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+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
+<!-- This component and the accompanying materials are made available under the terms of the License 
+"Eclipse Public License v1.0" which accompanies this distribution, 
+and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
+<!-- Initial Contributors:
+    Nokia Corporation - initial contribution.
+Contributors: 
+-->
+<!DOCTYPE concept
+  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
+<concept id="GUID-6C74A8B4-50B6-486C-A75F-A50636F4C566" xml:lang="en"><title>Register Access Overview</title><shortdesc>Provides a summary of the Register Access platform service.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
+<p>The Register Access platform service is intended for use in writing
+device drivers. Writing device drivers involves frequent access to
+hardware registers for reading, writing and modifying them. </p>
+<section id="GUID-65EDE628-937F-4472-9662-8FE36D77B12D">         
+   <title>What is a register</title>             <p>A register is
+a memory location on the ASSP hardware to store data that relates
+to the operation of that hardware. For example, a register can be
+a counter, or a bit field, or the next sequence number or the next
+byte or word of data that has arrived over a bus.</p><p>The Symbian
+platform provides access functions for registers that have the following
+sizes:<ul>
+<li><p>8–bit</p></li>
+<li><p>16–bit</p></li>
+<li><p>32–bit</p></li>
+<li><p>64–bit</p></li>
+</ul></p>         </section>
+<section id="GUID-25E7482D-B837-4228-9BE5-836DF48AD664"><title>What
+functions are available</title><p>There are three types of function
+provided for register access:<ul>
+<li><p><codeph>Read</codeph> - get the value of a register</p></li>
+<li><p><codeph>Write</codeph> - write a value to a register</p></li>
+<li><p><codeph>Modify</codeph> - use bitmasks to clear or set specific
+bits in a register</p></li>
+</ul></p><p>Each function takes a first argument of a <xref href="GUID-7452AD53-A7EE-3B1E-BC3D-C4202E5DAEBC.dita"><apiname>TLinAddr</apiname></xref> which is an address. The device driver only needs to know the address,
+and the size of the register. The implementation of the Register Access
+must map the exposed physical hardware register to a linear address.</p><p>Each type of function (read, write, modify) has 8–bit, 16–bit,
+32–bit and 64–bit versions.</p><p>The <codeph>Modify</codeph> functions
+take two bitmasks as parameters, to specify which bits to clear to
+zero (clear mask) and which bits to set to one (set mask). This means
+that you could call <codeph>Modify16(myaddress, 0xC000,0x000F)</codeph> and the top two bits would be set to zero, the bottom four bits
+would be set to one, and the ten bits in the middle would retain their
+current value.</p><p>See <xref href="GUID-DB55C1A0-2901-4661-B6B1-3B61BF6FF4FA.dita">Register Access Client
+Interface Guide</xref> for more details on each function and how to
+use them.</p></section>
+</conbody></concept>
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