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Adaptation/GUID-5E358AB4-03A7-5859-ABF2-A8B64B74AF56.dita
author Graeme Price <GRAEME.PRICE@NOKIA.COM>
Fri, 15 Oct 2010 14:32:18 +0100
changeset 15 307f4279f433
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<?xml version="1.0" encoding="utf-8"?>
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
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<!-- This component and the accompanying materials are made available under the terms of the License
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"Eclipse Public License v1.0" which accompanies this distribution,
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and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
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<!-- Initial Contributors:
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    Nokia Corporation - initial contribution.
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Contributors:
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-->
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<!DOCTYPE concept
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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept id="GUID-5E358AB4-03A7-5859-ABF2-A8B64B74AF56" xml:lang="en"><title>Vector Floating Point Architecture (VFP)</title><shortdesc>Describes the implementation of the ARM Vector Floating
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Point Architecture (VFPv2) on Symbian platform. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
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<p>ARM provide a hardware floating point coprocessor that provides
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floating point computation that is fully compliant with IEEE Std 754-1985.We
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refer to the coprocessor as the <i>VFP unit</i>. </p>
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<p>Symbian platform supports the use of VFPv2 on platforms where the
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required hardware is present in both <i>RunFast</i> mode and in <i>IEEE-without-exceptions</i> mode. See ARM's Vector Floating-point
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Coprocessor Technical reference Manual for more details on the coprocessor,
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its architecture, and its execution modes. </p>
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<p>You should read Floating point support in Symbian^3 Tools Guide
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&gt; Building. The guide contains information about applications
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and user-side code, which is also applicable to code running on the
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kernel side. However there are a number of restrictions that must
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be observed: </p>
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<ul>
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<li id="GUID-2205026D-0E6F-54AE-B74F-5478D6047B70"><p>You <i>cannot</i> use VFP instructions in any interrupt service routine. </p> </li>
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<li id="GUID-C8D896E1-CF36-52CD-A984-61D7A8189268"><p>You <i>cannot</i> use VFP instructions when the kernel is locked, for example, in
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an IDFC or after calling <xref href="GUID-3A3C08F3-3D33-3D9E-80E7-7855C7B21E02.dita#GUID-3A3C08F3-3D33-3D9E-80E7-7855C7B21E02/GUID-7CBBF72B-4519-38DD-92CA-38AF636AFD8A"><apiname>NKern::Lock()</apiname></xref>  </p> </li>
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<li id="GUID-A7466A83-A8F2-58CE-AB8B-E05607BB6D95"><p>You <i>cannot</i> use VFP instructions in any section of code which runs with a fast
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mutex held. </p> </li>
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</ul>
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<p>Using VFP instructions in these situations can lead to data being
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corrupted, or the kernel panicking. If you rely on the compiler to
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generate VFP instructions, rather than using inline assembler, it
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is extremely important that you do not use any floating point values
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in these situations. The compiler may generate VFP instructions for
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the most trivial floating point operations and even for simple assignments. </p>
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</conbody></concept>
MCL/sftools/depl/docscontent