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208 lines
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HTML
208 lines
10 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>Xtensa Options (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="Xtensa Options (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="Xtensa Options (Using the GNU Compiler Collection (GCC))">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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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="Submodel-Options.html#Submodel-Options" rel="up" title="Submodel Options">
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<link href="zSeries-Options.html#zSeries-Options" rel="next" title="zSeries Options">
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<link href="Xstormy16-Options.html#Xstormy16-Options" rel="prev" title="Xstormy16 Options">
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<style type="text/css">
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kbd {font-style: oblique}
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ul.no-bullet {list-style: none}
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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="Xtensa-Options"></a>
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<div class="header">
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<p>
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Next: <a href="zSeries-Options.html#zSeries-Options" accesskey="n" rel="next">zSeries Options</a>, Previous: <a href="Xstormy16-Options.html#Xstormy16-Options" accesskey="p" rel="prev">Xstormy16 Options</a>, Up: <a href="Submodel-Options.html#Submodel-Options" accesskey="u" rel="up">Submodel Options</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="Xtensa-Options-1"></a>
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<h4 class="subsection">3.18.59 Xtensa Options</h4>
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<a name="index-Xtensa-Options"></a>
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<p>These options are supported for Xtensa targets:
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</p>
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<dl compact="compact">
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<dt><code>-mconst16</code></dt>
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<dt><code>-mno-const16</code></dt>
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<dd><a name="index-mconst16"></a>
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<a name="index-mno_002dconst16"></a>
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<p>Enable or disable use of <code>CONST16</code> instructions for loading
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constant values. The <code>CONST16</code> instruction is currently not a
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standard option from Tensilica. When enabled, <code>CONST16</code>
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instructions are always used in place of the standard <code>L32R</code>
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instructions. The use of <code>CONST16</code> is enabled by default only if
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the <code>L32R</code> instruction is not available.
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</p>
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</dd>
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<dt><code>-mfused-madd</code></dt>
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<dt><code>-mno-fused-madd</code></dt>
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<dd><a name="index-mfused_002dmadd-6"></a>
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<a name="index-mno_002dfused_002dmadd-6"></a>
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<p>Enable or disable use of fused multiply/add and multiply/subtract
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instructions in the floating-point option. This has no effect if the
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floating-point option is not also enabled. Disabling fused multiply/add
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and multiply/subtract instructions forces the compiler to use separate
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instructions for the multiply and add/subtract operations. This may be
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desirable in some cases where strict IEEE 754-compliant results are
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required: the fused multiply add/subtract instructions do not round the
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intermediate result, thereby producing results with <em>more</em> bits of
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precision than specified by the IEEE standard. Disabling fused multiply
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add/subtract instructions also ensures that the program output is not
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sensitive to the compiler’s ability to combine multiply and add/subtract
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operations.
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</p>
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</dd>
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<dt><code>-mserialize-volatile</code></dt>
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<dt><code>-mno-serialize-volatile</code></dt>
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<dd><a name="index-mserialize_002dvolatile"></a>
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<a name="index-mno_002dserialize_002dvolatile"></a>
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<p>When this option is enabled, GCC inserts <code>MEMW</code> instructions before
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<code>volatile</code> memory references to guarantee sequential consistency.
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The default is <samp>-mserialize-volatile</samp>. Use
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<samp>-mno-serialize-volatile</samp> to omit the <code>MEMW</code> instructions.
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</p>
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</dd>
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<dt><code>-mforce-no-pic</code></dt>
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<dd><a name="index-mforce_002dno_002dpic"></a>
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<p>For targets, like GNU/Linux, where all user-mode Xtensa code must be
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position-independent code (PIC), this option disables PIC for compiling
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kernel code.
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</p>
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</dd>
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<dt><code>-mtext-section-literals</code></dt>
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<dt><code>-mno-text-section-literals</code></dt>
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<dd><a name="index-mtext_002dsection_002dliterals"></a>
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<a name="index-mno_002dtext_002dsection_002dliterals"></a>
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<p>These options control the treatment of literal pools. The default is
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<samp>-mno-text-section-literals</samp>, which places literals in a separate
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section in the output file. This allows the literal pool to be placed
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in a data RAM/ROM, and it also allows the linker to combine literal
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pools from separate object files to remove redundant literals and
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improve code size. With <samp>-mtext-section-literals</samp>, the literals
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are interspersed in the text section in order to keep them as close as
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possible to their references. This may be necessary for large assembly
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files. Literals for each function are placed right before that function.
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</p>
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</dd>
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<dt><code>-mauto-litpools</code></dt>
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<dt><code>-mno-auto-litpools</code></dt>
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<dd><a name="index-mauto_002dlitpools"></a>
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<a name="index-mno_002dauto_002dlitpools"></a>
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<p>These options control the treatment of literal pools. The default is
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<samp>-mno-auto-litpools</samp>, which places literals in a separate
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section in the output file unless <samp>-mtext-section-literals</samp> is
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used. With <samp>-mauto-litpools</samp> the literals are interspersed in
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the text section by the assembler. Compiler does not produce explicit
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<code>.literal</code> directives and loads literals into registers with
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<code>MOVI</code> instructions instead of <code>L32R</code> to let the assembler
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do relaxation and place literals as necessary. This option allows
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assembler to create several literal pools per function and assemble
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very big functions, which may not be possible with
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<samp>-mtext-section-literals</samp>.
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</p>
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</dd>
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<dt><code>-mtarget-align</code></dt>
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<dt><code>-mno-target-align</code></dt>
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<dd><a name="index-mtarget_002dalign"></a>
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<a name="index-mno_002dtarget_002dalign"></a>
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<p>When this option is enabled, GCC instructs the assembler to
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automatically align instructions to reduce branch penalties at the
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expense of some code density. The assembler attempts to widen density
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instructions to align branch targets and the instructions following call
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instructions. If there are not enough preceding safe density
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instructions to align a target, no widening is performed. The
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default is <samp>-mtarget-align</samp>. These options do not affect the
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treatment of auto-aligned instructions like <code>LOOP</code>, which the
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assembler always aligns, either by widening density instructions or
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by inserting NOP instructions.
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</p>
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</dd>
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<dt><code>-mlongcalls</code></dt>
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<dt><code>-mno-longcalls</code></dt>
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<dd><a name="index-mlongcalls"></a>
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<a name="index-mno_002dlongcalls"></a>
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<p>When this option is enabled, GCC instructs the assembler to translate
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direct calls to indirect calls unless it can determine that the target
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of a direct call is in the range allowed by the call instruction. This
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translation typically occurs for calls to functions in other source
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files. Specifically, the assembler translates a direct <code>CALL</code>
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instruction into an <code>L32R</code> followed by a <code>CALLX</code> instruction.
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The default is <samp>-mno-longcalls</samp>. This option should be used in
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programs where the call target can potentially be out of range. This
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option is implemented in the assembler, not the compiler, so the
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assembly code generated by GCC still shows direct call
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instructions—look at the disassembled object code to see the actual
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instructions. Note that the assembler uses an indirect call for
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every cross-file call, not just those that really are out of range.
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</p></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="zSeries-Options.html#zSeries-Options" accesskey="n" rel="next">zSeries Options</a>, Previous: <a href="Xstormy16-Options.html#Xstormy16-Options" accesskey="p" rel="prev">Xstormy16 Options</a>, Up: <a href="Submodel-Options.html#Submodel-Options" accesskey="u" rel="up">Submodel Options</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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