to use the rest, you need to
use the <code class="Ic">SHIFT</code> command.</p>
<p class="Pp"><code class="Ic">SHIFT</code> is a special command only available
in macros. Very useful in <code class="Ic">REPT</code> blocks. It will shift
the arguments by one to the left. <code class="Ic">\1</code> will get the
value of <code class="Ic">\2</code>, <code class="Ic">\2</code> will get the
value of <code class="Ic">\3</code>, and so forth.</p>
<p class="Pp">This is the only way of accessing the value of arguments from 10
to 256.</p>
<p class="Pp"><code class="Ic">SHIFT</code> can optionally be given an integer
parameter, and will apply the above shifting that number of times.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="Printing_things_during_assembly"><a class="permalink" href="#Printing_things_during_assembly">Printing
things during assembly</a></h2>
The next four commands print text and values to the standard output. Useful for
debugging macros, or wherever you may feel the need to tell yourself some
important information.
<div class="Bd Pp Bd-indent">
<pre>
PRINTT "I'm the greatest programmer in the whole wide world\n"
PRINTI (2 + 3) / 5
PRINTV $FF00 + $F0
PRINTF MUL(3.14, 3987.0)
</pre>
</div>
<dl class="Bl-inset">
<dt><a class="permalink" href="#PRINTT"><code class="Ic" id="PRINTT">PRINTT</code></a></dt>
<dd>prints out a string. Be careful to add a line feed (“\n”) at
the end, as it is not added automatically.</dd>
<dt><a class="permalink" href="#PRINTV"><code class="Ic" id="PRINTV">PRINTV</code></a></dt>
<dd>prints out an integer value in hexadecimal or, as in the example, the
result of a calculation. Unsurprisingly, you can also print out a constant
symbol's value.</dd>
<dt><a class="permalink" href="#PRINTI"><code class="Ic" id="PRINTI">PRINTI</code></a></dt>
<dd>prints out a signed integer value.</dd>
<dt><a class="permalink" href="#PRINTF"><code class="Ic" id="PRINTF">PRINTF</code></a></dt>
<dd>prints out a fixed point value.</dd>
</dl>
<p class="Pp">Be careful that none of those automatically print a line feed; if
you need one, use <code class="Ic">PRINTT \n</code>.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="Automatically_repeating_blocks_of_code"><a class="permalink" href="#Automatically_repeating_blocks_of_code">Automatically
repeating blocks of code</a></h2>
Suppose you want to unroll a time consuming loop without copy-pasting it.
<code class="Ic">REPT</code> is here for that purpose. Everything between
<code class="Ic">REPT</code> and the matching <code class="Ic">ENDR</code>
will be repeated a number of times just as if you had done a copy/paste
operation yourself. The following example will assemble
‘<code class="Li">add a,c</code>’ four times:
<div class="Bd Pp Bd-indent">
<pre>
REPT 4
add a,c
ENDR
</pre>
</div>
<p class="Pp">You can also use <code class="Ic">REPT</code> to generate tables
on the fly:</p>
<div class="Bd Pp Bd-indent">
<pre>
; --
; -- Generate a 256 byte sine table with values between 0 and 128
; --
ANGLE = 0.0
REPT 256
db (MUL(64.0, SIN(ANGLE)) + 64.0) >> 16
ANGLE = ANGLE+256.0
ENDR
</pre>
</div>
<p class="Pp">As in macros, you can also use the escape sequence
<code class="Ic">\@</code>. <code class="Ic">REPT</code> blocks can be
nested.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="Aborting_the_assembly_process"><a class="permalink" href="#Aborting_the_assembly_process">Aborting
the assembly process</a></h2>
<code class="Ic">FAIL</code> and <code class="Ic">WARN</code> can be used to
print errors and warnings respectively during the assembly process. This is
especially useful for macros that get an invalid argument.
<code class="Ic">FAIL</code> and <code class="Ic">WARN</code> take a string as
the only argument and they will print this string out as a normal error with a
line number.
<p class="Pp"><code class="Ic">FAIL</code> stops assembling immediately while
<code class="Ic">WARN</code> shows the message but continues afterwards.</p>
<p class="Pp">If you need to ensure some assumption is correct when compiling,
you can use <code class="Ic">ASSERT</code> and
<code class="Ic">STATIC_ASSERT</code>. Syntax examples are given below:</p>
<div class="Bd Pp Bd-indent">
<pre>
Function:
xor a
ASSERT LOW(Variable) == 0
ld h, HIGH(Variable)
ld l, a
ld a, [hli]
; You can also indent this!
ASSERT BANK(OtherFunction) == BANK(Function)
call OtherFunction
; Lowercase also works
assert Variable + 1 == OtherVariable
ld c, [hl]
ret
.end
; If you specify one, a message will be printed
STATIC_ASSERT .end - Function < 256, "Function is too large!"
