<?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-0A6C8DB8-ED41-4243-BA96-CA691CF9CD19" xml:lang="en"><title>Data

Buffers</title><shortdesc>This document describes how device drivers allocate and access

memory buffers.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-21C5B685-F546-45B5-A829-00B2DBCBF8E4">      

      <p>Most device drivers need to use memory buffers for I/O operations.

Drivers typically own memory buffers, allocate them, and access them through

pointers. The thread should be in a critical section when it allocates or

de-allocates memory. </p> <codeblock id="GUID-B222000C-8344-5239-9546-4E831A3C0A6E" xml:space="preserve">// Tx and Rx Buffers

TUInt8* iTxBuffer;    

TUInt8* iRxBuffer;</codeblock> <codeblock id="GUID-A921D206-7243-5F0A-ADA3-0330D93A137F" xml:space="preserve">// Logical Channel second stage constructor

TInt DExDriverLogicalChannel::DoCreate(TInt /*aUnit*/, const TDesC8* 

/*anInfo*/, const TVersion& aVer)

    {

    ...

    // Initialize the Tx Buffer

    iTxBuffer = (TUInt8*) Kern::Alloc(KTxBufferSize);

    if (!iTxBuffer)

        return KErrNoMemory;

    ...

    }</codeblock> <p>Memory buffers must be freed when they are not required.

If this is not done, a memory leak occurs. </p> <codeblock id="GUID-688A360C-1B7A-5F3A-BB83-98EB8A4658F3" xml:space="preserve">// Free Tx Buffer

Kern::Free(iTxBuffer)</codeblock>     </section>