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<!DOCTYPE concept
  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="GUID-30978E00-D244-44CD-8F4E-9676DF172A52" xml:lang="en"><title>Driver-side
Handling</title><shortdesc>This document describes how device drivers handle asynchronous
requests.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>Drivers generally implement the <xref href="GUID-9D910016-5611-30DD-A139-EE46705A4912.dita"><apiname>DoRequest()</apiname></xref> function
in the LDD to handle the received asynchronous messages. </p>
<p>The implementation reads the request type and other passed arguments, and
initiates handling of the request appropriately. </p>
<p>The return value of this function only indicates the status of the message
reception to the driver. It does not actually indicate the request completion
result. </p>
<codeblock id="GUID-335BB3F8-7B2B-5FC4-A8D1-204E6B24FECD" xml:space="preserve">TInt DExDriverLogicalChannel::DoRequest(TInt aReqNo, TRequestStatus* aStatus,
        TAny* a1, TAny* a2)
    {
    switch (aReqNo)
        {
        case RExDriverChannel::ERequestTransmitData:
            // Call TransmitData function
            r = TransmitData ((const TDesC8*)a1);
            // The status object is stored 
            // to be used when notifying the completion of the 
            // request at a later point.
            //
            iTxDataStatus = aStatus;
            break;
        }
    return r;
    }</codeblock>
</conbody></concept>