</pre>
</div>
<p class="Pp">First, the difference between <code class="Ic">ASSERT</code> and
<code class="Ic">STATIC_ASSERT</code> is that the former is evaluated by
RGBASM if it can, otherwise by RGBLINK; but the latter is only ever
evaluated by RGBASM. If RGBASM cannot compute the value of the argument to
<code class="Ic">STATIC_ASSERT</code>, it will produce an error.</p>
<p class="Pp">Second, as shown above, a string can be optionally added at the
end, to give insight into what the assertion is checking.</p>
<p class="Pp">Finally, you can add one of <code class="Ic">WARN</code>,
<code class="Ic">FAIL</code> or <code class="Ic">FATAL</code> as the first
optional argument to either <code class="Ic">ASSERT</code> or
<code class="Ic">STATIC_ASSERT</code>. If the assertion fails,
<code class="Ic">WARN</code> will cause a simple warning (controlled by
<a class="Xr" href="rgbasm.1.html">rgbasm(1)</a> flag <code class="Fl">-Wassert</code>) to be
emitted; <code class="Ic">FAIL</code> (the default) will cause a non-fatal
error; and <code class="Ic">FATAL</code> immediately aborts.</p>
</section>
<section class="Ss">
<h2 class="Ss" id="Including_other_source_files"><a class="permalink" href="#Including_other_source_files">Including
other source files</a></h2>
Use <code class="Ic">INCLUDE</code> to process another assembler file and then
return to the current file when done. If the file isn't found in the current
directory the include path list (see the <code class="Fl">-i</code> option in
<a class="Xr" href="rgbasm.1.html">rgbasm(1)</a>) will be searched. You may nest
<code class="Ic">INCLUDE</code> calls infinitely (or until you run out of
memory, whichever comes first).
<div class="Bd Pp Bd-indent">
<pre>
INCLUDE "irq.inc"
</pre>
</div>
</section>
<section class="Ss">
<h2 class="Ss" id="Conditional_assembling"><a class="permalink" href="#Conditional_assembling">Conditional
assembling</a></h2>
The four commands <code class="Ic">IF</code>, <code class="Ic">ELIF</code>,
<code class="Ic">ELSE</code>, and <code class="Ic">ENDC</code> let you have
<code class="Nm">rgbasm</code> skip over parts of your code depending on a
condition. This is a powerful feature commonly used in macros.
<div class="Bd Pp Bd-indent">
<pre>
IF NUM < 0
PRINTT "NUM < 0\n"
ELIF NUM == 0
PRINTT "NUM == 0\n"
ELSE
PRINTT "NUM > 0\n"
ENDC
</pre>
</div>
<p class="Pp">The <code class="Ic">ELIF</code> (standing for "else
if") and <code class="Ic">ELSE</code> blocks are optional.
<code class="Ic">IF</code> / <code class="Ic">ELIF</code> /
<code class="Ic">ELSE</code> / <code class="Ic">ENDC</code> blocks can be
nested.</p>
<p class="Pp">Note that if an <code class="Ic">ELSE</code> block is found before
an <code class="Ic">ELIF</code> block, the <code class="Ic">ELIF</code>
block will be ignored. All <code class="Ic">ELIF</code> blocks must go
before the <code class="Ic">ELSE</code> block. Also, if there is more than
one <code class="Ic">ELSE</code> block, all of them but the first one are
ignored.</p>
</section>
</section>
<section class="Sh">
<h1 class="Sh" id="MISCELLANEOUS"><a class="permalink" href="#MISCELLANEOUS">MISCELLANEOUS</a></h1>
<section class="Ss">
<h2 class="Ss" id="Changing_options_while_assembling"><a class="permalink" href="#Changing_options_while_assembling">Changing
options while assembling</a></h2>
<code class="Ic">OPT</code> can be used to change some of the options during
assembling from within the source, instead of defining them on the
command-line.
<p class="Pp"><code class="Ic">OPT</code> takes a comma-separated list of
options as its argument:</p>
<div class="Bd Pp Bd-indent">
<pre>
PUSHO
OPT g.oOX ;Set the GB graphics constants to use these characters
DW `..ooOOXX
POPO
DW `00112233
</pre>
</div>
<p class="Pp">The options that OPT can modify are currently:
<code class="Cm">b</code>, <code class="Cm">g</code> and
<code class="Cm">p</code>.</p>
<p class="Pp"><code class="Ic">POPO</code> and <code class="Ic">PUSHO</code>
provide the interface to the option stack. <code class="Ic">PUSHO</code>
will push the current set of options on the option stack.
<code class="Ic">POPO</code> can then later be used to restore them. Useful
if you want to change some options in an include file and you don't want to
destroy the options set by the program that included your file. The stack's
number of entries is limited only by the amount of memory in your
machine.</p>
</section>
</section>
<section class="Sh">
<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
ALSO</a></h1>
<a class="Xr" href="rgbasm.1.html">rgbasm(1)</a>, <a class="Xr" href="rgblink.1.html">rgblink(1)</a>,
<a class="Xr" href="rgblink.5.html">rgblink(5)</a>, <a class="Xr" href="rgbds.5.html">rgbds(5)</a>,
<a class="Xr" href="rgbds.7.html">rgbds(7)</a>, <a class="Xr" href="gbz80.7.html">gbz80(7)</a>
</section>
<section class="Sh">
<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1>
<code class="Nm">rgbasm</code> was originally written by Carsten Sørensen
as part of the ASMotor package, and was later packaged in RGBDS by Justin
Lloyd. It is now maintained by a number of contributors at
<a class="Lk" href="https://github.com/rednex/rgbds">https://github.com/rednex/rgbds</a>.
</section>
</div>
<table class="foot">
<tr>
<td class="foot-date">December 5, 2019</td>
<td class="foot-os">General</td>
</tr>
</table>
</body>
</html>