author | Dominic Pinkman <Dominic.Pinkman@Nokia.com> |
Fri, 22 Jan 2010 18:26:19 +0000 | |
changeset 1 | 25a17d01db0c |
child 3 | 46218c8b8afa |
permissions | -rw-r--r-- |
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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 |
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Floating Point Architecture (VFP)</title><shortdesc>Describes the implementation of the ARM Vector Floating Point Architecture |
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(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 floating |
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point computation that is fully compliant with IEEE Std 754-1985.We refer |
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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 required |
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hardware is present in both <i>RunFast</i> mode and in <i>IEEE-without-exceptions</i> mode. |
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See ARM's Vector Floating-point Coprocessor Technical reference Manual for |
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more details on the coprocessor, its architecture, and its execution modes. </p> |
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<p>You should read the information in <xref href="GUID-D525B9A9-6B32-535B-A282-60C85A48D3FB.dita">Floating |
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point support</xref> about applications and user side code as this is also |
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applicable to code running on the kernel side. However there are a number |
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of restrictions that must 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 |
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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 |
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VFP instructions when the kernel is locked, for example, in an IDFC or after |
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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 |
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VFP instructions in any section of code which runs with a fast 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 corrupted, |
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or the kernel panicking. If you rely on the compiler to generate VFP instructions, |
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rather than using inline assembler, it is extremely important that you do |
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not use any floating point values in these situations. The compiler may generate |
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VFP instructions for the most trivial floating point operations and even for |
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simple assignments. </p> |
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</conbody></concept> |