Symbian3/PDK/Source/GUID-5E358AB4-03A7-5859-ABF2-A8B64B74AF56.dita
author Dominic Pinkman <dominic.pinkman@nokia.com>
Fri, 16 Jul 2010 17:23:46 +0100
changeset 12 80ef3a206772
parent 5 f345bda72bc4
permissions -rw-r--r--
Week 28 contribution of PDK documentation content. See release notes for details. Fixes bugs Bug 1897, Bug 344, Bug 2681, Bug 463, Bug 1522.

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<!DOCTYPE concept
  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<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
Point Architecture (VFPv2) on Symbian platform. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>ARM provide a hardware floating point coprocessor that provides
floating point computation that is fully compliant with IEEE Std 754-1985.We
refer to the coprocessor as the <i>VFP unit</i>. </p>
<p>Symbian platform supports the use of VFPv2 on platforms where the
required hardware is present in both <i>RunFast</i> mode and in <i>IEEE-without-exceptions</i> mode. See ARM's Vector Floating-point
Coprocessor Technical reference Manual for more details on the coprocessor,
its architecture, and its execution modes. </p>
<p>You should read Floating point support in Symbian^3 Tools Guide
&gt; Building. The guide contains information about applications and
user-side code, which is also applicable to code running
on the kernel side. However there are a number of restrictions that
must be observed: </p>
<ul>
<li id="GUID-2205026D-0E6F-54AE-B74F-5478D6047B70"><p>You <i>cannot</i> use VFP instructions in any interrupt service routine. </p> </li>
<li id="GUID-C8D896E1-CF36-52CD-A984-61D7A8189268"><p>You <i>cannot</i> use VFP instructions when the kernel is locked, for example, in
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>
<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
mutex held. </p> </li>
</ul>
<p>Using VFP instructions in these situations can lead to data being
corrupted, or the kernel panicking. If you rely on the compiler to
generate VFP instructions, rather than using inline assembler, it
is extremely important that you do not use any floating point values
in these situations. The compiler may generate VFP instructions for
the most trivial floating point operations and even for simple assignments. </p>
</conbody></concept>