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Adaptation/GUID-6C74A8B4-50B6-486C-A75F-A50636F4C566.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-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>
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<p>The Register Access platform service is intended for use in writing
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device drivers. Writing device drivers involves frequent access to
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hardware registers for reading, writing and modifying them. </p>
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<section id="GUID-65EDE628-937F-4472-9662-8FE36D77B12D">
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   <title>What is a register</title>             <p>A register is
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a memory location on the ASSP hardware to store data that relates
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to the operation of that hardware. For example, a register can be
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a counter, or a bit field, or the next sequence number or the next
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byte or word of data that has arrived over a bus.</p><p>The Symbian
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platform provides access functions for registers that have the following
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sizes:<ul>
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<li><p>8–bit</p></li>
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<li><p>16–bit</p></li>
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<li><p>32–bit</p></li>
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<li><p>64–bit</p></li>
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</ul></p>         </section>
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<section id="GUID-25E7482D-B837-4228-9BE5-836DF48AD664"><title>What
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functions are available</title><p>There are three types of function
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provided for register access:<ul>
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<li><p><codeph>Read</codeph> - get the value of a register</p></li>
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<li><p><codeph>Write</codeph> - write a value to a register</p></li>
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<li><p><codeph>Modify</codeph> - use bitmasks to clear or set specific
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bits in a register</p></li>
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</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,
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and the size of the register. The implementation of the Register Access
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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,
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32–bit and 64–bit versions.</p><p>The <codeph>Modify</codeph> functions
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take two bitmasks as parameters, to specify which bits to clear to
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zero (clear mask) and which bits to set to one (set mask). This means
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that you could call <codeph>Modify16(myaddress, 0xC000,0x000F)</codeph> and the top two bits would be set to zero, the bottom four bits
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would be set to one, and the ten bits in the middle would retain their
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current value.</p><p>See <xref href="GUID-DB55C1A0-2901-4661-B6B1-3B61BF6FF4FA.dita">Register Access Client
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Interface Guide</xref> for more details on each function and how to
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use them.</p></section>
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</conbody></concept>
FCL/sftools/depl/docscontent