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156 lines
7.1 KiB
HTML
156 lines
7.1 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>MeP Variable Attributes (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="MeP Variable Attributes (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="MeP Variable Attributes (Using the GNU Compiler Collection (GCC))">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Variable-Attributes.html#Variable-Attributes" rel="up" title="Variable Attributes">
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<link href="Microsoft-Windows-Variable-Attributes.html#Microsoft-Windows-Variable-Attributes" rel="next" title="Microsoft Windows Variable Attributes">
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<link href="M32R_002fD-Variable-Attributes.html#M32R_002fD-Variable-Attributes" rel="prev" title="M32R/D Variable Attributes">
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-->
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</style>
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</head>
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<body lang="en">
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<a name="MeP-Variable-Attributes"></a>
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<div class="header">
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<p>
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Next: <a href="Microsoft-Windows-Variable-Attributes.html#Microsoft-Windows-Variable-Attributes" accesskey="n" rel="next">Microsoft Windows Variable Attributes</a>, Previous: <a href="M32R_002fD-Variable-Attributes.html#M32R_002fD-Variable-Attributes" accesskey="p" rel="prev">M32R/D Variable Attributes</a>, Up: <a href="Variable-Attributes.html#Variable-Attributes" accesskey="u" rel="up">Variable Attributes</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="MeP-Variable-Attributes-1"></a>
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<h4 class="subsection">6.32.8 MeP Variable Attributes</h4>
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<p>The MeP target has a number of addressing modes and busses. The
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<code>near</code> space spans the standard memory space’s first 16 megabytes
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(24 bits). The <code>far</code> space spans the entire 32-bit memory space.
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The <code>based</code> space is a 128-byte region in the memory space that
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is addressed relative to the <code>$tp</code> register. The <code>tiny</code>
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space is a 65536-byte region relative to the <code>$gp</code> register. In
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addition to these memory regions, the MeP target has a separate 16-bit
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control bus which is specified with <code>cb</code> attributes.
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</p>
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<dl compact="compact">
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<dt><code>based</code></dt>
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<dd><a name="index-based-variable-attribute_002c-MeP"></a>
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<p>Any variable with the <code>based</code> attribute is assigned to the
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<code>.based</code> section, and is accessed with relative to the
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<code>$tp</code> register.
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</p>
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</dd>
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<dt><code>tiny</code></dt>
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<dd><a name="index-tiny-variable-attribute_002c-MeP"></a>
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<p>Likewise, the <code>tiny</code> attribute assigned variables to the
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<code>.tiny</code> section, relative to the <code>$gp</code> register.
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</p>
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</dd>
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<dt><code>near</code></dt>
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<dd><a name="index-near-variable-attribute_002c-MeP"></a>
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<p>Variables with the <code>near</code> attribute are assumed to have addresses
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that fit in a 24-bit addressing mode. This is the default for large
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variables (<code>-mtiny=4</code> is the default) but this attribute can
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override <code>-mtiny=</code> for small variables, or override <code>-ml</code>.
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</p>
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</dd>
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<dt><code>far</code></dt>
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<dd><a name="index-far-variable-attribute_002c-MeP"></a>
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<p>Variables with the <code>far</code> attribute are addressed using a full
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32-bit address. Since this covers the entire memory space, this
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allows modules to make no assumptions about where variables might be
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stored.
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</p>
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</dd>
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<dt><code>io</code></dt>
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<dd><a name="index-io-variable-attribute_002c-MeP"></a>
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</dd>
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<dt><code>io (<var>addr</var>)</code></dt>
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<dd><p>Variables with the <code>io</code> attribute are used to address
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memory-mapped peripherals. If an address is specified, the variable
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is assigned that address, else it is not assigned an address (it is
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assumed some other module assigns an address). Example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">int timer_count __attribute__((io(0x123)));
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</pre></div>
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</dd>
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<dt><code>cb</code></dt>
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<dt><code>cb (<var>addr</var>)</code></dt>
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<dd><a name="index-cb-variable-attribute_002c-MeP"></a>
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<p>Variables with the <code>cb</code> attribute are used to access the control
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bus, using special instructions. <code>addr</code> indicates the control bus
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address. Example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">int cpu_clock __attribute__((cb(0x123)));
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</pre></div>
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</dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Microsoft-Windows-Variable-Attributes.html#Microsoft-Windows-Variable-Attributes" accesskey="n" rel="next">Microsoft Windows Variable Attributes</a>, Previous: <a href="M32R_002fD-Variable-Attributes.html#M32R_002fD-Variable-Attributes" accesskey="p" rel="prev">M32R/D Variable Attributes</a>, Up: <a href="Variable-Attributes.html#Variable-Attributes" accesskey="u" rel="up">Variable Attributes</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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