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1 <?xml version="1.0" encoding="utf-8"?> |
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2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. --> |
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3 <!-- This component and the accompanying materials are made available under the terms of the License |
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4 "Eclipse Public License v1.0" which accompanies this distribution, |
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5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". --> |
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6 <!-- Initial Contributors: |
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7 Nokia Corporation - initial contribution. |
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8 Contributors: |
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9 --> |
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10 <!DOCTYPE concept |
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11 PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
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12 <concept id="GUID-7C533836-0D27-5519-BC1D-7153AC8BE4C0" xml:lang="en"><title>Media |
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13 Driver Guide</title><shortdesc>Describes the issues that need to be considered, when writing a |
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14 media device driver for a writable data demand paging environment. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> |
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15 <section id="GUID-46C98F8A-1486-4FAD-918D-3FB0E7CA372E"><title>Purpose</title> <p>This |
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16 document explains the points that have to be considered when writing a media |
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17 driver in an environment that uses writable data paging. </p> </section> |
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18 <section id="GUID-1A89843E-B174-49F0-87D8-A8ADBE933A54"><title>Issues to consider</title> <p>The |
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19 main issue to consider when writing a media device driver for a writable demand |
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20 paging environment is to avoid page faults from occurring in DFCs, since this |
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21 can lead to a deadlock condition between the driver and the client process. </p> <p>This |
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22 can be avoided using the following methods: </p> <ul> |
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23 <li id="GUID-76EF65C9-63E8-5C9B-99CD-A8BFBBA9B68C"><p>Use shared chunks. </p> <p>Shared |
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24 chunks are memory areas that are accessible by both kernel-side and user-side |
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25 and they are never paged. </p> <p>This is the best solution for drivers that |
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26 involve fast throughput such as media drivers. </p> </li> |
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27 <li id="GUID-32198DFA-CCF9-5260-A677-88F5B9FBF315"><p>Use synchronous rather |
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28 than asynchronous data transfer </p> <p>This could be done by implementing |
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29 the following steps: </p> <ol id="GUID-8C359B63-D166-5A54-8772-811FC2656E66"> |
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30 <li id="GUID-018F2121-A883-5B2F-B70E-C77069B3F1A1"><p>The client requests |
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31 a notification when data is available. </p> </li> |
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32 <li id="GUID-0FC1D31E-4937-572B-BD80-99DDFABCC0BF"><p>The data arrives. </p> </li> |
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33 <li id="GUID-6B47B0FA-8921-5B12-A71C-0E66DD286FD1"><p>The driver writes data |
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34 into an internal buffer and completes the client request. </p> </li> |
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35 <li id="GUID-14E4D83B-7361-5DE4-90BF-B9CEB658FF1D"><p>The client makes a read |
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36 request. </p> </li> |
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37 <li id="GUID-FF2A912E-3FBB-5671-ADBE-090FED1CD873"><p>The driver writes the |
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38 data back to the client in the client thread context. </p> </li> |
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39 </ol> <p>This approach is easy to implement, however it requires the buffering |
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40 of data. </p> </li> |
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41 <li id="GUID-08F4A4BD-699B-5800-BD2D-78A5406C19EB"><p>Use the <xref href="GUID-066868C5-12F8-59A5-A2DE-FEDC4F459771.dita">flexible |
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42 memory model</xref> </p> <p>This provides the ability for the memory to be |
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43 mapped into a drive's address space as unpaged. </p> <p>This is an alternative |
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44 to the use of shared chunks. </p> <p>However, this is not supported on the |
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45 moving or multiple memory models. </p> </li> |
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46 </ul> </section> |
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47 </conbody></concept> |