<?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-2281F91F-67BD-5B85-A47F-30A5E683BBF6" xml:lang="en"><title>Double
Buffers</title><shortdesc>To improve throughput, Symbian platform provides the double buffer
mechanism. This is a feature that allows a block of data to be prepared by
the media driver while the hardware transfers a block of data. DMA transfers
data without interrupting the CPU. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>The MultiMediaCard subsystem performs multiple data transfers in a single
bus transaction. </p>
<p>If your implementation uses double buffers, you must set the <codeph>ESupportsDoubleBuffering</codeph> flag
into the <xref href="GUID-A8C79421-AA44-345D-9863-EA21F5FEEE72.dita#GUID-A8C79421-AA44-345D-9863-EA21F5FEEE72/GUID-8B9C1B71-9664-35B8-B3B3-EC5508E8E76A"><apiname>TMMCMachineInfoV4::iFlags</apiname></xref> data member in your
implementation of <xref href="GUID-B5193656-9819-3E00-A335-EEF1726115A5.dita#GUID-B5193656-9819-3E00-A335-EEF1726115A5/GUID-3E5532A5-4645-3F77-A7A9-7AFF334FA5A4"><apiname>DMMCStack::MachineInfo()</apiname></xref>. This flag causes
the platform independent layer to provide the support you need. </p>
<p>If your MultiMediaCard controller uses DMA and your platform specific layer
supports physical addresses, you must use double buffers. </p>
<p>See also: </p>
<ul>
<li id="GUID-629116CA-4B19-5F48-9F0D-0FEED4D26FEB"><p> <xref href="GUID-E55B4FE5-517C-5A23-8ACA-E28EE202330B.dita#GUID-E55B4FE5-517C-5A23-8ACA-E28EE202330B/GUID-CEF0EDF7-4B33-5452-8635-51C5319F78AE">MachineInfo()</xref> </p> </li>
<li id="GUID-5EF23F02-273E-5382-86C4-C04520AFD91E"><p> <xref href="GUID-E55B4FE5-517C-5A23-8ACA-E28EE202330B.dita#GUID-E55B4FE5-517C-5A23-8ACA-E28EE202330B/GUID-E50081BC-C923-5DAF-950C-9E1411916FED">Implement double buffers</xref>  </p> </li>
</ul>
</conbody></concept>