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     7     Nokia Corporation - initial contribution.

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    10 <!DOCTYPE concept

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

    12 <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

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

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

    15 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

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

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

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

    19 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;

    20 TRequestStatus status;

    21 

    22 TUsbcScChunkHeader chunkHeader(gChunk);

    23     

    24 chunkHeader.GetBuffer(0, 2, epInfo);  

    25 TInt outBuffNum = epInfo->iBufferNo;

    26 

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

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

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

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

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

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

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

    34 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);

    35 ... // Process data

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

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

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

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

    40 </conbody></concept>