<?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-4C4515EA-A5DD-56B4-94B0-EE48D66013F7" xml:lang="en"><title>Read Data from USB using Shared Chunks </title><shortdesc>This tutorial describes how to read shared chunk data from

a USB connection. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-0197C58A-668F-4C8F-966B-A41F31F41A7A"><title>Read data</title> <p>To read data from the host to

the device (<codeph>Out</codeph>) call the function <xref href="GUID-4D1AE286-41EE-3361-948A-3E8634D81DBA.dita#GUID-4D1AE286-41EE-3361-948A-3E8634D81DBA/GUID-4BE585C8-89BF-31D6-865D-85F6C7CBF88B"><apiname>RDevUsbcScClient::ReadDataNotify()</apiname></xref> to make a request to wait for data in the specified buffer and wait

for it to complete. </p> <p>If the buffer already has data in it,

it will return immediately with the code <codeph>KErrCompletion</codeph>. If there is no data in the buffer an asynchronous request is set

up that will complete when data is available. <b>Note</b>: check the

return code before attempting to wait for the request to complete. </p> <codeblock id="GUID-655AFB03-5EC8-5CA5-A15B-8DFC33126026" xml:space="preserve">TUsbcScHdrEndpointRecord* epInfo;

TRequestStatus status;

TUsbcScChunkHeader chunkHeader(gChunk);

chunkHeader.GetBuffer(0, 2, epInfo);  

TInt outBuffNum = epInfo->iBufferNo;

r = gPort.ReadDataNotify(outBuffNum,status);</codeblock> <p>The first

parameter required by <codeph>ReadDataNotify()</codeph> is the endpoint

buffer number. The endpoint buffer number can be found in the alternate

setting table in the chunk header. The location of the buffer can

be found by looking at the buffer offset table, which is also in the

chunk header. </p> <p>When the request has completed, process the

data in the buffer that was read from the driver. </p> <p>The transfer

buffer for an IN endpoint is always pointed to by the <codeph>iTail</codeph> member of the endpoint buffer struct <xref href="GUID-8A844723-82FA-3BB8-B6AD-4E5FC6B5431B.dita"><apiname>SUsbcScBufferHeader</apiname></xref>. When finished processing the current chunk move <codeph>iTail</codeph> to point to the next transfer buffer. </p> <codeblock id="GUID-FA53E100-1C6F-5252-9FC3-586EF4467EC6" xml:space="preserve">iTransfer = (TUsbcScTransferHeader*) (iHeader-&gt;iTail + iBase);

... // Process data

iHeader-&gt;iTail = iTransfer-&gt;iNext;</codeblock> <p>If there is no more

data to be read then close the channel and unload the driver. </p> </section>

<section id="GUID-F015D0C6-0325-45CA-A6FD-2E6E1D7FB78D"><title>Next steps</title> <p>When you have finished reading

and writing <xref href="GUID-BE73CFE6-D48D-5B92-AF49-E2D967ADF0EC.dita">Close and Unload the Driver</xref>. </p> </section>

</conbody></concept>