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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-7C533836-0D27-5519-BC1D-7153AC8BE4C0" xml:lang="en"><title>Media

    13 Driver Guide</title><shortdesc>Describes the issues that need to be considered, when writing a

    14 media device driver for a writable data demand paging environment. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 <section id="GUID-46C98F8A-1486-4FAD-918D-3FB0E7CA372E"><title>Purpose</title> <p>This document explains the points that

    16 have to be considered when writing a media driver in an environment that uses

    17 writable data paging. </p> </section>

    18 <section id="GUID-1A89843E-B174-49F0-87D8-A8ADBE933A54"><title>Issues to consider</title> <p>The main issue to consider when

    19 writing a media device driver for a writable demand paging environment is

    20 to avoid page faults from occurring in DFCs, since this can lead to a deadlock

    21 condition between the driver and the client process. </p> <p>This can be avoided

    22 using the following methods: </p> <ul>

    23 <li id="GUID-76EF65C9-63E8-5C9B-99CD-A8BFBBA9B68C"><p>Use shared chunks. </p> <p>Shared

    24 chunks are memory areas that are accessible by both kernel-side and user-side

    25 and they are never paged. </p> <p>This is the best solution for drivers that

    26 involve fast throughput such as media drivers. </p> </li>

    27 <li id="GUID-32198DFA-CCF9-5260-A677-88F5B9FBF315"><p>Use synchronous rather

    28 than asynchronous data transfer </p> <p>This could be done by implementing

    29 the following steps: </p> <ol id="GUID-8C359B63-D166-5A54-8772-811FC2656E66">

    30 <li id="GUID-018F2121-A883-5B2F-B70E-C77069B3F1A1"><p>The client requests

    31 a notification when data is available. </p> </li>

    32 <li id="GUID-0FC1D31E-4937-572B-BD80-99DDFABCC0BF"><p>The data arrives. </p> </li>

    33 <li id="GUID-6B47B0FA-8921-5B12-A71C-0E66DD286FD1"><p>The driver writes data

    34 into an internal buffer and completes the client request. </p> </li>

    35 <li id="GUID-14E4D83B-7361-5DE4-90BF-B9CEB658FF1D"><p>The client makes a read

    36 request. </p> </li>

    37 <li id="GUID-FF2A912E-3FBB-5671-ADBE-090FED1CD873"><p>The driver writes the

    38 data back to the client in the client thread context. </p> </li>

    39 </ol> <p>This approach is easy to implement, however it requires the buffering

    40 of data. </p> </li>

    41 <li id="GUID-08F4A4BD-699B-5800-BD2D-78A5406C19EB"><p>Use the <xref href="GUID-066868C5-12F8-59A5-A2DE-FEDC4F459771.dita">flexible

    42 memory model</xref>  </p> <p>This provides the ability for the memory to be

    43 mapped into a drive's address space as unpaged. </p> <p>This is an alternative

    44 to the use of shared chunks. </p> <p>However, this is not supported on the

    45 moving or multiple memory models. </p> </li>

    46 </ul> </section>

    47 <section id="GUID-4FD645F8-26C0-411E-9B82-56085E88CD74"><title>See also</title> <p> <xref href="GUID-91C11D80-7A62-5135-8EE0-6EC5576D1118.dita">Demand

    48 Paged Device Drivers Writing Guide</xref>  </p> <p>The above document is an

    49 guide writing to device drivers. </p> </section>

    50 </conbody></concept>