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<!DOCTYPE concept
  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="GUID-C3C89BD7-A56D-4597-8804-01A25BC71581" xml:lang="en"><title>Data
Transfer between LDD and PDD</title><shortdesc>This document describes how LDDs and PDDs exchange data.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<section id="GUID-F65FC583-DDC7-40B6-B875-44A8D11A2971">      
      <p>The device driver framework supplies each LDD with a pointer, <xref href="GUID-E7550422-5121-3393-A85E-BB797969CD2A.dita#GUID-E7550422-5121-3393-A85E-BB797969CD2A/GUID-CF58D3F1-8185-3A91-A7E8-338B43D329A5"><apiname>DLogicalChannelBase::iPdd</apiname></xref>,
through which it can access PDD functions. The pointer is initialised by the
Kernel while creating a physical channel. </p> <p>An example of this pointer
in use: </p> <codeblock id="GUID-55814834-E7CD-5F19-BA09-B91DA25C8FE3" xml:space="preserve">inline DExUartPhysicalChannel * DExDriverLogicalChannel::Pdd()
    { return (DExUartPhysicalChannel *)iPdd; }

// example use
Pdd()-&gt;SetDfcQ();</codeblock> <p>Similarly, a PDD can access a LDD, though
this access must be initialised by the LDD. In the following example, the
physical channel declares a pointer to a logical channel, which the LDD sets.
Callbacks to the LDD are done using this pointer. </p> <codeblock id="GUID-A4A52268-B5B9-53D4-9F69-B506F268201D" xml:space="preserve">// PDD channel class
class DExH4PhysicalChannel: public DBase
    {
    ...
public:
    DExDriverLogicalChannel* iLdd;
    }

// Second stage constructor of Logical channel
TInt DExDriverLogicalChannel::DoCreate(TInt /*aUnit*/, const TDesC8*
        /*anInfo*/, const TVersion&amp; aVer)
    {
    ...
    Pdd()-&gt;iLdd=this;
    }

// example use in PDD
iLdd-&gt;ReceiveDataComplete(KErrNone);</codeblock> <p>The logical channel class, <xref href="GUID-E7550422-5121-3393-A85E-BB797969CD2A.dita"><apiname>DLogicalChannelBase</apiname></xref>,
also has pointers to a logical device (<codeph>iDevice</codeph>) and a physical
device (<codeph>iPhysicalDevice</codeph>). These pointers are initialised
during the driver loading and channel open operations, so they can also be
used to pass information between the LDD and PDD. </p> <codeblock id="GUID-4B86BED0-22CB-53BC-A1C7-9BEB0CEA1EDE" xml:space="preserve">class DLogicalChannelBase: public DObject
    {
    ...
public:
    DLogicalDevice* iDevice;
    DPhysicalDevice* iPhysicalDevice;
    DBase* iPdd;
    }

// example use
TDynamicDfcQue* DExUartPhysicalChannelH4::DfcQ(TInt aUnit)
    {    
    ...
    return ((DExH4PhysicalDevice*)
            (iLdd-&gt;iPhysicalDevice))-&gt;iDfcQueue;    
    }</codeblock>     </section>
</conbody></concept>